Method for detecting dislocation defect of heavily doped silicon single crystal

Abstract

The invention provides a heavily-doped silicon single crystal dislocation defect detection method, which belongs to the technical field of silicon single crystal detection, and comprises the following steps: S1, cutting a silicon wafer from a heavily-doped silicon single crystal to be detected as a sample wafer; s2, putting the sample into alkali liquor for alkali washing; s3, the sample wafer subjected to alkali washing is put into a chromium-free corrosive liquid to be corroded, and the chromium-free corrosive liquid is composed of nitric acid, hydrofluoric acid and citric acid; s4, after corrosion is finished, the sample wafer is taken out for cleaning; and S5, putting the cleaned sample into a mixed acid solution for reaction, removing a surface layer, and observing the sample after the reaction is finished. By adopting the chromium-base-free corrosive liquid, heavy metal ion contamination caused by a common chromium-base preferential corrosive liquid to the environment is avoided, the corrosion time is greatly shortened while the cost is reduced, the corrosion efficiency is remarkably improved, dislocation of a heavily doped silicon wafer can be effectively and completely exposed, and missing detection is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of silicon single crystal detection, and in particular to a method for detecting dislocation defects of heavily doped silicon single crystals. Background Art

[0002] Dislocation is the most common line defect in CZ silicon single crystal. It will not only become a recombination center to reduce the minority carrier lifetime, but also gather metal impurities to cause additional leakage current, which will have an adverse effect on chip performance. The traditional method of detecting dislocation is to expose dislocation through chemical etching, and observe dislocation by optical microscope, infrared microscope, scanning or electron transmission microscope, X-ray morphology analysis and other methods. Commonly used chemical etching methods mainly include preferential etching method and non-preferential etching method. Preferential etching method achieves the purpose of revealing defects by different etching rates on different crystal planes and defects of crystalline silicon. At present, common preferential etching solutions include Stirl solution, Secco solution, Wright solution, SchimmelA solution, etc. These traditional etching solutions all contain heavy metal chromium ions, which not only produce a large amount of chromium-containing waste liquid, but also increase the treatment cost and are not friendly to the environment. In addition, traditional etching solutions cannot reveal all dislocation defects, there is a possibility of missed detection, and the defect detection effect is poor. Summary of the invention

[0003] In view of this, the present invention provides a method for detecting dislocation defects of heavily doped silicon single crystals to solve the technical problem that the traditional etching solution contains heavy metal chromium ions and cannot fully reveal the dislocation defects.

[0004] The technical solution adopted by the present invention to solve its technical problem is: A method for detecting dislocation defects in heavily doped silicon single crystals comprises the following steps: S1, cutting a silicon wafer from the heavily doped silicon single crystal to be tested as a sample; S2, placing the sample into an alkali solution for alkali washing; S3, placing the sample after alkali washing into a chromium-free etching solution for etching, wherein the chromium-free etching solution is composed of nitric acid, hydrofluoric acid and citric acid; S4. After the corrosion is completed, take out the sample and clean it; S5. Put the cleaned sample into a mixed acid solution for reaction to remove the surface layer, and observe the sample after the reaction is completed.

[0005] Preferably, in step S3, the chromium-free etching solution is composed of nitric acid with a mass concentration of 65%, hydrofluoric acid with a mass concentration of 49%, and citric acid, and is configured according to a certain mass percentage to satisfy Wt nitric acid%+Wt hydrofluoric acid%+Wt citric acid%=100%.

[0006] Preferably, the mass percentages of the component solutions are as follows: Wt% nitric acid: Wt% hydrofluoric acid: Wt% citric acid = 40% - 70%: 5% - 10%: 20% - 55%.

[0007] Preferably, in step S3, the alkali-washed sample wafer is placed in a chromium-free etching solution and shaken for etching for 10 - 20 minutes.

[0008] Preferably, in step S2, the component of the alkali solution is a sodium hydroxide solution with a mass concentration of 8%.

[0009] Preferably, in step S5, the mixed acid solution is composed of nitric acid with a mass concentration of 65% and hydrofluoric acid with a mass concentration of 49% in a certain volume ratio.

[0010] Preferably, the volume ratio of nitric acid to hydrofluoric acid in the mixed acid solution is 3 - 10:1.

[0011] Preferably, in step S5, the cleaned sample wafer is placed in the mixed acid solution for reaction for 1 - 3 minutes.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention first performs alkali washing on the sample wafer with an alkali solution to remove dirt and grease on the surface of the sample wafer, facilitating subsequent etching. Then, the sample wafer is placed in a chromium-free etching solution composed of nitric acid, hydrofluoric acid, and citric acid for etching. The sample wafer is etched by nitric acid and hydrofluoric acid, and then the reaction rate is adjusted by citric acid to increase the difference in etching rates between normal lattice positions and defect positions, thereby exposing dislocations. Finally, the sample wafer is placed in the mixed acid solution for reaction. After the reaction is completed, the sample wafer is observed under ordinary light to complete the detection of dislocation defects in heavily doped silicon single crystals. By using a chromium-free etching solution, the present invention avoids heavy metal ion contamination of the environment caused by commonly used chromium-based preferential etching solutions, significantly reduces the etching time while reducing costs, significantly improves the etching efficiency, and can effectively expose all dislocations in heavily doped silicon wafers, avoiding missed detections. Description of the Drawings

[0013] Figure 1 is a process flow chart of the method for detecting dislocation defects in heavily doped silicon single crystals of the present invention.

[0014] Figure 2 is a detection result diagram of Example 1.

[0015] Figure 3 is a detection result diagram of Comparative Example 1.

[0016] Figure 4 is a detection result diagram of Comparative Example 2. Detailed Embodiments

[0017] The technical solutions and technical effects of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings of the present invention.

[0018] Please see Figure 1 , a method for detecting dislocation defects in heavily doped silicon single crystals, comprising the following steps: S1, cutting a silicon wafer from the heavily doped silicon single crystal to be tested as a sample; S2, placing the sample into an alkali solution for alkali washing; S3, placing the sample after alkali washing into a chromium-free etching solution for etching, wherein the chromium-free etching solution is composed of nitric acid, hydrofluoric acid and citric acid; S4. After the corrosion is completed, take out the sample and clean it; S5. Put the cleaned sample into a mixed acid solution for reaction to remove the surface layer, and observe the sample after the reaction is completed.

[0019] The present invention firstly performs alkaline washing on the sample with alkaline solution to remove dirt and grease on the surface of the sample, so as to facilitate subsequent corrosion; then the sample is placed in a chromium-free etching solution composed of nitric acid, hydrofluoric acid and citric acid for corrosion, the sample is corroded by nitric acid and hydrofluoric acid, and then the reaction rate is adjusted by citric acid to increase the difference in corrosion rate between the normal lattice position and the defect position, thereby exposing the dislocation, and finally the sample is placed in a mixed acid solution for reaction, and after the reaction is completed, the sample is observed under ordinary light to complete the detection of dislocation defects of heavily doped silicon single crystals. The present invention avoids the heavy metal ion contamination of the environment by the commonly used chromium-based preferential etching solution by adopting a chromium-free etching solution, greatly shortens the corrosion time while reducing the cost, significantly improves the corrosion efficiency, and can effectively expose all the dislocations of the heavily doped silicon wafer to avoid missed detection.

[0020] In some embodiments, in step S1, a silicon wafer is cut from a heavily doped silicon single crystal to be tested as a sample. When there is a dislocation in the heavily doped silicon single crystal, a section of the sample is cut from any position of the heavily doped silicon single crystal, and the dislocation can be observed on its surface. Therefore, a silicon wafer can be cut from any position of the heavily doped silicon single crystal as a sample for observation. As an embodiment, a silicon wafer can be cut from the tail of the heavily doped silicon single crystal as a sample for observation. When cutting, a silicon wafer can be cut from the tail of the heavily doped silicon single crystal to be tested as a sample using a corundum wire saw, a corundum band saw or a cutter. The thickness of the cut sample is 1-3 mm.

[0021] Further, in step S3, the chromium-free etching solution is composed of nitric acid with a mass concentration of 65%, hydrofluoric acid with a mass concentration of 49%, and citric acid, and is configured according to certain mass percentages to satisfy Wt nitric acid%+Wt hydrofluoric acid%+Wt citric acid%=100%.

[0022] Traditional etching methods are applicable to heavily doped silicon single crystals. Since heavily doped silicon single crystals provide a high concentration of electrons for the redox reaction, the etching rate is relatively fast, reducing the difference in etching rates between normal lattice positions and defect positions, thus greatly weakening the preferential etching effect of traditional preferential etching solutions. In the chromium-free etching solution of the present invention, citric acid mainly plays a role in regulating the reaction rate, thereby effectively improving the oxidation reaction rate, increasing the difference in etching rates between normal lattice positions and defect positions, and exposing dislocations thereby.

[0023] Citric acid is an organic acid with stronger acidity than acetic acid and is an alternative acid to acetic acid. It can also be better miscible with nitric acid and hydrofluoric acid and can promote the reaction with silicon wafers in a mixed solution system. Citric acid forms soluble complexes with metal ions released during the etching process through carboxyl groups. In the defect area, due to lattice structure distortion, metal ions are more easily exposed and combined with citric acid, accelerating the dissolution of this area; while the structure of normal lattice positions is stable, less metal ions are released, and the etching rate is relatively slow. At the same time, as a weak acid, citric acid can maintain a low pH environment of the etching solution and promote proton transfer in the oxidation reaction. Defect sites have a higher surface charge density and stronger adsorption ability for H + , resulting in more significant local acidification, further accelerating the oxidation reaction rate and increasing the difference in etching rates between normal lattice positions and defect positions.

[0024] Furthermore, the mass percentages of each component solution are: Wt nitric acid%: Wt hydrofluoric acid%: Wt citric acid% = 40% - 70%: 5% - 10%: 20% - 55%. Among them, nitric acid undergoes a redox reaction with the sample wafer, and hydrofluoric acid reacts with the oxide layer and oxidation products on the surface of the sample wafer to remove the oxide layer on the surface of the sample wafer. Citric acid mainly plays a role in regulating the reaction rate, effectively improving the oxidation reaction rate, increasing the difference in etching rates between normal lattice positions and defect positions, and effectively exposing all the dislocation defects of the sample wafer.

[0025] Furthermore, in step S3, the alkali-washed sample wafer is placed in the chromium-free etching solution and shaken for etching for 10 - 20 minutes. By shaking for etching, the reaction rate can be accelerated, and because citric acid in the etching solution acts as a buffer for regulation, the etching effect will not be affected. And the traditional detection method requires 30 - 45 minutes of etching with Schimmel A solution and requires pickling and polishing the sample wafer in advance. The chromium-free etching solution used in this method can not only pickle and polish the sample wafer, but also selectively etch dislocation defects, so that the defects can be exposed due to the difference in reaction rates while directly removing the oxide layer. The etching time is only 10 - 20 minutes. Compared with traditional preferential etching solutions, the etching time is significantly shortened and the etching efficiency is significantly improved.

[0026] Further, in step S2, the lye component is a sodium hydroxide solution with a mass concentration of 8%. Specifically, the sample wafer can be put into a sodium hydroxide solution with a mass concentration of 8% for alkali washing. During the alkali washing process, the silicon wafer can be first immersed in the sodium hydroxide solution, and ultrasonic or stirring can be used to assist in removing residual metal ions and minute particle contaminants. Then, the sodium hydroxide solution is heated to accelerate the saponification decomposition of the grease, thereby removing the dirt and grease on the surface of the silicon wafer, making the sample wafer flat and the surface clean, meeting the subsequent detection conditions. Further, in step S5, the mixed acid solution is composed of nitric acid with a mass concentration of 65% and hydrofluoric acid with a mass concentration of 49% in a certain volume ratio. After the sample wafer is corroded by the chromium-free etching solution to expose the dislocations of the sample wafer, the sample wafer is taken out, washed in pure water to remove the acid solution on the surface, and then put into the mixed acid solution. The nitric acid reacts with the sample wafer through an oxidation-reduction reaction, and then the hydrofluoric acid reacts with the oxide layer and oxidation products on the surface of the sample wafer to further remove the oxide layer on the surface of the sample wafer, polish the sample wafer, and make the dislocation defects of the sample wafer more obvious.

[0027] Further, the volume ratio of nitric acid to hydrofluoric acid in the mixed acid solution is 3 - 10:1.

[0028] Further, in step S5, the washed sample wafer is put into the mixed acid solution and reacted for 1 - 3 minutes. The washed sample wafer is put into the mixed acid solution for reaction, taken out after removing the surface layer, washed clean in pure water to remove the mixed acid solution adhering to the surface of the sample wafer, and after the washing is completed, the water stains on the surface of the sample wafer are dried to start the detection. Since the detection method of the present invention can effectively expose the dislocation defects of the silicon single crystal, the dislocations on the silicon wafer can be clearly observed under natural light, the operation method is simple, the defect detection rate is high, and the detection efficiency is high.

[0029] The detection method for dislocation defects of heavily doped silicon single crystals of the present invention is applicable to ultra-heavily doped silicon single crystals with a resistivity lower than 0.01 Ω·cm.

[0030] The following is a specific experimental example to further illustrate the technical solution and technical effect of the present invention. It should be noted that the following experimental examples are only for further explaining the present invention and do not limit the technical solution of the present invention.

[0031] Three 12-inch red phosphorus 100 sample wafers are intercepted from the same heavily doped phosphorus silicon single crystal, and are respectively marked as No. 1, No. 2, and No. 3. The No. 1 sample wafer is detected by the method of this patent, the No. 2 sample wafer is detected by the traditional method, and the No. 3 sample wafer is detected by XRT for comparison. Example 1

[0032] First, put the No. 1 sample piece into a sodium hydroxide solution with a mass concentration of 8% for alkaline cleaning. Then, put the No. 1 sample piece into the pre-prepared chromium-free etching solution. The chromium-free etching solution is composed of nitric acid with a mass concentration of 65%, hydrofluoric acid with a mass concentration of 49%, and citric acid, and is prepared according to a certain mass percentage. The mass percentages of each component solution are: Wt nitric acid%: Wt hydrofluoric acid%: Wt citric acid% = 40% - 70%: 5% - 10%: 20% - 55%. During etching, first put the sample piece into the chromium-free etching solution and shake it for etching for 10 - 20 minutes. Then take out the No. 1 sample piece, wash the acid solution on the surface in pure water, and then put it into the mixed acid solution. The mixed acid solution is composed of nitric acid with a mass concentration of 65% and hydrofluoric acid with a mass concentration of 49% in a certain volume ratio, satisfying VHNO 3 : VHF = 3 - 10:1. After reacting in the mixed acid solution for 1 - 3 minutes to remove the surface layer, take it out, wash it clean in pure water, dry the water droplets on the surface, and then observe the No. 1 sample piece under ordinary light. The test results are as Figure 2 shown.

[0033] Comparative Example 1 First, put the No. 2 sample piece into a sodium hydroxide solution with a mass concentration of 8% for alkaline cleaning. Then, put the No. 2 sample piece into a mixed solution with a volume ratio of nitric acid (70%): hydrofluoric acid (49%): acetic acid (99%): water = (1 - 2): (3 - 4): (2 - 4): (5 - 6) to make the silicon wafer react with the mixed acid solution to remove the surface oxide layer. Immediately afterwards, put the pickled and cleaned sample piece into the prepared preferential etching solution, take it out after fully contacting for 30 - 40 minutes, and rinse off the remaining chemical solution with overflowing deionized water. The used preferential etching solution is Schimmel A solution, and this Schimmel A solution is composed of an HF solution with a mass concentration of 49% and CrO 3 solution. Finally, rinse the etched silicon wafer clean with deionized water and spin-dry it, and observe the No. 2 sample piece under ordinary light. The test results are as Figure 3 shown.

[0034] Comparative Example 2 To verify the accuracy of this method, perform XRT detection on the No. 3 sample piece. The XRT equipment selects the Rigaku XRTmicron detector. The test results are as Figure 4 shown.

[0035] Comparison Figure 2 and Figure 3 of the test results, among which, Figure 2 the part enclosed by the red frame in is the dislocation defect of the No. 1 sample piece, while Figure 3 no dislocation defect is observed in. Thus, it can be seen that by using the detection method of the present invention, compared with the traditional detection method, the defect recognition degree can be higher, and the dislocation defects of the silicon wafer can be effectively revealed. At the same time, comparisonFigure 2 and Figure 4 From the detection results, it can be found that Figure 2 and Figure 4 have relatively high consistency in detection results, and from the perspective of observation effect, the recognition rate of this method is higher. Therefore, the detection method of the present invention is more sensitive in recognizing dislocations than traditional methods and XRT. At the same time, the dislocations on the silicon wafer can be clearly observed under ordinary light in the present invention. Compared with the XRT detection method, it does not require complex detection instruments, has lower costs, a simple operation method, and high detection efficiency.

[0036] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A method for detecting dislocation defects in heavily doped silicon single crystals, characterized in that: The following steps are involved: S1, cutting a silicon wafer from the heavily doped silicon single crystal to be tested as a sample; S2, placing the sample into an alkaline solution for alkaline washing; S3, placing the sample after alkali washing into a chromium-free etching solution for etching, wherein the chromium-free etching solution is composed of nitric acid, hydrofluoric acid and citric acid; S4. After the corrosion is completed, take out the sample and clean it; S5. Put the cleaned sample into a mixed acid solution for reaction to remove the surface layer, and observe the sample after the reaction is completed.

2. The method for detecting dislocation defects in heavily doped silicon single crystals according to claim 1, characterized in that: In step S3, the chromium-free etching solution is composed of nitric acid with a mass concentration of 65%, hydrofluoric acid with a mass concentration of 49%, and citric acid, and is configured according to certain mass percentages to satisfy Wt nitric acid%+Wt hydrofluoric acid%+Wt citric acid%=100%.

3. The method for detecting dislocation defects of heavily doped silicon single crystals according to claim 2, characterized in that: The mass percentage of each component solution is: Wt nitric acid%: Wt hydrofluoric acid%: Wt citric acid%=40%-70%: 5%-10%: 20%-55%.

4. The method for detecting dislocation defects in heavily doped silicon single crystals according to claim 3, characterized in that: In step S3, the alkali-washed sample is placed in a chromium-free etching solution and shaken for etching for 10-20 minutes.

5. The method for detecting dislocation defects of heavily doped silicon single crystal according to claim 1, characterized in that: In step S2, the alkali solution is composed of a sodium hydroxide solution with a mass concentration of 8%.

6. The method for detecting dislocation defects of heavily doped silicon single crystals according to any one of claims 1 to 5, characterized in that: In step S5, the mixed acid solution is composed of nitric acid with a mass concentration of 65% and hydrofluoric acid with a mass concentration of 49% in a certain volume ratio.

7. The method for detecting dislocation defects in heavily doped silicon single crystals according to claim 6, characterized in that: The volume ratio of nitric acid to hydrofluoric acid in the mixed acid solution is 3-10:

1.

8. The method for detecting dislocation defects in heavily doped silicon single crystals according to claim 7, characterized in that: In step S5, the cleaned sample is placed in a mixed acid solution to react for 1-3 minutes.

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