Sacrificial etchback layer for improved spin-on-glass planarization

The method of forming a planar surface by uniformly etching back a spin-on-glass (SOG) layer over a substrate comprising:

• (1) forming a first insulating layer over a substrate;
• said substrate having an annular shape with a central area and a peripheral area:
• (2) forming a SOG layer over said first insulating layer;
• said SOG layer having a greater thickness in said central area than in said peripheral area:
• (3) forming a sacrificial layer over said SOG layer;
• said sacrificial layer having a greater thickness in said peripheral area of said substrate compared to said central area;
• the total thickness of said sacrificial layer and said SOG layer is approximately equal in said central area and said periphery area:
• said sacrificial layer is formed of silicon oxide formed by a chemical vapor deposition process where reactant gas is flowed over said substrate and controlling the reactant gas velocity so that the reactant gas flow rate is greater over said peripheral area than said central area, and
• (4) etching back said sacrificial layer and portions of said SOG layer, the etch back having a selectivity of said SOG layer to said sacrificial layer of about 1:1.

The method of forming a planar surface by uniformly etching back a spin-on-glass (SOG) layer over a substrate comprising:

• (1) forming a first insulating layer composed of silicon oxide over a substrate:
• said substrate having an annular shape with a central area and a peripheral area:
• (2) forming a SOG layer over said first insulating layer;
• said SOG layer having a greater thickness in said central area than in said peripheral area:
• said SOG layer having a thickness in a range of between about 3000 and 8000 .ANG.;
• (3) forming a sacrificial layer over said SOG layer;
• said sacrificial layer having a greater thickness in said peripheral area of said substrate compared to said central area;
• the total thickness of said sacrificial layer and said SOG layer is approximately equal in said central area and said periphery area;
• said sacrificial layer is formed of silicon oxide formed by a chemical vapor deposition process where reactant gas is flowed over said substrate and controlling the reactant gas velocity so that the reactant gas flow rate is greater over said peripheral area than said central area;
• said sacrificial layer having a thickness in a range of between about 3000 and 8000 .ANG.;
• and
• (4) etching back said sacrificial layer and portions of said SOG layer using a reactive ion etch using CHF.sub.3, CH.sub.4 and O.sub.2 gasses;
• the selectivity of the etch back of said SOG layer with respect to said sacrificial layer is approximately 1:1, wherein the etch back of said SOG layer is performed at about the following conditions:
• a flow of CH.sub.4 in the range of about 15 to 40 sccm and a flow of CHF.sub.3 in the range of about 50 to 100 sccm and a ratio of CH.sub.4 :
• CHF.sub.3 in the range between about 3:10 to 6:10, and an argon flow rate of between about 300 to 400 sccm and a RF power in the range of about 450 to 550 W and at a pressure in the range of 300 to 600 mTorr and a wafer temperature between about 25.degree. to 70.degree. C. during the etch process.