Method of forming planarized coatings on contact hole patterns of various duty ratios

Abstract

A method of forming a planarized photoresist coating on a substrate having holes with different duty ratios is described. A first photoresist preferably comprised of a Novolac resin and a diazonaphthoquinone photoactive compound is coated on a substrate and baked at or slightly above its Tg so that it reflows and fills the holes. The photoresist is exposed without a mask at a dose that allows the developer to thin the photoresist to a recessed depth within the holes. After the photoresist is hardened with a 250° C. bake, a second photoresist is coated on the substrate to form a planarized film with a thickness variation of less than 50 Angstroms between low and high duty ratio hole regions. One application is where the second photoresist is used to form a trench pattern in a via first dual damascene method. Secondly, the method is useful in fabricating MIM capacitors.

1. A method for forming a planar photoresist layer on a substrate with regions having holes of different duty ratios comprising:
 (a) providing a substrate with a layer comprised of a pattern containing holes in high duty ratio regions and in low duty ratio regions formed thereon,  
 (b) coating a first photoresist layer on said substrate,  
 (c) removing said photoresist from the surface of said substrate and forming a recessed layer of said photoresist in said holes,  
 (d) hardening said recessed photoresist layer, and  
 (e) coating a second photoresist layer on said substrate that forms a uniform thickness over holes in both high duty ratio regions and in low duty ratio regions.  
 
     
     
       2. The method of  claim 1  wherein the low duty ratio regions are comprised of isolated holes and the high duty ratio regions are comprised of dense holes wherein the spacing between holes is approaching the space width within the holes. 
     
     
       3. The method of  claim 1  wherein said first photoresist layer is a positive tone composition that includes a Novolac resin and a diazonaphthoquinone photoactive compound. 
     
     
       4. The method of  claim 3  wherein said first photoresist layer is baked at a temperature slightly above the glass transition temperature of said first photoresist layer, preferably between about 90° c. and about 130° C. 
     
     
       5. The method of  claim 4  wherein said photoresist is baked at a temperature such that said first photoresist reflows and completely fills said holes. 
     
     
       6. The method of  claim 3  wherein a recessed photoresist layer is formed in said holes by exposing said first photoresist with an appropriate exposure dose and developing said photoresist. 
     
     
       7. The method of  claim 6  wherein said first photoresist is exposed without a mask using one or more wavelengths in the range of about 300 nm to about 500 nm. 
     
     
       8. The method of  claim 6  wherein the exposure is performed with a scanner or stepper tool that has alignment capability or with a flood exposure tool that does not have alignment capability. 
     
     
       9. The method of  claim 1  wherein the depth of said recess in said holes is a distance that is from about 0% to 30% of the total depth of said hole. 
     
     
       10. The method of  claim 1  wherein a thermal treatment is used to harden said first photoresist and comprises a baking step at about 250° C. for about 2 minutes. 
     
     
       11. The method of  claim 1  wherein the second photoresist is a composition that is sensitive to one or more wavelengths in the range from about 10 nm to about 500 nm. 
     
     
       12. A method for forming a planar photoresist layer on a via hole pattern in a dual damascene process comprising:
 (a) providing a substrate with a stack of layers formed thereon, said stack comprising an upper dielectric layer and a lower etch stop layer, said dielectric layer includes a via hole pattern having holes in high and low duty ratio regions,  
 (b) coating a first photoresist layer on said dielectric layer, said photoresist is baked at a temperature such that the photoresist reflows and fills said via holes,  
 (c) removing said photoresist from the surface of said dielectric layer and forming a recessed layer of said first photoresist in said holes,  
 (d) hardening said recessed photoresist layer, and  
 (e) coating a second photoresist layer on said substrate that forms a uniform thickness over holes in both high duty ratio regions and in low duty ratio regions.  
 
     
     
       13. The method of  claim 12  further comprised of completing a dual damascene structure by exposing said second photoresist through a mask pattern to form trench openings that are aligned over said via holes, transferring said trench pattern into said dielectric layer with a plasma etch, removing first and second photoresists, forming a barrier metal liner in said trenches and via holes, depositing a metal layer to fill said trenches and via holes, and planarizing said metal layer. 
     
     
       14. The method of  claim 12  wherein said etch stop layer is preferably comprised of silicon nitride, silicon oxynitride, or silicon carbide. 
     
     
       15. The method of  claim 12  wherein said dielectric layer is selected from a group including SiO 2 , carbon doped SiO 2 , fluorosilicate glass, polysilsesquioxanes, polyarylethers, polyimides, and other low k dielectric materials. 
     
     
       16. The method of  claim 12  wherein said first photoresist layer is a positive tone composition that includes a Novolac resin and a diazonaphthoquinone photoactive compound. 
     
     
       17. The method of  claim 16  wherein said photoresist layer is baked at a temperature slightly above the glass transition temperature of the layer, preferably between about 90° C. and about 130° C. 
     
     
       18. The method of  claim 12  wherein said recessed photoresist layer is formed in said holes by exposing said first photoresist with an appropriate exposure dose and developing said photoresist. 
     
     
       19. The method of  claim 18  wherein said first photoresist is exposed without a mask using one or more wavelengths in the range of about 300 nm to about 500 nm. 
     
     
       20. The method of  claim 18  wherein the exposure is performed with a scanner or stepper tool that has alignment capability or with a flood exposure tool that does not have alignment capability. 
     
     
       21. The method of  claim 12  wherein the depth of said recess in said holes is a distance that is from 0% to 30% of the total depth of the hole. 
     
     
       22. The method of  claim 12  wherein a thermal treatment is used to harden said photoresist and comprises a baking step at about 250° C. for about 2 minutes. 
     
     
       23. The method of  claim 12  wherein the second photoresist is a composition that is sensitive to one or more wavelengths in the range from about 10 nm to about 500 nm. 
     
     
       24. The method of  claim 12  wherein the thickness variation in said second photoresist coating is less than about 50 Angstroms between high duty ratio regions and low duty ratio regions. 
     
     
       25. A method for forming a planar photoresist layer on a contact hole pattern in fabricating a metal-insulator-metal (MIM) capacitor comprising:
 (a) providing a substrate with a dielectric layer formed thereon, said dielectric layer contains a contact hole pattern having holes in high and low duty ratio regions,  
 (b) depositing a conformal metal layer on said dielectric layer and in said holes,  
 (c) coating a first photoresist layer on said metal layer, said photoresist is baked at a temperature such that the photoresist reflows and fills said contact holes,  
 (d) removing said photoresist from the surface of said metal layer and forming a recessed layer of said photoresist in said holes,  
 (e) hardening said recessed photoresist layer, and  
 (f) coating a second photoresist layer on said metal layer that forms a uniform thickness over holes in both high duty ratio regions and in low duty ratio regions.  
 
     
     
       26. The method of  claim 25  further comprised of completing the MIM capacitor by etching back said second photoresist to form a recessed layer within said holes, etching back said metal layer to be about coplanar with said recessed first photoresist layer, removing said first photoresist layer, depositing an insulator layer, depositing a top electrode layer, and defining a top plate pattern. 
     
     
       27. The method of  claim 25  wherein the dielectric layer is selected from a group including SiO 2 , carbon doped SiO 2 , fluorosilicate glass, polysilsesquioxanes, polyarylethers, polyimides, and other low k dielectric materials. 
     
     
       28. The method of  claim 25  wherein the metal layer is preferably TiN or TiN/W. 
     
     
       29. The method of  claim 25  wherein said first photoresist layer is a positive tone composition that includes a Novolac resin and a diazonaphthoquinone photoactive compound. 
     
     
       30. The method of  claim 25  wherein said photoresist layer is baked at a temperature slightly above the glass transition temperature of the layer, preferably between about 90° C. and about 130° C. 
     
     
       31. The method of  claim 25  wherein said recessed photoresist layer is formed in said holes by exposing said first photoresist with an appropriate exposure dose and developing said photoresist. 
     
     
       32. The method of  claim 31  wherein said first photoresist is exposed without a mask using one or more wavelengths in the range of about 300 nm to about 500 nm. 
     
     
       33. The method of  claim 31  wherein the exposure is performed with a scanner or stepper tool that has alignment capability or with a flood exposure tool that does not have alignment capability. 
     
     
       34. The method of  claim 25  wherein the depth of said recess in said holes is a distance that is from about 0% to 30% of the total depth of the hole. 
     
     
       35. The method of  claim 25  wherein said recessed photoresist is hardened by a thermal treatment comprises a baking step at about 250° C. for about 2 minutes. 
     
     
       36. The method of  claim 25  wherein the second photoresist is a composition that has an etch rate similar to that of the hardened first photoresist layer. 
     
     
       37. The method of  claim 25  wherein the thickness variation in said second photoresist coating is less than about 50 Angstroms between high duty ratio regions and low duty ratio regions. 
     
     
       38. The method of  claim 25  wherein the second photoresist is a composition that is sensitive to one or more wavelengths in the range from about 10 nm to about 500 nm. 
     
     
       39. A method for forming a light- sensitive layer over a low - k dielectric layer having openings of different duty ratios, the method comprising:      providing a substrate with the low - k dielectric layer thereover, the low - k dielectric layer having the openings in a first region and a second region, the first region having a first duty ratio and the second region having a second duty ratio;        forming a first light - sensitive layer over the low - k dielectric layer;        removing a portion of the first light - sensitive layer; and        forming a second light - sensitive layer over the openings in the first region and the second region.     
     
     
       40. A method for forming a light- sensitive layer over a dielectric layer having openings of different duty ratios, the method comprising:      providing a substrate with the dielectric layer thereover, the dielectric layer having openings in a first region and a second region, the first region having a first duty ratio and the second region having a second duty ratio;        forming a first light - sensitive layer over the dielectric layer;        removing a portion of the first light - sensitive layer; and        forming a second light - sensitive layer over the openings in the first region and in the second region.     
     
     
       41. The method of  claim 40 , wherein the removing a portion of the first light- sensitive layer includes forming a recess in the first light - sensitive layer in the openings.   
     
     
       42. The method of  claim 41 , wherein the forming the recess is performed at least in part by exposing the first light- sensitive layer with an appropriate exposure dose and developing the first light - sensitive layer.   
     
     
       43. The method of  claim 42 , wherein the first light- sensitive layer is exposed without a mask using one or more wavelengths in a range from about  300  nm to about  500  nm.   
     
     
       44. The method of  claim 42 , wherein the exposing is performed with a scanner or stepper tool that has alignment capability or with a flood exposure tool that does not have alignment capability. 
     
     
       45. The method of  claim 41 , wherein a depth of the recess in the openings is a distance that is from about  0 %  to about  30   %  of the total depth of each opening.   
     
     
       46. The method of  claim 40 , wherein the first region comprises isolated openings and the second region comprises dense openings. 
     
     
       47. The method of  claim 40 , wherein the first light- sensitive layer comprises a positive tone composition having a Novolac resin and a diazonaphthoquinone photoactive compound.   
     
     
       48. The method of  claim 47 , wherein the first light- sensitive layer has a glass transition temperature between about  90 ° C. to about  130 ° C.   
     
     
       49. The method of  claim 40 , further comprising hardening the first light- sensitive layer after the removing a portion of the first light - sensitive layer.   
     
     
       50. The method of  claim 49 , wherein the hardening is performed at least in part by a thermal treatment. 
     
     
       51. The method of  claim 40 , wherein the second light- sensitive layer is a photoresist layer having a composition that is sensitive to one or more wavelengths in a range from about  10  nm to about  500  nm.   
     
     
       52. The method of  claim 40 , wherein the dielectric layer comprises low- k material.   
     
     
       53. The method of  claim 40 , wherein the first region comprises isolated holes and the second region comprises dense holes wherein the spacing between holes is approaching the space width within the holes. 
     
     
       54. The method of  claim 40 , wherein the first duty ratio is less than about  0 . 05 . 
     
     
       55. The method of  claim 40 , wherein the second duty ratio is from about  0 . 15  to  0 . 5 . 
     
     
       56. The method of  claim 40 , wherein the dielectric layer has a thickness between about  2000  Å and  7000  Å.