ABRASIVE-FREE PLANARIZATION FOR EUV MASK SUBSTRATES

• US 20130209924A1
• Filed: 01/25/2013
• Published: 08/15/2013
• Est. Priority Date: 01/27/2012
• Status: Active Grant

• Current Assignee: Sematech, Inc., Clarkson University (Union Graduate College)
• Original Assignee: Suryadevara V. Babu
• Inventors: BABU, Suryadevara V., AMANAPU, Hariprasad, LAGUDA, Uma Rames Krishna, TEKI, Ranganath
• Granted Patent: US 9,097,994 B2
• Time in Patent Office: Days
• US Class Current: 430/5
• CPC Class Codes: B24B 1/00 Processes of grinding or polishing; Use of auxiliary equipment in connection with such processes
• CPC Class Codes: G03F 1/24 Reflection masks; Preparation thereof
• CPC Class Codes: G03F 1/72 Repair or correction of mask defects
• CPC Class Codes: H01L 21/3212 by chemical mechanical polishing [CMP]

Abstract

A process for abrasive-free chemical mechanical planarization of silicon thin film coated EUV mask substrates is disclosed. The process removes bumps and pits on the substrate thereby mitigating reflective errors in the mask. The process employs a two-step polishing procedure, in which the second step is abrasive-free and uses an amine or amine salt as the polishing agent.

Claims

1. A planarizing method comprising:

a) depositing upon a substrate that includes a defect a silicon material layer; and

b) planarizing said silicon material layer, first with an abrasive planarizing fluid and then with an abrasive-free planarizing fluid.

2. A method according to claim 1 wherein said silicon material layer is chosen from amorphous silicon and polycrystalline silicon.

3. A method according to claim 1 wherein said silicon material layer is deposited to a thickness between 10 nm and 250 nm.

4. A method according to claim 3 wherein silicon material layer is deposited to a thickness between 50 nm and 150 nm.

5. A method according to claim 1 wherein said substrate is a material having a coefficient of thermal expansion at 5°

C. to 35°

C. between zero and 1×

10<sup>−

7</sup> per degree K.

6. A method according to claim 5 wherein said substrate is chosen from quartz, glass, TiO₂-doped glass and lithium aluminum silicon oxide glass ceramic.

7. A method according to claim 1 wherein said abrasive-free fluid comprises at least one amine salt.

8. A method according to claim 7 wherein said amine salt is a salt of a polyamine.

9. A method according to claim 8 wherein said polyamine is polyethyleneimine.

10. A method according to claim 7 wherein said amine salt is a quaternary amine salt.

11. A method according to claim 10 wherein said quaternary amine salt is chosen from poly diallylammonium chloride and cetyl trimethyl ammonium bromide.

12. A method according to claim 7 wherein said abrasive-free fluid has a pH between 6.0 and 9.0.

13. A method according to claim 1 wherein said abrasive fluid is a colloidal silica dispersion at pH 2.

14. A substrate for a reflective mask for EUV lithography comprising

a) a first layer chosen from quartz, glass, TiO₂-doped glass and lithium aluminum silicon oxide glass ceramic;

b) a second layer chosen from amorphous silicon and polycrystalline silicon, said second layer being from 10 to 100 nm thick and having a surface roughness (RMS) between 0.01 nm and 0.2 nm.

15. A reflective mask for EUV lithography comprising

a) a first layer chosen from quartz, glass, TiO₂-doped glass and lithium aluminum silicon oxide glass ceramic;

b) a second layer chosen from amorphous silicon and polycrystalline silicon, said second layer being from 10 to 100 nm thick and having a surface roughness (RMS) between 0.01 nm and 0.2 nm

c) a plurality of alternating layers of molybdenum and silicon.