JP2000031225A - Semiconductor substrate defect evaluation method - Google Patents

Abstract

(57) Abstract: A semiconductor substrate capable of detecting pinhole defects in a buried oxide film formed inside a substrate by a SIMOX method and easily evaluating a wide range of pinhole defect distribution over the entire surface of the substrate. Provision of defect evaluation method. SOLUTION: A pinhole defect 4 itself is in a silicon state in which oxygen is not ion-implanted and a buried oxide film is not formed, and a thermal oxide film 5 is removed using an HF solution, and a TMAH solution is removed. By performing etching using
A region where the surface silicon active layer 3 and the buried oxide film 2 are not formed is etched to become an etch pit 6,
This can be observed as a pinhole defect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a semiconductor substrate obtained by a method of forming a buried oxide film in a silicon substrate by an ion implantation method. An etch pit caused by a pinhole defect formed in a buried oxide film without oxygen being implanted at the time of ion implantation is generated, and by detecting this, a pinhole defect can be easily and accurately detected. The present invention relates to a defect evaluation method.

[0002]

2. Description of the Related Art An SOI (Silicon On Insulato) in which a higher quality single crystal silicon layer is uniformly formed on an oxide film insulating layer formed on a silicon substrate.
r) Since a wafer having a structure greatly facilitates element isolation, high integration, low power consumption, and high speed of devices can be expected, and some of them have been put to practical use.

Various methods for manufacturing an SOI substrate have been proposed. As typical SOI substrates, a bonded SOI substrate and a SIMOX (Separation) are used.
by Implanted Oxygen) substrate.

[0004] In the bonding method, a bond wafer serving as an SOI active layer is thermally oxidized and bonded to a base wafer having no oxide film at room temperature, and then a bonding anneal is performed in an oxidizing atmosphere to increase bonding strength. It is manufactured by thinning a wafer by grinding and polishing.

[0005] The SIMOX substrate has a method comprising the steps of implanting oxygen into a silicon substrate by ion implantation of oxygen to form a buried oxide film in the silicon substrate, and a high-temperature annealing step at 1300 ° C. or higher for recovering crystallinity (hereinafter, referred to as “SIMOX”). SIMOX method).

However, in a silicon substrate formed by the SIMOX method, oxygen may not be implanted due to the influence of particles or the like adhering to the surface of the silicon substrate at the time of ion implantation, and a portion where a buried oxide film is not formed may occur. . Hereinafter, a portion where the oxide film is not formed is referred to as a pinhole defect.

[0007] Originally, the surface silicon layer, which is the active layer, and the substrate silicon are electrically separated by forming a buried oxide film. However, the presence of pinhole defects may cause a portion to be energized. When a device is formed on a SIMOX substrate, this is one of the causes for lowering the yield of the device.

[0008]

Therefore, it is necessary to minimize the occurrence of such pinhole defects during manufacturing, and the study of pinhole defect detection and evaluation methods has been considered in the development of SIMOX technology. Is one of the important issues.

As a method of detecting and evaluating pinhole defects, a filter paper impregnated with a CuSO ₄ solution is brought into close contact with the surface of a SIMOX substrate, a Cu plate serving as an electrode is placed above and below the SIMOX substrate, and a buried oxide film is formed by applying a voltage. If there is a pinhole defect inside, the transfer of electric charge occurs only in that portion, so that Cu is precipitated on the filter paper by electrolysis on the filter paper, and the density of the pinhole defect is determined from the precipitate density. Methods for determining the density have been proposed.

An electrode is attached to the surface of the SIMOX substrate, a bias is applied, an electric field is generated inside the wafer, and a particle beam or a light beam is radiated there to inject carriers into the substrate. When a pinhole defect is present in the active layer, since the active layer and the substrate silicon are energized, most of the carriers reach the electrodes and are taken out as external signals. (Japanese Patent Laid-Open No. Hei 6-338550) has been proposed.

In each of the methods, a great deal of time is required for preparing a pinhole defect, and information on the entire surface of the substrate cannot be easily evaluated.

The present invention detects a pinhole defect in a buried oxide film formed inside a substrate by a SIMOX method, and can easily evaluate a wide distribution of pinhole defects over the entire surface of the substrate. The purpose is to provide an evaluation method.

[0013]

The present inventors have conducted various studies for the purpose of easily detecting a pinhole defect in a buried oxide film. As a result, for example, after removing a thermal oxide film using an HF solution, By using an etching solution having a high etching rate with respect to silicon and a low etching rate with respect to an oxide film, the silicon layer of the surface layer of the substrate and the silicon portion of the pinhole defect can be easily removed by etching. The present inventors have found that by detecting pits, it is possible to easily evaluate a wide range of pinhole defect distribution over the entire surface of the substrate, and have completed the present invention.

That is, the present invention provides a semiconductor substrate for detecting and evaluating pinhole defects generated in a buried oxide film in a substrate having a buried oxide film formed in a silicon substrate by oxygen ion implantation and high-temperature annealing. Removing the thermal oxide film on the substrate surface, then removing the silicon layer of the substrate surface and the silicon portion of the pinhole defect by etching, and then detecting the etch pit generated by the etching. This is a defect evaluation method for a semiconductor substrate, comprising:

The present invention also relates to a method for evaluating defects in a semiconductor substrate having the above structure, wherein: a) an HF solution is used in the step of removing the thermal oxide film, and the silicon etching solution has a high etching rate for silicon and an oxide film; B) a method of performing an etching process using an alkali solution as a silicon etching solution, c) a tetramethylammonium hydroxide solution as a silicon etching solution, 2-15%, and a method of performing an etching treatment at a liquid temperature of 50 ° C. to 80 ° C. in combination.

[0016]

DETAILED DESCRIPTION OF THE INVENTION SIMO with pinhole defect
As shown in FIG. 1A, the X substrate is formed by implanting oxygen into the silicon substrate 1 to form a buried oxide film 2 in the silicon substrate 1 and then oxidizing at 1300 ° C. or higher to recover crystallinity. Finished by high temperature annealing in atmosphere
A thermal oxide film 5 is formed on the surface silicon active layer 3, but oxygen is not implanted due to the influence of particles or the like adhered to the surface of the silicon substrate 1 at the time of ion implantation, and a portion where a buried oxide film is not formed, That is, the pinhole defect 4 is generated.

As shown in FIG. 1B, the evaluation method according to the present invention is a first step of removing the thermal oxide film 5 during the high-temperature heat treatment, and as shown in FIG. 1C, a tetramethylammonium hydroxide (TMAH) solution or the like is used. A second step of etching the surface silicon active layer 3 using an etchant and etching a pinhole defect 4 in the oxide film 2 embedded in the silicon substrate 1; and a step generated by etching due to the pinhole defect. And a third step of evaluating the presence / absence and density of the etched pits and the distribution in the substrate surface using an optical microscope or the like.

First, in the first step, as an isotropic etching method for removing the thermal oxide film formed on the surface of the SIMOX substrate, it is preferable to perform washing with an aqueous solution having an HF concentration of 5 to 10% for several minutes.

Next, in the second step, an etching liquid having a high etching rate for silicon and a low etching rate for an oxide film is used as a silicon etching liquid. That is, a known alkaline solution capable of anisotropic etching can be used. However, for example, in the case of etching with a commonly used KOH solution, the etching rate for silicon is too fast, and it may not be possible to evaluate a silicon active layer of a SIMOX substrate having a thickness of at most 1000 ° or less. Is slower than the KOH solution and the etching rate for silicon is moderately high, which is optimal for the purpose of the present invention.

As an etching method using a TMAH solution, it is desirable to perform etching by warming an aqueous solution having a TMAH concentration of 2 to 15% to a temperature of 50 to 80 ° C. Also,
The etching time varies depending on the thickness of the surface silicon layer and the thickness of the buried oxide film, but in a short time of several seconds to several minutes, it is possible to form an etch pit that can be detected by an optical microscope or the like performed in the subsequent third step. it can.

Hereinafter, the etching action by the TMAH solution will be described. FIG. 2A shows the etching amount of silicon depending on the difference in TMAH solution concentration when the etching temperature is 70 ° C. FIG. 2B shows TMAH when the etching temperature is 70 ° C.
The amount of etching of the oxide film due to the difference in the liquid concentration is shown. TMA
The etching effect by the H solution has a peak when the TMAH concentration is 5%, which indicates that the etching amount is the largest. Therefore, the concentration of the TMAH aqueous solution is 2 to 15%.
Is preferred.

FIG. 3A shows an etching amount of silicon depending on a difference in etching temperature when the TMAH concentration is 5%. FIG. 3B shows the etching amount of the oxide film depending on the difference in the etching temperature when the TMAH concentration is 5%. Regarding the etching temperature, as the temperature increases, the amount of etching tends to increase. However, if the temperature is too high, the concentration of the TMAH solution changes due to evaporation of water, and the etching rate may be reduced. It is considered that a temperature range of 50 to 80 ° C. is optimal for performing the etching process.

In short, the feature of the etching with the TMAH solution is that the etching amount of silicon is several thousand times faster than the etching amount of the oxide film from the graphs of the etching rates of the silicon and the oxide film shown in FIGS. It can be seen that this is an etching method using a liquid.

As shown in FIG. 1, the pinhole defect 4 itself is in a silicon state in which oxygen is not ion-implanted and a buried oxide film is not formed, and the pinhole defect 4 is etched by using a TMAH solution. A region where the surface silicon active layer 3 and the buried oxide film 2 are not formed is etched to form an etch pit 6, which can be observed as a pinhole defect.

Next, as a third step, the occurrence of pinhole defects on the entire surface of the SIMOX wafer substrate can be evaluated by measuring the etch pits formed in a pinhole shape using an optical microscope or the like. . In addition to the above evaluation means, AFM (Atomic Force Mic)
Scope), SEM (Scanning Ele)
ctron Microscope).

[0026]

EXAMPLES Example 1 A sample was 4 inch silicon p pulled up by the CZ method.
A <100> wafer was used. Initial oxygen concentration is 13 × 1
0 ¹⁷ atoms / cm ³ , and specific resistance is 5Ω · cm.
Oxygen ions at a dose of 2 × 10 ¹⁷ / cm ² are implanted into the sample at an implantation energy of 30 keV and a substrate temperature of 500 ° C., and then heat treatment is performed at 1300 ° C. for 6 hours in an extremely diluted O ₂ / N ₂ mixed gas atmosphere. Then, a buried oxide film was formed in a silicon substrate to obtain a SIMOX substrate.

At the time of ion implantation, a pinhole defect according to the present invention is detected by using a SIMOX substrate in which a region (pinhole defect) in which a buried oxide film is not formed due to the influence of particles or the like adhering to the substrate surface has occurred. The presence or absence of a pinhole defect was confirmed by a defect evaluation method using an optical microscope and an AFM.

First, since a heat treatment is performed in a diluted oxidizing atmosphere, a thermal oxide film having a thickness of several hundreds of mm is formed on the surface of the substrate. The film was removed. Thereafter, an aqueous solution having a TMAH solution concentration of 5% was heated to 70 ° C. and etched for 1 minute to prepare a sample for evaluating pinhole defects.

As shown in FIG. 4A, etch pits were detected in a micrograph taken with an optical microscope of 800 times, and the density was 5.6 × 10 ⁵ / cm ² .

Next, A was used to confirm that the etch pits detected by the optical microscope were pinhole-shaped defects.
When the pit shape was observed using FM, as shown in FIG. 4B, it was confirmed that the defect was a pinhole defect. A
In the case of FM evaluation, even if the pinhole is linear, it seems like a V-shape because it cannot enter the bottom of the pinhole due to the size of the measuring needle, but it is actually concave. It can be guessed.

Therefore, the effectiveness of the pinhole defect evaluation in the buried oxide film according to the present invention using the TMAH solution was confirmed.

Example 2 A sample was a 4-inch silicon p raised by the CZ method.
A <100> wafer was used. Initial oxygen concentration is 14 × 1
0 ¹⁷ atoms / cm ³ and a specific resistance of 10 Ω · cm. Oxygen ions at a dose of 3 × 10 ¹⁷ / cm ² are implanted into this sample at an energy of 40 keV and a substrate temperature of 470 ° C.
At 1300 ° C. × 6 hours for extreme dilution O ₂ /
Heat treatment was performed in an N ₂ mixed gas atmosphere to form a buried oxide film in the silicon substrate, thereby obtaining a SIMOX substrate.

First, in order to remove the thermal oxide film, the substrate was washed with an aqueous solution having a HF concentration of 10% for 5 minutes, and then heated at 70 ° C. with an aqueous solution having a TMAH concentration of 5%, etched for 1 minute, and evaluated for pinhole defects. Made a sample.

For the evaluation, the pinhole density on the entire surface of the substrate was measured with an optical microscope of 800 times. As shown in FIG. 5A, FIG. 5B is a graph in which the scanning is performed in the X-axis and Y-axis directions with the orientation flat of the wafer down, and the pinhole defect density is measured.

It was found that there was no difference in defect density in the substrate plane in the X-axis (open circle) direction, whereas the defect density was low in the outer peripheral portion of the substrate in the Y-axis (black circle) direction. The evaluation using the TMAH solution according to the present invention and the evaluation of pinhole defects in the buried oxide film performed by an optical microscope are as follows.
A wide range of information on the entire surface of the substrate could be easily obtained.

[0036]

According to the defect evaluation method of the present invention, the distribution of pinhole defects present in a buried oxide film in a semiconductor substrate obtained by a method of forming a buried oxide film inside a silicon substrate by an ion implantation method is compared with that of silicon. Using an etching solution with a high etching rate,
By generating and detecting the etch pit caused by the pinhole defect, it is possible to easily and quickly detect the entire surface of the substrate over a wide area,
This is extremely effective as an evaluation means for developing high quality semiconductor substrates.

[Brief description of the drawings]

FIG. 1A is a cross-sectional explanatory view showing a SIMOX substrate,
7B and 7C are cross-sectional explanatory views showing a defect evaluation step.

FIG. 2A is a graph showing the relationship between the concentration of a TMAH solution and the etching amount of silicon, and FIG. 2B is a graph showing the relationship between the concentration of a TMAH solution and the etching amount of an oxide film.

3A is a graph showing a relationship between an etching temperature of a TMAH solution and an etching amount of silicon, and FIG.
4 is a graph showing a relationship between an etching temperature of an H solution and an etching amount of an oxide film.

FIG. 4A is a traced photograph of an optical microscope showing pinhole defect detection in Example 1, and FIG.
It is the figure which traced the photograph of M.

FIG. 5A is an explanatory top view of a wafer showing a scanning direction of the wafer in Example 2, and FIG. 5B is a graph showing a result of evaluation of a pinhole defect density, showing a relationship between a distance from an edge and an etch pit density. It is.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 buried oxide film 3 surface silicon active layer 4 pinhole defect 5 thermal oxide film 6 etch pit

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Nobuo Okumura, Inventor No. 4-33, Kitahama, Chuo-ku, Osaka City, Osaka Prefecture F-term (reference) 2G051 AA51 AB04 CA11 CB01 CB05 DA07 4M106 AA07 AA13 AB16 AB17 BA12 CA45 CB20 5F032 AA03 AA28 DA43

Claims (4)

[Claims] 1. A semiconductor substrate defect evaluation method for detecting and evaluating pinhole defects generated in a buried oxide film in a substrate having a buried oxide film formed in a silicon substrate by oxygen ion implantation and high-temperature annealing. A step of removing a thermal oxide film on a substrate surface, a step of etching and removing a silicon layer of a surface layer of the substrate and a silicon part of a pinhole defect, and a step of detecting an etch pit generated by the etching. Substrate defect evaluation method. 2. The semiconductor substrate according to claim 1, wherein an HF solution is used in the step of removing the thermal oxide film, and an etching solution having a high etching rate for silicon and a low etching rate for the oxide film is used as a silicon etching solution. Defect evaluation method. 3. The method according to claim 2, wherein an etching process is performed using an alkaline solution as a silicon etching solution. 4. The defect of a semiconductor substrate according to claim 2, wherein a tetramethylammonium hydroxide solution is used as an etching solution for silicon, the concentration of the solution is 2 to 15%, and the temperature of the solution is 50 to 80 ° C. Evaluation method.