Method for writing a pattern on a surface intended for use in exposure equipment and for measuring the physical properties of the surface
The present invention relates to a method for writing a pattern on a surface intended for use in exposure equipment, including the steps of: arranging an object having a thickness (T) provided with a surface on a stage of a pattern generating apparatus, dividing the surface into a number of measurement points, where two adjacent measurement points being spaced a distance (P) apart not exceeding a predetermined maximum distance, determining the gradient of the surface at each measurement point, calculating a 2-dimensional local offset (d) in the x-y plane for each measurement point as a function of the gradient, and the thickness (T) of object, and correcting the pattern to be written on said surface by using the 2-dimensional local offset (d). The invention also relates to a method for measuring the physical properties of a surface.
A method for writing a pattern on a surface intended for use in exposure equipment and for measuring the physical properties of the surface.
TECHNICAL FIELD OF THE INVENTIONThe present invention relates to a method for writing a pattern on a surface, preferably on a glass plate made from quartz, for use in exposure equipment, as defined in claim 1. The invention also relates to a method for measuring the physical properties of the surface to determine the shape of the surface of a plate as defined in claim 10.
BACKGROUND TO THE INVENTION When a large display or part of a display, colour filter or an other similar application, is produced, an exposure system transfer an image from a glass plate, preferably made from high quality quarts, onto a rather large substrate, which may have a dimension up to 1100 mm times 1300 mm or even more. The exposure system includes an aligner, or stepper, that emits light through the glass plate and onto the substrate, see
It is very important that the registration of masks, i.e. the absolute placement in a Cartesian coordinate system, is good enough to permit masks from different systems to fit together, e.g. the colour filter and the TFT-array. Furthermore, large TFT substrates may use two or more masks stitched together to cover a large exposure area.
In pattern generating systems for small plates, a three-foot device is used to support the plate during pattern generation and measurement, but the weight of a glass plate, with a thickness of 10 mm and a size of 1000×1000 mm, is approximately 40 kg, which will not be suitable to place on three pins. An alternative solution is to use an air cushion for plate support, but this introduces other problems like determining the exact position of the plate during exposure of the pattern. Another alternative is to handle the consequences that will arise when placing the plate directly on the stage (i.e. the support) of a pattern generating apparatus, although the plate will be deformed.
SUMMARY OF THE INVENTIONThe object of the invention is to provide a method for writing a pattern on a glass plate that is independent of any physical deformations that will occur when writing the pattern.
This object is achieved by the method as defined in claim 1.
A further object with the invention is to provide a method for measuring a glass plate being independent of any physical deformations that will occur when measuring the plate.
This object is achieved by the method as defined in claim 10.
An advantage with the present invention is that unevenness in the support of the pattern generating apparatus (or measuring apparatus) will not introduce any error in the pattern or the measurement.
A further advantage is that any unevenness of the back surface and/or the front surface of the glass plate will not introduce any errors in the pattern or the measurement.
Still a further advantage with the present invention is that contamination in form of particles and/or air trapped between the plate and the support can be compensated for, and therefore will not introduce any error in the pattern or measurement.
Still another advantage is that it is possible to even correct the deformation that will occur in the exposure equipment together with the deformation generated during the pattern writing process, provided that information regarding deformation in the exposure equipment is known when manufacturing the plate, as is disclosed in the published international patent application WO 00/72090 by the same applicant.
BRIEF DESCRIPTION OF THE DRAWINGS
Other necessary optics is not shown in
The apparatus 20 is also provided with an angled foot plate 26 arranged a constant distance above the surface 13 of the glass plate 11 by means of an air cushion 27. The foot plate 26 and the pattern writing means 21 are attached to the sliding support 24 via a flexible attachment 28, to allow the distance between the sliding support 24 and the pattern writing means/foot plate to vary dependent on the roughness of the surface 13 of the glass plate 11. The varying distance in the z direction, i.e. the height Hz, may be measured to calculate the roughness of the surface 13 in the z direction. The size of the foot plate that is parallel to the surface 13 of the glass plate 11 has an opening for a laser beam from the pattern writing means 21 and is preferably rather large, e.g. 5 mm on each side, since the purpose of the measurement is to detect deviations in height over a relatively large distance. The air cushion beneath foot plate will act as an auto focus device for the pattern generating apparatus due to the constant distance between the foot plate and the glass plate. The invention should however not be limited to this kind of pattern generating apparatus using an air cushion as an auto focus device, but other types of systems that will provide focus for the system could be used. The essential part is that the apparatus 20 is provided with means to measure the height Hz between the apparatus and the surface 13 of the glass plate 11 and thereby the variation in height when the pattern writing means 21 is moved in relationship to the stage 23, and thus the surface 13.
An essential part of the invention is to determine a reference surface against which the difference in height Hz is calculated. This difference is denoted H, as is illustrated in connection with
If it were possible, it may have been desirable to use the “free” (non gravity) form, i.e. the centre line of the plate as a reference surface, which is rather difficult to achieve in practise. The bottom surface of the plate is not a good alternative for a reference surface since a stepper or an aligner use the top surface as a reference.
On the other hand if the top surface would be used as a reference surface, there is an additional need to know the bottom shape of the plate and the shape of the support. The shape of the support may be obtained, but it is very difficult to achieve knowledge of the bottom surface in practice. The top surface may however be measured without the knowledge of the bottom surface. A large glass plate that is placed on a three-foot will be deformed due to the weight of the plate, but a deformation function for a perfect plate may be calculated if the thickness of the plate, the material of the plate and the configuration of the three-foot are known. A measurement of the non-perfect glass plate, when placed on the three-foot, will generate a measurement of the deformed plate. The shape of top surface is then calculated by subtraction the calculated deformation function for a perfect plate from the measurement of the deformed plate.
The top surface of a glass plate is normally much more even, i.e. less variation in height in relation to the centre line, compared to the bottom surface, and the best compromise should therefore be to make the top surface of the plate to be the reference surface. It should however be noted that it is not evident that the top surface is the best choice due to the deformation of the glass plate during the following step in the exposure system, as shown in
It should however be noted that any surface may be used as reference surface, although the top side is preferred.
A local offset d (as a function of x and y) is thereafter calculated for each measurement point and depends on three variables: the thickness of the glass plate (T), the distance between adjacent measurement points (P) and the measured height (H) between the reference surface 30 and the surface 13 of the glass plate 11. The local offset should be interpreted as the position deviation from the position where a pattern should be written in relationship to the reference surface, as described in connection with
The distance between adjacent measurement points should not exceed a predetermined distance, which is dependent on the required accuracy for the measurement to get a reasonable good result from the measurement. An example of maximum distance between adjacent measurement points is 50 mm if the thickness of the glass plate 11 is around 10 mm and the glass plate material is quartz. The distance between adjacent measurement points also vary dependent on the thickness of the glass plate to obtain the same measurement accuracy. The variations in thickness of the glass plate is may be around 10-15 μm, but could be larger. The measurement points could be randomly distributed across the surface 13, but are preferably arranged in a grid structure with a predetermined distance between each point, i.e. pitch, that is not necessarily the same in the x and y direction.
The local offset is a function of the gradient in x and y direction at each measurement point and could be calculated using very simple expressions.
An angle α may be calculated from the measured height H provided the distance P between two adjacent measurement points 31a is known.
For small angles α:
Furthermore the local offset d may be calculated provided a is small using the formula:
It should however be noted that the formula for calculating the local offset d above, only is a non-limiting example of a calculation to determine the offset d. The gradient in each measurement point could be directly measured by the system and the local offset is proportional to the gradient and the thickness of the plate.
As previously mentioned above,
As a non-limiting example we assume that the distance between two adjacent points 31 is 40 mm, the thickness of the glass plate is 10 mm, and that the measured height H is 1 μm, which will result in a one-dimensional local offset d of 125 nm.
When the glass plate 41 is arranged on the flat support 45, the shape of the top surface 43 is changed and the bottom surface 42 will generally follow the flat support 45. The result of this is that the pattern generated, illustrated by the dots 46 on the top surface, has to be expanded to obtain a correct reference surface.
When the glass plate 51 is arranged on the flat support 45, the shape of the top surface 43 is unchanged and the bottom surface 42 will follow the flat support 45. The pattern generated, illustrated by the dots 55 on the top surface, has to be expanded to obtain a correct reference surface, since the top surface will be flattened out when positioned in the exposure equipment as described in
When the glass plate 61 is arranged on the shaped support 62, the shape of the top surface 43 is changed and the bottom surface 42 will generally follow the shaped support 62. The pattern generated, illustrated by the dots 64 on the top surface, has to be expanded to obtain a correct reference surface, since the top surface will be flattened out when positioned in the exposure equipment as described in
The overall error is however much smaller since all errors from the bottom surface, support surface and contamination, see
The size of the glass plate is in this example 800×800 mm, and the distance between each dashed line 70 in
A transition from a low H value to high H value corresponds to that the glass plate has a “negative” bend, as illustrated in
Although a glass plate has been used as an illustrative example in the patent application, the scope of the claims should not be limited to a plate made of glass.
Furthermore, the pattern generating apparatus could of course include correction functions for any repeatable error, e.g. errors present in substrates for the manufacturing of TFT-arrays that are introduced in the substrates during the manufacture of the substrates, as well as repeatable errors introduced in the manufacturing process in the aligner, or stepper as previously mentioned.
The method may naturally be implemented into a computer program for performing the measurements, and calculating the local offset for each measurement point.
Claims
1. A method for writing a pattern on a surface intended for use in exposure equipment, comprising the steps of:
- arranging an object having a thickness (T) provided with a surface on a stage of a pattern generating apparatus,
- dividing the surface into a number of measurement points, where two adjacent measurement points being spaced a distance (P) apart not exceeding a predetermined maximum distance,
- determining the gradient of the surface at each measurement point,
- calculating a 2-dimensional local offset (d) in the x-y plane for each measurement point as a function of the gradient, and the thickness (T) of object, and
- correcting the pattern to be written on said surface by using the 2-dimensional local offset (d).
2. The method according to claim 1, wherein the step of correcting the pattern comprises the steps:
- determining a correction function for the surface using the calculated 2-dimensional local offset (d) for each measurement point, and
- writing the pattern on the surface using the correction function with the pattern generating apparatus.
3. The method according to claim 1, wherein the step of determining the gradient comprises measuring the variation in height of the surface at each measurement point.
4. The method according to claim 3, wherein the step of measuring the variations in height of the surface comprises the steps of:
- determining a reference surface, measuring the height (H) between the reference surface and the surface of the object at each measurement point, whereby the 2-dimensional local offset (d) in the x-y plane may be calculated as a function of the measured height (H), the distance (P) from each at least one adjacent measurement point, and the thickness (T) of the object.
5. The method according to claim 4, wherein the local offset (d) is calculated using the formula: d=(T*H)/(2*P)
6. The method according to claim 3, wherein the measurement points are arranged in a grid structure having a first predetermined pitch in the x direction and a second predetermined pitch in the y direction.
7. The method according to claim 4, wherein the height (H) between the reference surface and the surface of the object originate from unevenness of the stage, and/or unevenness of one or both surfaces of the object and/or undesired objects arranged between the stage and the object.
8. The method according to claim 7, wherein the undesired objects may be trapped air or particles.
9. The method according to claim 1, wherein the top surface of the object is selected to carry the pattern.
10. The method according to claim 1, wherein the correction function also compensates for expected deformation from the exposure equipment during subsequent processing steps.
11. A method for measuring the physical properties of a surface, including the steps of:
- arranging an object having a thickness (T) provided with a surface on a stage of a measuring apparatus,
- dividing the glass plate into a number of measurement point, where two adjacent measurement points being spaced a distance apart not exceeding a predetermined maximum distance,
- determining the gradient of the surface at each measurement point,
- calculating a 2-dimensional local offset (d) in the x-y plane for each measurement point as a function of the gradient, and the thickness (T) of object, and
- determining a correction function for the surface using the calculated 2-dimensional local offset (d) for each measurement point.
12. The method according to claim 11, wherein the step of determining the gradient comprises measuring the variation in height of the surface at each measurement point.
13. The method according to claim 12, wherein the step of measuring the variations in height of the surface comprises the steps of:
- determining a reference surface, measuring the height (H) between the reference surface and the surface of the object at each measurement point, whereby the 2-dimensional local offset (d) in the x-y plane may be calculated as a function of the measured height (H), the distance (P) from each at least one adjacent measurement point, and the thickness (T) of the object.
14. The method according to claim 11, wherein the object is a reference object, and said surface is provided with marks at each measurement point.
15. A computer program for performing the following steps:
- determining the gradient of the surface at each measurement point being defined on a surface of an object having a thickness (T),
- calculating a 2-dimensional, local offset; (d) in the x-y plane for each measurement point as a function of the gradient, and the thickness (T) of object, and determining a correction function for the surface, or correcting a pattern to be written on said surface, using the calculated 2-dimensional local offset (d) for each measurement point.
16. A computer program product for carrying the computer program as defined in claim 15.
Type: Application
Filed: Oct 27, 2003
Publication Date: Apr 28, 2005
Inventors: Lars Stiblert (Goteborg), Peter Ekberg (Lidingo)
Application Number: 10/692,863