Lithographic process for reducing the lateral chromium structure loss in photomask production using chemically amplified resists
View Patent ↗The invention relates to a process for the production of photomasks. A film of a photoresist, as used for structuring semiconductor substrates, for example a CARL resist, is applied to a chromium-coated quartz glass substrate. The photoresist layer is written on by means of a focused electron beam, heated and then developed. The now structured resist is treated with an amplification agent and thus increases in its etch resistance to an oxygen plasma. During etching of the bare chromium sections, the silicon introduced into the photoresist is converted into silicon dioxide, which forms a protective layer on the chromium layer. Thus, the structure written in by means of the electron beam can be transferred without loss into the chromium layer.
1. A process for producing photomasks for optical lithography, which comprises the steps of:
providing a transparent substrate;
applying a layer of a mask material on the transparent substrate;
applying a layer of photoresist on the layer of the mask material, the photoresist comprising:
a film-forming polymer containing acid-labile groups to be cleaved under action of acid and liberating groups resulting in an increase in solubility of the film-forming polymer in aqueous alkaline developers, and further containing anchor groups for linkage of amplification agents;
a photo acid generator; and
a solvent;
heating the layer of the photoresist to remove the solvent resulting in a photoresist film being obtained;
writing a structure in the photoresist film using a focused electron beam resulting in an exposed photoresist film having exposed parts, in which a strong acid is liberated from the photo acid generator, and unexposed parts, in which no acid has been liberated;
heating the exposed photoresist film so that, in the exposed parts, acid-labile groups on the film-forming polymer are cleaved and polar groups are liberated resulting in a contrasted resist film being obtained;
developing the contrasted resist film using a developer resulting in a structured resist having lands and trenches disposed between the lands and in which the mask material is bare;
adding an amplification agent to the structured resist, the amplification agent having at least one reactive group which can react with the anchor groups of the film-forming polymer resulting in the amplification agent bonding to the film-forming polymer contained in the lands, so that an amplified resist is obtained;
removing any excess amplification agent; and
etching away bare mask material resulting in the structure being transferred to the layer of the mask material.
2. The process according to claim 1 , which further comprises providing a quartz glass substrate as the transparent substrate.
3. The process according to claim 1 , which further comprises forming the layer of the mask material as a chromium layer.
4. The process according to claim 1 , which further comprises irradiating the photoresist film with the electron beam having a dose of 1 μC/cm 2 to 40 μC/cm 2 .
5. The process according to claim 1 , which further comprises forming the photoresist to contain a sensitizer.
6. The process according to claim 1 , which further comprises forming the photoresist to contain a base.
7. The process according to claim 1 , which further comprises forming the amplification agent with a silicon-containing group.
8. The process according to claim 1 , which further comprises forming the amplification agent with at least two reactive groups.
9. The process according to claim 1 , which further comprises applying the amplification agent in a form of a solution to the structured resist.
10. The process according to claim 1 , which further comprises:
applying a layer of a photoinsensitive bottom resist to the layer of the mask material; and
applying the layer of the photoresist to the layer of the photoinsensitive bottom resist.
11. The process according to claim 1 , which further comprises using protected anchor groups as the anchor groups.