Position Measurement with Illumination Profile having Regions Confined to Peripheral Portion of Pupil

Patent metadata

Field	Value
Publication number	US-2017160075-A1
Application number	US-201715439833-A
Country	US
Kind code	A1
Filing date	Feb 22, 2017
Priority date	Apr 12, 2012
Publication date	Jun 8, 2017
Grant date	—

Abstract

An apparatus (AS) measures positions of marks ( 202 ) on a lithographic substrate (W). An illumination arrangement ( 940, 962, 964 ) provides off-axis radiation from at least first and second regions. The first and second source regions are diametrically opposite one another with respect to an optical axis (O) and are limited in angular extent. The regions may be small spots selected according to a direction of periodicity of a mark being measured, or larger segments. Radiation at a selected pair of source regions can be generated by supplying radiation at a single source feed position to a self-referencing interferometer. A modified half wave plate is positioned downstream of the interferometer, which can be used in the position measuring apparatus. The modified half wave plate has its fast axis in one part arranged at 45° to the fast axis in another part diametrically opposite.

First claim

1 . An arrangement for producing off-axis radiation at first and second positions diametrically opposed to one another in a pupil of the arrangement, the radiation at the first and second positions being identical in polarization and coherence, the arrangement comprising:
a radiation source configured to generate radiation of a predetermined polarization at a single off-axis position; a self-referencing interferometer configured to receive and split the radiation from the radiation source so as to generate the radiation at the first and second positions; an element configured to adjust a polarization of the radiation at a first one of the first and second positions after the radiation emerges from the interferometer to match the polarization at a second one of the first and second positions, the element comprising a half wave plate whose fast axis is oriented differently at the first and second positions.

2 . The arrangement of claim 1 , wherein the single off-axis position is movable among a plurality of off-axis source feed positions within an entrance pupil of the apparatus to provide a plurality of off-axis illumination modes.

3 . The arrangement of claim 2 , wherein the plurality of off-axis source feed positions are spaced at 45° intervals around a periphery of the entrance pupil.

4 . The arrangement of claim 1 , wherein the arrangement includes a movable optical fiber configured to physically move so as to direct the radiation to different off-axis source feed positions.

5 . The arrangement of claim 1 , further comprising a plurality of switchable optical fibers each configured to direct the radiation to a different off-axis source feed position.

6 . The arrangement of claim 1 , wherein the radiation source is further configured to generate the radiation at an on-axis source feed position for an on-axis illumination mode.

7 . The arrangement of claim 1 , wherein the fast axis of the half wave plate is oriented parallel to a Y axis at the first position and the fast axis is oriented at 45° to a Y axis at the second position.

8 . The arrangement of claim 7 , wherein the half wave plate is split into two segments angled at 22.5° to the Y axis.

9 . The arrangement of claim 1 , wherein the half wave plate comprises a hole formed at an optical axis to permit on-axis radiation to pass unhindered.

10 . The arrangement of claim 1 , wherein the apparatus is configured to measure positions of marks on a substrate, the apparatus further comprising:
an objective lens configured to form a spot of radiation on one of the marks using radiation supplied by the arrangement while scanning the spot of radiation across the mark in a scanning direction; a second self-referencing interferometer configured to process radiation that is diffracted by the mark and re-enters the objective lens; and a detector configured to detect variations in an intensity of radiation output by the second self-referencing interferometer during the scanning and to calculate from the detected variations a position of the mark in at least a first direction of measurement.

11 . The arrangement of claim 1 , wherein the radiation source is a broadband radiation source configured to generate white light.

12 . An arrangement configured to produce off-axis radiation at first and second positions diametrically opposed to one another in a pupil of the arrangement, the radiation at the first and second position being identical in polarization and coherent, the arrangement comprising:
a radiation source configured to generate the radiation for a plurality of predetermined polarizations, each at a single off-axis position; a self-referencing interferometer configured to receive and split the radiation from the radiation source so as to generate the radiation at the first and second respective positions; an element configured to adjust a polarization of the radiation at one of the first and second positions after the radiation emerges from the self-referencing interferometer to match the polarization at another one of the first and second positions, the element comprising a half wave plate whose fast axis is oriented differently at the first and second positions.

13 . The arrangement of claim 11 , wherein the single off-axis position is movable among a plurality of off-axis source feed positions within an entrance pupil of the arrangement to provide a plurality of off-axis illumination modes.

14 . The arrangement of claim 11 , wherein the radiation source is further configured to multiplex the radiation of the plurality of predetermined polarizations to provide simultaneous illumination at a plurality of illumination modes.

15 . The arrangement of claim 13 , wherein the radiation source is further configured to multiplex by frequency division multiplexing.

16 . The arrangement of claim 13 , wherein the radiation source is further configured to multiplex by time division multiplexing.

17 . The arrangement of claim 11 , wherein the fast axis of the half wave plate is oriented parallel to a Y axis at the first position and the fast axis is oriented at 45° to a Y axis at the second position.

18 . The arrangement of claim 11 , wherein the half wave plate is split into two segments angled at 22.5° to the Y axis.

19 . The arrangement of claim 11 , wherein the half wave plate comprises a hole formed at an optical axis to permit on-axis radiation to pass unhindered.

20 . The arrangement of claim 11 , wherein the apparatus is configured to measure positions of marks on a substrate, the apparatus further comprising:
an objective lens configured to form a plurality of spots of radiation on one of the marks using radiation supplied by the arrangement while scanning the spot of radiation across different portions of the mark in a scanning direction; a second self-referencing interferometer configured to process radiation that is diffracted by the mark and re-enters the objective lens; and a detector configured to electronically separate the processed radiation according to a respective illumination mode, to detect variations in an intensity of radiation output by the second self-referencing interferometer during the scanning, and to calculate from the detected variations a position of the mark in at least a first direction of measurement.

Assignees

• Asml Netherlands Bv
• Asml Holding Nv

Inventors

• Kreuzer Justin Lloyd
• Den Boef Arie Jeffrey
• Mathijssen Simon Gijsbert Josephus

Classifications

• G03F9/7069 Primary

  Alignment mark illumination, e.g. darkfield, dual focus · CPC title

• G01B9/0207

  Error reduction by correction of the measurement signal based on independently determined error sources, e.g. using a reference interferometer · CPC title

• G03F9/7088

  Alignment mark detection, e.g. TTR, TTL, off-axis detection, array detector, video detection · CPC title

• G01B11/14 Primary

  for measuring distance or clearance between spaced objects or spaced apertures (G01B11/26 takes precedence; rangefinders G01C3/00) · CPC title

• G03F7/70108

  Off-axis setting using a light-guiding element, e.g. diffractive optical elements [DOEs] or light guides · CPC title