Method for determining laser-induced compaction in fused silica

• US 20020036188A1
• Filed: 09/26/2001
• Published: 03/28/2002
• Est. Priority Date: 08/29/1996
• Status: Active Grant

• Current Assignee: Charlene M. Smith, Douglas C. Allan, Nicholas F. Borrelli, Thomas P. Seward III, William R. Powell
• Original Assignee: Charlene M. Smith, Douglas C. Allan, Nicholas F. Borrelli, Thomas P. Seward III, William R. Powell
• Inventors: Powell, William R., Seward, Thomas P. III, Smith, Charlene M., Borrelli, Nicholas F., Allan, Douglas C.
• Granted Patent: US 6,543,254 B2
• Time in Patent Office: Days
• US Class Current: 219/121.62
• CPC Class Codes: C03B 19/06 by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction
• CPC Class Codes: C03B 19/066 for the production of quartz or fused silica articles other processes specially adapted for the production of quartz or fused silica articles C03B20/00
• CPC Class Codes: C03B 19/1065 by liquid phase reactions, e.g. by means of a gel phase
• CPC Class Codes: C03B 19/1453 Thermal after-treatment of the shaped article, e.g. dehydrating, consolidating, sintering
• CPC Class Codes: C03B 20/00 Processes specially adapted for the production of quartz or fused silica articles , not otherwise provided for C03B19/01, C03B19/066, C03B19/106, C03B19/12, C03B19/14, C03B37/00 take precedence
• CPC Class Codes: C03B 2207/32 Non-halide
• CPC Class Codes: C03C 1/006 to produce glass through wet route
• CPC Class Codes: C03C 2201/02 Pure silica glass, e.g. pure fused quartz
• CPC Class Codes: C03C 2203/50 After-treatment
• CPC Class Codes: C03C 23/0025 by a laser beam
• CPC Class Codes: C03C 3/06 with more than 90% silica by weight, e.g. quartz C03C3/045 takes precedence
• CPC Class Codes: G03F 7/70058 Mask illumination systems
• CPC Class Codes: G03F 7/70216 Mask projection systems
• CPC Class Codes: G03F 7/70958 Optical materials or coatings, e.g. with particular transmittance, reflectance or anti-reflection properties
• CPC Class Codes: Y10S 65/13 Computer control

Abstract

The invention relates to fused silica having low compaction under high energy irradiation, particularly adaptable for use in photolithography applications.

Claims

1. Fused silica glass exhibiting low compaction when exposed to high intensity excimer radiation, characterized in that said glass exhibits no optical path length distortion after exposure to a high intensity irradiation dose

2. Fused silica glass according to claim 1 characterized in that after said exposure to high intensity excimer radiation the glass exhibits no detectable changes in refractive index and/or density.

3. Fused silica glass according to claim 1 characterized in that said glass exhibits little or no structural change when exposed to said high intensity excimer radiation.

4. Method for improving the select ratio of fused silica glass for photolithographic applications, by predicting the optical path distortion of said glass under actual photolithographic use conditions.

5. The method of claim 4 wherein said optical path distortion is predicted by determining the intrinsic densification of said glass at a given number of pulses and fluence per pulse.

6. Method for producing fused silica glass stepper lens exhibiting low compaction when exposed to high intensity excimer radiation of a given dose N/², where N is the number of pulses, and / is the fluence per pulse, said method comprising:

(a) designing the lens by;

(1) determining the intrinsic densification, (δ

ρ

/ρ

)_p of a sample geometry of the fused silica;

(2) determining the optical path difference δ

(n/) of the fused silica glass at said dose; and

(3) calculating the densification, (δ

ρ

/ρ

) of the fused silica glass from the values determined in steps (a) (1) and (2); and

(b) producing the stepper lens designed in step (a).

7. The method of claim 6 wherein the intrinsic densification is determined from the stretched exponential function:

8. A fused silica stepper lens designed according to the method of claim 6.

9. The stepper lens of claim 8 characterized by exhibiting an optical path length distortion of less than 0.05 waves/cm after exposure to a high intensity irradiation of dose, N/²=8×

10⁹.

10. Method for producing fused silica glass stepper lens exhibiting low compaction when exposed to high intensity excimer radiation of a given dose N/² where N is the number of pulses, and / is the fluence per pulse, said method comprising:

(a) designing a lens by;

(1) selecting a sample size and geometry for the lens;

(2) determining the intrinsic densification, (δ

ρ

/ρ

)_p of the sample;

(3) determining the optical path difference δ

(n/) of the lens at said dose; and

(4) calculating the densification, (δ

ρ

/ρ

) of the lens from the values determined in steps (a) (2) and (3); and

(b) producing the stepper lens designed in step (a).

11. Method of determining optical path damage caused by high energy irradiation in fused silica glass by:

(a) using interferometry to determine the total optical path length change δ

(n/), by measuring (1) physical path change of the glass due to strain, and/or (2) change in refractive index due to any density change; and

/or

(b) using birefringence to map the stress distribution developed as a result of densification and using the stress measurements to characterize relative density changes across the fused silica glass.

12. Method of making a fused silica stepper lens for use in a photolithographic system, said lens being resistant to laser-induced densification, and said system having a predetermined expected life at an estimated excimer laser irradiation dose, the method comprising:

(a) providing a fused silica lens blank of appropriate dimension for the photolithographic system;

(b) using a finite element elastic model, extract the intrinsic laser-induced densification, (δ

ρ

/ρ

)_p of the blank;

(c) using interferometry, determine the optical path difference δ

(n/) of the fused silica glass at said dose; and

(d) calculating the expected total densification, (δ

ρ

/ρ

) of the fused silica glass from the values determined in steps (b) and (c);

(e) producing the stepper lens by precompacting a fused silica blank using said the expected life dose to density said blank by an amount equal to the calculated value of (δ

ρ

/ρ

) in step (d); and

(f) producing a stepper lens from the precompacted fused silica blank of step (e).