# US 2019/0378737 A1 · Overlay Measurement Using Phase and Amplitude Modeling

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- Number: US 2019/0378737 A1
- Document ID: US20190378737A1
- Status: Published application
- Kind: A1
- Application number: 16/068,462
- Filed: 2018-06-07
- Published: 2019-12-12
- Earliest claimed: 2018-06-07
- Assignees: KLA-Tencor Corporation
- Applicants: Kla-Tencor Corporation
- Inventors: Nadav Gutman; Moran Zaberchik; Eran Amit
- Web page: https://patentgrep.com/patent/US20190378737A1

## CPC

- G03F 7/70633: {Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching}
- H10P 72/53: {using optical controlling means}
- G01B 11/272: {using photoelectric detection means}
- G03F 7/70616: {Monitoring the printed patterns}
- G06T 1/0014: {Image feed-back for automatic industrial control, e.g. robot with camera (robots B25J19/023)}
- G06T 7/0004: {Industrial image inspection}
- G06T 2207/30148: Semiconductor; IC; Wafer
- 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)
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL

## Abstract

Methods and systems are disclosed for determining overlay in a semiconductor manufacturing process. Radiation reflected from a diffraction pattern in a metrology target may include +1 and −1 diffraction patterns at different wavelengths and focal positions. The different wavelengths of radiation may be in a waveband where the sensitivity of contrast to wavelength is at a maximum. The reflected radiation may be analysed to obtain measured values of overlay as well as amplitude and/or phase corresponding to points distributed over the target, for different wavelengths and focal positions. The measured values of overlay may undergo a series of operations to determine the overlay. The determination may use an assumption that the amplitude and phase are unequal in the +1 and −1 diffraction orders.

## Claims

### Claim 1

A method of determining overlay in a semiconductor wafer manufacturing process comprising:
receiving radiation reflected from a metrology target including +1 and −1 diffraction patterns at different wavelengths wherein the different wavelengths of radiation are in a waveband where a sensitivity of contrast to wavelength is at a maximum;
analysing the radiation reflected from the metrology target to obtain measured values of overlay and one or both of amplitude and phase corresponding to points distributed over the metrology target, for different wavelengths;
fitting the measured values of amplitude or phase or both to a first model of a variation of amplitude or phase or both, in which it is assumed that the amplitude or phase or both are equal and opposite in the +1 and −1 diffraction patterns;
using values of amplitude or phase or both determined using the first model to obtain estimated values of overlay for different wavelengths;
fitting the estimated values of overlay to a second model of a variation of the variation of amplitude or phase or both in which it is assumed that one or both of the amplitude and phase are unequal in the +1 and −1 diffraction patterns;
using values of amplitude difference or phase difference or both determined using the second model to obtain values of amplitude difference or phase difference or both corresponding to different values of wavelength; and
using values of amplitude difference or phase difference or both at a selected wavelength to determine an overlay.

### Claim 2 (depends on 1)

The method as claimed in claim 1 wherein the radiation reflected from the metrology target is at different wavelengths and different focal positions, the measured values are obtained for different wavelengths and focal positions, the overlay is estimated for different wavelengths and different focal positions, and the values of amplitude difference and phase difference or both correspond to different values of wavelength and focal position.

### Claim 3 (depends on 1)

The method as claimed in claim 1 wherein only radiation from first order diffraction patterns is present, or analysed.

### Claim 4 (depends on 1)

The method as claimed in claim 1, wherein the values of amplitude difference or phase difference or both at the selected wavelength are used to determine the overlay as a weighted average of phase difference over illumination points on the target.

### Claim 5 (depends on 4)

The method as claimed in claim 4 in which the phase difference is weighted by an average amplitude over the +1 and −1 diffraction orders.

### Claim 6 (depends on 1)

The method as claimed in claim 1 in which the selected wavelength is a wavelength at which the sensitivity of contrast to wavelength is at a maximum.

### Claim 7 (depends on 1)

The method as claimed in claim 1 comprising, prior to said receiving, determining one or both of an operating waveband and an operating focus range including a maximum in sensitivity of contrast to wavelength.

### Claim 8 (depends on 7)

The method as claimed in claim 7 wherein the determining is restricted to first order diffraction.

### Claim 9 (depends on 1)

A method of manufacturing a semiconductor wafer comprising determining overlay according to the method of claim 1 and compensating for the determined overlay.

### Claim 10

A method for determining overlay in a semiconductor manufacturing process comprising:
receiving radiation reflected from a metrology target including +1 and −1 diffraction patterns at different wavelengths in a waveband including a maximum of sensitivity of contrast to wavelength;
analysing the radiation reflected from the metrology target to obtain measured values of overlay and one or both of amplitude and phase corresponding to points distributed over the metrology target, for different wavelengths; and
performing a series of operations on the measured values of overlay to determine an overlay in which it is assumed that the amplitude and phase are unequal in the +1 and −1 diffraction orders.

### Claim 11 (depends on 10)

The method as claimed in claim 10 in which the radiation reflected from the metrology target is additionally at different focal positions corresponding to different wavelengths, and said analyzing comprises obtaining measured values of overlay corresponding to different focal positions.

### Claim 12 (depends on 10)

The method as claimed in claim 10 further comprising:
a) fitting the measured values of amplitude or phase or both to a first model, in which it is assumed that the measured values of amplitude or phase or both are equal and opposite in the +1 and −1 diffraction patterns;
b) using values of amplitude or phase or both determined using the first model to estimate values of overlay for different wavelengths;
c) fitting the estimated values of overlay to a second model in which it is assumed that the measured values of one or both of the amplitude and phase are unequal in the +1 and −1 diffraction patterns;
d) using values of amplitude difference or phase difference or both determined using the second model to obtain values of amplitude difference or phase difference or both corresponding to different values of wavelength and focal position; and
e) using values of amplitude difference or phase difference or both at a selected wavelength to determine the overlay.

### Claim 13 (depends on 10)

The method as claimed in claim 10 further comprising:
a) fitting the measured values of amplitude and phase to a first model, in which it is assumed that the measured values of amplitude and phase are equal and opposite in the +1 and −1 diffraction patterns;
b) using values of amplitude and phase determined using the first model to estimate values of overlay for different wavelengths;
c) fitting the estimated values of overlay to a second model in which it is assumed that the amplitude and phase are unequal in the +1 and −1 diffraction patterns;
d) using values of amplitude difference and phase difference determined using the second model to obtain values of amplitude difference and phase difference corresponding to different values of wavelength and focal position; and
e) using values of amplitude difference and phase difference at a selected wavelength to determine the overlay.

### Claim 14 (depends on 12)

The method as claimed in claim 12 in which operation b) further comprises estimating overlay for different focal positions.

### Claim 15 (depends on 10)

The method as claimed in claim 10 wherein determining overlay comprises fitting information on amplitude and/or phase from said points to a model relating the information to overlay, and updating the model based on measurements of overlay obtained by a different technique.

### Claim 16

A system for determining overlay in a semiconductor manufacturing process, the system comprising:
an illumination system and an imaging system, the illumination system including a radiation source and the imaging system being arranged to direct radiation from the illumination system towards the surface of a target and to receive radiation from the illumination system reflected from the target in the form of diffraction patterns;
a control unit arranged to control the imaging system or the illumination system or both to obtain diffraction patterns using different values of focal position or wavelength or both; and
an image analysis unit configured to:
receive radiation reflected from a metrology target including +1 and −1 diffraction patterns at different wavelengths in a waveband including a maximum of sensitivity of contrast to wavelength;
analyze the radiation reflected from the metrology target to obtain measured values of overlay and one or both of amplitude and phase corresponding to points distributed over the target, for different wavelengths; and
perform a series of operations on the measured values of overlay to determine an overlay in which it is assumed that the amplitude and phase are unequal in the +1 and −1 diffraction orders.

### Claim 17 (depends on 16)

The system as claimed in claim 16 wherein the imaging system comprises first and second cameras and the control unit is configured to vary the focal position of one camera with respect to the other.