Multi-layer hard mask for deep trench silicon etch

A method of etching trenches of close proximity on a silicon substrate comprising the steps of:

• (a) providing a silicon substrate capable of being etched with a first etchant;
• (b) depositing a layer of pad dielectric over said silicon substrate, said pad dielectric comprising a first layer and a second layer;
• (c) depositing a third layer of borosilicate glass over said layers of pad dielectric, said third layer comprising a first hard mask layer of said borosilicate glass having a slower etch rate than said pad dielectric and said silicon substrate when contacted with said first etchant;
• (d) depositing a fourth layer of silicon oxide over said third layer of borosilicate glass, said fourth layer comprising a second hard mask layer of said silicon oxide having a slower etch rate than said silicon substrate and said first hard mask layer of borosilicate glass when contacted with said first etchant;
• (e) applying a resist layer and exposing the pattern on said third and fourth layers and said layers of pad dielectric;
• (f) etching said third and fourth layers and said layers of pad dielectric;
• (g) stripping the remaining resist layer;
• and
• (h) etching said silicon substrate with said first etchant to form said trenches, said fourth layer of silicon oxide protecting said third layer of borosilicate glass from said first etchant by acting as a sacrificial hardmask, thereby completely removing said fourth layer of silicon oxide while partially removing said third layer, said fourth layer of silicon oxide reducing the sensitivity of first etchant to third layer of borosilicate glass moisture contamination thereby providing control in forming said trench.

A method of etching a plurality of trenches having the same or different dimensions and directions in a silicon substrate comprising the steps of:

• (a) providing a silicon substrate capable of being etched with a first etchant, having a layer of pad dielectric comprising a first layer and a second layer over said silicon substrate, and a dual layer hard mask comprising a third layer over said silicon substrate of silicon oxide deposited over said layers of said pad dielectric by plasma enhanced chemical vapor deposition, and a fourth layer over said silicon substrate of borosilicate glass deposited over said third layer of silicon oxide;
• (b) etching said layers of pad dielectric, silicon oxide and borosilicate glass in accordance with a desired pattern;
• (c) etching said silicon substrate with said first etchant to produce said plurality of trenches in said silicon substrate, said fourth layer of borosilicate glass protecting said third layer of silicon oxide from said first etchant by acting as a sacrificial hardmask, thereby substantially removing at least a portion of said layer of borosilicate glass, said layer of borosilicate glass reducing the sensitivity of first etchant to said third layer of silicon oxide moisture contamination thereby providing control in forming said plurality of trenches;
• and
• (d) removing remaining said layer of borosilicate glass with an etchant highly selective to said layer of silicon oxide and said layers of said pad dielectric to provide a planar surface on said third layer over said silicon substrate of silicon oxide after removing remaining said fourth layer over said silicon substrate of borosilicate glass, wherein said etchant is 50 times more likely to etch said third layer of borosilicate glass than said layer of said silicon oxide and said layers of said pad dielectric thereby minimizing undercutting of said first layer of said pad dielectric.