Method for testing iron metal content of lightly-doped borosilicate polished wafer body

Abstract

The invention discloses a method for testing the iron metal content of a lightly boron-doped silicon polished wafer, which comprises the following steps: (1) after finishing straight pulling of a lightly boron-doped crystal bar, tumbling and cutting off, and slicing along the crystal orientation (100) through a steel wire; (2) chamfering after slicing to form an R-shaped or T-shaped edge chamfer contour; (3) grinding after chamfering, and carrying out corrosion treatment on the surface after grinding; (4) polishing the slices; (5) cleaning the silicon wafer after polishing treatment; (6) feeding the cleaned silicon polished wafer into an epitaxial furnace for annealing treatment; and (7) testing the iron metal content of the 12-inch silicon polished wafer body. According to the method, the distribution of oxygen donors in the silicon wafer is changed through annealing treatment, so that the originally gathered oxygen donors are diffused, the interference of local high-concentration oxygen donors on the bulk iron metal test is reduced, and the content of the bulk iron metal of the silicon wafer is accurately obtained. The method is simple in technological process and obvious in effect, and has a good application prospect in the field of semiconductors.

Description

Technical Field

[0001] The present invention relates to a method for testing the content of metallic iron in lightly doped boron-silicon polished wafers, belonging to the technical field of semiconductor manufacturing. Background Art

[0002] The rapid development of single-crystal silicon materials plays an indispensable role in the microelectronics industry, especially in integrated circuits and semiconductor devices. Metal contamination is an unavoidable problem in the manufacturing process of integrated circuits. Transition metal impurities such as Fe, due to their large diffusion coefficients and precipitation properties in silicon, will diffuse into the active regions of devices during heat treatment processes, thereby harming the performance and yield of devices, damaging electrical properties, and even causing integrated circuits to fail. Therefore, the control of metal elements is very strict, and the detection of metal ions in silicon wafers has become an important topic.

[0003] For boron-doped P-type silicon wafers, positively charged interstitial Fe atoms and negatively charged B atoms at substitutional positions will exist in the form of iron-boron pairs (FeB pairs). Laser irradiation of the silicon wafer at different wavelengths will decompose the FeB pairs in the silicon wafer, generating iron ions, and the iron ions will combine with the minority carriers (electrons) in the silicon wafer. Based on this principle, the currently commonly used method for testing the bulk iron concentration of silicon wafers is the surface photovoltage method (SPV). After HF etching the surface of the silicon wafer, by measuring the diffusion lengths of minority carriers in the silicon wafer before and after light irradiation, the number of FeB pairs in the silicon wafer can be calculated, and then the content of iron elements per unit volume in the silicon wafer can be deduced. However, during the processing of 12-inch silicon polished wafers from the ingot to the formation of the final surface-clean silicon wafers, there are various influencing factors such as single-crystal defects, stress caused by deformation, the surface state of the silicon wafer, the thickness of the surface oxide layer, and oxygen donors. Among them, the presence of oxygen donors will affect the diffusion of iron atoms in silicon. On the one hand, oxygen donors interact with other defects in the silicon wafer to form diffusion channels or traps, making it easier for iron atoms to be captured or change the diffusion path during the diffusion process; on the other hand, the diffusion behavior of oxygen donors themselves may also drive the migration of iron atoms, resulting in changes in the distribution of iron in the silicon wafer, and thus affecting the final bulk iron test results of the silicon wafer, making it impossible to obtain a clear bulk iron metal content, which is not conducive to the monitoring and improvement of the production process. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a method for testing the content of metallic iron in lightly doped boron-silicon polished wafers. This method eliminates the influence of oxygen donors in silicon by performing high-temperature annealing on boron-doped P-type silicon wafers, accurately characterizes the content of Fe metal elements in the silicon wafer, provides reliable experimental data for analyzing process data, and is conducive to optimizing process parameters.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A test method for the content of interstitial iron in lightly doped boron-silicon polished wafers, comprising the following steps: (1) After the lightly doped boron crystal bar is grown by Czochralski method, it is ground and cut off, and sliced along the (100) crystal orientation; (2) After slicing, chamfering is carried out to form an R-type or T-type edge chamfer profile; (3) After chamfering, grinding is carried out, and the surface is etched after grinding; (4) The sliced wafers are polished to obtain silicon polished wafers with good flatness; (5) After polishing, the silicon polished wafers are cleaned to make the metal on the surface of the polished wafers reach 2E8 atoms / cm 2 level; (6) The cleaned silicon polished wafers are sent into an epitaxial furnace for annealing treatment; the furnace atmosphere is H 2 , the flow rate of H 2 is 70-90 slm, the furnace inlet temperature is 200 °C, after heating to 650 °C, it is kept warm for 30 min; after the heat preservation is over, it is cooled to room temperature to complete annealing; (7) The SPV method is used to test the content of interstitial iron in the silicon polished wafers.

[0006] In the method of the present invention, the thickness of the silicon polished wafers is 765-785 μm, and the diameter is 300 ± 0.2 mm. As a preferred technical solution of the present invention, the thickness of the polished wafers is 775 μm, and the diameter is 300 mm.

[0007] In the method of the present invention, the etching treatment of the sliced wafers includes acid etching or alkali etching. As a preferred technical solution of the present invention, acid etching is carried out using a mixed solution of hydrochloric acid / hydrofluoric acid, etc., and alkali etching is carried out using a mixed solution of ammonia water / potassium hydroxide, etc. to remove the damaged layer formed after grinding.

[0008] In the method of the present invention, the sliced wafers are polished. As a preferred technical solution of the present invention, the polishing treatment undergoes three polishing steps of double-sided polishing-edge polishing-final fine polishing, and each time after polishing, cleaning is carried out to obtain silicon wafers with good flatness.

[0009] In the method of the present invention, the cleaning of the polished silicon wafers is the final cleaning. As a preferred technical solution of the present invention, a single-wafer cleaning machine is used to adopt an O 3 + HF or SC1 (No. 1 solution) + SC2 (No. 2 solution) + O 3 + HF cleaning process to make the metal on the surface of the polished wafers reach 2E8 atoms / cm 2 level, and obtain polished wafers with a clean surface.

[0010] In the method of the present invention, the epitaxial furnace model is Naura Hesper E230A or ASM Epsilon 3200. After the heat preservation is completed, the temperature is decreased to room temperature at a rate of 1-2 °C / min, and the cooling atmosphere is N 2 ; after the cooling is completed, the manipulator picks up the silicon polished wafer and puts it back into the wafer cassette, and then the annealing is completed. As a preferred technical solution of the present invention, the model of the epitaxial furnace is Naura Hesper E230A, and the H 2 flow rate is 80 slm. After the heat preservation is completed, the temperature is decreased to room temperature at a cooling rate of 1.5 °C / min, and the cooling atmosphere is N 2 .

[0011] Beneficial effects of the present invention: The present invention is particularly suitable for the bulk iron test of 12-inch boron-doped P-type silicon polished wafers. By performing high-temperature annealing treatment on the boron-doped P-type silicon wafers, the distribution of oxygen donors in the silicon wafers is changed, so that the originally aggregated oxygen donors are diffused, and the interference of local high-concentration oxygen donors on the bulk iron metal test is reduced, thereby accurately characterizing the content of Fe metal elements in the silicon wafer body, providing reliable experimental data for analyzing process data, and being beneficial to optimizing process parameters.

[0012] Compared with the prior art, the present invention can eliminate the influence of oxygen donors in silicon, clearly obtain the content of bulk iron metal in 12-inch boron-doped P-type silicon polished wafers, and can effectively solve the problems of special Map or missing measurement data in the bulk iron test of silicon wafers, which is beneficial to the monitoring and improvement of the production process of silicon polished wafers. Description of the drawings

[0013] Figs. 1-3 are examples of Map diagrams of the bulk iron metal content of 12-inch lightly boron-doped silicon polished wafers of different ingots under the method of the embodiment of the present invention.

[0014] Figures 4 to 6 Figs. are examples of Map diagrams of the bulk iron metal content of 12-inch lightly boron-doped silicon polished wafers of different ingots obtained without annealing treatment in the comparative example. Detailed implementation manners

[0015] In order to more clearly understand the above objects, features and advantages of the present invention, the technical solutions of the invention will be further specifically described below through embodiments. Embodiment

[0016] The method for testing the bulk iron metal content of 12-inch boron-doped P-type silicon polished wafers in the embodiment includes the following steps: (1) After the lightly boron-doped B ingot is pulled and completed, it is ground and truncated, and sliced along the (100) crystal orientation by a steel wire; (2) After slicing, a primary chamfering is performed to form an R-type or T-type edge chamfering profile; (3) After chamfering, grinding is carried out, and after grinding, its surface is subjected to etching treatment; (4) The sliced wafers are polished. The silicon wafers are polished through double-sided polishing-edge polishing-final fine polishing. After each polishing, cleaning is carried out to obtain silicon wafers with a polished wafer thickness of 775 μm, a diameter of 300 mm, and good surface flatness; (5) After polishing treatment, the silicon wafers are cleaned. The final cleaning of the silicon wafers is carried out by using the cleaning process of single-wafer cleaning machine O 3 +HF, so that the surface metal of the polished wafer reaches 2E8 atoms / cm 2 level, and a polished wafer with a clean surface is obtained; (6) The cleaned silicon wafers are sent into a Naura Hesper E230A epitaxial furnace for annealing. The furnace inlet atmosphere is H 2 , H 2 The flow rate is 80 slm. The silicon wafers enter the epitaxial furnace. The furnace inlet temperature is 200 °C. After heating up to 650 °C, it is kept warm for 30 min. After the heat preservation is completed, it is cooled to room temperature at a cooling rate of 1.5 °C / min. The cooling atmosphere is N 2 . After the cooling is completed, the manipulator picks up the silicon wafers and puts them back into the cassette, and the annealing is completed; (7) After the annealing is completed, the silicon wafers are moved into a cassette containing hydrofluoric acid for corrosion pretreatment for 60 min. After the pretreatment is completed, they are moved into a test cassette and left standing for 60 min. After standing, through a WT2500 bulk metal detector, the SPV mode is selected in the shortcut to WINTAU32 software, and the 12inch_8mm_SPV_Fe_EE2 program is selected to test the bulk iron metal content.

[0017] Figures 1 to 3 are examples of Map diagrams of the bulk iron metal content of 12-inch lightly doped boron silicon polished wafers of different crystal bars under the method of the embodiment of the present invention. The average values of the bulk iron metal content shown in the figures are listed in Table 1. From Figures 1 to 3 It can be clearly seen that the iron metal in the polished wafer is relatively evenly distributed at the edge position of the polished wafer, and the iron metal distribution at the center position is relatively less.

[0018] Table 1 Figures 1 to 3 The average value of the bulk iron metal content shown in Comparative example The method for testing the bulk iron metal content of a 12-inch boron-doped P-type silicon polished wafer in the comparative example includes the following steps: (1) After the lightly doped B crystal bar is pulled and ground and truncated, it is sliced along the (100) crystal direction by a steel wire; (2) After slicing, a primary chamfering is carried out to form an R-type or T-type edge chamfering profile; (3) After chamfering, grinding is carried out, and after grinding, its surface is subjected to etching treatment; (4) The sliced wafer is polished. The silicon wafer undergoes double-sided polishing-edge polishing-final fine polishing, and is cleaned after each polishing. The obtained polished wafer has a thickness of 775 μm and a diameter of 300 mm; (5) After polishing treatment, the silicon wafer is cleaned. The final cleaning of the silicon wafer is carried out by using the cleaning process of single-wafer cleaning machine O 3 +HF to make the metal on the surface of the polished wafer reach 2E8 atoms / cm 2 level; (6) After cleaning is completed, the silicon wafer is transferred into a cassette containing hydrofluoric acid for corrosion pretreatment for 60 minutes. After the pretreatment is completed, it is transferred into a test cassette and left standing for 60 minutes. After standing is completed, through the WT2500 bulk metal detector, select the SPV mode in the shortcut to WINTAU32 software, and select the 12inch_8mm_SPV_Fe_EE2 program to test the bulk iron metal content.

[0019] Figures 4 to 6 Figure 14 is an example of a Map of the bulk iron metal content of 12-inch lightly doped boron-silicon polished wafers obtained from different crystal rods without annealing treatment in the comparative example. The average values of the bulk iron metal content shown in the figure are listed in Table 2. Figure 4 The center position of the Map is significantly missing and cannot reflect the true level of iron metal in the silicon polished wafer; Figure 5 The Map shows that iron metal is concentrated in the center position of the silicon wafer, which is inconsistent with the common sense that iron metal diffuses from the outside to the inside during the single crystal pulling process; Figure 6 The Map is a blank Map and also cannot reflect the true level of iron metal in the silicon polished wafer.

[0020] Table 2 Figures 4 to 6 The average values of the bulk iron metal content shown in By using the present invention to test the bulk iron of lightly doped boron-silicon polished wafers, it has strong practicability, can accurately obtain the content of bulk iron metal in the silicon polished wafer, has a simple process flow, obvious effects, can effectively solve the problems of special Map or missing measurement data in the bulk iron test of silicon wafers, is beneficial to the monitoring and improvement of the production process of silicon polished wafers, and has good application prospects in the semiconductor field.

Claims

1. A method for testing the iron content of lightly boron-doped silicon polishing sheets, characterized in that: The following steps are involved: (1) After the lightly boron-doped crystal rod is pulled, it is cut by rolling and then sliced ​​along the (100) crystal direction; (2) Chamfering after slicing to form an R-shaped or T-shaped edge chamfer profile; (3) Grinding after chamfering, and etching the surface after grinding; (4) Polishing the slices to obtain silicon polished slices with good flatness; (5) After polishing, the silicon polishing wafer is cleaned to make the metal content on the surface of the polishing wafer reach 2E8 atoms / cm 2 level; (6) Send the cleaned silicon polished wafer into the epitaxial furnace for annealing treatment; the furnace atmosphere is H2, the H2 flow rate is 70-90slm, the furnace temperature is 200°C, and after the temperature reaches 650°C, it is kept warm for 30 minutes; after the insulation is completed, the temperature is cooled to room temperature to complete the annealing; (7) The SPV method is used to test the iron content of silicon polished wafers.

2. The method for testing the iron content of lightly boron-doped silicon polishing slice according to claim 1, characterized in that: The thickness of the bulk iron test piece is 765-785 μm and the diameter is 300 ± 0.2 mm.

3. The method for testing the iron content of lightly boron-doped silicon polishing slice according to claim 1, characterized in that: In step (3), the corrosion treatment includes acid corrosion or alkaline corrosion.

4. The method for testing the iron content of lightly boron-doped silicon polishing slices according to claim 3, characterized in that: Acid corrosion uses a mixed solution of hydrochloric acid and hydrofluoric acid for corrosion, and alkaline corrosion uses a mixed solution of ammonia water and potassium hydroxide for corrosion.

5. The method for testing the iron content of lightly boron-doped silicon polishing slice according to claim 1, characterized in that: In step (4), the polishing process includes double-sided polishing, edge polishing, and final fine polishing, and cleaning is performed after each polishing.

6. The method for testing the iron content of lightly boron-doped silicon polishing slices according to claim 1, characterized in that: In step (5), the cleaning process includes using a single-chip cleaning machine to adopt a cleaning process of O3+HF or SC1+SC2+O3+HF.

7. The method for testing the iron content of lightly boron-doped silicon polishing slices according to claim 1, characterized in that: In step (6), the epitaxial furnace model is Naura Hesper E230A or ASM Epsilon 3200. After the insulation is completed, the temperature is cooled to room temperature at a cooling rate of 1-2°C / min, and the cooling atmosphere is N2.

Images