Page 138 - Sami Franssila Introduction to Microfabrication

Lithographic Patterns 117

CH 2 can be used as a model molecule for photoresist. Bruce, J.A. et al: Characterization of linewidth variation for
This calculation shows that 10.3 grams of ozone is single- and multiple-layer resist systems, IEEE TED, 34
needed to remove 1 gram of resist, for example, a batch (1987), 2428.
of 25 wafers (200 mm) would need ca. 10 to 100 kg of Brunner, T.: Pushing the limits of lithography for IC produc-
tion, IEDM 1997, p. 9.
ozonized water. But fortunately, much less is needed; Hartney, M.A. et al: Oxygen plasma etching for resist stripping
ozone breaks up longer molecules, and the smaller
and multilayer lithography, J. Vac. Sci. Technol., B7
molecules are water soluble. (1989), 1.
Heschel, M. & S. Bouwstra: Conformal coating by photoresist
of sharp corners of anisotropically etched through-holes in
10.8 EXERCISES
silicon, Sensors Actuators A70 (1998), 75.
1. What fraction of resist ends up on the wafer in Holmes, S.J. et al: Manufacturing with DUV lithography, IBM
spin coating? J. Res. Dev. 41 (1997), 7.
Ishibashi, T. et al: Advanced microlithography process with
2. Estimate the contrasts of resists in Figure 10.3.
chemical shrink technology, Jpn. J. Appl. Phys., 40 (2000),
3. How much resolution can be gained by adopt- 419.
ing TSI? Loechel, B.: Thick-layer resists for surface micromachining, J.
4. By how much will the swing ratio be reduced if a top Micromech. Microeng., 10 (2000), 108.
antireflection coating can reduce air/resist reflections Neureuther, A.R. & C.A. Mack: Optical lithography modeling,
by 20%? By how much will the swing ratio be in P. Rai-Choudhury (ed.): Handbook of Microlithography,
reduced if the absorbance increases from 0.5 to Micromachining and Microfabrication, SPIE.
−1
1 µm ? Peterson, B. et al: Approaches ro reducing edge roughness
5. Calculate some good and bad resist thicknesses for and substrate poisoning of ESCAP photoresists, Semicond.
novolak resist at 365 nm exposure. Fabtech., 8 (1996), 183.
6. What is the linewidth in Figure 10.4? Rai-Choudhury, P.: (ed.): Handbook of Microlithography,
Micromachining and Microfabrication, Vol. 1, SPIE 1997.
7. If a wafer with 350 µm thick resist is baked on a Satou, I. et al: Progress in top surface imaging process, Jpn. J.
hot plate that is 0.1 off-horizontal, what will be the Appl. Phys., 39 (2000), 6966–6971.
◦
resist non-uniformity due to gravitational flow? Usujima, A. et al: Generation mechanism of photoresist
residue after ashing, J. Electrochem. Soc., 141 (1994), 2487.
IBM J. Res. Dev., 41(1/2) (1997), special issue on optical
REFERENCES AND RELATED READINGS
lithography.
Ausschnitt, C.P. et al: Advanced DUV photolithography in a Conference series “Advances in Resist Technology and Pro-
pilot line environment, IBM J. Res. Dev., 41 (1997), 21. cessing” by SPIE is organized annually.