JP4357456B2 - Semiconductor substrate cleaning method - Google Patents

Description

  The present invention relates to a semiconductor substrate cleaning method, and more particularly to a technique for suppressing a watermark.

  In the process of manufacturing semiconductor devices, wet cleaning is widely used to remove contaminants and foreign matters such as particles, metals, organic substances, and surface films (natural oxide films, adsorbed molecules) on the wafer.

  Wet etching (cleaning) devices used for wet cleaning include spray wafer cleaning devices, single wafer etching devices (types that use etchant in circulation or disposable specifications), batch etching devices (circulation baths) Type or one-bus type). The spray-type wafer cleaning device sprays cleaning chemicals from the spray nozzle in the device container toward the wafer while rotating the cassette in which the wafer is inserted. There is a revolution type that rotates a set of turntables. In a single-wafer etching apparatus, an etching solution (cleaning chemical) is supplied from a nozzle onto a wafer held horizontally and cleaned by etching. In the batch type etching apparatus, the cassette in which the wafer is inserted is sequentially fed into a plurality of cleaning tanks filled with an etching solution, immersed therein, and cleaned by etching.

  In recent years, in semiconductor integrated circuit devices such as VLSI, miniaturization, high density, high speed, low power consumption, and the like have been promoted. The size of pollutants and stains is getting smaller. In the VLSI process, a cleaning method combining a plurality of chemical solutions is used to remove various contaminants and spots (for example, Patent Document 1).

A general cleaning sequence for a silicon wafer is shown in FIG. In step S11, cleaning is performed with dilute hydrofluoric acid mainly for the purpose of removing the natural oxide film on the wafer surface, rinsing with pure water is performed in step S12, and in step S13, cleaning is performed with sulfuric acid hydrogen peroxide water mainly for the purpose of removing organic substances. In step S14, pure water is rinsed. In step S15, cleaning with ammonia hydrogen peroxide water is performed mainly for the purpose of removing particles. After pure water is rinsed in step S16, a finishing drying process is performed in step S17.
JP 2001-44429 A

However, when a wafer is cleaned by the cleaning sequence shown in FIG. 5, the wafer outermost surface becomes hydrophobic due to cleaning with dilute hydrofluoric acid (hereinafter referred to as hydrogen fluoride), and the watermark is very high. There was a problem that it was likely to occur. In general, as a watermark generation mechanism, oxygen in the atmosphere dissolves in water droplets adhering to the Si surface of the silicon substrate, diffuses to the interface between the Si surface and water droplets, and an oxidation reaction occurs on the Si surface, thereby Through a series of steps in which the produced Si oxide (SiO ₂ ) is hydrated to form silicic acid (H ₂ SiO ₃ ), the concentration of Si oxide in the water droplets increases, It is said that it will remain as a watermark.

  In addition, if cleaning with sulfuric acid hydrogen peroxide solution is performed with moisture remaining on the wafer, heat is generated due to the mixing of water and sulfuric acid hydrogen peroxide solution, and the water temperature on the wafer is at or near the boiling point. To rise. This is based on the nature of sulfuric acid, that is, the dehydration effect in which sulfuric acid takes away hydrogen and oxygen from the partner in the proportion of water molecules. According to the knowledge of the present inventors, if a particle source is present when such dehydration and temperature rise are occurring, the particles are in an aggregated state, and as a result, a watermark is likely to occur.

  In other words, in order to generate the watermark, the outermost surface of the wafer after cleaning with hydrogen fluoride is in a hydrophobic state, and cleaning with sulfuric acid is performed with moisture remaining on the wafer. Implementation seems to be involved.

  In view of the above problems, an object of the present invention is to provide a semiconductor substrate cleaning method capable of suppressing watermarks even when cleaning with sulfuric acid is performed after cleaning with hydrogen fluoride.

In order to solve the above-mentioned problems, the present invention removes the oxide film on the surface of the silicon layer by cleaning the silicon layer of the semiconductor substrate with a chemical solution containing hydrogen fluoride when cleaning the semiconductor substrate. a second step of forming a first step of exposing the surface of the silicon layer, the surface of the exposed silicon layer was treated with a chemical solution is an aqueous solution containing an oxidizing agent, a chemical oxide film by the chemical oxide film Performing a third step of removing moisture remaining on the surface of the silicon layer on which is formed and drying, and a fourth step of cleaning the surface of the dried silicon layer with a chemical solution containing sulfuric acid. It is characterized by.
In each of the first step, the second step, and the fourth step, after the treatment with the chemical solution corresponding to the respective step, the chemical solution corresponding to the respective step existing on the silicon layer is purified water. It is characterized by replacing with .
The first to fourth steps are continuously performed in a single sealed processing tank. The first to fourth steps are performed without exposing the surface of the semiconductor substrate to the atmosphere.
The removal and drying of moisture remaining on the surface of the silicon layer in the third step is performed by rotating the semiconductor substrate. The chemical oxide film has a thickness of 0.5 nm to 0.9 nm.
The chemical solution containing hydrogen fluoride is an aqueous solution of hydrogen fluoride, and the concentration of the hydrogen fluoride in the chemical solution containing hydrogen fluoride is 0.1 wt% or more. The chemical solution containing hydrogen fluoride is dilute hydrofluoric acid, the chemical solution containing the oxidizing agent is hydrogen peroxide solution, and the chemical solution containing sulfuric acid is sulfuric acid hydrogen peroxide solution .

The method for cleaning a semiconductor substrate according to the present invention includes a step of forming a chemical oxide film between cleaning with hydrogen fluoride and cleaning with sulfuric acid, and moisture remaining on the substrate surface on which the chemical oxide film is formed. In addition, the generation of watermarks due to the hydrogen fluoride cleaning and sulfuric acid cleaning can be suppressed, and the reliability and yield of a semiconductor device using this semiconductor substrate can be improved. be able to.
When rinsing and drying treatment are performed after the hydrogen fluoride treatment to complete the treatment once and then the sulfuric acid treatment is carried out, the generation of watermark is not particularly problematic, but the sulfuric acid is continuously added after the hydrogen fluoride treatment. In the case of processing, the method of the present invention is useful. In general, in order to improve throughput and reduce cleaning costs, it is desirable to apply a plurality of chemical solutions in several steps in a single run. It becomes possible to do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view showing a schematic configuration of a wafer cleaning apparatus used in the present invention.
This wafer cleaning apparatus is called a spray-type wafer cleaning apparatus, and a bottomed cylindrical wafer holder 2 capable of holding a plurality of wafers W is placed in a sealed processing tank 1 from below by a rotating shaft 3. A spray nozzle 4 that is supported and arranged to be rotatable around the axis of the rotary shaft 3 and that can discharge a fluid 4a such as a chemical solution in the wafer holder 2 is arranged coaxially with the rotary shaft 3. The wafer W in the wafer holder 2 revolves around the spray nozzle 4, and the spray nozzle 4 ejects a fluid 4 a such as a chemical solution toward the wafer W.

  Specifically, a cassette holder 6 in which a support plate 5 that supports the wafer W in the horizontal direction is provided in a plurality of stages in the vertical direction is attached to and detached from the wafer holder 2. The spray nozzle 4 extends from the top of the container 1 to the vicinity of the bottom of the wafer holder 2, and a plurality of discharge holes 7 are arranged along the circumferential direction and along the axial direction. A fluid 4 a such as a chemical solution is uniformly sprayed on the wafer W supported by the support plate 5.

A wafer cleaning method in the wafer cleaning apparatus will be described.
A cassette holder 6 on which a plurality of wafers W are set is mounted on the wafer holder 2, and the wafer holder 2 is rotated around the axis of the rotary shaft 3, whereby the plurality of wafers W are simultaneously revolved around the spray nozzle 4.

  In this state, the chemical liquid is sprayed from the discharge holes 7 of the spray nozzle 4 and sprayed onto each of the plurality of wafers W to remove contaminants and foreign matters on the wafer W by reaction with the chemical liquid, and then spray pure water. Then, the chemical solution remaining on the wafer W is replaced with pure water. This washing step is performed for each predetermined chemical solution. When the cleaning is completed, the wafer W is rotated to remove the remaining moisture.

  The wafer cleaning / drying process described above is performed continuously. Thereby, the surface of the wafer W is exposed to the atmosphere, that is, the contact between the substance serving as a particle source in the atmosphere and the wafer can be avoided, and the cleanliness of the wafer surface can be further increased.

  The wafer cleaning sequence will be described with reference to FIG. 2 and with reference to FIG. FIG. 2 is a flowchart of the cleaning sequence, and FIG. 3 is a cross-sectional view of the wafer to be cleaned. This wafer cleaning / drying process is generally performed as a pre-cleaning of the film forming process.

  In step S1 shown in FIG. 2, the wafer is cleaned with dilute hydrofluoric acid for the main purpose of removing the oxide film on the wafer surface. As shown in FIG. 3A, the wafer before cleaning has a natural oxide film 12 grown on the surface of the silicon substrate 11. However, the oxide film 12 is removed by cleaning with dilute hydrofluoric acid, and FIG. ), The surface of the silicon substrate 11 is exposed. The concentration of hydrogen fluoride in dilute hydrofluoric acid at this time may be a concentration that removes the oxide film 12 and makes the wafer surface hydrophobic, and is, for example, 0.1 wt% or more. With the surface of the silicon substrate 11 exposed, pure water rinsing is performed in step S2 to replace dilute hydrofluoric acid on the wafer.

  In step S3, the wafer after rinsing with pure water is washed with hydrogen peroxide. As a result, a chemical oxide film 13 is formed on the surface of the silicon substrate 11 as shown in FIG. The chemical oxide film 13 at this time may be any thickness that is stably and uniformly formed on the surface of the substrate and functions as a protective film. For example, a thickness of about 0.5 nm to 0.9 nm is appropriate. In this state, in step S4, pure water rinsing is performed to replace the hydrogen peroxide solution on the wafer.

  In step S5, a spin dry process is performed to remove moisture on the wafer surface. In this spin dry process, for example, the silicon substrate 11 is rotated at a rotation speed of 500 rpm and a rotation time of 600 sec while introducing an inert gas (nitrogen) at a flow rate of 200 L / min into the sealed processing tank 1. Remove water by centrifugal force. The device structure may be explosion-proof and isopropyl alcohol or the like may be introduced instead of nitrogen.

  Here, the state of the wafer surface in steps S1 to S5 will be described. The surface layer (the surface of the silicon substrate 11) of the wafer cleaned with dilute hydrofluoric acid in step S1 is hydrophobic with hydrogen dangling bonds of silicon atoms terminated, and the remaining moisture becomes water droplets. The water mark is likely to be attached. However, since the chemical oxide film 13 is formed in step S3 and OH groups are present on the outermost surface thereof, the wafer surface is hydrophilic, and the remaining moisture is in a state of spreading uniformly, and in step S5. It is removed by the spin dry process.

  Thereafter, in step S6, the dried wafer is washed with a sulfuric acid hydrogen peroxide solution adjusted to about 140 ° C. to 160 ° C. mainly for the purpose of removing organic substances, and subsequently in step S7, the sulfuric acid hydrogen peroxide solution is replaced. Therefore, a pure water rinse is carried out.

  At this time, since the rinse water on the wafer surface after the cleaning with the hydrogen peroxide solution is removed as described above, heat generation due to the mixing of the sulfuric acid hydrogen peroxide solution does not occur as in the conventional case, and this is caused. Generation of watermarks to be performed can be suppressed. In addition, the outermost surface layer (chemical oxide film) of the wafer after cleaning with hydrogen peroxide solution has OH groups and is hydrophilic as described above. Water rinsing is unlikely to cause a watermark.

  After that, in step S8, the wafer is washed with ammonia hydrogen peroxide solution mainly for particle removal. In step S9, pure water rinsing is performed to replace the ammonia hydrogen peroxide solution, and finally, in step S10. Then, finish the drying process. Also at this time, since the outermost surface layer of the wafer is a chemical oxide film, a watermark is hardly generated.

  As described above, according to the present invention, it is possible to suppress the watermark by adding hydrogen peroxide water cleaning and spin drying to a cleaning method that sequentially uses hydrogen fluoride and sulfuric acid. It was.

  Considering these series of steps at the molecular level of the outermost surface of the wafer, when the outermost surface of the silicon wafer is an oxide film (insulating film), the state shown in FIG. 4A is obtained, and the oxide film is removed by dilute hydrofluoric acid. 4B, it is presumed that the dangling bonds are terminated by hydrogen H as shown in FIG.

  In addition, although it demonstrated as what uses dilute hydrofluoric acid (aqueous solution of hydrogen fluoride) by step S1, if it is a chemical | medical solution which makes the wafer surface tinge hydrophobicity, that is, if it is a chemical | medical solution containing the hydrogen fluoride component, it is. It can be used. Examples of such a chemical solution include buffered hydrofluoric acid (BHF) and the like, for example, one containing ammonium fluoride or the like in hydrofluoric acid.

  The semiconductor substrate cleaning method of the present invention is effective in suppressing watermarks when wet cleaning is performed for the purpose of removing contaminants and the like on the substrate, and semiconductors such as ultra LSIs in which minute spots also become fatal defects. This is useful for manufacturing integrated circuit devices.

Sectional drawing which shows schematic structure of the conventional wafer cleaning apparatus used by this invention Flowchart of wafer cleaning sequence in one embodiment of the present invention Cross section of wafer in wafer cleaning sequence of FIG. Cross-sectional view at the molecular level of the wafer in the wafer cleaning sequence of FIG. Conventional wafer cleaning sequence flowchart

Explanation of symbols

W Wafer 1 Processing tank 2 Wafer holder 3 Rotating shaft 4 Spray nozzle
4a Fluid such as chemicals
11 Silicon substrate
12 Natural oxide film
13 Chemical oxide film

Claims (8)

Silicon Sojo semiconductor substrate is washed with a chemical solution containing hydrogen fluoride, a first step of exposing the surface of the silicon layer by removing the oxide film on the surface of the silicon layer, silicon layer the exposed The surface of the second layer is treated with a chemical solution that is an aqueous solution containing an oxidizing agent to form a chemical oxide film, and moisture remaining on the surface of the silicon layer on which the chemical oxide film is formed is removed and dried. A method for cleaning a semiconductor substrate, comprising performing a third step of cleaning and a fourth step of cleaning the surface of the dried silicon layer with a chemical solution containing sulfuric acid. In each of the first step, the second step and the fourth step, after the treatment with the chemical solution corresponding to the respective step, the chemical solution corresponding to the respective step existing on the silicon layer is purified water. The method for cleaning a semiconductor substrate according to claim 1 , wherein: Wherein the fourth step from the first, a method for cleaning a semiconductor substrate according to claim 1 or 2, characterized in continuously be carried out in the processing bath was a single sealed. Wherein the first to fourth step, a semiconductor substrate cleaning method according to claim 3, the surface of the semiconductor substrate is characterized by being performed without Rukoto exposed to the atmosphere. Wherein in the third step, drying and removal of water remaining on the surface of the silicon layer, a semiconductor substrate cleaning method according to claim 1 or 2, characterized in that by rotating the semiconductor substrate. Chemical solution containing the hydrogen fluoride is an aqueous solution of hydrogen fluoride, to claim 1, wherein the concentration of the hydrogen fluoride in the chemical solution which contains the hydrogen fluoride is not less than 0.1 wt% A method for cleaning a semiconductor substrate as described. 2. The method of cleaning a semiconductor substrate according to claim 1 , wherein the thickness of the chemical oxide film is 0.5 nm to 0.9 nm. Billing chemical solution containing the hydrogen fluoride is hydrofluoric acid, the chemical liquid including the oxidizing agent is hydrogen peroxide, a chemical solution containing the sulfuric acid, which is a sulfuric acid hydrogen peroxide Item 8. A method for cleaning a semiconductor substrate according to any one of Items 1 to 7 .

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