Wafer defect photoluminescence detection device and method based on bifocal characteristics of ellipsoidal mirror

Abstract

The invention discloses a wafer defect photoluminescence detection device and method based on ellipsoidal mirror bifocus characteristics, and relates to the technical field of semiconductor manufacturing and detection, and the wafer defect photoluminescence detection device comprises an excitation light source, a bright field illumination light source, a light collector, a light detection channel and a motion platform. The excitation light source has the functions of excitation and focusing light sources and guides excitation light with a specific wavelength to the surface of a wafer so as to excite photoluminescence of the wafer; the bright field illumination light source guides illumination light emitted by the light source to the surface of the wafer so as to obtain bright field imaging of the surface of the wafer; the light collector adopts an ellipsoidal mirror to collect photoluminescence and reflected light caused by the excitation light source and collect reflected light of the bright field illumination light source; the light detection channel receives the two kinds of reflected light and photoluminescence collected by the light collector and is used for detection; the motion platform is used for placing the wafer, horizontally actuates the wafer to realize the scanning process of the excitation light source and the bright field illumination light source, and vertically actuates the wafer to realize fine focusing. According to the invention, the sensitivity and efficiency of wafer surface defect detection are improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing detection technology, and in particular to a wafer defect photoluminescence detection device and method based on the dual-focus characteristics of an ellipsoidal mirror. Background Art

[0002] Wafer defect detection is an indispensable part of semiconductor manufacturing. Crystal defects and surface defects are prone to occur during the growth and processing of wafers. Among them, crystal defects such as basal plane dislocations, stacking faults, micropipes, etc. below the surface of the wafer are difficult to detect and will affect the function and performance of the device. In severe cases, they will cause the device to fail completely. Therefore, it is very necessary to effectively detect and analyze wafer defects. Through wafer defect detection, production costs can be effectively controlled, defects can be located and their expansion can be suppressed, and production efficiency and the yield of semiconductor devices can be improved. With the gradual entry of 8-inch third-generation silicon carbide wafers into mass production, efficient non-destructive detection and classification of wafer defects are crucial to improving device performance and guiding process improvements. Traditional detection methods such as optical microscopy, scattering detection or laser confocal microscopy have the following shortcomings:

[0003] (1) The numerical aperture (NA) of ordinary objective lenses is limited, and photoluminescence is spontaneous radiation, which is prone to divergence loss, resulting in low photoluminescence collection efficiency;

[0004] (2) The focusing, imaging, and excitation optical paths are separated and independent, which makes the system complex and difficult to calibrate;

[0005] (3) Insufficient sensitivity makes it difficult to detect weak fluorescence signals.

[0006] Photoluminescence (PL) is a physical phenomenon in which a substance re-emit photons after absorbing photons (light energy). It is one of the important manifestations of the interaction between light and matter.

[0007] The excitation process of photoluminescence: After a substance (such as a semiconductor, fluorescent molecules, nanomaterials, etc.) absorbs photons of a specific energy, the internal electrons jump from the ground state to the excited state.

[0008] The luminescence process of photoluminescence: electrons in the excited state are unstable and will return to the ground state through radiative transition (releasing photons) or non-radiative transition (conversion into heat energy, etc.).

[0009] The energy of the excitation light must meet the quantization conditions (ie, the photon energy is greater than or equal to the energy gap of the material). Summary of the Invention

[0010] In order to overcome the above-mentioned defects in the prior art, the present invention provides a wafer defect photoluminescence detection device and method based on the dual-focus characteristics of an ellipsoidal mirror, which improves the sensitivity and efficiency of wafer surface defect detection while simplifying the operation process.

[0011] To achieve the above object, the present invention adopts the following technical solutions, including:

[0012] A wafer defect photoluminescence detection device based on the dual-focus characteristics of an ellipsoidal mirror includes an excitation light source, a bright field illumination light source, a light collector, a light detection channel, and a motion platform;

[0013] The excitation light source has the functions of both an excitation and a focusing light source, and is configured to direct excitation light of a specific wavelength toward the wafer surface along an excitation direction to stimulate photoluminescence of the wafer;

[0014] The bright field illumination light source is configured to direct illumination light emitted by the light source to the wafer surface to obtain a bright field image of the wafer surface;

[0015] The light collector uses an ellipsoidal mirror to collect the photoluminescence excited by the excitation light source in the wafer and the reflected light on the wafer surface, and uses a lens and a reflector to collect the reflected light of the bright field illumination light source on the wafer surface;

[0016] The light detection channel is configured to receive the two reflected lights and photoluminescence collected by the light collector for detection, including a photoluminescence detection channel formed by a first photomultiplier tube for detecting photoluminescence, a focus signal detection channel formed by a second photomultiplier tube for detecting light reflected from an excitation light source on a wafer surface, and a bright field imaging detection channel formed by a CCD for detecting light reflected from a bright field illumination light source on a wafer surface;

[0017] The motion platform is used to place the wafer; the motion platform horizontally actuates the wafer to realize the scanning process of the excitation light source and the bright field illumination light source; the motion platform vertically actuates the wafer to achieve fine focusing.

[0018] Preferably, the long axis of the ellipsoidal mirror is perpendicular to the motion platform; the bottom of the ellipsoidal mirror has a first opening, the first opening is facing the wafer to be inspected, so that the light reflected from the surface of the wafer to be inspected and the photoluminescence light beam enter the interior of the ellipsoidal mirror; the top of the ellipsoidal mirror has a second opening, and all the light collected by the ellipsoidal mirror is emitted from the second opening;

[0019] After focusing is completed, the lower focal plane of the ellipsoidal mirror coincides with the wafer surface; the upper focal plane of the ellipsoidal mirror coincides with the focal point of the third focusing mirror on the optical axis; wherein, the photoluminescence and reflected light caused by the excitation light source are collected by the ellipsoidal mirror and then pass through the third focusing mirror and the dichroic mirror in sequence, and enter the photoluminescence detection channel and the focus signal detection channel respectively.

[0020] Preferably, the excitation light emitted by the laser in the excitation light source passes through the first pinhole aperture serving as the focus of the light source, and is then focused by the ellipsoidal mirror on the wafer surface, i.e., the focus position under the ellipsoidal mirror; the reflected light on the wafer surface caused by the excitation light source is collected by the ellipsoidal mirror and focused on the second pinhole aperture serving as the detection focus, and is then received by the second photomultiplier tube; the focus of the light source, the focus under the ellipsoidal mirror, and the detection focus become image points of each other through optical conjugation, forming a confocal focusing system.

[0021] Preferably, the device further comprises a controller and a computer, wherein the controller is used to control the motion platform, the excitation light source and the bright field illumination light source, and to receive the detection signal of the light detection channel and send it to the computer.

[0022] Preferably, in the excitation light source, the excitation light emitted by the laser passes through the first aperture diaphragm and the first collimating mirror in sequence, and the excitation light after collimation and beam expansion enters the dichroic mirror and is reflected toward the third focusing mirror, and finally is focused on the wafer surface on the motion platform by the ellipsoidal mirror;

[0023] The wavelength of the laser is selected according to the wafer substrate, epitaxial thickness and defect observation position to stimulate wafer photoluminescence and obtain a photoluminescence scanning image.

[0024] Preferably, in the bright field illumination light source, the visible light emitted by the LED, i.e., the illumination light, is reflected by the second beam splitter toward the reflector, and finally focused by the fourth focusing mirror onto the surface of the wafer on the motion platform;

[0025] After acquiring the photoluminescence signal of the wafer, turn on the LED to obtain bright field imaging of the wafer surface.

[0026] Preferably, the photoluminescence and reflected light caused by the excitation light on the wafer surface are collected by the ellipsoidal mirror and then returned along the original optical path, passing through the third focusing mirror and then incident on the dichroic mirror. The dichroic mirror has different reflection and transmission characteristics for light of different wavelengths. The reflected light caused by the excitation light on the wafer surface is reflected by the dichroic mirror toward the first beam splitter, then reflected by the first beam splitter toward the first focusing mirror, focused through the second pinhole diaphragm, and finally received by the second photomultiplier tube, forming a focus signal detection channel. The photoluminescence caused by the excitation light on the wafer surface is transmitted by the dichroic mirror toward the second focusing mirror, and finally received by the first photomultiplier tube through the filter, forming a photoluminescence detection channel.

[0027] The reflected light caused by the illumination light on the wafer surface is collected by the fourth focusing mirror and the reflector and then returns along the original light path. After passing through the second beam splitter, it is transmitted to the fifth focusing mirror and received by the CCD, forming a bright field imaging detection channel.

[0028] Preferably, the filter in front of the first photomultiplier tube can be replaced with a narrowband filter of different wavelength bands. The photoluminescence peaks of different crystal defects in the crystal circle are different. Narrowband filters of different wavelength bands are used to allow the first photomultiplier tube to receive the photoluminescence of different defects.

[0029] The present invention also provides a wafer defect photoluminescence detection method based on the dual-focus characteristics of an ellipsoid mirror, which is characterized in that it is applicable to the wafer defect photoluminescence detection device based on the dual-focus characteristics of an ellipsoid mirror, and includes the following contents:

[0030] S1, perform confocal autofocus;

[0031] S11, after the excitation light of the laser in the excitation light source reaches the first aperture diaphragm, it passes through the first collimator and the first beam splitter, so that the excitation light is split into two light beams, including a transmitted light beam and a reflected light beam;

[0032] S12, the transmitted beam of the excitation light enters the dichroic mirror and is reflected by the dichroic mirror;

[0033] S13, the reflected light beam from the dichroic mirror passes through the third focusing mirror and the ellipsoidal mirror in sequence, and is finally focused on the surface of the wafer on the motion platform;

[0034] S14, the ellipsoidal mirror collects the reflected light beam from the wafer surface, and the collected light beam passes through the third focusing mirror and enters the dichroic mirror, and is reflected by the dichroic mirror;

[0035] S14, the reflected light beam from the dichroic mirror passes through the first beam splitter, the first focusing mirror, and the second aperture diaphragm in sequence, and is received by the second photomultiplier tube, which then sends a focus signal to the computer;

[0036] S15, the initial position of the motion platform is set to the bottom, and it moves upward in the vertical direction, with the distance of each movement set to σ and the time interval of each movement set to T;

[0037] The current number of moves is μ, and μ is initialized to 1;

[0038] S16, control the motion platform to move vertically upward for the μth time, and record the signal intensity of the second photomultiplier tube 7 after the μth movement, which is recorded as Q μ ;

[0039] S17, if Q μ+1 <Q μ >Q μ-1 , then stop moving, and take the μth moving position as the optimal position, thereby controlling the motion platform to reach the optimal position in the vertical direction and completing the focus;

[0040] S2, directing the excitation light of the excitation light source onto the wafer in a focused state;

[0041] S21, after the excitation light of the laser in the excitation light source reaches the first aperture diaphragm, it passes through the first collimator and the first beam splitter, so that the excitation light is split into two light beams, including a transmitted light beam and a reflected light beam;

[0042] S22, the transmitted beam of the excitation light enters the dichroic mirror and is reflected by the dichroic mirror;

[0043] S23, the reflected light beam from the dichroic mirror passes through the third focusing mirror and the ellipsoidal mirror in sequence, and is finally focused on the surface of the wafer on the motion platform to excite the wafer;

[0044] S3, collects the photoluminescence induced by the excitation light source;

[0045] S31, the ellipsoidal mirror collects the photoluminescent light beam emitted from one or more photoluminescent defects on the wafer. The collected light beam passes through the third focusing mirror and then enters the dichroic mirror, where it is transmitted. Simultaneously, the reflected light beam from the excitation light on the wafer surface is reflected by the dichroic mirror.

[0046] S32, the light beam transmitted by the dichroic mirror is focused by the second focusing mirror and then received by the first photomultiplier tube, and a photoluminescence signal is sent to the computer; the light beam reflected by the dichroic mirror is split into two light beams, including a transmitted light beam and a reflected light beam, after passing through the first beam splitter;

[0047] S33, the reflected light beam from the first beam splitter passes through the first focusing mirror and the second aperture diaphragm in sequence, is received by the second photomultiplier tube, and a focus signal is sent to the computer;

[0048] S4, bright-field imaging using a bright-field illumination source;

[0049] S41, after collecting the photoluminescence signal of the wafer, turning on the LED of the bright field illumination light source, the illumination light emitted by the LED is collimated by the second collimator and then enters the second beam splitter to be divided into two light beams, including a transmitted light beam and a reflected light beam;

[0050] S42, the reflected light beam from the second beam splitter is focused on the wafer surface after passing through the reflective mirror and the fourth focusing mirror in sequence, forming reflected light;

[0051] S43, the illumination light reflected from the wafer surface returns along the original optical path, passes through the fourth focusing mirror and the reflective mirror, and then enters the second beam splitter to be split into two light beams, including a transmitted light beam and a reflected light beam;

[0052] S44, the transmitted light beam from the second beam splitter is focused by the fifth focusing lens and then received by the CCD, and a bright field image is sent to the computer, and the LED is turned off;

[0053] S5, the motion platform moves in the horizontal direction, and S2-23 are repeated. After the scanning is completed, the computer generates wafer photoluminescence images according to the received photoluminescence signals and bright field imaging images, thereby performing wafer defect detection.

[0054] The present invention also provides a computer program product, which includes a computer program / instruction, and when the computer program / instruction is executed by a processor, it realizes the wafer defect photoluminescence detection method based on the dual-focus characteristics of the ellipsoidal mirror.

[0055] The advantages of the present invention are:

[0056] (1) The present invention utilizes the dual-focal conjugate properties of the ellipsoidal mirror to converge the excitation light from the upper focal point to the wafer surface at the lower focal point, fully utilizing the laser efficiency and ensuring that the excitation light has sufficient power density to excite defects. Simultaneously, the wide-angle light collection capability of the ellipsoidal mirror allows the photoluminescent light beam excited at the wafer surface at the lower focal point to be converged to the upper focal point through the ellipsoidal mirror, achieving efficient collection of the photoluminescent light beam.

[0057] (2) The present invention uses an ellipsoidal mirror to efficiently collect photoluminescence and integrates an imaging optical path to ensure that the excitation light power density on the wafer surface is sufficient, thereby achieving high-sensitivity, integrated defect detection and providing data support for wafer device production.

[0058] (3) Based on the optical conjugate relationship between the light source focus, the focus under the ellipsoidal mirror and the detection focus, the present invention integrates a confocal focusing system into the excitation light path, so that the excitation light source has both excitation and focusing functions, which can realize real-time focus detection, avoid crosstalk from other bands of light and simplify the system structure.

[0059] (4) The present invention integrates bright-field microscopy, which can complement the optical signals and characterize the defects in multiple dimensions on the wafer surface, display the macroscopic morphological defects on the wafer surface, and provide intuitive visual information such as the position, size, and shape of the defects.

[0060] (5) The excitation light source in the present invention can rotate between lasers of various wavelength bands, and the filter can rotate between narrow-band filters of various wavelength bands. By optimizing the excitation and receiving wavelengths in practice, the best signal-to-noise ratio can be provided for different epitaxial layer thicknesses and defects inside the wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 Schematic diagram of a wafer defect photoluminescence detection device of the present invention.

[0062] Figure 2 Schematic diagram of the optical path of the excitation light source and the reflected light and photoluminescence collected by the ellipsoidal mirror.

[0063] Figure 3Schematic diagram of the optical path of the bright field illumination light source and its reflected light collected by the lens.

[0064] Figure 4 Schematic diagram of the collection angle of an ellipsoidal mirror.

[0065] Figure 5 Schematic diagram of the principle of ellipsoidal mirror.

[0066] Figure 6 Figure 2 shows the PL peak wavelengths of Frank and Shockley type stacking faults described using stacking symbols and schematics.

[0067] Description of reference numerals:

[0068] Laser 1, first aperture diaphragm 2, first collimator 3, first beam splitter 4, first focusing mirror 5, second aperture diaphragm 6, second photomultiplier tube 7, first photomultiplier tube 8, filter 9, second focusing mirror 10, dichroic mirror 11, third focusing mirror 12, ellipsoidal mirror 13, motion platform 14, fourth focusing mirror 15, reflector 16, second beam splitter 17, second collimator 18, LED 19, fifth focusing mirror 20, CCD 21, computer 22. DETAILED DESCRIPTION

[0069] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0070] Figure 1 Schematic diagram of a wafer defect photoluminescence detection device according to the present invention, comprising Figure 1 As shown, the device specifically includes a laser 1, a first aperture diaphragm 2, a first collimating mirror 3, a first beam splitter 4, a first focusing mirror 5, a second aperture diaphragm 6, a second photomultiplier tube 7, a first photomultiplier tube 8, a filter 9, a second focusing mirror 10, a dichroic mirror 11, a third focusing mirror 12, an ellipsoidal mirror 13, a motion platform 14, a fourth focusing mirror 15, a reflector 16, a second beam splitter 17, a second collimating mirror 18, an LED 19, a fifth focusing mirror 20, a CCD 21, and a computer 22.

[0071] The device is divided into an excitation light source, a bright field illumination light source, a light collector, a light detection channel, a motion platform and a controller.

[0072] The excitation light source has the functions of both excitation and focusing light source, such as Figure 2As shown, laser 1 emits excitation light, which passes through first aperture 2 and first collimator 3. The collimated and expanded excitation light then enters dichroic mirror 11, is reflected toward third focusing mirror 12, and finally focused by ellipsoidal mirror 13 onto the wafer surface on motion platform 14. Photoluminescence can only be generated when the excitation light source's energy exceeds the wafer's bandgap. Furthermore, the information depth of photoluminescence is limited by the material's optical absorption characteristics of the laser beam. The actual excitation depth can be defined as the sum of the light penetration depth and the carrier diffusion length. Furthermore, the shorter the excitation light wavelength, the shorter the penetration depth. The laser wavelength can be selected based on the wafer substrate, epitaxial thickness, and defect observation location to effectively stimulate wafer photoluminescence and obtain high-quality photoluminescence scan images.

[0073] The bright field illumination light source is Figure 3 As shown, LED 19 emits visible light, or illumination light, which is reflected by second beam splitter 17 toward reflector 16 and finally focused by fourth focusing mirror 15 onto the wafer surface on motion platform 14. To prevent visible light from affecting the photoluminescence image, LED 19 is typically turned on after acquiring the photoluminescence signal from the target point to obtain a bright-field image of the wafer surface.

[0074] The light collector, such as Figure 2 As shown, the photoluminescence excited by the excitation light source in the wafer and the reflected light on the wafer surface are collected by an ellipsoidal mirror 13. There are two advantages of using an ellipsoidal mirror. One is that it can collect light at a large angle, such as Figure 4 As shown, the collection angle is β~γ, the numerical aperture can reach above 0.9, and the detection sensitivity is higher. Second, the ellipsoidal reflector has no chromatic aberration and the imaging quality is higher. Figure 3 As shown, the reflected light of the bright field illumination light source on the wafer surface is collected by the fourth focusing mirror 15 and the reflecting mirror 16 .

[0075] The light detection channel is configured to receive the two reflected lights and photoluminescence collected by the light collector and use them for detection. It includes a photoluminescence detection channel formed by the first photomultiplier tube 8, a focus signal detection channel formed by the second photomultiplier tube 7, and a bright field imaging detection channel formed by the CCD 21 (charge coupled device). Figure 2As shown, the photoluminescence and reflected light caused by the excitation light are collected by the ellipsoidal mirror 13 and then returned along the original light path. After passing through the third focusing mirror 12, they are incident on the dichroic mirror 11. The dichroic mirror 11 has different reflection and transmission characteristics for light of different wavelengths. It can reflect light in a specific wavelength range and allow light in other wavelength ranges to pass through. The reflected light of the excitation light and the photoluminescence have different wavelength bands. The wavelength of the photoluminescence is greater than the reflected light of the excitation light. After the collected light beam passes through the dichroic mirror 11, the reflected light of the excitation light is reflected toward the first beam splitter 4, and then reflected by the first beam splitter 4 to the first focusing mirror 5, focused through the second pinhole aperture 6, and finally received by the second photomultiplier tube 7. This is the focus signal detection channel. In addition, the photoluminescence is transmitted through the dichroic mirror 11 to the second focusing mirror 10, and finally received by the first photomultiplier tube 8 through the filter 9. This is the photoluminescence detection channel. As shown Figure 3 As shown, the reflected light caused by the bright field illumination beam is collected by the fourth focusing mirror 15 and the reflector 16 and then returns along the original optical path. After passing through the second beam splitter 17 and being transmitted to the fifth focusing mirror 20, it is received by the CCD 21. This is the bright field imaging detection channel.

[0076] The motion platform 14 is configured to secure the wafer and selectively actuate the wafer horizontally to perform a scanning process using an excitation light source and a bright field illumination light source, and can be actuated vertically to achieve fine focusing.

[0077] The controller is configured to process the signals from the first photomultiplier tube 8, the second photomultiplier tube 7, and the charge-coupled device (CCD 21) and transmit the signals to a computer to generate a photoluminescence image, focus data, and a bright field image of the wafer. The outputs of the two photomultiplier tubes and the one charge-coupled device are connected to the input of the controller, and the output of the controller is externally connected to the computer and the motion platform 14.

[0078] The long axis of the ellipsoidal mirror 13 is perpendicular to the motion platform 14. Figure 5 As shown, F1 and F2 are the two foci of the ellipsoid, the focal length of the ellipsoid is c, F1A is the light after excitation and reflection from the wafer surface, A is an arbitrary point on the inner wall of the ellipsoid reflector, F2A is the light after F1A is reflected from point A, and O is the center of the ellipsoid. During the inspection process, the wafer surface and the lower focal plane of the ellipsoid are in the same plane, and the focus of the third focusing mirror 12 coincides with the upper focal point of the ellipsoid on the optical axis. The ellipsoid surface equation is:

[0079]

[0080] Wherein, a and b are the major axis radius and minor axis radius of the ellipsoid main axis respectively. The bottom of the ellipsoidal mirror 13 has a first opening, and the first opening is facing the wafer to be detected so that the light beam reflected from the surface of the wafer to be detected and the photoluminescence light beam can enter the interior of the ellipsoidal mirror. At the same time, the top of the ellipsoidal mirror 13 has a second opening, and all the light collected by the ellipsoidal mirror 13 is emitted from the second opening. The lower focus of the ellipsoidal mirror 13 is on the surface of the wafer to ensure that the excitation light has sufficient intensity and can collect as much photoluminescence as possible from the wafer at the lower focus to the upper focus. The upper focus of the ellipsoidal mirror 13 coincides with the focus of the third focusing mirror 12 on the optical axis to ensure that all the collected light enters the internal light path.

[0081] After the excitation light passes through the first pinhole aperture 2 which serves as the focus of the light source, it is focused by the ellipsoidal mirror 13 on the ellipsoidal focus of the wafer surface. The reflected light of the focus is collected by the ellipsoidal mirror 13 and focused on the second pinhole aperture 6 which serves as the detection focus. The focus of the light source, the focus under the ellipsoidal mirror and the detection focus are image points of each other through optical conjugation, forming a confocal focusing system.

[0082] The filter 9 in front of the first photomultiplier tube 8 can be replaced with a narrowband filter of different wavelength bands. The photoluminescence peaks of different crystal defects in the wafer are different. By using narrowband filters of different wavelength bands, the first photomultiplier tube 8 receives photoluminescence within a narrow band pass range, thereby better distinguishing defect types. Figure 6 The PL peak wavelengths of Frank and Shockley type stacking faults are described using stacking symbols and schematics. Choosing a narrowband filter with the defect luminescence peak band can better classify the defects.

[0083] The motion platform 14 performs horizontal motion for scanning and vertical motion for fine focusing.

[0084] The controller is configured to control communication with the motion platform 14 , the excitation light source, the bright field illumination light source, and the light detection channel.

[0085] By utilizing the dual-focus characteristic of the ellipsoidal mirror 13 , the excitation light is focused at the upper focus, and the wafer area to be tested is placed at the lower focus, and efficient collection of fluorescence is achieved through reflection by the ellipsoidal mirror 13 .

[0086] The integrated confocal focusing system realizes automatic focusing on the wafer surface by changing the intensity of reflected light at the focus under the ellipsoidal mirror 13.

[0087] A switchable bright field microscopy module is embedded in the main optical path of the ellipsoidal mirror 13 to achieve defect positioning and morphology verification.

[0088] A wafer defect photoluminescence detection method, the steps of which are as follows:

[0089] S1, perform confocal autofocus.

[0090] S11, after the outgoing light (excitation light) of the laser 1 in the excitation light source reaches the first aperture 2, the first collimator 3 and the first beam splitter 4 split the outgoing light into two light beams, including a transmitted light beam and a reflected light beam;

[0091] S12, the transmitted light beam passes through the dichroic mirror 11. The dichroic mirror 11 is specially coated to highly reflect light in the excitation light band, so that only the reflected light beam is emitted from the dichroic mirror 11.

[0092] S13 , the reflected light beam emitted by the dichroic mirror 11 passes through the third focusing mirror 12 and the ellipsoidal mirror 13 in sequence, and is finally focused on the surface of the wafer on the motion platform 14 .

[0093] S14, the ellipsoidal mirror 13 collects the reflected light beams from the surface of the wafer. All the collected light beams pass through the third focusing mirror 12 and enter the dichroic mirror 11. Due to the wavelength selectivity of the dichroic mirror 11, the reflected light beams on the surface of the wafer are all reflected through the dichroic mirror 11.

[0094] S14, the reflected light beam of the dichroic mirror 11 passes through the first beam splitter 4, the first focusing mirror 5 and the second aperture diaphragm 6 in sequence, and is received by the second photomultiplier tube 7, and a focus signal is sent to the computer 22 through the controller;

[0095] S15, the initial position of the motion platform 14 is set to the bottom, and it moves vertically upward, and the distance of each movement is set to σ, and the time interval of each movement is set to T; the current number of movements is μ, and μ is initialized to 1;

[0096] S16, the computer 22 uses the electric translation stage to control the motion platform 14 to move in the vertical upward direction for the μth time, and records the signal intensity of the second photomultiplier tube 7 after the μth movement, which is recorded as Q μ .

[0097] S17, if Q μ+1 <Q μ >Q μ-1 , the movement is stopped, and the μth moving position is taken as the optimal position, thereby controlling the motion platform 14 to reach the optimal position in the vertical direction and completing the focusing.

[0098] S2, directing the light beam of the excitation light source onto a portion of the wafer in a focused state.

[0099] S21, after the outgoing light (excitation light) of the laser 1 in the excitation light source reaches the first aperture 2, the first collimator 3 and the first beam splitter 4 split the outgoing light into two light beams, including a transmitted light beam and a reflected light beam;

[0100] S22, the transmitted light beam passes through the dichroic mirror 11. The dichroic mirror 11 is specially coated to highly reflect light in the excitation light band, so that only the reflected light beam is emitted from the dichroic mirror 11.

[0101] S23 , the reflected light beam emitted by the dichroic mirror 11 passes through the third focusing mirror 12 and the ellipsoidal mirror 13 in sequence, and is finally focused on the surface of the wafer on the motion platform 14 to excite the wafer.

[0102] S3, collecting the photoluminescence induced by the excitation light source.

[0103] At step S31, the ellipsoidal mirror 13 collects the photoluminescence beams emitted from one or more photoluminescence defects on the wafer. All collected beams pass through the third focusing mirror 12 and then enter the dichroic mirror 11. Due to the wavelength selectivity of the dichroic mirror 11, the photoluminescence beams emitted from the one or more photoluminescence defects on the wafer are transmitted through the dichroic mirror 11. Simultaneously, all reflected beams from the wafer surface are reflected through the dichroic mirror 11.

[0104] S32, the transmitted light beam of the dichroic mirror 11 is focused by the second focusing mirror 10 and then received by the first photomultiplier tube 8, and a photoluminescence signal is sent to the computer 22 through the controller; the reflected light beam of the dichroic mirror 11 is split into two light beams after passing through the first beam splitter 4, including a transmitted light beam and a reflected light beam;

[0105] S33 , the reflected light beam of the first beam splitter 4 passes through the first focusing mirror 5 and the second aperture diaphragm 6 in sequence, is received by the second photomultiplier tube 7 , and sends a focus signal to the computer 22 .

[0106] S4, performing bright field imaging using the bright field illumination light source.

[0107] S41, after collecting the photoluminescence signal behind the target point on the wafer, turning on the LED 19, and its output light is collimated by the second collimator 18 and then enters the second beam splitter 17, so that the output light is split into two light beams, including a transmitted light beam and a reflected light beam;

[0108] S42 , the reflected light beam from the second beam splitter 17 is focused on the wafer surface after passing through the reflective mirror 16 and the fourth focusing mirror 15 in sequence, forming reflected light.

[0109] S43 , the reflected light from the wafer surface returns along the original optical path, passes through the fourth focusing mirror 15 and the reflective mirror 16 in sequence, and then enters the second beam splitter 17 to be split into two beams, including a transmitted beam and a reflected beam.

[0110] S44 , the transmitted light beam of the second beam splitter 17 is focused by the fifth focusing mirror 20 and then received by the CCD 21 , and a bright field image is sent to the computer 22 via the controller, and the LED 19 is turned off.

[0111] S5, the motion platform 14 moves in the horizontal direction, and S2-23 are repeated. After the scanning is completed, the computer 22 generates wafer photoluminescence images according to the received photoluminescence signals and bright field imaging images, thereby performing wafer defect detection.

[0112] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A wafer defect photoluminescence detection device based on the dual-focus characteristics of an ellipsoidal mirror, characterized in that: It includes an excitation light source, a bright field illumination light source, a light collector, a light detection channel and a motion platform; The excitation light source has the functions of both an excitation and a focusing light source, and is configured to direct excitation light of a specific wavelength toward the wafer surface along an excitation direction to stimulate photoluminescence of the wafer; The bright field illumination light source is configured to direct illumination light emitted by the light source to the wafer surface to obtain a bright field image of the wafer surface; The light collector uses an ellipsoidal mirror to collect the photoluminescence excited by the excitation light source in the wafer and the reflected light on the wafer surface, and uses a lens and a reflector to collect the reflected light of the bright field illumination light source on the wafer surface; The light detection channel is configured to receive the two reflected lights and photoluminescence collected by the light collector for detection, including a photoluminescence detection channel formed by a first photomultiplier tube for detecting photoluminescence, a focus signal detection channel formed by a second photomultiplier tube for detecting light reflected from an excitation light source on a wafer surface, and a bright field imaging detection channel formed by a CCD for detecting light reflected from a bright field illumination light source on a wafer surface; The motion platform is used to place the wafer; the motion platform horizontally actuates the wafer to achieve the scanning process of the excitation light source and the bright field illumination light source; The motion stage actuates the wafer vertically to achieve fine focus.

2. The wafer defect photoluminescence detection device based on the dual-focus characteristics of the ellipsoidal mirror according to claim 1, characterized in that: The long axis of the ellipsoidal mirror is perpendicular to the motion platform; the bottom of the ellipsoidal mirror has a first opening, the first opening is facing the wafer to be inspected, so that the light reflected from the surface of the wafer to be inspected and the photoluminescence light beam enter the interior of the ellipsoidal mirror; the top of the ellipsoidal mirror has a second opening, and all the light collected by the ellipsoidal mirror is emitted from the second opening; After focusing is completed, the lower focal plane of the ellipsoidal mirror coincides with the wafer surface; the upper focal plane of the ellipsoidal mirror coincides with the focal point of the third focusing mirror on the optical axis; wherein, the photoluminescence and reflected light caused by the excitation light source are collected by the ellipsoidal mirror and then pass through the third focusing mirror and the dichroic mirror in sequence, and enter the photoluminescence detection channel and the focus signal detection channel respectively.

3. The wafer defect photoluminescence detection device based on the dual-focus characteristics of the ellipsoidal mirror according to claim 1, characterized in that: The excitation light emitted by the laser in the excitation light source passes through the first pinhole aperture as the focus of the light source, and is then focused by the ellipsoidal mirror on the wafer surface, that is, the focus position under the ellipsoidal mirror; the reflected light on the wafer surface caused by the excitation light source is collected by the ellipsoidal mirror and focused on the second pinhole aperture as the detection focus, and is then received by the second photomultiplier tube; the focus of the light source, the focus under the ellipsoidal mirror and the detection focus are optically conjugated to form each other's image points, forming a confocal focusing system.

4. The wafer defect photoluminescence detection device based on the dual-focus characteristics of the ellipsoidal mirror according to claim 1, characterized in that: The device also includes a controller and a computer. The controller is used to control the motion platform, the excitation light source and the bright field illumination light source, and to receive the detection signal of the light detection channel and send it to the computer.

5. The wafer defect photoluminescence detection device based on the dual-focus characteristics of the ellipsoidal mirror according to claim 1, characterized in that: In the excitation light source, the excitation light emitted by the laser passes through the first aperture diaphragm and the first collimating mirror in sequence. After collimation and beam expansion, the excitation light enters the dichroic mirror and is reflected to the third focusing mirror. Finally, it is focused on the wafer surface on the motion platform by the ellipsoidal mirror. The wavelength of the laser is selected according to the wafer substrate, epitaxial thickness and defect observation position to stimulate wafer photoluminescence and obtain a photoluminescence scanning image.

6. The wafer defect photoluminescence detection device based on the dual-focus characteristics of the ellipsoidal mirror according to claim 1, characterized in that: In the bright field illumination light source, the visible light emitted by the LED, i.e. the illumination light, is reflected by the second beam splitter toward the reflector, and finally focused by the fourth focusing mirror onto the wafer surface on the motion platform. After acquiring the photoluminescence signal of the wafer, turn on the LED to obtain bright field imaging of the wafer surface.

7. The wafer defect photoluminescence detection device based on the dual-focus characteristics of the ellipsoidal mirror according to claim 1, characterized in that: The photoluminescence and reflected light caused by the excitation light on the wafer surface are collected by the ellipsoidal mirror and then returned along the original optical path. After passing through the third focusing mirror, they are incident on the dichroic mirror. The dichroic mirror has different reflection and transmission characteristics for light of different wavelengths. The reflected light caused by the excitation light on the wafer surface is reflected by the dichroic mirror toward the first beam splitter, and then reflected by the first beam splitter toward the first focusing mirror. It is focused through the second aperture diaphragm and finally received by the second photomultiplier tube, forming a focus signal detection channel. The photoluminescence caused by the excitation light on the wafer surface is transmitted by the dichroic mirror toward the second focusing mirror and finally received by the first photomultiplier tube through the filter, forming a photoluminescence detection channel. The reflected light caused by the illumination light on the wafer surface is collected by the fourth focusing mirror and the reflector and then returns along the original light path. After passing through the second beam splitter, it is transmitted to the fifth focusing mirror and received by the CCD, forming a bright field imaging detection channel.

8. The wafer defect photoluminescence detection device based on the dual-focus characteristics of the ellipsoidal mirror according to claim 1 or 7, characterized in that: The filter in front of the first photomultiplier tube can be replaced with a narrowband filter of different wavelength bands. The photoluminescence peaks of different crystal defects in the crystal circle are different. Narrowband filters of different wavelength bands are used to enable the first photomultiplier tube to receive the photoluminescence of different defects.

9. A wafer defect photoluminescence detection method based on the dual-focus characteristics of an ellipsoidal mirror, characterized in that: A wafer defect photoluminescence detection device based on the dual-focus characteristics of an ellipsoidal mirror, applicable to any one of claims 1 to 8, comprising the following: S1, perform confocal autofocus; S11, after the excitation light of the laser in the excitation light source reaches the first aperture diaphragm, it passes through the first collimator and the first beam splitter, so that the excitation light is split into two light beams, including a transmitted light beam and a reflected light beam; S12, the transmitted beam of the excitation light enters the dichroic mirror and is reflected by the dichroic mirror; S13, the reflected light beam from the dichroic mirror passes through the third focusing mirror and the ellipsoidal mirror in sequence, and is finally focused on the surface of the wafer on the motion platform; S14, the ellipsoidal mirror collects the reflected light beam from the wafer surface, and the collected light beam passes through the third focusing mirror and enters the dichroic mirror, and is reflected by the dichroic mirror; S14, the reflected light beam from the dichroic mirror passes through the first beam splitter, the first focusing mirror, and the second aperture diaphragm in sequence, and is received by the second photomultiplier tube, which then sends a focus signal to the computer; S15, the initial position of the motion platform is set to the bottom, and it moves upward in the vertical direction, with the distance of each movement set to σ and the time interval of each movement set to T; The current number of moves is μ, and μ is initialized to 1; S16, control the motion platform to move vertically upward for the μth time, and record the signal intensity of the second photomultiplier tube 7 after the μth movement, which is recorded as Q μ ; S17, if Q μ+1 <Q μ >Q μ-1 , then stop moving, and take the μth moving position as the optimal position, thereby controlling the motion platform to reach the optimal position in the vertical direction and completing the focus; S2, directing the excitation light of the excitation light source onto the wafer in a focused state; S21, after the excitation light of the laser in the excitation light source reaches the first aperture diaphragm, it passes through the first collimator and the first beam splitter, so that the excitation light is split into two light beams, including a transmitted light beam and a reflected light beam; S22, the transmitted beam of the excitation light enters the dichroic mirror and is reflected by the dichroic mirror; S23, the reflected light beam from the dichroic mirror passes through the third focusing mirror and the ellipsoidal mirror in sequence, and is finally focused on the surface of the wafer on the motion platform to excite the wafer; S3, collects the photoluminescence induced by the excitation light source; S31, the ellipsoidal mirror collects the photoluminescent light beam emitted from one or more photoluminescent defects on the wafer. The collected light beam passes through the third focusing mirror and then enters the dichroic mirror, where it is transmitted. Simultaneously, the reflected light beam from the excitation light on the wafer surface is reflected by the dichroic mirror. S32, the light beam transmitted by the dichroic mirror is focused by the second focusing mirror and then received by the first photomultiplier tube, and a photoluminescence signal is sent to the computer; the light beam reflected by the dichroic mirror is split into two light beams, including a transmitted light beam and a reflected light beam, after passing through the first beam splitter; S33, the reflected light beam from the first beam splitter passes through the first focusing mirror and the second aperture diaphragm in sequence, is received by the second photomultiplier tube, and a focus signal is sent to the computer; S4, bright-field imaging using a bright-field illumination source; S41, after collecting the photoluminescence signal of the wafer, turning on the LED of the bright field illumination light source, the illumination light emitted by the LED is collimated by the second collimator and then enters the second beam splitter to be divided into two light beams, including a transmitted light beam and a reflected light beam; S42, the reflected light beam from the second beam splitter is focused on the wafer surface after passing through the reflective mirror and the fourth focusing mirror in sequence, forming reflected light; S43, the illumination light reflected from the wafer surface returns along the original optical path, passes through the fourth focusing mirror and the reflective mirror, and then enters the second beam splitter to be split into two light beams, including a transmitted light beam and a reflected light beam; S44, the transmitted light beam from the second beam splitter is focused by the fifth focusing lens and then received by the CCD, and a bright field image is sent to the computer, and the LED is turned off; S5, the motion platform moves in the horizontal direction, and S2-23 are repeated. After the scanning is completed, the computer generates wafer photoluminescence images according to the received photoluminescence signals and bright field imaging images, thereby performing wafer defect detection.

10. A computer program product, characterized in that It includes a computer program / instruction, which, when executed by a processor, implements the wafer defect photoluminescence detection method based on the dual-focus characteristics of an ellipsoidal mirror as described in claim 9.

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