JPH06160063A - Method for inspecting surface - Google Patents

Abstract

PURPOSE:To provide a method with high reliability for inspecting the surface of a specimen. CONSTITUTION:A method for inspecting a surface consists of a first process for enlarging the surface of a specimen 1 with a microscope 2, a second process for converting an enlarged image into an electric signal, a third process for judging a defect by only a specific signal out of the electric signals and a fourth process for counting the judged defects. The first process serves to enlarge the surface of the specimen 1 at a position where a reference coordinate axis and the direction of a crystal axis of the specimen 1 have certain relation and the third process gives service to judge the defect by only the electric signal having a certain direction and a certain length or more on the reference coordinate axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a surface defect of a sample such as a silicon wafer.

[0002]

2. Description of the Related Art For example, silicon having a face-centered cubic structure
After performing a heat treatment on the wafer in an oxygen atmosphere at 1100 ° C., a light etching process is performed.
g) When etching is performed with the liquid, etch pits as shown in FIG. 5 are observed with a microscope. A wafer having a smaller areal density of the etch pits has a higher quality, which is one item in the shipping inspection.

In the conventional visual inspection, the visual acuity of the measurer is deteriorated and the fatigue is increased. Therefore, there are problems that the inspection cost is large and the individual error is large. Therefore, in recent years, automatic inspection devices have come to be used.

A schematic structure of an automatic inspection apparatus for carrying out a conventional surface inspection method will be described with reference to FIG. The sample 1 is set on the sample stage 3 of the microscope 2, and an enlarged image of the sample surface is converted into an electric signal using the television camera 4.

Electric signals corresponding to these images are stored in the frame memory 5. Then, the image calculation processing device 6 performs image processing such as binarization based on the shading, and extracts the portion of the dark area as a surface defect.

The frame memory 5 and the image calculation processing device 6 constitute a so-called image processing device 7. The system computer 8 controls the image processing device 7 and the stage controller 9.

According to this method, dust (arrow 11 in FIG. 5) attached to the surface of the sample during etching of the sample is also measured as a defect corresponding to the quality of the sample, or two defects are in contact with each other (see FIG. 5 arrow 12), 1
The reliability of the inspection result is low because it is measured as one defect.

[0008]

SUMMARY OF THE INVENTION
It is to obtain a highly reliable surface inspection method for a sample such as a wafer.

[0009]

A surface inspection method according to the present invention includes a first step of enlarging a sample surface with a microscope, a second step of converting the enlarged image into an electric signal, and specifying one of the electric signals. And a fourth step of counting the determined defects. The first step is a step of enlarging the sample surface at a position where the reference coordinate axis and the crystal axis direction of the sample maintain a constant relationship. The third step is a determination step of determining only an electric signal having a certain direction with respect to the reference coordinate axis and having a certain length or more as a defect.

[0010]

Function: A sample having a crystal structure such as a semiconductor (for example, Si
On the surface of a wafer, a GaAs wafer, etc.), surface defects such as etch pitch corresponding to quality appear as lines parallel to the specific crystal axis direction. Therefore, in the case of image processing of an image obtained by enlarging it with a microscope etc. and converting the electrical signal with a television camera, in order to determine in which crystal axis direction of the sample the linear defect shown in the image is long, And the reference coordinate axis of the image accumulated for image processing are made to coincide with each other.

Usually, in a sample having a crystal structure, the specific crystal axis direction determined by the x-ray diffraction method or the like can be determined from the sample shape or the mark on the sample surface. Therefore, based on the shape or mark, the sample stage is rotated, the television camera is rotated with respect to the optical axis so that the reference coordinate axis matches the specific crystal axis direction of the sample, and the image once accumulated There is also a device for coordinate conversion.

[0012]

EXAMPLES Examples of the surface inspection method of the present invention will be described with reference to FIGS.

FIG. 1 shows a schematic configuration of an apparatus for carrying out the method of the present invention. In FIG. 1, the same reference numerals as those in FIG. 6 indicate the same parts or devices.

A sample 1 obtained by etching a (001) plane silicon wafer subjected to heat treatment in an oxygen atmosphere at 1100 ° C. with a light etching solution will be described.

On the silicon wafer, an orientation flat 13 (FIG. 2) is formed parallel to the [110] direction determined by the x-ray diffraction method during processing.

This orientation flat 13 is used for the television camera 4
The image is picked up and stored as an image. The rotary stage 14 is controlled by the rotary stage controller 10 so that the image of the orientation flat 13 becomes the reference coordinate axis (x axis) of the image. It may be controlled manually.

After that, by controlling the XY stage 15,
Image of the surface of a given sample magnified with the microscope 2 (approximately 200x)
Is converted into an electric signal by the television camera 2 and stored as an image in the frame memory 5.

FIG. 3 shows the change in the image. In the figure, (a) shows an image when the crystal axis direction and the reference coordinate axis of the image are not aligned. A and B are defects to be measured, and C and D are mere dust, and therefore should not be measured originally.

FIG. 2B shows an image in which the crystal axis direction is aligned with the reference coordinate axis (x axis) of the image. Y for each defect
The length in the axial direction is measured, and if the length is a certain length or more, it is determined as "0", and if not, "x" is determined. Therefore, in this case, if B and B ′ have a certain length or more, it is determined as a defect.

FIG. 3C shows an image obtained by rotating the reference coordinate axis by 90 °. In this case, if A and A ′ have a certain length or more, it is determined as a defect.

In FIGS. (B) and (c), the defects judged by the combination of "0" and "x" are in the [110] direction or [11] direction.
[0] is a line extending perpendicularly and is a defect to be measured. Therefore, only A and B are measured as defects, and C and D are not measured.

If the defects are in contact with each other (for example,
A'and B '), when the reference coordinate axis and the [110] direction are matched before performing the above-described defect determination, as shown in FIG. 4, when the reference coordinate axis direction shrinks more than the width of the defect image. , Defects A, C, D and A ′ remain. Next, when the reference coordinate axis is rotated by 90 ° and similarly contracted, defects B, C, and
D and B'remain. By comparing the two, it becomes possible to treat A'and B'which were in contact with each other as separate defects,
If the defect is determined by the above-mentioned method, A, A ', B, B'
Can be determined as a defect.

These image processes are performed by the image calculation processing device 6
And the system computer 8.

In the case of a (111) plane silicon wafer,
The linear defects corresponding to the quality are 60 ° from each other as shown in FIG.
It extends to the corner. One of the linear defects is
Since it appears in parallel with the orientation flat in the [110] direction, the rotary stage is controlled so that the orientation flat image becomes the reference coordinate axis (x axis) of the image, and the length of each defect in the x axis direction is measured to obtain a certain value or more. Those with a length are counted as defects. Next, the reference coordinate axes are rotated by 60 ° and the same image processing as described above is performed, whereby the defects E, F, and G can be measured separately from dust and scratches.

[0025]

EFFECTS OF THE INVENTION According to the present invention, irregular dust adhered during etching of a silicon wafer or the like and scratches (mechanically generated) that do not directly correspond to the quality are easily determined and excluded from measurement. It will be possible. Further, even if two defects are connected, they can be measured separately, so that highly reliable inspection results can be obtained and the inspection cost can be reduced. Since the accuracy of distinguishing dust and the like is high, clean room equipment is not required and the inspection cost can be further reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view of an apparatus for carrying out the method of the present invention.

FIG. 2 is an explanatory diagram of the shape of a silicon wafer.

FIG. 3 is an explanatory diagram showing an example of image processing.

FIG. 4 is an illustration showing a pre-process when defects are in contact with each other.

FIG. 5 is an explanatory diagram of an image of (111) plane silicon wafer surface etch pits.

FIG. 6 is an explanatory diagram of a microscope image of a silicon wafer surface etch pit.

FIG. 7 is a schematic configuration explanatory diagram of an apparatus for performing a conventional surface inspection method.

[Explanation of symbols]

1: Sample 2: Microscope 3: Sample Stage 4: Television Camera 7: Image Processing Device 14: Rotating Stage 15: XY Stage

Claims (1)

[Claims] 1. A first step of enlarging a sample surface with a microscope, a second step of converting the enlarged image into an electric signal, and a third step of judging only a specific signal of the electric signal as a defect. In the surface inspection method having a fourth step of counting the determined defects, the first step is a step of enlarging the sample surface at a position where the reference coordinate axis and the crystal axis direction of the sample maintain a constant relationship. 3. The surface inspection method, wherein the three steps are determination steps of determining only an electric signal having a certain direction with respect to the reference coordinate axis and having a certain length or more as a defect.