JPH09199558A - Method for measuring surface oxygen concentration of semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely measure the surface oxygen concentration of a silicon wafer in a short time, by forming a dent on a substrate surface, heat-treating the substrate, measuring the moving distance of dislocation from the dent which is made distinctive by defect selective etching, and estimating the oxygen concentration from the relation between the oxygen concentration and the dislocation moving distance. SOLUTION: After a dent is formed on the surface of a semiconductor substrate by a load of 1-2000g, the substrate is heat-treated at 600-1000 deg.C for 1-60 minutes. By performing defect selective etching to be 0.1-30μm deep, dislocation generated during the heat treatment is made distinctive, and the moving distance of the dislocation from the dent is measured. The surface oxygen concentration of the substrate is estimated from the relation between the previously set oxygen concentration and the dislocation moving distance. For example, dent formation, heat treatment and defect selective etching are previously performed for various kinds of silicon wafers different in oxygen concentration, and the moving distances of the dislocations from the dents are measured. Thereby the relation, shown in figure, between known oxygen concentrations and measured dislocation moving distances is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the surface oxygen concentration of a semiconductor substrate used as a substrate for an LSI or the like, in which an indentation is provided on the substrate surface for heat treatment, and then dislocation is revealed by defect selective etching. The present invention relates to a method for measuring the surface oxygen concentration of a semiconductor substrate, which can be easily measured in a short time by estimating the oxygen concentration from the moving distance from the indentation.

[0002]

2. Description of the Related Art In a semiconductor crystal such as silicon, oxygen mixed from a crucible during crystal growth exists as interstitial oxygen. This interstitial oxygen is precipitated in the crystal as an oxygen precipitate in a device manufacturing process such as LSI and affects the device characteristics. Therefore, it is very important to understand the oxygen concentration.

To measure the oxygen concentration of a silicon wafer,
In general, infrared absorption methods such as FT-IR are used (Koma et al., "Physical properties and evaluation methods of silicon" (Maruzen) 19
87). However, since this method determines the oxygen concentration from the wafer transmitted light spectrum, it was impossible to determine the oxygen concentration only in the surface layer of the crystal. Therefore, for example, it is difficult to measure the oxygen concentration of only the outer diffusion layer generated during the crystal heat treatment.

Another method for measuring the surface oxygen concentration is secondary ion mass spectrometry (Secondary Ion M).
Ass Spectrometry; hereinafter abbreviated as SIMS) (above-mentioned "Physical properties and evaluation method of silicon" 198)
7). This method is indispensable for the evaluation of semiconductor materials because it enables highly accurate elemental analysis in the depth direction of the wafer. However, because the sputtering phenomenon at the atomic level is used,
There is a drawback that measurement on the order takes a considerable amount of time.

[0005]

As described above, the conventional infrared absorption method cannot determine the oxygen concentration of only the μm-order surface layer of a silicon wafer, and SIMS requires a considerable amount of time. was there.

The present invention has been made in view of the current state of the conventional method described above.
An object of the present invention is to provide a method for measuring the surface oxygen concentration of a semiconductor substrate, which enables accurate measurement of the surface oxygen concentration of a silicon wafer in a short time.

[0007]

Means for Solving the Problems The inventors have proposed a measuring method capable of easily obtaining the oxygen concentration of only a μm-order surface layer of a silicon wafer in a short time.
As a result of various examinations, heat treatment was performed by providing an indentation on the substrate surface
After that, it was found that it is possible to estimate the oxygen concentration from the relationship between the oxygen concentration and the dislocation migration distance by measuring the migration distance from the indentation of dislocations revealed by defect selective etching.
The present invention has been completed.

That is, according to the present invention, after indenting the surface of the semiconductor substrate with a load of 1 to 2000 g, the temperature of 600.degree.
The heat treatment at 1000 ° C. is performed for 1 to 60 minutes, the defect selective etching is performed at 0.1 μm to 30 μm to reveal the dislocations generated during the heat treatment, and the moving distance from the dislocation indentation is measured.
This is a method for measuring the surface oxygen concentration of a semiconductor substrate, in which the surface oxygen concentration of the substrate is estimated from the relationship between the preset oxygen concentration and the dislocation movement distance.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The method for measuring surface oxygen concentration according to the present invention is as follows. First, as shown in the flow chart of FIG.
Make an impression with a load of ~ 2000g. The load must be 1 g or more to apply sufficient stress for dislocation generation.
Since a wafer will crack under a load of more than 00g,
It is 1 to 2000 g.

After making the indentation, heat treatment is performed in a furnace at 600 ° C. to 1000 ° C. for 1 to 60 minutes. Heat treatment temperature is 600
If the temperature is lower than ℃ and the processing time is less than 1 minute, dislocations cannot move sufficiently, and if the temperature exceeds 1000 ° C. and the processing time exceeds 60 minutes, outward diffusion of oxygen from the wafer surface occurs during measurement. Since the accurate measurement cannot be performed, the heat treatment temperature is 600 ° C. to 1000 ° C. and the treatment time is 1 to 60 minutes.

Following the heat treatment, dislocations are revealed by defect selective etching of 0.1 to 30 μm. further,
The migration distance of the dislocation from the indentation is measured with an optical microscope. If the defect selective etching depth is less than 0.1 μm, it is difficult to observe with an optical microscope, and dislocations are at most 3 from the surface.
Since the region having a depth of 0 μm is moved, it is not necessary to perform the etching over 30 μm. Therefore, the etching depth is 0.1 to 30 μm.
m.

The present invention is characterized in that the oxygen concentration is obtained from the distance traveled from the dislocation indentation. Therefore, various silicon wafers having different oxygen concentrations are subjected to the above-mentioned indentation, heat treatment, and defect selective etching. It is necessary to perform each of them, measure the moving distance of the dislocation from the indentation, and obtain the relationship between the known oxygen concentration and the measured dislocation moving distance. The relationship between the oxygen concentration and the dislocation movement distance is shown in FIG.

As is clear from FIG. 2, it is understood that the dislocation migration distance becomes shorter as the oxygen concentration in the wafer becomes higher. From the relationship between the oxygen concentration and the dislocation movement distance, the oxygen concentration of a silicon wafer having an unknown oxygen concentration can be easily known.

[0014]

【Example】

Example 1 The oxygen concentration of a silicon wafer whose oxygen concentration is unknown was measured using the measuring method according to the present invention. First, the surface of the wafer was indented with a Vickers hardness meter under a load of 100 g. Next, heat treatment was performed for 30 minutes in a furnace at 900 ° C. The loading and unloading to and from the furnace are performed at a boat speed (15c) so that defects due to thermal stress are not introduced into the silicon wafer.
m / min) and the wafer interval (20 mm). Subsequently, defect selective etching having a depth of 5 μm was performed.

Further, the dislocation movement distance was measured with an optical microscope. The state of dislocations spreading from the indentation is shown in FIG. The dislocation movement distance was measured and found to be 90 μm. From the relationship between oxygen concentration and dislocation migration distance obtained in FIG. 2, the surface oxygen concentration of this wafer was 11 × 10 ¹⁷ cm ⁻³ (old AS
TM).

When the surface oxygen concentration at the same location on the wafer was measured by SIMS, it was 11 × 10 ¹⁷ cm ^-3 (ol
d ASTM) and the same measurement results as the measurement method according to the present invention were obtained. Therefore, it can be understood that the oxygen concentration can be easily and accurately estimated from the conversion graph of FIG. 2 by measuring the dislocation movement distance with an optical microscope.

Example 2 Next, a comparison was made between SIMS and the measurement time of the method of the present invention. Table 1 shows the measurement time when 100 points on the wafer surface were measured to a depth of 10 μm. It can be seen that the measuring method according to the present invention can significantly reduce the measuring time as compared with SIMS.

[0018]

[Table 1]

[0019]

According to the present invention, it is possible to obtain the oxygen concentration of only the surface layer of the μm order in a silicon wafer.
The conventional infrared absorption method is not possible, and SIMS has a problem that it takes a considerable amount of time. However, as is clear from the examples, the oxygen concentration in the surface region of the semiconductor substrate can be accurately measured in a short time. Became.

[Brief description of drawings]

FIG. 1 is a flowchart showing steps of a method for measuring surface oxygen concentration of a semiconductor substrate according to the present invention.

FIG. 2 is a graph showing the relationship between oxygen concentration and dislocation movement distance.

FIG. 3 is an explanatory diagram tracing a micrograph showing a state of dislocations spreading from an indentation.

Claims (1)

[Claims] 1. A semiconductor substrate is indented with a load of 1 to 2000 g and then heat treated at 600 ° C. to 1000 ° C. for 1 to 60 minutes to perform defect selective etching of 0.1 μm to 0.1 μm.
The surface oxygen concentration of the semiconductor substrate is estimated by demonstrating the dislocation generated during the heat treatment by applying 30 μm, measuring the displacement distance of the dislocation from the indentation, and estimating the surface oxygen concentration of the substrate from the preset relationship between the oxygen concentration and the dislocation displacement distance. Concentration measurement method.