Minimization of mask undercut on deep etch

Abstract

A method for forming features in a silicon layer is provided. A mask is formed with a plurality of mask openings over the silicon layer. A polymer layer is deposited over the mask by flowing a hydrogen free deposition gas comprising C 4 F 8 , forming a plasma from the deposition gas, depositing a polymer from the plasma for at least 20 seconds, and stopping the depositing the polymer after the at least 20 seconds. The deposited polymer layer is opened by flowing an opening gas, forming a plasma from the opening gas which selectively removes the deposited polymer on bottoms of the plurality of mask openings with respect to deposited polymer on sides of the plurality of mask openings, and stopping the opening when at least some of the plurality of mask features are opened. The silicon layer is etched through the mask and deposited polymer layer.

1 - 18 . (canceled) 
     
     
         19 . An apparatus for etching features in a silicon layer under a mask with openings, comprising:
 a plasma processing chamber, comprising:
 a chamber wall forming a plasma processing chamber enclosure; 
 a substrate support for supporting a substrate within the plasma processing chamber enclosure; 
 a pressure regulator for regulating the pressure in the plasma processing chamber enclosure; 
 an upper electrode for providing power to the plasma processing chamber enclosure; 
 a lower electrode; 
 a first RF power source electrically connected to the upper electrode; 
 a second RF power source electrically connected to the lower electrode; 
 a gas inlet for providing gas into the plasma processing chamber enclosure; and 
 a gas outlet for exhausting gas from the plasma processing chamber enclosure; 
   a gas source in fluid connection with the gas inlet, comprising:
 a hydrogen free C 4 F 8  deposition gas source; 
 an opening gas source; and 
 an etching gas source; and 
   a controller controllably connected to the gas source, the first RF power source, and the second RF power source, comprising:
 at least one processor; and 
 computer readable media, comprising:
 computer readable code for depositing a polymer layer over the mask, comprising:
 computer readable code for flowing a hydrogen free deposition gas comprising C 4 F 8  from the hydrogen free C 4 F 8  deposition gas source into the plasma processing chamber; 
 computer readable code for forming a plasma from the deposition gas; 
 computer readable codes for depositing a polymer from the plasma for at least 20 seconds; and 
 computer readable code for stopping the depositing the polymer after the at least 20 seconds; 
 
 computer readable code for opening the deposited polymer layer, comprising:
 computer readable code for flowing an opening gas from the opening gas source into the plasma processing chamber; 
 computer readable code for forming a plasma from the opening gas which selectively removes the deposited polymer on bottoms of the plurality of mask openings with respect to deposited polymer on sides of the plurality of mask openings; and 
 computer readable code for stopping the opening when at least some of the plurality of mask features are opened; and 
 
 computer readable code for etching the silicon layer through the mask and deposited polymer layer. 
 
   
     
     
         20 . The apparatus, as recited in  claim 19 , wherein the computer readable code for etching the silicon layer through the mask and deposited layer, comprises computer readable code for completely etching away the deposited polymer layer by etching the silicon layer. 
     
     
         21 . The apparatus, as recited in  claim 20 , wherein the computer readable code for flowing a hydrogen free deposition gas comprising C 4 F 8  from the hydrogen free C 4 F 8  deposition gas source into the plasma processing chamber, further comprises computer readable code for flowing a hydrogen free deposition gas that consists essentially of C 4 F 8 . 
     
     
         22 . The apparatus, as recited in  claim 21 , wherein the computer readable code for etching the silicon layer, further comprises:
 computer readable code for flowing an etching gas; and   computer readable code for forming a plasma from the etching gas, which etches the silicon layer.   
     
     
         23 . The apparatus, as recited in  claim 22 , wherein the opening gas is different from the etching gas. 
     
     
         24 . The apparatus, as recited in  claim 23 , wherein the mask is a photoresist mask. 
     
     
         25 . The apparatus, as recited in  claim 24 , wherein the computer readable code for depositing a polymer deposits a polymer layer at least 200 nm thick on the sides of the plurality of mask openings. 
     
     
         26 . The apparatus, as recited in  claim 25 , wherein the at least 200 nm thick deposited polymer on the sides of the plurality of mask openings eliminates undercutting. 
     
     
         27 . The apparatus, as recited in  claim 19 , wherein the mask is a photoresist mask. 
     
     
         28 . The apparatus, as recited in  claim 19 , wherein the computer readable code for depositing a polymer deposits a polymer layer at least 200 nm thick on the sides of the plurality of mask openings. 
     
     
         29 . The apparatus, as recited in  claim 28 , wherein the at least 200 nm thick deposited polymer on the sides of the plurality of mask openings eliminates undercutting. 
     
     
         30 . The apparatus, as recited in  claim 19 , wherein the deposited polymer layer on the sides of the plurality of mask openings eliminates undercutting. 
     
     
         31 . An apparatus for etching features in a silicon layer under a mask with openings, comprising:
 a plasma processing chamber, comprising:
 a chamber wall forming a plasma processing chamber enclosure; 
 a substrate support for supporting a substrate within the plasma processing chamber enclosure; 
 a pressure regulator for regulating the pressure in the plasma processing chamber enclosure; 
 an upper electrode for providing power to the plasma processing chamber enclosure; 
 a lower electrode; 
 a first RF power source electrically connected to the upper electrode; 
 a second RF power source electrically connected to the lower electrode; 
 a gas inlet for providing gas into the plasma processing chamber enclosure; and 
 a gas outlet for exhausting gas from the plasma processing chamber enclosure; 
   a gas source in fluid connection with the gas inlet, comprising:
 a hydrogen free C 4 F 8  deposition gas source; 
 an opening gas source; and 
 an etching gas source; and 
   a controller controllably connected to the gas source, the first RF power source, and the second RF power source, comprising:
 at least one processor; and 
 computer readable media, comprising:
 computer readable code for placing the silicon layer in a plasma process chamber; 
 computer readable code for depositing a polymer layer over the mask, comprising:
 computer readable code for flowing a hydrogen free deposition gas consisting essentially of C 4 F 8  into the plasma process chamber; 
 computer readable code for forming a plasma from the deposition gas; 
 computer readable code for depositing a polymer from the plasma for at least 20 seconds to form a layer at least 200 nm thick; and 
 computer readable code for stopping the depositing the polymer after the at least 20 seconds; 
 
 computer readable code for opening the deposited polymer layer, comprising:
 computer readable code for flowing an opening gas into the plasma process chamber; 
 computer readable code for forming a plasma from the opening gas which selectively removes the deposited polymer on bottoms of the plurality of mask openings with respect to deposited polymer on sides of the plurality of mask openings; and 
 computer readable code for stopping the opening when at least some of the plurality of mask features is opened; 
 
 computer readable code for etching the silicon layer through the mask and deposited polymer layer, comprising:
 computer readable code for flowing an etching gas different from the opening gas; and 
 computer readable code for forming a plasma from the etching gas, which etches the silicon layer, wherein the deposited polymer layer prevents undercutting of the silicon layer under the photoresist mask, and the deposited polymer layer is completely etched away by the etching the silicon layer; and 
 
 computer readable code for removing the silicon layer from the plasma process chamber. 
 
   
     
     
         32 . The apparatus, as recited in  claim 31 , wherein the mask is a photoresist mask. 
     
     
         33 . The apparatus, as recited in  claim 32 , further comprising computer readable code for removing the photoresist mask and deposited polymer layer in the plasma process chamber. 
     
     
         34 . The apparatus, as recited in  claim 31 , wherein the computer readable code for etching the silicon layer through the mask and deposited layer, further comprises computer readable code for completely etching away the deposited polymer layer by etching the silicon layer. 
     
     
         35 . The apparatus, as recited in  claim 34 , wherein the computer readable code for flowing a hydrogen free deposition gas comprising C 4 F 8  from the hydrogen free C 4 F 8  deposition gas source into the plasma processing chamber, further comprises computer readable code for flowing a hydrogen free deposition gas that consists essentially of C 4 F 8 .