WO2005045527A2

WO2005045527A2 - Method of lacquering semiconductor substrates

Info

Publication number: WO2005045527A2
Application number: PCT/EP2004/012552
Authority: WO
Inventors: Jürgen HÖPPNER
Original assignee: Süss Microtec Lithography Gmbh
Priority date: 2003-11-07
Filing date: 2004-11-05
Publication date: 2005-05-19
Also published as: WO2005045527A3; TW200534044A; DE10351963B4; DE10351963A1

Abstract

The invention provides a method of lacquering substrates, in particular semiconductor substrates, whose surfaces have three-dimensional topographies. For this purpose, the substrate is sprayed with a lacquer that is modified with a solvent, and subsequently the applied lacquer layer is homogenized in a solvent atmosphere. The lacquering process can then be finished by baking the lacquer layer.

Description

Method of Lacquering Semiconductor Substrates

The invention relates to a method of lacquering or coating substrates, in particular of applying a resist layer to semiconductor substrates having a three-dimensional topography on the surface to be lacquered.

For lacquering a substrate, in particular a semiconductor substrate or wafer with a photoresist during a lithography process, a rotational coating method, i.e. the so-called spin coating, is conventionally used. In this conventional method, the photoresist being dissolved in a solvent is applied to the rotating substrate. By means of the centrifugal force caused by the rotation, the photoresist is distributed more or less uniformly over the entire surface of the substrate.

DE 42 28 344 Al and EP 0 540 447 Al both disclose a spin coating method of lacquering a substrate, in which the lacquer to be applied is modified with a solvent.

Further prior art documents are US 6,174,651 Bl, EP 1 046 959 A2, US 2001/0004467 Al, US 4,022,932 A as well as the publication of MOREAU, Wayne, M.: Semiconductor Lithography, Principles, Practices, and Materials, New York, Plenum Press, 1988, pages 329-333, ISBN 0-306-42185-2.

If substrates having three-dimensional topographies on their surfaces are to be coated, the classic spin coating method comes up against its limitations. What is particularly disadvantageous in this case is the bad uniformity of the applied lacquer layer, in particular the occurrence of radial irregularities, i.e. so-called spin shadowing, which can be caused, for example, by the accumulation of lacquer in front of raised portions on the substrate surface. Moreover, there are problems related with the coating of sharp edges, e.g. it is possible that the resist layer tears on the edge in case of convex topologies, or it is possible that meniscuses are formed on concave surface portions.

Therefore, it is an object of the present invention to provide an improved method of lacquering substrates. The method of the present invention allows, in particular, a uniform lacquering or coating of substrates having three-dimensional topographies.

The objects are achieved with the features of the claims. The present invention starts out from the basic idea that the substrate to be lacquered is sprayed with a modified lacquer or resist. The thus applied layer can then be homogenized or planed in a solvent-containing atmosphere for the subsequent lithography steps.

In accordance with the present method, the lacquer is modified with a solvent, e.g. acetone or ethyl methyl ketone, and preferably the substrate is heated during the spraying process. This measure leads to the fact that the applied resist remains on the desired place, because due to the resist modification, the modified lacquer already dries during flying or - by heating the substrate - immediately after contacting the substrate. The lacquer thus deposits on the substrate in the form of small semi-dry droplets.

For some applications, the surface roughness of the generated coating is too high. The applied lacquer layer can therefore be subsequently treated. For this purpose, the lacquer surface is placed in a gas stream being enriched with a suitable solvent, so that the lacquer layer is homogenized and planed. Preferably, an N2 stream being passed through a gas washing bottle that is filled with ethyl methyl ketone or acetone is used for this purpose.

The coating process is preferably finished by baking the thus planed lacquer layer.

The present method of lacquering semiconductor substrates allows a uniform lacquering of three-dimensional topographies due to a spraying method in which it is assured that the uniformly sprayed lacquer remains on the desired positions after having been sprayed onto the substrate. Additionally, the resulting non-uniform or non-dense layer can be subsequently homogenized or planed. During this subsequent treatment, the resist is softened and thus forms a smooth layer, wherein a suitable selection of the subsequent treatment period and/or temperature prevents the resist from leaving the edges.

In the following, the invention will be described in more detail on the basis of embodiments and with reference to the drawings in which

Figure 1 schematically shows a device for spraying the photoresist onto a substrate according to the present invention, and

Figure 2 schematically shows a device for homogenizing the sprayed lacquer layer according to the present invention.

Figure 1 shows a device for spraying modified lacquer or photoresist onto a substrate 1 in accordance with the method of the present invention. The substrate 1, preferably a semiconductor substrate or wafer, is fixed onto a heatable and thus temperature-adjustable and temperature-controllable and rotatably supported chuck, and set to a temperature. During the spraying process, the temperature of the substrate should lie between about 40°C and 90°C, preferably at about 70°C.

An atomizing system 2, which atomizes the lacquer that is modified with a solvent and thus sprays it onto the substrate 1, is moved on a predetermined path at a defined and adjustable distance over the substrate 1 by means of a suitable system of axes 22 and 23, so that the surface of the substrate 1 is covered completely by the lacquer mixture atomized by the atomizing system 2. For this purpose, the atomizing head 2 is moved optionally several times over the substrate 1, for example along meandering paths 21 that can be different in subsequent phases or runs, so that the lacquer is distributed as uniformly as possible. Additionally, the rotatable position of the substrate 1 on the chuck can be changed during spraying or between the individual spraying phases. The angle of the spray jet with which the lacquer mixture from the atomizing system 2 hits the substrate surface can be adjusted or varied by inclining the atomizing system 2 with respect to the substrate plane.

Since surface roughness of the lacquer layer often occurs during the spraying process, the lacquer layer can be subsequently homogenized and planed in a further process step. Figure 2 schematically shows a device which is suitable for this process step. By means of a gas washing bottle, a gas stream 3, preferably an N2 stream, is enriched with a suitable solvent 4 and directed towards the lacquer surface. Suitable solvents 4 are preferably ethyl methyl ketone or acetone. For guaranteeing a uniform treatment of the surface of the substrate 1, the latter can be moved, by means of a positioning table, uniformly with respect to a nozzle system from which the gas stream that is enriched with the solvent streams out.

Suitable photoresists for being used in the method of the present invention are, e.g., Clariant AZ5214E, Clariant AZ520D, Clariant AZ1512, Clariant AZ111, MicroResist Technologies Mr-P 11, Shipley 1818 and BCB. When using these photoresists, e.g. the following lacquer modifications are suitable.

- 1 part lacquer: 5 to 15 parts acetone - 1 part lacquer: 2 to 10 parts ethyl methyl ketone

- 1 part lacquer: 2 to 10 parts ethyl methyl ketone: 5 to 15 parts ethanol

- 1 part lacquer: 2 to 5 parts ethyl methyl ketone: 0.5 to 2 parts propylene glycol methyl ether acetate - 1 part lacquer: 5 to 15 parts acetone: 0 to 2 parts propylene glycol methyl ether acetate.

One to four layers of the correspondingly modified resist are applied by spraying. For a better coating of the substrate, the entire surface or parts of the surface can be subsequently treated during the application of the individual layers and/or after the entire coating process in a solvent atmosphere for 10 to 90 seconds, wherein an N2 stream streaming through a gas washing bottle that is filled with ethyl methyl ketone or acetone is preferred for this purpose. Then, the lacquer layer is baked on the hot plate at 60°C to 90°C for 0.5 to 3 minutes.

Claims

1. A method of lacquering a substrate comprising the steps of (a) modifying the lacquer to be applied by means of a solvent;

(b) spraying the modified lacquer onto the substrate.

2. The method according to claim 1, further comprising the step (c) of homogenizing the lacquer layer in a solvent atmosphere.

3. The method according to claim 1 or 2, further comprising the step (d) of baking the lacquer layer.

4. The method according to claim 1, 2 or 3, wherein in step (a) the lacquer is modified with acetone, ethyl methyl ketone and/or propylene glycol methyl ether acetate.

5. The method according to any one of the preceding claims, wherein in step (b) the substrate is heated while the modified lacquer is sprayed.

6. The method according to claim 5, wherein the substrate is heated to a temperature of about 40°C to 90°C.

7. The method according to any one of the preceding claims, wherein in step (b) an atomizing system for spraying the modified lacquer onto the substrate is moved in meandering paths over the substrate, so that a layer is formed.

8. The method according to any one of the preceding claims, wherein in step (b) also a plurality of layers can be spayed onto each other.

9. The method according to any one of the preceding claims, wherein in step (b), when a plurality of layers are applied, the substrate is rotated by 90° between the application of the individual layers.

10. The method according to claim 2, wherein a gas stream being enriched with a solvent is directed towards the lacquer layer for homogenizing the lacquer layer.

11. The method according to any one of claims 3 to 10, wherein in step (d) the temperature during baking the lacquer layer is about 60°C to 90°C.

12. The method according to any one of the preceding claims, wherein the substrate has a three-dimensional structure.

13. The method according to any one of the preceding claims, wherein the area covered by the meandering path approximately corresponds to at least the size of the substrate.

14. The method according to claim 1, wherein the lacquers modified in step (a) have a viscosity of 0.5 to 5 cp at 25°C.