JP2010008048A - Method of etching silicon wafer surface oxide film, metal contamination analysis method of silicon wafer with oxide film, and method of manufacturing silicon wafer with oxide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for analyzing easily with high sensitivity, metal contamination of a silicon wafer surface. <P>SOLUTION: In a method, while being cooled, a silicon wafer 3 with an oxide film is brought into contact with hydrogen fluoride gas, and hereby condensation (not including a silicon oxide component) is generated on a wafer surface, to thereby etch an oxide film on the silicon wafer surface. In a metal contamination analysis method of the silicon wafer with the oxide film, the oxide film on the silicon wafer surface is etched and removed by the method, and scanning is performed with a solution along the silicon wafer surface after removal of the oxide film, and then a metal component in the solution is analyzed. In a method of manufacturing the silicon wafer, the metal contamination analysis method is used. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an etching method suitable for metal contamination analysis of a silicon wafer with an oxide film, and a metal contamination analysis method for a silicon wafer with an oxide film using the etching method. Furthermore, this invention relates to the manufacturing method of the silicon wafer with an oxide film which can provide a high quality silicon wafer with an oxide film by determining a non-defective product using the said analysis method.

The metal contamination of the silicon wafer surface layer is caused by the slurry supplied to the silicon wafer at the time of wafer polishing, the SC-1 (NH ₄ OH / H ₂ O ₂ / H ₂ O) cleaning liquid and SC-2 for cleaning the polished silicon wafer. (HCl / H ₂ O ₂ / H ₂ O) Occurs due to metal components contained in the cleaning solution or the like. However, in the semiconductor manufacturing field, with high integration and device miniaturization, reduction of metal impurities existing on the surface of the silicon wafer and on the surface layer, which significantly deteriorates the device performance, has become an important issue. Therefore, in order to improve the quality control and manufacturing process of silicon wafers, it is desirable to establish an analysis method that can analyze metal impurities on the surface layer of silicon wafers with high accuracy and high sensitivity using a simplified chemical analysis method. Yes.

As a method of analyzing metal impurities contained in the surface layer of a silicon wafer, the silicon wafer surface layer is etched (decomposed) and then the metal components on the silicon wafer surface are recovered. The recovered metal components are analyzed by an atomic absorption spectrophotometer (Atomic Absorption Spectrophotometer). Spectrophotometers (AAS), inductively coupled plasma mass spectrometers (ICP-MS) and the like are widely used. As an etching method, for example, as described in Patent Documents 1 to 3, a method using steam generated from a hydrofluoric acid solution is known.
JP-A-6-213805 JP-A-8-330271 JP 2005-265718 A

As in the methods described in Patent Documents 1 to 3, in the etching method using the vapor generated from the hydrofluoric acid solution, the following reaction for decomposing the oxide film (SiO ₂ ) proceeds on the wafer surface.
SiO ₂ + 6HF → H ₂ SiF ₆ + 2H ₂ O (1)
H ₂ SiF ₆ → SiF ₄ ↑ + 2HF (2)

  However, in the methods described in Patent Documents 1 to 3, the solution for generating the etching vapor includes a component that oxidizes silicon such as nitric acid, hydrogen peroxide solution, and ozone water together with hydrofluoric acid. Along with the reaction, the oxidation reaction of Si proceeds. Therefore, in these methods, a large amount of Si component is contained in the decomposition residue. However, if a large amount of Si component is contained in the recovered solution from which the decomposition residue has been recovered, if the recovered solution is directly applied to an atomic absorption spectrophotometer, the background becomes high during analysis or the peak shape of the sample becomes abnormal. . In addition, in the inductively coupled plasma mass spectrometer, an abnormal peak is detected as an interference molecule peak during analysis. Generally, in such a case, for the purpose of sublimating and removing silicon, a solution obtained by recovering the decomposition residue is dissolved in a liquid mixture such as aqua regia or sulfuric acid and concentrated. However, since this method uses a large amount of chemicals, there is a risk of introducing metal impurities contained in the chemicals and contamination of metal impurities from the atmosphere or jigs due to long-time concentration.

  Accordingly, an object of the present invention is to provide a means for analyzing metal contamination on the surface of a silicon wafer simply and with high sensitivity.

  In the methods described in Patent Documents 1 to 3, the solution that generates etching vapor contains a component that oxidizes silicon together with hydrofluoric acid (silicon oxidation component) because hydrogen fluoride gas decomposes the oxide film. Although it is possible to etch silicon, Patent Documents 1 to 3 are intended to decompose and analyze the surface layer of the silicon wafer together with the oxide film. However, in recent years, there is an increasing need for analyzing metal impurities in an oxide film of a silicon wafer on which a relatively thick oxide film is formed. Examples of the relatively thick oxide film include a back oxide film of an Epi wafer and a BOX film and a back oxide film of a bonded SOI wafer. The back oxide film of the Epi wafer is formed on the back surface of the Epi wafer in order to prevent the resistance value of the Epi layer from changing due to diffusion of B · P in the wafer from the back surface during heat treatment and diffusion to the surface. The BOX film and the back surface oxide film of the SOI wafer may form a thick oxide film depending on the specifications required by the user. Under such circumstances, the present inventor does not need to use a silicon oxide component if analyzing metal impurities in the oxide film on the surface of the silicon wafer. By not using the silicon oxide component, the inventor can remove the silicon component in the decomposition residue. Under the knowledge that it can be reduced, the present invention has been completed through extensive studies.

That is, the above object was achieved by the following means.
[1] A method of etching an oxide film on the surface of a silicon wafer by generating condensation that does not include a silicon oxide component on the wafer surface by contacting the silicon wafer with an oxide film while cooling it with a hydrogen fluoride gas.
[2] The etching method according to [1], including generating the hydrogen fluoride gas by bubbling a hydrofluoric acid-containing solution with a carrier gas.
[3] The etching method according to [2], wherein the hydrofluoric acid-containing solution further contains sulfuric acid.
[4] performing the etching in a container having at least one vent;
The etching method according to any one of [1] to [3], further comprising exhausting air through the vent during the etching.
[5] The method according to any one of [1] to [4], wherein the oxide film thickness removed by etching is 10 to 5000 mm.
[6] The oxide film on the surface of the silicon wafer is removed by etching by the method according to any one of [1] to [5], and the solution is scanned on the surface of the silicon wafer after the oxide film is removed. A method for analyzing metal contamination of a silicon wafer with an oxide film, comprising analyzing a metal component.
[7] preparing a wafer lot including a plurality of silicon wafers with oxide films;
Extracting at least one silicon wafer from the lot;
Analyzing the metal contamination in the oxide film of the extracted silicon wafer;
A method for producing a silicon wafer with an oxide film, including shipping as a product wafer another silicon wafer in the same lot as the silicon wafer determined to be non-defective by the analysis,
The method according to claim 6, wherein the analysis of metal contamination in the oxide film of the extracted silicon wafer is performed by the method according to [6].

  According to the present invention, even when an oxide film on the surface of a silicon wafer is relatively thick, metal impurities can be analyzed with high sensitivity and high accuracy without performing concentration.

The present invention relates to a method for etching an oxide film on a silicon wafer surface (hereinafter also referred to as “etching method”). The etching method of the present invention etches an oxide film on the surface of a silicon wafer by causing condensation on the wafer surface by bringing it into contact with hydrogen fluoride gas while cooling the silicon wafer with the oxide film. Here, the dew condensation generated on the wafer surface in the etching method of the present invention does not include a silicon oxide component for the reason described above. The silicon oxide component refers to a component that generates SiO ₂ by reacting with Si, and examples thereof include hydrogen peroxide, ozone, and nitric acid.
Hereinafter, the etching method of the present invention will be described in more detail.

The etching target in the etching method of the present invention is an oxide film (SiO ₂ ) on the silicon wafer surface. The oxide film may be an unintentionally formed oxide film such as a natural oxide film, or may be an oxide film formed through an oxide film forming process such as a thermal oxidation process. Since the etching method of the present invention can etch a relatively thick oxide film in a short time, the latter is preferable as the oxide film.

  The thickness of the oxide film is not limited, but is preferably 10 mm or more for the above reasons. Considering the etching time, it is preferably 5000 mm or less. A preferable range of the thickness of the oxide film is 10 to 3000 mm, and a more preferable range is 10 to 1000 mm.

In the etching method of the present invention, the silicon wafer with an oxide film is brought into contact with hydrogen fluoride gas while being cooled. As a result, condensation occurs on the wafer surface (oxide film surface). Since this condensation includes hydrogen fluoride (HF) capable of decomposing SiO _{2 according} to the above reaction formulas (1) and (2), the oxide film can be decomposed. An example of an apparatus capable of causing a contact reaction between hydrogen fluoride gas and the silicon wafer surface is shown in FIG. Hereinafter, although demonstrated based on FIG. 1, the etching method of this invention is not limited to the aspect shown in FIG.

  As shown in FIG. 1, the reaction vessel in which the silicon wafer surface is brought into contact with hydrogen fluoride gas is preferably a closed vessel as shown in FIG. Here, the closed container is not limited to a container in which the entire gas container is completely sealed as long as the supplied gas can be retained in the container for a certain period of time. As shown in FIG. Those having a mouth and an exhaust port are also included.

  The supply of hydrogen fluoride gas onto the wafer surface can be performed, for example, by introducing hydrogen fluoride gas into the container from the gas supply port of the reaction container as shown in FIG. The hydrogen fluoride gas can be generated by bubbling a hydrofluoric acid-containing solution with a carrier gas. Bubbling is preferable because a constant amount of gas can be always supplied. As the carrier gas, an inert gas such as nitrogen gas is suitable. As the hydrofluoric acid-containing solution, a solution containing no silicon oxide component is used in order to generate condensation on the wafer surface that does not contain a silicon oxide component.

The hydrofluoric acid-containing solution is preferably a hydrofluoric acid aqueous solution, and more preferably an aqueous solution containing sulfuric acid together with hydrogen fluoride. The etching rate can be increased by using a hydrofluoric acid aqueous solution containing sulfuric acid. This is because the dehydration action of sulfuric acid (the following reaction formula (3)) can prevent the supply of moisture into the chamber and increase the supply of HF gas into the chamber.
H ₂ SO ₄ + 4H ₂ O → H ₂ SO ₄ .4 (H ₂ O) (3)
In particular, when a thick oxide film is etched, it is preferable to use a hydrofluoric acid aqueous solution containing sulfuric acid because the etching time can be shortened.

  The concentration of hydrogen fluoride in the hydrofluoric acid solution is preferably 5% by mass or more from the viewpoint of stably generating hydrogen fluoride by bubbling, and 50% by mass or less from the viewpoint of operability. preferable. When sulfuric acid is contained, the sulfuric acid concentration is preferably 5% by mass or more from the viewpoint of effectively suppressing the supply of moisture in the chamber by dehydration, and preferably 50% by mass or less from the viewpoint of operability. . The amount of carrier gas to be bubbled may be set as appropriate.

  As a method for cooling the silicon wafer, a method of disposing a cooling device below the wafer held horizontally with the oxide film as the upper surface can be used. The temperature of the cooled semiconductor wafer is preferably 0 to 20 ° C. If the temperature is within the above range, condensation can be stably generated.

It is preferable to evacuate the reaction vessel while performing the etching according to the above-described reaction formulas (1) and (2) due to the above-mentioned condensation generation. Exhaust is preferably performed, for example, through a vent provided in a closed container as shown in FIG. Thereby, the etching gas can be supplied and the SiF ₄ produced by the reaction formula (2) can be exhausted. In particular, when the oxide film is thick and the etching amount is large, if a large amount of SiF ₄ is present in the chamber, the reaction is in an equilibrium state and a large amount of H ₂ SiF ₆ remains on the wafer, and the Si component (H in the decomposition residue (H ₂ SiF ₆ ) increases. In order to analyze the metal component with high accuracy and high sensitivity by AAS or ICP-MS without removing the thick oxide film, it is preferable to exhaust as described above. Exhaust can also be performed using an exhaust pump. The displacement is, for example, about 50 to 200 hPa, but is not particularly limited. There may be at least one vent hole, and from the viewpoint of ventilation efficiency, the vent hole is preferably provided on the side wall facing the side wall having the gas supply port.

  Part or all of the oxide film on the silicon wafer can be removed by the etching method described above. The etching time may be set in accordance with the oxide film thickness to be removed by etching, the supply gas flow rate, etc., and can be set to about 0.2 to 180 minutes, for example. Since the metal component contained in the etched oxide film remains on the surface of the etched silicon wafer, the metal component on the surface is collected and analyzed to analyze the metal contamination of the etched oxide film. can do. Details of the analysis method are as described later for the metal contamination analysis method of the present invention.

  Furthermore, the present invention relates to a method for analyzing metal contamination of a silicon wafer with an oxide film. The analysis method of the present invention removes the oxide film on the surface of the silicon wafer by the etching method of the present invention, scans the surface of the silicon wafer after the removal of the oxide film, and then analyzes the metal component in the solution.

  As a solution to be scanned on the surface of the silicon wafer after etching, for example, pure water, a mixed solution of hydrofluoric acid and hydrogen peroxide, a mixed solution of hydrogen peroxide and hydrochloric acid, or the like can be used. JP, 2005-265718, A, etc. can be referred for the solution which can be used.

Furthermore, in the analysis method of the present invention, it is preferable to use a mixed solution of hydrofluoric acid, hydrogen peroxide solution and hydrochloric acid as the metal component recovery solution in order to increase the recovery rate of the metal component. When this solution is brought into contact with the surface of the silicon wafer from which the oxide film has been removed, for example, the following reaction occurs on the surface where Ag is present as a metal component.
HCl → H ⁺ + Cl ⁻ (4)
Ag → Ag ⁺ + e ⁻ (5)
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O (6)
In addition, the following reaction occurs simultaneously with the above reaction.
Si + 2H ₂ O ₂ → SiO ₂ + 2H ₂ O (7)
SiO ₂ + 6HF → H ₂ SiF ₆ + 2H ₂ O (8)
That is, when the silicon wafer surface is dissolved by the above mixed solution, the dissolution reaction (4 · 5 · 6) and the etching reaction (7 · 8) occur at the same time, so that Ag, Cu and other elements on the silicon wafer surface can be removed. It can be recovered at a high recovery rate.

  The mixed solution preferably contains 0.01 to 10.0% by mass of hydrogen fluoride, 0.01 to 20.0% by mass of hydrogen peroxide, and 0.01 to 10.0% by mass of hydrogen chloride. When the content of hydrogen fluoride, hydrogen peroxide, and hydrogen chloride is within the above ranges, the reactions of the above-described reaction formulas (4) to (8) can be favorably progressed. The amount of solution supplied and scanned on the wafer surface is preferably about 50 to 250 μl.

  As a method for causing the solution to scan on the surface of the silicon wafer, for example, a method in which the wafer is tilted and rotated so that the solution dropped on the surface of the wafer can be applied to the entire surface can be used. This method may be performed manually or automatically. Examples of the automatic method include a method in which a wafer is placed on a rotary table and the solution is dropped and then rotated. As shown in FIG. 2, as shown in FIG. 2, droplets are held by a nozzle on the surface of a horizontally arranged silicon wafer, and the nozzle is rotated from the center to the outer periphery or while rotating the silicon wafer in the circumferential direction. A method of moving in the radial direction is preferable. According to this method, the droplet can be reliably scanned over the entire surface of the wafer, and the metal component on the wafer surface can be recovered at a high recovery rate. The wafer rotation speed and the nozzle movement speed may be appropriately set. For example, the rotation speed is preferably 5 to 100 mm / min, and the nozzle movement speed is preferably about 1 to 10 mm / rotation. In particular, the above-mentioned mixed solution of hydrofluoric acid, hydrogen peroxide solution and hydrochloric acid can take the metal component into the droplets with a high recovery rate even if the contact time with the wafer is short, so This is advantageous in that the metal component can be reliably recovered even when the scanning speed is relatively high as in the case of the rotational speed and the nozzle moving speed.

  Next, by analyzing the metal component in the solution scanned on the surface of the silicon wafer, qualitative analysis and quantitative analysis of the metal component contained in the oxide film on the wafer can be performed. Since the metal component contained in the oxide film removed by etching remains on the surface of the etched silicon wafer, the metal component on the surface is collected and analyzed, so that the metal contamination of the etched oxide film is detected. Can be analyzed.

  The analysis of the metal component can be performed by a known method capable of analyzing the metal component in the solution. Such methods can include atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS). AAS and ICP-MS are preferable because trace metal components can be analyzed with high sensitivity. According to the present invention, when analyzing metal contamination in a relatively thick oxide film, it is possible to perform highly sensitive and highly accurate analysis without concentrating the recovered solution. Examples of metals that can be analyzed include various metals such as Ag, Cu, Li, Na, Mg, Al, K, Ca, Cr, Fe, Ni, and Zn.

  Furthermore, the present invention provides a process for preparing a wafer lot including a plurality of silicon wafers with oxide films, a process for extracting at least one silicon wafer from the lot, and a process for analyzing metal contamination of the extracted silicon wafer; The present invention relates to a method for manufacturing a silicon wafer with an oxide film, including shipping another silicon wafer in the same lot as a silicon wafer determined to be non-defective by the analysis. In the production method of the present invention, the extracted silicon wafer is analyzed by the analysis method of the present invention. According to the analysis method of the present invention, it is possible to evaluate the presence / absence and / or degree of metal contamination in an oxide film, specify the contamination metal species, and determine the contamination metal. Therefore, by shipping a silicon wafer in the same lot as a silicon wafer determined to be a non-defective product by this analysis method, it becomes possible to provide a high-quality product wafer with high reliability. In addition, the reference | standard which determines with a good product can be set in consideration of the physical property calculated | required by the wafer according to the use etc. of a wafer. The number of wafers contained in one lot and the number of wafers to be extracted may be set as appropriate.

  Hereinafter, the present invention will be described with reference to examples. However, this invention is not limited to the aspect shown in the Example.

Example 1 Etching of Oxide Film on Silicon Wafer The lid 2 of the apparatus shown in FIG. 1 is opened, and a silicon wafer 3 having an oxide film of about 100 mm contaminated with 11th power of Ag by spin coating is used as a reaction vessel 1. It was arranged on the stage 5 inside. The cooling device 4 was cooled, and the stage and the silicon wafer were cooled to 10 ° C. A 50 mass% hydrofluoric acid solution 6 (300 ml) was placed in the etching chemical solution container 8, and N ₂ gas 7 was allowed to flow at a flow rate of 1 l / min and exhausted at an exhaust rate of 100 hPa from the exhaust hole 9. It was left in that state for 20 minutes. During the standing, it was visually confirmed that condensation occurred on the wafer surface. After leaving it to stand, the surface of the silicon wafer was visually observed to confirm that the oxide film on the silicon wafer was removed. Thereafter, only the N ₂ gas 7 was allowed to flow into the reaction vessel 1 for 5 minutes to perform N ₂ gas replacement, and then the lid 2 was opened and the silicon wafer 3 was taken out.

Example 2: Quantitative analysis of metal components in oxide film (1)
The silicon wafer from which the oxide film was removed by etching in Example 1 was placed on the rotary table 10 of the apparatus shown in FIG. 2 with the wafer surface exposed by removing the oxide film facing upward, and hydrofluoric acid and 100 μl of a mixed solution 12 of hydrogen peroxide and hydrochloric acid (an aqueous solution prepared by mixing 1.0% by mass of hydrogen fluoride, 10.0% by mass of hydrogen peroxide and 5.0% by mass of hydrogen chloride) with pure water was dropped. The droplet was held on the wafer surface by the nozzle 13. With the droplet held on the wafer surface, the nozzle was moved from the center to the outer periphery at 3 mm / rotation while rotating the rotary table at 100 mm / sec to dissolve the entire surface of the silicon wafer with the chemical solution. Thereafter, the recovered solution was diluted to 1 ml and analyzed by ICP / MS. As a result, no abnormal peak was detected as an interference molecule peak at the time of analysis, so it was confirmed that there was no influence of the Si component in the decomposition residue. Furthermore, the quantified amount of Ag was about 90% of the amount of contamination, and metal contamination could be analyzed with high accuracy and high sensitivity.

Example 3: Quantitative analysis of metal components in oxide film (2)
Except that the contaminated metal was changed to Li, Na, Mg, Al, K, Ca, Cr, Fe, Ni, Cu, and Zn, the metal contamination analysis was performed in the same manner as in Example 1. The amount of metal was in the range of about 90% to 100% of the amount of contamination, and metal contamination could be analyzed with high accuracy and high sensitivity.

  From the above results, it was shown that the present invention can analyze metal contamination in the oxide film on the silicon wafer surface with high sensitivity and high accuracy in a short time by a simplified method.

  According to the present invention, the presence and / or extent of metal contamination in the oxide on the silicon wafer surface can be evaluated simply, with high sensitivity and high accuracy.

An example of the reaction apparatus which can be used for the etching method of this invention is shown. An example of the apparatus which can be used for the scanning of the metal recovery solution in the analysis method of the present invention is shown.

Explanation of symbols

1 Reaction vessel 2 Lid 3 Silicon wafer 4 Cooling device 5 Stage 6 Hydrofluoric acid solution 7 N ₂ gas 8 Etching chemical solution container 9 Exhaust 10 Rotating stage 11 Silicon wafer 12 Mixing of hydrofluoric acid, hydrogen peroxide solution and hydrochloric acid Solution 13 Nozzle 14 Stage

Claims (7)

A method of etching an oxide film on the surface of a silicon wafer by generating condensation on the wafer surface by bringing it into contact with hydrogen fluoride gas while cooling the silicon wafer with an oxide film. The etching method according to claim 1, wherein the hydrogen fluoride gas is generated by bubbling a hydrofluoric acid-containing solution with a carrier gas. The etching method according to claim 2, wherein the hydrofluoric acid-containing solution further contains sulfuric acid. Performing the etching in a container having at least one vent;
The etching method according to claim 1, further comprising exhausting through the vent during the etching. The method according to any one of claims 1 to 4, wherein the oxide film thickness removed by etching is 10 to 5000 mm. The oxide film on the surface of the silicon wafer is removed by etching by the method according to any one of claims 1 to 5, and the solution is scanned over the surface of the silicon wafer after the oxide film is removed, and then the metal component in the solution is removed. A method for analyzing metal contamination of a silicon wafer with an oxide film, comprising analyzing. Preparing a wafer lot including a plurality of silicon wafers with oxide films;
Extracting at least one silicon wafer from the lot;
Analyzing the metal contamination in the oxide film of the extracted silicon wafer;
A method for producing a silicon wafer with an oxide film, including shipping as a product wafer another silicon wafer in the same lot as the silicon wafer determined to be non-defective by the analysis,
The method according to claim 6, wherein analysis of metal contamination in the oxide film of the extracted silicon wafer is performed by the method according to claim 6.

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