Method for representing micro-defects of nearly perfect czochralski silicon wafer by regulating and controlling near-surface copper concentration

Abstract

The invention belongs to the technical field of semiconductor material detection, and particularly relates to a method for representing micro-defects of a near-perfect czochralski silicon wafer by regulating and controlling near-surface copper concentration. The invention discloses a method for representing micro-defects of a near-perfect czochralski silicon wafer by regulating and controlling the concentration of near-surface copper. The method specifically comprises the following steps: (S.1) cleaning the silicon wafer and immersing the silicon wafer into a copper nitrate solution for standing; (S.2) rinsing the silicon wafer with ionized water, taking out the silicon wafer and airing the silicon wafer; (S.3) performing high-temperature heat treatment on the silicon wafer for a period of time, and quickly cooling; (S.4) carrying out chemical polishing on the cooled silicon wafer; (S.5) horizontally placing the silicon wafer in the corrosive liquid; and (S.6) observing the surface of the silicon wafer by using an optical microscope or a scanning electron microscope so as to display the microdefects. According to the invention, copper precipitates at different depths are observed after copper is introduced at high temperature, so that the microdefect condition of the silicon wafer can be reflected. The method can clearly display the micro-defects in the nearly perfect czochralski silicon wafer, and has high detection efficiency and accuracy. The method is easy to operate, low in cost and suitable for silicon wafer microdefect detection in large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor material detection, and particularly relates to a method for characterizing micro-defects of near-perfect Czochralski silicon wafer by regulating and controlling near-surface copper concentration. BACKGROUND

[0002] Silicon is the most common and widely used semiconductor material. When molten elemental silicon solidifies, silicon atoms arrange into crystal nuclei in a diamond lattice, the crystal nuclei grow into crystal grains with the same crystal face orientation, and form monocrystalline silicon. With the rapid development of semiconductor and integrated circuit technology, the demand for low defect concentration monocrystalline silicon materials is increasing. Czochralski silicon wafer (CZ-Si) is a key material for semiconductor manufacturing, and its micro-defects (such as vacancy clusters, self-interstitial atom clusters, oxygen precipitates, dislocation loops, etc.) can significantly affect device performance. Near-perfect Czochralski silicon wafer is a high-quality silicon wafer that does not contain crystal original defects (COP) with a size greater than 65 nm in the surface and thickness directions. However, even in such high-quality silicon wafers, there may still be bulk defects that have a significant impact on the performance and reliability of semiconductor devices. Therefore, it is of great significance to develop a method that can effectively display and detect bulk defects in near-perfect Czochralski silicon wafers.

[0003] There are several methods for detecting silicon wafer defects. Optical detection methods can use visible or ultraviolet light to irradiate the surface of the silicon wafer, and image through reflected light (bright field) or scattered light (dark field). Electron microscope techniques include scanning electron microscope (SEM) detection and transmission electron microscope (TEM) detection, both of which are through electron beam scanning surface electron imaging. Metal etching method (Metal Decorating Etching) is a classic method for defect visualization through chemical etching, which is particularly suitable for detecting crystal defects (such as dislocations, stacking faults, oxidation-induced stacking faults, etc.). The core principle is to use the chemical activity difference between defects and complete lattice regions to make defects visible through metal deposition or selective etching.

[0004] The diffusion behavior and precipitation behavior of copper, as an important transition metal, in silicon have been widely studied. Copper atoms have the characteristics of fast diffusion and high sensitivity of solubility to temperature. During the cooling process, copper tends to nucleate and form copper precipitates at microdefects, thus directly revealing the presence of these microdefects. After introducing copper precipitates at high temperature, microdefects in the silicon wafer can usually be observed by cross-section observation. However, the preparation process of the cross-section may cause additional damage to the silicon wafer, further interfering with the accurate detection of microdefects. To solve this problem, the present application proposes a method for truly reflecting the microdefects of the silicon wafer by observing copper precipitates at different depths. As the depth increases, the copper concentration gradually decreases, and the diffusion path of copper atoms becomes more complex. Different depths correspond to different copper concentrations, resulting in different morphologies and characteristics of copper precipitates. These differences provide rich information for accurately characterizing the microdefects of the silicon wafer. By analyzing copper precipitates at different depths, the distribution of microdefects inside the silicon wafer can be more comprehensively understood, providing a reliable basis for quality control of the silicon wafer and optimization of the chip manufacturing process, effectively solving the limitations of traditional cross-section characterization methods.

[0005] In patent CN119556095A, a method for detecting defects in a silicon wafer is provided. The method involves three-stage heat treatment to increase the amount of oxygen precipitates in a certain region of the crystal, thereby enabling clear differentiation of the boundary of the crystal region with an oxygen concentration below 9ppma. By differentiating the boundary of the crystal region, the quality level of the silicon wafer with an oxygen concentration below 9ppma can be quickly determined. However, the sensitivity and detection of low-density dislocations of this patent are still insufficient. In patent CN115791818A, a method for detecting defects in a silicon wafer is provided. The method uses copper contamination to detect two sub-silicon wafers and performs different heat treatments on the two sub-silicon wafers. By utilizing the characteristics of the pv and pi regions, different results are obtained for the two sub-silicon wafers, thereby accurately determining the pv and pi regions. However, the etching or metal deposition process in this patent permanently changes the surface structure of the silicon wafer, making the sample unable to continue to be used for subsequent processes or electrical tests. Moreover, metal residues (such as copper) may interfere with other analysis methods (such as secondary ion mass spectrometry (SIMS) or electrical tests), and the accuracy of this method is low. SUMMARY

[0006] The present application solves the problems of low accuracy, low efficiency, and high cost in detecting microdefects in silicon wafers in the prior art. By using a metal etching method and observing copper precipitates at different depths after introducing copper at high temperature, a method for characterizing near-perfect Czochralski silicon wafers by regulating the near-surface copper concentration is provided.

[0007] The present application specifically adopts the following technical solutions to achieve the above objectives:

[0008] The first aspect of the present application provides a method for characterizing near perfect Czochralski silicon wafer micro-defects by regulating near-surface copper concentration, and the specific method comprises the following steps:

[0009] (S.1) cleaning the silicon wafer and immersing it in a copper nitrate solution for standing;

[0010] (S.2) rinsing the silicon wafer with ionized water and drying it after taking it out;

[0011] (S.3) high-temperature heat treatment of the silicon wafer for a period of time, followed by rapid cooling;

[0012] (S.4) chemical polishing of the cooled silicon wafer;

[0013] (S.5) placing the silicon wafer horizontally in an etching solution;

[0014] (S.6) observing the surface of the silicon wafer with an optical microscope or a scanning electron microscope to show micro-defects.

[0015] The copper contamination method (Copper Decoration Method) is a classic and effective metal contamination method for detecting silicon wafer defects, and has unique advantages in the development of crystal defects (such as dislocations, stacking faults, etc.). Copper ions (Cu 2+ ) are preferentially reduced and deposited at crystal defects (such as dislocations, stacking faults), and even if the defect density is very low (such as <10 3 cm -2 ), the distribution of copper particles can be clearly observed under a microscope. Micro-dislocations or oxidation-induced stacking faults (OSF) that are difficult to directly observe with a traditional optical microscope can be developed.

[0016] Further, the concentration of the copper nitrate solution in step S.1 is 0.5-10 mol / L.

[0017] The present application uses copper nitrate to contaminate the silicon wafer. Since copper nitrate is easily soluble in water and has strong stability, the oxidation of nitrate (NO3 - ) enhances defect selectivity, and does not introduce halogen or sulfide ions that may interfere with the surface state of the silicon wafer. The copper deposition rate is controllable and the morphology is clear.

[0018] Further, the standing time in step S.1 is 5-30 min.

[0019] Further, the temperature range of the high-temperature heat treatment in step S.3 is 800-1000℃.

[0020] Further, the high-temperature heat treatment in step S.3 uses an atmosphere, and the atmosphere includes one of nitrogen, argon, oxygen or air.

[0021] Further, the rapid cooling in step S.3 is air cooling, and the cooling speed is about 30K / s.

[0022] The present application can avoid additional defects caused by thermal stress by air cooling, and can uniformly cool the silicon wafer and maintain the integrity of the crystal. At the same time, air cooling can prevent copper secondary diffusion or contamination, reduce copper migration, and avoid surface contamination.

[0023] Further, the polishing solution used in the chemical polishing in step S.4 is a mixture of HNO3 and HF.

[0024] Further, the volume ratio of HNO3 to HF in the polishing solution in step S.4 is 3:1.

[0025] Further, the chemical polishing in step S.4 is performed in multiple times.

[0026] Multiple polishing can improve the surface flatness and reduce excessive corrosion. Multiple polishing can remove damage layer by layer, avoiding the introduction of new surface undulations or pits due to excessive corrosion in single polishing. Moreover, this method can more accurately develop defects, reduce the risk of defect masking, and is especially suitable for low defect density silicon wafers. At the same time, this method can reduce the scrap rate. If single polishing fails (such as excessive corrosion), the silicon wafer is directly scrapped; multiple polishing can stop the problem batch in time and save part of the sample.

[0027] Further, the etching solution in step S.5 is standard Yang1 etching solution or Secco etching solution, and the etching time is 5-10min.

[0028] The present application has the following beneficial effects:

[0029] (1) The present application can truly reflect the micro-defect condition of the silicon wafer by observing copper precipitation at different depths after introducing copper at high temperature. This method can clearly show the micro-defects in near-perfect Czochralski silicon wafers in a short time, and has high detection efficiency and accuracy.

[0030] (2) The present application is simple to operate and low in cost, and is suitable for micro-defect detection of silicon wafers in large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Fig. 4 is an optical microscope image of copper precipitation at different depths of a silicon wafer after chemical polishing and etching treatment.

[0032] Figure 2 Fig. 6 is an optical microscope image showing the effect of different concentrations of copper nitrate solution and different etching solutions on copper precipitation at different depths of a silicon wafer. DETAILED DESCRIPTION

[0033] The present application is illustrated by way of specific examples below, which are presented for the purpose of explanation only and should not be considered as limiting the scope of the present application. Other advantages and benefits of the present application will be apparent to those skilled in the art upon reading the description of the present application in conjunction with the accompanying drawings. The present application can also be implemented or applied in other different ways, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following examples and features in the examples can be combined with each other without conflict. The methods used in the examples of the present application are conventional methods unless otherwise specified, and the reagents used are commercially available.

[0034] Example 1: Silicon wafer defect detection

[0035] I. Experimental method:

[0036] 1) Clean the near-perfect silicon wafer to remove surface impurities.

[0037] 2) Immerse the cleaned silicon wafer A in a 0.8M copper nitrate solution for 20 minutes to contaminate the surface of the silicon wafer with copper ions; immerse the cleaned silicon wafer B in a 0.5M copper nitrate solution for 20 minutes to contaminate the surface of the silicon wafer with copper ions.

[0038] 3) Rinse the silicon wafer in deionized water to remove excess copper ions on the surface, then take it out and dry.

[0039] 4) Put the dried silicon wafer into a high-temperature furnace for heat treatment, the high-temperature heat treatment atmosphere is nitrogen, the heat treatment temperature is 800℃, 900℃, 1000℃ respectively, the time is 3min30s respectively.

[0040] 5) Rapidly cool the heat-treated silicon wafer to room temperature, the rapid cooling is air cooling, the cooling speed is about 30K / s.

[0041] 6) Chemically polish the cooled silicon wafer for 0s, 40s, 100s, 220s, the polishing liquid is HNO3:HF=3:1, and the corresponding polishing depths are 0μm, 35μm, 85μm, 185μm respectively, to expose the copper deposits in the deep part.

[0042] 7) Place the polished silicon wafer A horizontally in Yang1 etching solution for 10 minutes; place the polished silicon wafer B horizontally in Secco etching solution for 10 minutes.

[0043] 8) Observe the surface of silicon wafer A with an optical microscope or a scanning electron microscope, as shown in Figure 1 , observe the surface of silicon wafer B with an optical microscope or a scanning electron microscope, as shown in Figure 2 , observe the morphology and distribution of copper deposits, thereby showing micro-defects.

[0044] II. Experimental results

[0045] Figure 1 、 Figure 2 The optical microscope images of copper precipitates at different depths of the silicon wafer after chemical polishing and etching are shown. It can be seen that there are obvious differences in the shape, size and density of copper precipitates at different depths. Figure 1 The copper precipitates on the surface are dense and small in size, and are in the form of branches. With the increase of depth, the copper concentration density gradually decreases. The size is the largest at 35 μm, and the copper precipitates in the deep part are in the form of nearly invisible point pits. Figure 1 The copper precipitates on the surface are dense and in the form of points and polyhedrons. With the increase of depth, the copper concentration density gradually decreases. The copper precipitates in the deep part are in the form of nearly invisible point pits.

[0046] The copper concentration at different depths is different, resulting in different forms and characteristics of copper precipitates. These differences provide rich information for accurately characterizing the micro-defects of the silicon wafer. By analyzing the copper precipitates at different depths, the distribution of micro-defects inside the silicon wafer can be more comprehensively understood.

Claims

1. A method for characterizing microdefects in near perfect Czochralski silicon wafers by regulating the near surface copper concentration, characterized in that, The specific method comprises: (S.1) taking the cleaned silicon wafer and immersing it in a copper nitrate solution for copper contamination treatment; (S.2) taking the silicon wafer after the copper contamination treatment and performing deionized water floating, and then drying after being taken out; (S.3) taking the cleaned silicon wafer and performing high-temperature heat treatment, and then rapidly cooling; (S.4) taking the cooled silicon wafer and performing chemical polishing treatment; (S.5) taking the polished silicon wafer and horizontally placing it in an etching solution for etching; (S.6) observing the surface of the silicon wafer by using an optical microscope or a scanning electron microscope to show micro-defects.

2. A method of characterizing near perfect FZ silicon wafers for microdefects by modulating the near surface copper concentration as claimed in claim 1 wherein, The concentration of the copper nitrate solution in step S.1 is 0.5-10 mol / L.

3. A method of characterizing near perfect Czochralski silicon wafers for microdefects by modulating the near surface copper concentration as claimed in claim 2, wherein, The standing time in step S.1 is 5-30 min. ​ 4. A method of characterizing near perfect Czochralski silicon wafers for microdefects by modulating the near surface copper concentration as recited in claim 1, wherein, The temperature range of the high-temperature heat treatment in step S.3 is 800-1000℃.

5. A method of characterizing near perfect Czochralski silicon wafers for microdefects by modulating the near surface copper concentration as claimed in claim 4 wherein, The high-temperature heat treatment in step S.3 adopts an atmosphere, and the atmosphere includes one of nitrogen, argon, oxygen or air.

6. A method of characterizing near perfect, Czochralski silicon wafers for microdefects by modulating the near surface copper concentration as recited in claim 1, wherein, The rapid cooling in step S.3 is air cooling, and the cooling speed is 20-40 K / s.

7. A method of characterizing near perfect, Czochralski silicon wafers for microdefects by modulating the near surface copper concentration as recited in claim 1, wherein, The polishing solution used in the chemical polishing in step S.4 is a mixed solution of HNO3 and HF.

8. A method of characterizing near perfect, Czochralski silicon wafers for microdefects by modulating the near surface copper concentration as recited in claim 7, wherein, The volume ratio of HNO3 to HF in the polishing solution in step S.4 is 3:

1.

9. A method of characterizing near perfect Czochralski silicon wafers for microdefects by modulating the near surface copper concentration as recited in claim 7, wherein, The chemical polishing in step S.4 adopts multiple polishing.

10. A method of characterizing near perfect Czochralski silicon wafers for microdefects by modulating the near surface copper concentration as recited in claim 1, wherein, The etching solution in step S.5 is standard Yang1 etching solution or Secco etching solution, and the etching time is 5-10 min.

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