Multiple step trench etching process
AssigneeMotorola, Inc.
InventorHoward K. H. Leung
Life of this patent
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Abstract
A process having three steps to etch a vertical trench with rounded top corners and rounded bottom corners. The first step involves anisotropically etching a vertical trench through an opening in a masking layer to approximately 85 to 90% of the final trench depth to give a trench with sharp or abrupt top corners and sharp bottom corners. The second step rounds the top corners and the third step extends the trench depth and provides rounded bottom corners. Using CHF.sub.3 as an etch species and adjusting the DC bias differently for each step gives better profile control and better critical dimension (CD) control.
Claims15
A process for etching trenches with rounded corners in a semiconductor substrate comprising the sequence of steps of:
- performing a first etch using NF.sub.3 and CHF.sub.3 etch species at a first DC etch bias, to form a preliminary trench having sharp top corners and sharp bottom corners;
- performing a second etch using NF.sub.3 and CHF.sub.3 as etch species at a second DC etch bias higher than said first DC etch bias, to etch the sharp corners of the trench into rounded top corners;
- and
- performing a third etch using only NF.sub.3 as etch species, to further extend the depth of the trench while forming rounded bottom corners.
A process for plasma etching trenches in a semiconductor substrate comprising the steps of:
- forming a masking layer over a surface of the semiconductor substrate;
- forming an opening in the masking layer to expose a selected portion of the semiconductor substrate surface;
- performing a first plasma etch using NF.sub.3 and CHF.sub.3 as etch species at a first DC etch bias, of the semiconductor substrate through the opening anisotropically forming a preliminary trench having sharp top corners and sharp bottom corners;
- performing a second plasma etch using NF.sub.3 and CHF.sub.3 as etch species at a second DC etch bias higher than said first DC bias, of the semiconductor substrate to etch the top corners of the preliminary trench providing rounded top corners;
- and
- performing a third plasma etch using only NF.sub.3 as species of the semiconductor substrate further extending the depth of the trench while forming rounded bottom corners providing a finished trench profile having rounded corners.
A process for plasma etching trenches having rounded corners in a silicon substrate comprising the steps of:
- forming a top masking layer of a photoresist material and a bottom masking layer of silicon dioxide over a surface of the silicon substrate;
- forming an opening in the top masking layer and bottom masking layer to expose a selected portion of the silicon substrate surface;
- performing a long first plasma etch of the silicon substrate through the opening anisotropically using NF.sub.3 and CHF.sub.3 as etch species at a first DC bias voltage, forming a preliminary trench having sharp top corners and sharp bottom corners and a depth of from 85 to 95% of the depth of the finished trench, and removing the top masking layer;
- performing a short second plasma etch of the silicon substrate using NF.sub.3 and CHF.sub.3 as etch species at a second DC bias voltage higher than said first DC bias voltage to etch away edges of the bottom mask layer while etching the top corners of the preliminary trench providing a rounded profile;
- and
- performing a short third plasma etch of the silicon substrate using NF.sub.3 only as etch species at a third DC bias voltage lower than said second DC bias voltage, further extending the depth of the trench while forming rounded bottom corners providing a finished trench profile having rounded corners.
Dependencies are inferred from the claim text.