Process including silo-chloro passivation for etching tungsten silicide overlying polysilicon
First Claim
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1. A method of etching a tungsten silicide layer, comprising the steps of:
- placing within a plasma reaction chamber a substrate containing the tungsten silicide layer;
flowing into the plasma reaction chamber a first gas mixture comprising an etching gas comprising a chlorine- and fluorine-containing gas and a passivating gas comprising constituents including silicon and chlorine; and
exciting the first gas mixture into a plasma.
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Abstract
A method of plasma etching tungsten silicide over polysilicon particularly useful in fabricating flash memory having both a densely packed area and an open (iso) area requiring a long over etch due to microloading. Wafer biasing is decreased in the over etch. The principal etchant include NF3 and Cl2. Argon is added to prevent undercutting at the dense/iso interface. Oxygen and nitrogen oxidize any exposed silicon to increase etch selectivity and straightens the etch profile. SiCl4 as an example of a silicon and chlorine containing passivating gas may be added for additional selectivity.
28 Citations
20 Claims
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1. A method of etching a tungsten silicide layer, comprising the steps of:
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placing within a plasma reaction chamber a substrate containing the tungsten silicide layer; flowing into the plasma reaction chamber a first gas mixture comprising an etching gas comprising a chlorine- and fluorine-containing gas and a passivating gas comprising constituents including silicon and chlorine; and exciting the first gas mixture into a plasma. - View Dependent Claims (3, 4, 5, 6)
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2. (canceled)
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7. A multi-step method of etching tungsten silicide over silicon, comprising the steps of:
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placing a substrate containing a tungsten silicide layer of tungsten overlying a silicon layer onto a pedestal electrode in a plasma reaction chamber; a first step of flowing into the plasma reaction chamber a first gas mixture comprising an etching gas comprising nitrogen trifluoride and chlorine gas, a first gas comprising oxygen gas and nitrogen gas, and argon; exciting the first gas mixture into a plasma to etch through the tungsten silicide layer in at least a portion of the substrate while biasing the pedestal electrode with a first level of RF power; a subsequent second step of flowing into the plasma reaction chamber a second gas mixture comprising the etching gas, the oxidizing gas, and a passivating gas comprising constituents including silicon and chlorine and exciting the second gas mixture into a plasma while biasing the pedestal electrode with a second level of RF power greater than the first level. - View Dependent Claims (8, 9, 10)
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11. A method of etching a tungsten-containing layer overlying a silicon layer, comprising the steps of:
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placing onto a pedestal electrode in a plasma reaction chamber a substrate containing the tungsten-containing layer and the silicon layer, and by an etching mask overlying the tungsten-containing layer, wherein the silcon layer consists principally of silicon; a first step of flowing into the chamber a first gas mixture comprising a first gas comprising chorine and fluorine and a second gas comprising oxygen gas and nitrogen gas; biasing the pedestal electrode with a first level of RF power; applying a second level of RF power to excite the first gas mixture into a plasma to thereby etch at least the tungsten-containing layer sufficiently that at least some of the silicon layer is exposed, wherein a ratio of the second level to the first level is between 4 and 8; a subsequent second step of flowing into the chamber a second gas mixture comprising the etching gas having a smaller fraction of NF3 than in the first step, the oxidizing gas having a larger fraction of nitrogen gas than in the first step, and a passivating gas comprising silicon and chlorine constituents; biasing the pedestal electrode with a third level of RF power greater than the first level; and applying a fourth level of RF power to excite the second gas mixture into a plasma. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification