Laser detection method for water adsorbed on wafer surface

Abstract

The invention discloses a laser detection method for water adsorbed on the surface of a wafer, which comprises the following steps of: arranging two laser beams in a laser detection device, focusing one main laser beam to form a smaller light spot on the wafer, and quickly heating in a small area; and the other beam is probe light which is coaxial with the main laser and is used for carrying out moisture detection on the wafer while heating. The method has the advantages that the whole wafer does not need to be heated, the evaporation speed of water is high, and the water is detected immediately if the water is not diffused after evaporation.

Description

Technical Field

[0001] The present 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 critical in semiconductor manufacturing. This is because, when water reacts with the gases used in semiconductor manufacturing, it can corrode wetted surfaces of gas handling components and gas delivery equipment, generate troublesome particles, and affect process tool performance. Furthermore, system failures can lead to serious safety issues and damage the system.

[0003] During the front-end process, wafers must be cleaned while being transported through various semiconductor processing equipment. After exiting the cleaning equipment, they must be kept dry, a practice known as "dry-in-dry-out." This is because if the wafers are exposed to moisture, their surfaces will rapidly oxidize, and invisible water droplets can form stains that affect subsequent processing.

[0004] Moisture detection on the surface of semiconductor wafers is primarily based on a Chinese invention patent application, publication number CN115684265A, published on February 3, 2023. This involves heating the surface of the wafer to convert the moisture into water vapor, which is then collected and measured. This method relies on either dry hot carrier gas or heating lamps, resulting in a large heating area and slow speed. Furthermore, the analysis of water vapor content and heating occur at different locations and times, resulting in slower measurement speeds. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the existing technology for detecting moisture on wafer surfaces uses a large heating area and slow heating, resulting in slow measurement speed. This invention provides a laser detection method for detecting water adsorbed on a wafer surface, which uses a primary light source for rapid heating and an auxiliary light source as a probe light to measure water vapor concentration.

[0006] The technical solutions adopted are as follows: A laser detection method for water adsorbed on a wafer surface comprises the following steps: arranging two laser beams in a laser detection device; one is a main laser beam, which forms a small light spot on the wafer after focusing, thereby rapidly heating the small area; and the other is a detection light beam, which is coaxial with the main laser beam and detects moisture on the wafer while heating.

[0007] Further optimization 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 spaced inside the device housing, the main laser reflector has high transmittance to the detection light and high reflectance to the main laser; the detection light reflector has a reflectivity of 50% for the detection light and is highly transparent to the main laser; the main laser emitted by the main laser light source is reflected by the main laser reflector and then passes through the detection light reflector with high transmittance before irradiating into the wafer to be tested, the detection light emitted by the detection laser light source passes through the main laser reflector with high transmittance and then enters the detection light reflector and then irradiates into the wafer to be tested, the detection light is reflected by the wafer to be tested and enters the detection light reflector, and is reflected by the detection light reflector into the water vapor detector, the water vapor detector detects water vapor 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.

[0008] In a further preferred embodiment of the present invention, the main laser uses a wavelength with a high absorptivity. When the wafer to be tested is made of silicon, the main laser wavelength is 1.06μm, 1.5μm, or 2.0μm. When the wafer to be tested is made of sapphire or lithium niobate, the main laser wavelength is 4μm-12μm. High absorptivity wavelengths provide heating, and the main laser wavelength is within the absorption range of the object to be tested.

[0009] 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.

[0010] In a further preferred embodiment of the present invention, the probe light uses a wavelength with a high absorption rate, and the probe laser light source is a near-infrared DFB semiconductor laser or a mid-infrared QCL laser. The QCL laser has a wavelength of 3-12 microns, which is also within the water vapor absorption peak.

[0011] 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.

[0012] In a further embodiment of the technical solution of the present invention, the laser detection method comprises the following steps: Step 1: Place the wafer to be tested in the laser detection device, and place the wafer to be tested at the focus of the main laser and the detection light; Step 2: The laser detection device is sealed and vacuumed, and then filled with dry nitrogen; Step 3: Turn on the main laser light source and the detection laser light source at the same time. The detection light and the main laser are focused on the wafer to be tested. The main laser quickly heats the wafer to above 100°C within the 100μm diameter spot, causing the moisture adsorbed on the surface of the wafer to evaporate into water vapor. At the same time, the detection light emitted by the wafer to be tested enters the water vapor detector. Step 4: Calculate the water vapor concentration based on the TDLAS principle.

[0013] In this method, the focal spot is very small, which is beneficial to improving the heating efficiency.

[0014] In a further preferred embodiment of the technical solution of the present invention, in step 2, dry nitrogen is added, and the addition of nitrogen is stopped when the pressure of the added nitrogen is equal to the atmospheric pressure. Nitrogen helps to reduce the interference of air.

[0015] 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: S1. Modulate the detection light into a triangular wave with a frequency of 100 Hz and a scanning wavelength of 10 GHz. S2, superimpose a sine wave on the probe light in S1, the frequency of the sine wave is 1KHz, and the scanning wavelength of the sine wave is 1GHz; S3. Multiply the received detection light signal in S2 by a sine wave with a frequency of 2 kHz and integrate the result to obtain a modulated detection light.

[0016] Adding the detection light modulated according to the TDLAS method before step 3 can improve the detection sensitivity.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a laser detection method for water adsorbed on the wafer surface, which is implemented by using two laser beams. One of the beams is called the main laser, which has higher power and forms a smaller light spot on the wafer after focusing, so that the heating area is very small; the other beam is called the detection light, which is coaxial with the main laser and is used for moisture detection.

[0018] 2. The laser detection method of water adsorbed on the wafer surface of the present invention does not require heating the entire wafer. The water evaporates quickly and is detected immediately after evaporation before it diffuses. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the optical path inside the laser detection device of the present invention; Figure 2 Schematic diagram of the principle of the laser detection method of the present invention; Figure 3 The waveform diagram of the public data of the absorption peak of water vapor; Figure 4 This is the waveform diagram of the water vapor detection signal of the detection light; Wherein: 1-detection laser source; 2-main laser source; 3-main laser reflector; 4-detection light reflector; 5-water vapor detector; 6-lock-in amplifier; 7-wafer to be tested; 8-detection light; 9-main laser. DETAILED DESCRIPTION

[0020] 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.

[0021] In order to make the content of the present invention more clear and easy to understand, the following Figure 1 -Attached Figure 4 The specific implementation methods are further described.

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to 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 intended to limit the present invention.

[0023] 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 set in a laser detection device, one is a main laser, which forms a small spot on the wafer after focusing to perform rapid heating of a small area; the other is a detection light, which is coaxial with the main laser and detects moisture on the wafer while heating.

[0024] A laser detection method for water adsorbed on a wafer surface comprises the following steps: Step 1: Place the wafer 7 to be tested in a laser detection device, and place the wafer 7 to be tested at the focus of the main laser 9 and the detection light 8; Step 2: The laser detection device is sealed and vacuumed, and then filled with dry nitrogen; Step 3: Simultaneously turn on the main laser light source 2 and the detection laser light source 1. The detection light 8 and the main laser 9 are focused on the wafer 7 to be tested. The main laser 9 rapidly heats the wafer 7 to above 100°C within the 100 μm diameter spot, causing the moisture adsorbed on the surface of the wafer 7 to evaporate into water vapor. At the same time, the detection light 8 emitted by the wafer 7 to enter the water vapor detector 5. Step 4: Calculate the water vapor concentration based on the TDLAS principle.

[0025] 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 reflecting mirror 3, a detection light reflecting mirror 4, a water vapor detector 5, and a lock-in amplifier 6. Figure 1 shown.

[0026] The detection laser light source 1, the main laser light source 2, the main laser reflecting mirror 3, the detection light reflecting mirror 4, the water vapor detector 5 and the phase-locked amplifier 6 are all arranged in the device housing.

[0027] 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 to be tested 7 and overlap. The wafer to be tested 7 is placed horizontally in the device housing and is located at the focus of the main laser light 9 and the detection light 8. Figure 2 shown.

[0028] The probe light 8 and the primary laser 9 are combined and split by a coupler. The beam splitter uses a dichroic mirror positioned at a 45-degree angle. This mirror is highly transparent to the primary laser and semi-transparent and semi-reflective to the probe light. The reflected input probe light is then reflected back out and detected by a detector.

[0029] Furthermore, in the method of this embodiment, the main laser and the detection light do not need to be coaxial, and it is only necessary that the light spots of the two on the wafer overlap, and they can also be incident at an angle.

[0030] like Figure 2 As shown, in the method of this embodiment, the priority is as follows: 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 has high transmittance to the main laser 9; the detection light 8 and the main laser 9 are both placed at 45 degrees.

[0031] like Figure 1 As 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 with 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 through 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.

[0032] 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.

[0033] 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.

[0034] like Figure 3 As shown in FIG, 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 the detection laser light source.

[0035] To improve sensitivity, the water vapor detector 5 in this embodiment is a commercially available VIGO single-point mid-infrared detector, specifically the LabM-I-6-01. Tunable diode laser absorption spectroscopy (TDLAS) is used to detect water vapor based on the VIGO single-point mid-infrared detector.

[0036] 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: A high-frequency sinusoidal signal (with a frequency of ) to achieve wavelength (QCL laser wavelength) modulation, the instantaneous frequency of the QCL laser output for: ; is the initial probe light frequency corresponding to the scanning signal, is the frequency modulation amplitude corresponding to the modulation signal, and t is the time.

[0037] Laser intensity after gas absorption It can be expressed as: ; 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: ; make , the transmitted light intensity is expanded into a Fourier series ; in is the harmonic component, the size of which is measured by the lock-in amplifier ; In the formula, each harmonic component is proportional to the gas concentration C. Usually the second harmonic component is taken as , that is ; At this time, the values ​​except C in the above formula are attributed to K, which is usually calibrated by standard gas concentration to obtain ; and Obtained from the signal measured by the lock-in amplifier.

[0038] Example Wafer 7 under test 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 primary laser source. A 5.935 μm QCL laser is used as the detection light source. A VIGO single-point mid-infrared detector is used for detection light collection.

[0039] 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 in Figure 1, the absorption peak is depressed by water molecules, generating a second harmonic signal. This signal is then inverted to calculate the water vapor concentration using traditional TDLAS theory. Specifically, this signal is multiplied by a 2f = 2 kHz sine wave and integrated over 1 second. The resulting integral is 9.8E6, corresponding to a water vapor concentration of 12%.

[0040] 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 the surface of a wafer, It is 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 small light spot on the wafer after focusing, and performs 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, It is 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, It is characterized in that 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 1.06 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, It is 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, It is characterized in that The detection light (8) uses a wavelength with a high absorption rate, and 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, It is 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, It is 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, It is 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, It is 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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