Dry-etch for selective tungsten removal
Methods of selectively etching tungsten relative to silicon-containing films (e.g. silicon oxide, silicon carbon nitride and (poly)silicon) as well as tungsten oxide are described. The methods include a remote plasma etch formed from a fluorine-containing precursor and/or hydrogen (H 2 ). Plasma effluents from the remote plasma are flowed into a substrate processing region where the plasma effluents react with the tungsten. The plasma effluents react with exposed surfaces and selectively remove tungsten while very slowly removing other exposed materials. Sequential and simultaneous methods are included to remove thin tungsten oxide which may, for example, result from exposure to the atmosphere.
1. A method of etching a patterned substrate in a substrate processing region of a substrate processing chamber, wherein the patterned substrate has a exposed tungsten region and an exposed second material region, the method comprising:
flowing a fluorine-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a plasma in the plasma region to produce plasma effluents; and
etching the exposed tungsten from the substrate by flowing the plasma effluents into the substrate processing region through through-holes in a showerhead, wherein the operation of etching the tungsten comprises etching tungsten faster than an exposed silicon region by a ratio of about 100:1 or more, faster than an exposed silicon oxide region by a ratio of about 15:1 or more, faster than an exposed silicon carbon nitride region by a ratio of about 3:1 or more, or faster than an exposed tungsten oxide region by a ratio of about 10:1 or more.
2. The method of claim 1 wherein the exposed tungsten region has a thickness of at least 5 nm.
3. The method of claim 1 wherein the exposed tungsten region consists of tungsten.
4. The method of claim 1 wherein etching the exposed tungsten region comprises etching the exposed tungsten region comprises etching tungsten with a tungsten etch rate greater than ten times the etch rate of the exposed second material region.
5. The method of claim 1 wherein the fluorine-containing precursor comprises nitrogen trifluoride.
6. The method of claim 1 wherein the fluorine-containing precursor comprises a partially fluorinated hydrocarbon.
7. The method of claim 1 wherein the fluorine-containing precursor comprises methyl fluoride.
8. The method of claim 1 further comprising a pretreatment step which occurs prior to etching the exposed tungsten region, wherein the pretreatment step comprises flowing hydrogen (H 2 ) into the remote plasma region and flowing the produced plasma effluents into the substrate processing region to remove a thin tungsten oxide layer overlying a near-surface tungsten region to create the exposed tungsten region.
9. The method of claim 1 wherein the fluorine-containing precursor comprises carbon tetrafluoride.
10. The method of claim 1 wherein flowing a fluorine-containing precursor and hydrogen (H 2 ) results in an atomic flow ratio (H:F) of greater than 1:1 entering the substrate processing region.
11. The method of claim 1 wherein flowing a fluorine-containing precursor and hydrogen (H 2 ) results in an atomic flow ratio (H:F) of less than 15:1 entering the substrate processing region.
12. The method of claim 1 wherein a pressure within the substrate processing region is between about 0.01 Torr and about 50 Torr during the etching operation.
13. The method of claim 1 wherein forming a plasma in the plasma region to produce plasma effluents comprises applying RF power between about 10 watts and about 400 watts to the plasma region.
14. The method of claim 1 wherein a temperature of the substrate is greater than or about −30° C. and less than or about 400° C. during the etching operation.