JPH1031009A - Silicon wafer for environmental cleanliness evaluation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detecting ability of degree of environmental contamination by metal impurity for clean room or the like by providing an anionic group on a silicon wafer surface used for monitoring. SOLUTION: An anionic group is an ion functional group having a negative charge, which includes Cl-, Br- or the like, and it is preferably situated on a wafer surface as terminal. Therefore, a silicon wafer 2 is, for example, dipped in an anionic solution 1 and then rinsed with pure water. The density of anionic group on the wafer 2 surface can be controlled by the concentration of the anionic solution 1 and the pure water rinsing time. As the anionic solution 2, aqueous solutions of NaCl, NaBr, and the like, HCl, and HNO3 are used. The wafer 6 thus subjected to the anionic treatment is exposed to a semiconductor manufacturing environment 7. When Fe adhered to the wafer 6 surface is eluted to a mixture of hydrofluoric acid, hydrogen peroxide, and pure water and quantitatively determined, the adsorption quantity of Fe is about 100 times the non-treated one. Namely, the detecting ability of degree of environmental contamination is remarkably improved by the anionic treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon wafer used for examining the degree of environmental pollution caused by metal impurities, wherein an anion group is introduced on the surface of the silicon wafer. The present invention relates to a wafer and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have become finer and thinner, requirements for cleanliness of a semiconductor manufacturing environment have become more and more severe. It is known that the influence of impurity contamination increases as the thickness of the CMOS gate oxide film becomes thinner. In particular, contamination by metal impurities on the surface of a silicon wafer is a small amount of contamination that has not been a problem in the past. However, it has been found that it has a significant effect on device characteristics and reliability, and affects product yield and the like. Specifically, 10 ⁹ atoms / cm ²
A level of contamination is problematic and requires lower levels of cleanliness. At present, development of a high-precision cleanliness evaluation method corresponding to such a demand is strongly desired.

There are roughly two types of methods for inspecting the degree of environmental pollution caused by metal impurities. One of them is a method called an impinger method. this is,
This is a method in which metal impurities contained in the measurement environment are dissolved in pure water or a dilute hydrochloric acid solution and analyzed. In this method, the lower limit of measurement is usually 10 ng / cm ^{3 for} Fe and 1 ng / c for Cu.
m ³ , which is not always sufficient as the detection sensitivity. In addition, if sufficient measurement accuracy is to be obtained, the number of man-hours required for the analysis is greatly increased, which is not practical.

The other is a method in which a silicon wafer is exposed to a measurement environment for a predetermined time, and metal impurities captured on the wafer surface are analyzed. In this method, as a means for analyzing the adhered metal on the silicon wafer surface,
Atomic absorption spectroscopy, total reflection X-ray fluorescence, radiochemical analysis. The lower limit of the measurement is about 10 ⁹ atoms / cm ² in the method and about 10 ¹⁰ atoms / cm ² in the method. Also,
The lower limit of measurement is about 10 ⁷ to 10 ⁸ atoms / cm ² , and the detection sensitivity is sufficient, but the pre-processing and analysis operations are complicated and pose practical problems.

[0005] As an improvement of the conventional evaluation technique, there is an example in which a monitor wafer is improved instead of a means for analyzing metal impurities. Japanese Patent Application Laid-Open No. Hei 6-283585 proposes a method in which the surface of a silicon wafer is anodized to be porous. This aims to improve the detection sensitivity by increasing the effective surface area of the silicon wafer and increasing the amount of metal impurities attached. That is, since the amount of adhered metal when exposed to the same environment is larger than that of an untreated wafer, the lower limit of measurement can be reduced even if the method of analyzing the adhered metal is the same as the conventional method. However, in this method, it is difficult to avoid contaminations during the anodizing treatment of the silicon wafer surface, and it is difficult to substantially increase the measurement sensitivity. Also, since it is not possible to estimate the amount of increase in surface area after the formation of the porous material, it is difficult to determine how much the ability to capture metal impurities on the wafer surface has improved compared to an untreated wafer, making it difficult to perform quantitative comparison. There are also problems.

[0006]

As described above, most of the conventionally known methods have insufficient measurement accuracy when further miniaturizing and thinning semiconductor devices.
Alternatively, even if the method has sufficient measurement accuracy, there are problems such as requiring large-scale equipment and complicated operations. In other words, it is a simple method, and at present, 10 ⁷
An evaluation method for detecting a minute amount of metal contamination at a level of 〜１０10 ⁸ atoms / cm ² has not been found so far. An object of the present invention is to provide a method for evaluating the degree of contamination by metal impurities that satisfies such requirements.

[0007]

SUMMARY OF THE INVENTION The present invention, which achieves the above object, is a silicon wafer used as a monitor for inspecting the degree of environmental pollution caused by metal impurities, and has an anionic group on the surface of the silicon wafer. It is characterized by the following. Since the metal adsorption ability is increased by the action of the anionic group, the use of the monitoring wafer of the present invention makes it possible to detect even a very small amount of metal contamination by conventional analysis means.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The anion group in the present invention is
Negatively charged ionic functional groups such as Cl ⁻ , B
_{^{r -, NO 2 -, NO}} 3 -, SO 4 2- , and the like. This anionic group is preferably located as a terminal on the surface of the silicon wafer.

In the present invention, various methods can be applied as a method for introducing an anionic group to the surface of a silicon wafer, and examples thereof include a dipping method and a spin coating method. The immersion method is a method for producing a wafer by immersing in an anion solution and rinsing with pure water. The anionic group density on the wafer surface can be controlled by the anion solution concentration and the pure water rinsing time. On the other hand, the spin coating method is a method in which a concentration-adjusted anion solution is dropped on a silicon wafer set on a spin coater.
The anionic group density on the surface can be controlled by the anion solution concentration.

Here, NaCl, NaB
r, aqueous solution of NaNO ₂ , NaNO ₃ , Na ₂ SO ₄ , HCl, HNO ₃ , H ₂ SO
₄ etc. can be used, and the concentration should be adjusted according to the level of metal contamination of the environment to be evaluated. The anionic group density is preferably set to 10 ¹² atoms / cm ² or more.

Using a silicon wafer into which an anionic group has been introduced by the above method, the degree of environmental pollution by metal impurities can be examined as follows. First, the silicon wafer is exposed to an environment to be evaluated. Here, since the silicon wafer having an anion group on the surface is considered to be negatively charged, metal ions existing in the environment are captured by electrostatic attraction. Therefore, the ability to capture metal impurities on the surface is significantly improved as compared with an unprocessed wafer, and environmental contamination due to a trace amount of metal impurities can be detected. In other words, the amount of deposited metal increases when exposed to an environment with the same degree of contamination as compared to an untreated wafer.
Even if the analysis of the adhered metal itself is the same as the conventional method, the lower limit of measurement is reduced as a result. The standing time in the measurement environment is about several hours to several days, and is determined depending on the level of the contamination degree and the like. After standing for a certain period of time, the degree of environmental pollution is evaluated by analyzing the attached metal. Conventional methods such as atomic absorption spectrometry and total reflection X-ray fluorescence can be used as the analysis method.

[0012]

An embodiment of the present invention will be described with reference to FIGS. First, a 6-inch Si (100) p-type wafer was immersed in 72% sulfuric acid for 10 minutes. Next, sulfate ions remaining on the wafer surface were removed by pure water rinsing. The relationship between the pure water rinsing time and the residual sulfate ions was as shown in FIG. In this embodiment, the rinsing time is 12 minutes,
The O ₄ ^2- concentration was set to 10 ¹⁴ atoms / cm ² . Here, the measurement of the residual sulfate ion was performed as follows. First, a measurement wafer and 100 ml of pure water were put into a commercially available bag film for ion chromatography, the film was sealed with a thermocompression bonding machine, and heated and extracted with an oven. Next, SO ₄ ^{2- in} pure water was quantified by ion chromatography.

Subsequently, as shown in FIG. 1, the wafer 6 subjected to the anion treatment was exposed to a semiconductor manufacturing environment 7. Thereafter, Fe adhering to the wafer surface was eluted into a mixed solution of hydrofluoric acid, hydrogen peroxide solution and pure water, and quantified by atomic absorption spectrometry. The Fe adsorption amount was about 1 × 10 ¹² ions / cm ² . On the other hand, the amount of Fe adsorption of the unprocessed wafer is about 5 × 10 ⁹ atoms / cm
^2, it was approximately 100 times the amount of adsorption by anionic processes. That is, the ability to detect metal contamination by Fe is about 1
Improved by 00 times. The SO ₄ ^2- concentration on the wafer surface and F
3. The relationship between the amounts of adsorption was as shown in FIG. It can be seen that the Fe adsorption amount increases with an increase in the amount of SO ₄ ²⁻ .

If a wafer having an improved metal-capturing ability is used for monitoring the degree of environmental pollution, it is possible to detect a very small amount of metal contamination. In the above examples, it was shown that the ability to capture Fe can be significantly improved.However, the present invention promotes metal adsorption by introducing an anionic group to the wafer surface, and can also be applied to various other metals. It is valid. Further, since the anion group density can be controlled by adjusting the rinsing time as described above, the metal trapping ability can be quantitatively controlled. For this reason, quantitative comparison of evaluation results becomes possible.

In the above embodiment, the anion treatment of the wafer surface can be performed by spin coating. For example, 5 cc of an anion solution adjusted to a concentration of 10 ppb to 1000 ppm is dropped on the surface of the wafer, and the solution is applied with a spin coater.
0 revolutions / minute for 10 seconds, followed by 3500 revolutions / minute for 2 seconds
By performing the treatment for 0 second, a monitor wafer having the same effect as in the above embodiment can be manufactured.

[0016]

By using a monitor wafer having an anionic group on the surface, the sensitivity to metal contamination can be improved about 100 times as compared with a case where an untreated wafer is used. As a result, highly accurate environmental cleanliness evaluation corresponding to miniaturization and thinning of a semiconductor device becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a process for evaluating a semiconductor manufacturing environment according to the present invention.

FIG. 2 shows a case where anion treatment was performed using a 72% sulfuric acid solution.
Rinsing time and SO _Four ^2-The relationship between the surface adsorption amount
FIG.

FIG. 3 is a diagram showing the relationship between the concentration of SO ₄ ^{2− on the} surface of a silicon wafer and the amount of Fe adsorbed.

[Explanation of symbols]

 Reference Signs List 1 Anion solution 2 Silicon wafer 3 Anion group 4 HEPA filter 5 Vertical laminar flow in clean room 6 Silicon wafer after anion solution treatment 7 Clean room environment

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication // G01N 21/31 G01N 21/31 A

Claims (6)

[Claims] 1. A silicon wafer for monitoring, which is used for monitoring the degree of environmental pollution due to metallic impurities, wherein the silicon wafer has an anionic group on the surface of the silicon wafer. 2. The monitoring silicon wafer according to claim 1, wherein an anionic group is introduced into the surface of the silicon wafer by bringing the surface of the silicon wafer into contact with an anion solution. 3. A method for producing a monitoring silicon wafer for inspecting the degree of environmental contamination due to metal impurities, comprising a step of bringing an anion solution into contact with the surface of the silicon wafer to introduce an anionic group into the surface of the silicon wafer. A method for manufacturing a silicon wafer for monitoring, characterized by comprising: 4. An immersion treatment step in an anion solution and a rinsing step with pure water, wherein the anion group density on the wafer surface is controlled by adjusting the anion concentration of the anion solution and the pure water rinsing time. A method for manufacturing a silicon wafer according to claim 3. 5. The method according to claim 3, further comprising a step of performing a surface treatment with an anion solution by a spin coating method, wherein the anion group density on the wafer surface is controlled by adjusting the anion concentration of the anion solution. Manufacturing method of silicon wafer. 6. After exposing the monitor silicon wafer according to claim 1 to an environment to be measured,
A method for evaluating the degree of environmental pollution by metal impurities, comprising measuring the amount of metal impurities attached to the silicon wafer.