Process for etching tungsten silicide overlying polysilicon particularly in a flash memory
First Claim
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1. A method of etching a tungsten-containing layer overlying a silicon layer, comprising the steps of:
- placing onto an electrode in a plasma reaction chamber a substrate containing the tungsten-containing layer and an etching mask overlying the tungsten-containing layer, wherein the silicon layer consists principally of silicon;
a first step of flowing into the chamber a first gas mixture comprising an etching gas comprising chlorine and fluorine and an oxidizing gas comprising oxygen gas and nitrogen gas;
biasing the electrode with a first level of RF power; and
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.
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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 may be added for additional selectivity.
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Citations
25 Claims
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1. A method of etching a tungsten-containing layer overlying a silicon layer, comprising the steps of:
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placing onto an electrode in a plasma reaction chamber a substrate containing the tungsten-containing layer and an etching mask overlying the tungsten-containing layer, wherein the silicon layer consists principally of silicon;
a first step of flowing into the chamber a first gas mixture comprising an etching gas comprising chlorine and fluorine and an oxidizing gas comprising oxygen gas and nitrogen gas;
biasing the electrode with a first level of RF power; and
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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of etching a tungsten-containing layer, comprising the steps of:
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placing within a plasma reaction chamber a substrate containing the tungsten-containing 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 a silo-chloro compound; and
exciting the first gas mixture into a plasma. - View Dependent Claims (18, 19, 20, 21, 22)
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23. 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 overlying a silicon layer onto an 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, an oxidizing 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 electrode with a first level of RF power;
a second step of flowing into the plasma reaction chamber a second gas mixture comprising the etching gas and the oxidizing gas while biasing the electrode with a second level of RF power lower than the first level. - View Dependent Claims (24, 25)
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Specification