Resist for electron beam lithography and a process for producing photomasks using electron beam lithography
The invention relates to a resist for electron beam lithography and to a process for producing photomasks for optical lithography. The inventive resist includes repeating units that are derived from maleic anhydride and that can act as an anchor group for the subsequent binding of silicon-containing groups. The etch stability of the resist can thus be subsequently increased so that there is no dimensional loss on transfer of the resist structure to a chromium layer arranged under the resist.
1. A process for producing a photomask for optical lithography, the process which comprises:
providing a transparent substrate;
depositing a first layer of a mask material on the transparent substrate;
providing a resist including a film-forming polymer obtained by copolymerization of a comonomer mixture, the comonomer mixture including at least one first comonomer having a polymerizable carbon-carbon double bond and an anchor group, the comonomer mixture including at least one further comonomer, the resist including a solvent or a solvent mixture;
applying a layer of the resist to the first layer and evaporating the solvent in the resist to obtain a second layer of the film-forming polymer contained in the resist;
producing an image including exposed parts and unexposed parts in the second layer by writing on the second layer using a focused electron beam;
adding a developer to the second layer to dissolve the exposed parts of the image and to obtain a structured resist in which the unexposed parts of the image form lands and the exposed parts of the image form trenches configured between the lands;
adding an amplification agent to the structured resist, the amplification agent including a group for coordinating to the anchor group of the polymer;
obtaining an amplified structure by leaving the amplification agent on the structured resist for a time required to bound the amplification agent to the polymer; and
transferring the amplified structure to the first layer, the amplification agent being provided as a solution in the developer.
2. The process according to claim 1 , which comprises removing the developer, after performing the step of adding the developer to the second layer to dissolve the exposed parts of the image and to obtain the structured resist.
3. The process according to claim 1 , which comprises removing excess amplification agent, after performing the step of obtaining the amplified structure.
4. The process according to claim 1 , which comprises providing the amplification agent as a solution.
5. The process according to claim 1 , which comprises providing the amplification agent as a solution in the developer.
6. The process according to claim 1 , wherein the amplification agent includes at least one silicon-containing group.
7. The process according to claim 1 , wherein the amplification agent includes at least two groups that coordinate to anchor groups of the film-forming polymer.
8. The process according to claim 1 , which comprises providing the mask material as chromium.
9. The process according to claim 1 , wherein the step of transferring the amplified structure to the first layer includes transferring the amplified structure by plasma etching to the first layer.
10. A photomask for electron beam lithography obtained by using the method according to claim 1 .
11. The photomask of claim 10 , wherein said first comonomer is maleic anhydride and said further comonomer is methyl methacrylate.
12. The photomask of claim 10 , further comprising a reaction product of said copolymer with an amplification agent.
13. The photomask of claim 12 , wherein said amplification agent is an aminosiloxane represented by the formula
14. A resist for electron beam lithography provided on a photomask according to claim 1 .
15. The resist according to claim 14 , wherein said first comonomer is an at least monounsaturated carboxylic anhydride.
16. The resist according to claim 15 , wherein said at least monounsaturated carboxylic anhydride is maleic anhydride.
17. The resist according to claim 14 , wherein said further comonomer is selected from a group consisting of alkyl esters of (meth)acrylic acid.
18. The resist according to claim 14 , wherein said further comonomer is methyl methacrylate.