Method for bonding a pellicle, and a bonding apparatus used in this method

Abstract

Here is proposed a method for bonding a pellicle to a stencil such as mask plate, which is characteristic in that the stencil-bonding agglutinant layer of the pellicle is warmed under load while the pellicle is being bonded to the stencil, preferably at a temperature in a range of 35 through 80 degrees C., and the load is increased stepwise and with intermittent removal of the load.

Claims

1. A method for bonding a pellicle for lithography to a stencil, comprising: providing said pellicle comprising a pellicle frame having first and second faces, a membrane bonded to the first face of the frame via an adhesive, and an agglutinant layer of an acrylic adhesive or silicone adhesive laid on the second face of the pellicle frame, the agglutinant layer being agglutinant at a room temperature; warming and softening said agglutinant layer, and bonding the pellicle with the stencil via the warmed and softened agglutinant layer under a bonding load pressure.

2. A method for bonding a pellicle for lithography to a stencil as claimed in claim 1, wherein said warming of the agglutinant layer is effected by heating the stencil to a temperature in a range of 35 through 80 degrees C.

3. A method for bonding a pellicle for lithography to a stencil as claimed in claim 1, wherein said bonding load pressure is 100 N or lower.

4. A method for bonding a pellicle for lithography to a stencil as claimed in claim 3, wherein said bonding load pressure of 100 N or lower is not to be reached in less than one minute.

5. A method for bonding a pellicle for lithography to a stencil as claimed in claim 3, wherein said bonding load pressure of 100 N or lower is to be reached stepwise.

6. A method for bonding a pellicle for lithography to a stencil as claimed in claim 5, wherein said bonding load pressure of 100 N or lower is to be reached stepwise in a manner such that when an intermediate load pressure lower than the load pressure is reached, the intermediate load pressure is kept for a period of time and then increased to the bonding load pressure.

7. A method for bonding a pellicle for lithography to a stencil as claimed in claim 5, wherein said bonding load pressure of 100 N or lower is to be reached stepwise in a manner such that when an intermediate load pressure is reached, the intermediate load pressure is kept for a first period of time and then load pressure is removed for a second period of time and then the load pressure is increased to the bonding load pressure.

8. A method for bonding a pellicle for lithography to a stencil as claimed in claim 7, wherein said second period of time is 30 seconds or longer.

9. A method for bonding a pellicle for lithography to a stencil as claimed in claim 2, wherein said bonding load pressure is 100 N or lower.

10. A method for bonding a pellicle for lithography to a stencil as claimed in claim 4, wherein said bonding load pressure of 100 N or lower is to be reached stepwise.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 This is a schematic drawing showing a basic structure of a pellicle.

EMBODIMENTS OF PRACTICING THE INVENTION

(2) Now, examples for practicing the present invention will be described, but the scope of the invention is not to be construed to be limited by them.

(3) The method of the present invention relates to a pellicle comprising a frame, a membrane bonded to one annular face of the frame via an adhesive and an agglutinant layer laid on the other annular face of the frame, and is characteristic in that the agglutinant layer and the mask plate are warmed on the occasion of bonding the pellicle to the mask plate.

(4) The basic structure of the pellicle 10 used in the present invention is as shown in FIG. 1. A pellicle membrane 1 is bonded to one annular face of a pellicle frame 3 of the pellicle 10 in a slack-free manner via an adhesive layer 2. An agglutinant layer 4 for bonding the pellicle 10 to a mask plate or a reticle 5 (an exposure stencil) is formed on the other annular face of the pellicle frame 3. Also, usually, over the exposed face of this stencil-bonding agglutinant layer 4 is laid a releasable liner (not shown) for protecting the agglutinant layer 4; a pressure control hole 6 (air vent) is made through a bar of the pellicle frame 3 and, when need be, a dust-stopping filter 7 is provided for prevention of contamination with particles.

(5) The pellicle 10 of such construction of the present invention may be of various sizes, including, for example, pellicles for semiconductor lithography and a lithography for manufacturing a large-sized liquid crystal display panel, and the materials to make such pellicle 10 can be selected from conventionally used ones as those described above.

(6) The kind of the pellicle membrane 1 to be used is not particularly specified, but amorphous fluorine-based polymers and the like which have conventionally been used for excimer laser are preferable. Examples of such amorphous fluorine-based polymer are CYTOP (a product name of ASAHI GLASS CO. LTD.), Teflon (registered trademark), and AF (a product name of Du Pont). If need be, it is permissible to dissolve such polymers in a solvent such as fluorine-based solvent to produce the pellicle membrane 1.

(7) As for the material to make the pellicle frame 3, conventionally used aluminum alloys, such as JIS A7075, JIS A6061, and JIS A5052 are preferable, and in a case where an aluminum alloy is used, there is no specific requirement so long as the strength of the pellicle frame 3 is properly secured. It is preferable that the surface of the pellicle frame 3 is coarsen by sand blasting or chemical polishing before the surface is coated with a polymer layer, but the method of coarsening the surface of the pellicle frame 3 can be any other conventionally used method. Particularly in the case of an aluminum alloy frame, it is preferable that its surface is first blasted with beads of stainless, carborundum, glass or the like, followed by chemical polishing with NaOH or the like so as to coarsen the surface.

(8) The material to make the agglutinant layer 4 can be selected from various adhesives, but acrylic adhesive and silicone adhesive are better. Also, the shape of the agglutinant layer is preferably such that its face to be bonded to the mask plate is flattened.

(9) In the present invention, it is necessary to suppress the residual stress created at the time of bonding the pellicle to the mask plate so as to minimize the coercive effects of the pellicle frame upon the mask plate such as deforming effect, so that the pellicle 10 is preferably machined to have a highly flat face.

(10) New, the method for bonding the pellicle according to the present invention will be explained with reference to an example. First, the pellicle 10 is set to a pellicle holder equipped on a stage of a pellicle bonding apparatus in a manner such that the agglutinant layer of the pellicle frame faces upward; then, the releasable liner for protecting the agglutinant layer is released therefrom; the mask plate is set in a manner such that its face to receive the pellicle faces downward; next, a start button is depressed so as to energize the heater of the pellicle boding apparatus where by the pellicle frame and the mask plate start being heated. When the temperatures of the pellicle frame and the mask plate are raised to a predetermined point, the mask plate is slowly descended onto the pellicle frame and the mask plate is let to press itself on the pellicle frame with its own weight.

(11) In this pellicle bonding procedure, the temperatures of the pellicle frame and the mask plate greatly affect the bonding performance so that it is preferable that the temperatures are controlled to be between 35 and 80 degrees C. by monitoring them with a radiation thermometer or the like because thereby the stencil-bonding agglutinant layer is suitably softened such that it becomes possible to conduct a low load bonding which does not ill-affect the mask plate. Then, it is necessary that in actual bonding operation the temperatures of the pellicle frame and the mask plate be ascertained to be stably within the predetermined range. If the temperatures are lower than this predetermined range, the stencil-bonding agglutinant does not soften so much so that it becomes impossible to sufficiently lower the pellicle bonding load. On the other hand, if the temperatures are higher than this temperature range, the stencil-bonding agglutinant can degenerate or release outgas, hence not recommendable.

(12) In the boding step of the present invention, the bonding load is preferably 100 N or lower, and the time for the load to reach the target value is preferably one minute or longer. When the bonding load is so great as to exceed 100 N, the mask plate can be over-stressed and the flatness of the mask face during the pellicle bonding operation may undergo deterioration, so the this if not recommendable. Also, if the target bonding load is reached in less than one minute, the mask plate may receive localized stress so that the uniformity of the mask flatness may be ill-affected, and hence not recommended. Hence in a concrete practice of the bonding step, the peripheral area of the back face of the mask plate is pressed by a press member provided in the upper part of the bonding apparatus, when one minute has passed since the landing of the pellicle on the mask plate. In this primary pressurizing step, as soon as a predetermined primary target load value is reached, which has taken one minute or longer, the load is maintained unchanged for 30 seconds, and then the load is completely removed for 30 seconds. Thereafter, in the secondary pressurizing step, the predetermined secondary target load value is reached by the working of the same press member, which again has taken one minute or longer, whereat the load is held unchanged for 30 seconds, and thus the pellicle bonding operation is completed. If need be, it is possible to conduct the pellicle bonding operation going through a further similar pressurizing step in addition to the primary and the secondary steps.

(13) Also, in the bonding operation, it is preferable to conduct at least one pressure-holding step, whereat the load is held unchanged, before reaching the predetermined target load, rather than directly reaching the predetermined target load without a break, because in the former case it is possible to reduce the residual stress created in the mask plate by the pellicle adhesion. Furthermore, it is more preferable to conduct at least one pressure-removal step, whereat the load is cancelled between the pressure-holding step and the subsequent pressurizing step, for in this way more of the residual stress created in the mask plate by the pellicle adhesion is released. This stress releasing time is preferably 30 seconds or longer, for if it is shorter than 30 seconds, it is not possible to release the residual stress created in the mask plate sufficiently.

(14) In the bonding method of the present invention, the reduction of the pellicle induced deformation of the mask plate is effected by lowering the load pressure as much as possible at the time of pellicle bonding operation so that if the flatness of the pellicle frame used and the flatness of the agglutinant face to which the mask plate is bonded and also the softness of the agglutinant layer are optimized, it is possible to render the method an excellent one for cancelling PID.

(15) Next, the bonding apparatus of the present invention will be explained. This bonding apparatus is an apparatus for practicing the bonding method of the present invention so that it is equipped with a heating means for warming the agglutinant layer which bind the pellicle frame and the mask plate (exposure stencil) together. The apparatus is also equipped with a releasing device for peeling the releasable liner off the agglutinant layer by which it is protected, as well as with a lift means for raising and lowering the mask plate slowly to, for example, place the mask plate on the pellicle frame to thereby allow the mask plate to press itself to the pellicle frame by its own gravity; the apparatus is further equipped with a press means for pressing upon the peripheral part of the back face of the mask plate.

(16) Also, this bonding apparatus is equipped with a control means which is capable of being programmed to control the load pressure, load time duration, load free time duration, etc. in any of the at least one pressuring cycle in order to help the proper bonding of the pellicle frame to the mask plated to be achieved.

EXAMPLES

(17) Now, examples of the present invention will be explained in detail. Incidentally, in the following examples and comparative examples, the exposure stencil is embodied as a mask plate but the present invention can be equally applicable in cases wherein the exposure stencil is a reticle.

Example 1

(18) In Example 1, a pellicle frame made of an aluminum alloy (external dimensions were 149 mm115 mm3.5 mm and width was 2 mm; the flatness of the annular face to which the agglutinant layer is laid was 15 micrometers) was prepared; this was cleaned with precision washing; a silicone agglutinant (X-40-3264, a product name of Shin-Etsu Chemical Co., Ltd.) was applied to the 15-micrometer-flat face; the frame was let to sit for 60 minutes at a room temperature. Thereafter, a flat separator was laid on a 5-micrometer-flat face of an aluminum plate, and the pellicle frame with the agglutinant layer was laid on this in a manner such that the agglutinant layer contacts the separator, whereby the surface of the agglutinant layer was made flat.

(19) The pellicle frame and the aluminum plate were brought in an oven and heated at 60 degrees C. for 60 minutes whereby the agglutinant layer was hardened; then this pellicle frame together with the aluminum plate was brought out and the separator was peeled off. Next, the other annular face of the pellicle frame that was not coated with the agglutinant layer was coated with an adhesive CYTOP CTX-A, (a product name of ASAHI GLASS CO. LTD.), and this pellicle frame was heated at 130 degrees C., whereby the adhesive was hardened. Finally, the adhesive-bearing annular face of the pellicle frame was attached to a pellicle membrane, which had been temporarily put on a tool aluminum frame, which has a larger span than the pellicle frame, and that portion of the pellicle membrane that extends beyond the outer periphery of the pellicle frame was trimmed off, and thus a pellicle was completed.

(20) Next, a 6025 mask plate, which is a square plate measuring 6.0 inch6.0 inch0.25 inch (thickness), was prepared and it was measured and found to have a flatness of 0.25 micrometer. After this measurement, this mask plate was set in the pellicle bonding apparatus, and was heated to 35 degrees C. by means of a heating device; then the pellicle, which had already been completed as described above, was set in the bonding apparatus, and was pressed against the mask plate in a manner such that the bonding load was increased for 60 seconds, at the end of which a predetermined load value of 100 N was reached; this bonding load was kept for 30 seconds and thus the pellicle was bonded to the mask plate, which was kept at 35 degrees C. throughout this bonding operation.

(21) The flatness of the mask plate after being bonded to the pellicle was measured, and it was found to be 0.32 micrometer as opposed to the pre-bonding flatness of 0.25 micrometeran increase by 0.07 micrometer, and this pellicle induced deformation was considered sufficiently small and hence the effect of the present invention was confirmed.

(22) Table 1 shows the results of this Example 1 as well as Examples 2-4 and Comparative Examples 1-4, which will be explained herein below; in particular the flatness values of the mask plates before and after the bonding operation, the increments, and the pellicle bonding conditions are shown.

(23) TABLE-US-00001 TABLE 1 time required mask flatness (micrometer) to reach predetermined plate heating before after predetermined bonding loads temperature bonding bonding increment final load Example 1 100N 35 degrees C. 0.25 0.32 0.07 60 sec Example 2 100N 80 degrees C. 0.26 0.30 0.04 60 sec Example 3 50N .fwdarw. 0N.fwdarw. 35 degrees C. 0.25 0.30 0.05 60 sec 100N Example 4 50N .fwdarw. 0N.fwdarw. 80 degrees C. 0.25 0.28 0.03 60 sec 100N Comparative 50N .fwdarw. 0N.fwdarw. 25 degrees C. 0.25 0.36 0.11 60 sec Example 1 100N Comparative 50N .fwdarw. 0N.fwdarw. 100 degrees C. 0.26 0.28 0.02 60 sec Example 2 100N Comparative 50N .fwdarw. 0N.fwdarw. 80 degrees C. 0.25 0.37 0.12 15 sec Example 3 100N Comparative 50N .fwdarw. 0N.fwdarw. 80 degrees C. 0.25 0.38 0.13 60 sec Example 4 150N * In Comparative Example 2, a small amount of haze showed on the face of the mask plate in the vicinity of the agglutinant

Example 2

(24) In Example 2, a pellicle was produced in the same procedure as in Example 1. Then, a 6025 mask plate was prepared and it was measured and found to have a flatness of 0.26 micrometer. This mask plate was set in the pellicle bonding apparatus, and was heated to 80 degrees C. by the heating device; then the pellicle was set in the bonding apparatus, and was pressed against the mask plate in a manner such that the bonding load was increased for 60 seconds, at the end of which a predetermined load value of 100 N was reached; this bonding load was kept for 30 seconds and thus the pellicle was bonded to the mask plate, which was kept at 80 degrees C. throughout this bonding operation; thus the bonding was effected.

(25) The flatness of the mask plate after being bonded to the pellicle was measured, and it was found to be 0.30 micrometer as opposed to the pre-bonding flatness of 0.26 micrometeran increase by 0.04 micrometer, and this pellicle induced deformation was considered sufficiently small and hence the effect of the present invention was confirmed.

Example 3

(26) In Example 3, a pellicle was produced in the same procedure as in Example 1. Again, a 6025 mask plate was prepared and it was measured and found to have a flatness of 0.25 micrometer. This mask plate was set in the pellicle bonding apparatus, and was heated to 35 degrees C. by the heating device; then the pellicle was set in the bonding apparatus, and was pressed against the mask plate in a manner such that the bonding load was increased for 60 seconds, at the end of which a predetermined load value of 50 N was reached; this bonding load was kept for 30 seconds and then removed for 30 seconds, and then pressure was applied anew whereby the load increased for 60 seconds, at the end of which a predetermined value of 100 N was reached; this 100-N load was maintained for 30 seconds longer and the mask plate was maintained at 35 degrees C. throughout this bonding operation; thus the bonding was effected.

(27) The flatness of the mask plate after being bonded to the pellicle was measured, and it was found to be 0.30 micrometer as opposed to the pre-bonding flatness of 0.25 micrometeran increase by 0.05 micrometer, and this pellicle induced deformation was considered sufficiently small and hence the effect of the present invention was confirmed.

Example 4

(28) In Example 4, a pellicle was produced in the same procedure as in Example 1. Again, a 6025 mask plate was prepared and it was measured and found to have a flatness of 0.25 micrometer. This mask plate was set in the pellicle bonding apparatus, and was heated to 80 degrees C. by the heating device; then the pellicle was set in the bonding apparatus, and was pressed against the mask plate in a manner such that the bonding load was increased for 60 seconds, at the end of which a predetermined load value of 50 N was reached; this bonding load was kept for 30 seconds and then removed for 30 seconds, and then boding pressure was applied anew whereby the load increased for 60 seconds, at the end of which a predetermined value of 100 N was reached; this 100-N load was maintained for 30 seconds longer and the mask plate was maintained at 80 degrees C. throughout this bonding operation; thus the bonding was effected.

(29) The flatness of the mask plate after being bonded to the pellicle was measured, and it was found to be 0.28 micrometer as opposed to the pre-bonding flatness of 0.25 micrometeran increase by 0.03 micrometer, and this pellicle induced deformation was considered sufficiently small and hence the effect of the present invention was confirmed.

Comparative Example 1

(30) In Comparative Example 1, a pellicle was produced in the same procedure as in Example 1. Then, a 6025 mask plate was prepared and it was measured and found to have a flatness of 0.25 micrometer. This mask plate was set in the pellicle bonding apparatus; it was not heated but kept at a room temperature of 25 degrees C. Then the pellicle was set in the bonding apparatus, and was pressed against the mask plate in a manner such that the bonding load was increased for 60 seconds, at the end of which a predetermined load value of 50 N was reached; this bonding load was kept for 30 seconds and then removed for 30 seconds, and then pressure was applied anew whereby the load increased for 60 seconds, at the end of which a predetermined value of 100 N was reached; this 100-N load was maintained for 30 seconds longer and the mask plate was maintained at 25 degrees C. throughout this bonding operation; thus the bonding was effected.

(31) The flatness of the mask plate after being bonded to the pellicle was measured, and it was found to be 0.36 micrometer as opposed to the pre-bonding flatness of 0.25 micrometeran increment by 0.11 micrometer, and this pellicle induced deformation was greater than an upper limit of an aimed range.

Comparative Example 2

(32) In Comparative Example 2, a pellicle was produced in the same procedure as in Example 1. Again, a 6025 mask plate was prepared and it was measured and found to have a flatness of 0.26 micrometer. This mask plate was set in the pellicle bonding apparatus, and was heated by the heating device to 100 degrees C.; then the pellicle was set in the bonding apparatus, and was pressed against the mask plate in a manner such that the bonding load was increased for 60 seconds, at the end of which a predetermined load value of 50 N was reached; this bonding load was kept for 30 seconds and then removed for 30 seconds, and then pressure was applied anew whereby the load increased for 60 seconds, at the end of which a predetermined value of 100 N was reached; this 100-N load was maintained for 30 seconds longer and the mask plate was maintained at 100 degrees C. throughout this bonding operation; thus the bonding was effected.

(33) The flatness of the mask plate after being bonded to the pellicle was measured, and it was found to be 0.28 micrometer as opposed to the pre-bonding flatness of 0.26 micrometeran increment by 0.02 micrometer, and this pellicle induced deformation was considered sufficiently small; however, haze occurred on the face of the mask plate in the vicinity of the agglutinant layer and hence the effect of the present invention was not confirmed; the occurrence of the haze is thought to be a result of that the temperature at which the mask plate was maintained was too high.

Comparative Example 3

(34) In Comparative Example 3, a pellicle was produced in the same procedure as in Example 1. Again, a 6025 mask plate was prepared and it was measured and found to have a flatness of 0.25 micrometer. This mask plate was set in the pellicle bonding apparatus, and was heated to 80 degrees C. by the heating device; then the pellicle was set in the bonding apparatus, and was pressed against the mask plate in a manner such that the bonding load was increased for 5 seconds, at the end of which a predetermined load value of 50 N was reached; this bonding load was kept for 30 seconds and then removed for 30 seconds, and then boding pressure was applied anew whereby the load increased for 15 seconds, at the end of which a predetermined value of 100 N was reached; this 100-N load was maintained for 30 seconds longer and the mask plate was maintained at 80 degrees C. throughout this bonding operation; thus the bonding was effected.

(35) The flatness of the mask plate after being bonded to the pellicle was measured, and it was found to be 0.37 micrometer as opposed to the pre-bonding flatness of 0.25 micrometeran increment by 0.12 micrometer, and this pellicle induced deformation was greater than the upper limit of the aimed range.

Comparative Example 4

(36) In Comparative Example 4, a pellicle was produced in the same procedure as in Example 1. Again, a 6025 mask plate was prepared and it was measured and found to have a flatness of 0.25 micrometer. This mask plate was set in the pellicle bonding apparatus, and was heated to 80 degrees C. by the heating device; then the pellicle was set in the bonding apparatus, and was pressed against the mask plate in a manner such that the bonding load was increased for 60 seconds, at the end of which a predetermined load value of 50 N was reached; this bonding load was kept for 30 seconds and then removed for 30 seconds, and then boding pressure was applied anew whereby the load increased for 60 seconds, at the end of which a predetermined value of 150 N was reached; this 150-N load was maintained for 30 seconds longer, and the mask plate was maintained at 80 degrees C. throughout this bonding operation; thus the bonding was effected.

(37) The flatness of the mask plate after being bonded to the pellicle was measured, and it was found to be 0.38 micrometer as opposed to the pre-bonding flatness of 0.25 micrometeran increment by 0.13 micrometer, and this pellicle induced deformation was greater than the upper limit of the aimed range.

REPRESENTATION OF REFERENCE NUMERALS

(38) 1: pellicle membrane 2: adhesive layer for bonding pellicle membrane 3: pellicle frame 4: agglutinant layer for bonding mask 5: stencil such as mask and reticle 6: pressure control hole 7: dust-stopping filter 10: pellicle