JPH0376244A - Instrumentation of etch pit - Google Patents

Abstract

PURPOSE:To measure etch pits using optical interference even when the contrast between the etch bits and a background is low by a method wherein the amount of the features of the etch pits is measured from image data on a sample obtained by a shearing interference method. CONSTITUTION:Light which is passed through a sample is first divided into two by a shearing type interference microscope 2 with shift of a shearing amount S to form an interference image. This sample 1 is one formed by irradiating protons having various energies and various incident angle. A biimage which is the feature of a shearing interference is seen and the structure of interference fringes can be seen. The major axis, minor axis and central position of the outermost interference fringe, the central position of the innermost interference fringe, the number of the interference fringes and the like are measured. From the instrumentation of these, the calculation of etch pits is performed. Whether a measurement of the etch pits ends or not is checked and the measurement is repeated until a prescribed measurement ends. When the prescribed measurement ends, these data are processed and are outputted to a printer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring etch pits, and particularly to a method for measuring etch pits that have a low contrast with the background.

[Conventional technology]

When a semiconductor wafer is corroded with chemicals and observed under a microscope, many spots are seen.These spots are called etch pits and represent dislocations in the crystal.

For semiconductor-based silicon (crystalline) wafers, any number of etch bits is evaluated as a defect, and only etch pits with a certain density or less are adopted.

Furthermore, when a special film is exposed to radiation and subjected to a chemical etching process, radiation tracks appear as spots, which are also called etch pits and are used to measure radiation dose.

When measuring the above-mentioned etch pits, if noise and the like are present, it is necessary to distinguish between this background noise and the etch pits. Conventionally, etch pits on a sample are magnified using an optical microscope, photographed using a TV camera, and after performing some kind of image processing on the resulting grayscale image, a certain threshold is determined to create a binary image and extracted as etch pits. things were being done.

[Problem to be solved by the invention]

By the way, when automatic measurement is performed by a machine using such a method, it becomes difficult to determine etch pits.

For example, in the case of radiation measurement, the conventional method of binarizing a grayscale image is based on the contrast of the image (
It is necessary that the light intensity ratio (light intensity ratio between the track portion and the background portion) be high. Heavy particles, α particles, etc. have a large energy loss in the film, and therefore the track depth is deep and the image contrast is high, so image analysis is relatively easy. On the other hand, since protons having an energy of MeV or more have a small energy loss, the etch pits are shallow and the image contrast is reduced.

For example, a proton etch pit of several MeV has a diameter of 1
The depth is only several μm compared to about 0 μm, and it is extremely difficult to distinguish it from the bank ground. Therefore, information in the depth direction is required to extract etch pits. Depth information 2
One way to obtain this on a dimensional screen is to utilize the fact that the light transmittance is different between etch pits and noise tracks.

However, since the light transmittance depends on the etch pit shape and surface condition, it is difficult to determine the relationship between the depth and the transmittance.

An object of the present invention is to provide an etch pit measurement method that uses optical interference to measure etch pits even when the contrast between the etch focus and the background is low.

[Means to solve the problem]

In order to achieve the above object, etch pits may be identified from the background using shearing interferometry, and the etch pit measurement method of the present invention is based on image data of a sample obtained by shearing interferometry. It is characterized by measuring the feature quantity of. Also,
A first image is constructed by displacing the light that has passed through or reflected from the sample by a predetermined shearing amount, a binary image is created from the first image by determining a certain threshold, and this binary image is subjected to hole filling processing. A second image is created, a third image is created by edge-emphasizing the third image, a fourth image is created by ANDing this third image and the second image, and on this fourth image, A fifth image may be created by a logical product of mutual images separated by a distance corresponding to the predetermined shearing amount, and the characteristic amount of the etch pit may be measured from this fifth image.
It is preferable that the second image and the third image are created after performing a repair process on the first image according to the shape of the interference fringes of the value image.

[For production]

The light that has passed through or reflected from the sample is shifted by a predetermined amount of shearing, producing interference fringes, and one etch pit becomes two images (twin images) separated by the amount of shearing, and the first image consisting of these twin images is Form. The feature amount of the etch pit is extracted from this image. Furthermore, this first
The image is converted into a binary image using a certain threshold value. This 2
A second image is obtained by filling in each etch pit of the value image (processing to fill in the inside of the etch bit).

Taking advantage of the fact that deep etch pits produce multiple rings due to interference, a third image is created in which the edges of the image are emphasized by applying Laplace transform and differential processing to the first image, which is the original image.
An image is created, a logical AND is performed with the second image that has been subjected to hole-filling processing, and the third image having a plurality of rings within the area of the second image is determined as the fourth image. In the fourth image, when the two images with the shearing equivalent amount are logically ANDed, each etch pit in the binary image returns to the original single image in the fifth image. The specific amount of etch pits can be extracted from this fifth drawing image. In this way, by using the shearing interferometry, even shallow etch pits can be easily identified mechanically, and automatic measurement becomes possible.

Furthermore, some rings may not be completed because the image is unclear in the binary image. In such a case, repair processing is performed on the first hundred images, the ring is repaired and filled, and then the holes are filled in to create a second image, the edges are emphasized, and the third image is created. create. In addition,
Repair treatments include fleshing (D I LATE) and erosion (
ERO3I 0-N) or 5TRETCI
(), thinning (THI NN I G>) is known. Thinning is to expand the image by a preset number of pixels, and if a small portion of the ring is missing, thinning is done from both sides. After filling in the holes, if you erode (make the image thinner) by the number of pixels set during fleshing, the filled part will remain as it is, and the outer diameter of the ring will become smaller. Return to the original second image.Alternatively, you can perform line stretching processing.Line stretching processing recognizes that the image is a line from the ratio of width and length, and stretches it by a certain small length in the line direction. This is a method of repair by crossing over.

Alternatively, it can also be obtained by performing a thinning process to thin the image and making it into a skeleton, and then stretching the ends of the skeletonized image by a certain small length and making them intersect.

Here, an example of a known shearing method will be explained using FIGS. 7, 8, and 8.

FIG. 7 shows a shearing device equipped with transmission and reflection devices, and FIG. 8 shows interference fringes generated in this device. In FIG. 7, 31 to 39 constitute a transmission system, and 36
-39 and 46-49 constitute a reflection system, and 40-45 constitute an interference system.

In the transmission system, light emitted from a light source 31 passes through a convex lens 32, is reflected by a mirror 33, and passes through a slit 34. It passes through the condenser lens 35, becomes a parallel beam of light, passes through the sample 36, is deformed, becomes an object wave 37, and passes through the objective lens 38. half mirror 3
9 and enters the interference system. In the reflection system, the light emitted from the light source 46 passes through a convex lens 47 and passes through a slit 48. condenser lens 49
The beam is reflected by a half mirror 39, enters an objective lens 38, is reflected and deformed by a sample 36, becomes an object wave 37, and enters an interference system via an objective lens 38 again.

In the interference system, there are two courses, A and B.

The light flux entering the A course is reflected by a mirror 41, further reflected by a half mirror 42, and then passes through an eyepiece lens 43 and enters the observer's eye.

The light entering the B course is reflected by the mirror 44, given shear (S) by the shear ring 45, and then transferred to the half mirror 42.
The light passes through the eyepiece lens 43 and enters the observer's eye. 8th
The interference image visible to the observer will be explained using figures.

Figure 8(a) shows the object wave 3 from courses A and B that enters the i sound measurement eye after passing through the transmission system and entering the interference system.
This shows the situation in No.7. B deviates from A by shear S.

Figure 8 (b) shows the interference fringes in Figure 8 (a). Image A, which is fixed without moving (does not receive shear), is an interference image in the same format as a general interference microscope; (S) The processed B image has the opposite displacement of interference fringes.

Here, S is the shear amount, D is the interval between interference fringes, and d is the deviation of the interference fringes due to the sample 36, and λ is the wavelength of the light from the light source 31.
Then, in the case of a transmission system, the relational expression (n-N) ・Z# λ---(1) holds true.

Here, n is the refractive index of the sample 36, N is the refractive index of the surroundings, and if it is in air, N-1, and Z is the thickness of the sample. Therefore, the thickness Z of the sample can be obtained from equation (1).

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

FIG. 1 is a block diagram of an apparatus implementing this embodiment.

In FIG. 1, reference numeral 1 indicates a sample to be measured, and in this example, it is a film that has been chemically etched after being irradiated with radiation and has etch pits. 2 is a shearing-type interference microscope, 3 is a TV camera that takes out images obtained by the interference microscope, 4 is a focus control unit that adjusts the focus of the microscope 2, and 5 is an X of the sample 1 placed on the interference microscope 2. -Y
A position control unit that adjusts the position on a plane; 6 is a TV camera 3;
7 is a monitor CRT, 8 is a printer, 9 is a disk, 10 is a digitizer, and 11 is a keyboard.

Next, the operation will be explained.

FIG. 2 is a measurement flowchart. Sample 1 is species 1.・
Since there are a wide variety of types, shapes, dimensions, etc., we first measure the contours macroscopically and then determine the microscopic measurement points.

In step 20, measurement conditions such as sample type and measurement point spacing are input. In step 21, the sample 1 is set on the interference microscope 2. In step 22, constants such as threshold values are determined when performing binarization processing.

In step 23, macro measurement is performed to measure the overall shape of sample 1, and in step 24, the contour point positions of sample 1 are determined,
In step 25, measurement points are determined. Based on this measurement point, the position mm section 5 sets the measurement position of the sample 1. Step 2
After adjusting the focus of the ξ-cro measurement position by the focus control unit 4 in step 6, micro measurement begins.

First, the light after passing through the sample 1 is shifted by a shearing amount S using a shearing type interference microscope 2 and divided into two parts to create an interference image. FIG. 3 shows an example of an interference image.

This sample 1 was made by being irradiated with protons having various energies and various incident angles.

A twin image, which is a characteristic of shearing interference, can be seen, and the structure of the interference fringes can be seen. The image indicated by the arrow a has interference fringes and is therefore treated as an etch pit, and the image indicated by the arrow where no interference fringes are clearly recognized even though it is the same size is treated as a background.

FIG. 4 shows a binarized image obtained by binarizing the above-mentioned shearing interference image. Although it is a twin image, the background has been removed and the etch pits are clearly visible. Figure 5 shows the final image in which the twin images have been combined into one image by the processing described in the [Function] section, and the major and minor axes of the outermost interference fringes are determined from this final image.

The center position, the center position of the innermost interference fringe (corresponds to the pit position, from which the flying direction is determined), the number of interference fringes, etc. are measured. Based on these measurements, the etch pits are calculated in step 27. In step 28, check whether the measurement is completed or not.
7. When the predetermined measurements are completed, these data are processed in step 29 and output to a printer in step 30.

In addition, as shown in Figure 6 a, b, and c, actual interference fringes may be cut off in the middle or come into contact with adjacent ones, and even such incomplete interference fringes cannot be filled out, eroded, or stretched. , Correct measurement values can be obtained by repair processing such as line thinning.

The above is an example of a method of measuring interference fringes using transmitted light, but in the case of etch pits in crystals, reflected light is used to generate shearing interference fringes of etch bits.
It can be measured in the same way as in the case of transmitted light.

By the way, there are several types of interference microscopes. A commonly used method, such as the Matsuhatsuender method or the Twyman method, is to place a sample on one side of two optical paths and cause the object beam passing therethrough to interfere with the reference beam passing through the other optical path. However, these methods are susceptible to mechanical vibrations, and the interference fringes are affected by local thickness changes in the sample. On the other hand, the shearing method divides the light after passing through the sample into two optical paths and shifts the two images to cause them to interfere.

Therefore, the effect of vibration acts equally on the two light beams, and has little effect on interference.Also, although the shearing method uses mutual interference between object waves, there is a local thickness change that is larger than the amount of shearing. However, if the gradient of the thickness change is gentle, the effect is small.As a disadvantage, due to the nature of shearing interference, twin images appear, but this can be eliminated by the image processing described in the present invention.

〔Effect of the invention〕

As is clear from the above, according to the present invention, by using the shearing interference method, it is possible to analyze etch bits with low contrast with the background, and by solving the twin images generated by the shearing interference method using image processing technology. It becomes possible to measure the feature amount of the etch bit.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a device implementing an embodiment of the present invention, FIG. 2 is a flowchart of this embodiment, FIGS. 3 to 6 are diagrams showing analysis results of this embodiment, and FIG. 7 is a diagram showing the analysis results of this embodiment. FIG. 8 is a diagram showing an example of a known shearing interference device, and FIG. 8 is a diagram showing an example of interference fringes obtained by the device of FIG. 1--One sample 2-m-Shearing interference microscope 3=-
TV camera 4-m-focus control unit 5, -position control unit 6----image analysis device 7---monitor CRT 8
-11 Printer 9---Disk 10-M-Digitizer 11---Keyboard

Claims (3)

[Claims] (1) A method for measuring etch pits, characterized by measuring the characteristic amount of etch pits from image data of a sample obtained by shearing interferometry. (2) Create a first image by displacing the light that has passed through or reflected from the sample by a predetermined amount of shearing, set a certain threshold value, create a binary image from the first image, and create a binary image from the first image. A second image is created by performing hole-filling processing, a third image is created by emphasizing the edges of the first image, a fourth image is created by ANDing this third image and the second image, and this fourth image is 2. A fifth image is created by logical producting of mutual images separated by a distance corresponding to the predetermined shearing amount on the image, and the characteristic amount of the etch pit is measured from this fifth image. How to measure etch pits. (3) The etch pit according to claim 2, wherein the second image and the third image are created after performing a repair process on the first image according to the shape of interference fringes of the binary image. Measurement method.