Method for detecting l-band defects in silicon single crystals
By employing steps of dissociation, pre-cleaning, heat treatment, mixed acid cleaning, and selective etching, and utilizing gradient temperature control and oxidation differential amplification to amplify L-band defects, the problem of difficult initial detection of silicon single crystals is solved, achieving efficient and low-cost defect detection.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- FERROTEC (NINGXIA) SEMICON TECH CO LTD
- Filing Date
- 2025-07-28
- Publication Date
- 2026-06-26
AI Technical Summary
Existing technologies cannot accurately detect L-band defects in the early stages of silicon single crystal production, resulting in high detection costs and long cycles, which hinders process improvement.
By employing steps of dissociation, pre-cleaning, heat treatment, mixed acid cleaning, and selective etching, L-band defects are amplified through gradient temperature control and oxidation differences, avoiding the introduction of new defects and precisely exposing defect areas.
This enables efficient early detection of L-band defects, saving costs, shortening detection time, and facilitating rapid process improvement.
Smart Images
Figure CN120890760B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of silicon single crystal defect detection technology, and in particular to a method for detecting L-band defects in silicon single crystals. Background Technology
[0002] Currently, in the process of defect detection in single-crystal silicon, it is common to encounter situations where the initial COP (Crystal Optimization) test is qualified, but SP7 scanning reveals defective particles. These defects typically exhibit several patterns: center aggregation, edge rings, full coverage, and a combination of center aggregation and full coverage. SEM scanning confirmed that this defect is not a COP defect. For several years, our company has been unable to determine this type of particle defect, and no other researchers have provided a clear definition. Therefore, we have been unable to identify a direction for improvement in crystal pulling technology, severely impacting the company's economic costs. After long-term research, this type of defect has been identified as L-band. For details, please refer to Lin Mingxian's "Silicon Wafer Semiconductor Material Technology".
[0003] The P-band is a region with almost no vacancy concentration and is also the area where OISF-rings are generated. On either side of the P-band are the H-band and L-band regions with higher residual vacancy concentrations; these two regions are prone to high levels of oxygen precipitates. The L-band is the lower edge of the P-band and connects to the Pv region. Studies have shown that this particulate defect phenomenon occurs entirely in samples where full Pv is detected. According to this theory, the occurrence pattern of L-band corresponds precisely to several particulate defect patterns detected by SP7.
[0004] However, L-band defects cannot be detected using current OISF detection methods or copper-doped wafer methods; they can only be detected using SP7 equipment. However, SP7 equipment requires the silicon wafer to be polished, which is time-consuming and costly, making it impossible to accurately detect defects in the early stages of ingot production. This has hindered process improvement. Summary of the Invention
[0005] In view of this, and to address the above shortcomings, it is necessary to propose a method for detecting L-band defects in silicon single crystals, so as to achieve rapid early detection of L-band defects and thus promote rapid process improvement.
[0006] This invention provides a method for detecting L-band defects in silicon single crystals, comprising the following steps:
[0007] Step 1: Disassemble the silicon wafer to obtain the first silicon wafer;
[0008] Step 2: Perform a pre-cleaning process on the first silicon wafer to obtain the second silicon wafer;
[0009] Step 3: Heat-treat the second silicon wafer to obtain the third silicon wafer; wherein, the heat treatment process is as follows: when the heat treatment furnace is heated to 750℃~800℃, the second silicon wafer is put into the furnace and held at 980℃~1020℃ for 2.5~3.5 hours in a humid oxygen atmosphere, and then held at 1130℃~1170℃ for 90~130 minutes.
[0010] Step 4: Clean the third silicon wafer with a mixed acid solution to remove the surface oxide film and obtain the fourth silicon wafer;
[0011] Step 5: Use a selective etching solution to selectively etch the fourth silicon wafer, and send the resulting sample to the testing room for testing.
[0012] Preferably, step 1 specifically includes: using diamond wire cutting to separate the 12-inch sample into quarter pieces to obtain the first silicon wafer; wherein the cutting rate is 0.25-0.35 mm / s, the coolant is a 5% polyethylene glycol solution, and the edge chipping depth is no more than 0.5 mm.
[0013] Preferably, step 2 specifically includes:
[0014] S21: Use ammonia water with a concentration of 5-8% to ultrasonically clean the first silicon wafer for 5-10 minutes to remove organic contaminants from the surface; wherein the temperature during ultrasonic cleaning is 40℃-50℃.
[0015] S22: Soak the first silicon wafer after ultrasonic cleaning in 8-15% hydrofluoric acid for 2-5 minutes to remove natural oxidation;
[0016] S23: The first silicon wafer, after being soaked in hydrofluoric acid, is ultrasonically cleaned for 3-5 minutes using ultrapure water and then dried using high-purity nitrogen gas to obtain the second silicon wafer.
[0017] Preferably, step 3 specifically includes: heating the temperature to 800°C at a rate of 6°C / min, then feeding the second silicon wafer into the furnace, and heating it to 1000°C at a rate of 6°C / min in a humid oxygen atmosphere and holding it for 3 hours; then heating it to 1150°C at a rate of 6°C / min and holding it for 110 minutes, and finally cooling it down and removing it from the furnace after the holding period.
[0018] Preferably, the process is carried out in a dry oxygen atmosphere at a heating rate of 6°C / min to 800°C.
[0019] Preferably, after holding at 1150℃ for 110 min, the temperature is lowered to 800℃ at a rate of 3.1–3.5℃ / min under a dry oxygen atmosphere. After being removed from the furnace, the sample is allowed to cool naturally to room temperature before being taken out.
[0020] Preferably, step 4 specifically includes:
[0021] S41: Place the third silicon wafer, cooled to room temperature, vertically into the acid mixing tank, ensuring that the surface is completely submerged;
[0022] S42: Ultrasonic-assisted cleaning in a mixed acid tank for 1-2 minutes to enhance oxide film removal;
[0023] S43: Immediately after removing the silicon wafer from the mixed acid tank, rinse it several times with ultrapure water for 30-60 seconds each time to remove residual acid.
[0024] S44: After rinsing with ultrapure water, use nitrogen to dry the surface to avoid watermarks remaining on the surface.
[0025] Preferably, the mixed acid solution in the mixed acid tank is prepared by mixing 49% hydrofluoric acid and 68% nitric acid in a volume ratio of 1:4 to 6.
[0026] Preferably, step 5 specifically includes:
[0027] S51: Place the fourth silicon wafer into the etching tank with the etched side facing down, and ensure that the liquid level is at least 2 cm above the silicon wafer; wherein, the etching tank is filled with Wright preferred etching solution;
[0028] S52: The fourth silicon wafer is selectively etched in the etching tank for 1 to 5 minutes, and the rate of bubble generation on the etched surface is observed every 30 seconds. Uniform bubbles indicate a normal state.
[0029] S53: After selective etching, the silicon wafer is transferred to an ultrapure water bath and ultrasonically cleaned several times to remove residual etching solution; each ultrasonic cleaning session lasts 2 to 5 minutes.
[0030] S54: After ultrasonic cleaning, dry with nitrogen gas, and the blowing pressure should not exceed 0.2 MPa.
[0031] Preferably, the Wright preferred etching solution is prepared from chromic acid solution, copper acid solution, nitric acid, acetic acid and hydrofluoric acid in a volume ratio of 1:(1-3):1:(1-3):(2-4).
[0032] As can be seen from the above technical solution, the solution provided by this invention, when detecting L-band defects in silicon single crystals, firstly separates the silicon wafer to obtain a first silicon wafer, and then pre-cleans the first silicon wafer to obtain a second silicon wafer, removing surface contaminants and oxide layers. Further, the second silicon wafer undergoes heat treatment. Specifically, the second silicon wafer is placed into the heat treatment furnace when the temperature is raised to 750℃~800℃, and held at 980℃~1020℃ for 2.5~3.5 hours in a humid oxygen atmosphere, followed by holding at 1130℃~1170℃ for 90~130 minutes. Thus, by controlling the gradient temperature, a difference in oxide layer can be formed between the L-band defect area and the normal area of the silicon wafer. That is, while avoiding the introduction of new defects, the oxidation difference between the L-band defect and the normal area is precisely amplified, thereby more fully exposing the L-band defect and achieving efficient early detection of L-band defects. Furthermore, cleaning the third silicon wafer with a mixed acid solution can remove the surface oxide film, thereby preventing any impact on preferred etching. Finally, a selective etching solution is used to selectively etch the fourth silicon wafer after mixed acid cleaning, effectively etching out defects and highlighting them on the wafer surface. Therefore, this method allows for early detection of L-band defects without the need for defect scanning using the SP7 equipment. This not only saves on inspection costs but also significantly reduces inspection time, facilitating rapid progress in early-stage process improvements. Attached Figure Description
[0033] Figure 1 This is a flowchart of a method for detecting L-band defects in silicon single crystals, provided as an embodiment of the present invention.
[0034] Figure 2 This is a diagram showing the results of edge ring detection.
[0035] Figure 3 The image shows the detection effect of the central cluster ring.
[0036] Figure 4 This is a diagram showing the results of a full-area inspection.
[0037] Figure 5 The result of center aggregation + edge ring detection. Detailed Implementation
[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0039] like Figure 1As shown, the present invention provides a method for detecting L-band defects in silicon single crystals, which may include the following steps:
[0040] Step 1: Disassemble the silicon wafer to obtain the first silicon wafer;
[0041] Step 2: Perform a pre-cleaning process on the first silicon wafer to obtain the second silicon wafer;
[0042] Step 3: Heat-treat the second silicon wafer to obtain the third silicon wafer; wherein, the heat treatment process is as follows: when the heat treatment furnace is heated to 750℃~800℃, the second silicon wafer is put into the furnace and held at 980℃~1020℃ for 2.5~3.5 hours in a humid oxygen atmosphere, and then held at 1130℃~1170℃ for 90~130 minutes.
[0043] Step 4: Clean the third silicon wafer with a mixed acid solution to remove the surface oxide film and obtain the fourth silicon wafer;
[0044] Step 5: Use a selective etching solution to selectively etch the fourth silicon wafer, and send the resulting sample to the testing room for testing.
[0045] In this embodiment, the silicon wafer is first dissociated to obtain a first silicon wafer. Then, the first silicon wafer undergoes pre-cleaning to obtain a second silicon wafer, removing surface contaminants and oxide layers. Further, the second silicon wafer undergoes heat treatment. Specifically, the second silicon wafer is placed into the heat treatment furnace when the temperature reaches 750℃~800℃, and held at 980℃~1020℃ for 2.5~3.5 hours in a humid oxygen atmosphere, followed by holding at 1130℃~1170℃ for 90~130 minutes. This gradient temperature control allows for a difference in oxide layer between the L-band defect area and the normal area of the silicon wafer. That is, without introducing new defects, the oxidation difference between the L-band defect and the normal area is precisely amplified, thus exposing the L-band defect more fully and achieving efficient early detection of L-band defects. Furthermore, cleaning the third silicon wafer with a mixed acid solution removes the surface oxide film, preventing any impact on preferred etching. Finally, a selective etching solution is used to selectively etch the fourth silicon wafer after mixed acid cleaning, effectively etching out defects and highlighting them on the wafer surface. Therefore, this method allows for early detection of L-band defects without the need for defect scanning using the SP7 equipment. This not only saves on inspection costs but also significantly reduces inspection time, facilitating rapid progress in early-stage process improvements.
[0046] In one embodiment, during step 1, when dissecting the silicon wafer, a 12-inch sample can be dissected into quarter pieces using diamond wire cutting to obtain the first silicon wafer; wherein, the cutting rate is 0.25 to 0.35 mm / s, and the coolant is a 5% polyethylene glycol solution to ensure that there is no edge chipping or that the edge chipping depth is no more than 0.5 mm.
[0047] Since organic contaminants and natural oxidation may exist on the surface of the silicon wafer, in one embodiment, step 2 can be performed by cleaning the first silicon wafer in the following manner to remove surface organic contaminants and natural oxidation:
[0048] S21: Use ammonia water with a concentration of 5-8% to ultrasonically clean the first silicon wafer for 5-10 minutes to remove organic contaminants from the surface; wherein the temperature during ultrasonic cleaning is 40℃-50℃.
[0049] S22: Soak the first silicon wafer after ultrasonic cleaning in 8-15% hydrofluoric acid for 2-5 minutes to remove natural oxidation;
[0050] S23: The first silicon wafer, after being soaked in hydrofluoric acid, is ultrasonically cleaned for 3-5 minutes using ultrapure water and then dried using high-purity nitrogen gas to obtain the second silicon wafer.
[0051] In this embodiment, the resistivity of ultrapure water is not less than 18.2 MΩ·cm. When ultrasonically cleaning in ammonia water, the ultrasonic power can be 300W, and when ultrasonically cleaning in ultrapure water, the ultrasonic power can be 200W. When using high-purity nitrogen to dry the silicon wafer, the purity of the nitrogen can be 99.999%, the pressure should not exceed 0.3 MPa, and the distance from the silicon wafer should not be less than 30 cm to avoid damaging the surface of the silicon wafer.
[0052] In one embodiment, during the heat treatment of the silicon wafer in step 3, the second silicon wafer can be fed into the furnace at a heating rate of 6°C / min to 800°C, and then held at 1000°C for 3 hours at a rate of 6°C / min under a humid oxygen atmosphere. Afterward, the temperature is increased to 1150°C at a rate of 6°C / min and held for 110 minutes. The wafer is then cooled and removed from the furnace. Specifically, the heating rate of 6°C / min to 800°C is performed under a dry oxygen atmosphere, and after holding at 1150°C for 110 minutes, the temperature is decreased to 800°C at a rate of 3.1–3.5°C / min under a dry oxygen atmosphere. After removal from the furnace, the wafer is allowed to cool naturally to room temperature before being taken out.
[0053] In this embodiment, during specific operation, when the furnace temperature reaches 750°C, dry oxygen is activated 5 minutes in advance to purge air from the furnace. When the temperature rises to 950°C, the water level in the wet oxygen generator is checked to ensure a stable gas supply. During the cooling phase, when the temperature drops to 900°C, dry oxygen is switched to prevent water vapor condensation. Finally, the sample is removed and allowed to cool naturally to room temperature. During natural cooling, the quartz boat is placed on a heat-insulating pad to prevent sudden cooling.
[0054] The crystal structure of L-band defects (located in the lower edge ring region of P-band) exhibits microscopic distortions (such as vacancy aggregation and micro-dislocations). Under specific temperatures and humid oxygen atmospheres, the oxidation rate of these distorted regions differs significantly from that of perfect crystal regions; for example, defective regions typically oxidize faster, forming a thicker oxide film. Heat treatment can amplify this difference. During subsequent removal of the surface oxide film using mixed acid, defective regions, due to differences in oxide film thickness or structure, will be preferentially developed during selective etching, ultimately allowing macroscopic observation to identify the distribution of the L-band. Therefore, this scheme employs a temperature gradient heat treatment method: dry oxygen heating to 800℃ → humid oxygen heating to 1000℃ (holding for 3 hours) → humid oxygen heating to 1150℃ (holding for 110 minutes) → dry oxygen cooling to 800℃.
[0055] In the first stage, considering that heating the silicon wafer from room temperature to 1150°C in the furnace results in a maximum temperature difference of 1125°C, significant thermal stress would be generated inside the wafer due to the temperature gradient. When the stress exceeds the critical fracture strength of the silicon wafer, it will directly lead to cracking, edge chipping, or even complete breakage, making subsequent polarity testing impossible. Moreover, even without macroscopic cracking, the instantaneous thermal stress generated by the drastic heating will cause new defects such as dislocations and vacancy clusters inside the silicon wafer. These defects may have similar morphology and distribution to L-band defects and may be misjudged as L-band defects in subsequent etching steps, leading to distorted test results. Therefore, this solution considers placing the silicon wafer into the furnace at 800°C to reduce thermal shock damage. Furthermore, the subsequent slow heating at 6°C / min to 1000°C allows the silicon wafer temperature to gradually increase, dispersing and releasing thermal stress, and avoiding mechanical damage. In addition, 800°C is the starting temperature for the oxidation reaction on the silicon wafer surface; at this temperature, the reactivity of the silicon wafer with oxygen is significantly enhanced. After the silicon wafers are placed into the furnace at 800°C, the atmosphere is immediately switched to a humid oxygen atmosphere and the temperature is increased. This ensures that the oxidation reaction in the L-band defect area is under control from the initial stage, avoiding the problem of indistinct defect differences caused by insufficient oxidation at low temperatures (such as below 600°C). Furthermore, in the first stage, the silicon wafers are placed in a dry oxygen atmosphere to eliminate the interference of residual air in the furnace on the oxidation reaction. Dry oxygen can quickly replace impurity gases in the furnace, ensuring the purity of the subsequent humid oxygen atmosphere and preventing impurities from adsorbing on the silicon wafer surface and hindering oxide layer formation.
[0056] The second stage aims to promote the initial oxidation of the L-band defect region, forming the basis for a differentiated oxide layer. Specifically, 1000℃ is the critical temperature for silicon wafer oxidation: in a moist oxygen atmosphere (H2O provides hydroxyl groups, accelerating the oxidation reaction), silicon (Si) reacts with oxygen to generate silicon dioxide (SiO2), the reaction formula being Si + 2H2O → SiO2 + 2H2↑. Due to the distorted crystal structure and loose atomic arrangement in the L-band defect region, hydroxyl groups (-OH) diffuse more easily to the defect, resulting in an oxidation rate 1.2-1.5 times faster than in the normal region, forming the initial difference of "slightly thicker oxide film in the defect region". A 3-hour holding time ensures that this difference is stably formed: if the time is too short (e.g., <2h), the difference is insufficient, while if it is too long (e.g., >4h), it may lead to an excessively thick surface oxide film, increasing the difficulty of subsequent cleaning.
[0057] The third stage aims to enhance the oxidation difference between defective and normal areas, activating the development activity of defects. Specifically, 1150℃ falls within the high-temperature oxidation range, further accelerating the oxidation reaction in defective areas: at high temperatures, the atomic diffusion rate increases, and microscopic distortions in defective areas (such as vacancy clusters) become "active centers" for the oxidation reaction, further amplifying the oxide film thickness difference beyond that of the second stage, making it more readily identifiable by subsequent etching steps. A 110-minute holding period balances "difference enhancement" with "wafer damage": if the time is too short (e.g., <90 minutes), the difference is not sufficiently amplified, while if it is too long (e.g., >130 minutes), it may cause thermal deformation of the wafer surface due to high temperatures, or excessive oxidation of normal areas, masking the defect differences.
[0058] The fourth stage aims to stabilize the oxide layer structure and prevent secondary contamination of the surface by moisture during cooling. Specifically, when cooling directly from 1150℃ to room temperature, moisture (residual wet oxygen) inside the furnace may condense on the silicon wafer surface, leading to localized dissolution or contamination of the oxide layer. Switching to a dry oxygen atmosphere for cooling isolates moisture, allowing the oxide layer (especially the differentiated oxide film in defect areas) to cool in a stable atmosphere, maintaining structural integrity. 800℃, as the "final temperature" before unloading, prevents sudden cooling cracking caused by direct contact between the silicon wafer and room temperature air at high temperatures, ensuring the physical integrity of the silicon wafer.
[0059] In one embodiment, step 4, when cleaning the silicon wafer using mixed acid, can be achieved through the following steps:
[0060] S41: Place the third silicon wafer, cooled to room temperature, vertically into the acid mixing tank, ensuring that the surface is completely submerged;
[0061] S42: Ultrasonic-assisted cleaning in a mixed acid tank for 1-2 minutes to enhance oxide film removal;
[0062] S43: Immediately after removing the silicon wafer from the mixed acid tank, rinse it several times with ultrapure water for 30-60 seconds each time to remove residual acid.
[0063] S44: After rinsing with ultrapure water, use nitrogen to dry the surface to avoid watermarks remaining on the surface.
[0064] In this embodiment, the mixed acid solution in the mixed acid tank can be prepared by mixing 49% hydrofluoric acid and 68% nitric acid in a volume ratio of 1:4 to 6. The mixed acid should be prepared and used immediately. During preparation, nitric acid is slowly added to hydrofluoric acid while stirring. Ultrasonic assistance is considered during cleaning to shorten the cleaning time.
[0065] In one embodiment, step 5, when selectively etching the silicon wafer, can be achieved through the following steps:
[0066] S51: Place the fourth silicon wafer into the etching tank with the etched side facing down, and ensure that the liquid level is at least 2 cm above the silicon wafer; wherein, the etching tank is filled with Wright preferred etching solution;
[0067] S52: The fourth silicon wafer is selectively etched in the etching tank for 1 to 5 minutes, and the rate of bubble generation on the etched surface is observed every 30 seconds. Uniform bubbles indicate a normal state.
[0068] S53: After selective etching, the silicon wafer is transferred to an ultrapure water bath and ultrasonically cleaned several times to remove residual etching solution; each ultrasonic cleaning session lasts 2 to 5 minutes.
[0069] S54: After ultrasonic cleaning, dry with nitrogen gas, and the blowing pressure should not exceed 0.2 MPa.
[0070] In this embodiment, the Wright preferred etching solution is prepared from chromic acid solution, copper acid solution, nitric acid, acetic acid, and hydrofluoric acid in a volume ratio of 1:(1-3):1:(1-3):(2-4). Simultaneously, the condition of the silicon wafer is monitored during the etching process to avoid over-etching that could obscure defects.
[0071] Furthermore, after the selective etching is completed, the silicon wafer is transferred to a darkroom for macroscopic inspection.
[0072] (I) The effects of the heat treatment process and the preferred corrosion process of this scheme will be explained below through specific experimental comparisons. In the following experiments, the processes before heat treatment and the pickling process are the same.
[0073] Experiment 1: Dry oxygen 6℃ / min to 800℃ → silicon wafer into furnace → wet oxygen 6℃ / min to 1000℃ and hold for 3h → wet oxygen 6℃ / min to 1150℃ and hold for 110min → dry oxygen 3.3℃ / min to 800℃ → natural cooling to room temperature; Wright solution was selected as the preferred etching solution.
[0074] Experiment 2: Dry oxygen 6℃ / min to 800℃ → silicon wafer into furnace → wet oxygen 6℃ / min to 1000℃ and hold for 3h → wet oxygen 6℃ / min to 1150℃ and hold for 110min → dry oxygen 3.3℃ / min to 800℃ → natural cooling to room temperature; Secco solution was selected as the preferred etching solution.
[0075] Experiment 3: N2 atmosphere is introduced into the furnace → dry oxygen is introduced at 700-800℃ (constant temperature for 1-3 hours) → the temperature is raised to 900-1100℃ (dry oxygen, constant temperature for 15-20 hours) → dry oxygen is turned off at 700℃ and N2 is introduced → natural cooling; Wright solution is selected as the preferred corrosion solution.
[0076] Experiment 4: N2 atmosphere is introduced into the furnace → dry oxygen is introduced at 700-800℃ (constant temperature for 1-3 hours) → the temperature is raised to 900-1100℃ (dry oxygen, constant temperature for 15-20 hours) → dry oxygen is turned off at 700℃ and N2 is introduced → natural cooling; Secco solution is selected as the preferred corrosion solution.
[0077] Experiment 5: N2 atmosphere is introduced into the furnace → temperature is increased to 1100℃ (held for 3 hours) → temperature is increased to 1050℃ (held for 4 hours) → temperature is increased to 700℃ and then discharged from the furnace → natural cooling; Wright solution is selected as the preferred etchant.
[0078] Experiment 6: N2 atmosphere is introduced into the furnace → temperature is increased to 1100℃ (held for 3 hours) → temperature is increased to 1050℃ (held for 4 hours) → temperature is increased to 700℃ and then discharged from the furnace → natural cooling; Secco solution is selected as the preferred corrosion solution.
[0079] The detection results of the above 6 groups of experiments are shown in Table 1 below:
[0080] Table 1
[0081] Experiment 1 Experiment 2 Experiment 3 Experiment 4 Experiment 5 Experiment 6 Macro effect A A × × × B microscale 30-50μm 10-15μm <1μm <1μm <10μm 8-13μm
[0082] In Table 1, A and B represent the clarity of macroscopic detection, with A having a higher clarity than B. × indicates no defect was observed. Therefore, as shown in Table 1, the process conditions in Experiment 1 are optimal for detecting L-band defects.
[0083] (II) Based on Experiment 1, the effects of this scheme are further illustrated through experiments using different heat treatment processes, as shown in Table 2 below. The processes other than heat treatment are the same as in Experiment 1 of this scheme, and the first and fourth stages of the heat treatment process are also the same as in Experiment 1 of this scheme.
[0084] Table 2
[0085] Second stage temperature Second phase time Third stage temperature Phase Three Experiment 1 1000℃ 3h 1150℃ 110min Experiment 7 950℃ 3h 1150℃ 110min Experiment 8 1050℃ 3h 1150℃ 110min Experiment 9 1000℃ 2h 1150℃ 110min Experiment 10 1000℃ 4h 1150℃ 110min Experiment 11 1000℃ 3h 1100℃ 110min Experiment 12 1000℃ 3h 1200℃ 110min Experiment 13 1000℃ 3h 1150℃ 80min Experiment 14 1000℃ 3h 1150℃ 140min
[0086] L-band defect detection was performed on the silicon wafers processed according to the experimental processes in Table 2 to detect the micro-size of the defects, and the results are shown in Table 3 below.
[0087] Table 3
[0088]
[0089]
[0090] The experimental results in Table 3 show that in Experiment 7, when the temperature in the second stage was below 1000℃, insufficient wet oxygen oxidation resulted in blurred defect development, smaller defect size, and decreased matching with SP7. In Experiment 8, when the temperature in the second stage was above 1000℃, excessive oxidation led to defect edge fusion and reduced clarity. In Experiment 11, when the temperature in the third stage was below 1150℃, insufficient defect activation occurred at high temperatures, resulting in the worst development effect. In Experiment 12, when the temperature in the third stage was above 1150℃, the oxide layer on the silicon wafer surface was too thick, and the defect outline was unclear after etching. In Experiment 9, the holding time in the second stage was less than 3 hours, or in Experiment 13, the holding time in the third stage was less than 110 minutes, resulting in insufficient defect development and smaller defect size. In Experiment 10, the holding time in the second stage was greater than 3 hours, or in Experiment 14, the holding time in the third stage was greater than 110 minutes. Although the development was relatively clear, excessive defect expansion led to a large local matching deviation with the SP7 image.
[0091] like Figure 2-5 The verification was carried out using the process provided in this scheme (i.e., the scheme in Experiment 1). Figure 2 For edge ring, Figure 3 As a central gathering ring, Figure 4 For a full face, Figure 5 It consists of a central cluster and an edge ring. Figure 2-5 In the image, the left side shows the SP7 scan image, and the right side shows the macroscopic inspection image. Comparing the SP7 image and the macroscopic inspection image, it can be seen that this method can clearly detect the four defect morphologies of the L-band.
[0092] The modules or units in the device of this invention can be merged, divided, and deleted according to actual needs. The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the processes of the above embodiments and making equivalent changes according to the claims of this invention still fall within the scope of the invention.
Claims
1. A method for detecting L-band defects in silicon single crystals, characterized in that, Includes the following steps: Step 1: Disassemble the silicon wafer to obtain the first silicon wafer; Step 2: Perform a pre-cleaning process on the first silicon wafer to obtain the second silicon wafer; Step 3: Heat-treat the second silicon wafer to obtain the third silicon wafer; wherein, the heat treatment process is as follows: when the heat treatment furnace is heated to 750℃~800℃, the second silicon wafer is put into the furnace and held at 980℃~1020℃ for 2.5~3.5 hours in a humid oxygen atmosphere, and then held at 1130℃~1170℃ for 90~130 minutes; after the holding period, the temperature is lowered to 800℃ at 3.1~3.5℃ / min in a dry oxygen atmosphere, and after being taken out of the furnace, it is naturally cooled to room temperature and the sample wafer is taken out. Step 4: Clean the third silicon wafer with a mixed acid solution to remove the surface oxide film and obtain the fourth silicon wafer; Step 5: Use a selective etching solution to selectively etch the fourth silicon wafer, and send the resulting sample to the testing room for testing.
2. The method for detecting L-band defects in silicon single crystals according to claim 1, characterized in that, Step 1 specifically includes: using diamond wire cutting to separate the 12-inch sample into quarter pieces to obtain the first silicon wafer; wherein the cutting rate is 0.25~0.35mm / s, the coolant is a 5% polyethylene glycol solution, and the edge chipping depth is no more than 0.5mm.
3. The method for detecting L-band defects in silicon single crystals according to claim 1, characterized in that, Step 2 specifically includes: S21: Use ammonia water with a concentration of 5~8% to ultrasonically clean the first silicon wafer for 5~10 minutes to remove surface organic contaminants; wherein, the temperature during ultrasonic cleaning is 40℃~50℃; S22: Soak the first silicon wafer after ultrasonic cleaning in 8-15% hydrofluoric acid for 2-5 minutes to remove natural oxidation; S23: The first silicon wafer, after being soaked in hydrofluoric acid, is ultrasonically cleaned for 3-5 minutes using ultrapure water and then dried using high-purity nitrogen gas to obtain the second silicon wafer.
4. The method for detecting L-band defects in silicon single crystals according to claim 1, characterized in that, Step 3 specifically includes: heating the temperature to 800°C at a rate of 6°C / min, then placing the second silicon wafer into the furnace, and holding it at 1000°C for 3 hours in a humid oxygen atmosphere at a rate of 6°C / min; then heating the temperature to 1150°C at a rate of 6°C / min and holding it for 110 minutes, and finally cooling it down and removing it from the furnace after the holding period.
5. The method for detecting L-band defects in silicon single crystals according to claim 4, characterized in that, The temperature was increased to 800°C at a rate of 6°C / min under a dry oxygen atmosphere.
6. The method for detecting L-band defects in silicon single crystals according to claim 1, characterized in that, Step 4 specifically includes: S41: Place the third silicon wafer, cooled to room temperature, vertically into the acid mixing tank, ensuring that the surface is completely submerged; S42: Ultrasonic-assisted cleaning in a mixed acid bath for 1-2 minutes to enhance oxide film removal; S43: Immediately after removing the silicon wafer from the mixed acid tank, rinse it several times with ultrapure water for 30-60 seconds each time to remove residual acid. S44: After rinsing with ultrapure water, use nitrogen to dry the surface to avoid watermarks remaining on the surface.
7. The method for detecting L-band defects in silicon single crystals according to claim 6, characterized in that, The mixed acid solution in the mixed acid tank is prepared by mixing 49% hydrofluoric acid and 68% nitric acid in a volume ratio of 1:4 to 6.
8. The method for detecting L-band defects in silicon single crystal according to claim 1, characterized in that, Step 5 specifically includes: S51: Place the fourth silicon wafer into the etching tank with the etched side facing down, and ensure that the liquid level is at least 2 cm above the silicon wafer; wherein, the etching tank is filled with Wright preferred etching solution; S52: The fourth silicon wafer is selectively etched in the etching tank for 1~5 minutes, and the rate of bubble generation on the etched surface is observed every 30 seconds. Uniform bubbles are normal. S53: After selective etching, the silicon wafer is transferred to an ultrapure water bath and ultrasonically cleaned several times to remove residual etching solution; each ultrasonic cleaning session lasts 2-5 minutes. S54: After ultrasonic cleaning, dry with nitrogen gas, and the blowing pressure should not exceed 0.2 MPa.