Radiant energy – Irradiation of objects or material
Reexamination Certificate
2000-09-21
2003-07-29
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
C250S310000, C250S397000
Reexamination Certificate
active
06600162
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This invention claims priority of a German filed patent application DE-A-198 53 093.5.
FIELD OF THE INVENTION
The invention refers to a method for exposing a substrate, equipped with an n-layer photoresist system, with a corpuscular radiation, an electrically conductive connection being created between a ground potential and the substrate and/or at least one of the layers S
1
through S
n
of the photoresist system in order to dissipate electrical charges. The invention further refers to an arrangement for carrying out this method.
BACKGROUND OF THE INVENTION
Methods and arrangements for patterning substrates, for example masks or wafers, in which the substrate is coated with a photoresist and that photoresist layer is exposed to a corpuscular radiation, for example an electron radiation, in order to impress the predefined pattern upon the substrate, are known. For exposure, the substrates are placed onto the support surface of a stage movable in the X and Y coordinates and retained there while the stage is moved step by step in the X and/or Y direction and thereby brought at successive points in time into predefined exposure positions in which the corpuscular radiation is directed at right angles, corresponding to the Z coordinate, onto the photoresist layer.
The photoresist is made of an electrically nonconductive material that becomes electrostatically charged during irradiation. The substrate can also become electrostatically charged. This side effect, referred to generally as “charging,” can unintentionally result, especially in the case of photoresist layer material thicknesses>1 &mgr;m, in an influence on the radiation direction of the corpuscular radiation and thus in exposure errors and pattern defects, thus defeating efforts in the microelectronics industry toward increasingly finer patterns. To remedy this, a variety of methods and arrangements for dissipating electrical charges out of the photoresist layer and/or out of the substrate during exposure have been developed.
JP Patent 60-117720, for example, describes an electron beam exposure method in which the electrical charge is dissipated from a specimen equipped with a nitride or oxide layer by the fact that a needle made of a very hard, initially electrically nonconductive material, such as diamond, sapphire, or the like, is made conductive by the implantation of, for example, boron ions and is then used to penetrate through the layer until contact is made with the specimen. This results in grounding of the specimen via the grounded needle, and thus causes dissipation of the charge that has accumulated in the specimen during exposure. Because of the hardness of the material, the needle has a long service life, although relatively large forces must act on the needle in order to penetrate the nitride or oxide layer.
In this context, the advance movement of the needle is limited by the specimen material, i.e. the specimen constitutes the stop for the needle and prevents it from pushing forward into the specimen material beyond a desired degree. Disadvantageously, this method and the arrangement depicted in this context are suitable only for contacting a specimen concealed beneath a layer, by penetration through that layer. If, however, what is provided as the specimen is a substrate onto which a photoresist system made up of several layers has been applied, and if each of the layers is to be individually contacted and connected to a ground potential by way of a separate needle, this procedure is unsuitable, since the needles are always pushed through the entire layer structure until contact is made with the substrate.
A further JP Patent 3-263814 assumes that it is known, for example in the case of a mask board that is equipped with a chromium layer and a photoresist located above the chromium layer, to penetrate through the photoresist layer with the tip of a contact pin, to create an electrically conductive connection to the chromium layer lying therebeneath, and thereby to dissipate the undesired electrons out of the chromium layer through the pin to a ground potential. According to the patent, this method is improved in that the contact pin, upon penetration through the photoresist layer and while contact is made with the chromium layer lying therebeneath, is caused to rotate about its longitudinal axis in order to achieve reliable contact and at the same time to increase the service life of the tip of the contact pin, since the pin can now be of rounded configuration. Leaving aside the increased equipment complexity involved in a rotational drive for the pin, here again the disadvantage exists that contacting of each individual one of a plurality of layers of a photoresist system cannot be performed in this fashion.
JP Patent 2-125416 describes an arrangement for creating an electrical contact between a cassette (ground potential) and a chromium layer that is located on a mask baseplate beneath a photoresist. In this, outside the area that is reserved on the mask of the patterning, a pin is pushed by way of a leaf spring onto the surface of the (electrically nonconductive) photoresist layer. The tip of an electrode that is connected to a high-voltage source is then pushed through the photoresist, in the vicinity of said pin, as far as the chromium layer, and then a voltage of a few hundred to ten thousand volts is applied to the electrode; the photoresist thereby experiences an insulation breakdown as a result of which the pin resting on the photoresist is conductively connected to the chromium layer, and dissipation of charges occurs to the cassette via the pin and the leaf spring.
This technical solution is also not suitable, nor is it provided, for contacting each individual one of a plurality of layers of a photoresist system.
SUMMARY OF THE INVENTION
Proceeding from this existing art, it is the object of the invention to develop a method of the kind described above in such a way that in the case of a substrate equipped with a multi-layer photoresist system, before exposure begins each individual one of the layers S
1
through S
n
of the photoresist system, and if necessary also the substrate itself, is brought into electrically conductive connection with a ground potential.
According to the present invention, the object is achieved in that in a process step before exposure begins, the substrate and/or the layers S
1
through S
n
are brought into electrically conductive connection with the ground potential by way of a quantity of m contact tips K
1
through K
m
, by the fact that the coated substrate and the contact tips K
1
through K
m
are moved relative to one another until the electrically conductive connection between the ground potential and the substrate and/or each individual layer S
1
through S
n
is created by way of at least one of the contact tips K
1
through K
m
in each case.
This uncomplicated process step advantageously ensures that there is created, between the ground potential and each individual one of the layers S
1
through S
n
and the substrate, an ohmic contact by way of which the electrical charges occurring during exposure are effectively dissipated. Any undesired influence on the radiation direction caused by electrical charges is thus prevented, and an essential prerequisite for accurate exposure and for a further refinement in patterns is thus created. The disadvantages of the existing art described above are thus eliminated.
According to the invention, what is achieved in a single process step is that, for example, a contact tip K
1
is advanced until contact is made with the layer S
1
, a contact tip K
2
is advanced through the layer S
1
until contact is made with the layer S
2
, a contact tip K
3
is advanced through the layers S
1
and S
2
until contact is made with the layer S
3
, and so forth, and lastly a contact tip K
m
is advanced through the layers S
1
through S
n
until contact is made with the substrate. The electrical charges from the layer S
1
are dissipated to the ground potential via the contact tip K
1
, th
Beyer Dirk
Elster Thomas
Hahmann Peter
Krauhs Dorothee
Foley & Lardner
Johnston Phillip A
Leica Microsystems Lithography GmbH
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