A Novel Integrated MEMS Process Using Fluorocarbon Films Deposited With a Deep Reactive Ion Etching (DRIE) Tool
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However, there has been little effort to characterize films deposited with a high-density inductively coupled plasma (ICP) tool, particularly with equipment that employs the patented Bosch process4 . For instance, the measured deposition rate in one of these tools can exceed 25 A/sec, whereas information found in the literature describes deposition rates some 3 times lower when using pulsed power high-density plasmas 2' and much lower when utilizing reactive ion etching (RIE) tools'. The comparatively fast deposition rates of ICP tools, and the ability to remove these films from horizontal surfaces using a simple oxygen plasma in a parallel-plate RIE piece of equipment5 , permit their utilization in electrostatic actuators, relays and other devices requiring the presence of a passivating or antistiction film. The demonstration of in situ microfabrication of electrostatic actuators that exhibit a sidewall passivation film is explored in a subsequent section. Furthermore, the measured etching selectivity to silicon in combination with the observed deposition rate suggests the use of these films as masking material for bulk micromachining. Therefore, fluorocarbon films in combination with positive photoresist and silicon oxide films permit the realization of triple nested mask schemes. Section II describes the experimental approach, followed by the measured performance in section III. Section IV introduces some MEMS applications of fluorocarbon films.
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Mat. Res. Soc. Symp. Proc. Vol. 605 © 2000 Materials Research Society
II. EXPERIMENTAL APPROACH This experiment was conducted in a high-density inductively coupled plasma tool from Surface Technology Systems that has been described elsewhere5 . In this exercise, the equipment was operated with all etching inputs excluded. Four variables were studied in this experiment: C 4 F 8 flow rate, throttle or automatic pressure control (APC) valve position in degrees, electrode power, and coil power. The corresponding ranges explored are presented in table I. Table I. Range of explored variables. VARIABLE
MINUMUM
MAXIMUM
C4F8 Flow Rate (sccm)
10
150
APC Position (0) Electrode Power (W) Coil Power (W)
15 1 300
75 29 950
In this experiment the pressure was controlled by entering a fixed position for the APC valve (see table I) and allowing the flow rate to determine the operating pressure. Higher pressures correspond to higher values of the APC position in degrees. The samples were prepared in the following fashion: 4" single crystal silicon wafers with resistivity 5 to 20 f2-cm, were exposed to the high density glow discharge for 5 minutes, and analyzed as described in the following paragraphs. The commercial software package ECHIP was used to create and analyze a matrix of 20 different experimental points spanning the parameter space detailed in Table I. The experimental design included 5 additional replicate runs to verify the repeatability of the deposited films and the fit of the curves generated. The resultant response surfaces have proven to be valuable in mo
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