Soft vacuum, pulsed electron-beam hardening of lithographic polymers
- PDF / 5,647,102 Bytes
- 9 Pages / 593.28 x 841.68 pts Page_size
- 53 Downloads / 264 Views
H. Hiraoka IBMAlmaden Research Center, San Jose, California 95120-6099
M.A. Caolo Hewlett-Packard Company, Fort Collins, Colorado 80525 (Received 1 June 1988; accepted 17 August 1988) A 25 kV pulsed electron beam was used to harden O.5-3.O//m thick^Z-type, MacDermid, and polyamic acid (PMDA + ODA) resist patterns. The resist profiles are stable against hightemperature treatment that ranges between 200-350 °C. The short pulse ~ 100 ns, electron beams employed in resist hardening are produced from a cold cathode in 30-50 mTorr air by discharging energy stored in a 7.5 nF capacitor producing a dose/pulse ~ 1 //C/cm 2 at the processed surface. Comparisons with conventional hardening methods using ultraviolet emission from a high-pressure mercury lamp, a windowless, vacuum ultraviolet (VUV) lamp, and low-energy electron emission from a cw source are also made.
I. INTRODUCTION Preserving the physical integrity of relief images of developed resist during subsequent high-temperature processes such as reactive ion etching, ion implantation, lift-off, and metal deposition is extremely important in microelectronic manufacturing.' For example, preserving the integrity of microlithographic structures is important in portable conformable bilayer resist systems using AZ-type resists.2 There is a need both to maintain vertical etch profiles and maintain critical dimensions as well as prevent undesired rounding of developed image edges. These issues are critical for positive resist images that experience outgassing, reticulation, edge rounding, and flow during high-temperature process steps. Both wet chemical3 as well as physical methods of resist hardening have been proposed and implemented.4"14 Ultraviolet (UV) hardening4-910 of both photoresists and electron beam resists is being increasingly practiced in manufacturing using commercial systems." Hiraoka and Pacansky4 have used UV photons to thermophysically harden ^Z-type photoresists. Orvek et al.l0 have shown the possibility of cross-linking even 1.5 /nm thick Shipley S 1400-31 resist using simultaneously UV radiation and heat energy. The UV-photohardening, while practical for treating thin layers, is not suitable for hardening thick layers. The reason for this is due to the high optical extinction coefficient in the ultraviolet of most organic groups (0.5 to l.OxlO 4 liter/ mol-cm). Hence 95% of the UV energy is absorbed
1 Present
address: Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695.
J. Mater. Res. 3 (6), Nov/Dec 1988
http://journals.cambridge.org
within 300 nm of the surface of most resists.15 As a consequence, for thick resists nonuniform exposure occurs versus depth. Finally, to produce the required UV energy at a wavelength around 300 nm from a conventional UV lamp, the input electrical energy needed is quite large due to poor electrical-to-photon conversion efficiency ( ~ 10~3) of these lamps. The limited operating lifetime of the lamps ( ~ 1 0 0 0 h ) , the external lamp cooling required, and the requirement
Data Loading...
