JPH0982769A - Impurity analyzing method for silicon wafer interior - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to simply, accurately distribute impurity with high sensitivity by altering the surface layer of one side of a wafer that strain is introduced by causing mechanical damage, dissolving the surface layer containing the thermal oxide film with reagent, and distributing it as to the recovery liquid. SOLUTION: After mechanical damage is caused to the main surface of a silicon wafer 1 of one side to introduce strain 3, the surface layer of the wafer of the side that the strain 3 is introduced is altered to a thermal oxide film 5. The film 5, or the film 5 and a silicon surface layer 6a directly under the film 5 are dissolved with reagent, the dissolved liquid 7 is recovered, and the recovered liquid is distributed. For example, a sample sandblasted with SiO2 powder at one side is oxidized in an oxygen atmosphere at 430 deg.C for 10min, and the surface layer of the sandblasted side is altered to a thermal oxide film 5. The film 5 is dissolved with hydrofluoric acid, the dissolved liquid 7 is recovered, and the quantitative distribution of metal element is obtained by a flameless atomic absorption analyzer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing impurities inside a silicon wafer in a simple, highly accurate and highly sensitive manner.

[0002]

2. Description of the Related Art Impurities (Al, Na, Fe, Cr, Ni, Cu) such as metal elements are formed on the surface or inside of a silicon wafer.
Is present, it is well known that these impurities have a great influence on the electrical characteristics and the like of the semiconductor element. For this reason, it is important to keep the amount of these impurities as small as possible, and it is required to accurately analyze the type, amount of adhesion, and content.

Conventionally, as a method for analyzing metallic impurities in a silicon wafer surface layer, (1) secondary ion mass spectrometry or total reflection fluorescent X-ray analysis method is adopted as a method for directly analyzing the silicon wafer surface layer. (2) As a sample for collecting an analysis sample from the surface layer of a silicon wafer, for example, a natural oxide film formed on the silicon surface is dissolved by vapor of hydrofluoric acid (HF), and the solution is collected as a sample. , The method of analysis has been implemented.

However, the analysis methods (1) and (2) above are
All of them only analyze the impurities in the surface layer of the silicon wafer, and it is difficult to analyze the impurities inside the silicon wafer. Also, when impurities are present in a large amount inside the wafer as compared with the surface of the wafer,
Accurate quantitative evaluation could not be expected when the diffusion rate of impurities was high.

On the other hand, as a method for analyzing impurities inside the wafer, a method of dissolving the whole wafer with a chemical solution and analyzing the dissolved solution, and a secondary ion mass spectrometry method have been adopted.

[0006]

However, in the former case, a large amount of the solution is required, so that sufficient analysis accuracy and sensitivity cannot be obtained, and the analysis takes time, and the sample wafer is completely consumed. There was a problem. In the latter case, not only expensive equipment is required, but the information obtained by one-time sputtering is only for a sample portion of 2 mm square, for example (actually, the area of 1 mm diameter can be analyzed). ), The analysis is time consuming and, in addition, there is a problem that it is a destructive test.

Therefore, the object of the present invention is to analyze impurities in a silicon wafer easily, with high accuracy and with high sensitivity, and to minimize the consumption of the sample wafer and the damage to the sample wafer. Thus, it is to provide a method that can be used with useful silicon wafer products.

[0008]

A method for analyzing impurities in a silicon wafer according to the first invention is a method of mechanically damaging one main surface of a silicon wafer to introduce strain,
After subjecting the silicon wafer to thermal oxidation treatment to getter the impurities inside the silicon wafer into the strained region,
Characterized in that the thermal oxide film formed including a strained region, or the thermal oxide film and the silicon surface layer immediately thereunder are dissolved by a chemical solution to recover the dissolved solution, and the recovered solution is analyzed. Is.

In the first invention, when the wafer surface layer is changed to a thermal oxide film, the silicon wafer is heated in the presence of oxygen gas at a temperature of 300 ° C. to 650 ° C.
It is preferable to heat for 120 minutes. Under these conditions,
The heating facilitates the formation of a thermal oxide film including a strained region and the movement of impurities inside the silicon wafer to the strained layer to facilitate the trapping of the impurities, but below 300 ° C, the migration rate of impurities inside the silicon wafer Is small, and it takes a long time to fully capture it. When the temperature exceeds 650 ° C., the diffusion rate of impurities (inside of the silicon wafer) becomes faster, and the diffusion energy becomes larger than the capture energy in the strained region, so that it becomes difficult to capture the impurities. The reason for setting the heat treatment time in the above range is that if it is too short, a sufficient trapping effect cannot be obtained, and it becomes difficult to grasp the absolute amount of impurities present inside. Further, it is because the efficiency of the treatment is lowered for a long time, and the heat treatment for a long time may cause contamination from the outside even at a low temperature.

The method for analyzing impurities in the silicon wafer according to the second aspect of the invention is such that mechanical stress is applied to one main surface of the silicon wafer to introduce strain, and then the wafer surface is subjected to a natural oxide film (SiO ₂ film) or After changing to a chemically formed oxide film (SiO ₂ film) and performing heat treatment at a temperature of 300 ° C. or higher and 650 ° C. or lower for 2 to 120 minutes, (1) the natural oxide film, (2) the natural oxide film and the natural oxide film The silicon surface layer directly underneath, (3) the chemically formed oxide film, (4) any one of the chemically formed oxide film and the silicon surface layer immediately thereunder is dissolved by a chemical solution to form the solution. Is collected, and the collected liquid is analyzed.

The natural oxide film is formed by a known method, for example, by storing a silicon wafer in the atmosphere at room temperature and pressure. The above "chemically formed oxide film" is
It can be formed, for example, by immersing one main surface of the silicon wafer in a mixed solution of hydrogen peroxide and ammonia used for cleaning the silicon wafer. In the second invention, at a temperature of 300 ° C. or higher and 650 ° C. or lower, 2 to
By performing the heat treatment for 120 minutes, the impurities inside the silicon wafer move to one or both of the strained layer and the oxide film of the silicon wafer.

According to the method for analyzing impurities in a silicon wafer according to the third aspect of the invention, after mechanical strain is applied to one main surface of the silicon wafer to introduce strain, an oxide film is formed on the main surface on which the strain is introduced. (SiO ₂ film) is deposited by a normal pressure CVD method or a low pressure CVD method, and the oxide film, or the oxide film and the surface layer of the silicon wafer directly under the oxide film are dissolved by a chemical solution to recover the solution, and the recovered solution It is characterized by carrying out an analysis.

In depositing the oxide film according to the third aspect of the invention, the process by the CVD method is performed at a temperature of 300 ° C. or higher and 650
It is preferable to carry out the treatment at a temperature of 0 ° C or lower for 2 to 120 minutes. 3
If the temperature is lower than 00 ° C., the migration rate of impurities inside the silicon wafer becomes small. If the temperature exceeds 650 ° C., the diffusion rate of impurities becomes faster and the diffusion energy becomes larger than the capture energy in the strained region, so that it is difficult to be captured by the strained layer of the silicon wafer. Further, the reason why the CVD processing time is set within the above range is that if it is too short, a sufficient trapping effect cannot be obtained and it becomes difficult to grasp the absolute amount of impurities existing inside. Further, it is because the efficiency of the treatment is lowered for a long time, and the heat treatment for a long time may cause contamination from the outside even at a low temperature.

In the present invention (first to third inventions), sand blasting is a method for imparting mechanical damage to the surface of a silicon wafer; dry ice, pure water, an aqueous solution of acid, and a solid at -20 to 10 ° C. When the temperature exceeds ℃, it is possible to apply blasting utilizing collision of particles or powder of liquid organic substance; lapping, laser irradiation and the like. Whether the mechanical damage should be applied to the surface of the silicon wafer on which the semiconductor elements are formed (front surface side) or the opposite side (back surface side) should be given first the internal impurity recovery rate to the chemical solution for wafer dissolution. It is preferable to decide.

In the present invention, the thermal oxide film (the natural oxide film, the chemically formed oxide film or the CVC) is used.
A known etching solution can be used as the chemical solution for dissolving only the deposited oxide film by the method) or the thermal oxide film and the silicon surface layer immediately thereunder. In the former case, for example, hydrofluoric acid is preferable, and in the latter case, for example, hydrofluoric acid / nitric acid /
A mixture of acetic acid is preferred.

In both cases of qualitative and quantitative analysis of internal impurities, the thermal oxide film (natural oxide film, chemically formed oxide film or deposited oxide film) of the sample wafer and the surface of the silicon wafer immediately below it It is desirable to contact the entire layer with the etchant. This is to increase the recovery rate of internal impurities in the chemical solution for wafer dissolution. As a method therefor, for example, (1) a sample wafer is housed in a closed container, and the vapor of the mixed etching solution is supplied and condensed on the entire surface of the thermal oxide film; or (2) a sample wafer is housed in a closed container, A method in which vapor of hydrofluoric acid is supplied and condensed on the entire surface of the thermal oxide film to make it hydrophobic, and then the above-mentioned mixed etching solution is dropped onto the sample surface and the droplets are moved / contacted over the entire sample surface (JP-A-2- No. 28533: See "Method and apparatus for measuring impurities").

In the present invention, in order to confirm that only the oxide film of the sample wafer could be dissolved, for example, when hydrofluoric acid was used as the chemical solution for dissolving the oxide film, it was hydrophilic when the oxide film was present. However, it is possible to use a phenomenon in which hydrofluoric acid becomes hydrophobic as the oxide film dissolves, and hydrofluoric acid is repelled on the surface of the silicon wafer to form round water droplets. Also, to confirm that the silicon surface layer just below the oxide film could be dissolved,
In the process of melting, measure the thickness of the silicon wafer appropriately,
It suffices to confirm that the difference from the thickness before melting is sufficiently larger than the thickness of the oxide film.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In the first invention, FIG.
Silicon wafer 1 containing impurities 2 inside as shown in
As shown in FIG. 1B, strain 3 is introduced into the main surface on one side of. As shown in FIG. 1C, the strained layer 4 is formed by changing the surface layer of the wafer 1 on which the strained 3 is introduced into a thermal oxide film 5.
Becomes the surface layer of the thermal oxide film 5 and the internal impurities 2 existing below the interface between the thermal oxide film 5 and the silicon layer 6.
Is moved in silicon by thermal energy and is trapped in the strained layer 4 and moved into the interface or the thermal oxide film 5, and the internal impurity 2 existing in the interface or in the vicinity thereof and in the upper layer is
It moves into the thermal oxide film 5 or to the interface.

Therefore, as shown in FIG. 1 (d), the surface layer (upper layer) 6a of the thermal oxide film 5 and the silicon layer 6 immediately below the thermal oxide film 5 is dissolved with a chemical solution to recover the solution 7, and the solution 7 is dissolved. Performing a highly accurate and highly sensitive quantitative analysis of the total amount of the impurities adhering to the surface of the wafer 1, the impurities adsorbed on the surface of the wafer 1, and the internal impurities 2 by analyzing the liquid 7. You can The impurity recovery rate when only the thermal oxide film 5 is dissolved and removed is slightly lower than that in the case of FIG.

In the analysis method of the first invention, only the surface layer of the sample wafer is changed to the thermal oxide film, and the range up to the surface layer of the thermal oxide film and the silicon layer immediately thereunder is dissolved and removed.
It takes no time to collect an analytical sample. Moreover, since the amount of the analysis sample, that is, the predetermined solution is small, sufficient analysis accuracy and sensitivity can be obtained. In addition, the thickness of the wafer after the analysis sample collection is smaller than that before the analysis sample collection by the amount close to the thickness of the thermal oxide film, but most of the impurities on the surface and inside are removed. Since the wafer has excellent electrical characteristics, there is also an advantage that a high-quality wafer in which impurities are removed can be obtained at the same time as the analysis sample is taken.

In the second invention, a natural oxide film or a chemically formed oxide film may be formed in place of the thermal oxide film 5, and then heat treatment may be performed under predetermined conditions. Almost the same.

In the third aspect of the invention, strain 3 is introduced into the main surface on one side of the silicon wafer 1 containing impurities 2 inside as shown in FIG. 2A, as shown in FIG. 2B. FIG.
As shown in (c), internal impurities 2 in the silicon layer 6 cause the oxide film 15 and the silicon layer to move due to thermal energy when the oxide film 15 is deposited on the main surface of the wafer 1 on which the strain 3 is introduced. It moves to the interface with 6 or into the oxide film 15.

Therefore, as shown in FIG. 2D, the surface layer 6 of the oxide film 15 and the silicon layer 6 immediately thereunder.
a is dissolved with a chemical solution to recover the solution 17, and the solution 17
By analyzing the above, the total amount of impurities adhering to the surface of the wafer 1, impurities adsorbed on the surface of the wafer 1 and internal impurities 2 can be qualitatively and quantitatively analyzed with relatively high accuracy and high sensitivity. It can be carried out.

In the analysis method of the third invention, an oxide film is formed on the surface of the sample wafer, and the oxide film and the range up to the surface layer of the silicon layer immediately below the oxide film are dissolved and removed. It doesn't take long. Moreover, since the amount of the analysis sample, that is, the predetermined solution is small, sufficient analysis accuracy and sensitivity can be obtained. In addition, the remaining portion of the sample wafer has a thickness that is hardly reduced as compared with that before the analysis sample is collected, and most of the impurities on the surface and inside are removed, so that the wafer has excellent electrical characteristics. Another advantage is that a high-quality wafer free from impurities can be obtained at the same time as the analysis sample is taken.

[0025]

Next, examples of the present invention and comparative examples will be described. Example 1 As a sample, a diameter of 200 obtained through the same steps
A plurality of p-type <100> silicon wafers having a thickness of 725 mm and a thickness of 725 mm were prepared. One surface of one sample selected from these was sandblasted with SiO ₂ powder, and this sample was dried at 100% dryness in an oxygen atmosphere at 430 ° C.
Oxidation treatment was performed for 0 minutes to change the wafer surface layer on the sandblast side to a thermal oxide film. The thermal oxide film was dissolved with hydrofluoric acid, the solution was recovered, and the quantitative analysis of the metal element was performed by a flameless atomic absorption spectrometer. As a result, the Ni content is 100 × 10 ¹⁰ atoms / cm ² , and the Cu content is 1 × 1.
It was found to be 0 ¹⁰ atoms / cm ² .

Comparative Example 1 One of the silicon wafers remaining in Example 1 was selected, and the same treatment as in Example 1 was performed except that the sand blast treatment with SiO ₂ powder was not performed for this sample.
The thermal oxide film was dissolved with hydrofluoric acid, and the solution was collected and subjected to qualitative and quantitative analysis of metal elements by a flameless atomic absorption spectrometer. As a result, neither Ni nor Cu could be detected.

Comparative Example 2 One of the silicon wafers remaining in Example 1 was selected, and this sample was subjected to SiO _{2 on} one side of the sample in the same manner as in Example 1.
After sandblasting with powder, it was left in a clean booth to grow a natural oxide film on the surface of the wafer. This natural oxide film was dissolved with hydrofluoric acid, and the solution was collected and quantitatively analyzed for the metal element by a flameless atomic absorption spectrometer. As a result, neither Ni nor Cu could be detected.

[0028]

As is apparent from the above description, according to the first invention, the silicon wafer is thermally oxidized after the mechanical damage is applied to one main surface of the silicon wafer to introduce the strain. , The impurities inside the silicon wafer can be collected in the oxide film and the silicon surface layer (strained region) immediately thereunder, and the thermal oxide film or the thermal oxide film and the silicon surface layer immediately thereunder are dissolved by a chemical solution. Since the solution is collected and the collected solution is analyzed, the impurities in the wafer can be easily and accurately analyzed with high sensitivity. According to the second invention, the impurities inside the silicon wafer are moved to, for example, the natural oxide film forming the surface layer of the wafer and the silicon surface layer immediately below the natural oxide film. Since the solution is prepared and analyzed, the same effect as the first invention can be obtained. According to the third invention, the impurities inside the silicon wafer are moved in the silicon wafer by the thermal energy when the strained region formed on the surface layer of the wafer is subjected to the CVD treatment, and the impurities in the deposited oxide film and immediately below it are moved. Since it is moved to the silicon surface layer (strained region) and a predetermined solution is prepared and analyzed by the same procedure as in the first invention, the same effect as the first invention can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a processing step according to the first invention and its operation.

FIG. 2 is a cross-sectional view illustrating a processing step according to the third invention and its operation.

[Explanation of symbols]

 1 Silicon Wafer 2 Internal Impurity 3 Strain 4 Strained Layer 5 Thermal Oxide Film 6 Silicon Layer 7 Dissolution Solution 15 Oxide Film 17 Dissolution Solution

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiro Saijo Niigata Prefecture Nakakubiki-gun Kubiki-mura large size 596 Jono Koshi Nitta 2 Naoetsu Electronics Industry Co., Ltd. Jono Koshi Nitta 596 Address 2 Naoetsu Electronics Industry Co., Ltd.

Claims (5)

[Claims] 1. A silicon wafer is mechanically damaged on one main surface thereof to introduce strain, and then the wafer surface layer on the strain-introduced side is changed to a thermal oxide film. A method for analyzing impurities in a silicon wafer, characterized in that an oxide film and a silicon surface layer immediately below the oxide film are dissolved by a chemical solution, the solution is recovered, and the recovered solution is analyzed. 2. When converting the surface layer of the wafer into a thermal oxide film, the silicon wafer is treated in the presence of oxygen gas for 300 times.
The method for analyzing impurities in a silicon wafer according to claim 1, wherein heating is performed at a temperature of not less than ℃ and not more than 650 ° C for 2 to 120 minutes. 3. A silicon wafer is subjected to mechanical damage on one main surface thereof to introduce strain, and then the wafer surface layer on the strain-introduced side is changed to a natural oxide film or a chemically formed oxide film. After heat treatment at a temperature of 300 ° C. or higher and 650 ° C. or lower for 2 to 120 minutes, (1) the natural oxide film,
(2) The natural oxide film and the silicon surface layer immediately below it,
(3) Any one of the chemically formed oxide film, (4) the chemically formed oxide film and the silicon surface layer immediately thereunder is dissolved by a chemical liquid to recover the dissolved liquid, and the recovery is performed. A method for analyzing impurities in a silicon wafer, which comprises performing analysis on a liquid. 4. A silicon wafer is subjected to mechanical damage on one main surface thereof to introduce strain, and then an oxide film is deposited on the main surface on which the strain is introduced by atmospheric pressure CVD method or low pressure CVD method. A method for analyzing impurities in a silicon wafer, characterized in that the oxide film, or the oxide film and the surface layer of the silicon wafer immediately below the oxide film are dissolved by a chemical solution to recover the solution, and the recovered solution is analyzed. 5. The inside of the silicon wafer according to claim 4, wherein the deposition process of the oxide film by the atmospheric pressure CVD method or the low pressure CVD method is performed at a temperature of 300 ° C. or higher and 650 ° C. or lower for 2 to 120 minutes. Impurity analysis method.