A method for eliminating surface metal interference in silicon wafer bulk metal measurement

Abstract

The present invention provides a method for eliminating surface metal interference in bulk metal measurement of a silicon wafer, comprising: (1) preparing a silicon wafer to be measured and preparing a metal sampling liquid; (2) removing an oxide film on the surface of the silicon wafer to be measured using a gas phase decomposition system; (3) treating the surface of the silicon wafer with a portion of the metal sampling liquid to obtain a recovery liquid 1, collecting and measuring the recovery liquid 1, and calculating a metal concentration C1; (4) heating the silicon wafer, and then naturally cooling the silicon wafer to room temperature; (5) treating the cooled silicon wafer surface with a portion of the metal sampling liquid to obtain a recovery liquid 2, collecting and measuring the recovery liquid 2, and calculating a metal concentration C2; (6) the bulk metal concentration of the silicon wafer is C2, and the sum of the surface metal and film metal concentrations is C1. The present invention removes the surface metal and film metal of the silicon wafer before the bulk metal is heated and diffuses to the silicon wafer surface, thereby eliminating the interference C1 in bulk metal measurement.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon wafer detection, and in particular relates to a method for eliminating surface metal interference in silicon wafer body metal measurement. Background Art

[0002] Silicon wafers are a critical raw material for the integrated circuit industry. Increased bulk metal content can degrade minority carrier lifetimes and create crystal defects, severely impacting chip quality. Silicon wafers are highly susceptible to metal contamination during the manufacturing process. For example, during the etching process, contact with a corrosive solution containing metallic impurities can significantly increase the surface metal content. High-temperature etching processes, where the bulk metal concentration is low and the surface metal concentration is high, can lead to surface metal atoms diffusing into the lower-concentration bulk at high temperatures, causing an increase in bulk metal content. Therefore, monitoring bulk metal content in silicon wafers is crucial. Compared to surface metal content, bulk metal testing is difficult and inefficient. Inaccurate measurement results can lead to unnecessary scrap or rework. For example, Chinese patent application CN109904089A discloses a method for testing bulk metal in a silicon wafer. The method involves baking a silicon wafer at a constant temperature in a constant temperature furnace, where metal atoms diffuse from the silicon wafer's bulk to its surface in a high-temperature environment. However, this process ignores the impact of the silicon wafer's surface metal and film metal on bulk metal testing. If the silicon wafer's surface metal concentration is much higher than the bulk metal concentration, the surface metal will diffuse into the silicon wafer's bulk during measurement. In addition, the lower the bulk metal content, the greater the interference of the surface metal and film metal on the bulk metal measurement. Therefore, how to provide a method to eliminate interference from other metals in bulk metal measurement and accurately measure the bulk metal content of silicon wafers has become a technical problem that urgently needs to be solved. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the present invention aims to provide a method for eliminating surface metal interference in silicon wafer metal measurement to solve the technical problems in the related art.

[0004] To achieve the above object, the present invention provides a method for eliminating surface metal interference in silicon wafer body metal measurement, comprising:

[0005] (1) preparing a silicon wafer to be tested and preparing a metal sampling solution, wherein the metal sampling solution comprises: 2.5 wt % hydrofluoric acid, 4.5 wt % hydrogen peroxide and ultrapure water;

[0006] (2) using a gas phase decomposition system to remove the oxide film on the surface of the silicon wafer to be tested;

[0007] (3) using a metal sampling solution to treat the silicon wafer surface to obtain a recovery solution 1, collecting and measuring the recovery solution 1, and calculating the metal concentration C1;

[0008] (4) Heating the silicon wafer and then cooling it naturally to room temperature;

[0009] (5) Using a portion of the metal sampling liquid to treat the cooled silicon wafer surface to obtain a recovery liquid 2, collecting and measuring the recovery liquid 2, and calculating the metal concentration C2;

[0010] (6) The bulk metal concentration of the silicon wafer is C2, and the sum of the surface metal and film metal concentrations is C1;

[0011] The present invention utilizes a vapor phase decomposition system and a metal sample preparation device to remove the oxide film from the silicon wafer surface before the bulk metal diffuses onto the wafer surface. The metal sample preparation device then recovers and removes the surface metal and film metal from the wafer surface. During the subsequent thermal diffusion of the bulk metal onto the wafer surface, both the surface metal and film metal have been removed, resulting in a bulk metal concentration analysis result that is solely contributed by the diffused bulk metal.

[0012] The beneficial effects of the present invention are, firstly, that only conventional semiconductor sample preparation devices and testing equipment are used without increasing any equipment costs; secondly, while eliminating surface metal interference, the specific value of the interference can also be obtained. The present invention effectively solves the problem in the prior art that the metal measurement results of silicon wafers are higher than the true value and the measurement is inaccurate.

[0013] In an embodiment of the present invention, in step (1), the specific steps of preparing the metal sampling solution include:

[0014] (1-1) Using a clean PFA measuring cup, measure a certain volume of 38%wt hydrofluoric acid, 35wt% hydrogen peroxide, and ultrapure water according to the volume ratio.

[0015] (1-2) Mix 38% wt hydrofluoric acid, 35 wt% hydrogen peroxide, and ultrapure water in a clean PFA sample bottle and shake gently to mix the components evenly to obtain a metal sampling solution with a volume ratio of 2.5 wt% hydrofluoric acid and 4.5 wt% hydrogen peroxide.

[0016] In an embodiment of the present invention, the specific proportions according to volume ratio are as follows: the blended metal sampling solution includes: 2.5wt% hydrofluoric acid, 4.5wt% hydrogen peroxide and 93% ultrapure water.

[0017] In the embodiment of the present invention, the volume of the metal sampling solution prepared each time is 100-500 mL.

[0018] In an embodiment of the present invention, the metal specification of the 38%wt hydrofluoric acid and 35wt% hydrogen peroxide should be less than 0.1ppb; the ultrapure water specifications are: resistance greater than 18MΩ.cm, TOC less than 5ppb.

[0019] In an embodiment of the present invention, in step (2), the specific steps of removing the oxide film on the surface of the silicon wafer to be tested by using a gas phase decomposition system include:

[0020] (2-1) Place the silicon wafer to be tested horizontally in a gas phase decomposition system.

[0021] (2-2) The gas phase decomposition system sprays a decomposition liquid, which reacts with the oxide film on the surface of the silicon wafer and decomposes the oxide film.

[0022] In an embodiment of the present invention, in step (2-2), the decomposition liquid is 38 wt % hydrofluoric acid.

[0023] In an embodiment of the present invention, in step (2-2), the gas-phase decomposition system sprays the decomposition liquid, specifically by impinging the decomposition liquid within a bubbler with ultrapure nitrogen at a fixed flow rate, thereby generating an atomized decomposition liquid with the ultrapure nitrogen as a carrier gas. The bubbler includes a liquid storage unit, an air inlet unit, and an air outlet unit. The liquid storage unit is used to store the decomposition liquid, the air inlet unit is used to control the flow rate of the ultrapure nitrogen, and the air outlet unit is connected to the gas-phase decomposition system.

[0024] In an embodiment of the present invention, the ultrapure nitrogen gas impacts the decomposition liquid in the bubbler at a fixed flow rate, with specific parameters being an ultrapure nitrogen flow rate of 15 L / min and a nitrogen duration of 1 min.

[0025] In an embodiment of the present invention, in step (3), the recovered liquid is collected and measured, and the collection is performed by a metal sample preparation device, and the measurement is performed by an electric rod coupled plasma mass spectrometer.

[0026] In an embodiment of the present invention, in step (4), the specific steps of heating the silicon wafer and then cooling the silicon wafer to room temperature include:

[0027] (4-1) Use a vacuum pen to place the silicon wafer to be tested horizontally on the heating plate.

[0028] (4-2) Set the heating plate to 400°C and heat for 1 hour.

[0029] (4-3) Heating will stop automatically after 1 hour and the device will cool naturally to room temperature after 3 hours.

[0030] In an embodiment of the present invention, in step (4-1), the heating plate is a constant temperature heating plate with a surface made of ceramic glass.

[0031] In an embodiment of the present invention, the bulk metal concentration of the silicon wafer is C2, and the sum of the surface metal concentration and the film metal concentration is C1. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a flow chart of a method for eliminating surface metal interference in silicon wafer bulk metal measurement. DETAILED DESCRIPTION

[0033] As described in the background art, how to accurately test the metal content in silicon wafers is very important for silicon wafer quality control. The silicon wafers in the present invention are bare wafers that have not undergone integrated circuit processing. To facilitate understanding of the present invention, the present invention will be described in more detail below with reference to relevant drawings.

[0034] Example 1

[0035] Step (1): Prepare the silicon wafer to be tested and prepare the metal sampling solution.

[0036] In the field of silicon wafer manufacturing, the final cleaning process is the last step before the silicon wafers are packaged and shipped. Therefore, it is necessary to monitor the metal content of the final cleaned products to determine whether the metal content of the products meets the shipping standards. After the silicon wafer comes into contact with air, it will react with the oxygen in the air to form a natural oxide film. Some metals are easily present in the silicon-silicon oxide medium. Representative metals of this type are Cu and Ni. Therefore, the present invention uses a gas phase decomposition system to remove the oxide film on the surface of the silicon wafer, and uses a metal sample preparation device to recover and remove the surface metal and film metal on the surface of the silicon wafer. In particular, for silicon wafers that have been stored for a long time and have an oxide film on the surface, the present invention eliminates the interference of the surface metal while also eliminating the interference of the film metal.

[0037] In an embodiment, the specific steps of preparing the metal sampling solution include: using a clean PFA measuring cup, measuring a certain volume of 38%wt hydrofluoric acid, 35wt% hydrogen peroxide and ultrapure water according to the volume ratio, mixing the measured 38%wt hydrofluoric acid, 35wt% hydrogen peroxide and ultrapure water in a clean PFA sample bottle, shaking slightly to mix the components evenly, and obtaining a metal sampling solution with a volume ratio of 2.5wt% hydrofluoric acid and 4.5wt% hydrogen peroxide.

[0038] Step (2): using a gas phase decomposition system to remove the oxide film on the surface of the silicon wafer to be tested.

[0039] The silicon wafer to be tested is placed horizontally in a gas phase decomposition system, which sprays a decomposition liquid. The decomposition liquid reacts with the oxide film on the surface of the silicon wafer and decomposes the oxide film.

[0040] In the embodiment, ultrapure nitrogen gas is injected into the decomposition liquid within the bubbler at a flow rate of 15 L / min, generating an atomized decomposition liquid with ultrapure nitrogen as the carrier gas. The atomized decomposition liquid enters the gas-phase decomposition system through a pipeline connected to the system and is evenly sprayed onto the surface of the silicon wafer, where it reacts with and removes the oxide film.

[0041] In the embodiment, the gas generated by the reaction of silicon oxide with the atomized decomposition liquid, ultrapure nitrogen, and unreacted hydrofluoric acid gas flow out from the exhaust system below the gas phase decomposition system to ensure the stability of the system pressure.

[0042] In the embodiment, after the oxide film of the original silicon wafer is removed, a new silicon wafer surface is exposed. It can be understood that the metal atoms on the surface of the original silicon wafer and the metal atoms of the film layer fall onto the surface of the new silicon wafer under the action of gravity.

[0043] Step (3): using a portion of the metal sampling solution to treat the surface of the silicon wafer to obtain a recovered solution 1, collecting and measuring the recovered solution 1, and calculating the metal concentration C1.

[0044] The recovered liquid is collected and measured, wherein the collection is performed by a metal sample preparation device, and the measurement is performed by an electric rod coupled plasma mass spectrometer.

[0045] In the embodiment, the specific steps of collecting the recovery liquid by the metal sampling device include: ① placing the wafer box containing the silicon wafer to be tested horizontally on the sample table; ② the robot arm takes the wafer from the wafer box and transfers it to the rotating adsorption table, and the rotating adsorption table adsorbs the silicon wafer through vacuum; ③ the robot arm controls the pipette to absorb 1mL of metal sampling liquid, and controls the sampling liquid to move on the surface of the silicon wafer. When the sampling liquid passes through the surface of the silicon wafer, the metal on the surface of the silicon wafer dissolves in the sampling liquid to form a recovery liquid containing metal; ④ the robot arm controls the pipette to collect the recovery liquid and inject it into the sample bottle.

[0046] In an embodiment, the specific steps of measuring the recovery liquid by inductively coupled plasma mass spectrometry include:

[0047] The sample bottle containing the recovery liquid 1 is placed on the sample tray of the pole-coupled plasma mass spectrometer; the sampling tube of the pole-coupled plasma mass spectrometer is inserted into the sample bottle; the metal concentration in the recovery liquid is obtained by analysis, and the metal concentration on the silicon wafer surface is obtained by unit conversion.

[0048] In the embodiment, it can be understood that the method for recovering and measuring the metal on the surface of the heated silicon wafer is consistent with the above method.

[0049] Step (4): Heat the silicon wafer and then cool it down to room temperature.

[0050] In an embodiment, a vacuum suction pen is used to take the silicon wafer out of the wafer box and placed on the center of a heating plate. The heating plate is a constant temperature heating plate with a surface made of ceramic glass.

[0051] In the embodiment, the temperature of the heating plate is set at 400° C., and the silicon wafer is heated at a constant temperature for 1 hour.

[0052] In the embodiment, the heating is automatically stopped after 1 hour, and the silicon wafer is allowed to cool naturally to room temperature for 3 hours.

[0053] In the embodiment, after cooling for 3 hours, the silicon wafer is transferred from the hot plate to a wafer cassette using a vacuum pen.

[0054] This method can be used for single crystal silicon wafers with a diameter not limited to 8 inches.

[0055] The above detailed description is a specific description of the present invention. According to the above description, combined with the technology in the field, the solution of the present invention can be implemented. The scope of protection of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for eliminating surface metal interference in silicon wafer bulk metal measurement, characterized in that: The method comprises the following steps: (1) preparing a silicon wafer to be tested and preparing a metal sampling solution, the metal sampling solution comprising: 2.5wt% hydrofluoric acid, 4.5wt% hydrogen peroxide and ultrapure water; (2) using a gas phase decomposition system to remove the oxide film on the surface of the silicon wafer to be tested; (3) using a metal sampling solution to treat the silicon wafer surface to obtain a recovery solution 1, collecting and measuring the recovery solution 1, and calculating the metal concentration C1; (4) Heating the silicon wafer and then cooling it naturally to room temperature; (5) treating the cooled silicon wafer surface with a portion of the metal sampling solution to obtain a recovered solution 2, collecting and measuring the recovered solution 2, and calculating the metal concentration C2; (6) The bulk metal concentration of the silicon wafer is C2, and the sum of the surface metal and film metal concentrations is C1.

2. The method according to claim 1, characterized in that The types of silicon wafers to be tested are single crystal polished wafers and single crystal non-polished wafers.

3. The method according to claim 1, characterized in that The volume of a sample is 1-2 mL.

4. The method according to claim 1, wherein In step (2), the specific method of removing the oxide film on the surface of the silicon wafer to be tested by using the gas phase decomposition system includes placing the silicon wafer to be tested horizontally in the gas phase decomposition system, spraying a decomposition liquid from the gas phase decomposition system, and the decomposition liquid reacts with the oxide film on the surface of the silicon wafer to decompose the oxide film.

5. The method according to claim 4, characterized in that The decomposition liquid is 38wt% hydrofluoric acid.

6. The method according to claim 4, characterized in that The specific method of spraying the decomposition liquid in the gas phase decomposition system includes: ultrapure nitrogen gas impacting the decomposition liquid in the bubbler at a fixed flow rate to generate atomized decomposition liquid with ultrapure nitrogen gas as carrier gas.

7. The method according to claim 6, characterized in that The bubbler includes a liquid storage unit, an air inlet unit, and an air outlet unit. The liquid storage unit is used to store decomposition liquid, the air inlet unit is used to control the flow rate of ultrapure nitrogen, and the air outlet unit is connected to a gas phase decomposition system.

8. The method according to claim 6, characterized in that The ultrapure nitrogen gas impacts the decomposition liquid in the bubbler at a fixed flow rate, the ultrapure nitrogen flow rate is 15 L / min, and the nitrogen time is 1 min.

9. The method according to claim 1, characterized in that In step (3), the recovered liquid is collected and measured, the collection is performed by a metal sample preparation device, and the measurement is performed by an inductively coupled plasma mass spectrometer.

10. The method according to any one of claims 1 to 9, characterized in that Hydrofluoric acid specifications: 38wt%, metal concentration less than 0.1ppb; hydrogen peroxide specifications: 35wt%, metal concentration less than 0.1ppb; ultrapure water specifications: resistance value greater than 18MΩ·cm, TOC less than 5ppb.

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