# US 5,703,685 A · Alignment method

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- Number: US 5,703,685 A
- Document ID: US5703685A
- Status: Granted
- Kind: A
- Application number: 08/508,879
- Filed: 1995-07-20
- Granted: 1997-12-30
- Earliest claimed: 1993-03-05
- Assignees: Kabushiki Kaisha Toshiba
- Inventors: Shinya Senda; Hiroshi Haraguchi
- Web page: https://patentgrep.com/patent/US5703685A

## CPC

- G03F 9/70: {for microlithography (measuring printed patterns for monitoring overlay G03F7/70633 or focus G03F7/70641; projection system adjustment G03F7/70258; position control G03F7/70775)}
- G03F 9/7065: {Production of alignment light, e.g. light source, control of coherence, polarization, pulse length, wavelength}
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

An alignment method is provided for determining a mark position by using any of a first method for determining a mark position with one of photodiodes for colors which shows a maximal contrast between a mark area and a non-mark area, a second method for determining a mark position by detecting mark positions with photodiodes for colors and taking an average for these positions and a third method for determining a mark position by determining a ratio for determining that mark position, through the photodiodes for colors, by using different contrast levels between a mark area and a non-mark area and a CCD color area sensor.

## Claims

### Claim 1

An alignment method for controlling an exposure position of a wafer comprising the steps of:
generating light having multiple wavelengths;
directing the light to the wafer through a filter;
directing a plurality of wavelengths of reflected light from the wafer to a CCD camera;
generating a wafer image by the CCD camera, the wafer image being composed of three colors;
transferring the wafer image as a video signal from the CCD camera to an image processing unit, the video signal being composed of three colors;
processing the wafer image from the image processing unit the video signal by a computer to establish the location of an alignment mark on the wafer utilizing a contrast between a portion of the wafer with the alignment mark and a portion of the wafer without the alignment mark; and
adjusting the position of the wafer to place the alignment mark in a predetermined position.

### Claim 2 (depends on 1)

The method of claim 1, wherein the processing step comprises the steps of:
establishing an intensity signal for each of the three colors from the plurality of wavelengths of reflected light, each intensity signal including a first portion corresponding to the reflected light from a portion of the wafer with the alignment mark and a second portion corresponding to the reflected light from a portion of the wafer without the alignment mark;
associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors from the plurality of wavelengths of reflected light;
establishing a maximum contrast signal by selecting from the three colors the contrast signal with the greatest magnitude; and
equating the position of the alignment mark with the position signal of the maximum contrast signal.

### Claim 3 (depends on 1)

The method of claim 1, wherein the processing step comprises the steps of:
establishing an intensity signal for each of the three colors from the plurality of wavelengths of reflected light, each intensity signal including a first portion corresponding to the reflected light from a portion of the wafer with the alignment mark and a second portion corresponding to the reflected light from a portion of the wafer without the alignment mark;
associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
averaging the position signals for each intensity signal together to establish an average position signal; and
equating the position of the alignment mark with the average position signal.

### Claim 4 (depends on 1)

The method of claim 1, wherein the processing step comprises the steps of:
establishing an intensity signal for each of the three colors from the plurality of wavelengths of reflected light, each intensity signal including a first portion corresponding to the reflected light from a portion of the wafer with the alignment mark and a second portion corresponding to the reflected light from a portion of the wafer without the alignment mark;
associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors from the plurality of wavelengths of reflected light;
establishing a weighted average of the position signals through a ratio between the position signal and contrast signal for each of the three colors from the plurality of wavelengths of reflected light; and
equating the position of the alignment mark with the weighted average of the position signals.

### Claim 5

A method for determining a position of an alignment mark on a wafer comprising the steps of:
generating light having multiple wavelengths;
illuminating the wafer with light;
detecting a plurality of wavelengths of reflected light from the wafer;
establishing an intensity signal for each of three colors from the plurality of wavelengths of reflected light, each intensity signal including a first portion corresponding to the reflected light from a portion of the wafer with the alignment mark and a second portion corresponding to the reflected light from a portion of the wafer without the alignment mark;
associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors from the plurality of wavelengths of reflected light;
establishing a maximum contrast signal by selecting from the three colors the contrast signal with the greatest magnitude; and
equating the position of the alignment mark with the position signal of the maximum contrast signal.

### Claim 6

A method for determining a position of an alignment mark on a wafer comprising the steps of:
generating light having multiple wavelengths;
illuminating the wafer with the light;
detecting a plurality of wavelengths of reflected light from the wafer;
establishing an intensity signal for each of three colors from the plurality of wavelengths of reflected light, each intensity signal including a first portion corresponding to the reflected light from a portion of the wafer with the alignment mark and a second portion corresponding to the reflected light from a portion of the wafer without the alignment mark;
associating a position signal with each intensity signal corresponding to the first portion of each intensity signal; and
averaging the position signals to establish an average position signal; and
equating the position of the alignment mark with the average position signal.

### Claim 7

A method for determining a position of an alignment mark on a wafer comprising the steps of:
generating light having multiple wavelengths;
illuminating the wafer with the light;
detecting a plurality of wavelengths of reflected light from the wafer;
establishing an intensity signal for each of three colors from the plurality of wavelengths of reflected light, each intensity signal including a first portion corresponding to the reflected light from a portion of the wafer with the alignment mark and a second portion corresponding to the reflected light from a portion of the wafer without the alignment mark;
associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors from the plurality of wavelengths of reflected light;
establishing a weighted average of the position signals through a ratio between the position signal and contrast signal for each of the three colors from the plurality of wavelengths of reflected light; and
equating the position of the alignment mark with the weighted average of the position signals.

### Claim 8

An alignment method for controlling an exposure position of a wafer comprising the steps of:
generating light having multiple wavelengths;
directing the light to the wafer through an angle-variable prism, the angle-variable prism polarizing the light;
directing a plurality of wavelengths of reflected light from the wafer to a CCD camera;
generating a wafer image by the CCD camera, the wafer image being composed of three colors;
transferring the wafer image as a video signal from the CCD camera to an image processing unit, the video signal being composed of three colors;
processing the video image by a computer to establish the location of an alignment mark on the wafer utilizing the polarization to establish a contrast between a portion of the wafer with the alignment mark and portion of the wafer without the alignment mark; and
adjusting the position of the wafer to place the alignment mark in a predetermined position.

### Claim 9 (depends on 8)

The method of claim 8 wherein the processing step comprises the steps of:
establishing an intensity signal for each of three colors from the plurality of wavelengths of reflected light, each intensity signal including a first portion corresponding to the reflected light from a portion of the wafer with the alignment mark and a second portion corresponding to the reflected light from a portion of the wafer without the alignment mark;
associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors from the plurality of wavelengths of reflected light;
establishing a maximum contrast signal by selecting from three colors the contrast signal with the greatest magnitude; and
equating the position of the alignment mark with the position signal of the maximum contrast signal.

### Claim 10 (depends on 8)

The method of claim 8, wherein the processing step comprises the steps of:
establishing an intensity signal for each of the three colors from the plurality of wavelengths of reflected light, each intensity signal including a first portion corresponding to the reflected light from a portion of the wafer with the alignment mark and a second portion corresponding to the reflected light from a portion of the wafer without the alignment mark;
associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
averaging the position signals for each intensity signal together to establish an average position signal; and
equating the position of the alignment mark with the average position signal.

### Claim 11 (depends on 8)

The method of claim 8, wherein the processing step comprises the steps of:
establishing an intensity signal for each of the three colors from the plurality of wavelengths of reflected light, each intensity signal including a first portion corresponding to the reflected light from a portion of the wafer with the alignment mark and a second portion corresponding to the reflected light from a portion of the wafer without the alignment mark;
associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors from the plurality of wavelengths of reflected light;
establishing a weighted average of the position signals through a ratio between the position signal and contrast signal for each of the three colors from the plurality of wavelengths of reflected light; and
equating the position of the alignment mark with the weighted average of the position signals.

### Claim 12

An alignment apparatus for controlling an exposure position of a wafer, comprising:
a light source that generates visible light with a plurality of wavelengths;
a filter that removes some wavelengths of light from the visible light;
means for directing the visible light from the light source, through the filter, to the wafer;
a CCD camera;
means for directing light reflected from the wafer to the CCD camera, wherein the CCD camera generates an electronic wafer image from the light reflected from the wafer, the electronic wafer image being composed of three colors;
a processing unit;
means for transferring the electronic wafer image to the processing unit, wherein the processing unit establishes a location of an alignment mark; and
means for adjusting the position of the wafer to position the alignment mark in a predetermined position.

### Claim 13 (depends on 12)

The apparatus of claim 12, wherein the processing unit comprises:
means for establishing an intensity signal for each of the three colors, each intensity signal including a first portion corresponding to light reflected from a portion of the wafer with the alignment mark and a second portion corresponding to light reflected from a portion of the wafer without the alignment mark;
means for associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
means for comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors;
means for establishing a maximum contrast signal by selecting from the three colors the contrast signal with the greatest magnitude; and
means for equating the position of the alignment mark with the position signal of the maximum contrast signal.

### Claim 14 (depends on 12)

The apparatus of claims 12, wherein the processing unit comprises:
means for establishing an intensity signal for each of the three colors, each intensity signal including a first portion corresponding to light reflected from a portion of the wafer with the alignment mark and a second portion corresponding to light reflected from a portion of the wafer without the alignment mark;
means for associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
means for averaging the position signals for each intensity signal together to establish an average position signal; and
means for equating the position of the alignment mark with the average position signal.

### Claim 15 (depends on 12)

The apparatus of claim 12, wherein the processing unit comprises:
means for establishing an intensity signal for each of the three colors, each intensity signal including a first portion corresponding to light reflected from a portion of the wafer with the alignment mark and a second portion corresponding to light reflected from a portion of the wafer without the alignment mark;
means for associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
means for comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors;
means for establishing a weighted average of the position signals through a ratio between the position signal and contrast signal for each of the three colors; and
means for equating the position of the alignment mark with the weighted average of the position signals.

### Claim 16

An alignment apparatus for controlling are exposure position of a wafer, comprising:
a light source that generates visible light with multiple wavelengths;
an angle-variable prism that polarizes the visible light;
means for directing the visible light from the light source, through the angle-variable prism, to the wafer;
a CCD camera;
means for directing light reflected from the wafer to the CCD camera, wherein the CCD camera generates an electronic wafer image from the light reflected from the wafer, the electronic wafer image being composed of three colors;
a processing unit;
means for transferring the electronic wafer image to the processing unit, wherein the processing unit establishes a location of an alignment mark; and
means for adjusting the position of the wafer to position the alignment mark in a predetermined position.

### Claim 17 (depends on 16)

The apparatus of claim 16, wherein the processing unit comprises:
means for establishing an intensity signal for each of the three colors, each intensity signal including a first portion corresponding to light reflected from a portion of the wafer with the alignment mark and a second portion corresponding to light reflected from a portion of the wafer without the alignment mark;
means for associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
means for comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors;
means for establishing a maximum contrast signal by selecting from the three colors the contrast signal with the greatest magnitude; and
means for equating the position of the alignment mark with the position signal of the maximum contrast signal.

### Claim 18 (depends on 16)

The apparatus of claims 16, wherein the processing unit comprises:
means for establishing an intensity signal for each of the three colors, each intensity signal including a first portion corresponding to light reflected from a portion of the wafer with the alignment mark and a second portion corresponding to light reflected from a portion of the wafer without the alignment mark;
means for associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
means for averaging the position signals for each intensity signal together to establish an average position signal; and
means for equating the position of the alignment mark with the average position signal.

### Claim 19 (depends on 16)

The apparatus of claim 16, wherein the processing unit comprises:
means for establishing an intensity signal for each of the three colors, each intensity signal including a first portion corresponding to light reflected from a portion of the wafer with the alignment mark and a second portion corresponding to light reflected from a portion of the wafer without the alignment mark;
means for associating a position signal with each intensity signal corresponding to the first portion of each intensity signal;
means for comparing the first and second portions of each intensity signal to establish a contrast signal for each of the three colors;
means for establishing a weighted average of the position signals through a ratio between the position signal and contrast signal for each of the three colors; and
means for equating the position of the alignment mark with the weighted average of the position signals.