JPH0895229A - Photomask for exposure device and its pattern plotter - Google Patents

Abstract

PURPOSE: To suppress the curvature of field and image distortions on the imag ing planes of the projecting lenses of reduction steppers and to absorb the difference from one stepper to another by forming the pattern previously distorting the shape and pattern of a photomask. CONSTITUTION: The metallic pattern 3 of the photomask 1 for correcting distortions are plotted with distortion in some places in such a manner that the image distortions of the projecting lenses using the photomask 1 are offset on a wafer at the time the pattern is plotted by a reticle plotter. For example, the photomask is provided with a pattern 4 plotted in such a manner that the image distortion generated at the time of assembling the respective projecting lenses in the stepper offset on the wafer by the pattern shape (distortion correcting patterns) plotted to offset the image distortion intrinsic to the projecting lenses on the wafer. On the other hand, the surface shape of a photomask 2 is so worked as to form an aspherical surface that the curvature of image intrinsic to the projecting lenses and the curvature of image field generated at the time of assembling the respective projecting lenses are offset on the wafer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask (hereinafter also referred to as a reticle) used in an exposure process of a semiconductor integrated circuit, and more particularly to a field curvature and an image distortion in an image forming plane of a projection lens of an exposure apparatus. The present invention relates to a photomask for an exposure apparatus, which is suitable for suppressing the difference between the exposure apparatuses and suppressing the difference.

[0002]

2. Description of the Related Art As an exposure apparatus used in an exposure process of a semiconductor integrated circuit, for example, a reduction projection exposure apparatus has been conventionally used.

A reduction projection exposure apparatus irradiates a semiconductor wafer with light emitted from a light source through a reticle and a reduction lens, reduces a pattern formed on the reticle by the reduction projection lens, and transfers it onto the semiconductor wafer. It is a device that does.

The reticle used in the reduction projection exposure apparatus has a metal pattern made of chromium (Cr) or the like formed on a flat transparent glass substrate having, for example, a plane quadrangle, and the portion where the metal pattern is formed is A light shielding area is formed, and a portion where the metal pattern is not formed forms a transparent area.

[0005]

The image plane of the projection lens of the reduction projection exposure apparatus is characterized in that it is not flat but is deformed into a curved shape, and this curvature is called field curvature. Has been. The image plane is an ideal lattice (square lattice).
There is distortion that does not take the form, and this distortion is called image distortion.

By the way, the semiconductor wafer to which the pattern is transferred is held so that its upper surface is substantially flat (horizontal state). For this reason, there is a problem that a part of the exposure area, particularly the peripheral portion, is defocused due to the curvature of field, and the transfer accuracy is deteriorated.

[0007] This problem becomes remarkable especially as the resolution of the exposure apparatus is improved with the miniaturization of semiconductor elements and wirings. This is usually the numerical aperture for high resolution
This is because a projection lens with high (Numerical Aperture, abbreviated as NA hereinafter) is used, but if NA is increased, the curvature of field becomes large and the depth of focus becomes considerably narrow.

In order to avoid such a problem, conventionally, for example, in the reduction projection exposure apparatus, the focus is not blurred around the exposure area, that is, the optical path length of the light passing through the projection lens is the exposure area. In order to make the center and the peripheral part of the projection lens equal, a plurality of lenses are arranged in an overlapping manner and the material and shape of the projection lens itself are appropriately set. There have been various problems such as a complicated mechanism and an increase in restrictions on the projection lens.

On the other hand, regarding the distortion of the image from the ideal lattice,
Since there is a difference in pattern density in the exposure area, there is a problem that an exposure apparatus with less image distortion must be selected and used in a step that influences the performance of the semiconductor, such as a gate step.

Further, as shown in FIG. 9, when an attempt is made to automate an exposure process by avoiding an apparatus that cannot be used due to a failure or the like among a plurality of lines and selecting and using an empty apparatus that has not failed, If the difference between the image distortion of the exposure device used in the previous step and the image distortion of the exposure device to be used from now on is not within a certain allowable value, a short circuit or disconnection may occur and the exposure device cannot be used. It had a problem of being restricted by machine difference.

Further, since the projection lens has an image field curvature and an image distortion peculiar to each projection lens due to an assembly error at the time of assembling the projection lens, an optimum focal plane and an alignment offset amount are set by each exposure apparatus. Is different. Therefore, in order to automate the exposure process, there is a problem that only an exposure apparatus equipped with a projection lens having almost the same features (characteristics) can be used.

The present invention has been made in view of the above problems of the prior art.
An object of the present invention is to provide a photomask for an exposure apparatus capable of suppressing field curvature and image distortion on the image forming plane of the projection lens of the reduction projection exposure apparatus and absorbing machine differences between the exposure apparatuses.

[0013]

In order to achieve the above object, the photomask for an exposure apparatus of the present invention transfers a pattern to the sample by irradiating the sample through a projection optical system of a semiconductor exposure apparatus. In the photomask for the exposure apparatus, the shape and pattern of the photomask are preliminarily distorted so that the field curvature and the image distortion in the image forming plane of the pattern are canceled and the image is formed in an ideal lattice pattern. It has a structure that is not formed.

A distortion correcting substrate formed by distorting the photomask whose shape and pattern are distorted so as to be able to correct the field curvature and the image distortion and an ideal lattice pattern. It is preferable that the photomask is drawn and is in close contact with the distortion correction substrate.

On the other hand, the pattern drawing apparatus for a photomask for an exposure apparatus of the present invention determines the drawing coordinates by sending the mask design value database which stores the design data of the pattern to be drawn and the pattern data from the mask design value database. In a pattern drawing apparatus including a drawing coordinate calculation unit, a drawing method control unit that controls the determined drawing coordinates, and a reticle drawing device that draws the controlled drawing coordinates on a photomask, (i) the photomask is The exposure apparatus image distortion database for sending the image distortion data of the exposure apparatus used to the drawing coordinate calculation unit, and (ii) the pattern shape by the image distortion data and the pattern data from the mask design value database. Distortion correction pattern drawing seat distorted so that image distortion is canceled on the wafer and imaged in conformity with an ideal lattice. , A drawing coordinate calculation unit for determining a is obtained by the configuration in which the.

A photomask pattern drawing apparatus for an exposure apparatus according to another aspect of the present invention includes a mask design value database that stores design data of a pattern to be drawn, and pattern data sent from the mask design value database to set drawing coordinates. A pattern drawing apparatus comprising: a drawing coordinate calculation unit that determines the drawing coordinates; a drawing method control unit that controls the determined drawing coordinates; and a reticle drawing device that draws the controlled drawing coordinates on a photomask. An exposure apparatus image distortion database that sends image distortion data of an exposure apparatus in which a mask is used to the drawing coordinate calculation unit, and (ii) a pattern shape based on the image distortion data and the pattern data from the mask design value database. The distortion correction pattern is drawn so that the image distortion is canceled on the wafer to form an image in conformity with an ideal lattice. A drawing coordinate calculation unit for determining the coordinates,
(Iii) A configuration in which the surface shape of the photomask is provided with a photomask processing section that performs processing with a thickness distribution so that the curvature of field on the wafer is canceled and the curvature of the wafer matches the ideal lattice shape. Is.

Then, the photomask processing section receives the process step design database for storing the design value data of the process step, the design value data of the process step and the field curvature data of the exposure apparatus, and the photomask processing section From a mask surface processing shape calculation unit that determines the surface processing shape, a processing control unit that controls the determined surface processing shape of the photomask, and a mask shape processing apparatus that processes the surface of the photomask based on the control. It is preferable to have the following structure.

[0018]

With the above structure, the field curvature and the image distortion in the image forming plane of the projection lens of the exposure apparatus are corrected, and even if the semiconductor element, wiring, etc. are miniaturized, the periphery of the exposure area caused by the field curvature is corrected. The defocus of the part is eliminated, and the resolution can be increased and the transfer accuracy can be improved. And at the same time,
It is possible to absorb the machine difference between the exposure apparatuses, and it is possible to eliminate the restriction of using a specific exposure apparatus due to image distortion.

On the other hand, the shape and pattern of the photomask are calculated by calculating the back projection image of the wafer onto the reticle by the projection lens when an ideal lattice-shaped and planar image exists on the wafer. The reticle is processed with the thickness distribution of the reticle based on the values, and the reticle is processed and formed by correcting the field curvature and image distortion peculiar to the projection lens by drawing with the pattern shape distorted. be able to.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various photomasks according to the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a photomask for an exposure apparatus for image distortion correction, FIG. 1A is a plan view, and FIG.
(B) is a bb sectional view of FIG. FIG. 2 is a modification of FIG. 1 in consideration of the step shape on the wafer.
2A is a plan view, and FIG. 2B is a sectional view taken along the line bb of FIG. FIG. 3 is a diagram showing an example of a reticle in which a correction function for image distortion and field curvature is separated from a photomask, and the correction function is provided on the upper surface of the photomask. FIG. 4 is a modification example of FIG. FIG. 5 is a diagram showing an example of a reticle provided on the lower surface of a mask, and FIG. 5 is a diagram showing an example of a reticle in which a distortion correction substrate is brought into close contact with the lower surface of a photomask and a pellicle film is put on the upper surface of the photomask.

FIG. 1 is a diagram showing the basic structure of a photomask for an exposure apparatus of the present invention. As shown in FIG. 1B, the distortion-correcting photomask 1 is composed of a photomask substrate 2 made of, for example, transparent synthetic quartz, and a metal pattern 3 made of, for example, Cr, drawn on the surface thereof. Has been done. The portion where the metal pattern 3 is drawn forms a light-shielding area, and the portion where the metal pattern 3 is not drawn forms a non-light-shielding transparent area.

When the metal pattern 3 is drawn by the reticle drawing device, the image distortion of the projection lens using the photomask 1 is offset on the wafer so as to be offset depending on the position as shown in FIG. 1 (a). Is drawn in. Eg 4
Is a pattern shape (hereinafter referred to as a distortion correction pattern) that is drawn so that the image distortion peculiar to the projection lens is canceled on the wafer, and the image distortion generated when assembling each projection lens in the exposure apparatus is on the wafer. The pattern is drawn so as to be offset by. On the other hand, the surface shape of the photomask substrate 2 is processed into an aspherical surface so that the field curvature peculiar to the projection lens and the field curvature generated at the time of assembling each projection lens are offset on the wafer.

The image distortion of the projection lens is usually obtained by dividing the projection area into several grids and calculating from the difference between the ideal grid point at each grid point and the grid point actually projected by the projection lens. The field curvature is obtained by changing the focus and measuring the focus position of each lattice point.

In order to manufacture the photomask 1 shown in FIG. 1, first, as an example, the surface shape of a transparent synthetic quartz glass substrate is subjected to the above calculation and measurement so that the field curvature is canceled on the wafer. The shape of the value obtained in advance, that is, Z
The shape is processed so that the directional distortion remains only as a planar image distortion. Here, the field curvature is about 0.4 μm at maximum,
Converting this into a change in the height shape of the photomask 1, if the magnification of the projection lens is 5 times, it corresponds to about 10 μm. The processing accuracy of the surface shape of the synthetic quartz glass substrate is 1 μm
Since it is below, it is converted to 0.04μ on the wafer.
m, and sufficient correction accuracy can be obtained.

The photomask 1 processed in this way
On the other hand, after depositing a metal film of Cr or the like by a sputtering apparatus or the like, a resist film is applied on the metal film. Then, the reticle drawing device draws the distortion correction pattern 4 in the pattern shape shown in FIG. 1A which is obtained in advance by the calculation and measurement so that the image distortion is canceled on the wafer. Here, the maximum image distortion is about 0.1 μm, which is 0.5 μm when converted on the photomask 1. Since the drawing accuracy of the reticle drawing apparatus is 0.1 μm, sufficient correction accuracy can be obtained. After the distortion correction pattern 4 is transferred by the reticle drawing device, the metal film is patterned by using the pattern transferred to the resist as a mask to form the metal pattern 3, and the photomask 1 is manufactured.

FIG. 2 is a diagram showing a modification of FIG. 1 in consideration of the height of the product (chip) on the wafer. In an actual wafer, a step is generated in the chip as the process goes through, and the step reaches a maximum of about 1 μm. Therefore, if a fine pattern exists on both steps, the margin for focusing on both patterns is extremely large. Becomes smaller. Therefore, it is possible to increase the focus margin and prevent defocusing by processing the surface shape of the photomask 1b as shown in FIG. 2B in consideration of such a step. .

FIG. 3 shows an example in which the function of correcting the image distortion and field curvature in the first embodiment shown in FIG. 1 and the photomask are separated, and the correction function is provided on the upper surface of the photomask 1 '. . The substrate 5 for correcting distortion of image distortion and field curvature and the photomask 1'on which a pattern as designed is drawn are closely attached by vacuum suction. Reference numeral 5a is a distortion correction surface.
According to this configuration, one such distortion correction substrate 5 may be prepared for each exposure apparatus, and the photomask 1'can be used for each exposure apparatus.

FIG. 4 shows a photomask 1'having the above correction function.
It is an example of putting it on the lower surface of. According to this configuration, the photomask 1'can be held on a flat surface, so that the holding method becomes easy.

FIG. 5 shows an example in which the distortion correction substrate 5 is adhered to the lower surface of the photomask and the pellicle film 17 is attached to the upper surface of the photomask. Reference numeral 18 is a reticle stocker, 19 is a space, and 20 is a reticle having a conventional configuration. According to this structure, foreign matter attached to the upper surface of the photomask is removed from the pellicle film 17
Can be prevented by.

FIG. 6 shows that the above-mentioned correction function is built in the exposure apparatus,
It is an example when it is brought close to the photomask. Since the correction function is built in the exposure apparatus, the photomask can be shared by each exposure apparatus. In the figure, the same reference numerals as those in FIG. 3 or FIG. 5 indicate the same functions. 21 is a wafer, A
Indicates an exposure area. By using this device, distortion peculiar to the projection lens is corrected, and it becomes possible to suppress defocus due to field curvature and limitation of the device used due to image distortion.

FIG. 7 is a block diagram showing the structure of a pattern drawing apparatus for drawing the distortion correction pattern 4 of the photomask 1 shown in FIG. When the photomask to be drawn is carried into the drawing apparatus, first, the image distortion data of the exposure apparatus using this photomask is sent from the image distortion database 6 to the drawing coordinate calculation unit 7. The image distortion database 6 is preliminarily measured and the characteristic data of various exposure apparatuses are input so that the field curvature and the image distortion can be understood. On the other hand, ideal design data of the pattern to be drawn is sent from the mask design value database 8 to the drawing coordinate calculation unit 7, and the drawing coordinates of the distortion correction pattern 4 are determined from these data. The drawing coordinates determined here are controlled by the drawing method controller 9 and drawn on the photomask by the reticle drawing device 10.

FIG. 8 is a block diagram showing the structure of a pattern drawing apparatus in consideration of the step shape on the wafer. The pattern drawing apparatus shown in FIG. 7 is provided with a photomask processing section 11 to 14. is there.

In FIG. 8, when the photomask to be drawn is loaded into the drawing apparatus, first, the data of the field curvature of the exposure apparatus using this photomask and the data of the design value of the process step are provided in the exposure apparatus image distortion database 6 Then, it is sent from the process step design database 11 to the photomask surface processing shape calculation unit 12, and the surface processing shape of the photomask is determined. The surface shape determined here is the processing control unit 13
And is processed into a desired shape by the photomask shape processing device 14. When this processed photomask is carried into the reticle drawing apparatus 10, image distortion data of the exposure apparatus using this photomask is sent from the image distortion database 6 to the drawing coordinate calculation unit 7. Ideal design data of the pattern to be drawn is also sent from the mask design value database 8 to the drawing coordinate calculation unit 7, and the drawing coordinates of the distortion correction pattern 4 are determined from these data. The drawing coordinates determined here are controlled by the drawing method controller 9 and drawn on the photomask by the reticle drawing device 10.

[0034]

As described above, according to the present invention,
In addition to suppressing the field curvature and image distortion on the image plane of the projection lens of the reduction projection exposure system to enable transfer exposure as designed, it also increases the process margin and absorbs machine differences between exposure systems. Thus, it is possible to eliminate the restriction of using a specific exposure apparatus when automating the exposure process.

[Brief description of drawings]

FIG. 1 is a diagram showing a photomask for an exposure apparatus for image distortion correction.

FIG. 2 is a modified example of FIG. 1 in consideration of a step shape on a wafer.

FIG. 3 is a diagram showing an example of a reticle in which a correction function for image distortion and a curvature of field and a photomask are separated, and the correction function is provided on the upper surface of the photomask.

FIG. 4 is a diagram showing an example of a reticle provided with a correction function on the lower surface of a photomask in the modification of FIG. 3;

FIG. 5 is a diagram showing an example of a reticle in which a distortion correction substrate is brought into close contact with a lower surface of a photomask and a pellicle film is provided on the upper surface of the photomask.

FIG. 6 shows an example in which a correction function is incorporated in an exposure apparatus and brought close to the photomask according to the present invention.

7 is a block diagram of a pattern drawing device that draws the distortion correction pattern shown in FIG. 1. FIG.

FIG. 8 is a block diagram of a pattern drawing apparatus in consideration of a step shape on a wafer.

FIG. 9 is a block diagram showing an automation line of an exposure process.

[Explanation of symbols]

1 ... Photomask for distortion correction, 2 ... Photomask substrate,
3 ... Metal pattern, 4 ... Distortion correction pattern, 5 ... Distortion correction substrate, 6 ... Exposure device image distortion database, 7 ... Drawing coordinate calculation unit, 8 ... Mask design value database, 9 ... Drawing method control unit, 10 ... Reticle Drawing device, 11 ... Process step design database, 12 ... Mask surface processing shape calculation unit, 1
3 ... Processing control unit, 14 ... Mask shape processing device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitada Oshida 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Kanagawa Manufacturing Technology Research Institute

Claims (5)

[Claims] 1. A photomask for an exposure apparatus, wherein a pattern is transferred to the sample by irradiating the sample through a projection optical system of a semiconductor exposure apparatus, wherein the shape and pattern of the photomask is a combination of the patterns. A photomask for an exposure apparatus, which is preliminarily distorted so that an image curvature and an image distortion in an image plane are canceled and an image is formed in conformity with an ideal lattice shape. 2. A distortion-correcting substrate formed by a photomask whose shape and pattern are distorted so that the field curvature and the image distortion are offset and can be corrected, and an ideal lattice pattern. 2. The photomask for an exposure apparatus according to claim 1, wherein the photomask is drawn and is in close contact with the distortion correction substrate. 3. A mask design value database that stores design data of a pattern to be drawn, a drawing coordinate calculation unit that sends pattern data from the mask design value database to determine drawing coordinates, and controls the determined drawing coordinates. A photomask pattern drawing apparatus for an exposure apparatus, comprising: a drawing method control unit; and a reticle drawing apparatus for drawing controlled drawing coordinates on a photomask, wherein (i) image distortion of the exposure apparatus using the photomask. The image distortion of the exposure apparatus is sent to the drawing coordinate calculation unit by the exposure apparatus image distortion database, and (ii) the image distortion data and the pattern data from the mask design value database cancels the image distortion of the pattern shape on the wafer. And a drawing coordinate calculation unit that determines the drawing coordinates of the distortion correction pattern that is distorted so as to form an image in conformity with an ideal grid. Pattern writing apparatus of an exposure apparatus for photomask, characterized in that the. 4. A mask design value database that stores design data of a pattern to be drawn, a drawing coordinate calculation unit that sends pattern data from the mask design value database to determine drawing coordinates, and controls the determined drawing coordinates. A photomask pattern drawing apparatus for an exposure apparatus, comprising: a drawing method control unit; and a reticle drawing apparatus for drawing controlled drawing coordinates on a photomask, wherein (i) image distortion of the exposure apparatus using the photomask. The image distortion of the exposure apparatus is sent to the drawing coordinate calculation unit by the exposure apparatus image distortion database, and (ii) the image distortion data and the pattern data from the mask design value database cancels the image distortion of the pattern shape on the wafer. And a drawing coordinate calculation unit that determines drawing coordinates of the distortion correction pattern that is distorted so as to form an image in conformity with an ideal lattice. The surface shape of the photomask, and the photomask processing unit for performing processing having a thickness distribution such curvature coincides are offset to the ideal grid pattern on the wafer,
A pattern drawing apparatus for a photomask for an exposure apparatus, comprising: 5. The photomask processing unit receives a process step design database that stores process step design value data, a process step design value data, and a field curvature data of an exposure apparatus, and a photomask of the photomask is received. From a mask surface processing shape calculation unit that determines the surface processing shape, a processing control unit that controls the determined surface processing shape of the photomask, and a mask shape processing apparatus that processes the surface of the photomask based on the control. The pattern drawing apparatus for a photomask for an exposure apparatus according to claim 4.