Selective etch process for silicon nitride
A method for selectively etching a substrate is described. The method includes preparing a substrate comprising a silicon nitride layer overlying a silicon-containing contact region, and patterning the silicon nitride layer to expose the silicon-containing contact region using a plasma etching process in a plasma etching system. The plasma etching process uses a process composition having as incipient ingredients a process gas containing C, H and F, and a non-oxygen-containing additive gas, wherein the non-oxygen-containing additive gas includes H, or C, or both H and C, and excludes a halogen atom.
1. A method for selectively etching a substrate, comprising:
preparing a substrate comprising a silicon nitride layer overlying a silicon-containing contact region;
patterning said silicon nitride layer to expose said silicon-containing contact region using a plasma etching process in a plasma etching system, wherein said plasma etching process uses a process composition consisting of, as incipient ingredients, CH 3 F, C 2 H 4 as a halogen-free additive gas, O 2 and an optional noble gas; and
optimizing said plasma etching process to achieve an etch selectivity between said silicon nitride layer and said silicon-containing contact region that exceeds 20:1.
2. The method of claim 1 , further comprising:
preparing said substrate with a silicon oxide layer; and
optimizing said plasma etching process to achieve an etch selectivity between said silicon nitride layer and said silicon oxide layer that exceeds 20:1.
3. The method of claim 2 , wherein a flow rate of said CH 3 F gas ranges from about 1 sccm to about 50 sccm, a flow rate of said C 2 H 4 gas ranges from about 5 sccm to about 20 sccm; and a flow rate of said O 2 gas ranges from about 1 sccm to about 50 sccm.
4. The method of claim 1 , wherein said plasma etching process includes setting a pressure in said plasma etching system ranging from 10 mTorr to 80 mTorr.
5. The method of claim 1 , wherein said plasma etching process includes coupling first radio frequency (RF) power at a first frequency to a substrate holder upon which said substrate rests in said plasma etching system, and coupling second radio frequency (RF) power at a second frequency to an upper electrode opposing said substrate on said substrate holder.
6. The method of claim 1 , wherein said substrate rests on a temperature controlled substrate holder in said plasma etching system, said temperature controlled substrate holder comprises:
a support base having fluid channels to circulate a temperature controlled thermal fluid in said support base; and
a substrate support coupled via a thermal insulator to an upper portion of said support base, said substrate support comprising:
one or more heating elements embedded within said substrate support,
an upper surface to support said substrate by contact between said upper surface and a backside of said substrate, and
an electrostatic clamp electrode to hold said substrate on said upper surface of said substrate support.
7. The method of claim 6 , wherein said temperature controlled substrate holder further comprises:
a backside gas supply system configured to supply a heat transfer gas to the backside of said substrate through at least one of a plurality of orifices or channels disposed on said upper surface of said substrate support, wherein said plurality of orifices of said backside gas supply system are arranged in a plurality of zones on said upper surface of said substrate support to vary a backside pressure in a radial direction between a substantially central region of the backside of said substrate and a substantially edge region of the backside of said substrate.
8. The method of claim 1 , wherein said silicon-containing contact region comprises a source region or drain region for a transistor.
9. The method of claim 1 , wherein said silicon-containing contact region comprises doped silicon or metal silicide.