Patterning silicon carbide films

A method of etching an opening having tapered wall in a layer of silicon carbide (SiC) includes forming a layer of a resist on the SiC layer. An opening having tapered wall is formed in the resist layer so as to expose a portion of the SiC layer. The exposed portion of the SiC layer is then exposed to a plasma of a gas containing carbon and fluorine to etch an opening through the SiC layer with the opening having tapered walls. If a layer of a glass is provided under the SiC layer, the plasma will also etch through the glass layer to provide an opening in the glass layer having tapered walls.

FIELD OF THE INVENTION 
The present invention relates to a method of patterning silicon carbide 
(SiC) films, and, more particularly, to a method of etching tapered holes 
in a film of SiC. 
BACKGROUND OF THE INVENTION 
In certain types of semiconductor devices, films of SiC are used for 
various purposes. Often the SiC film is applied over a layer of a glass. 
In such devices it is often desirable to pattern the SiC film and the 
glass layer beneath the SiC film by etching it. One reason for patterning 
the SiC film is to form holes in the film through which conductors of a 
metal film can extend. To provide for greater ease of forming the 
conductors in the etched holes in the SiC film, it is desirable to form 
the holes with tapered walls. Various techniques and materials have been 
developed for etching tapered holes in various materials used in the 
semiconductor field. However, heretofore there have been no readily and 
successful method of etching tapered holes in a film of SiC, and 
particularly, also through a glass layer beneath the SiC film. 
SUMMARY OF THE INVENTION 
An opening is etched in a layer of silicon carbide (SiC) by first forming 
on the SiC layer a layer of a resist having an opening therethrough to 
expose a portion of the SiC layer. The exposed portion of the SiC layer is 
then exposed to a plasma of a gas containing carbon and fluorine so as to 
etch away the exposed portion of the SiC layer.

DETAILED DESCRIPTION 
Referring initially to FIG. 1, there is shown a portion of a semiconductor 
device 10 which can be made by the method of the present invention. The 
semiconductor device 10 comprises a substrate 12 of a semiconductor 
material, such as single crystalline silicon. In the substrate 12 and at 
the surface 14 thereof there can be a plurality of regions, not shown, of 
different conductivity types which form various active and passive 
devices. A layer 16 of a glass is on the substrate surface 14, and a layer 
18 of silicon carbide (SiC) is over the glass layer 16. The SiC layer 18 
and the glass layer 16 have aligned holes 20 and 22 therethrough to the 
substrate surface 14. The walls of the holes 20 and 22 are tapered. A 
strip 24 of a conductive metal is on the SiC layer 18 and extends into and 
through the holes 20 and 22 to contact the substrate surface 14. 
To make the semiconductor device 10, the glass layer 16 is first coated 
over the substrate surface 14 by any well known technique for the glass 
used. The SiC layer 18 is then coated over the glass layer 16 using any 
well known technique for depositing SiC. As shown in FIG. 2, a layer 26 of 
a resist material is then coated over the SiC layer 18. Preferably, the 
resist layer 26 is of a thickness 2 or more times the thickness of the SiC 
layer 18. An opening 28 is then formed in the resist layer 26. The opening 
28 must have tapered walls in order to form tapered wall openings in the 
SiC layer 18 and the glass layer 16. There are several well known 
techniques for producing tapered resist wall profiles. Most low resolution 
printing techniques, such as proximity gap or scanning projection 
printers, produce sloped wall profiles of less than 70.degree. with 
respect to the horizontal. Some resist systems require special resist 
processing procedure to produce tapered wall profiles, such as flood 
exposure (see the article by L. K. White and D. Meyerhofer, JOURNAL OF 
ELECTRO-CHEMICAL SOCIETY, Vol. 134(12), 1987, pg. 3125). 
The opening 28 exposes a portion of the surface of the SiC layer 18. In an 
embodiment, the exposed surface of the SiC layer 18 is then exposed to a 
non-oxygen containing plasma of a gas containing carbon (C) and fluorine 
(F). It has been found that oxygen containing plasmas erode the resist 
much faster than the SiC etches. Also, the oxygen tends to etch the 
polymer depositions in the system over time producing wide etch rate 
variations and unacceptable etch residue remaining behind after etching. 
The most successful etching of SiC films has been done in plasmas of pure 
CF.sub.4, C.sub.2 F.sub.6 or these gases mixed with small additions of 
CHF.sub.3. Positive results also have been obtained using NF.sub.3 and 
SF.sub.6 as etch gases and these gases mixed with O.sub.2, which have 
proven to be less deleterious to the resist than CF.sub.4 or C.sub.2 
F.sub.6 mixed with oxygen. This plasma etches a hole 20 in the SiC layer 
18 having a tapered wall. By controlling the power, pressure and gas flow 
of the plasma gas, it is not only possible to etch through the SiC layer 
18, but also the opening 22 can be etched through the glass layer 16. For 
example, in a parallel plate plasma etcher a power of 50 W, a flow rate of 
CF.sub.4 of 60 ssccm, and a pressure of 150 mTorr., will etch both the SiC 
layer 18 and the glass layer 16 and provide holes 20 and 22 having tapered 
walls. 
Thus, there is provided by the present invention a method of etching SiC 
layers so as to pattern the layer with the opening in the SiC layer having 
a tapered wall. Also, the method will etch through a layer of glass 
beneath the SiC layer and provide an opening in the glass layer having a 
tapered wall.