JPH02271253A - Surface analysis of silicon semiconductor substrate - Google Patents

Abstract

PURPOSE:To analyze a very small amount of the impurity adhered to the surface of a silicon semiconductor substrate by dissolving the same by decomposing the natural oxide film of the silicon semiconductor substrate not by a liquid but by the vapor of volatile substance. CONSTITUTION:At first, the vapor of volatile substance is applied to the surface of a silicon semiconductor substrate for a definite time. As a result, the natural oxide film present on the surface of the substrate is reacted with the volatile substance to be decomposed. Next, a definite amount of purified nitric acid and other acid is applied to the surface to be measured of the silicon semiconductor substrate to dissolve the same so as to etch the surface of the substrate to collect a reaction product and this metal element-containing solution is recovered by a micropipette and used as a sample to be measured by a flameless atomic absorption analyzer. Therefore, the impurity to be detected is adhered to the surface of the silicon semiconductor substrate until collected by purified nitric acid and other acid and no positional variation is generated. Since the impurity is collected by a purified acid, it is unnecessary to fear contamination from chemicals.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for analyzing the surface of a silicon semiconductor substrate, and particularly relates to a method for analyzing the surface of a silicon semiconductor substrate, and particularly to a method for analyzing the surface of a silicon semiconductor substrate (hereinafter simply referred to as a "sample"). ).
It has its characteristics at the stage of collection.

(Prior Art) In an element manufacturing process, a silicon semiconductor substrate is cleaned to remove contaminants adhering to its surface. After this cleaning, various surface analyzes are performed to evaluate cleanliness. In order to properly understand the analytical value in this surface analysis,
Although it is indispensable to improve the performance and yield of VLSI devices, the analytical values obtained from conventional surface analysis do not represent the appropriate cleanliness of the silicon semiconductor substrate surface and are difficult to apply to VLSI devices. Even among silicon semiconductor substrates that are evaluated to be highly clean, there are often those with poor electrical properties. The reason for this is that, as described below, the sample is contaminated by substances other than the silicon semiconductor substrate at the stage of collecting the analysis sample.

Conventionally, as a means of measuring impurities on a substrate surface, there is a method of spraying a solution of a mixture of hydrofluoric acid and nitric acid purified by low-temperature distillation onto a silicon semiconductor substrate, and measuring the dripped solution. However, even if the chemicals are purified by low-temperature distillation, they already contain 0.1 ppb or more of impurities (Na, K, etc.), so direct spraying of the mixed solution will not prevent contamination from the chemicals. Further, the reacted solution is dropped into a separate container, but this separate container may be contaminated, and there are many problems in detecting minute amounts of substrate surface contaminants.

For example, as seen in JP-A No. 61-221649, in ultra-high purity analysis of semiconductor thin films, an analysis sample and hydrofluoric acid are placed in a closed container, and hydrogen fluoride vapor evaporated by heating means is used to oxidize SiO2. □ and Si3N.

The solution is analyzed using a flameless atomic absorption spectrometer. This method is suitable for suppressing impurities in chemicals and contamination during solution collection.

(Problems to be Solved by the Invention) However, this method has the following problems when limited to analysis of surface contaminants on silicon semiconductor substrates.

That is, the above method requires a step of growing an SiO3 film on the substrate surface in advance in an oxidation furnace because metallic silicon cannot be dissolved with hydrofluoric acid. However, there is no guarantee that new contaminants will not be added during the thermal oxidation stage, and the analysis results may differ if silicon substrates that have undergone the same cleaning are oxidized in different furnaces. In other words, in this case as well, there is a possibility of contamination during the oxidation stage due to contamination from the equipment or other factors. Furthermore, problems exist in the steps of dissolving and recovering the reaction products. That is, if an element in the reaction product is more friendly to silicon than the solution, for example, Cu is an element that is more friendly to Si than H2O,
Such elements are not recovered by the solution but instead are reversely adsorbed onto the silicon semiconductor substrate. Therefore, in order to obtain more accurate analytical values, it is necessary to appropriately select the solution for dissolution and recovery.

(Means for Solving the Problems) In order to solve the problems of the prior art, the present invention
The purpose of this study was to propose a method for dissolving and analyzing extremely small amounts of impurities attached to the surface of a silicon semiconductor substrate without applying a thermal oxide film, and the following technical means were adopted.

That is, the method of the present invention decomposes the natural oxide film of a silicon semiconductor substrate using a vapor of a volatile substance, such as a mixed vapor of hydrofluoric acid and nitric acid, instead of a liquid, and removes reaction products existing on the decomposed silicon semiconductor substrate. The purpose of this method is to dissolve and recover the substances using purified nitric acid or other acids, and to conduct elemental analysis of the recovered substances as samples.

Here, the term "natural oxide film" refers to a thin oxide film that is naturally formed on the surface of a silicon semiconductor substrate, rather than an artificial oxide film formed in an oxidation furnace.

Note that the steps of dissolving with purified nitric acid or other acid, recovering, and analyzing are exactly the same as in the conventional wet analysis method. In other words, the sample is subjected to a flameless atomic absorption spectrometer, and purified acid has the advantage of suppressing impurities in chemicals (Japanese Patent Laid-Open No. 60-6953).
No. 1). The reason why acid is used is that acid is suitable for etching the surface of the silicon semiconductor substrate and dissolving and recovering metal attached to the surface of the silicon semiconductor substrate.

(Function) In the present invention, first, vapor of a volatile substance is applied to the surface of a silicon semiconductor substrate for a certain period of time. As a result, the natural oxide film existing on the surface of the silicon semiconductor substrate reacts with volatile substances,
Decomposed. However, the state of the decomposition reaction described above cannot be visually confirmed, and no decomposition liquid is produced. This simply means that there are decomposition reaction products of the natural oxide film on the surface of the silicon semiconductor substrate that cannot be visually confirmed.

Next, a certain amount of purified nitric acid or other acid is added to the surface of the silicon semiconductor substrate to be measured, and the surface of the silicon semiconductor substrate is dissolved in an etching manner to collect the reactants. This is collected in a bed and measured using a flameless atomic absorption spectrometer as a sample.

Therefore, until the impurity to be detected is collected with purified nitric acid or other acid, it remains attached to the surface of the silicon semiconductor substrate, and no positional fluctuation occurs that may cause the contamination of other impurities. Additionally, since impurities are collected with purified acid, there is no need to worry about contamination from chemicals, which was the case in the past.

In carrying out the present invention described above, if the decomposition reaction of the natural oxide film is carried out in a closed container, the decomposition reaction rate will be increased and contamination from the environment during the reaction can be reduced.

Of course, it is also important to avoid contact with the surface of the silicon semiconductor substrate to be measured in order to prevent contamination of the sample.

In addition, after the decomposition reaction of the natural oxide film, vacuum-chuck the surface other than the surface to be measured, remove the silicon semiconductor substrate, and add purified nitric acid or other acid to obtain a more accurate sample more easily. Become.

(Example) An embodiment of the present invention will be described below based on the drawings.

FIG. 1 shows a cross section of an example of an apparatus used for carrying out the present invention. In the figure, 11 is a decomposition container, 12 is a lid body having a handle 13, 14 is a semiconductor wafer, and 14a is a surface of the semiconductor wafer. It is a Sin2 layer applied. A plurality of holding stands 15 are arranged in a stacked manner in the center of the decomposition vessel 11, and a mixed solution 16 of a hydrofluoric acid solution and a nitric acid solution is placed around the holding stands 15 inside the decomposition vessel 11. Evaporation container 1
7 are arranged.

As shown in FIG. 1, the holding table 15 has an open top and a support portion 15a protruding from the bottom that supports the semiconductor wafer 14 horizontally. In addition, the holding table 15 has a plurality of legs 15b for stacking on other holding tables 15, and between these leg parts 15b, as shown by arrows in the figure, evaporated hydrogen fluoride and nitric acid It has an open structure that allows the mixed vapor to pass through. In addition, each of the above containers 11, 17
are all made of Teflon in this embodiment.

In order to obtain a decomposition liquid using such a surface decomposition device, first, Sin to be decomposed,
The semiconductor wafer 14 is set with the thin film facing upward, and then each holding table 15 is stacked and arranged in the center of the decomposition container 11, and the decomposition container 11 is sealed with the lid body 12, and then,
Leave it at room temperature for the specified time.

In the hermetically sealed decomposition vessel 11, the mixed vapor evaporated from the mixed solution 16 of hydrofluoric acid and nitric acid flows through the opening in the holding table 15 at the top of the stack, as shown by the arrow, and to other parts. In the holding stand 15, the legs 15b, 15b
Through the process, the top surface of the semiconductor wafer 14 in each holding table 15 is reached, and the front and back surfaces of the semiconductor wafer 14 are decomposed by the mixed vapor. Reaction products existing on the decomposed silicon semiconductor substrate on the surface of the semiconductor wafer 14 are recovered by dissolving them with purified nitric acid or other acids, and this recovered material is used as a sample for elemental analysis. That is, the solution dissolved with purified nitric acid or other acid collects as droplets 18 on the upper surface of each semiconductor wafer 14. After removing the lid 12, each collected droplet 18 is collected using a micro and a bed, thereby obtaining a sample of each semiconductor wafer 14. In the example,
In this case, by sequentially removing the upper holding table 15, samples of the semiconductor wafers 14 on the lower holding table 15 can be sequentially obtained. Each sample is analyzed for impurities using, for example, a flameless atomic absorption spectrometer.

In this way, in this example, it is possible to obtain a decomposition solution containing only information on the surface of the semiconductor wafer, so information on both sides is not included in the decomposition solution as in the conventional method, and it is optimal for impurity amount analysis. This makes it possible to obtain a sample that is accurate. Furthermore, since the decomposition solution is directly collected with a micropipette, contamination from the receptor itself, which conventionally occurs, can be removed.

A specific example in which elemental analysis was performed using a frameless atomic absorption spectrometer will be described below. The conditions of the flameless atomic absorption spectrometer are: drying: 150'C for 30 seconds, ashing: 1000°C for 5 seconds in the case of Na, and atomization: 2200°C for 4 seconds in the case of Na.

[First Example] A silicon semiconductor substrate with a natural oxide film of several tens of thickness and a diameter of 4 inches was placed in a 1,600 cm airtight container, and was heated with 15Z hydrofluoric acid at a temperature of 30 degrees Celsius. 100m
The above natural oxide film was decomposed and reacted by applying a mixed vapor of 70% nitric acid and 100ml of 70% nitric acid for 120 minutes.
A sample was obtained by dropping 0 ILfL of purified nitric acid (specific resistance of 17 Ωcm or more), and elemental analysis was performed using a flameless atomic absorption spectrometer, and the following analytical values were obtained.

Na: 6. OX 10' atoms/cm2Cu
:8. OX 10109ato/cm2F e:3
．． 5X 10109ato/cm'' [Second Example] In this example, a conventional method was implemented, and a silicon semiconductor substrate with an oxide film thickness of 750 mm after heat treatment and a diameter of 4 inches was heated to 1600 cm. 100n of 15% hydrofluoric acid at a temperature of 30 degrees.
+fL steam was applied for 120 minutes to decompose the oxide film, and the resulting decomposed liquid was collected with pure water, and this was used as a sample for elemental analysis using a flameless atomic absorption spectrometer. As a result, the following analysis was obtained. Got the value.

Na:9. OX 10109ato/cm2Cu
: (2,OX 10'atoms/cm"F e
:4. OX 10109ato/cm2 In this way, it was possible to clearly distinguish between the first example and the second example in terms of the differences in the values of Na, Cu, and Fe. Here, C
The analysis values for u are significantly different, but this is due to H2
There is a huge difference in the affinity of Cu to O and acid, and H2
This is thought to be due to the difference that O merely dissolves and collects, whereas acid collects metal attached to the surface while etching the silicon semiconductor substrate.

Note that even though the same cleaning was performed, the analytical value was higher after thermal oxidation. This is thought to be due to the high analytical value due to some kind of contamination during oxidation.

(Effects of the Invention) As explained above, the present invention does not require heat treatment to attach a 5in2 film to the silicon substrate surface, and analyzes are performed using the naturally attached oxide film. This eliminates the source of contamination from furnaces, etc. Furthermore, since the chemical is not directly sprayed onto the silicon substrate to decompose it, but it is decomposed using the vapor of a volatile substance, contamination from the chemical can be reduced, and furthermore, it is possible to measure every reaction from reaction to recovery. carried out on the surface of a silicon substrate,
Since there is no need to transfer to another container, contamination from the container can be reduced, and since the solution used for recovery is purified acid, recovery is performed as if etching the surface of the silicon semiconductor substrate. As a result, it is possible to accurately perform elemental analysis of impurities without contaminating the silicon substrate to be measured, which improves the cleanliness of the silicon semiconductor substrate. Improve management.

[Brief explanation of drawings]

FIG. 1 is a schematic longitudinal cross-sectional view of a surface disassembly device used for carrying out the present invention. 11... Container 14... Holding stand 15...
・Semiconductor wafer 16...Mixed solution of hydrofluoric acid and nitric acid Patent applicant Kyushu Electronic Metals Co., Ltd. Patent applicant Osaka Titanium Manufacturing Co., Ltd. Agent
Patent Attorney Masa Sumi Mori Figure 1 11... Container 14... Holding stand 15... Semiconductor wafer 16... q Procedural amendment for matching solutions (voluntary) May 25, 1990 Commissioner of the Japan Patent Office Yoshi 1 ) Moon Yi 1. υ゛- 1 Display of the case 1999 Patent Application No. 091971 2 Name of the invention Method for analyzing the surface of a silicon semiconductor substrate 3 Person making the amendment Relationship to the case Patent applicant 4 attorney 164 Telephone (03) 373-9510 residence
Address: 2-9-10-7, Honmachi, Nakano-ku, Tokyo Contents of the amendment (1) In the specification, page 4, lines 6 to 8, “When the elements in the reaction product B are more familiar with silicon than with the solution.” 4.For example, Cu is an element that is more closely related to St than H and O,'' is corrected as follows. ``If the elements in the reaction product are difficult to dissolve in the solution, for example, Cu on St is difficult to dissolve in H2O. (resistance 17 Ωcm or more)" is deleted. (3) From page 11, line 11 to 191' of the specification, "
In this example...the analysis value was obtained. ” should be corrected as follows. ``Put a silicon semiconductor substrate with a natural oxide film of several tens of thickness and a diameter of 4 inches into a 1600 cm3 airtight container, and place it in 15% fluoride water,
Mixed steam of 0m and 70% nitric acid 100m for 120 minutes.
The natural oxide film is subjected to a decomposition reaction, and then 50~
1.00PM purified water (specific resistance 17Ωcm force)
A sample was obtained by dropping it, and elemental analysis was performed using a flameless atomic spectrometer. As a result, the following new values were obtained. J (4) Page 12, line 11 to line 14 of the specification?
``In addition, it is considered that the same cleaning...'' will be deleted. Te〈 ■ λ resistance

Claims (1)

[Claims] The natural oxide film on the silicon semiconductor substrate is decomposed by vapor of a volatile substance, and the reaction products present on the decomposed silicon semiconductor substrate are dissolved and recovered with purified nitric acid or other acids, and this recovered material is used as a sample. A method for analyzing the surface of a silicon semiconductor substrate, characterized by elemental analysis.