Holographic lithography

• US 5,142,385 A
• Filed: 01/09/1991
• Issued: 08/25/1992
• Est. Priority Date: 07/18/1989
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Anderson, Erik H., Schattenburg, Mark L., Smith, Henry I.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): RYAN, JAY
• Application Number:
  US07/643,141
• Time in Patent Office: 594 Days
• Field of Search: 350/3.6, 350/3.67, 350/3.74, 350/3.83, 350/3.89, 350/162.17, 250/201.9
• US Class Current: 359/10
• CPC Class Codes: G03F 7/001 Phase modulating patterns, e.g. refractive index patterns
• CPC Class Codes: G03F 7/70408 Interferometric lithography; Holographic lithography; Self-imaging lithography, e.g. utilizing the Talbot effect
• CPC Class Codes: G03H 1/0486 Improving or monitoring the quality of the record, e.g. by compensating distortions, aberrations
• CPC Class Codes: G03H 2001/0489 by using phase stabilized beam

Abstract

First and second coherent beams illuminate a common area on an exposure station. A phase detector senses the relative phase between the first and second beams to provide a control signal. There is at least one phase shifter in the path of at least one of the coherent beams. The control signal is coupled to the phase shifter to adjust the phase imparted thereby so that the relative phase between the first and second coherent beams is substantially constant.

Claims

1. A method of holographic lithography which method includes the steps of illuminating a substrate with coherent radiant energy from first and second beams,

using a first beam splitter near the substrate to intercept said first and second beams to reflect a portion of the first and transmit a portion of the second beams from which the respective portions are interfered to produce thereby at least a first pattern of interference fringes at a first location with the path between said first location and said first beam splitter free of optical components,

photodetecting at said first location at least said first pattern of interference fringes to provide a control signal representative of the phase difference between said first and second beams,

and using said control signal to control the relative phase shift between said first and second beams to maintain the phase difference therebetween substantially constant.

2. A method of holographic lithography in accordance with claim 1 and further including the step of illuminating second beam splitter with radiant energy from a laser to form said first and second beams,

establishing the intensity of said first and second beams to be of substantially equal intensity on said substrate,

and maintaining the relative phase shift between said first and second coherent beams with said control signal to maintain at least said first pattern of interference fringes substantially stationary.

3. A method of holographic lithography in accordance with claim 1 and further including providing a second pattern of interference fringes by transmitting a portion of said first beam and reflecting a portion of said second beam from which the respective portions are interfered and further comprising,

photodetecting said first and second patterns of interference fringes to provide first and second photodetected signals,

and combining said first and second photodetected signals to provide said control signal.

4. Holographic lithographic apparatus comprising,

a source of first and second coherent beams of radiant energy,

an exposure station illuminated by the first and second coherent beams,

at least one phase shifter in the path of at least one of said coherent beams,

a first beam splitter at said exposure station arranged to reflect a portion of said first and transmit a portion of said second beams from which the respective portions are interfered to produce thereby at least a first pattern of interference fringes at a first location with the path between said first location and said first beam splitter free of optical components,

at least a first radiant energy detector at said first location for detecting at least said first pattern of interference fringes which is representative of the phase difference between energy in the first and second coherent beams illuminating said exposure station to provide a control signal representative of said phase difference,

and a feedback path intercoupling at least said first radiant energy detector with the phase shifter to deliver said control signal to the phase shifter which establishes the phase imparted by the phase shifter so that the relative phase between the first and second coherent beams at the exposure station remains substantially constant.

5. Holographic lithographic apparatus in accordance with claim 4 wherein said source of first and second coherent beams of radiant energy comprises,

a second beam splitter,

a laser illuminating said second beam splitter to provide said first and second coherent beams,

a variable attenuator in the path of at least one of said first and second coherent beams,

and at least said first radiant energy detector comprises at least a first photocell.

6. Holographic lithographic apparatus in accordance with claim 4 wherein said first beam splitter also provides a second pattern of interference fringes by transmitting a portion of said first beam and reflecting a portion of said second beam from which the respective portions are interfered and further comprising,

a second radiant energy detector illuminated by said second pattern of interference fringes for providing a second detected signal,

and a combiner for combining said first and second detected signals to provide said control signal.

7. Holographic lithographic apparatus in accordance with claim 6 wherein said combiner is a differential combiner that differentially combines said first and second detected signals to provide said control signal.

8. Holographic lithographic apparatus comprising,

a source of first and second coherent beams of radiant energy,

an exposure station illuminated by the first and second coherent beams,

a first beam splitter arranged to reflect a portion of said first and transmit a portion of said second beam from which the respective portions are interfered to produce thereby at least a first pattern of interference fringes,

at least a first radiant energy detector for detecting at least said first pattern of interference fringes which is representative of the phase difference between energy in the first and second coherent beams illuminating said exposure station to provide a control signal representative of said phase difference,

and a feedback path intercoupling at least said first radiant energy detector with the phase shifter to deliver said control signal to the phase shifter which establishes the phase imparted by the phase shifter so that the relative phase between the first and second coherent beams at the exposure station remains substantially constant,

wherein said source of first and second coherent beams of radiant energy comprises,

a second beam splitter,

a laser illuminating said second beam splitter to provide said first and second coherent beams,

a variable attenuator in the path of at least one of said first and second coherent beams,

and at least said first radiant energy detector comprises at least a first photocell.

9. A method of holographic lithography which method includes the steps of illuminating a substrate with coherent radiant energy from first and second beams,

using a first beam splitter to intercept said first and second beams to reflect a portion of the first and transmit a portion of the second beams from which the respective portions are interfered to produce thereby at least a first pattern of interference fringes,

photodetecting at least said first pattern of interference fringes to provide a control signal representative of the phase difference between said first and second beams,

and using said control signal to control the relative phase shift between said first and second beams to maintain the phase difference therebetween substantially constant,

and further including providing a second pattern of interference fringes by transmitting a portion of said first beam and reflecting a portion of said second beam from which the respective portions are interfered and further comprising,

photodetecting said first and second patterns of interference fringes to provide first and second photodetected signals,

and combining said first and second photodetected signals to provide said control signal.

10. A method of holographic lithography in accordance with claim 9 wherein said step of combining said first and second photodetected signals includes differentially combining said first and second photodetected signals to provide said control signal.

11. Holographic lithographic apparatus comprising,

a source of first and second coherent beams of radiant energy,

an exposure station illuminated by the first and second coherent beams,

a first beam splitter arranged to reflect a portion of said first and transmit a portion of said second beams from which the respective portions are interfered to produce thereby at least a first pattern of interference fringes,

at least a first radiant energy detector for detecting at least said first pattern of interference fringes which is representative of the phase difference between energy in the first and second coherent beams illuminating said exposure station to provide a control signal representative of said phase difference,

and a feedback path intercoupling at least said first radiant energy detector with the phase shifter to deliver said control signal to the phase shifter which establishes the phase imparted by the phase shifter so that the relative phase between the first and second coherent beams at the exposure station remains substantially constant,

wherein said first beam splitter also provides a second pattern of interference fringes by transmitting a portion of said first beam and reflecting a portion of said second base from which the respective portions are interfered and further comprising,

a second radiant energy detector illuminated by said second pattern of interference fringes for providing a second detected signal,

and a combiner for combining said first and second detected signals to provide said control signal.

12. Holographic lithographic apparatus in accordance with claim 11 wherein said combiner is a differential combiner that differentially combines said first and second detected signals to provide said control signal.