Summer Processing Lab: Week 5/6 (7/7 & 7/14)

This week marks the completion of the second mask exposure for our MOSCAP manufacturing process. We further calibrated our exposure time based on observed results from the first layer, Manufacturer datasheets for estimated reflectivity, and the measured radiance of our lamp.

D = D0 * (1 + R_eff*e^(-αT)) | Levinson, Harry J. Principles of Lithography, 4th Ed.

Parameters:
60-80nm SiO2 ~ 70nm = 7 * 10^-8
4000rpm for 60 sec with nLOF 2035 -> ~3.5 µm
2.5 minute post spin bake
1 minute post exposure bake
D_0: 75 mJ/cm^2 based on experimental resolution falloff.
lamp power: 8.55 mW/cm^2

Thompson, L. F., Willson, C. G., & Bowden, M. J. (1994). Introduction to microlithography. American Chemical Society.

Full Stack Reflectivity via Transfer Matrix Method:

Reff = ((r_12 + r_23 * e^(4i * pi * n_2 * d/λ)/(1 + r_12 * r_23 * e^(4i * pi * n_2 * d/λ))^2

Refraction Constants:
n_1 = n_resist = 1.64
n_2 = n_SiO₂ = 1.46
n_3 = n_Si = |3.8 + 0.02i| ~ 3.80

Fresnel reflection coefficients:
r_12 = (n_1 - n_2)/(n_1 + n_2) = (1.64 - 1.46)/(1.64 + 1.46) = 0.0580645161
r_23 = (n_2 - n_3)/(n_2 + n_3) = (1.46 - 3.80)/(1.46 + 3.80) = -0.44487

Reff_wet = ((0.058 - 0.44487 e^(4i pi 1.46 * 6.459/40))/(1 - 0.0258 * e^(4i * pi * 1.46 * 6.459/40)))^2 = 0.2398
Reff_dry = ((0.058 - 0.44487 * e^(4i * pi * 1.46 * 9.701/40))/(1 - 0.0258 * e^(4i * pi * 1.46 * 9.701/40)))^2 = 0.2117

Dosage Calculations:
D_wet = 75 * (1 + 0.2117*e^(-0.55 * 10^6 * 3.25 * 10^-6)) = 77.6575 mJ/cm^2
D_dry = 75 * (1 + 0.2398*e^(-0.55 * 10^6 * 3.25 * 10^-6)) = 78.0103 mJ/cm^2

Exposure Time Calculations:
t_wet = (77.6575 mJ/cm^2)/(8.55 mW/cm^2) = 9.08274854 seconds
t_wet = (78.0103 mJ/cm^2)/(8.55 mW/cm^2) = 9.1240117 seconds