# US 7,609,373 B2 · Reducing variations in energy reflected from a sample due to thin film interference

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- Number: US 7,609,373 B2
- Document ID: US7609373B2
- Status: Granted
- Kind: B2
- Application number: 11/223,851
- Filed: 2005-09-09
- Published: 2006-11-30
- Granted: 2009-10-27
- Earliest claimed: 2005-05-31
- Assignees: KLA-Tencor Technologies Corporation
- Inventors: Yung-Ho Chuang; J. Joseph Armstrong
- Web page: https://patentgrep.com/patent/US7609373B2

## CPC

- G01N 21/9501: {Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)}
- G01B 11/0625: {with measurement of absorption or reflection}
- G01N 21/21: Polarisation-affecting properties (G01N21/19 takes precedence)
- G01N 21/95607: {using a comparative method}
- G01N 2021/8809: {Adjustment for highlighting flaws}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS

## Abstract

A system and method for inspecting a multi-layer sample, such as a silicon wafer, is disclosed. The design reduces variations in total reflected energy due to thin film interference. The design includes illuminating the sample at two incident angle ranges, where the two incident angle ranges are such that variation in total reflected energy at a first incident angle range may be employed to balance variation in total reflected energy at a second incident angle range. Defects are detected using die-to-die subtraction of the sample illuminated at the two incident angle ranges.

## Claims

### Claim 1

A method to reduce variations in total reflected energy due to thin film interference when inspecting a sample, comprising:
producing p-polarized light based on at least one from a group comprising linear, circular, and random polarized light; and
illuminating the sample at an incident angle similar to Brewster's angle for a top most film, wherein said illuminating uses p-polarized light from said producing;
wherein the incident angle, polarization of the p-polarized light, and illumination wavelength of the p-polarized light are configured to be selectively altered based on thin film interference encountered on the sample.

### Claim 2 (depends on 1)

The method of claim 1 where the illuminating is quatrupole illumination.

### Claim 3 (depends on 1)

The method of claim 1 wherein illumination from said illuminating comprises a ring with a range of incident angles both greater than and less than Brewster's angle.

### Claim 4 (depends on 3)

The method of claim 3 where the variation in total reflected energy at incident angles less than Brewster's angle is used to balance the variation in the total reflected energy at angles greater than Brewster's angle.

### Claim 5 (depends on 1)

The method of claim 1 where p-polarization is obtained by using a mosaic of waveplates.

### Claim 6 (depends on 1)

The method of claim 1 where p-polarization is obtained directly from a laser.

### Claim 7 (depends on 1)

The method of claim 1 where p-polarization is obtained using an axicon.

### Claim 8 (depends on 1)

The method of claim 1 where p-polarization is obtained using form birefringence.

### Claim 9 (depends on 1)

The method of claim 1 where p-polarization is obtained using a diffractive element.

### Claim 10 (depends on 1)

The method of claim 1 where p-polarization is obtained using a plastic sheet polarizer.

### Claim 11

A method to reduce variations in total reflected energy due to thin film interference when inspecting a sample, comprising:
illuminating the sample using ring illumination provided using two light energies of different polarizations produced using at least one segmented waveplate, providing variation in total reflected energy at a first incident angle range to balance variation in total reflected energy at a second incident angle range;
and further comprising transmitting light energy having a first polarization at the first incident angle range and light energy having a second polarization at the second incident angle range.

### Claim 12 (depends on 11)

The method of claim 11 where each incident angle range uses azimuthal ring illumination.

### Claim 13 (depends on 12)

The method of claim 12 where each incident angle range includes a range of incident angles.

### Claim 14 (depends on 13)

The method of claim 13 where one range of incident angles is p-polarized and another range is s-polarized.

### Claim 15 (depends on 13)

The method of claim 13 where both ranges of incident angles are s-polarized.

### Claim 16 (depends on 13)

The method of claim 13 where both ranges of incident angles are p-polarized.

### Claim 17 (depends on 14)

The method of claim 14 where s-polarized light comes from a first laser pulse and p-polarized light comes from a second laser pulse.

### Claim 18 (depends on 11)

The method of claim 11, wherein said illuminating employs light energy comprising at least one from a group comprising linearly, circularly, or randomly polarized light transformed into one from a group comprising p polarization and s polarization.

### Claim 19

A method for inspecting a sample, comprising:
producing p-polarized light based on at least one from a group comprising linear, circular, and random polarized light;
illuminating the sample at an incident angle, wherein said illuminating uses p-polarized light from said producing, and
additionally illuminating the sample at a second incident angle, wherein further illumination at said second incident angle differs in wavelength from illumination at the incident angle;
wherein the first incident angle, second incident angle, polarization of the p-polarized light, and illumination wavelength of the p-polarized light are configured to be selectively altered based on thin film interference encountered on the sample.

### Claim 20 (depends on 19)

The method of claim 19, wherein said producing and said illuminating reduces variations in total reflected energy due to thin film interference during inspection.

### Claim 21 (depends on 19)

The method of claim 19, wherein the incident angle is similar to Brewster's angle.

### Claim 22 (depends on 21)

The method of claim 21, wherein illumination from said illuminating comprises a ring with a range of incident angles both greater than and less than Brewster's angle.

### Claim 23 (depends on 20)

The method of claim 20, where variation in total reflected energy at incident angles less than Brewster's angle is used to balance variation in the total reflected energy at angles greater than Brewster's angle.