Method pre-compaction of fused silica

• US 6,295,841 B1
• Filed: 02/25/1999
• Issued: 10/02/2001
• Est. Priority Date: 08/29/1996
• Status: Expired due to Fees

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Powell, William R., Smith, Charlene M., Borrelli, Nicholas F., Allan, Douglas C., Seward, Thomas P. III
• Primary Examiner(s): VINCENT, SEAN E
• Application Number:
  US09/254,113
• Time in Patent Office: 950 Days
• Field of Search: 65/291.1, 65/332, 65D/IG.13, 653/92
• US Class Current: 65/29.11
• 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

A fused silica glass which exhibits low compaction when exposed to high intensity excimer radiation, also exhibits low optical path distortion after exposure to a high intensity radiation dose. Also disclosed is a method for improving the select ratio of fused silica glass for photolithography, by predicting the optical path distortion of the glass under use by determining the intrinsic densification of the glass at a given number of pulses and fluence per pulse. Mathematical modeling methods are also disclosed for use in producing a fused silica stepper lens having low compaction under high intensity excimer radiation; and for determining optical path distortion caused by high energy radiation in fused silica glass.

Claims

1. A method for 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) selecting a fused silica for the stepper lens;

(b) determining an intrinsic densification value for the selected fused silica for the estimated excimer laser irradiation dose;

(c) calculating the expected total densification of the lens using the intrinsic densification value determined in step (b);

(d) pre-densifying a blank of the selected fused silica based on the expected total densification calculated in step (c); and

(e) producing the stepper lens from the pre-densified blank.

2. The method of claim 1 wherein step (b) comprises:

(i) irradiating a sample of the selected fused silica with excimer laser light having the estimated excimer laser irradiation dose, said sample having a predetermined geometry and said dose having a predetermined profile;

(ii) measuring at least one of;

(a) a change in optical path length as a result of the irradiation for at least one path through the sample, or

(b) a change in birefringence as a result of the irradiation for at least one path through the sample; and

(iii) determining the intrinsic densification from the measurements of step (ii) and a model of the response of a sample having the predetermined geometry to laser light having the predetermined profile.

3. The method of claim 2 wherein the model is a finite-element model.

4. The method of claim 1 wherein step (c) is performed using a model for said stepper lens.

5. The method of claim 4 wherein said model is a finite-element model.

6. A fused silica stepper lens produced according to the method of claim 1.

7. The stepper lens of claim 6 wherein the lens exhibits an optical path distortion of less than 0.05 waves/cm after exposure to an excimer laser irradiation dose of NI²=8×

10⁹, where N is the number of pulses and I is the pulse fluence in mJ/cm².