Laser detection method for water adsorbed on wafer surface

Abstract

The present invention discloses a laser detection method for water adsorbed on the surface of a wafer, wherein two laser beams are arranged in a laser detection device, one of which is a main laser beam, which forms a small light spot on the wafer after focusing, and performs rapid heating of a small area; the other is a detection light beam, which is coaxial with the main laser beam, and performs moisture detection on the wafer while heating. Advantages: the method of the present invention does not require heating the entire wafer, the water evaporates quickly, and the water is detected immediately after evaporation before it diffuses.

Description

Technical Field

[0001] The invention relates to the fields of optical lenses and precision measurement, and in particular to a laser detection method for water adsorbed on a wafer surface. Background Art

[0002] Controlling moisture levels throughout the chemical delivery system is a critical task in semiconductor manufacturing. This is because, when water reacts with the gases used in semiconductor manufacturing, it can corrode the wetted surfaces of gas handling components and gas delivery equipment, generate troublesome particles and affect the performance of processing tools. In addition, if the system fails, it can cause serious safety issues and damage the system.

[0003] In the front-end process, the wafer must be cleaned during the transfer of various semiconductor process equipment. After coming out of the cleaning equipment, it must be kept dry, which is called "Dry-In-Dry-Out". If the wafer is in a state of water, the surface of the wafer will oxidize quickly, and the water droplets that are invisible to the naked eye will form water stains that affect the subsequent processes.

[0004] The moisture detection on the surface of semiconductor wafers is mainly as disclosed in the invention patent application published in China, publication number CN115684265A, publication date February 3, 2023, which converts the moisture into water vapor by heating, and then collects and measures the water vapor content. The heating of this method is either heated by dry hot carrier gas or heated by heating lamp irradiation. The heating area is large and the speed is slow; the analysis of water vapor content is not at the same place and time as heating, and the measurement speed is slow. Summary of the invention

[0005] The technical problem to be solved by the present invention is that in the prior art, when detecting moisture on the wafer surface, the heating area is large and the heating is slow, and the measurement speed is slow. The present invention provides a laser detection method for water adsorbed on the wafer surface, which uses a main light source for rapid heating and uses an auxiliary light source as a detection light to measure the water vapor concentration.

[0006] The technical solutions adopted are as follows:

[0007] A laser detection method for water adsorbed on a wafer surface, the method comprising: arranging two laser beams in a laser detection device, one being a main laser, which forms a small light spot on the wafer after focusing, and performs rapid heating of a small area; and the other being a detection light, which is coaxial with the main laser, and performs moisture detection on the wafer while heating.

[0008] Further preferred embodiment of the technical solution of the present invention is that the laser detection device includes a device housing, a detection laser light source that emits detection light, a main laser light source that emits main laser, a main laser reflector, a detection light reflector, a water vapor detector and a phase-locked amplifier; the detection laser light source and the main laser light source are both arranged in the device housing, and the wafer to be tested is placed horizontally in the device housing and is located at the focus of the main laser and the detection light; the main laser reflector and the detection light reflector are coaxial and arranged at intervals inside the device housing, the main laser reflector has high transmittance to the detection light and high reflection to the main laser; the detection light reflector has a reflectivity of 50% to the detection light and high transmittance to the main laser; the main laser emitted by the main laser light source is reflected by the main laser reflector and then irradiated into the wafer to be tested after being highly transparent through the detection light reflector, the detection light emitted by the detection laser light source enters the detection light reflector after being highly transparent through the main laser reflector and then irradiated into the wafer to be tested, the detection light is reflected by the wafer to be tested and then enters the detection light reflector, and then enters the water vapor detector after being reflected by the detection light reflector, the water vapor detector performs water vapor detection and inputs the signal into the phase-locked amplifier to extract the harmonic signal. In the laser detection device, the main laser is used to heat a very small area (about 100 microns). The heating time is short and the surface moisture can be quickly evaporated into gas.

[0009] In a further preferred embodiment of the technical solution of the present invention, the main laser uses a wavelength with a high absorption rate; when the material of the wafer to be tested is silicon, the wavelength of the main laser is 1.06μm, 1.5μm, and 2.0μm; when the material of the wafer to be tested is sapphire or lithium niobate, the wavelength of the main laser is 4μm-12μm. The wavelength with a high absorption rate plays a heating role, and the wavelength of the main laser is within the absorption range of the object to be tested.

[0010] In a further preferred embodiment of the technical solution of the present invention, the wavelength of the main laser is 4 μm-12 μm, and the detection laser light source is a carbon dioxide laser. The wavelength of the carbon dioxide laser is about 12 microns, which is within the water vapor absorption peak.

[0011] In a further preferred embodiment of the technical solution of the present invention, the detection light adopts a wavelength with high absorption rate, and the detection laser light source is a near-infrared DFB semiconductor laser or a mid-infrared QCL laser. The wavelength of the QCL laser is 3-12 microns, which is also within the water vapor absorption peak.

[0012] In a further preferred embodiment of the technical solution of the present invention, the water vapor detector is a VIGO single-point mid-infrared detector.

[0013] In a further embodiment of the technical solution of the present invention, the laser detection method comprises the following steps:

[0014] Step 1: The wafer to be tested is placed in a laser detection device, and the wafer to be tested is placed at the focus of the main laser and the detection light;

[0015] Step 2, the laser detection device is sealed and evacuated and then filled with dry nitrogen;

[0016] Step 3: Turn on the main laser light source and the detection laser light source at the same time, and focus the detection light and the main laser on the wafer to be tested; the main laser quickly heats the wafer to be tested within the 100 μm diameter spot to above 100°C, so that the moisture adsorbed on the surface of the wafer to be tested evaporates into water vapor, and at the same time, the detection light emitted by the wafer to be tested enters the water vapor detector;

[0017] Step 4: Calculate the water vapor concentration according to the TDLAS principle.

[0018] In this method, the focal spot is very small, which is beneficial to improving the heating efficiency.

[0019] In a further preferred embodiment of the technical solution of the present invention, in step 2, dry nitrogen is charged, and the charging of nitrogen is stopped when the pressure of the charged nitrogen is the same as the atmospheric pressure. Nitrogen helps to reduce the interference of air.

[0020] In a further preferred embodiment of the technical solution of the present invention, the following step is added before step 3: modulating the detection light according to the TDLAS method; the specific method is as follows:

[0021] S1. Modulate the detection light into a triangular wave, the frequency of the triangular wave is 100 Hz, and the scanning wavelength of the triangular wave is 10 GHz;

[0022] S2, superimpose a sine wave on the detection light in S1, the frequency of the sine wave is 1KHz, and the scanning wavelength of the sine wave is 1GHz;

[0023] S3, multiplying the received detection light signal in S2 by a sine wave with a frequency of 2 kHz, and integrating the result to obtain the modulated detection light.

[0024] Adding the detection light modulated in TDLAS mode before step 3 can improve the detection sensitivity.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. A laser detection method for water adsorbed on a wafer surface of the present invention is implemented by using two laser beams, one of which is called a main laser, which has a higher power and forms a smaller light spot on the wafer after focusing, so that the heating area is very small; the other is called a detection light, which is coaxial with the main laser and is used for moisture detection.

[0027] 2. The laser detection method of water adsorbed on the wafer surface of the present invention does not need to heat the entire wafer, the water evaporates quickly, and can be detected immediately after evaporation before it diffuses. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the optical path inside the laser detection device of the present invention;

[0029] Figure 2 Schematic diagram of the principle of the laser detection method of the present invention;

[0030] Figure 3 The waveform diagram of the public data of the absorption peak of water vapor;

[0031] Figure 4 It is a waveform diagram of the water vapor detection signal of the detection light;

[0032] Among them: 1-detection laser light source. 2-main laser light source, 3-main laser reflector, 4-detection light reflector, 5-water vapor detector, 6-locked amplifier, 7-wafer to be tested, 8-detection light, 9-main laser. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described in detail below, but the protection scope of the present invention is not limited to the embodiments.

[0034] To make the content of the present invention more clearly understood, the following Figure 1 -Attached Figure 4 The specific implementation manner is further described.

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] like Figure 2 As shown, this embodiment is a laser detection method for water adsorbed on the surface of a wafer. The method is as follows: two laser beams are arranged in a laser detection device, one of which is a main laser, which forms a smaller light spot on the wafer after focusing, and performs rapid heating of a small area; the other is a detection light, which is coaxial with the main laser, and performs moisture detection on the wafer while heating.

[0037] A laser detection method for water adsorbed on a wafer surface comprises the following steps:

[0038] Step 1, the wafer 7 to be tested is placed in a laser detection device, and the wafer 7 to be tested is placed at the focus of the main laser 9 and the detection light 8;

[0039] Step 2, the laser detection device is sealed and evacuated and then filled with dry nitrogen;

[0040] Step 3, turn on the main laser light source 2 and the detection laser light source 1 at the same time, and focus the detection light 8 and the main laser 9 on the wafer 7 to be tested; the main laser 9 quickly heats the wafer 7 to be tested within the 100 μm diameter spot to above 100° C., so that the moisture adsorbed on the surface of the wafer 7 to be tested evaporates into water vapor, and at the same time, the detection light 8 emitted by the wafer 7 to be tested enters the water vapor detector 5;

[0041] Step 4: Calculate the water vapor concentration according to the TDLAS principle.

[0042] The laser detection device mentioned in the laser detection method of this embodiment includes a device housing ( Figure 1 (not shown), a detection laser light source 1 that emits a detection light 8, a main laser light source 2 that emits a main laser 9, a main laser reflector 3, a detection light reflector 4, a water vapor detector 5, and a lock-in amplifier 6. Figure 1 shown.

[0043] The detection laser light source 1, the main laser light source 2, the main laser reflector 3, the detection light reflector 4, the water vapor detector 5 and the phase-locked amplifier 6 are all arranged in the housing of the device.

[0044] The detection light 8 emitted by the detection laser light source 1 and the main laser light 9 emitted by the main laser light source 2 need to converge on the wafer 7 to be tested and need to overlap. The wafer 7 to be tested is placed horizontally in the housing of the device and is located at the focus of the main laser light 9 and the detection light 8. Figure 2 shown.

[0045] The detection light 8 and the main laser 9 are combined and split by the coupler. The beam splitter uses a dichroic mirror placed at 45 degrees, which is highly transparent to the main laser and semi-transparent and semi-reflective to the detection light. The detection light input by reflection is then output by reflection and detected by the detector.

[0046] Furthermore, in the method of this embodiment, the main laser and the detection light do not need to be coaxial, and only need the light spots of the two on the wafer to overlap, and they can also be incident at an angle.

[0047] like Figure 2 As shown, in the method of this embodiment, the following are preferred: the main laser reflector 3 and the detection light reflector 4 are coaxial and spaced apart inside the device housing, the main laser reflector 3 has high transmittance to the detection light 8 and high reflectance to the main laser 9; the detection light reflector 4 has a reflectivity of 50% to the detection light 8 and high transmittance to the main laser 9; the detection light 8 and the main laser 9 are both placed at 45 degrees.

[0048] like Figure 1As shown, the main laser 9 emitted by the main laser light source 2 is reflected by the main laser reflecting mirror 3 and then passes through the detection light reflecting mirror 4 for high transmittance before irradiating into the wafer to be tested 7. The detection light 8 emitted by the detection laser light source 1 is highly transmittance-transmitted by the main laser reflecting mirror 3 and then enters the detection light reflecting mirror 4 and then irradiates into the wafer to be tested 7. The detection light 8 is reflected by the wafer to be tested 7 and then enters the detection light reflecting mirror 4. After being reflected by the detection light reflecting mirror 4, it enters the water vapor detector 5. The water vapor detector 5 performs water vapor detection and inputs the signal into the phase-locked amplifier 6 to extract the harmonic signal.

[0049] In the method of this embodiment, the main laser 9 uses a wavelength with a high absorption rate; when the material of the wafer 7 to be tested is silicon, the wavelength of the main laser 9 is 1.06μm, 1.5μm, or 2.0μm; when the material of the wafer 7 to be tested is sapphire or lithium niobate, the wavelength of the main laser 9 is 4μm-12μm, for example, a 10μm carbon dioxide laser is used as the main laser light source 2.

[0050] In the method of this embodiment, the detection light 8 uses a wavelength with a high water vapor absorption rate, and the detection laser light source 1 is a near-infrared DFB semiconductor laser or a mid-infrared QCL laser.

[0051] like Figure 3 As shown, when the absorption peaks of gaseous water molecules are near 1.35 μm, 1.9 μm and 6 μm, a near-infrared DFB semiconductor laser or a mid-infrared QCL laser can be used as a detection laser light source.

[0052] In the method of this embodiment, in order to improve the sensitivity, the water vapor detector 5 in the method of this embodiment is a VIGO single-point mid-infrared detector, which is a commercially available part, and the specific model is LabM-I-6-01. Based on the VIGO single-point mid-infrared detector, tunable semiconductor laser absorption spectroscopy (TDLAS) is used to detect water vapor.

[0053] In the method of this embodiment, in step 4, the algorithm for calculating the water vapor concentration according to the TDLAS principle is as follows:

[0054] A high-frequency sinusoidal signal (with a frequency of ) to achieve wavelength (QCL laser wavelength) modulation, then the instantaneous frequency of the QCL laser output for: ;

[0055] is the initial detection light frequency corresponding to the scanning signal, is the frequency modulation amplitude corresponding to the modulation signal, and t is the time.

[0056] Laser intensity after gas absorption It can be expressed as: ;

[0057] in is the incident light intensity, is the absorption coefficient, C is the gas concentration, and L is the optical path. In the detection of trace gas concentration, <<1, so the formula is approximately: ;

[0058] make , the transmitted light intensity is expanded into a Fourier series ;

[0059] in is the harmonic component, and its magnitude is measured by the phase-locked amplifier ;

[0060] In the formula, each harmonic component is proportional to the gas concentration C. Usually the second harmonic component is taken as , that is ;

[0061] At this time, the values ​​except C in the above formula are attributed to K, which is usually calibrated by the standard gas concentration to obtain ;

[0062] and Obtained from the signal measured by a lock-in amplifier.

[0063] Example

[0064] The wafer 7 to be tested is a silicon wafer with a diameter of 4 inches and a thickness of 0.5 mm. A continuous wave fiber laser with a wavelength of 1064 nm and an output power of 15 W is used as the main laser light source. A 5.935 μm QCL laser is used as the detection light source. A VIGO single-point mid-infrared detector is used to collect the detection light.

[0065] Water molecules in gaseous state have a very strong absorption peak at 5.935 μm, such as Figure 3 As shown in the figure, the modulated detection light is used to detect the local evaporated high concentration water molecules, and the returned detection signal is as follows Figure 4 As shown. The absorption peak position is depressed due to absorption by water molecules, generating a second harmonic signal. The water vapor concentration is calculated by inversion of this signal according to the traditional TDLAS theory. Specifically, this signal is multiplied by a 2f=2KHz sine wave and integrated over 1 second. The integral value is 9.8E6, corresponding to a water vapor concentration of 12%.

[0066] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A laser detection method for water adsorbed on a wafer surface, characterized in that: The method is as follows: two laser beams are arranged in a laser detection device, one is a main laser, which forms a light spot on the wafer after focusing to perform small-area rapid heating; the other is a detection light, which is coaxial with the main laser and performs moisture detection on the wafer while heating.

2. The laser detection method for water adsorbed on the wafer surface according to claim 1, characterized in that: The laser detection device comprises a device housing, a detection laser light source (1) for emitting detection light (8), a main laser light source (2) for emitting main laser light (9), a main laser reflector (3), a detection light reflector (4), a water vapor detector (5) and a lock-in amplifier (6); The detection laser light source (1) and the main laser light source (2) are both arranged in a device housing, and the wafer to be tested (7) is placed horizontally in the device housing and is located at the focal points of the main laser (9) and the detection light (8); the main laser reflector (3) and the detection light reflector (4) are coaxially and spaced apart and arranged inside the device housing, the main laser reflector (3) has high transmittance to the detection light (8) and high reflectance to the main laser (9); the detection light reflector (4) has a reflectivity of 50% to the detection light (8) and high transmittance to the main laser (9); The main laser (9) emitted by the main laser light source (2) is reflected by the main laser reflector (3) and then passes through the detection light reflector (4) with high transmittance before being irradiated into the wafer to be tested (7). The detection light (8) emitted by the detection laser light source (1) is highly transmittance-transmitted by the main laser reflector (3) and then enters the detection light reflector (4) before being irradiated into the wafer to be tested (7). The detection light (8) is reflected by the wafer to be tested (7) and then enters the detection light reflector (4). After being reflected by the detection light reflector (4), it enters the water vapor detector (5). The water vapor detector (5) detects water vapor and inputs the signal into the phase-locked amplifier (6) to extract the harmonic signal.

3. The laser detection method for water adsorbed on the wafer surface according to claim 2, characterized in that: When the material of the wafer (7) to be tested is silicon, the wavelength of the main laser (9) is 1.06 μm, 1.5 μm, or 2.0 μm; when the material of the wafer (7) to be tested is sapphire or lithium niobate, the wavelength of the main laser (9) is 4 μm-12 μm.

4. The laser detection method for water adsorbed on the wafer surface according to claim 3, characterized in that: The wavelength of the main laser (9) is 4 μm-12 μm, and the main laser light source (2) is a carbon dioxide laser.

5. The laser detection method for water adsorbed on the wafer surface according to claim 2, characterized in that: The detection laser light source (1) is a near-infrared DFB semiconductor laser or a mid-infrared QCL laser.

6. The laser detection method for water adsorbed on the wafer surface according to claim 2, characterized in that: The water vapor detector (5) is a VIGO single-point mid-infrared detector.

7. The laser detection method for water adsorbed on the wafer surface according to claim 2, characterized in that: The laser detection method comprises the following steps: Step 1: The wafer to be tested (7) is placed in a laser detection device, and the wafer to be tested (7) is placed at the focus of the main laser (9) and the detection light (8); Step 2, the laser detection device is sealed and evacuated and then filled with dry nitrogen; Step 3, the main laser light source (2) and the detection laser light source (1) are turned on simultaneously, and the detection light (8) and the main laser (9) are focused together on the wafer to be tested (7); the main laser (9) quickly heats the wafer to be tested (7) within the 100 μm diameter spot to a temperature above 100° C., so that the moisture adsorbed on the surface of the wafer to be tested (7) evaporates into water vapor, and at the same time, the detection light (8) emitted by the wafer to be tested (7) enters the water vapor detector (5); Step 4: Calculate the water vapor concentration according to the TDLAS principle.

8. The laser detection method for water adsorbed on the wafer surface according to claim 7, characterized in that: In step 2, dry nitrogen is charged, and the charging of nitrogen is stopped when the pressure of the charged nitrogen is the same as the atmospheric pressure.

9. The laser detection method for water adsorbed on the wafer surface according to claim 7, characterized in that: Add the following step before step 3: modulate the detection light (8) according to the TDLAS method; the specific method is as follows: S1, modulating the detection light (8) into a triangular wave, the frequency of the triangular wave is 100 Hz, and the scanning wavelength of the triangular wave is 10 GHz; S2, superimpose a sine wave on the detection light in S1, the frequency of the sine wave is 1KHz, and the scanning wavelength of the sine wave is 1GHz; S3, multiplying the received detection light signal in S2 by a sine wave with a frequency of 2KHz and integrating it; The modulated detection light (8) is obtained.

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