Reactive Ion Etching Techniques for Silicon Sidewall Angle Control in Microengineering

Abstract

This paper describes reactive ion etching (RIE) techniques with silicon substrates for initial processing of semiconductor field emitter array cathodes for vacuum microelectronics. A secondary focus is process research for optical reflecting gratings for opto-and micromechanical devices. These applications each require control of the sidewall angle and apex radius. In this paper, we describe micromachining control of trenches with remainder sidewall angles varying from 15-60 ~ and resulting apex ridge radii of as small as 40 nm. A fluorine-based chemistry (CF4/O2) with oblique angles for the incident beam (tilted substrates) and overetching is used. The use of both deep UV-hardened photoresist and aluminum as RIE shadowmasks is compared. Unannealed aluminum as a shadowmask for RIE micromachining has the advantage of lower etch/sputtering rates and higher process temperature tolerance compared to photoresist in the CF402 RIE system. Etch environments in the pressure range 30-80 mTorr with CF4/O2 flow rates of 20/2 sccm, RF power 100-200 W, and etch duration 30 min are described. Both tilted and untilted substrates mountings were studied. Under these conditions, the surface erosion is primarily a combination of ion milling and chemical etch mechanisms. Both P-type and N-type substrates of 100 nm diam wafers were used. Relatively sharp single-and double-ridged silicon structures were obtained using the photoresist shadowmask on untilted substrates. The photoresist shadowmask provides an advantage over A1 only for the sidewall orientation 0 t : 20 ~ where we were able to specify a condition for obtaining a smooth optically reflective surface. The more vertical sidewall angles obtainable with the unannealed A1 shadowmask should permit fabrication of field emitter cone or ridge cathodes on pedestals with higher height-to-width ratios. A field cathode pedestal with a more vertical sidewall results in a higher electric field at the electron emission tip or ridge.

Height Equivalent to a Theoretical Plate Theory for Rectangular GC Columns

“…This involves etching a groove on a silicon wafer and covering it with a cover plate using fabrication processes available to the microelectronics industry. , While wet chemical etched columns have been assembled, their performance has been variable compared to more conventional GC technology. − Much of this is due to the inability to provide a satisfactory bonded phase and to match the geometry of the column to the detector. With the advent of deep-etching capabilities and newer wafer-bonding techniques, this is changing. − State-of-the-art reactive ion etchers (RIE) allow rectangular columns to be microfabricated with a rectangular cross section and provide an aspect ratio where the corners of the rectangle are sharply defined. − Unfortunately, any attempt to microfabricate such a column is muddled by a lack of theoretical models to predict performance. Such a model is necessary if optimum design parameters are to be selected for what could be a very expensive development effort.…”

Applications of nanoimprint lithography/hot embossing: a review

“…[65] Nanostructures with 3D profiles are equally important and widely needed in nanolens, blazed gratings, grayscale embossing, sharp tips and staggered configurations.…”

Optimal parameter estimation for the online control of ion milling etch depth

“…Given these trends and the inherently tight product specifications, automatic process control is becoming an increasingly impor-Ž . tant issue Kim et al, 1992;Edgar et al, 2000 . The etching process is a critical step in the manufacturing process. It is not uncommon for a single wafer to be etched several times at various stages of the fabrication line.…”