Deep reactive ion etching of PMMA$

The deep reactive ion etching of PMMA in O2, O2/CHF3 discharges has been examined as a function of plasma parameters such as pressure, power and relative composition. It is demonstrated that the etching rate initially increases with pressure but decreases after 6.65 Pa. The etching rate increased linearly with power, but the rough surface will occur and sample will be distorted, so power cannot surpass 50 W. The etching rate decreases with CHF3 ratio in O2/CHF3 discharges. The sidewall undercut becomes serious when the profile depth etched in pure O2 plasma is more than 100 mm. By addition of proper proportion of CHF3 to O2, the sidewall undercut can be reduced. The sidewall profile is vertical even the etching depth is as deep as 400 mm when etched in O2/CHF3 discharges(40% CHF3), 30 W, 3.99 Pa, and high aspect ratio microstructure is achieved. # 2003 Elsevier B.V. All rights reserved