DE10241620A1 - Lithographic structurization of substrate with electron beam, used for making photo-mask, e.g. of chrome-on-glass type, uses system of electroconductive, water-insoluble lower resist layer and upper layer of electron beam resist - Google Patents

Abstract

Lithographic structurization of a substrate with an electron beam, especially for producing photo-masks, comprises production of a resist system (1, 2) on the substrate (10) by applying electroconductive, water-insoluble lower resist layer(s) (1) and then upper resist layer(s) (2) of electron beam-sensitive photoresist. An Independent claim is also included for resist system of the specified layers (1) and (2) on a substrate, for use in an electron writing process for structurizing the substrate, especially a photo-mask.

Description

The invention relates to a method for the lithographic structuring of a substrate according to the generic term of claim 1 and a paint system according to the preamble of the claim 13th

Playing in semiconductor manufacturing in addition to the development of ever finer lithography techniques for wafer structuring, also the development of such techniques for the production of photomasks ever greater role. Despite a four or five times Reduction factor are the structures to be imaged on the masks now so small that the laser pens used to this day ever higher due to higher resolution electron beam recorders need to be replaced.

Also through the introduction of the OPC (optical proximity correction) must have auxiliary structures in the mask layout integrated, which are much smaller than the ones to be imaged Structural elements are. For that too conventional ones are sufficient Exposure systems no longer work.

Due to the increasing complexity and before all the number of structures contained on the mask (in particular with OPC elements) the writing time for a mask increases drastically. the must go through the introduction new lithography techniques can be encountered around the writing times to keep at least at today's level and better still reduce it.

In electron beam lithography are the photo masks, which are usually made of a quartz glass substrate with an applied chrome layer (chrome on glass: CoG), with a Photoresist (photoresist) coated, which is then in a mask pen exposed (structured) with an electron beam and subsequently is developed. Even if it is not with electron beams to "light" in the conventional Radiation with electron beams also works called exposure.

In an etching step following the exposure step the chrome on the mask is no longer attached to the photoresist protected areas removed so that subsequently the photo mask is ready.

In particular the PSM technology (Phase-Shift Masks: Phase Shift Masks) sets to mask manufacturing special requirements, because here on the mask additional Layers are applied or the substrate is removed in a defined manner needs to be the one you want phase jumps to reach. At the same time, there is currently a PSM mask production not yet a process with which e.g. two of the plotted levels can be written using an electron mask writer. The second level has been described optically.

The reason for this is a lack of charge dissipation in photoresist; by writing the photoresist with an electron beam will the mask during of the write process negatively charged, which is commonly referred to as "charging".

The present invention lies based on the task of creating a process and a coating system, where the problem of charging is solved or at least mitigated can be.

This object is achieved by a Method with the features of claim 1 solved.

By applying at least one electrically conductive, water-insoluble bottom layer of varnish on a substrate allows for electron beam structuring at least one electron-sensitive upper lacquer layer negative The charges flow away well can.

In an advantageous embodiment, at least one lower lacquer layer has polythiophene as the polymer, in particular in position 3 or 4 substituted and as a counter ion a polystyrene sulfonate. It is particularly advantageous if at least one lower lacquer layer has poly (3,4-ethylenedioxy-thiophene) as the polymer and a polystyrene sulfonate as the counter ion. These materials can be used to produce thin, stable layers. It is also advantageous if at least one lower lacquer layer is designed as a photoresist with an added conductive component.

In an advantageous embodiment of the method according to the invention the lower layer of lacquer is applied to the substrate to be structured applied, in particular by means of spin coating, followed by a thermal treatment step for evaporation of solvent is carried out in the lower layer of lacquer. Through one physical process creates a particularly stable layer, which is a suitable basis for other coatings. It is advantageous if the thermal Treatment step of the lower lacquer layer at one temperature between 70 and 200 ° C he follows. It is particularly advantageous if the temperature is 130 ° C. during thermal Treatment step is and the temperature treatment lasts 300s.

It is also advantageous if the upper layer of varnish after exposure to electron beams thermal treatment step is subjected.

It is also advantageous if the upper layer of varnish after exposure to electron beams an aqueous Standard TMAH developer solution (TMAH = tetramethylammonium hydroxide) developed and therefore targeted Will get removed.

In a further advantageous embodiment, the structure obtained in the photoresist of the upper lacquer layer is at least one plasma etch transfer into the lower layer of lacquer.

To reduce process times it is advantageous if after structuring the lower layer of paint another etching step immediately for the Substrate, especially for the chrome or the glass of a phase shift mask. Most notably It is advantageous if the further etching step for the substrate is carried out in situ, by switching the process gases and machine parameters. The substrate does not have to be taken out of the machine, which in addition to saving time reduces the risk of contamination.

The job is also done with a paint system solved the advantages of claim 13.

A paint system according to the invention has an electrical conductive, water lower layer of varnish and one above top layer of lacquer made of electron beam sensitive photoresist on. You can charges generated during electron beam writing via the drain off the lower layer of varnish, so that no deflection or other influence on the electron beam can be done.

The invention is described below Reference to the figures of the drawing on several exemplary embodiments explained in more detail. It shows:

1 is a schematic sectional view through a substrate with a coating system according to the invention.

In 1 is a schematic representation of a paint system according to the invention 1 . 2 on a substrate 10 shown. The substrate 10 Here is a chrome-on-glass substrate used in the production of photo masks. On the substrate 10 glass is an already structured chrome layer 11 arranged. Above this is an electrically conductive, lower layer of lacquer 1 arranged. Above that is an upper layer of paint 2 arranged from an electron beam sensitive photoresist. Such a paint system 1 . 2 is used in a method according to the invention.

The individual steps are described below, with the structuring of the chrome layer 11 is started.

In the first step of the process, the chrome layer 11 the photomask is structured by means of a photoresist, the resulting negative electrical charge of the mask being able to be easily removed by suitable grounding of the mask blank in the mask writer.

In the second step, however, a newly applied photoresist must now be placed on an already incomplete (pre-structured) chrome layer 11 electron-written (exposed). Because of the broken chrome layer 11 it is no longer possible to discharge the charge over the entire surface by earthing, the blank mask charges negatively during the writing process. However, this negative charge influences the electron beam striking the sample in the mask writer, which is necessary both for writing and for checking the adjustment.

This influence leads to a undesirable Deflection and expansion of the electron beam, which is particularly during the Adjusting disturbing is, but also undesirable Distortions, misspellings when writing the second level of lithography a phase shift mask. I agree this problem is to be solved in the present invention.

The invention also solves the problem with the aid of two separate layers of paint 1 . 2 ,

On the structured chrome layer 11 and the intermediate free surfaces of the substrate 10 According to the invention, an electrically conductive, organic, water-insoluble (hydrophobic) lacquer layer 1 applied, which should ensure the necessary discharge of the load. On this conductive lower layer of paint 1 is now the structurable photoresist as the top layer of lacquer 2 applied and this photoresist is then written on electron beam.

The lower layer of paint 1 is not water-soluble and cannot be removed from the top layer of lacquer 2 be resolved. This is done through a thermal process, which hardens the conductive lower lacquer layer 1 causes and makes this paint very stable and in particular inert to all common paint solvents. However, there is no cross-linking based on chemical reactions, as is used in similar processes; it is a purely physical process which, due to the special properties of the material used, leads to an inert layer.

After structuring the top layer of lacquer 2 becomes the conductive lower layer of paint 1 then not removed by the wet chemical development step, but only by a plasma etching process.

The conductive lower varnish view 1 is based on a solution or dispersion of special polymers, additives and auxiliaries in mixtures of water and suitable organic solvents. For example, the most important components are a polymer poly- (3,4-ethylenedioxy-thiophene) (PEDOT, also called PEDT) which is present with a polystyrene sulfonate (PSS) as a counter ion.

Such an electrically conductive paint is sold by BAYER AG under the name Baytron®. This paint is mainly used in the large-scale Photo film production used. Here the material is used as a charge-dissipating Additional coating for the film strips that run through the production machines at high speed, used.

However, experiments surprisingly showed that this material can also be used with special heating processes in photo mask production for semiconductor technology possible is.

By the step of thermal Treatment creates a stable layer, due to the ionic character of the PEDOT / PSS polyelectrolyte complex inert against organic solvents and is the following photoresist, on the other hand due to the lipophilic character of the polymers sufficient resistance to the shows the following water-based process steps.

The process offers the following advantages:

• - The conductive paint layer 1 is directly on the structured chrome layer 11 applied and thus ensures optimum charge dissipation by simply electrically connecting existing chrome structures and thus additionally using their conductivity.
• - By the thermal hardening process comes there are no intermixing effects.
• - Due to the thermal curing process, the conductive lacquer layer remains stable in the wet chemical development step and is not detached. Only the top layer of paint 2 is developed and thus optimally and cleanly structured. This guarantees optimal resolution.
• - Compared to the chemical cross-linking process of the bottom resist, the thermal treatment of the lower lacquer layer is required 1 significantly lower temperatures. This makes it possible to use cheaper hotplates in production, and the heating process time can also be shortened.
• - All the advantages of already commercially developed and also to be developed chemically reinforced photoresists (CA resists, CAR) can be used, regardless of the special characteristics of the conductive lacquer layer 1 to have to take. The thermal heating step means that it can be treated like a neutral plastic layer.
• - The one for structuring (developing) the conductive lacquer layer 1 the necessary plasma etching process is then anyway necessary in the mask production for the subsequent chrome etching. As part of this process, the conductive lacquer layer and then the chrome layer can be etched in situ by simply modifying the etching process with an additional step upstream in one and the same operation.

In principle, there are also other electrically conductive polymers in a lower lacquer layer 1 usable.

The use according to the invention of a very stable electrically-conductive Paint layer gives significant advantages over the prior art. According to the state Technology should paint layer as possible be easily removable to avoid the mask making process complicate.

The present invention goes exactly the other way, in that here a lower lacquer layer which is very difficult to remove during wet chemical development 1 is used. However, the removal is easily possible with direct inclusion of the above-mentioned chrome etching process, here the entire process of mask production was simply considered and not only the problem of coating / electron beam writing / wet chemical resist development was focused.

The following is the overall process the production of a photomask using the method according to the invention described.

• 1. Provision of a commercially available 6 inch CoG mask blank ("Chrome on glass", quartz glass plate with sputtered or vapor-deposited chrome layer). This can be a raw blank or already a pre-structured chrome layer 11 contain.
• 2. Lacquer this mask blank with a water-insoluble, lower lacquer layer 1 which, in addition to one or more solvents, contains auxiliary components, in particular one or more components which bring about an electrical conductivity of the lacquer layer which has subsequently hardened.
• 3rd heating step (especially at 130 ° C for 300s) to dry and solidify the lower lacquer layer 1 , The majority of the paint solvent evaporates, resulting in a firm, dry lower paint layer 1 with very high mechanical and chemical stability, the layer thickness of which is, for example, in the range 0.1 to 0.5 μm, in particular 0.30 μm, on the chrome layer of the mask blank. Common. Paint solvents such as ethyl acetate or methoxypropylacetate can then no longer stain the paint layer.
• 4. Lacquer the mask blank with a second upper lacquer layer 2 , The lacquer used is a positive or negative structurable electron beam resist.
• 5. Heating step (in particular 120 ° C for 120s) for drying the electron beam resist. The solvent evaporates, resulting in a second top coat 2 with, for example, a layer thickness between 0.1 to 0.4 μm, in particular 0.2 μm.
• 6. Describe the double-coated mask blank with a Electron beam mask writer (e.g. ETEC MEBES series)
• 7. Heating step (post exposure bake) for fixing the latent image written in the photoresist layer of the upper lacquer layer 2 ,
• 8. Treat the complete mask blank with an aqueous alkaline developer solution (eg 2.38% tetramethylammonium hydroxide in water) for eg 60 s. During this development step, depending on the character of the lacquer, either the described (positive resist) or unwritten (negative resist) area of the upper lacquer layer 2 detached and removed. The lower conductive paint layer 1 remains completely intact.
• 9. Plasma etching of the complete mask blank in a reactive oxygen ion plasma. The lower conductive paint layer 1 removed in places where it is no longer protected by the top layer of lacquer.
• 10. Plasma etching of the complete mask blank for structuring the chrome layer 11 or etching the quartz glass substrate 10 , This also happens in a reactive inner plasma and can also be done as a direct follow-up step in the same apparatus as in step 9.
• The invention is limited not in their execution to the preferred embodiments given above. Rather is a number of variants conceivable by the inventive method and the coating system according to the invention also in principle different types Make use.

1

lower paint layer

2

upper paint layer

10

substratum (COG substrate)

11

chromium layer a CoG substrate

Claims (14)

Process for the lithographic structuring of a substrate by means of an electron beam, in particular for the production of photomasks, characterized in that to create a lacquer system ( 1 . 2 ) on the substrate ( 10 ) at least one electrically conductive, water-insoluble lower layer of paint ( 1 ) and then at least one upper layer of paint ( 2 ) is applied from electron beam sensitive photoresist. Method according to claim 1 or 2, characterized in that at least one lower lacquer layer ( 1 ) as polymer polythiophene, especially at position 3 or 4 substituted and has a polystyrene sulfonate as counterion. Method according to claims 1 or 2, characterized in that at least one lower lacquer layer ( 1 ) as the polymer poly (3,4-ethylenedioxy-thiophene) and as a counter ion has a polystyrene sulfonate. Method according to at least one of the preceding, characterized in that at least one lower lacquer layer ( 1 ) is designed as a photoresist with an added conductive component. Method according to at least one of the preceding claims, characterized in that the lower lacquer layer ( 1 ) on the substrate to be structured ( 10 ) is applied, in particular by means of spin coating, and then a thermal treatment step for evaporating solvent in the lower lacquer layer ( 1 ) is carried out. Method according to claim 5, characterized in that the thermal treatment step of the lower lacquer layer ( 1 ) at a temperature between 70 and 200 ° C. A method according to claim 5 or 6, characterized in that the thermal treatment step of the lower lacquer layer ( 1 ) lasts between 60 s and 1000 s. Method according to at least one of claims 5 to 7, characterized in that the temperature 130 ° C during the thermal treatment step of the lower lacquer layer ( 1 ) and the temperature treatment lasts 300s. Method according to at least one of the preceding claims, characterized in that the upper lacquer layer ( 2 ) is subjected to a thermal treatment step after exposure to electron beams. Method according to at least one of the preceding claims, characterized in that the upper lacquer layer ( 2 ) after exposure to electron beams with an aqueous standard TMAH developer solution (TMAH = tetramethylammonium hydroxide) and thus removed in a targeted manner. Method according to at least one of the preceding claims, characterized in that the structure obtained in the photoresist of the upper lacquer layer ( 2 ) by at least one plasma etching process in the lower lacquer layer ( 1 ) is transmitted. Method according to at least one of the preceding claims, characterized in that after the structuring of the lower lacquer layer ( 1 ) another etching step for the substrate ( 10 ), especially for the chrome or the glass of a phase shift mask. A method according to claim 12, characterized in that the further etching step for the substrate ( 10 ) takes place in-situ, with switching of the process gases and machine parameters. Lacquer system on a substrate for use in an electron writing process for structuring the substrate, in particular a photo mask, characterized by an electrically conductive, water-insoluble lower lacquer layer ( 1 ) and an overlying top layer of lacquer ( 2 ) out electron-sensitive photoresist.