JP3395695B2 - Mask drawing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a mask portrayal method, in particular, in the mask writing apparatus and multipath gray printing method in a raster scan method, to mask drawing Ekata method that reduces the exposure time.

[0002]

2. Description of the Related Art In photolithography, transmitted light of a pattern of a light-shielding portion / transparent portion formed on a photomask is transferred through a projection lens system onto a device substrate coated with a resist, and then developed by a desired method. A resist pattern is formed. High NA of projection lens (Numerica
Although the limit of photolithography is being improved due to (1 Application) and the like, there is a strong demand for device miniaturization, and device manufacturing has come to be performed near the resolution limit of photolithography. In manufacturing devices near the resolution limit, optical proximity correction (Optical Pro
ximity Correction) has become important. Optical Proximity (Optical Proximity
y Effect) is, for example, a decrease in which the line width / shape of a pattern changes due to the influence of other patterns around it. For example, even if the line patterns have the same size, the size of the resist pattern formed on the semiconductor substrate is large depending on whether it is a line-and-space pattern (a repeated pattern of lines and spaces having the same size) or an isolated pattern. different. Further, even with a periodic pattern, the dimensions of the resist pattern obtained by the pitch vary. Specifically, when a 0.2 μm line is transferred using a KrF excimer laser exposure device (NA 0.6), a line width variation of about 10% occurs depending on the pattern pitch. In the gate pattern of the logic device, it is necessary to keep the line width within ± several% in order to obtain the designed device property, so the effect of this optical proximity effect cannot be ignored. Therefore, when the desired resist pattern is to be formed on the device substrate by adjusting the pattern size on the mask, it is necessary to correct the optical proximity effect.

As a method of correcting the optical proximity effect, an exposure experiment is conducted using a test mask in which various sizes / shapes / pitches are formed, the obtained results are stored in a database, and the actual device pattern is stored in the database. There is a method of making corrections. Software for that purpose is also commercially available from several companies, and the proximity effect correction is generally applied to products. Here, the address size of the mask drawing device may become a problem.

There are two types of mask drawing apparatuses, a raster scan method and a vector method. The vector method is generally used in electron beam exposure equipment for device direct writing,
This is a so-called one-stroke drawing method. That is, only the drawing area is traced by the electron beam. In the raster scan method, the entire mask area is scanned without distinction between the drawing area and the non-drawing area. At this time, the electron beam is turned on in the drawing area and O is set in the non-drawing area.
This is a method of drawing a mask pattern by performing FF (correctly bending and cutting in the middle by deflection). US E
It is used in the electron beam mask drawing device of TEC: MEBES series and the laser drawing device ALTA of the same.

In this raster scan system, the address during mask drawing is generally 0.1 to 0.08 μm. This is because the mask drawing time is limited. In the raster scan method, all addresses are scanned regardless of the presence or absence of data, so the address size is set to 1
If you / n, the number of addresses increases the nxn times, increases also scan time ^twice n. In addition to the restriction of drawing time, it is difficult to narrow the electron beam to a small size (currently 0.04 μm).

For example, in the case of an x5 exposure device (photomask pattern: transfer pattern = 5: 1), 0.2
The μm gate pattern is 1 μm on the photomask,
Then, change the dimension on the device by 1% (0.0
02 μm), 0.0 on the mask
Address sizes of 1 μm have become necessary. When the address size is large as it is at present, the gate line width becomes thicker, but when it is made thin, it becomes too thin, and optical proximity correction cannot be performed with sufficient dimensional accuracy.

In the raster-scan type drawing apparatus, a method of drawing a pattern with a size step smaller than the address size has been conventionally proposed. One is a method called a virtual address, which is a method of thinning out an address to be drawn in half, as shown in FIG. 5, when the address takes only half as shown in FIG. In this way, the size of the mask pattern can be adjusted with the size of 1/2 of the address. However, in this case, there is a problem that the shape of the obtained mask pattern is deteriorated (edge roughness is increased).

[0008] The other is a method called multi-pass gray printing (SPIEE).
Proceedings 3096 Volume Photomask and X-Ray Mask Technology IV ,: "Mul
tipspassing printing for n
ew MEBES 4500 mask lithog
raphy system ”, SPE Proceed
ings Vol. 3096 Photomask a
nd X-Ray Mask Technology
IV, pp. 125-136). Originally, these are techniques for improving the dimensional accuracy of drawing. That is, in the case of one exposure, the illuminance variation of the electron beam directly becomes the mask pattern variation. However, by overlapping exposures with a low exposure amount, variations in the electron beam illuminance at each exposure are averaged, and the dimensional accuracy of the mask pattern is improved. Then, using this method, it is possible to realize the dimensional increments equal to or less than the drawing address of the device. That is, this is a method of dividing the exposure into a plurality of times and reducing the number of times of exposure for a portion not on the address, thereby realizing a dimensional step equal to or smaller than the drawing address. For example,
As shown in FIG. 6, the exposure is divided into four passes (in raster scanning, scanning the entire surface once is called one pass),
The line width of ½ address size is realized by exposing the area where the address is ½ only twice in four passes. Similarly, the address is 1/4 or 3 /
When there is a shift of 4, only one or three passes are exposed. However, in this method as well, when the address size is reduced to 1 / n (n-pass exposure), the exposure time becomes n times longer. Therefore, there has been a demand for a method of reducing the exposure time.

[0009]

An object of the present invention is to provide a, to improve the drawbacks of the prior art described above, in particular, in the mask writer multipath gray printing method, a new mask drawing Ekata method that reduces the exposure time Is provided. Another object of the present invention, the following dimensions increments drawing address, is to provide a novel mask drawing Ekata method that enables the drawing of patterns.

[0010]

Since the present invention SUMMARY OF] is to achieve the above object, basically, Ru der should be adopted technical construction as described below.

The first aspect of the drawing method of the mask drawing apparatus according to the present invention is that of a raster scan type and multi-pass gray printing type mask drawing apparatus for drawing a predetermined pattern on a resist coated on a substrate . In the mask drawing method, the exposure of the part on the drawing address
When the amount is standardized as 1, the exposure amount for each pass is 1 /
n is set to m (any integer) at least two different exposure times of (n = an integer obtained by the drawing address width / design grid width) exposed overlapping each the same drawing region, before sharp The present invention is characterized in that a predetermined pattern is drawn on a resist, and the second mode is a drawing address.
The total amount of exposure in the area that does not exceed
It is the total, and the sum in the area where the drawing address is
If the total exposure is standardized as 1, the drawing address shift
The feature is that when the quantity is x, the value is multiplied by x / n.
Is intended to also third aspect, the mask writing process of the mask writing apparatus and multipath gray printing method in a raster scan method for drawing a predetermined pattern on <br/> resist coated on a substrate, Drawing address width /
Step S1 of obtaining an integer n (initial number of passes) obtained by the design grid width, and an exposure amount D0 required for exposing the drawing address of the drawing area is divided by the integer n to obtain an initial value D of the exposure amount. At the same time, step S2 in which the integer n is the number of remaining paths PN, step S3 in which it is determined whether the number of remaining paths PN is odd or even, and the number of paths PN
Is an even number, step S5 of performing the pass of the exposure amount D twice and the number of remaining passes PN after the execution of step S5.
Is divided by 2 to obtain twice the exposure amount D as a new exposure amount, step S8 for determining whether the remaining pass number PN obtained in step S7 is 0, and step S8. If the number of paths PN is 0, the operation is terminated. If the number of paths PN is not 0, the process returns to the step 3 to determine whether the number of remaining paths PN is odd or even,
If the number of passes PN is even, steps S5 and below are repeated. If the number of passes PN is odd, step S4 is performed in which the pass of the exposure amount D held in the step immediately preceding step 3 is performed once. , Step S6 in which the number of remaining passes PN after execution of Step S4 and twice the exposure amount D are newly obtained as an exposure amount, and the number of passes PN and exposure amount obtained in Step S6 are input to the step 8. If the number of passes P N is 0, the process is terminated. If the number of passes PN is not 0, the process returns to step 3 and steps 3 and below are repeated to form a predetermined pattern on the resist on the substrate. It is characterized by drawing.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A mask drawing apparatus according to the present invention is a raster scan type mask drawing apparatus which exposes a resist on a wafer and draws a predetermined pattern. It is characterized in that it is provided with an exposure amount setting means for setting the exposure amount and performing exposure, and is also characterized in that it is provided with an exposure amount varying means for varying the exposure amount for each pass. is there.

[0013]

EXAMPLES Hereinafter, a specific example of a mask drawing Ekata method according to the present invention with reference to the drawings. (First Specific Example) FIG. 2 is a diagram showing a first specific example of a mask drawing apparatus and a drawing method according to the present invention. In these figures, a resist on a wafer is exposed, A raster scan type mask drawing apparatus for drawing a predetermined pattern is provided with an exposure amount setting means (steps S4 to S7) for setting the exposure amount to a predetermined exposure amount for each pass and performing exposure. A mask drawing device is shown, and in a raster scan type mask drawing device that exposes a resist on a wafer to draw a predetermined pattern, an exposure amount changing means (step) for changing the exposure amount for each pass. S4 ~ S
7) is provided, and the means is configured so that it can be exposed with at least two kinds of different exposure amounts, and draws with a size step less than a drawing address. A mask drawing device is shown,
Further, when the deviation amount x of the size increment x / n (n is a dimension increment less than the drawing address, x is a deviation amount less than the drawing address) equal to or smaller than the drawing address is an odd number, the means is set to a predetermined exposure amount. A mask drawing apparatus characterized in that when the exposure amount is 1 / n and the displacement amount x is an even number, the means performs the exposure twice with an exposure amount of 1 / n of a predetermined exposure amount. Further, there is shown a mask drawing apparatus characterized in that, in addition to the above-mentioned exposure, exposure is possible with an exposure amount of 2 m / n (m = 1 or more integer).

The present invention will be described in more detail below. In the following description, a mask pattern made with a design grid of 0.01 μm (values on a mask, in CAD of mask data creation, can be placed only at fixed intervals, and that grid is called a grid) A description will be given of the case of drawing with a mask drawing device having a drawing address of 0.08 μm (in a raster scan drawing device, drawing is not performed with a drawing size is performed in a fixed mesh unit, and its grid is referred to as an address). In addition, a multi-pass method is used for drawing in four times. FIG. 1 shows a part of the mask pattern to be drawn. The width (W) of the line pattern in the figure is 0.8
It is 3 μm. Since a positive type resist is used for mask drawing, the line pattern portion is not exposed and becomes the non-exposed region 1. The area other than the line pattern is the drawing area 2, but the right side of the line that does not get on the address is the gray drawing area 3. The address size of 0.
After 08 μm, 0.05 μm is the drawing area and the remaining 0.0
3 μm is the non-drawing area. In such a case, it is sufficient that the gray drawing area 3 is irradiated with 5/8 of the regular exposure amount. Therefore, three types of exposure amounts of 1/2, 1/4, 1/8, and 1/8 are used for the exposure of four multi-pass drawing. Then, in this gray drawing area, 1/8
The exposure amount and the ½ exposure amount were set to be exposed once twice (1/8 + 1/2 = 5/8).

The above design grid (0.01 μm)
, The address shift is 0.01-0.07μ
It may occur up to m in steps of 0.01 μm. The case of these, and measuring the area ratio of the portion not on the address, the exposure amount in proportion to the area to be irradiated to a portion not climb address. Since only the vertical line pattern is considered here, the area ratio is equal to the dimensional ratio at the X position, and the drawing as shown in Table 1 below is performed.

[0016]

[Table 1]

By drawing as shown in Table 1 above, it is possible to change the exposure amount from 1/8 to 7/8 by four-pass exposure. Therefore, it is possible to manufacture a mask pattern in which the line width is changed with a fineness of 1/2 as compared with the conventional method in which the same exposure amount is used. The above-described exposure method is basically based on performing 1/8 exposure once when the shift amount x from the drawing address is odd, and performing 1/8 exposure twice when the shift amount x is even.

Further, if necessary, 1/4 (= 1
/ 8 + 1/8) exposure once or 1/2 (= 1/4 + 1 /)
4) The exposure is performed once, or the 1/4 exposure and the 1/2 exposure are performed once. To further explain, in the above-described specific example, first, when the drawing data is arranged on the drawing address, what percentage of the address dimension is misaligned (a fraction of one) of the address size is considered. In this specific example, the interval is 1/8. Therefore, first, the minimum unit is divided into eight by 1/8. Then, of these eight, two are set to 1/8 (exposure amount) so that the rest are even. Then, 6 pieces of ⅛ that have not been determined yet are added together in increments of 2 pieces to make 3 pieces of ¼ (exposure amount). Then, by removing one of the three quarters so that the rest is an even number, this quarter (exposure amount) is also fixed. Add 1/4 of the last two remaining, 1/2 (exposure amount) is 1
Individual exposure can be made and exposure is performed with a combination of these exposure amounts.

More generally, when the address shift is 1 / n of the address size (design grid / drawing address = 1 / n), a flow chart for determining the exposure amount and the number of exposures in each exposure pass. Is shown in FIG. That is,
Initially, 1 / n is made into PN (= n) pieces (a), and one or two pieces are excluded so that the rest of them becomes an even number. Here, “excluding” means that it is decided that the amount of exposure is to be performed. Next, the remaining ones are added two by two (b). That is, the next pass doubles the exposure dose. Then, if there is not one remaining, the step (b) is repeated again. When PN becomes 0, the routine ends.

In the above flow chart, the address shift is 1
If the case of / 20 is applied, it is 1/2 of the normal exposure amount.
A total of 6 passes of exposure of 0, 1/20, 1/10, 1/5, 1/5, 2/5 will be performed. Therefore, the number of exposures can be remarkably reduced as compared with 20 passes when the same exposure amount (1/20) is used for exposure. (Second Specific Example) Next, a second specific example of the present invention will be described with reference to FIG. The address of the drawing device is 0.08 μm, which is the same as the above. Here, the mask drawing data is arranged on the address, and all the deviation amounts of the portion not on the address are checked. Here, as a result of performing the optical proximity correction, the address shift is 0.01 μm.
(Area 3b in the figure) and 0.02 μm (area 3a in the figure)
There are two types. In this case, the number of exposures is set to 3 times, the first time the area 2 + 3a + 3b is drawn with the exposure amount 1/8, and the second time is also the area 2 + 3a with 1/8 and the remaining 3/4 exposure area at the third time. By irradiating with 2, the required line width can be formed.

As described above, even if the mask data design grid is 0.01 μm, the number of passes can be further reduced if the actually used line width is not too narrow. Generally, as in the first specific example, the number of passes and the exposure amount of each pass are determined in consideration of all the address shifts, and the exposure amount for the address shift not used in the actual device pattern is determined. By collecting the paths and reducing the total number of paths,
Further, the mask drawing time can be shortened.

As described above, the mask drawing method of the present invention is
In the mask drawing method that draws by the raster scan method, the exposure amount for each pass is set to a predetermined exposure amount and the exposure is performed, and a predetermined pattern is drawn on the resist on the wafer with a step size smaller than the drawing address. Further, the exposure dose is characterized by exposing at least two types of exposure doses different from each other, and the exposure dose is dimensional increments x / n less than a drawing address.
It is characterized in that exposure is performed with an exposure amount set on the basis of (n is a step size equal to or smaller than a drawing address, and x is a displacement amount equal to or smaller than a drawing address).

[0023]

Mask drawing Ekata method according to the present invention is, since it is configured as described above, in the multipath gray printing, by varying the exposure amount of each path,
It has become possible to shorten the exposure time than before.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a first specific example of a mask drawing method according to the present invention.

FIG. 2 is a flowchart generally showing a drawing method according to a first example of the present invention.

FIG. 3 is a diagram illustrating a drawing method according to a second specific example of the present invention.

FIG. 4 is a diagram illustrating a relationship between drawing data and address size.

FIG. 5 is a diagram illustrating a conventional drawing method.

FIG. 6 is a diagram illustrating another conventional drawing method.

[Explanation of symbols]

1 non-drawing area 2 drawing area 3, 3a, 3b Gray drawing area x Address shift amount

Claims (3)

(57) [Claims] 1. In a mask drawing method of a mask drawing apparatus of a raster scan system and a multi-pass gray printing system for drawing a predetermined pattern on a resist applied on a substrate, an exposure amount of a portion on a drawing address is set to 1 Standardized as
In this case, the exposure amount for each pass is set to at least two different exposure amounts that are m (arbitrary integer) times 1 / n (n = an integer obtained by the drawing address width / design grid width). the same drawing region exposed overlapping each previous mask writing method of characteristics and 3 to draw a predetermined pattern to sharp resist. 2. An exposure amount of an area which is not included in a drawing address
The total is the total exposure of the passes
Normalized with the total exposure amount in the area on the address as 1.
Then, assuming that the shift amount of the drawing address is x, x / n is
The mask according to claim 1, wherein the mask is a multiplied value.
How to draw. 3.Apply the specified pattern to the resist applied on the substrate.
Raster scan method that draws turns and multi-pass
Mask drawing by the mask printing device of the gray printing method
In the drawing method, Integer n obtained by drawing address width / design grid width
Step S1 for obtaining the (initial number of passes) and the drawing area
Adjust the exposure dose D0 required to expose the drawing address
Divide by the number n to obtain the initial value D of the exposure amount and
Step S2 in which the number n is the remaining path number PN, and
Step S3 of judging whether the number of paths PN is odd or even
And the number of passes PN is an even number, the number of passes of the exposure amount D is
Step S5, which is performed twice, and after performing Step S5
Divide the remaining number of passes, PN, by 2 to obtain twice the exposure amount D
Step S7 for obtaining a new exposure amount and the step
It is determined whether or not the number of remaining paths PN obtained in step S7 is 0.
In step S8 and in step S8, the number of paths PN is
If it is 0, the operation is terminated, and the number of paths PN is not 0.
If not, the process returns to step 3 and the number of remaining paths PN is odd.
If the number of passes PN is even,
Repeat step S5 and subsequent steps, and the number of passes PN is an odd number.
In the case of,
Step S4 of making one pass of the exposure amount D
After the execution of step S4, the number of remaining paths PN and Of the exposure amount D
Step S6 in which twice the exposure amount is newly obtained, and
The pass number PN and the exposure amount obtained in step S6 are set to the above step.
If the number of paths PN is 0, it is finished,
If the number of paths PN is not 0, return to step 3.
By repeating steps 3 and above again, the substrate
Characterized by drawing a predetermined pattern on the upper resist
How to draw the mask.