Semiconductor inspecting device and semiconductor inspecting method

Abstract

A semiconductor inspecting device 1A comprises: an inspection optical system 11 that irradiates a semiconductor device D with probe light and outputs reflected light; a light measurement unit 20 that detects the reflected light and outputs an electric signal of a time waveform corresponding to a temporal change in the intensity of the reflected light; a signal conversion unit 30 that intensity-modulates the measurement light on the basis of the electric signal and outputs the intensity-modulated light as an optical signal corresponding to the electric signal; a waveform measurement unit 40 that measures a time waveform of the optical signal; and a waveform analysis unit 52 that determines a time waveform of the electric signal on the basis of a measurement result of the optical signal. The waveform measurement unit 40 includes: a streak tube including a photoelectric surface to which an optical signal is input, a sweep electrode, and a fluorescent surface; and an imaging element for capturing a fluorescence image generated on the fluorescent surface and outputting a waveform image. The waveform analysis unit 52 obtains a time waveform of the electric signal on the basis of the waveform image. As a result, it is possible to realize a semiconductor inspecting device and an inspecting method with which it is possible to measure, at high speed, the temporal change in the intensity of reflected light when a semiconductor device is irradiated with probe light.

Description

Semiconductor inspection device and semiconductor inspection method

[0001] The present disclosure relates to a semiconductor inspection apparatus and a semiconductor inspection method for inspecting semiconductor devices.

[0002] Known methods for inspecting the operating state of semiconductor devices include electro-optical probing (EOP), electro-optical frequency mapping (EOFM), laser voltage probing (LVP), and laser voltage imaging (LVI) (see, for example, Patent Documents 1 and 2).

[0003] In EOP, a semiconductor device whose state changes over time due to the application of a voltage pattern with a predetermined cycle is irradiated from the backside with probe light of a predetermined wavelength, and the change in the intensity of the reflected light over time is measured to inspect the operating state of the semiconductor device.In addition, in EOFM, a spectrum analyzer is used to perform frequency analysis of the reflected light from the semiconductor device, and an image of the part operating at a predetermined frequency is created.

[0004] International Publication No. WO 2022 / 064798 International Publication No. WO 2007 / 136681 European Patent Application Publication No. 0197196 European Patent Application Publication No. 0344986

[0005] In semiconductor inspection methods such as the EOP and EOFM described above, when an oscilloscope or digitizer is used to measure the electrical signal output from the photodetector that detects reflected light, the upper limit of the measurable frequency is, for example, approximately 7 to 8 GHz. Meanwhile, LSI performance continues to improve, and the inspection of such semiconductor devices may require measuring jitter in the 10 ps range. However, conventional inspection equipment has difficulty measuring the temporal change in the intensity of reflected light at such high speeds with sufficient accuracy.

[0006] Furthermore, in the above-described inspection method, the change in the intensity of the light reflected from the semiconductor device due to the application of the voltage pattern may be weak. In such cases, in order to measure the change in the intensity of the weak reflected light with a sufficient S / N ratio, it is possible to perform multiple integrations of the electrical signal output from the photodetector. However, with conventional inspection devices, it is difficult to perform high-speed integration of the electrical signal.

[0007] The embodiments aim to provide a semiconductor inspection apparatus and a semiconductor inspection method that are capable of measuring, at high speed, the change in the intensity of reflected light over time when a probe light is irradiated onto a semiconductor device to be inspected.

[0008] The embodiment is a semiconductor inspection apparatus, which includes: (1) an inspection optical system that irradiates a semiconductor device whose state changes over time in a predetermined test period with probe light of a first wavelength and outputs reflected light of the probe light reflected by the semiconductor device; (2) an optical measurement unit that has a photodetector that detects the reflected light output from the inspection optical system and outputs an electrical signal having a time waveform corresponding to the time change in intensity of the reflected light; (3) a signal conversion unit that has a measurement light source that supplies measurement light of a second wavelength different from the first wavelength and an optical modulator that intensity-modulates the measurement light based on the electrical signal output from the optical measurement unit and outputs the measurement light modulated by the optical modulator as an optical signal having a time waveform corresponding to the time waveform of the electrical signal; and (4) a signal conversion unit that converts the measurement light output from the signal conversion unit into an optical signal having a time waveform corresponding to the time waveform of the electrical signal. (4) a waveform measurement unit that measures the time waveform of the optical signal inputted into the streak tube; (5) a waveform analysis unit that determines the time waveform of the electrical signal based on the measurement results of the time waveform of the optical signal by the waveform measurement unit; (6) the waveform measurement unit has a photocathode that generates electrons in response to the input of an optical signal, a sweep electrode that sweeps the electrons from the photocathode in a predetermined sweep direction at a sweep period set according to the test period, and a streak tube including a fluorescent screen that receives the electrons swept by the sweep electrode and generates a fluorescent image showing the time waveform of the optical signal; and an image pickup element that captures the fluorescent image generated on the fluorescent screen of the streak tube and outputs a waveform image; and (7) the waveform analysis unit determines the time waveform of the electrical signal based on the waveform image outputted from the image pickup element.

[0009] The embodiment is a semiconductor inspection method, which includes: (1) an inspection step of irradiating a semiconductor device whose state changes over time in a predetermined test period with probe light of a first wavelength and outputting reflected light resulting from reflection of the probe light by the semiconductor device; (2) an optical measurement step of using a photodetector to detect the reflected light output in the inspection step and outputting an electrical signal having a time waveform corresponding to the time change in intensity of the reflected light; (3) a signal conversion step of using an optical modulator to intensity-modulate measurement light of a second wavelength different from the first wavelength based on the electrical signal output in the optical measurement step and outputting the measurement light modulated by the optical modulator as an optical signal having a time waveform corresponding to the time waveform of the electrical signal; and (4) a time conversion step of converting the optical signal output in the signal conversion step into a time waveform corresponding to the time waveform of the electrical signal. and (5) a waveform analysis step of determining the time waveform of the electrical signal based on the measurement results of the time waveform of the optical signal by the waveform measurement step, wherein the (6) waveform measurement step uses a streak tube including a photocathode that generates electrons in response to an input of an optical signal, a sweep electrode that sweeps the electrons from the photocathode in a predetermined sweep direction at a sweep period set according to the test period, and a fluorescent screen that inputs the electrons swept by the sweep electrode and generates a fluorescent image that shows the time waveform of the optical signal, and captures the fluorescent image generated on the fluorescent screen of the streak tube to output a waveform image, and the (7) waveform analysis step determines the time waveform of the electrical signal based on the waveform image output by the waveform measurement step.

[0010] Another embodiment is a semiconductor inspection device. The semiconductor inspection apparatus includes: (1) an inspection optical system that irradiates a semiconductor device whose state changes over time in a predetermined test period with probe light of a first wavelength and outputs reflected light obtained by reflecting the probe light from the semiconductor device; (2) an optical measurement unit that has a photodetector that detects the reflected light output from the inspection optical system and outputs an electrical signal having a time waveform corresponding to the change in intensity of the reflected light over time; (3) a signal conversion unit that has a measurement light source that supplies measurement light of a second wavelength different from the first wavelength and an optical modulator that intensity-modulates the measurement light based on the electrical signal output from the optical measurement unit and outputs the measurement light modulated by the optical modulator as an optical signal having a time waveform corresponding to the time waveform of the electrical signal; (4) a waveform measurement unit that has a streak camera and measures the time waveform of the optical signal output from the signal conversion unit; and (5) a waveform analysis unit that determines the time waveform of the electrical signal based on the measurement result of the time waveform of the optical signal by the waveform measurement unit; (6) the streak camera outputs a waveform image showing the time waveform of the optical signal in response to the input of the optical signal; and (7) the waveform analysis unit determines the time waveform of the electrical signal based on the waveform image output from the streak camera.

[0011] In the semiconductor inspection apparatus and semiconductor inspection method described above, a semiconductor device to be inspected is irradiated with probe light of a first wavelength, the reflected light is detected by a photodetector, and an electrical signal having a time waveform corresponding to the change in the intensity of the reflected light over time is generated. This electrical signal is then converted into an optical signal of a second wavelength by an optical modulator, and the time waveform of the optical signal is measured by a waveform measurement unit configured as a streak camera including a streak tube, and the time waveform of the electrical signal is determined based on the obtained waveform image.

[0012] According to this configuration, by converting the electrical signal into an optical signal and then performing waveform measurement using a streak tube, it is possible to measure at high speed the time waveform of the electrical signal corresponding to the time change in the intensity of reflected light from the semiconductor device. Furthermore, in the above configuration, by appropriately setting the first wavelength of the probe light and the second wavelength of the measurement light which is different from the first wavelength, it is possible to suitably achieve both inspection of the semiconductor device using the probe light and waveform measurement using the streak tube of the optical signal obtained by intensity-modulating the measurement light with an electrical signal, thereby making it possible to accurately measure the time change in the intensity of reflected light.

[0013] According to the semiconductor inspection apparatus and semiconductor inspection method of the embodiment, it is possible to measure at high speed the change over time in the intensity of reflected light when a probe light of a predetermined wavelength is irradiated onto a semiconductor device to be inspected.

[0014] FIG. 1 is a block diagram illustrating a schematic configuration of an embodiment of a semiconductor inspection device. FIG. 2 is a block diagram illustrating an example of the specific configuration of a voltage application unit, an inspection optical system, and an optical measurement unit. FIG. 3 is a block diagram illustrating a schematic configuration of a first embodiment of an electrical signal measurement device including a signal conversion unit and a waveform measurement unit. FIG. 4 is a diagram illustrating an example of the configuration of an optical modulator in the signal conversion unit. FIG. 5 is a diagram illustrating an example of the configuration of a streak tube in the waveform measurement unit. FIG. 6 is a side view illustrating an example of the configuration of the waveform measurement unit. FIG. 7 is (a) a top view and (b) a side view illustrating an example of the configuration of an input optical system in the waveform measurement unit. FIG. 8 is (a) a diagram illustrating an optical image of an optical signal incident on the photocathode of the streak tube, and (b) a diagram illustrating the sweep of an electron image on the phosphor screen. FIG. 9 is a diagram illustrating an example of a fluorescent image generated on the phosphor screen corresponding to the optical image of an optical signal input to the photocathode of the streak tube. FIG. 10 is a diagram illustrating (a) a waveform image acquired when optical signal generation in the signal conversion unit is ON, and (b) an example of a base image acquired when optical signal generation is OFF. FIG. 11 is a graph showing the measurement results of an electrical signal using an oscilloscope and the measurement results using the electrical signal measuring device shown in FIG. 3 . FIG. 12 is a diagram showing the relationship between (a) the intensity of reflected light, (b) the intensity of an electrical signal, and (c) the intensity of an optical signal. FIG. 13 is a top view (a) and a side view (b) showing a first modified example of the configuration of the input optical system of the waveform measuring unit. FIG. 14 is a top view (a) and a side view (b) showing a second modified example of the configuration of the input optical system of the waveform measuring unit. FIG. 15 is a top view (a) and a side view (b) showing a third modified example of the configuration of the input optical system of the waveform measuring unit. FIG. 16 is a diagram showing the configuration of a second embodiment of an electrical signal measuring device. FIG. 17 is a diagram schematically showing the main sweep and return sweep in a streak tube. FIG. 18 is a diagram showing an example of setting the measurement period and the phase of the sweep period in a streak tube. FIG. 19 is a diagram showing the configuration of a third embodiment of an electrical signal measuring device. Fig. 20 is a diagram showing input of two types of optical signals to a photocathode in the configuration shown in Fig. 19. Fig. 21 is a diagram showing the configuration of a fourth embodiment of an electrical signal measuring device.

[0015] Hereinafter, embodiments of a semiconductor inspection device and a semiconductor inspection method will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted. Furthermore, the dimensional proportions of the drawings do not necessarily match those in the description.

[0016] 1 is a block diagram showing a schematic configuration of one embodiment of a semiconductor inspection apparatus. The semiconductor inspection apparatus 1A according to this embodiment is an apparatus that performs inspection by irradiating a semiconductor device D with probe light, and is configured to include a semiconductor inspection unit 10, an optical measurement unit 20, a probe light source 21, an electrical signal measurement device 2A, a control device 50, an input unit 53, a display unit 54, and a scan control unit 55. The semiconductor inspection apparatus 1A also includes a second optical measurement unit 61, a second waveform measurement unit 62, and a frequency analysis unit 63.

[0017] In the following drawings, double lines between each part of the device indicate optical transmission paths for probe light, reflected light, measurement light, optical signals, etc. Preferably, optical fibers such as single-mode optical fibers are used as such optical transmission paths. Alternatively, spatial transmission paths using lenses, mirrors, etc. may be used as the optical transmission paths depending on the transmission conditions. Furthermore, single lines and arrowed lines between each part of the device indicate transmission paths for electrical signals, synchronization signals, trigger signals, control signals, etc., or optical paths for probe light and reflected light for the semiconductor device D.

[0018] The semiconductor device D, which is the device under test (DUT) to be inspected by the semiconductor inspection apparatus 1A shown in FIG. 1, can be any semiconductor device, but specific examples include an integrated circuit (IC) having a PN junction such as a transistor, or a logic device, memory device, or analog device that is a large-scale integrated circuit (LSI).

[0019] Furthermore, the semiconductor device D may further comprise a mixed signal device that combines the above, or a power semiconductor device (power device) such as a high current / high voltage MOS transistor, a bipolar transistor, or an IGBT. The inspection of the semiconductor device D performed by the semiconductor inspection apparatus 1A utilizes techniques such as EOP and EOFM, and includes verifying the operating state of each part of the device and identifying fault locations. Examples of the parts of the semiconductor device D to be inspected include transistors, diodes, capacitors, wiring, etc. to which voltage is applied.

[0020] The semiconductor inspection unit 10 includes an inspection optical system 11 and a voltage application unit 12. The inspection optical system 11 irradiates a semiconductor device D to be inspected with probe light of a first wavelength supplied from a probe light source 21 via an optical measurement unit 20. The inspection optical system 11 also outputs reflected light of the probe light reflected by the semiconductor device D to the optical measurement unit 20.

[0021] The semiconductor device D is usually irradiated with probe light from the back side of the device, for example, the Si substrate side. Therefore, light having a wavelength that can transmit through silicon is used as the probe light. In this case, the first wavelength of the probe light is preferably set within the wavelength range of 1050 nm to 5000 nm. Specifically, for example, light having a wavelength of 1.3 μm can be used as such probe light.

[0022] The probe light supplied from the probe light source 21 may be coherent light or incoherent light. Specific examples of the probe light source 21 that can be used include a laser light source, a super luminescent diode (SLD), an amplified spontaneous emission (ASE) light source, and a light emitting diode (LED).

[0023] The voltage application unit 12 applies a test pattern in which a voltage repeatedly changes over time in a predetermined test period to the semiconductor device D. At this time, in the semiconductor device D to which the test pattern is applied, the state of each part of the device changes over time in the test period of the voltage change. The optical measurement unit 20 supplies probe light output from the probe light source 21 to the inspection optical system 11, and inputs reflected light from the semiconductor device D output from the inspection optical system 11. The intensity of the reflected light from the semiconductor device D changes over time in the test period in accordance with the change in the state of the semiconductor device D over time.

[0024] 2 is a block diagram showing an example of a specific configuration of the voltage application unit 12, the inspection optical system 11, and the optical measurement unit 20. In this example configuration, the voltage application unit 12 is configured to have a tester head 12a of a semiconductor tester (LSI tester) and a test board 12b. The tester head 12a mounts a semiconductor device D via the test board 12b, and repeatedly applies a test pattern to the semiconductor device D, which includes a predetermined operating pulse signal and drives the semiconductor device D, at the above-mentioned test period.

[0025] The tester head 12a includes, for example, a pulse generator that generates an operating pulse signal for driving transistors and the like included in the semiconductor device D, a tester unit that inputs the operating pulse signal to the semiconductor device D, and a power supply. The test board 12b is a semiconductor substrate on which the semiconductor device D is mounted. The test board 12b includes peripheral chips, circuits, terminals, and the like required for the operation of the semiconductor device D.

[0026] The inspection optical system 11 is configured to include a stage 14, a scanning optical system 15, an imaging optical system 16, and an objective lens 17. The scanning optical system 15, the imaging optical system 16, and the objective lens 17 are placed on the stage 14 and arranged in a dark box 13. The objective lens 17 is arranged between the imaging optical system 16 and the semiconductor device D. In this configuration example, a plurality of objective lenses are provided as the objective lens 17, which can be switched by a turret 18. The plurality of objective lenses 17 include, for example, a low-magnification (e.g., 5x) objective lens and a high-magnification (e.g., 50x) objective lens.

[0027] The scanning optical system 15 guides the probe light input from the probe light source 21 through the optical measurement unit 20 and the optical fiber to the imaging optical system 16. The output end of the probe light in the optical fiber is preferably an APC type to reduce light reflection. The scanning optical system 15 is configured with an optical scanner including an optical scanning element such as a galvanometer mirror or a MEMS mirror, and scans and sets the irradiation position of the probe light on the semiconductor device D based on the control of the scan control unit 55.

[0028] The imaging optical system 16 guides the probe light input from the scanning optical system 15 to the objective lens 17 via a predetermined optical path. The objective lens 17 focuses and irradiates the probe light onto a set irradiation position on the semiconductor device D. Furthermore, reflected light (returned light) generated by irradiating the semiconductor device D with the probe light is input to the optical measurement unit 20 via the objective lens 17, imaging optical system 16, scanning optical system 15, and optical fiber. The wavelength of this reflected light is the first wavelength, the same as that of the probe light. Furthermore, a solid immersion lens may be installed between the objective lens 17 and the semiconductor device D, if necessary.

[0029] The reflectance and absorptance of the light reflected from the semiconductor device D to the probe light change slightly (on the order of several tens of ppm / V) due to the electric field and heat generated at the measurement point where the probe light is irradiated, and the resulting changes in carrier density, etc. This causes a slight change in the intensity of the reflected light over time. By measuring this change in the intensity of the reflected light over time, the semiconductor device D can be inspected.

[0030] The optical measurement unit 20 includes an optical coupler 22, an optical amplifier 23, an optical branching unit 24, a photodetector 25, and an AC amplifier 26. The optical coupler 22 is optically coupled to the probe light source 21, the optical amplifier 23, and the scanning optical system 15 via optical fibers, and outputs the probe light input from the probe light source 21 to the scanning optical system 15, and outputs the reflected light from the semiconductor device D input from the scanning optical system 15 to the optical amplifier 23. The optical coupler 22 and the scanning optical system 15 are connected using, for example, an APC FC adapter.

[0031] Specifically, for example, a PBS-type optical coupler, a circulator-type optical coupler, or the like can be used as the optical coupler 22. When the optical coupler 22 is a PBS-type optical coupler, a λ / 4 wave plate may be provided in the scanning optical system 15. When the optical coupler 22 is a circulator-type optical coupler, a λ / 2 wave plate may be provided in the scanning optical system 15. A Faraday rotator may be provided in the scanning optical system 15 instead of the wave plate. An optical splitter may also be used as the optical coupler 22.

[0032] The optical amplifier 23 amplifies the intensity of the reflected light from the semiconductor device D input from the optical coupler 22 within a range that does not cause gain saturation and does not cause saturation of the downstream photodetector 25, and outputs the amplified reflected light to the optical splitter 24. Specific examples of the optical amplifier 23 that can be used include a semiconductor optical amplifier, an optical fiber amplifier, a solid optical amplifier (SOA), a tapered optical amplifier, and a booster optical amplifier. Alternatively, the optical amplifier 23 may be an optical amplifier that uses a crystal, gas, liquid, or the like as an amplification medium.

[0033] The optical branching device 24 is optically coupled to the photodetector 25, the second optical measurement unit 61, and the optical amplifier 23 via optical fibers, and outputs the reflected light input from the optical amplifier 23 to the photodetector 25 and the second optical measurement unit 61 at a predetermined branching ratio. Specifically, for example, a 90:10 optical splitter can be used as the optical branching device 24. In this case, the light from the optical amplifier 23 is branched by the optical branching device 24 at a branching ratio of 90:10 to the photodetector 25 and the second optical measurement unit 61. Furthermore, for example, an FC connector is used to connect the optical branching device 24 and the second optical measurement unit 61.

[0034] The photodetector 25 detects the amplified reflected light input from the optical branching device 24 and outputs an electrical signal (detection signal) indicating the detection result. The electrical signal output from the photodetector 25 has a time waveform corresponding to the change over time in the intensity of the reflected light from the semiconductor device D. It is preferable to use, for example, a PIN photodiode (PIN-PD) capable of high-speed detection operations as the photodetector 25.

[0035] When a high-speed optical sensor such as a PIN-PD is used as the photodetector 25, the input is basically via a single-mode optical fiber. For this reason, it is preferable that the input optical fiber, optical coupler, etc. are all configured using a combination of single-mode optical fibers. However, such a light guide system may also be configured using an optical system that combines a half mirror, a polarizing beam splitter, a collimator, etc. Furthermore, other photodiodes such as an avalanche photodiode (APD), a photomultiplier tube, etc. may also be used as the photodetector 25 in addition to a PIN-PD.

[0036] The AC amplifier 26 amplifies the AC component of the detection signal input as an electrical signal from the photodetector 25 and outputs the amplified electrical signal to the electrical signal measuring device 2A. This signal amplification in the AC amplifier 26 extracts the time-varying component of the intensity of the detection signal, and also appropriately adjusts and sets the offset level of the electrical signal before it is input to the electrical signal measuring device 2A. This offset reset operation will be described in more detail below.

[0037] Referring again to Figure 1, the electrical signal measuring device 2A includes a signal converting unit 30 and a waveform measuring unit 40. The signal converting unit 30 converts the electrical signal input from the AC amplifier 26 of the optical measuring unit 20 into an optical signal for signal waveform measurement, and outputs the converted optical signal to the waveform measuring unit 40. The waveform measuring unit 40 measures the time waveform of the optical signal input from the signal converting unit 30, and outputs the measurement result to the control device 50. The configuration of the electrical signal measuring device 2A will be described in detail later.

[0038] The control device 50 is configured to include an inspection control unit 51 and a waveform analysis unit 52. The inspection control unit 51 controls the operation of each unit of the device, such as the semiconductor inspection unit 10, the optical measurement unit 20, the probe light source 21, the scan control unit 55, and the electrical signal measurement device 2A, thereby controlling and executing the inspection of the semiconductor device D in the semiconductor inspection device 1A. The waveform analysis unit 52 determines the time waveform of the electrical signal generated by the optical measurement unit 20 in accordance with the time change in the intensity of the reflected light, based on the measurement result of the time waveform of the optical signal input from the waveform measurement unit 40 of the electrical signal measurement device 2A.

[0039] 1, the control device 50 is provided with an input section (input device) 53 and a display section (display device) 54. The input section 53 is made up of, for example, a keyboard, a mouse, etc., and is used to input information necessary for semiconductor inspection, electrical signal measurement, and waveform analysis in the semiconductor inspection equipment 1A. The display section 54 is made up of, for example, a liquid crystal display, etc., and is used to display inspection results of the semiconductor device D, results of waveform analysis of electrical signals, etc.

[0040] Specifically, the control device 50 can be configured, for example, by a computer having a CPU as a processing unit, and ROM, RAM, an external storage device, etc. as a storage unit. In this case, the computer functions as an inspection control device and a waveform analysis device. Furthermore, the inspection control unit 51 and the waveform analysis unit 52 may be configured by separate computers or by a single computer.

[0041] In the semiconductor inspection apparatus 1A shown in FIG. 1 , the second optical measurement unit 61, the second waveform measurement unit 62, and the frequency analysis unit 63 are device parts that perform EOP and EOFM in the same manner as conventional inspection apparatuses. The second optical measurement unit 61 includes a photodetector such as an avalanche photodiode and an amplifier. The second waveform measurement unit 62 is configured using, for example, a digitizing board or a digital oscilloscope. The frequency analysis unit 63 is configured using, for example, a spectrum analyzer for acquiring EOFM images or a lock-in amplifier.

[0042] In this configuration, the electrical signal measuring device 2A functions as a high-speed digitizing unit, and the second waveform measuring unit 62 functions as a low-speed digitizing unit. Furthermore, a sine-wave synchronization signal, a square-wave trigger signal, etc. are output from the voltage application unit 12 of the semiconductor testing unit 10, and these synchronization signals and trigger signals are supplied as necessary to each unit of the device, such as the electrical signal measuring device 2A, the second waveform measuring unit 62, and the frequency analysis unit 63. The synchronization signal is not limited to the sine-wave signal described above, and may be, for example, a square-wave signal.

[0043] Next, the configuration and operation of the electrical signal measuring device 2A used in the semiconductor inspection device 1A shown in FIG. 1 will be described.

[0044] 3 is a block diagram showing a schematic configuration of a first embodiment of an electrical signal measuring device including a signal conversion unit 30 and a waveform measurement unit 40. The electrical signal measuring device 2A according to this embodiment is configured as a streak oscilloscope using a streak camera (see, for example, Patent Documents 3 and 4). As shown in FIG. 3, the electrical signal measuring device 2A also includes a waveform analysis unit (waveform analyzer) 52 of a control device 50 as needed.

[0045] 3 illustrates the optical measurement unit 20, the tester head 12a, and a delay generator (DG) 19 connected to the tester head 12a for the electrical signal measuring device 2A, and for convenience, these are referred to as an electrical signal supply unit 80. In the electrical signal supply unit 80, the optical measurement unit 20 functions as an electrical signal output unit 81, the tester head 12a functions as a synchronization signal output unit 82, and the delay generator 19 functions as a trigger signal output unit 83. The delay generator 19 adjusts the delay time and pulse width of the signal supplied from the tester head 12a and outputs it as a trigger signal.

[0046] The signal conversion unit 30 is configured to include a measurement light source 31, an optical attenuator 32, and an optical modulator 33. The measurement light source 31 supplies measurement light of a second wavelength different from the first wavelength of the probe light for semiconductor inspection. This measurement light is continuous light that is the source of the optical signal input to the waveform measurement unit 40. The measurement light used is light of a wavelength that can be modulated by the optical modulator 33 and whose waveform can be measured by a streak tube 42 in the waveform measurement unit 40, which will be described later.

[0047] In this case, the second wavelength of the measurement light is preferably set within a wavelength range of 115 nm to 1600 nm inclusive, taking into consideration the sensitivity distribution of the photocathode used in the streak tube 42, and more preferably within a wavelength range of 200 nm to less than 1050 nm in order to obtain sufficient sensitivity. Specifically, light with a wavelength of 850 nm or 780 nm can be used as such measurement light. Furthermore, in order to suppress deterioration of time resolution due to dispersion in the optical fiber, it is preferable to use narrow-band light as the measurement light.

[0048] Specifically, for example, a laser light source, an SLD (Super Luminescent Diode), an LED (Light Emitting Diode), etc. can be used as the measurement light source 31. The measurement light source 31 to be actually used is preferably selected depending on the type of modulator used as the optical modulator 33. The measurement light output from the measurement light source 31 is attenuated and adjusted in intensity (light amount) by an optical attenuator 32, and then input to the optical modulator 33 as continuous light.

[0049] An electrical signal from the optical measurement unit 20 is input to the optical modulator 33 as a modulation control signal. The optical modulator 33 intensity-modulates the measurement light supplied from the measurement light source 31 based on the electrical signal input from the optical measurement unit 20, and outputs the modulated measurement light as an optical signal having a time waveform corresponding to the time waveform of the electrical signal. The optical modulator 33 is configured to be capable of analog light intensity modulation.

[0050] Specific examples of the optical modulator 33 that can be used include an electro-optic (EO) modulator, an acousto-optic (AO) modulator, a magneto-optic (MO) modulator, and a Pockels cell. However, among these, a Pockels cell requires a voltage of about several hundred volts, which poses a problem when modulating a weak electrical signal. Furthermore, the bandwidth of an AO modulator is limited to about several hundred megahertz. Furthermore, an MO modulator requires a relatively large magnetic field (current).

[0051] Considering these points, it is preferable to use an EO modulator as the optical modulator 33. This makes it possible to suitably achieve intensity modulation of the measurement light by a high-speed electrical signal. When an EO modulator, AO modulator, or MO modulator is used as the optical modulator 33, it is preferable to use a laser light source as the measurement light source 31. When a Pockels cell is used as the optical modulator 33, it is preferable to use an SLD or LED as the measurement light source 31.

[0052] 4 is a diagram showing an example of the configuration of the optical modulator 33 in the signal conversion unit 30. The optical modulator 33 in this example configuration has an EO crystal 330, optical waveguides 331 to 334 formed on the crystal 330, an RF electrode 335, a bias electrode 336, and ground electrodes 337a to 337d, and is configured as an EO modulator capable of modulating light intensity. Specific examples of the EO crystal 330 include lithium niobate (LiNbO ３ ) can be used.

[0053] 4, an input optical waveguide 331 is provided on the left side of a rectangular EO crystal 330, and an output optical waveguide 334 is provided on the right side. The input optical waveguide 331 is branched into a first branch optical waveguide 332 and a second branch optical waveguide 333 via a 50:50 optical coupler. These first and second branch optical waveguides 332 and 333 are again coupled via a 50:50 optical coupler and connected to the output optical waveguide 334.

[0054] Measurement light to be modulated, input from the measurement light source 31 to the input optical waveguide 331, is branched by the input-side optical coupler to first and second branch optical waveguides 332 and 333. The branched light guided through the first and second branch optical waveguides 332 and 333 interfere when combined in the output-side optical coupler, and is output as interference light having a predetermined intensity from the output optical waveguide 334. This interference light output from the output optical waveguide 334 becomes an optical signal to be input to the waveform measurement unit 40 as an object to measure the time waveform.

[0055] An RF electrode 335 is provided on the input side between the first and second branch optical waveguides 332 and 333, and a bias electrode 336 is provided on the output side. A ground electrode 337a is provided to the RF electrode 335, with the first branch optical waveguide 332 sandwiched between them, and a ground electrode 337b is provided to the second branch optical waveguide 333 sandwiched between them. Furthermore, a ground electrode 337c is provided to the bias electrode 336, with the first branch optical waveguide 332 sandwiched between them, and a ground electrode 337d is provided to the bias electrode 336, with the second branch optical waveguide 333 sandwiched between them.

[0056] In the above configuration, the hatched region between the electrodes in the figure is the region where an electric field is applied to the optical waveguide by applying a voltage to the RF electrode 335 or the bias electrode 336. When an electric field is applied to the EO crystal 330, the refractive index in the optical waveguide formed in the electric field application region changes. This changes the optical path difference between the first and second branch optical waveguides 332 and 333, and the intensity of the interference light output from the output optical waveguide 334 changes.

[0057] An electrical signal from the optical measurement unit 20, which is used for intensity modulation of the measurement light, is applied to the RF electrode 335 located on the input side of the EO crystal 330. This causes the optical modulator 33 to convert the electrical signal into an optical signal. Furthermore, the application of a voltage to the bias electrode 336 is used to adjust the phase of the optical interference, and is used, for example, to adjust the offset in the signal conversion from an electrical signal to an optical signal, as will be described later.

[0058] As described above, in the optical modulator 33 using an EO modulator, the polarization direction of the modulated light is fixed, and the optical modulator 33 needs to have a longer interference distance than the interferometer, so it is preferable to use laser light as the measurement light to be modulated. Furthermore, particularly when the Z direction of the crystal is the up-and-down direction in the figure, the amount of change in the refractive index is reversed when the direction of the electric field applied to the Z axis is reversed, so light can be modulated at a lower voltage and at a higher speed. It is also possible to use a thin-film EO modulator that uses a photonic integrated circuit (PIC) as the optical modulator 33.

[0059] 3, the waveform measurement unit 40 is configured as a streak camera and includes an input optical system 41, a streak tube 42, an output optical system (imaging optical system) 43, an image sensor 44, and a synchronization unit 45. A rectangular wave trigger signal is input to the waveform measurement unit 40 including the streak tube 42 from the delay generator 19, and a sine wave or other synchronization signal is input from the tester head 12a via the synchronization unit (synchronization circuit) 45.

[0060] The configuration of the streak camera of the waveform measurement unit 40 including the streak tube 42 will be described. Fig. 5 is a perspective view showing an example of the configuration of the streak tube 42. Fig. 6 is a side view showing an example of the configuration of the waveform measurement unit 40 including the streak tube 42. The streak tube 42 in this configuration example is configured to include an outer tube 420, a photocathode 421, an accelerating electrode 422, a vertical sweep electrode 423, a horizontal sweep electrode 424, a microchannel plate (MCP) 425, and a phosphor screen 426. The streak tube 42 may also be configured without the MCP 425.

[0061] 5 shows an xyz Cartesian coordinate system, and in the configurations of the streak tube 42, input optical system 41, and output optical system 43, the traveling direction of the optical signal and electrons is defined as the z-axis direction, the sweep direction of electrons in the streak tube 42 perpendicular to the z-axis direction is defined as the y-axis direction, and the direction perpendicular to the z-axis and y-axis directions is defined as the x-axis direction. Also, FIG. 6 is a side view of the configuration of the waveform measurement unit 40 as seen from the x-axis direction.

[0062] In the configuration shown in Figure 5, an outer tube 420 extends in the z-axis direction, and a photocathode 421 is provided on its input side, and a phosphor screen 426 is provided on its output side opposite the photocathode 421. An optical signal from the signal conversion unit 30 is incident on the photocathode 421 via the input optical system 41, and forms an optical image P1 on the photocathode 421. The photocathode 421 generates electrons (photoelectrons) in response to the input optical signal. At this time, the number of electrons generated by the photocathode 421 corresponds to the intensity of the optical signal at each point in time. The electrons emitted from the photocathode 421 are accelerated in the z-axis direction by an accelerating electrode 422 within the outer tube 420.

[0063] The vertical sweep electrode 423, horizontal sweep electrode 424, and MCP 425 are provided in this order from the photocathode 421 side within the outer tube 420 between the photocathode 421 and the phosphor screen 426. When a sweep voltage of a predetermined pattern is applied to the vertical sweep electrode 423, the vertical sweep electrode 423 sweeps electrons from the photocathode 421 in a predetermined sweep direction (y-axis direction) at a sweep period set according to the test period in the semiconductor testing unit 10. The electrons swept by the sweep electrode 423 are multiplied by the MCP 425 and enter the phosphor screen 426. The size of the phosphor screen 426 is, for example, φ18 mm.

[0064] At this time, the electron image P2 formed on the phosphor screen 426 moves in the y-axis direction over time due to the sweep of electrons by the sweep electrode 423. As a result, a fluorescent image is generated on the phosphor screen 426, showing the time waveform of the optical signal input to the photocathode 421, with the y-axis direction being the time axis. Note that, for ease of illustration, FIG. 5 only shows the movement of the electron image P2 in the y-axis direction on the incident surface of the MCP 425. Furthermore, the horizontal sweep electrode 424 is used when it is necessary to sweep or move the electron image P2 in the x-axis direction, which is perpendicular to the normal sweep direction.

[0065] As shown in Fig. 6, the fluorescent image formed on the fluorescent screen 426 of the streak tube 42 is input to the image sensor 44 via the output optical system 43. The image sensor 44 captures the fluorescent image formed on the fluorescent screen 426 and outputs a waveform image, which is a two-dimensional image. As the image sensor 44, a two-dimensional image sensor such as a CMOS image sensor or a CCD image sensor is used, and specifically, for example, a CMOS camera with 2048 x 2048 pixels and a pixel size of 6.5 µm x 6.5 µm is used. In the configuration shown in Fig. 6, the output optical system 43 is made up of lenses 430 and 431.

[0066] The waveform image acquired by the image sensor 44, like the fluorescent image on the fluorescent screen 426, is an image showing the time waveform of the optical signal input to the waveform measurement unit 40, with the y-axis direction as the time axis. The waveform analysis unit 52 (see FIG. 3) of the control device 50 determines the time waveform of the electrical signal corresponding to the time waveform of the optical signal based on the waveform image output from the image sensor 44. The time waveform of this electrical signal corresponds to the change over time in the intensity of reflected light from the semiconductor device D in the semiconductor inspection unit 10. Therefore, by referring to the time waveform of the electrical signal acquired by the waveform analysis unit 52, it is possible to inspect the semiconductor device D.

[0067] Furthermore, in order to accurately measure weak temporal changes in the intensity of reflected light in the semiconductor inspection unit 10, an optical signal from the signal conversion unit 30 may be repeatedly input to the waveform measurement unit 40 over multiple cycles, and a fluorescent image may be generated on the fluorescent screen 426 of the streak tube 42 by integrating the time waveform of the optical signal over multiple cycles for the test period. In this case, the waveform image acquired by the image sensor 44 is also similarly an integrated time waveform of the optical signal over multiple cycles.

[0068] In order to suitably perform the above-described inspection of the semiconductor device D, the streak camera of the waveform measurement unit 40 controls the measurement operation of the time waveform of the optical signal based on a synchronization signal or a trigger signal supplied from the voltage application unit 12. Specifically, the waveform measurement unit 40 has two measurement modes for measuring the time waveform of the optical signal: a single sweep mode and a synchro scan mode.

[0069] In the single sweep mode, the waveform measurement unit 40 performs single-shot measurement in synchronization with a rectangular waveform trigger signal from the tester head 12a or the delay generator 19. In this case, the sweep voltage applied to the sweep electrode 423 has, for example, a linearly varying voltage pattern. The test period for voltage application in the semiconductor tester can be freely determined. In the single sweep mode, it is also possible to repeat the single-shot measurement multiple times and integrate the time waveform.

[0070] In the synchronous scan mode, the waveform measurement unit 40 synchronizes with a sinusoidal synchronization signal from the tester head 12a and performs measurement by integrating multiple cycles of time waveforms. In this case, the sweep voltage applied to the sweep electrode 423 is controlled by the synchronization unit 45 and has, for example, a sinusoidal voltage pattern similar to the synchronization signal. In this mode, high time accuracy of, for example, 800 fs or less can be achieved. However, in this case, the test cycle in the semiconductor tester is limited to an integer multiple of the cycle of the synchronization signal.

[0071] The conditions for inputting an optical signal to the photocathode 421 of the streak tube 42 and the configuration of the input optical system 41 provided upstream of the streak tube 42 will now be described. In the above configuration, shot noise based on the light quantity of the optical signal input to the streak tube 42 determines the noise floor of the measurement. In this case, it is preferable to increase the light quantity in order to reduce the proportion of shot noise, but the photocathode 421 has an upper limit on the density of the input light quantity. Furthermore, when performing multiple integrated measurements of the time waveform of the optical signal, deterioration of the photocathode due to this can also become a problem.

[0072] Considering these points, in order to reduce the light intensity density input to the photocathode and to suppress deterioration of the photocathode, it is preferable that the input optical system 41 input the optical signal to the photocathode 421 as a line-shaped optical image extending in a direction intersecting the sweep direction (y-axis direction) of the streak tube 42. This makes it possible to reduce the input light intensity density compared to when the optical signal is input as a point-shaped optical image P1 as shown in Fig. 5. In this case, it is preferable to set the image formation direction of the line-shaped optical image to a direction (x-axis direction) perpendicular to the sweep direction.

[0073] Fig. 7 is a diagram showing an example of the configuration of the input optical system 41 in the waveform measurement unit 40. In Fig. 7, Fig. 7(a) shows a top view seen from the y-axis direction, and Fig. 7(b) shows a side view seen from the x-axis direction. The lens configuration in the input optical system 41 shown in Fig. 7 is similar to the lens configuration schematically shown in Fig. 6.

[0074] 6 and 7 is composed of, in order from the input side of the optical signal from the signal conversion unit 30 (the optical fiber end side from which the optical signal is output), a cylindrical lens 410, a lens 411, and a lens 412. In this way, by using the cylindrical lens 410 in the input optical system 41, a line-shaped optical image can be formed on the photocathode 421, as shown by the spread of the light beam in FIG.

[0075] Fig. 8 is a diagram schematically showing the optical image and electron image formed in the streak tube 42. In Fig. 8, Fig. 8(a) is a diagram showing an optical image P3 of an optical signal incident on the photocathode 421 of the streak tube 42, and Fig. 8(b) is a diagram showing the sweep of an electron image P4 on the phosphor screen 426. The optical image P3 and electron image P4 shown in Fig. 8 are formed in a configuration using the input optical system 41 shown in Fig. 7.

[0076] As shown in Fig. 8(a), the optical signal is input to the photocathode 421 as a linear optical image P3 extending in the x-axis direction. As shown in Fig. 8(b), a linear electron image P4 extending in the x-axis direction corresponding to the optical image P3 is formed on the fluorescent screen 426, and this electron image P4 is swept in the y-axis direction to generate a fluorescent image showing the time waveform of the optical signal.

[0077] 9 shows an example of a fluorescent image generated on the fluorescent screen 426 in response to a line-shaped optical image of an optical signal input to the photocathode 421 of the streak tube 42. Here, the fluorescent image corresponding to the line-shaped electron image is measured as is, without sweeping electrons using the sweep electrode 423. The line-shaped optical image on the photocathode 421 corresponding to the fluorescent image shown in FIG. 9 has a length of approximately 5 mm in the x-axis direction and a width of approximately 15 μm in the y-axis direction.

[0078] 10 shows an example of an image obtained by capturing a fluorescent image generated on the fluorescent screen 426 with the image sensor 44 during normal measurement in which electrons are swept by the sweep electrode 423. In Fig. 10, Fig. 10(a) shows a waveform image acquired when the generation of an optical signal in the signal conversion unit 30 is ON, and Fig. 10(b) shows a base image (background image) acquired when the generation of an optical signal is OFF. In the waveform image in Fig. 10(a), a fluorescent image obtained by sweeping a line-shaped electron image is measured.

[0079] 1 to 3, the semiconductor inspection method performed by the semiconductor inspection device 1A and the electrical signal measurement device 2A includes an inspection step, an optical measurement step, a signal conversion step, a waveform measurement step, and a waveform analysis step. In the inspection step, the semiconductor inspection unit 10 irradiates a semiconductor device D with probe light and outputs reflected light from the semiconductor device D. Note that in the inspection step, a voltage application step may be performed in which a predetermined test pattern is applied to the semiconductor device D using the voltage application unit 12.

[0080] In the optical measurement step, the optical measurement unit 20 including the photodetector 25 detects reflected light from the semiconductor device D and outputs an electrical signal having a time waveform corresponding to the temporal change in the intensity of the reflected light. In the signal conversion step, the signal conversion unit 30 of the electrical signal measurement device 2A intensity-modulates the measurement light using the optical modulator 33 based on the electrical signal output from the optical measurement unit 20, and outputs an optical signal having a time waveform corresponding to the time waveform of the electrical signal.

[0081] In the waveform measurement step, the waveform measurement section 40 of the electrical signal measurement device 2A uses the streak tube 42, the image pickup element 44, etc. to measure the time waveform of the optical signal output from the signal conversion section 30, and outputs the obtained waveform image. In the waveform analysis step, the waveform analysis section 52 of the control device 50 determines the time waveform of the electrical signal based on the waveform image output from the waveform measurement section 40, and performs a predetermined inspection of the semiconductor device D using the waveform.

[0082] The effects of the semiconductor inspection device 1A, the electrical signal measuring device 2A, and the semiconductor inspection method according to the above embodiment will be described.

[0083] 1 to 8, a semiconductor device D to be inspected is irradiated with probe light of a first wavelength from a probe light source 21, and the reflected light is detected by a photodetector 25 to generate an electrical signal having a time waveform corresponding to the change in the intensity of the reflected light over time. This electrical signal is then converted into an optical signal of a second wavelength by an optical modulator 33, after which the time waveform of the optical signal is measured by a waveform measurement unit 40 including a streak tube 42, and the time waveform of the electrical signal is determined based on a waveform image acquired by an image sensor 44.

[0084] According to this configuration, by converting the electrical signal into an optical signal and then performing waveform measurement using the streak tube 42, it is possible to quickly measure the time waveform of the electrical signal corresponding to the time change in the intensity of the reflected light from the semiconductor device D. Furthermore, in the above configuration, by appropriately setting the first wavelength of the probe light and the second wavelength of the measurement light which is different from the first wavelength, it is possible to suitably achieve both inspection of the semiconductor device D using the probe light and waveform measurement by the streak tube 42 of the optical signal obtained by intensity-modulating the measurement light with an electrical signal, thereby making it possible to accurately measure the time change in the intensity of the reflected light.

[0085] Fig. 11 is a graph showing the measurement results of the time waveform of the electrical signal. In the graph of Fig. 11, the horizontal axis represents time (ps) and the vertical axis represents signal intensity (a.u.). In Fig. 11, graph G1 shows the measurement results obtained by measuring the electrical signal using a 20 GHz oscilloscope, and graph G2 shows the measurement results obtained by using the electrical signal measuring device 2A configured as shown in Fig. 3.

[0086] Here, pulsed laser light from a femtosecond laser is detected by a 40 GHz band PIN-PD, and the output electrical signal is measured. The wavelength of the laser light is 1550 nm, the repetition frequency is 100 MHz, and the pulse width is 100 fs or less. The measurement results in graph G1 were obtained using a Tektronix DPO72004C oscilloscope with a 20 GHz band.

[0087] For the measurement results of graph G2, the integration speed of the streak camera of the waveform measurement unit 40 was 50 MHz, the frame rate was 60 Hz, and the integration time was 1.6 seconds (100 frames with an exposure time of 10 ms), and the integration time of the base image for subtraction, which will be described later, was also 1.6 seconds. As shown in the graph of Figure 11, in the configuration of the above embodiment, when measuring a weak signal, integration is performed at a high speed that cannot be achieved with an oscilloscope, and a time waveform is suitably acquired. The FWHM of the measured waveform is 31.85 ps for graph G1 and 19.21 ps for graph G2.

[0088] In the inspection apparatus 1A and inspection method of the above embodiment, the waveform measurement unit 40 may be configured so that the fluorescent screen 426 of the streak tube 42 generates a fluorescent image in which the time waveform of the optical signal for multiple periods is accumulated for the test period of the semiconductor device D.

[0089] In this case, after converting the electrical signal into an optical signal, waveform measurement is performed using the streak tube 42, and the time waveform of the optical signal is integrated in generating a fluorescent image using the phosphor screen 426 and acquiring the waveform image using the image sensor 44, thereby enabling the time waveform of the electrical signal to be integrated multiple times at high speed optically. In this case, the number of integrations of the time waveform of the optical signal is preferably set appropriately depending on conditions such as the intensity of reflected light from the semiconductor device D to be measured. For example, when a synchronous scan is performed at 40 MHz with a streak camera, the number of integrations per second is determined depending on the test period, etc., within a range of up to 40 million times per second.

[0090] In the inspection device 1A and inspection method of the above embodiment, a voltage application unit 12 is provided to apply a test pattern in which the voltage changes over time in a test period to the semiconductor device D, and the waveform measurement unit 40 may be configured to control the measurement operation of the time waveform of the optical signal based on a synchronization signal or a trigger signal supplied from the voltage application unit 12.

[0091] In this case, by applying a test pattern to the semiconductor device D, the state of the semiconductor device D changes over time in a test period. Then, by using a synchronization signal or a trigger signal from the voltage application unit 12 to control the measurement operation of the time waveform of the optical signal in the waveform measurement unit 40 including the streak tube 42, it is possible to suitably measure the change over time in the intensity of the reflected light from the semiconductor device D caused by the application of the test pattern.

[0092] In the inspection apparatus 1A and inspection method of the above embodiment, as for setting the wavelengths of the probe light and the measurement light, as described above, it is preferable that the first wavelength of the probe light is set within the wavelength range of 1050 nm to 5000 nm, and the second wavelength of the measurement light is set within the wavelength range of 200 nm to less than 1050 nm. This makes it possible to preferably perform both the inspection of the semiconductor device D using the probe light and the waveform measurement by the streak tube 42 of the optical signal obtained by intensity-modulating the measurement light with an electrical signal.

[0093] Regarding the application of a streak camera to a semiconductor inspection device, for example, a configuration in which the streak camera directly measures the infrared reflected light of the probe light from the semiconductor device D is also conceivable. However, in the wavelength range of infrared light used in semiconductor inspection, the quantum efficiency of the photocathode of a streak tube is low, for example, about 1%, making it impossible to obtain sufficient measurement efficiency. Furthermore, infrared photocathodes that are applicable to light in such wavelength ranges have the problem of low manufacturing yield. In contrast, by detecting the reflected light as described above to generate an electrical signal, converting the electrical signal into an optical signal of a different wavelength, and then measuring it with a streak camera, waveform measurement can be performed efficiently and quickly.

[0094] In the inspection device 1A and inspection method of the above embodiment, the waveform analysis unit 52 may be configured to correct a waveform image acquired when the generation of an optical signal in the signal conversion unit 30 is ON, based on a base image acquired when the generation of an optical signal is OFF. In this way, the waveform analysis unit 52 corrects the waveform image based on the base image, and by using this corrected waveform image to determine the time waveform of the electrical signal, it is possible to accurately measure the change in the intensity of reflected light over time.

[0095] Acquisition of such a base image and the resulting base correction of the waveform image can be used, for example, to correct variations in measurement efficiency due to position on the fluorescent screen 426 of the streak tube 42 or the image pickup element 44 (gain correction). Also, performing base correction as described above is effective for correcting drift of measurement characteristics over time in the semiconductor inspection device 1A.

[0096] For example, the EO modulator used in the optical modulator 33 of the signal conversion unit 30 may experience characteristic drift due to heat, and the offset may still be shifted even after gain correction. In such a case, it is preferable to take measures to dissipate heat from the optical modulator 33 and correct the characteristic drift over time for the waveform image acquired by the waveform measurement unit 40.

[0097] In correcting the characteristic drift over time as described above, it is preferable to switch between waveform image acquisition and base image acquisition in a short time to obtain a sufficient correction effect. However, because this device must handle high-speed signals, it is difficult to switch measurements using a switch or the like. Therefore, the above measurement switching can be performed, for example, by controlling the power supply of the SOA used as the optical amplifier 23 to turn it on / off, by switching the PIN-PD used as the photodetector 25, or by switching the AC amplifier 26 to turn it on / off. In particular, it is preferable to use ON / OFF switching of the SOA of the optical amplifier 23 as the method that is the fastest and has the least impact on the gain characteristics.

[0098] In the inspection device 1A and inspection method of the above embodiment, the optical measurement unit 20 may have an optical amplifier 23 that amplifies and outputs the reflected light output from the inspection optical system 11, and the photodetector 25 may be configured to detect the reflected light amplified by the optical amplifier 23. Furthermore, the photodetector 25 of the optical measurement unit 20 may be configured as a PIN-PD.

[0099] These configurations enable the optical measurement unit 20 to measure the reflected light from the semiconductor device D and output an electrical signal at high speed and with high accuracy. That is, when inspecting the semiconductor device D, the intensity of the probe light must be set to an extent that does not destroy the semiconductor device D, and the intensity of the reflected light will also be small. For example, when a solid immersion lens that achieves an NA of 1 or more is used, the upper limit of the intensity of the probe light is about several mW, and the upper limit of the intensity of the reflected light from the semiconductor device D at this time is about 0.1 mW.

[0100] For this reason, when the reflected light is directly detected by the photodetector 25, for example, an APD is used as the photodetector 25. However, the capacity of an APD is relatively large, making it difficult to adequately support high-speed signal measurement. In contrast, by providing an optical amplifier 23 such as an SOA in the preceding stage of the photodetector 25, it becomes possible to use a high-speed optical sensor such as a PIN-PD as the photodetector 25, and in combination with waveform measurement using a streak camera, high-speed signal measurement can be suitably realized.

[0101] In the inspection device 1A and inspection method of the above embodiment, the optical measurement unit 20 may be configured to have an amplification element such as an AC amplifier 26 that amplifies the alternating current component (AC component) of the detection signal output from the photodetector 25 and outputs it as an electrical signal.

[0102] According to this configuration, the AC amplifier 26 downstream of the photodetector 25 removes the DC component of the detection signal and performs offset resetting to amplify only the AC component, thereby extracting the time-varying component of the intensity of the detection signal and appropriately adjusting and setting the offset level of the electrical signal before conversion to an optical signal in the signal conversion unit 30. Note that, other than the AC amplifier 26, other elements that remove DC components or extract AC components may also be used as the amplifying element that extracts and amplifies the AC component of the detection signal.

[0103] Here, we will explain the relationship between the time change in the intensity of reflected light, the time waveform of the electrical signal, and the time waveform of the optical signal, and the setting of the signal offset level in the semiconductor inspection apparatus 1A. Figure 12 is a diagram showing the relationship between (a) the intensity of reflected light from the semiconductor device D, (b) the intensity of the electrical signal generated by the optical measurement unit 20, and (c) the intensity of the optical signal generated by the signal conversion unit 30.

[0104] For example, when a probe beam with a wavelength of 1.3 μm is irradiated, the intensity of the reflected light from the semiconductor device D is about 0.1 mW, as described above. In this case, for the reflected light intensity shown in FIG. 12( a), if the reflected light intensity level (DC component) A0 is 1, the shot noise level in the 100 GHz band is 2.25% at 1σ. In contrast, the signal level (AC component) A1 of the time change in the reflected light intensity used in semiconductor inspection is very small, ranging from 0.001% to 0.01%.

[0105] The signal level of the electrical signal generated by the optical measurement unit 20, which includes the optical amplifier 23, photodetector 25, and AC amplifier 26, in response to this reflected light is, for example, as shown in Figure 12(b). The detection signal output from the photodetector 25 contains DC and AC components, just like the intensity of the reflected light. However, by removing the DC component of the detection signal in the AC amplifier 26 and amplifying only the AC component, the signal level corresponding to the intensity level A0 of the reflected light becomes almost zero. The shot noise level is approximately 300 mV at 1 σ. Meanwhile, the signal level B1 corresponding to the signal level A1 of the time change in the intensity of the reflected light is approximately 0.15 mV to 1.5 mV.

[0106] The signal level of the optical signal generated by the optical modulator 33 modulating the intensity of the measurement light based on this electrical signal is, for example, as shown in Fig. 12(c) In Fig. 12(c) , curve C5 shows the sinusoidal relationship between the voltage (vertical axis) of the electrical signal applied to the EO modulator constituting the optical modulator 33 and the intensity (horizontal axis) of the generated optical signal.

[0107] As shown in FIG. 12( c), in the signal conversion from an electrical signal to an optical signal in the optical modulator 33, in order to maximize sensitivity to voltage changes in the electrical signal and improve the linearity of the signal conversion, it is preferable to apply an offset bias voltage, as indicated by signal level C0, so that the transmitted light intensity of the measurement light when the voltage of the electrical signal is zero is a predetermined light intensity, e.g., 50% of the maximum transmitted light intensity. In this case, the intensity change range C2 of the converted optical signal can be sufficiently widened relative to the voltage change range C1 of the electrical signal. Furthermore, by adjusting the offset in the optical measurement unit 20 and the signal conversion unit 30, it is possible to accurately and suitably measure the time change in the intensity of the reflected light and integrate the time waveform. It is preferable to appropriately set the maximum intensity of the optical signal using an optical attenuator 32 or the like so that it is equal to or less than the upper limit of the incident light density on the photocathode.

[0108] The conditions for measuring the temporal change in the intensity of reflected light in the above configuration will now be described in more detail. When measuring and integrating an optical signal, it is important to remove its DC component. Optical sensors have a problem called saturation, which places an upper limit on the amount of light they can measure. Therefore, if the temporal change in the optical signal (AC component) is measured without removing the DC component, problems such as an increase in the proportion of shot noise and a decrease in the efficiency of measuring the AC component arise.

[0109] First, let's consider the optical signal detection side. As a specific example, a waveform consisting of 2000 data points per second is created from 100 frames of images captured by a 2000 x 2000 pixel streak camera. In this case, if the saturated charge per pixel is 30k, the maximum number of electrons that can be contained in one data point when integrated over one second is 2000 x 30k x 100, or 6 billion. Furthermore, the total number of electrons in the data when integrated over one second is 12 trillion.

[0110] In the above case, the S / N ratio based on the shot noise standard for the signal amount is 1 / 77,000. In reality, since it is difficult to measure at the very edge of saturation, if we assume about half of saturation, the S / N ratio becomes 1 / √2, and the amount of noise becomes about 1 / 50,000 of the signal amount. In this case, since the EOP signal level is about 1 / 10,000 to 1 / 100,000 of the light amount as mentioned above, the S / N ratio on the image acquisition side is ideally about 0.5 to 5.

[0111] Next, let's consider the input side of the optical signal. As mentioned above, the amount of light reflected at the EOP is, for example, about 0.1 mW. Furthermore, the number of photons at this time is about 660 trillion per second when converted to a wavelength of 1.3 μm. The expected S / N ratio at this time is also about 2.3 to 23 for a waveform with 2000 points. Note that here, we are considering 1 / 6 of the aperture time in synchronous scan mode.

[0112] However, when reflected light is actually input directly to a streak camera, taking into consideration the durability of the streak camera's photocathode (1 / 10 of the light amount due to about 10 μW), quantum efficiency (1 / 100 in the case of an infrared crystal photocathode), and the utilization efficiency of the internal electrons (1 / 10), the S / N ratio drops to 1 / 100, or about 0.02 to 0.2. In other words, when measurements are made without removing the offset, the S / N ratio in the measurement is limited by the shot noise due to the number of electrons in the streak camera.

[0113] In contrast, as described above, by removing the offset via an AC amplifier or the like, it is possible to improve the S / N ratio of the measurement while suppressing the amount of light input to the photocathode. In a system with the above configuration, the offset can be reduced to, for example, 1 / 10. This allows the S / N ratio to be improved by approximately 10 times by increasing the amplitude of the optical signal relative to the shot noise, which is determined by the number of electrons, while maintaining the amount of light input to the photocathode.

[0114] Furthermore, by inputting light only during the aperture time, the average light intensity can be increased by six times, and by shifting the wavelength to achieve a quantum efficiency of 20%, the number of electrons can be increased by 20 times. However, as the wavelength of the optical signal becomes shorter, quantum noise increases by approximately 25%. As a result, the expected S / N ratio in measurements using the above configuration is improved by approximately 90 times, to approximately 1.8 to 18.0. In other words, by removing the offset described above, it is possible to exceed the upper limit of the S / N ratio imposed on the detection side.

[0115] The above explanation is based on the assumption that measurements are made at the fastest synchronous frequency. However, if the test cycle of a semiconductor tester is an integer multiple of the synchronous frequency, there will be a margin of light intensity on the photocathode side and the camera side. Therefore, in such cases, it is possible to increase the instantaneous input light intensity accordingly. This reduces the problem of a decrease in S / N ratio when the cycle is extended in a normal EOP.

[0116] The following describes how to set the number of integration times for a time waveform when measuring a signal using the electrical signal measuring device 2A. As described above, the shot noise level in reflected light measurement is 2.25% in the 100 GHz band and 0.225% in the 1 GHz band. The signal level is 0.001% to 0.01%.

[0117] In this case, for example, to obtain a time waveform with an S / N ratio of 10 or more, in the case of a 1 GHz band and a signal level of 0.001%, the required number of integrations is 2250 squared, or approximately 5 million. Furthermore, if the band is increased by 10 times, the required number of integrations also simply increases by 10 times; for example, the required number of integrations for a 10 GHz band is 50 million, and the required number of integrations for a 40 GHz band is 200 million.

[0118] The higher the signal strength relative to noise, the smaller the required number of integrations; for example, if the S / N ratio is 10 times higher, the required number of integrations will be 1 / 100. One method for improving the S / N ratio is to increase the light intensity to change the ratio between shot noise and signal. However, as described above, the light intensity of the probe light must be set to a level that does not destroy the semiconductor device D. Therefore, it may be difficult to increase the signal strength in this way. Considering practical conditions in semiconductor inspection, it is preferable to set the number of integrations of the time waveform in reflected light measurement to, for example, between 1 million and 1 billion.

[0119] A specific example of an inspection method for a semiconductor device D executed using the semiconductor inspection apparatus 1A will be described. First, a pattern image and an EOFM image of the semiconductor device D to be inspected are acquired, and a measurement target position is set on the semiconductor device D. Next, a normal EOP measurement is performed using the second optical measurement unit 61 and the second waveform measurement unit 62, and a time waveform indicating the change over time in the intensity of reflected light from the semiconductor device D is acquired. In addition, a measurement range is set for EOP measurement by the electrical signal measurement apparatus 2A using a streak camera.

[0120] Next, the time waveform acquired by EOP measurement is displayed on the display unit 54, and the measurement period (measurement start time and duration) for which actual measurement is to be performed on that waveform is set and selected. Then, for the set measurement period, measurement is performed using the optical measurement unit 20 and the electrical signal measurement device 2A, a time waveform showing the time change in the intensity of the reflected light is obtained in the waveform analysis unit 52, and the measurement results are displayed on the display unit 54. Furthermore, if there are multiple measurement periods for which measurement is to be performed, similar measurements are performed multiple times while changing the phase as necessary. Furthermore, waveform image acquisition and base image acquisition may be performed alternately to perform base correction.

[0121] The configuration of the input optical system 41 in the streak camera of the waveform measurement unit 40 will now be described further. As described above, it is preferable that the input optical system 41 inputs an optical signal as a line-shaped optical image to the photocathode 421. As an example of a specific configuration for this purpose, Fig. 7 shows the configuration of the input optical system 41 including a cylindrical lens 410, a lens 411, and a lens 412, but various specific configurations other than the configuration shown in Fig. 7 can also be used for the input optical system 41.

[0122] 13A and 13B are a top view and a side view, respectively, showing a first modified example of the configuration of the input optical system 41 in the waveform measurement unit 40. The input optical system 41 of the first modified example is composed of, in order from the input side of the optical signal, a lens 413 and a cylindrical lens 414. With this configuration, a line-shaped optical image can be formed on the photocathode 421, similar to the configuration in FIG.

[0123] 7, in which the cylindrical lens 410 is arranged in the front stage of the lens configuration of the input optical system 41, and the configuration of Fig. 13, in which the cylindrical lens 414 is arranged in the rear stage, the arrangement direction of the cylindrical lens is different. In addition, in the configuration shown in Fig. 13, the rear cylindrical lens 414 also serves as an imaging lens.

[0124] 14A and 14B are a top view and a side view, respectively, showing a second modified example of the configuration of the input optical system 41 in the waveform measurement unit 40. The input optical system 41 of the second modified example is composed of, in order from the input side of the optical signal, a lens 413, a cylindrical lens 414, a lens 415, and a lens 416. The configuration in Fig. 14 is configured by adding a relay optical system composed of lenses 415 and 416 to the configuration in Fig. 13.

[0125] 15A and 15B are a top view and a side view, respectively, showing a third modified example of the configuration of the input optical system 41 in the waveform measurement unit 40. The input optical system 41 of the third modified example is composed of, in order from the input side of the optical signal, a lens 417, a Powell lens 418, and a lens 419. The Powell lens is a lens that spreads parallel light into a fan shape, and can form a thin, uniform, linear optical image by using it in combination with a normal lens or a cylindrical lens.

[0126] In the configuration shown in Figure 15, the rear lens 419 may be replaced with a combination of two cylindrical lenses arranged in different directions and with orthogonal axes. In this case, it becomes easier to adjust the light imaging position. In addition to the cylindrical lens and Powell lens described above, a combination of an anamorphic prism pair and a slit may also be used to form a line-shaped optical image. In general, it is preferable that the input optical system 41 includes at least one of a cylindrical lens, a Powell lens, and an anamorphic prism pair.

[0127] The configuration and operation of the electrical signal measuring device used in the semiconductor inspection device 1A will be further described.

[0128] Fig. 16 is a block diagram showing a schematic configuration of a second embodiment of an electrical signal measuring device including a signal converting unit 30 and a waveform measuring unit 40. The configuration of an electrical signal measuring device 2B according to this embodiment is the same as that shown in Fig. 3 with respect to the waveform measuring unit 40, but differs in the configuration of the signal converting unit 30. Note that Fig. 16 does not show the waveform analyzing unit 52 of the control device 50 that constitutes part of the electrical signal measuring device 2B.

[0129] The signal conversion unit 30 is configured to include a measurement light source 31, an optical attenuator 32, a conversion control optical modulator 34, and an optical modulator 33. Of these, the configurations of the measurement light source 31, the optical attenuator 32, and the optical modulator 33 are the same as those shown in FIG.

[0130] The conversion control optical modulator 34 is provided between the optical attenuator 32 and the optical modulator 33, and controls ON / OFF of the signal conversion operation from an electrical signal to an optical signal in the signal conversion unit 30 according to measurement conditions such as the test period in the semiconductor inspection unit 10. Specifically, the conversion control optical modulator 34 controls ON / OFF of the signal conversion operation by switching between passing and not passing the measurement light from the optical attenuator 32 based on a trigger signal input from the delay generator 19 or a control signal input from the inspection control unit 51 of the control device 50.

[0131] In this way, by providing the conversion control optical modulator 34 in the signal conversion unit 30 separately from the optical modulator 33 used for signal conversion, it becomes possible to perform various measurement controls according to the specific measurement conditions of the semiconductor inspection device 1 A. As with the optical modulator 33, the conversion control optical modulator 34 can be an EO modulator, an AO modulator, an MO modulator, a Pockels cell, or the like, and it is particularly preferable to use an EO modulator.

[0132] The control of the signal conversion operation using the conversion control optical modulator 34 can be, for example, control according to the main sweep and return sweep in the streak tube 42 of the waveform measurement unit 40. Here, Fig. 17 is a diagram schematically showing the main sweep and return sweep in the streak tube 42. In the streak tube 42, for example, in the synchronous scan mode, electrons are swept by a sinusoidal sweep voltage, and in this case, the main sweep in the original sweep direction and the return sweep in the opposite direction are alternately repeated.

[0133] In this case, as shown in FIG. 17, an electron image P5 generated by the main sweep and an electron image P6 generated by the return sweep are alternately input to the phosphor screen 426. However, if the electron image pattern generated by this return sweep is measured while being superimposed on the electron image pattern generated by the main sweep, the target time waveform cannot be measured correctly.

[0134] 16, on the other hand, the conversion control optical modulator 34 provided in the signal conversion unit 30 controls the signal conversion operation to be ON during the period corresponding to the main sweep in the streak tube 42, and to be OFF during the period corresponding to the return sweep, thereby making it possible to selectively measure only the electron image pattern due to the main sweep.

[0135] Note that, for the measurement control of the main sweep and return sweep in the streak tube 42, various specific configurations can be used other than the configuration using the conversion control optical modulator 34 of the signal conversion unit 30 as described above. For example, a configuration can be used in which a voltage is applied in a predetermined pattern to the horizontal sweep electrode 424 (see FIG. 5) in the streak tube 42 to shift the electron image to a position outside the phosphor screen 426 during the return sweep.

[0136] It is also possible to use a configuration in which the high voltage applied to the streak tube 42 is modulated and controlled, or the voltage applied to the MCP 425 is modulated and controlled.Instead of the MCP 425, it is also possible to use a configuration in which an image intensifier is provided between the streak tube 42 and the output optical system 43, and the ON / OFF of this image intensifier is controlled in accordance with the main sweep and return sweep.

[0137] However, with these configurations, the optical image of the optical signal is incident on the photocathode 421 even during the return sweep period when the time waveform is not measured, thereby degrading the photocathode 421. In contrast, with the configuration described above in which the signal conversion operation is controlled on / off using the conversion control optical modulator 34 of the signal conversion unit 30, the optical image of the optical signal is not incident on the photocathode 421 during the return sweep period, thereby suppressing degradation of the photocathode 421. Note that although the conversion control optical modulator 34 is disposed before the optical modulator 33 in FIG. 16 , it may also be disposed after the optical modulator 33.

[0138] Furthermore, in controlling the measurement period and measurement conditions of the time waveform of the electrical signal in the electrical signal measuring device 2B, in addition to controlling the measurement period by the conversion control optical modulator 34, the phase in the waveform measurement may also be controlled. Specifically, for example, in the waveform measuring unit 40, the streak tube 42 may be configured to adjust the phase of the sweep period according to the period during which the time waveform of the electrical signal should be measured within the test period in the semiconductor testing unit 10. Even with such a configuration, it is possible to perform various measurement controls according to specific measurement conditions.

[0139] 18 is a diagram showing an example of setting the measurement period and the phase of the sweep period in the streak tube. From top to bottom, Fig. 18 shows (a) a synchronization signal supplied from the tester head 12a, (b) a trigger signal supplied from the tester head 12a or the delay generator 19, (c) a measurement period T1 set as a period during which waveform measurement is required within the time waveform of the electrical signal (time change in the intensity of reflected light), (d) a sweep voltage pattern in the streak tube 42, and (e) a control signal pattern supplied to the conversion control optical modulator 34.

[0140] 18, in each test period in the semiconductor testing unit 10, as shown in Fig. 18(c), a measurement period (measurement time window) T1 to be measured is set when testing the semiconductor device D. Furthermore, in accordance with this measurement period T1, as shown in Fig. 18(e), a control signal pattern to the conversion control optical modulator 34 is determined, thereby controlling the ON / OFF of the signal conversion operation.

[0141] 18(d), the timing of the electron sweep in the streak tube 42 is delayed by a time T2 from the synchronization signal so that the measurement period T1 of the time waveform is included in the main sweep period, thereby adjusting the phase of the sweep period. In this way, by setting the measurement period of the time waveform using the conversion control optical modulator 34 of the signal conversion unit 30 and setting and adjusting the phase of the electron sweep period in the streak tube 42, it is possible to perform waveform measurement under desired conditions. The phase adjustment can be performed using, for example, the phase delay function of a streak camera. Alternatively, the phase adjustment can be performed by providing a phase delay device on the synchronization line connecting the tester head 12a of the electrical signal supply unit 80 and the waveform measurement unit 40.

[0142] Fig. 19 is a block diagram showing a schematic configuration of a third embodiment of an electrical signal measuring device including a signal converting unit 30 and a waveform measuring unit 40. The configuration of an electrical signal measuring device 2C according to this embodiment is the same as that shown in Fig. 3 with respect to the waveform measuring unit 40, but differs in the configuration of the signal converting unit 30. Note that Fig. 19 does not show the waveform analyzing unit 52 of the control device 50, the supply of a synchronization signal from the tester head 12a, and the supply of a trigger signal from the delay generator 19.

[0143] The signal conversion unit 30 includes a measurement light source 31, an optical attenuator 32, an optical modulator 33, an optical coupler 35, a first optical delay 36 a, and a second optical delay 36 b. Of these, the measurement light source 31, the optical attenuator 32, and the optical modulator 33 have the same configurations as those shown in FIG.

[0144] The optical coupler 35 branches the optical signal (modulated measurement light) input from the optical modulator 33 and outputs it to the first optical delay device 36a and the second optical delay device 36b. The first optical delay device 36a delays the optical signal by a first delay time and then outputs it to the waveform measurement unit 40. The second optical delay device 36b delays the optical signal by a second delay time and then outputs it to the waveform measurement unit 40. The first and second delay times may be different or the same. One of the first and second delay times may be zero.

[0145] In order to measure the respective time waveforms, the two types of optical signals from the first and second optical delay devices 36a and 36b are preferably input to different regions on the photocathode 421 in the streak tube 42. Fig. 20 is a diagram showing the input of two types of optical signals to the photocathode 421 in the configuration shown in Fig. 19.

[0146] 20, the optical signal from the first optical delay device 36a passes through the cylindrical lens 410a, the lens 411a, and the reflecting mirror 428 and is incident as an optical image P7 on the left region of the photocathode 421 in the drawing. The optical signal from the second optical delay device 36b passes through the cylindrical lens 410b, the lens 411b, and the reflecting mirror 428 and is incident as an optical image P8 on the right region of the photocathode 421 in the drawing. This makes it possible to measure the time waveforms of the optical signals from the first and second optical delay devices 36a and 36b.

[0147] In this way, the signal conversion unit 30 generates two types of optical signals each having a time waveform corresponding to the time waveform of the electrical signal and having different conversion conditions, and the waveform measurement unit 40 measures the time waveform of each of these optical signals, making it possible to perform a variety of measurements.

[0148] For example, in the configuration shown in Fig. 19, the conversion control optical modulator 34 in the configuration of Fig. 16 may be further provided to turn on / off the signal conversion operation and to vary the delay times in the first and second optical delay devices 36a, 36b, thereby enabling eye pattern observation. Furthermore, although the number of optical signals generated in the signal conversion unit 30 is two types in the above example configuration, three or more types of optical signals may be generated.

[0149] 21 is a block diagram showing a schematic configuration of a fourth embodiment of an electrical signal measuring device including a signal converting section 30 and a waveform measuring section 40. The configuration of an electrical signal measuring device 2D according to this embodiment is the same as that shown in FIG. 3 with respect to the waveform measuring section 40, but differs in the configuration of the signal converting section 30. Note that the omission of the waveform analyzing section 52 of the control device 50 and the like is the same as in FIG. 19 .

[0150] The signal conversion unit 30 includes a measurement light source 31, an optical attenuator 32, an optical coupler 37, and first and second optical modulators 33 a and 33 b. Of these, the measurement light source 31 and the optical attenuator 32 have the same configurations as those shown in FIG.

[0151] The optical coupler 37 branches the measurement light input from the optical attenuator 32 and outputs it to the first optical modulator 33 a and the second optical modulator 33 b. An electrical signal is input to the first and second optical modulators 33 a and 33 b from the optical measurement unit 20. Each of the first and second optical modulators 33 a and 33 b intensity-modulates the measurement light based on the electrical signal input from the optical measurement unit 20, and outputs the modulated measurement light as an optical signal having a time waveform corresponding to the time waveform of the electrical signal.

[0152] The two types of optical signals from the first and second optical modulators 33 a, 33 b are preferably input to different regions on the photocathode 421 of the streak tube 42. In this configuration, different electrical signals may be input to the first and second optical modulators 33 a, 33 b, or an optical delay may be provided for each of the first and second optical modulators 33 a, 33 b. With this configuration, it is possible to perform various measurements, similar to the configuration shown in FIG.

[0153] The semiconductor inspection device and semiconductor inspection method are not limited to the above-described embodiment and configuration examples, and various modifications are possible. For example, while the optical measurement unit 20 is configured to include the optical amplifier 23, the photodetector 25, and the AC amplifier 26 in FIG. 2, the optical amplifier 23 and the AC amplifier 26 may be omitted if they are not required. Furthermore, the configuration of the semiconductor inspection unit 10 is not limited to the configurations shown in FIGS. 1 and 2, and various specific configurations may be used.

[0154] Furthermore, the configuration of the electrical signal measuring device 2A is not limited to the configurations shown in Figures 3, 16, 19, and 21, and various other configurations may be used. For example, the configuration shown in Figure 19 or 21 may be configured to further include the conversion control optical modulator 34 in the configuration of Figure 16. Furthermore, in the streak tube 42 of the waveform measuring unit 40, the horizontal sweep electrode 424 and the MCP 425 may not be provided if they are unnecessary. Furthermore, various other configurations may be used for the signal level and offset adjustment settings shown in Figure 12, depending on the configurations of the optical measuring unit 20 and the electrical signal measuring device.

[0155] The semiconductor inspection apparatus of the first aspect according to the above embodiment includes: (1) an inspection optical system that irradiates a probe light of a first wavelength onto a semiconductor device whose state changes over time in a predetermined test period and outputs a reflected light of the probe light reflected by the semiconductor device; (2) an optical measurement unit that has a photodetector that detects the reflected light output from the inspection optical system and outputs an electrical signal having a time waveform corresponding to the time change in intensity of the reflected light; (3) a signal conversion unit that has a measurement light source that supplies measurement light of a second wavelength different from the first wavelength and an optical modulator that intensity-modulates the measurement light based on the electrical signal output from the optical measurement unit and outputs the measurement light modulated by the optical modulator as an optical signal having a time waveform corresponding to the time waveform of the electrical signal; and (4) a signal conversion unit that converts the measurement light modulated by the optical modulator into an optical signal having a time waveform corresponding to the time waveform of the electrical signal. (5) a waveform measurement unit that measures the time waveform of the optical signal output from the switching unit; and (6) a waveform analysis unit that determines the time waveform of the electrical signal based on the measurement results of the time waveform of the optical signal by the waveform measurement unit, wherein the waveform measurement unit has a photocathode that generates electrons in response to the input of an optical signal, a sweep electrode that sweeps the electrons from the photocathode in a predetermined sweep direction at a sweep period set according to the test period, and a streak tube that includes a fluorescent screen that inputs the electrons swept by the sweep electrode and generates a fluorescent image that shows the time waveform of the optical signal, and an image pickup element that captures the fluorescent image generated on the fluorescent screen of the streak tube and outputs a waveform image, and (7) the waveform analysis unit determines the time waveform of the electrical signal based on the waveform image output from the image pickup element.

[0156] The semiconductor inspection method of the first aspect according to the above embodiment includes: (1) an inspection step of irradiating a semiconductor device whose state changes over time in a predetermined test period with probe light of a first wavelength and outputting reflected light of the probe light reflected by the semiconductor device; (2) an optical measurement step of using a photodetector to detect the reflected light output in the inspection step and outputting an electrical signal having a time waveform corresponding to the time change in intensity of the reflected light; (3) a signal conversion step of using an optical modulator that intensity-modulates measurement light of a second wavelength different from the first wavelength based on the electrical signal output in the optical measurement step, and outputting the measurement light modulated by the optical modulator as an optical signal having a time waveform corresponding to the time waveform of the electrical signal; and (4) a signal conversion step of converting the measurement light output in the signal conversion step into an optical signal having a time waveform corresponding to the time waveform of the electrical signal. and (5) a waveform analysis step of determining the time waveform of an electrical signal based on the measurement results of the time waveform of the optical signal by the waveform measurement step, wherein the (6) waveform measurement step uses a streak tube including a photocathode that generates electrons in response to the input of an optical signal, a sweep electrode that sweeps the electrons from the photocathode in a predetermined sweep direction at a sweep period set according to the test period, and a fluorescent screen that receives the electrons swept by the sweep electrode and generates a fluorescent image showing the time waveform of the optical signal, and captures the fluorescent image generated on the fluorescent screen of the streak tube to output a waveform image, and the (7) waveform analysis step determines the time waveform of the electrical signal based on the waveform image output by the waveform measurement step.

[0157] A semiconductor inspection apparatus according to a thirteenth aspect of the above-described embodiment includes: (1) an inspection optical system that irradiates a probe light of a first wavelength onto a semiconductor device whose state changes over time in a predetermined test period and outputs a reflected light of the probe light reflected by the semiconductor device; (2) an optical measurement unit that has a photodetector that detects the reflected light output from the inspection optical system and outputs an electrical signal having a time waveform corresponding to the change over time in the intensity of the reflected light; and (3) a measurement light source that supplies measurement light of a second wavelength different from the first wavelength, and an optical modulator that intensity-modulates the measurement light based on the electrical signal output from the optical measurement unit, (3) a signal conversion unit that outputs the measurement light modulated by the modulated light as an optical signal having a time waveform corresponding to the time waveform of the electrical signal; (4) a waveform measurement unit that has a streak camera and measures the time waveform of the optical signal output from the signal conversion unit; and (5) a waveform analysis unit that determines the time waveform of the electrical signal based on the measurement result of the time waveform of the optical signal by the waveform measurement unit, (6) the streak camera outputs a waveform image showing the time waveform of the optical signal in response to the input of the optical signal, and (7) the waveform analysis unit determines the time waveform of the electrical signal based on the waveform image output from the streak camera.

[0158] In the semiconductor inspection device of the second aspect, in the configuration of the first aspect, the waveform measurement unit may be configured so that the fluorescent screen of the streak tube generates a fluorescent image in which the time waveform of the optical signal for multiple periods is integrated for the test period.

[0159] In a semiconductor inspection method of a second aspect, in the configuration of the first aspect, in the waveform measurement step, the fluorescent screen of the streak tube may be configured to generate a fluorescent image in which time waveforms of the optical signal for a plurality of test periods are integrated.

[0160] In the above configuration, after converting the electrical signal into an optical signal, the waveform is measured using a streak tube, and by integrating the time waveform of the optical signal when generating a fluorescent image using a fluorescent screen and acquiring a waveform image using an image sensor, it is possible to optically integrate the time waveform of the electrical signal multiple times at high speed.

[0161] A semiconductor inspection device of a third aspect may be configured in the configuration of the first or second aspect described above, further comprising a voltage application unit that applies to the semiconductor device a test pattern in which the voltage changes over time in a test period, and the waveform measurement unit controls the measurement operation of the time waveform of the optical signal based on a synchronization signal or a trigger signal supplied from the voltage application unit.

[0162] In a semiconductor inspection method of a third aspect, in the configuration of the first or second aspect, the method may further include a voltage application step of applying to the semiconductor device a test pattern in which the voltage changes over time in a test period, and the waveform measurement step may be configured to control the measurement operation of the time waveform of the optical signal based on a synchronization signal or a trigger signal supplied in the voltage application step.

[0163] In the above configuration, by applying a test pattern to the semiconductor device, the state of the semiconductor device changes over time in a test period. Then, by using a synchronization signal or a trigger signal from the voltage application unit to control the measurement operation of the time waveform of the optical signal in the waveform measurement unit including the streak tube, it is possible to suitably measure the time change in the intensity of reflected light from the semiconductor device caused by the application of the test pattern.

[0164] In a fourth aspect of the semiconductor inspection device, in the configuration of any one of the first to third aspects, the optical measurement unit may have an optical amplifier that amplifies and outputs reflected light output from the inspection optical system, and the photodetector may detect the reflected light amplified by the optical amplifier. Also, in the semiconductor inspection device, in the configuration of any one of the above aspects, the photodetector of the optical measurement unit may be a PIN photodiode.

[0165] According to these configurations, the light measurement unit can measure the reflected light from the semiconductor device and output an electrical signal at high speed with high accuracy.

[0166] In the semiconductor inspection device of the fifth aspect, in the configuration of any one of the first to fourth aspects, the optical measurement unit may be configured to have an amplifying element such as an AC amplifier that amplifies the AC component of the detection signal output from the photodetector and outputs it as an electrical signal.

[0167] With this configuration, the amplifier element downstream of the photodetector amplifies only the AC component of the detection signal, thereby extracting the time variation in the signal strength of the detection signal and appropriately adjusting and setting the offset level of the electrical signal before conversion to an optical signal in the signal conversion unit.

[0168] In the semiconductor inspection device of the sixth aspect, in the configuration of any one of the first to fifth aspects, the optical modulator of the signal conversion section may be an EO modulator.

[0169] In this way, by using an EO modulator as an optical modulator that modulates the intensity of the measurement light, it is possible to suitably convert an electrical signal into an optical signal.

[0170] In the semiconductor inspection device of the seventh aspect, in the configuration of any of the above first to sixth aspects, the signal conversion unit may be configured to have a conversion control optical modulator that controls ON / OFF of the signal conversion operation from an electrical signal to an optical signal in accordance with the test period.

[0171] In the semiconductor inspection method of the fourth aspect, in the configuration of any of the first to third aspects, the signal conversion step may be configured to use an optical modulator for conversion control that controls ON / OFF of the signal conversion operation from an electrical signal to an optical signal in accordance with the test period.

[0172] In this case, in the semiconductor inspection device of the eighth aspect, in the configuration of the seventh aspect, the conversion control optical modulator of the signal conversion unit may be configured to turn on the signal conversion operation during a period corresponding to the main sweep in the streak tube, and to turn off the signal conversion operation during a period corresponding to the return sweep.

[0173] Furthermore, in the semiconductor inspection method of the fifth aspect, in the configuration of the fourth aspect, in the signal conversion step, the conversion control optical modulator may be configured to turn on the signal conversion operation during a period corresponding to the main sweep in the streak tube, and to turn off the signal conversion operation during a period corresponding to the return sweep.

[0174] In this way, by providing a conversion control optical modulator in the signal conversion unit in addition to the optical modulator used for signal conversion, it becomes possible to perform various measurement controls according to specific measurement conditions, such as controlling the ON / OFF of the signal conversion operation according to the main sweep and return sweep in the streak tube as described above. Furthermore, as the conversion control optical modulator, an EO modulator, for example, can be suitably used, similar to the signal conversion optical modulator.

[0175] In the semiconductor inspection device of the ninth aspect, in the configuration of any one of the first to eighth aspects, the waveform measurement unit may be configured so that the streak tube adjusts the phase of the sweep period in accordance with a period during the test period during which the time waveform of the electrical signal is to be measured.

[0176] In the semiconductor inspection method of the sixth aspect, in the configuration of any one of the first to fifth aspects, in the waveform measurement step, the streak tube may be configured to adjust the phase of the sweep period in accordance with a period within the test period during which the time waveform of the electrical signal is to be measured.

[0177] In this way, in the streak tube of the waveform measurement section, a configuration for adjusting the phase of the sweep period also makes it possible to perform various measurement controls according to specific measurement conditions.

[0178] In the semiconductor inspection device of the tenth aspect, in the configuration of any one of the first to ninth aspects, the signal conversion unit may be configured to generate, as optical signals, two or more types of optical signals each having a time waveform corresponding to the time waveform of the electrical signal and having different conversion conditions.

[0179] In the semiconductor inspection method of the seventh aspect, in the configuration of any of the first to sixth aspects, the signal conversion step may be configured to generate, as the optical signal, two or more types of optical signals each having a time waveform corresponding to the time waveform of the electrical signal and having different conversion conditions.

[0180] In this way, by generating two or more different types of optical signals in the signal conversion unit and measuring the time waveforms of each of these optical signals in the waveform measurement unit, it becomes possible to perform various measurements, such as measuring two types of optical signals with different delay times and observing eye patterns.

[0181] In the semiconductor inspection device of the eleventh aspect, in the configuration of any one of the first to tenth aspects, the first wavelength of the probe light may be set within a wavelength range of 1050 nm or more and 5000 nm or less, and the second wavelength of the measurement light may be set within a wavelength range of 200 nm or more and less than 1050 nm.

[0182] In the semiconductor inspection method of the eighth aspect, in the configuration of any one of the first to seventh aspects, the first wavelength of the probe light may be set within a wavelength range of 1050 nm or more and 5000 nm or less, and the second wavelength of the measurement light may be set within a wavelength range of 200 nm or more and less than 1050 nm.

[0183] By setting the first wavelength of the probe light and the second wavelength of the measurement light, which is different from the first wavelength, as described above, it is possible to suitably perform both inspection of a semiconductor device using the probe light and waveform measurement using a streak tube of an optical signal obtained by intensity-modulating the measurement light with an electrical signal.

[0184] In the semiconductor inspection device of the twelfth aspect, in the configuration of any of the above first to eleventh aspects, the waveform analysis unit may be configured to correct a waveform image acquired when the generation of an optical signal in the signal conversion unit is ON, based on a base image acquired when the generation of an optical signal is OFF.

[0185] In the semiconductor inspection method of the ninth aspect, in the configuration of any of the first to eighth aspects, in the waveform analysis step, the waveform image acquired in the signal conversion step when the generation of the optical signal is ON may be corrected based on a base image acquired in the signal conversion step when the generation of the optical signal is OFF.

[0186] In this way, by correcting the waveform image based on the base image and using this corrected waveform image to determine the time waveform of the electrical signal, it is possible to measure the time change in the intensity of the reflected light with even greater accuracy.

[0187] The embodiments can be used as a semiconductor inspection apparatus and a semiconductor inspection method capable of measuring, at high speed, the change in the intensity of reflected light over time when a probe light is irradiated onto a semiconductor device to be inspected.

[0188] 1A...semiconductor inspection apparatus, 2A to 2D...electrical signal measuring apparatus, D...semiconductor device, 10...semiconductor inspection section, 11...inspection optical system, 12...voltage application section, 12a...tester head, 12b...test board, 13...black box, 14...stage, 15...scanning optical system, 16...imaging optical system, 17...objective lens, 18...turret, 19...delay generator, 20...optical measurement section, 21...probe light source, 22...optical coupler, 23...optical amplifier, 24...optical branching device, 25...photodetector, 26...AC amplifier 30...signal conversion unit, 31...measurement light source, 32...optical attenuator, 33...optical modulator, 33a...first optical modulator, 33b...second optical modulator, 34...optical modulator for conversion control, 35...optical coupler, 36a...first optical delay unit, 36b...second optical delay unit, 37...optical coupler, 40...waveform measurement unit, 41...input optical system, 42...streak tube, 43...output optical system, 44...image pickup element, 45...synchronization unit, 50...control device, 51...inspection control unit, 52...waveform analysis unit, 53...input unit, 54...display unit, 55...scanning control unit, 61...second optical measurement unit, 62...second waveform measurement unit, 63...frequency analysis unit, 330...EO crystal, 331...input optical waveguide, 332...first branch optical waveguide, 333...second branch optical waveguide, 334...output optical waveguide, 335...RF electrode, 336...bias electrode, 337a to 337d...ground electrodes, 410, 414...cylindrical lens, 418...Powell lens, 411, 412, 413, 415, 416, 417, 419...lens, 430, 431...lens, 420...enveloping tube, 421...photocathode, 422...acceleration electrode, 423...vertical sweep electrode, 424...horizontal sweep electrode, 425...MCP, 426...phosphor screen, 428...reflection mirror, 80...electrical signal supply unit, 81...electrical signal output unit, 82...synchronization signal output unit, 83...trigger signal output unit.

Claims

1. An inspection optical system that irradiates a probe light of a first wavelength onto a semiconductor device whose state changes over time in a predetermined test period, and outputs reflected light of the probe light reflected by the semiconductor device; an optical measurement unit that has a photodetector that detects the reflected light output from the inspection optical system, and outputs an electrical signal having a time waveform corresponding to the change in intensity of the reflected light over time; a signal conversion unit that has a measurement light source that supplies measurement light of a second wavelength different from the first wavelength, and an optical modulator that intensity-modulates the measurement light based on the electrical signal output from the optical measurement unit, and outputs the measurement light modulated by the optical modulator as an optical signal having a time waveform corresponding to the time waveform of the electrical signal; a waveform measurement unit that measures the time waveform of the optical signal output from the signal conversion unit; and a waveform analysis unit that determines the time waveform of the electrical signal based on a measurement result of the time waveform of the optical signal by the waveform measurement unit, wherein the waveform measurement unit a streak tube including a photocathode that generates electrons in response to an input of the optical signal, a sweep electrode that sweeps electrons from the photocathode in a predetermined sweep direction at a sweep period set according to the test period, and a fluorescent screen that inputs the electrons swept by the sweep electrode and generates a fluorescent image indicative of the time waveform of the optical signal; and an image pickup element that picks up the fluorescent image generated on the fluorescent screen of the streak tube and outputs a waveform image, wherein the waveform analysis unit determines the time waveform of the electrical signal based on the waveform image output from the image pickup element.

2. A semiconductor inspection device as described in claim 1, wherein in said waveform measurement section, said fluorescent screen of said streak tube generates said fluorescent image by integrating said time waveform of said optical signal for a plurality of periods for said test period.

3. A semiconductor inspection device as described in claim 1 or 2, further comprising a voltage application unit that applies to the semiconductor device a test pattern in which the voltage changes over time in the test period, and the waveform measurement unit controls the measurement operation of the time waveform of the optical signal based on a synchronization signal or a trigger signal supplied from the voltage application unit.

4. A semiconductor inspection device according to any one of claims 1 to 3, wherein the optical measurement section has an optical amplifier that amplifies and outputs the reflected light output from the inspection optical system, and the photodetector detects the reflected light amplified by the optical amplifier.

5. A semiconductor inspection device according to any one of claims 1 to 4, wherein the optical measurement section has an amplifier element that amplifies the AC component of the detection signal output from the photodetector and outputs it as the electrical signal.

6. The semiconductor inspection device according to any one of claims 1 to 5, wherein the optical modulator of the signal conversion section is an EO modulator.

7. A semiconductor inspection device according to any one of claims 1 to 6, wherein the signal conversion section has an optical modulator for conversion control that controls ON / OFF of the signal conversion operation from the electrical signal to the optical signal in accordance with the test period.

8. A semiconductor inspection device as described in claim 7, wherein the conversion control optical modulator of the signal conversion section turns on the signal conversion operation during a period corresponding to a main sweep in the streak tube, and turns off the signal conversion operation during a period corresponding to a return sweep.

9. A semiconductor inspection device according to any one of claims 1 to 8, wherein in the waveform measurement section, the streak tube adjusts the phase of the sweep period in accordance with a period during which the time waveform of the electrical signal is to be measured within the test period.

10. A semiconductor inspection device according to any one of claims 1 to 9, wherein the signal conversion section generates, as the optical signal, two or more types of optical signals each having a time waveform corresponding to the time waveform of the electrical signal and having different conversion conditions.

11. A semiconductor inspection device according to any one of claims 1 to 10, wherein the first wavelength of the probe light is set within a wavelength range of 1050 nm or more and 5000 nm or less, and the second wavelength of the measurement light is set within a wavelength range of 200 nm or more and less than 1050 nm.

12. A semiconductor inspection device according to any one of claims 1 to 11, wherein the waveform analysis unit corrects the waveform image acquired when the generation of the optical signal in the signal conversion unit is ON, based on a base image acquired when the generation of the optical signal is OFF.

13. An inspection optical system that irradiates a probe light of a first wavelength onto a semiconductor device whose state changes over time in a predetermined test period, and outputs reflected light of the probe light reflected by the semiconductor device; an optical measurement unit that has a photodetector that detects the reflected light output from the inspection optical system, and outputs an electrical signal having a time waveform corresponding to the change in intensity of the reflected light over time; a signal conversion unit that has a measurement light source that supplies measurement light of a second wavelength different from the first wavelength, and an optical modulator that intensity-modulates the measurement light based on the electrical signal output from the optical measurement unit, and outputs the measurement light modulated by the optical modulator as an optical signal having a time waveform corresponding to the time waveform of the electrical signal; a waveform measurement unit that has a streak camera and measures the time waveform of the optical signal output from the signal conversion unit; and a waveform analysis unit that determines the time waveform of the electrical signal based on a measurement result of the time waveform of the optical signal by the waveform measurement unit, wherein the streak camera outputs a waveform image indicative of the time waveform of the optical signal in response to the input of the optical signal, The waveform analysis unit determines the time waveform of the electrical signal based on the waveform image output from the streak camera.

14. A method for manufacturing a semiconductor device, comprising: an inspection step of irradiating a probe light of a first wavelength onto a semiconductor device whose state changes over time in a predetermined test period, and outputting reflected light of the probe light reflected by the semiconductor device; an optical measurement step of using a photodetector to detect the reflected light outputted in the inspection step, and outputting an electrical signal having a time waveform corresponding to the change in intensity of the reflected light over time; a signal conversion step of using an optical modulator to intensity-modulate measurement light of a second wavelength different from the first wavelength based on the electrical signal outputted in the optical measurement step, and outputting the measurement light modulated by the optical modulator as an optical signal having a time waveform corresponding to the time waveform of the electrical signal; a waveform measurement step of measuring the time waveform of the optical signal outputted in the signal conversion step; and a waveform analysis step of determining the time waveform of the electrical signal based on a measurement result of the time waveform of the optical signal by the waveform measurement step, A semiconductor inspection method, wherein the waveform measurement step uses a streak tube including a photocathode that generates electrons in response to the input of the optical signal, a sweep electrode that sweeps electrons from the photocathode in a predetermined sweep direction at a sweep period set according to the test period, and a fluorescent screen that inputs the electrons swept by the sweep electrode and generates a fluorescent image indicative of the time waveform of the optical signal, and the fluorescent image generated on the fluorescent screen of the streak tube is captured to output a waveform image, and the waveform analysis step determines the time waveform of the electrical signal based on the waveform image output in the waveform measurement step.

15. A semiconductor inspection method according to claim 14, wherein in said waveform measuring step, said fluorescent screen of said streak tube generates said fluorescent image in which said time waveform of said optical signal for a plurality of periods is integrated for said test period.

16. A semiconductor inspection method as described in claim 14 or 15, further comprising a voltage application step of applying to said semiconductor device a test pattern in which the voltage changes over time in said test period, and in said waveform measurement step, a measurement operation for the time waveform of said optical signal is controlled based on a synchronization signal or a trigger signal supplied in said voltage application step.

17. A semiconductor inspection method according to any one of claims 14 to 16, wherein in the signal conversion step, an optical modulator for conversion control is used that controls ON / OFF of a signal conversion operation from the electrical signal to the optical signal in accordance with the test period.

18. A semiconductor inspection method as described in claim 17, wherein in the signal conversion step, the conversion control optical modulator turns on the signal conversion operation during a period corresponding to a main sweep in the streak tube, and turns off the signal conversion operation during a period corresponding to a return sweep.

19. A semiconductor inspection method according to any one of claims 14 to 18, wherein in the waveform measurement step, the streak tube adjusts the phase of the sweep period in accordance with a period during which the time waveform of the electrical signal is to be measured within the test period.

20. A semiconductor inspection method according to any one of claims 14 to 19, wherein in the signal conversion step, two or more types of optical signals are generated as the optical signals, each having a time waveform corresponding to the time waveform of the electrical signal and having different conversion conditions.

21. A semiconductor inspection method according to any one of claims 14 to 20, wherein the first wavelength of the probe light is set within a wavelength range of 1050 nm or more and 5000 nm or less, and the second wavelength of the measurement light is set within a wavelength range of 200 nm or more and less than 1050 nm.

22. A semiconductor inspection method according to any one of claims 14 to 21, wherein in the waveform analysis step, the waveform image acquired in the signal conversion step while the generation of the optical signal is ON is corrected based on a base image acquired while the generation of the optical signal is OFF.

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