JPH09246153A - Forming method for electron beam image drawing data - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct irradiation quantities with high precision without increasing the number of specified irradiation quantity values. SOLUTION: On the occasion of forming a table of irradiation quantities, the frequency of obtaining the computed irradiation quantity value is examined. By using the distribution of these irradiation quantity values, assignment of a specified irradiation quantity value and an irradiation quantity value corresponding to the specified value is increased for a densely distributed irradiation quantity region, and is reduced for a coarsely distributed irradiation quantity region. Here, four of 84, 123, 147, 447% exist as computed appropriate irradiation quantities, so these are assigned to specified irradiation quantity values 0, 1, 2, 3 respectively. In this case, four specified irradiation quantity values become only necessary, and it becomes possible to perform precise irradiation quantity setting by the use of restricted specified irradiation quantity values for a wide range of irradiation quantities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to creation of electron beam drawing data to be given to an electron beam exposure apparatus, and more particularly to a method of creating electron beam drawing data for realizing highly accurate proximity effect correction.

[0002]

2. Description of the Related Art In recent years, high dimensional accuracy is required for pattern drawing of a super-resolution photomask or an equal-magnification projection type X-ray mask using an electron beam exposure apparatus. In particular, in order to realize the pattern dimensional accuracy required for the X-ray mask used in the X-ray exposure method of the same-magnification projection type, a high-precision proximity effect which has not been required in the photomasks up to now. Correction has become indispensable. The proximity effect is a phenomenon in which incident electrons or reflected electrons spread to areas other than the irradiation area due to scattering of incident electron beams in the resist, reflection from the underlying substrate, and scattering, causing an effective energy change due to electron beam irradiation. Is. The effective energy change due to the proximity effect is the deformation of the pattern formed after development. Therefore, it is necessary to correct the proximity effect in order to form a pattern having a desired shape.

As a method of correcting the proximity effect, an irradiation amount modulation method in which the irradiation amount of the electron beam is changed for each drawing pattern is generally used. The setting of the irradiation amount to which the proximity effect correction of the irradiation amount modulation method is applied is performed in the following procedure. First, the pattern to be exposed is divided into exposure units of a predetermined size, the degree of proximity effect is estimated for each exposure unit, and appropriate irradiation is performed for each exposure unit so that a desired pattern shape can be obtained based on this estimation. Determine the amount. An irradiation intensity distribution function is used to determine the irradiation amount for each exposure unit. This irradiation intensity distribution function is obtained by irradiating a certain point with an electron beam and determining the irradiation amount intensity at a point separated by an arbitrary distance r from this point as a function with respect to the distance r. In general, an irradiation intensity distribution function standardized so that the irradiation intensity at the time of uncorrection becomes 1 at the center point of the pattern sufficiently larger than the range affected by the proximity effect is used.

In the electron beam exposure apparatus, a reference irradiation amount is set as an irradiation amount set at the time of exposure, and a value corresponding to this reference irradiation amount (this is referred to as a temporary reference irradiation amount) is set. Then, the irradiation dose treated by the exposure data is a relative value based on the temporary reference irradiation dose,
The exposure device converts the irradiation amount in the exposure data into an actual irradiation amount (this is the actual irradiation amount) based on the above correspondence. Therefore, the irradiation dose handled below is a temporary irradiation dose that is a value indicating this actual irradiation dose, unlike the actual irradiation dose, but in the following, it will be simply described as the irradiation dose.

Next, after determining an appropriate dose for each exposure unit as described above, a dose table is created. The dose table is data in a tabular format that associates the designated dose value with the designated dose value. The dose table conventionally used is an arithmetic series dose table. The arithmetic series dose table is a dose designation value Rn, a reference dose designation value Rb that designates a reference dose, a reference dose Db, and a dose variation amount per dose designation value Dd. Is a dose table in which the dose D satisfies the relationship of the following equation between the dose D and the designated dose value Rn. D = Dd × (Rn−Rb) + Db (1)

FIG. 3 shows an example of a dose table. The irradiation amount in FIG. 3 is a relative irradiation amount (that is, D / Db, hereinafter referred to as relative irradiation amount) relative to the reference irradiation amount Db, which is described in percentage. To the exposure data, in addition to the information regarding the position coordinates and size (vertical and horizontal dimensions) of each exposure unit, information regarding the irradiation amount is added. That is, in the data conversion for converting CAD (Computer Aided Design) data into exposure data, the dose value closest to the appropriate dose calculated for each exposure unit is searched from the dose table, The corresponding designated dose value is stored in the exposure data as information about the dose.

In this way, the appropriate dose for each exposure unit is replaced with the dose designation value. In the actual exposure data, data corresponding to the irradiation amount table is stored separately from the irradiation amount designated value, and these are passed to the exposure device. Then, the exposure apparatus converts the designated dose value into the dose value using the dose table. When replacing the appropriate dose of each exposure unit with the dose specified value, the dose of each exposure unit is rounded to the nearest dose stored in the dose table, so the calculated appropriate dose and the actual dose There is an error between the dose and the applied dose.

Therefore, in order to carry out highly accurate proximity effect correction, it is necessary to make the dose variation Dd a small value to perform a fine dose modulation (in the example of FIG. It corresponds to reducing the increase / decrease in the relative irradiation dose with respect to 1 increase or 1 decrease). FIG. 4 shows an example of a dose table with a small dose variation. In the dose table of FIG. 3, the increase / decrease in the relative dose with respect to the increase / decrease of the designated dose value is set to 5%, but in FIG. 4 it is set to 1%.

By the way, the size of the dose table, that is, the total number of designated dose values in the table is limited by the data conversion program and the memory of the exposure apparatus (128 in FIGS. 3 and 4, 0 to 127). Therefore, the dose range, which is the difference between the minimum dose and the maximum dose, is 5 to 5 in FIG.
While 640% is set, if the dose variation is reduced as shown in FIG. 4, it is 5 to 132%, and the settable dose range is narrowed. However, when a minute pattern is irradiated with an electron beam, the amount of electron scattered around the electron beam is large, and thus it is generally necessary to increase the irradiation amount for a smaller pattern. Therefore, when drawing data in which a minute pattern and a large pattern are mixed is targeted, the range of the required irradiation amount becomes large, and the irradiation amount table with a small variation in the irradiation amount cannot be used for the entire range. .

In such a case, the maximum value or the minimum value of the designated dose amount is given to the exposure unit to which the dose that cannot be stored in the dose table should be given. For example, when the appropriate dose is calculated to be 145% in a certain exposure unit, this can be represented by the dose designation value 28 according to the dose table of FIG. 3, but according to the dose table of FIG. Then, the specified dose 127 is obtained. Since the irradiation amount represented by the irradiation amount designated value 127 is 132%, there is a large difference from the proper irradiation amount 145%.

[0011]

As described above, in the conventional dose table, the total number of dose designation values is limited due to the restrictions of the memory of the exposure apparatus or the data conversion program. If an attempt is made to perform, a dose that cannot be accurately represented by the designated dose will occur. Therefore, even if the maximum (or minimum) irradiation amount in the irradiation amount table is applied, an exposure unit in which the applied irradiation amount is too small (too large) is generated, and the irradiation amount cannot be corrected with high accuracy. was there. The present invention has been made in order to solve the above problems, and provides a method of creating electron beam drawing data capable of highly accurately performing dose correction without changing the total number of dose designation values. The purpose is to

[0012]

According to the present invention, when a dose table is created, the frequency of appearance of an appropriate dose determined for each exposure unit is checked, and a dose is designated in a dose region having a high frequency of appearance. The value and the assigned dose value corresponding to this designated value are increased, and the assigned dose amount and the assigned dose value corresponding to this designated value are assigned less in the dose region where the appearance frequency is low. is there. In this way, the dose designation value and the dose value corresponding to this designated value are assigned more to the dose region with high appearance frequency, and the assignment is reduced to the dose region with low frequency of appearance, which is calculated. An irradiation amount equal to the appropriate irradiation amount can be stored in the irradiation amount table, and this can be designated by the corresponding irradiation amount designation value, so that accurate irradiation amount setting can be performed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an electron beam drawing data creating method of the present invention will be described with reference to the drawings. FIG. 1 shows the first embodiment of the present invention.
It is a figure which shows the irradiation amount table which becomes embodiment of this. In this embodiment, in order to verify the effect, 0.05
The pattern data in which two rectangles of 10 μm square and 100 μm square exist 100 μm apart, that is, data including both a small pattern and a large pattern at the same time will be described as an example.

As a result of dividing the pattern to be exposed into exposure units of a predetermined size and determining an appropriate irradiation amount for each exposure unit, a 0.05 μm square is not divided and 16 10 μm squares are obtained. Was divided into exposure units. 10 after division
FIG. 2 shows a rectangle of μm square. Since the deflector of the electron beam exposure apparatus has a limited area in which the electron beam can be deflected, it is usually necessary to place a sample (a resist-coated wafer) on a moving stage and move this stage. It is common. Therefore, the above division includes division due to the size of the electron beam deflection area in the exposure apparatus.

As a result of calculating an appropriate irradiation amount for each exposure unit, 447% (relative irradiation amount) of the reference irradiation amount was a proper irradiation amount in a 0.05 μm square pattern. Similarly, of the 16 exposure units in a 10 μm square, 84% of the reference dose in exposure unit 1 shown in FIG. 2, 123% in exposure unit 2, and 1 in exposure unit 3
47% was the proper dose.

Before describing the dose table of FIG. 1 according to the producing method of the present invention, the case of the dose table according to the conventional producing method will be described. In the case of the dose table of FIG. 3 in which the increment / decrement of the relative dose with respect to the increment or decrement of the designated dose value is set to 5%, the reference dose that specifies the reference dose (100% in relative dose) The designated amount is 19.

According to the dose table of FIG. 3, 0.05
The proper dose 447% of the square of μm square is replaced with the dose designation value 88 in the exposure data by the closest value 445% in the dose table, and the proper dose 84% of the exposure unit 1 is The closest value 85% in the dose table is replaced with the designated dose value 16. Similarly, the proper irradiation amount 123% of the exposure unit 2 is replaced with the designated irradiation amount value 24, and the proper irradiation amount 147% of the exposure unit 3 is replaced with the designated irradiation amount value 28.

Thus, the specified dose values 16, 24, 2
The numbers of exposure units set to 8 and 88 are 4 (exposure unit 1), 8 (exposure unit 2), 4 (exposure unit 3), and 1 respectively.
(Rectangle of 0.05 μm square). At this time, a dose setting error of 2% at maximum occurs between the dose indicated by the designated dose amount and the calculated proper dose (for example, the proper dose of exposure unit 3 is 147%. However, the irradiation amount indicated by the irradiation amount specified value 28 after conversion is 145%).

Next, in the case of the dose table of FIG. 4 in which the increment / decrement of the relative dose with respect to the dose increment or decrement of the dose designation value is set to 1%, the reference dose designation value is 95. According to the dose table of FIG. 4, the proper dose 447% of a rectangle of 0.05 μm square is replaced with the dose designation value 127 in the exposure data. The original designated dose value at this time should be 442, but since only 132% of the maximum dose is stored in the dose table, the dose can be specified by setting it to the closest value. The value is 127
Becomes

Further, the proper irradiation amount 84% of the exposure unit 1 is the designated irradiation amount value 79, the proper irradiation amount 123% of the exposure unit 2 is the designated irradiation amount value 118, and the proper irradiation amount 147% of the exposure unit 3 is the designated irradiation amount. Replaced with the value 127. For the exposure unit 3, the original designated dose value should be 142, but the designated dose value is 127 for the same reason as above. In this way, the numbers of exposure units for which the designated dose values 79, 118, 127 are set are 4, 8 and 5, respectively.

When the drawing data to which the specified dose value is given is given to the electron beam exposure apparatus and a pattern is actually drawn, the 0.05 μm square pattern disappears due to the insufficient exposure amount and the 10 μm square pattern. In the pattern as well, a resist residue was generated in a portion corresponding to the exposure unit 3.

In the conditions of FIG. 4, the minimum dose designation value is set to 5% of the reference dose, but the increase / decrease in the relative dose for 1 increment or decrement of the dose designation value is set to 1%. FIG. 5 shows a dose table when the minimum dose designation value is set to 75% of the reference dose. According to the dose table of FIG. 5, the proper dose 447% of the rectangle of 0.05 μm square is
The designated dose 127 is replaced. Further, the proper irradiation amount 84% of the exposure unit 1 is the designated irradiation amount value 9, the proper irradiation amount 123% of the exposure unit 2 is the designated irradiation amount value 48, and the proper irradiation amount 147% of the exposure unit 3 is the designated irradiation amount value 72. Will be replaced. Therefore, under this condition, only the 0.05 μm square pattern does not provide an accurate dose.

Summarizing the above results, when the exposure data is created based on the dose table of FIG. 3, an error occurs between the dose and the proper dose indicated by the designated dose value, and the high precision is achieved. When the exposure data is created based on the dose table of FIG. 4 in which the dose variation is reduced for the proximity effect correction, an accurate dose cannot be set for the 0.05 μm square and the exposure unit 3. . Similarly, when the exposure data is created based on the dose table of FIG. 5 in which the dose variation is small, the dose can be set accurately for the exposure unit 3, but 0.05 μm
Accurate dose cannot be set for the corner rectangle.

This result shows that the conventional method cannot set an accurate dose for each exposure unit in the pattern data that simultaneously includes patterns of extremely different sizes.

Next, the dose table of FIG. 1 will be described. After calculating an appropriate dose for each exposure unit in the same manner as above, a list of all dose values obtained by calculation is created at the stage of creating a dose table. Then, by using the distribution of the dose values created from this list, the assigned dose values and the dose values corresponding to these designated values are assigned to the densely distributed dose regions, and the dose values are roughly distributed. The assigned dose value and the assigned dose value corresponding to the designated value are reduced in the dose area.

In this embodiment, as the calculated proper irradiation amount, 84% of the reference irradiation amount (exposure unit 1), 123
% (Exposure unit 2), 147% (exposure unit 3), 447%
Since there are four (0.05 μm rectangles), these are assigned to the designated dose values 0, 1, 2, and 3, respectively.
In this case, only 4 specified dose values are needed,
Using a limited specified dose for a wide range of doses,
Accurate dose setting can be performed and the dose table can be used effectively.

[0027]

According to the present invention, the assigned dose value and the assigned dose value corresponding to this designated value are assigned more to the dose region having a high appearance frequency, and assigned to the dose region having a low appearance frequency. Therefore, it is possible to use the limited dose amount specified value effectively and set the accurate dose amount without increasing the total number of dose amount specified values that are restricted by the memory of the exposure apparatus or the restrictions on the program. Therefore, highly accurate proximity effect correction can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a dose table according to a first embodiment of the present invention.

FIG. 2 is a plan view of a 10 μm square pattern divided into exposure units.

FIG. 3 is a diagram showing an example of a conventional irradiation amount table.

FIG. 4 is a diagram showing another example of a conventional irradiation amount table.

FIG. 5 is a diagram showing another example of a conventional irradiation amount table.

[Explanation of Codes] 1, 2, 3 ... Exposure unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Komatsu 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inhito Ito Matsuda 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo No. within Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A pattern to be exposed is divided into exposure units of a predetermined size, an appropriate dose is determined for each exposure unit, and a designated dose value and a dose value designated by this designated value are set. Create a dose table to associate with,
In the method of creating electron beam drawing data in which the exposure data and a dose designation value corresponding to an appropriate dose of this exposure unit are stored in the pattern data, when creating the dose table, Check the appearance frequency of the determined appropriate dose, increase the assigned dose value and dose value corresponding to this designated value to the dose region with high appearance frequency, and assign the dose value corresponding to this specified value to the dose region with low occurrence frequency. A method of creating electron beam drawing data, characterized in that the assigned dose value and the assigned dose value corresponding to this designated value are reduced.