JP2004335512A - Method for exposure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for exposure by which the nonlinear strain of a mask can be corrected highly accurately at the time of mounting an exposure device. <P>SOLUTION: In the method for exposure, the positional data of a sub-field (SF) are obtained by measuring the position of the whole surface of the mask 10 by setting the mask 10 in an attitude inverted from the attitude of the mask 10 in the exposure system, by means of an inspecting device which is different from the exposure system (S2). Then, after the elastic deformation of the mask 10 caused by the gravity at the time of inverting the mask 10 is calculated (S3), the elastic deformation is subtracted from the positional data of the SF (S4) and the positional data are inverted (S5). In addition, the absorptivity of a chuck and the elastic deformation of the mask 10 caused by the gravity when the mask 10 is loaded in the exposure system are calculated by simulation (S6) and the calculated results are added to the previous positional data of the SF (S7). Based on the positional data of the SF thus obtained, exposure is performed while the position of the mask 10 is corrected (S8). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exposure method used for lithography of a semiconductor integrated circuit or the like. In particular, the present invention relates to an exposure method capable of correcting mask distortion with high accuracy.
[0002]
[Prior art]
In a lithography process for a semiconductor integrated circuit or the like, a pattern formed on a mask (including a reticle) is exposed and transferred onto a wafer using an exposure apparatus. At the time of this exposure, if there is a defect or distortion in the pattern on the mask, the accuracy (exposure accuracy) of the position and shape of the pattern transferred by exposure is reduced.
[0003]
The causes of these defects and distortions include those generated during the manufacture of the mask, those caused by its own weight (gravity), and those caused by the film stress of the mask. Further, distortion due to the holding force of the chuck (mask holder) in the exposure apparatus also occurs.
[0004]
As a method of inspecting and correcting the mask distortion as described above, a position measuring mark is provided on a beam portion of a mask (see reference numeral 45 in FIG. 6), and an inspection device such as a coordinate measuring device different from the exposure device There is a method in which the mark position is measured to obtain position data, and the data is used to correct the pattern transfer position during exposure. Alternatively, there is a method of measuring and correcting the mark position in the exposure apparatus. Patent Literature 1 proposes a method in which linear distortion is measured in an exposure apparatus, non-linear distortion is measured in an inspection apparatus, and both are superimposed to estimate position data of a mask in the exposure apparatus.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-319533
[Problems to be solved by the invention]
However, even with the above-described method, if the nonlinear distortion due to the chuck when mounting the mask in the exposure apparatus is large, exposure accuracy may be difficult to secure.
In view of the above, it is an object of the present invention to provide an exposure method capable of correcting non-linear distortion of a mask when mounted on an exposure apparatus with high accuracy.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, an exposure method according to the present invention divides a device pattern to be transferred onto a sensitive substrate into small regions (subfields) and forms the device pattern on a mask. Having a pattern surface formed thereon, a support layer for mechanically supporting the pattern surface, and a holding portion provided around the support layer. The device pattern is illuminated with a line, and the energy ray passing through the sub-field is projected and imaged at an appropriate position on the sensitive substrate, and the image of the pattern of each sub-field is joined on the sensitive substrate to thereby form the device pattern. In the exposure method for transferring the whole, a) using the inspection device different from the exposure device, using the inspection device different from the exposure device, The subfield position data is obtained by measuring the positions of all the subfields on the screen, and b) the change in the position of the subfield due to elastic deformation due to gravity in the inspection device is calculated. C) The position data obtained in a) , The position change data calculated in b is subtracted, d) the position data obtained in c is turned upside down, and e) the chucking force when the mask is mounted in the exposure apparatus and the elastic deformation caused by gravity. F) calculating the position data of all subfields on the mask in the exposure apparatus by adding the position change data calculated in e to the position data inverted upside down in d); g) The exposure is performed while correcting the position error of each subfield on the mask based on the position data obtained in f.
[0008]
According to the exposure method of the present invention, it is not necessary to measure the position of the mask in the exposure apparatus (or the number of measurement points can be reduced), so that the time for exchanging the mask can be shortened. Nevertheless, since exposure correction can be performed in consideration of the deformation state of the mask in the exposure apparatus, accurate pattern transfer can be performed.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described in detail with reference to the drawings.
First, an outline of an electron beam exposure method which is one of the exposure methods for a semiconductor device or the like will be described.
FIG. 5 is a schematic diagram showing an image forming relationship in the entire optical system of the electron beam exposure apparatus of the division transfer system.
An electron gun 1 is arranged at the uppermost stream (upper in FIG. 5) of the optical system. The electron gun 1 emits an electron beam downward in the figure. Below the electron gun 1, two condenser lenses 2, 3 are provided. The electron beam is converged by these condenser lenses 2 and 3, and crossed over the blanking aperture 7 by the C.V. O. Is imaged.
[0010]
Below the condenser lens 3, an illumination beam shaping aperture 4 is arranged. The image of the opening 4 is formed on the mask 10 by the lens 9.
[0011]
Below the illumination beam shaping aperture 4, a blanking deflector 5 is arranged. The deflector 5 deflects the illumination beam as needed and hits the non-opening of the blanking opening 7 so that the beam does not hit the mask 10.
[0012]
An illumination beam deflector 8 is arranged below the blanking opening 7. The deflector 8 sequentially scans the illumination beam in the X-axis direction to illuminate each subfield of the mask 10 within the field of view of the optical system. At this time, scanning of the illumination beam is performed while performing position correction based on SF position data calculated in advance (the procedure for calculating SF position data will be described later).
An illumination lens 9 is arranged below the deflector 8. The illumination lens 9 images the illumination beam shaping aperture 4 on the mask 10.
[0013]
The mask 10 extends in a plane (XY plane) perpendicular to the optical axis, and has a number of subfields (see FIG. 6; details will be described later). On the mask 10, a device pattern forming one semiconductor chip as a whole is formed. Note that the device pattern forming one chip may be divided and formed on a plurality of masks.
The mask 10 is mounted on a movable mask stage 11. By moving the mask stage 11 in the X and Y directions, each subfield on the mask 10 that spreads more widely than the field of view of the illumination optical system can be obtained. Can be illuminated. The mask stage 11 is provided with a position detector (interferometer) 12 so that the position of the mask stage 11 can be accurately grasped.
[0014]
Below the mask 10, projection lenses 15, 19 and a deflector 16 are provided. The electron beam passing through one subfield of the mask 10 is imaged at a desired position on the wafer 23 by the projection lenses 15 and 19 and the deflector 16.
[0015]
An appropriate resist is applied on the wafer 23. The resist is given a dose of an electron beam, and the device pattern on the mask 10 is reduced and transferred.
[0016]
A crossover C.C. is located at a position where the mask 10 and the wafer 23 are internally divided at a reduction ratio. O. Is formed, and a contrast opening 18 is provided at this position. The opening 18 blocks the electron beam scattered by the non-pattern portion of the mask 10 from reaching the wafer 23. At this time, most scattered electron beams can be blocked, but a small amount of scattered electron beams reach the wafer 23 without being completely blocked.
[0017]
The wafer 23 is placed on a wafer stage 24 that can move in the X-axis and Y-axis directions via an electrostatic chuck (not shown). By synchronously moving the mask stage 11 and the wafer stage 24 in directions opposite to each other, a device pattern extending beyond the field of view of the optical system can be sequentially exposed and transferred. It should be noted that a position detector 25 is attached to the wafer stage 24 as well as the mask stage 11 described above.
[0018]
Above the wafer 23, a backscattered electron detector 22 is arranged. The reflected electron detector 22 detects the amount of electrons reflected on the exposure surface of the wafer 23 and the mark on the wafer stage 24. For example, by scanning a mark on the wafer 23 with a beam that has passed through a mark pattern on the mask 10 and detecting electrons reflected by the mark, the relative positional relationship between the mask 10 and the wafer 23 can be known.
[0019]
The lenses 2, 3, 9, 15, 19 and the deflectors 5, 8, 16 are respectively connected to the corresponding coil power supply control units 2a, 3a, 9a, 15a, 19a and 5a, 8a, 16a. , And is controlled by the controller 31. The mask stage 11 and the wafer stage 24 are also controlled by the controller 31 via the corresponding stage controllers 11a and 24a.
[0020]
The stage position detectors 12 and 25 send signals to the controller 31 via interfaces 12a and 25a including an amplifier and an A / D converter. Similarly, the backscattered electron detector 22 sends a signal to the controller 31 via the interface 22a.
[0021]
The controller 31 grasps the positioning error of the stage, and corrects the error by the image position adjusting deflector 16. Thus, the reduced image of the subfield on the mask 10 is accurately transferred to the target position on the wafer 23. Then, the images of the respective subfields are joined on the wafer 23, and the entire device pattern on the mask 10 is transferred onto the wafer.
[0022]
Hereinafter, the mask 10 will be described.
FIG. 6 is a diagram schematically illustrating an example of a mask used in electron beam exposure. 6A is an overall plan view, FIG. 6B is a partial perspective view, and FIG. 6C is a plan view of one small membrane region. Such a mask can be manufactured, for example, by drawing on a silicon wafer using an electron beam and then performing etching.
[0023]
The device pattern is divided and arranged on the mask 10 shown in FIG. Many squares 41 shown in FIG. 6A are small membrane areas each including a device pattern corresponding to one subfield. The small membrane region 41 has a thickness of, for example, 0.1 μm to several μm.
[0024]
As shown in FIG. 6C, the small membrane region 41 includes a central subfield 42 and a skirt 43 surrounding the subfield 42 in a frame shape.
The subfield 42 is, for example, a square having a side of 0.5 to 5 mm. Assuming that the reduction ratio at the time of projection is 1/5, the image of the subfield 42 projected on the wafer 23 is a square having one side of 0.1 to 1 mm.
As a form of forming such a subfield pattern, a scattering stencil type in which holes are formed in a scattering membrane through which an electron beam is scattered and transmitted, and a pattern layer made of a high scatterer that scatters an electron beam well. Is a continuous membrane type in which is formed on a very thin membrane as an electron permeable material.
In this example, the pattern surface is a membrane surface on which a pattern is formed.
[0025]
The skirt 43 is a frame-shaped portion (width is 0.05 mm in one example) on which no pattern is formed, and hits the edge of the illumination beam.
[0026]
The grid-like portion (support layer) around the small membrane region 41 in FIGS. The grenage 45 is a beam (0.5 to 1 mm in thickness and 0.1 mm in width in one example) for maintaining the mechanical strength of the mask 10.
[0027]
As shown in FIG. 6A, a large number of small membrane regions 41 are arranged side by side in the X-axis direction in FIG. 6 to form one group (electrical stripe 44), and a large number of electrical stripes 44 are arranged in the Y-axis direction in FIG. One mechanical stripe 49 is formed side by side.
The length of the electrical stripe 44 (the width 49 of the mechanical stripe) is limited by the width of the field of view that can be covered by the deflection of the optical system.
In addition, a method in which a non-pattern area such as a skirt or a grey-age is not provided between adjacent subfields in one electrical stripe 44 is being studied.
[0028]
A plurality of mechanical stripes 49 are arranged in the X-axis direction in FIG. The strut 47 is located between the adjacent mechanical stripes 49. The strut 47 is a beam that is slightly thicker than the grenage 45, and reduces the deflection of the mask 10. The strut 47 and the grenage 45 are integrated.
[0029]
In the exposure of the mask 10, the electron beam is deflected in the X-axis direction in FIG. 6 to sequentially expose the columns of the subfield 41 of the electrical stripe 44. On the other hand, in the Y-axis direction in FIG. 6, exposure is sequentially performed by continuous stage scanning.
[0030]
Next, an embodiment of the exposure method of the present invention will be described.
FIG. 1 is a flowchart for explaining an exposure method according to the first embodiment of the present invention.
In the present embodiment, first, a mask serving as a pattern master of a device to be manufactured is manufactured (S1).
Next, the mask is held in a mask inspection device different from the exposure device in a posture inverted upside down from the posture in the exposure device, and the positions of all subfields on the mask are measured to determine the subfield (SF). ) Position data is obtained (S2).
FIG. 2A is a diagram schematically illustrating the posture of the mask in the inspection apparatus, and FIG. 2B is a diagram schematically illustrating the posture of the mask in the exposure apparatus.
2A and 2B, the direction of gravity is downward in the figure. As shown in FIG. 2A, the mask 10 is placed on the holder 111 in the inspection apparatus with the upper surface 101 in the exposure apparatus facing downward in the direction of gravity. Here, the holders 111 are provided at a plurality of positions (three positions in one example) and stably support the mask 10.
In S2, the position of the entire surface of the observation surface 102 (the upper surface in FIG. 2A) of the mask 10 is measured, and position data (SF position data) is obtained.
[0031]
Then, the position change of the subfield due to the elastic deformation of the mask 10 due to gravity in the inverted posture of S2 is calculated (S3), and the calculation result of S3 is subtracted from the SF position data obtained in S2 (S4).
The SF position data obtained in S4 is inverted upside down (S5).
Further, the elastic deformation of the mask 10 due to the chucking force and gravity when the mask 10 is mounted in the exposure apparatus is calculated (S6), and added to the SF position data obtained in S5 (S7).
In the above calculations of S3 and S6, the elastic deformation caused by the chucking force and gravity is analyzed by using a three-dimensional CAD simulation based on the finite element method.
FIG. 3 is an example of an analysis model of position data of a mask and a holder. FIG. 3A is a diagram illustrating an example of analysis of mask position data, and FIG. 3B is a diagram illustrating position data of a mask holder (chuck).
In FIG. 3, the attracted portion 334 a of the mask 331 is attracted to the attracting portion 334 b of the chuck 333, and the contact portion 335 a of the mask 331 contacts the contact portion 335 b of the chuck 333. Reference numeral 332 corresponds to the pattern surface of the mask 331.
In the calculation of S3 and S5, the elastic deformation of the mask is calculated in consideration of the load applied to the mask due to the chucking force and gravity and the chuck shape data 333 (FIG. 3B) acquired in advance. I do.
Finally, exposure is performed while correcting the position error of each subfield on the mask 10 based on the SF position data obtained in S7 (S8).
[0032]
According to the present embodiment, by predicting the elastic deformation of the mask by simulation, highly accurate exposure position control can be performed without measuring subfield position data in the exposure apparatus.
[0033]
FIG. 4 is a flowchart for explaining an exposure method according to the second embodiment of the present invention.
In the present embodiment, first, a mask to be a pattern master of a device to be manufactured is manufactured (S1 ′).
Next, in a mask inspection apparatus different from the exposure apparatus, the mask is held in a posture inverted upside down from the posture in the exposure apparatus, and comes into contact with the mask chuck of the observation surface 102 of the mask in the Z direction. The position of only the portion (104 in FIG. 2) is measured to obtain subfield (SF) position data (S2 ').
[0034]
Then, the position change of the subfield due to the elastic deformation of the mask 10 due to the gravity in the inverted posture of S2 'is calculated (S3'), and subtracted from the SF position data obtained in S2 '(S4').
The SF position data obtained in S4 'is inverted upside down (S5').
Further, the elastic deformation of the mask 10 caused by the chucking force and the gravity when the mask 10 is mounted in the exposure apparatus is calculated (S6 '), and this calculation result is added to the SF position data obtained in S5' (S7). ').
Based on the SF position data obtained in S7 ', the position of the portion not in contact with the chuck is calculated, and the SF position data of the entire surface of the mask is calculated (S7 ").
In the calculation of S3 ′, S6 ′, and S7 ″, similarly to the above-described first embodiment, the elastic deformation due to the chucking force and gravity is calculated using the three-dimensional CAD simulation by the finite element method.
Finally, exposure is performed while correcting the position error of each subfield on the mask 10 based on the SF position data obtained in S7 '(S8').
[0035]
According to the present embodiment, the number of position measurement points on the mask can be reduced, so that the cost for measurement and calculation can be reduced.
[0036]
【The invention's effect】
As described above, according to the present invention, by estimating the elastic deformation of a mask by simulation, highly accurate exposure position correction can be performed without measuring subfield position data during exposure.
[Brief description of the drawings]
FIG. 1 is a flowchart for explaining an exposure method according to a first embodiment of the present invention.
FIG. 2A is a view schematically showing a posture of a mask in an inspection apparatus.
FIG. 4B is a diagram schematically illustrating the attitude of the mask in the exposure apparatus.
FIG. 3 is an example of an analysis model of position data of a mask and a holder.
(A) is a figure showing an example of analysis of mask position data.
FIG. 3B is a diagram showing position data of a mask holder (chuck).
FIG. 4 is a flowchart illustrating an exposure method according to a second embodiment of the present invention.
FIG. 5 is a schematic diagram showing an image forming relationship in the entire optical system of the electron beam exposure apparatus of the division transfer system.
FIG. 6 is a diagram schematically illustrating an example of a mask used in electron beam exposure.
(A) is an overall plan view.
(B) It is a partial perspective view.
(C) It is a top view of one small membrane area.
[Explanation of symbols]
Reference Signs List 1 electron gun 2, 3 condenser lens 4 illumination beam shaping aperture 5 blanking deflector 7 blanking aperture 8 illumination beam deflector 9 illumination lens 10 mask 11 mask stage (chuck)
12, 25 Position detector 15, 19 Projection lens 16 Deflector 18 Contrast aperture 22 Backscattered electron detector 23 Wafer 24 Wafer stage 2a, 3a, 5a, 8a, 9a, 15a, 16a, 19a Coil power supply controller 31 Controller 42 Sub Field 41 Small membrane area 43 Skirt 44 Electrical stripe 45 Grating 47 Strut 49 Mechanical stripe 50 Holder 101 Upper surface of mask in exposure apparatus 102 Upper surface of mask in inspection apparatus (observation plane)
103 Pattern portion 104 Surface 111 of mask in contact with chuck 111 Mask holder 331 of inspection device Chuck distortion analysis data of mask 332 Pattern portion 333 of chuck distortion analysis data of mask Pattern data 334a of chucked portion 334b of mask Suctioned portion 335a of chuck Contact part 335b of mask Contact part of chuck

Claims (1)

A device pattern to be transferred onto a sensitive substrate is divided into small regions (subfields) and formed on a mask, wherein the mask mechanically divides the pattern surface on which the pattern is formed and the pattern surface. A support layer to support, and a holding portion provided around the support layer,
Illuminating the mask with energy rays for each subfield,
Projecting and forming an energy ray passing through the subfield at an appropriate position on the sensitive substrate,
On the sensitive substrate, an exposure method for transferring the entire device pattern by joining images of patterns of each subfield,
a) measuring the positions of all the sub-fields on the mask by using an inspection device different from the exposure device and in a posture inverted in the direction of gravity with respect to that in the exposure device to obtain sub-field position data; Get it,
b) calculating a change in position of the subfield due to elastic deformation due to gravity in the inspection device;
c) Subtract the position change data calculated in b from the position data obtained in a,
d) The position data obtained in c is inverted upside down,
e) calculating a change in position of the subfield due to elastic deformation caused by chucking force and gravity when the mask is mounted in the exposure apparatus;
f) adding the position change data calculated in e to the position data inverted upside down in d to calculate position data of all subfields on the mask in the exposure apparatus;
g) An exposure method, wherein the exposure is performed while correcting the position error of each subfield on the mask based on the position data obtained in f.

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