Dual-wavelength exposure for reduction of implant shadowing
View Patent ↗A method for generating a photoresist structure is disclosed in which a layer of photoresist is deposited over a semiconductor substrate. In a first exposure, the layer of photoresist is exposed to deep ultraviolet light. A second exposure is then performed using a different wavelength of light to pattern the layer of photoresist. The photoresist is then developed so as to form a photoresist structure having reduced thickness and rounded corners. This gives a photoresist structure having a reduced shadow area. An angled ion implant can then be performed using the photoresist structure as a mask.
1. A method for forming a photoresist structure comprising:
forming a layer of photoresist over a semiconductor substrate, said layer of photoresist having a designated wavelength, a first thickness and high optical absorption of light having a first wavelength;
exposing said layer of photoresist to said light having a first wavelength;
exposing portions of said layer of photoresist to light having a second wavelength so as to pattern said layer of photoresist, said second wavelength approximately said designated wavelength; and
developing said layer of photoresist, after said exposing said layer of photoresist to said light having a first wavelength and said exposing portions of said layer of photoresist to light having a second wavelength, so as to form a photoresist structure having a second thickness that is less than said first thickness.
2. A method for forming a photoresist structure as recited in claim 1 wherein said layer of photoresist has sufficiently high absorption of said light having a first wavelength such that said light having a first wavelength is completely absorbed by said layer of photoresist near a top surface of said layer of photoresist.
3. A method for forming a photoresist structure as recited in claim 2 wherein said layer of photoresist is i-line photoresist and wherein said designated wavelength is approximately 365 nanometers.
4. A method for forming a photoresist structure as recited in claim 3 wherein said light having a first wavelength comprises light having a deep ultraviolet wavelength.
5. A method for forming a photoresist structure comprising:
forming a layer of i-line photoresist having a first thickness over a semiconductor substrate;
exposing said layer of i-line photoresist to deep ultraviolet light;
exposing portions of said layer of i-line photoresist to light having a wavelength of approximately 365 nanometers so as to pattern said layer of i-line photoresist; and
developing said layer of i-line photoresist, after said exposing said layer of i-line photoresist to deep ultraviolet light and said exposing portions of said layer of i-line photoresist to light having a wavelength of approximately 365 nanometers, so as to form a photoresist structure having a second thickness that is less than said first thickness.
6. A method for forming a photoresist structure as recited in claim 5 wherein said deep ultraviolet light has a wavelength of approximately 248 nanometers.
7. A method for forming a photoresist structure as recited in claim 5 wherein said deep ultraviolet light has a wavelength of approximately 193 nanometers.
8. A method for forming a photoresist structure as recited in claim 5 wherein said exposing said layer of i-line photoresist to deep ultraviolet light comprises exposing the entire top surface of said layer of i-line photoresist to deep ultraviolet light.
9. A method for forming an implant region comprising:
forming a layer of photoresist over a semiconductor substrate, said layer of photoresist having a designated wavelength, a first thickness and high optical absorption of light having a first wavelength;
exposing said layer of photoresist to said light having a first wavelength;
exposing portions of said layer of photoresist to light having a second wavelength so as to pattern said layer of photoresist, said second wavelength approximately said designated wavelength;
developing said layer of photoresist, after said exposing said layer of photoresist to said light having a first wavelength and said exposing portions of said layer of photoresist to light having a second wavelength, so as to form a photoresist structure having an opening extending therethrough and having a second thickness that is less than said first thickness; and
implanting ions at an angle that is not orthogonal to a top surface of said semiconductor substrate, said ions passing through said opening so as to form an implant region.
10. A method for forming an implant region as recited in claim 9 wherein said light having a first wavelength comprises deep ultraviolet light.
11. A method for forming an implant region as recited in claim 10 wherein said layer of photoresist comprises i-line photoresist and wherein said light having a second wavelength comprises light having a wavelength of approximately 365 nanometers.
12. A method for forming an implant region as recited in claim 10 wherein said first exposure further comprises illuminating said layer of photoresist using a deep ultraviolet scanner.
13. A method for forming an implant region as recited in claim 10 wherein said first exposure comprises exposing the entire top surface of said semiconductor substrate to light having a wavelength of 248 nanometers.
14. A method for forming an implant region as recited in claim 10 wherein said deep ultraviolet light has a wavelength of approximately 157 nanometers.