Photoresist Removal Using Atomic Hydrogen Generated by Hot-Wire Catalyzer and Effects on Si-Wafer Surface

Abstract

We investigated an environmentally friendly method using atomic hydrogen generated by contact catalysis on a tungsten hot-wire catalyzer to remove photoresist instead of using chemicals and its effects on a Si-wafer surface. We eventually obtained a photoresist removal rate of 2.5 mm/min attributable to a reaction of atomic hydrogen with a positive-tone novolak photoresist, without thermal shrinkage of the photoresist film during atomic hydrogen irradiation because the photoresist shrank only under the influence of substrate heating by the catalyzer. The effects of atomic hydrogen irradiation on the substrate surfaces cannot be confirmed.

Enhancement of Photoresist Removal Rate by Using Atomic Hydrogen Generated under Low-pressure Conditions

“…Some findings related to the use of atomic hydrogen generated on a tungsten hot-wire catalyst for photoresist removal have already been reported [10][11][12][13][14][15][16]. In a past study we achieved a best removal rate of 2.5 μm/min using atomic hydrogen by heating up the catalyst and the substrate [12].…”

“…It should be noted that the H-atom density saturates against the H 2 pressure under such high pressure conditions [26] and that the H atoms produced may be completely thermalized before arriving at the substrate surfaces. In our past study, we reported that the removal rate increases with hydrogen pressure between 0.4 and 7.2 Pa [12]. This increase can easily be ascribed to the increase in the H-atom density [26].…”

“…Here, λ is the wavelength of the light source (532 nm) and n is the refractive index of the photoresist film (1.6 -1.7). The refractive index varies with changes in the substrate temperature because the photoresist is shrunk by baking [12]. Then, the photoresist removal rate, , can be calculated from the film thickness change in each time interval, .…”

“…(1) The time-averaged substrate temperature, T avg-subst , was calculated by the following integration [12]. (2) In both equations, m is an integer greater than or equal to one.…”

“…In a past study we achieved a best removal rate of 2.5 μm/min using atomic hydrogen by heating up the catalyst and the substrate [12]. But this rate is not as good as that obtained by using chemicals, which exceeds 3 μm/min [17,18].…”