JP2003188222A - Silicon wafer etching method and surface layer analyzing method for silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon wafer etching method for uniformly etching a wafer surface to μm orders, for applying to an element having a high diffusion speed, even at a low temperature such as Cu, and further for quickly carrying out etching, while being suited for routine analyses. <P>SOLUTION: In the silicon wafer etching method, the analysis surface of a silicon wafer is allowed to face the mixing solution of hydrofluoric acid and nitric acid, the silicon wafer is cooled from the rear of the analysis surface, by using a volatile coolant for allowing acid vapor to freeze and adhere to the analysis surface, and further the frozen acid is dissolved at a normal temperature for etching the analysis surface. Additionally, in the surface layer analyzing method, the quantity of a metal element is determined also, by using an inductively-coupled plasma mass spectrometer or a flameless atomic absorption apparatus with an acid droplet obtained by the silicon wafer etching method as a sample. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching a silicon wafer and a method for analyzing a surface layer of a silicon wafer, and more particularly to a method for etching a silicon wafer in which acid vapor is freeze-deposited on an analysis surface and melted at room temperature to etch the analysis surface. The present invention relates to a method for analyzing a surface layer of a silicon wafer.

[0002]

2. Description of the Related Art With the high integration and miniaturization of semiconductor devices, high-purity materials in which the impurity concentration is suppressed as much as possible are required. In particular, since metal impurities existing in the surface layer from the surface of the silicon wafer to the inside of the substrate have a great influence on the device characteristics, it is important to reduce the concentration of metal element in this region.

Therefore, it is important to control the metal element concentration in the surface layer of the silicon wafer, and this control is performed by using the surface layer analysis method of the silicon wafer.

As a surface layer analysis method for this silicon wafer, conventionally, there has been a method in which a mixed acid of nitric acid and hydrofluoric acid is used as an etching solution and the surface layer of the silicon wafer is directly dissolved to measure the amount of metal impurities contained in the etching solution. is there. However, in this conventional method, although it is possible to change the etching thickness to 0.01 to 10 μm by appropriately setting the conditions for dissolving with an etching solution, the acid in which the silicon wafer is dissolved is used for the measurement. Therefore, there is a problem that the lower limit of quantification is increased due to impurities contained in the acid itself, and there is a problem that bubbles are generated during the etching reaction and the surface cannot be uniformly etched.

As another conventional method, a wafer, hydrofluoric acid, and nitric acid are placed in a closed container, and the surface layer of a silicon wafer is etched by about several μm by using vapor of hydrofluoric acid and nitric acid generated by heating, and the surface is etched. There is a method of measuring the amount of metal impurities in the condensed liquid or the silicofluoride formed on the surface. However, in this conventional method, the influence of impurities contained in the acid itself is reduced, but there is a drawback that the etching plate is large in the outer peripheral portion where vapor reaches quickly.

Further, in order to solve the problems of the above-mentioned conventional methods, a surface analysis method for a silicon wafer described in Japanese Patent Laid-Open No. 11-37992 has been proposed. The method described in this publication is such that the analysis surface of the silicon wafer is faced with a mixed solution of hydrofluoric acid and nitric acid, the silicon wafer is heated from the back side of the analysis surface, steam is generated from the mixed solution by the heat, and analysis is performed by this steam. A surface analysis method for silicon wafers, in which the surface is etched to form a thin film of a fluorinated compound (ammonium fluorinated compound) on the surface of the analysis surface, the generated thin film of the fluorinated compound is dissolved, and the amount of metal impurities is measured based on the dissolution. As a result, the blank test value is dramatically reduced as compared with the conventional direct acid decomposition method described above, and moreover, in-plane uniform etching (depth 1 to 20 μm) becomes possible. However, in the method described in this publication, since heating is performed from the back side of the silicon wafer as a means for generating acid vapor, an element having a large diffusion rate such as Cu is diffused and moved during heating even at a low temperature. It has no distribution and is difficult to apply to these elements. In addition, heating causes a large amount of impurities to be eluted from the material of the equipment that comes into contact with the acid, and a large amount of time is spent for cleaning. Furthermore, when a silicon wafer is heated, the time required to start etching is about 10 minutes to perform 1 μm, which is not suitable for routine analysis. Also,
The resulting ammonium silicofluoride thin film has a desensitizing effect on measuring instruments (inductively coupled plasma mass spectrometer and flameless atomic absorption spectrometer), and therefore needs to be decomposed with an oxidizer such as aqua regia. Moreover, in order to keep the blank test value low, it is necessary to expose it to aqua regia for a certain period of time, which further lengthens the time required for analysis.

[0007]

Therefore, it is possible to uniformly etch the surface of a wafer up to the μm order, and
Applicable to elements with a high diffusion rate even at low temperatures such as u,
Further, there has been a demand for a silicon wafer etching method which can perform etching in a short time and is suitable for routine analysis.

The present invention has been made in consideration of the above-mentioned circumstances. The wafer surface can be uniformly etched to the order of μm, and it can be applied to elements such as Cu having a large diffusion rate even at low temperature. An object of the present invention is to provide a silicon wafer etching method which can perform etching in time and is suitable for routine analysis.

[0009]

In order to achieve the above object, according to one aspect of the present invention, the analysis surface of a silicon wafer is made to face a silicon-soluble solution such as a mixed solution of hydrofluoric acid and nitric acid, A silicon wafer etching method characterized in that a silicon wafer is cooled from the back surface of the analysis surface using a volatile refrigerant to freeze-adhere the acid vapor to the analysis surface, and the frozen acid is melted at room temperature to etch the analysis surface. Will be provided. As a result, the wafer surface can be uniformly etched up to the μm order, it can be applied to elements such as Cu that have a large diffusion rate even at low temperatures, and further, etching can be performed in a short time, which is suitable for routine analysis.

In a preferred example, the analysis surface is faced with pure water before and after the acid vapor is frozen and adhered to the analysis surface, and a silicon wafer is removed from the back surface of the analysis surface using a volatile refrigerant such as liquid nitrogen or dry ice. After cooling, water vapor is frozen and attached to the analysis surface. As a result, the reaction becomes mild and becomes one of the means for controlling the etching rate, and the uniformity is improved.

According to another aspect of the present invention, acid droplets after etching by the silicon wafer etching method according to claim 1 or 2 are collected and used as they are, or after evaporating and concentrating by sulfuric acid white smoke treatment. There is provided a method for analyzing a surface layer of a silicon wafer, which comprises quantifying a metal element using an inductively coupled plasma mass spectrometer or a flameless atomic absorption spectrometer. This significantly improves the overall throughput of the analysis.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a silicon wafer etching method according to the present invention will be described below with reference to the accompanying drawings and etching flow charts.

FIG. 1 is a conceptual diagram of a silicon wafer etching apparatus used in a silicon wafer etching method.

The silicon wafer etching method according to the present invention is performed by using the silicon wafer etching apparatus 1 as shown in FIG. 1 according to an etching flow chart as shown in FIG.

For example, a mixed solution 3 of hydrofluoric acid and nitric acid is put into a flat cylindrical acid container 2 as an etching acid (S
1).

The mixed solution 3 is used at room temperature, but may be heated if necessary, and if heated, the amount of freezing increases and the amount of etching increases.

Further, by setting the ratio of HF in the mixed solution 3 to a certain value or less, it is possible to suppress the generation of ammonium fluorosilicofluoride.

The ring-shaped frame 4 holding the silicon wafer W is placed on the acid container 2 and the analysis surface Wa of the silicon wafer W is faced with the mixed solution 3 of hydrofluoric acid and nitric acid (S2).

A volatile refrigerant such as liquid nitrogen 5 is poured on the back surface Wb of the analysis surface Wa and left for a certain time (S3).

As the volatile refrigerant, dry ice or the like is preferable in addition to liquid nitrogen.

By leaving it in this state, the analysis surface W
a cools the acid vapor that has been cooled and adhered to the analysis surface Wa (S4).

After the liquid nitrogen 5 is evaporated, the analysis surface Wa is turned upside and left at room temperature to dissolve the frozen acid to etch the analysis surface Wa (S5).

The acid droplets after etching are collected (S
6).

As described above, by etching the silicon wafer using the method for etching a silicon wafer according to the present invention, it is not necessary to heat the silicon wafer as in the conventional method. It is possible to perform analysis using acid vapor while keeping the original profile of the element having a large coefficient.

Further, the temperature at which the etching is performed is as low as an extremely low temperature to a room temperature, the influence of impurities elution from the container is small, and more accurate analysis becomes possible. Further, it takes 1 to 2 minutes per 1 μm from the start of cooling to the end of etching, which is much shorter than the conventional example (about 10 minutes) described in the publication.

Further, in the conventional example described in the publication, ammonium silicofluoride is produced, so that it is necessary to decompose it.
According to the method of the present invention, etching can be performed under the condition that ammonium fluorosilicic acid is not produced, so that the blank test value and the analysis time can be shortened.

Next, another embodiment of the silicon wafer etching method according to the present invention will be described.

In the present embodiment, in contrast to the above embodiment, after the analysis surface of the silicon wafer is faced with the mixed solution, the silicon wafer is cooled and the acid vapor is frozen and adhered to the analysis surface. Before freeze-adhering, the analysis surface is faced with pure water, and then the silicon wafer is cooled to freeze-bond the water vapor on the analysis surface.

For example, the etching is performed according to the etching flow shown in FIG.

The same etching apparatus as shown in FIG. 1 is used, and pure water is first put in the container (S11).

Although pure water is used at room temperature, it may be heated if necessary.

The ring-shaped frame holding the silicon wafer W is placed on the pure water container so that the analysis surface of the silicon wafer faces the pure water (S12).

Liquid nitrogen is poured on the back surface of the analysis surface and left for a certain period of time (S13).

If left in this state, the analysis surface is cooled and the water vapor adhering to the analysis surface is frozen (S1).
4).

The steam-frozen silicon wafer is held in the frame while being placed in an acid container containing the mixed solution, and the analysis surface frozen with the steam is opposed to the mixed solution (S15).

Thereafter, in S16 to S19, the same steps as in S3 to S6 of the above-described embodiment are performed to collect the acid droplets.

As a result, the reaction becomes mild and can be one of the means for controlling the etching rate, and the effect of improving the uniformity can be obtained.

Next, an embodiment of the surface layer analysis method for a silicon wafer according to the present invention will be described.

A silicon wafer surface layer analysis method as shown in FIG. 2, for example, an inductively coupled plasma mass spectrometer 11 used in inductively coupled plasma mass spectrometry was used to collect the silicon wafer according to the above-described embodiment or another embodiment. The acid droplets are contained in the container 12 as the sample S, and argon gas is sent to the nebulizer 14 to generate a sample aerosol. The sample aerosol is sent to the inductively coupled plasma unit 15 and ionized by the inductively coupled plasma torch 16. The sample ions are transferred from the atmospheric pressure plasma to the mass spectrometer section 20 which is located in the vacuum chamber 18 through the differentially pumped interface section 17 and which is equipped with the electron multiplication type detector 19. These sample ions pass through two orifices in the interface section 17 and separate the sample ions based on their mass / charge ratio,
Then, it is analyzed by the electron multiplier detector 19. Each isotope appears in a different mass position with a peak intensity that is directly proportional to the initial concentration of that isotope in the sample. In this way, the elemental concentration of S in the sample is analyzed.

Each isotope appears in a different mass position having a peak intensity that is directly proportional to the initial concentration of the isotope in the sample, and the metal element such as the Cu concentration in the sample is analyzed.

As described above, the acid of the sample obtained by the etching is directly introduced into the inductively coupled plasma mass spectrometer of the spray introduction type, and the concentration work of the sample, which has been conventionally required, is not required. The throughput is significantly improved.

When importance is attached to sensitivity, it is possible to carry out evaporation concentration as in the conventional case.

Further, in order to remove the interfering components caused by the solvent, it is possible to use a heating vaporization introducing method as the sample introducing method instead of the solution spraying.

Another embodiment of the method for analyzing the surface layer of a silicon wafer according to the present invention will be described.

The present embodiment is a method of using flameless atomic absorption spectrometry, whereas the analysis method of the above-mentioned embodiment is inductively coupled plasma mass spectrometry.

For example, as shown in FIG. 5, by using a flameless atomic absorption spectrometer 31 used in flameless atomic absorption spectrometry, acid droplets collected by the above-mentioned embodiment or other embodiments are used as they are or The sample 33 is treated with white sulfuric acid smoke and stored in a furnace 32 as a sample S, and an electrode 33 is supplied while supplying an argon gas as a carrier gas.
Is energized to heat the sample S to form a sample aerosol. Further, for example, by heating to 2000 to 2800 ° C. to atomize the metal element and irradiating the atomic vapor layer guided to the irradiation chamber 34 with light of a specific wavelength emitted from the light source 35, the intensity of the light passing through the atomic vapor layer. Is analyzed by a light intensity detector 36 for detecting
The amount of atomic vapor can be obtained to quantify the metal.

As described above, when the sample solution is introduced into the furnace as it is, the pretreatment of the sample, which has been conventionally required, is not necessary, and the throughput of the whole analysis is remarkably improved.

[0048]

EXAMPLES Test 1 Method: Using the silicon wafer etching method according to the present invention as shown in FIGS. 1 and 2, the standing time after the introduction of liquid nitrogen was changed and the etching depth was examined.

Results: The results are shown in Table 1.

[0050]

[Table 1]

It was found that the etching depth is almost proportional to the standing time. It was also found that etching up to the μm order can be performed in a short time.

Test 2 Method: By the same method as in Test 1, the recovery rate of metal impurities was examined.

Results: The results are shown in Table 2.

[0054]

[Table 2]

It was found that each metal element was close to 100% and recovery could be completed completely.

Test 3 Method: In the same manner as in Test 1, the lower limit of quantification was examined.

Results: The results are shown in Table 3.

[0058]

[Table 3]

It has been found that the method of the present invention can improve the lower limit of quantitation by about 2 orders of magnitude as compared with direct acid decomposition, and can also improve the lower limit of quantitation by about half even in the gas phase (heating).

[0060]

According to the silicon wafer etching method of the present invention, the wafer surface can be uniformly etched to the order of μm, and can be applied to elements such as Cu that have a large diffusion rate even at a low temperature, and can be used for a short time. Thus, it is possible to provide a silicon wafer etching method that can perform etching with and suitable for routine analysis.

Further, according to the silicon wafer surface layer analysis method of the present invention, it is possible to provide a silicon wafer surface layer analysis method in which the throughput of the entire analysis is significantly improved.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a silicon wafer etching apparatus used in a silicon wafer etching method according to the present invention.

FIG. 2 is an etching flow chart of an embodiment of a silicon wafer etching method according to the present invention.

FIG. 3 is an etching flow chart of another embodiment of the silicon wafer etching method according to the present invention.

FIG. 4 is a conceptual diagram of an inductively coupled plasma mass spectrometer used in the surface layer analysis method for a silicon wafer according to the present invention.

FIG. 5 is a conceptual diagram of a flameless atomic absorption spectroscope used in the surface layer analysis method for a silicon wafer according to the present invention.

[Explanation of symbols]

1 Silicon wafer etching equipment 2 acid containers 3 mixed solution 4 frame 5 Liquid nitrogen W Silicon wafer Wa analysis surface Wb back side

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeaki Sugisaki             30 Soya, Hadano City, Kanagawa Prefecture             Kusu Co., Ltd. Development Laboratory (72) Inventor Seiji Taniike             30 Soya, Hadano City, Kanagawa Prefecture             Kusu Co., Ltd. Development Laboratory F term (reference) 2G059 AA05 BB16 CC03 DD01 DD18                       EE01 GG10 KK01                 4M106 AA01 BA20 CA29 CA41 CB01                       CB30 DH55 DJ32

Claims (3)

[Claims] 1. An analysis surface of a silicon wafer is made to face a silicon-soluble solution such as a mixed solution of hydrofluoric acid and nitric acid,
A silicon wafer etching method characterized in that a silicon wafer is cooled from the back surface of the analysis surface using a volatile refrigerant to freeze-adhere the acid vapor to the analysis surface, and the frozen acid is melted at room temperature to etch the analysis surface. . 2. The method for etching a silicon wafer according to claim 1, wherein before and after the acid vapor is frozen and adhered to the analysis surface, the analysis surface is faced with pure water, and a volatile refrigerant is used from the back surface of the analysis surface. A method for etching a silicon wafer, which comprises cooling the silicon wafer to freeze and attach water vapor to the analysis surface. 3. An inductively coupled plasma mass spectrometer or a frame, which collects acid droplets after etching by the silicon wafer etching method according to claim 1 or 2, and then directly or after evaporative concentration by sulfuric acid white smoke treatment. A method for analyzing a surface layer of a silicon wafer, which comprises quantifying a metal element using a less atomic absorption spectrometer.