JPH08202018A - Mask and its formation and charged particle beam exposure method - Google Patents

Abstract

PURPOSE: To prevent the throughput of an exposure device from being lowered and to completely and easily correct a proximity effect. CONSTITUTION: A pattern similar to a desired transfer pattern is divided into the 1st rectangles 45 of the same size. The 2nd rectangle of the same size is formed in each 1st rectangle 45, and the amount of the proximity effect from the 2nd rectangle itself and the rectangles surrounding it is obtained for the 2nd rectangle. The size of the 2nd rectangle is corrected in accordance with the obtained amount so as to obtain the 3rd rectangle 56, then the 3rd rectangle 56 is set as a transmission hole. The correction is performed by making the sum of the direct exposure to a resist by an electron beam passing through the 2nd rectangle and the exposure added to the direct exposure based on the scattering in the resist of the electron beam passing through the 2nd rectangle itself and the 2nd rectangles surrounding it nearly the same for the 2nd rectangle and making the maximum size of the 3rd rectangle 56 equal to the 2nd rectangle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask used for charged particle beam exposure, a method for producing the same, and a charged particle beam exposure method.

[0002]

2. Description of the Related Art With the miniaturization of elements of semiconductor integrated circuits,
Charged particle beam exposure apparatuses have come into use. In the charged particle beam exposure, when a basic pattern is repeatedly exposed like a memory, a block exposure method of using a block mask and performing a reduced projection exposure of the block pattern with one shot is effective.

As shown in FIG. 8, when a charged particle beam 4 is applied to a resist film 3 deposited on an object to be exposed 1, for example, a semiconductor wafer, via an insulating film 2, the resist film 3, the insulating film 2 and A charged particle beam (usually an electron beam, the same applies hereinafter) is scattered inside the exposure object 1 and the proximity effect as shown in FIG. 7 becomes a problem. Although many block patterns are formed on the mask 10, only one is shown in FIG. 7 for simplification. When one shot of the charged particle beam is projected on this block pattern, the charged particle beam passes through the transmission holes (through holes) 11 to 14, is reduced by the electromagnetic lens, and is irradiated onto the resist film 3 in FIG. Curves 21 to 24 are the exposure amounts of the charged particle beams on the resist film 3 which have passed through the AA line of the transmission holes 11 to 14, respectively, and the curve 20 is a superposition thereof. When developed, transfer patterns 31 to 33 corresponding to the transmission holes 11 to 13 and having an exposure amount equal to or larger than a threshold value are obtained. In FIG. 7, the horizontal axis of the graph and the transfer pattern are multiplied by 1 / (reduction ratio).

Due to the proximity effect, the width of the transfer pattern 33 becomes narrow, and the transfer pattern corresponding to the transmission hole 14 cannot be obtained. Further, for example, from the periphery of the position P1 to the position P
The amount of scattered electrons to 1 is larger than the amount of scattered electrons from around the position P2 to the position P2, so that the transfer pattern becomes swelled, and the transfer patterns 31 and 32 are located at the center rather than the ends. Approach each other in the department.

For the proximity effect, the following correction method has been conventionally proposed. (1) After exposing the mask 10 with a reverse pattern weakly,
Expose in a positive pattern (ghost exposure method). (2) The exposure pattern is decomposed into rectangles, an appropriate exposure amount is calculated for each rectangle, and a block pattern having a size capable of proximity effect correction is obtained by an appropriate exposure amount for each block.

(3) A metal mesh is provided in the transmission hole, and the electron transmission amount is changed depending on the size of the mesh.

[0007]

However, the method (1) requires exposure with both a positive pattern and a reverse pattern, and the method (2) requires a smaller block size. Neither method is practical because it lowers the throughput of the exposure apparatus. In the method (3), the metal net is fragile and easily broken, the mask cannot be easily manufactured, and the mask manufacturing time becomes long. Further, although the appropriate proximity effect correction amount is different in each part in one transmission hole, (1) to (3)
None of these methods can deal with this and cannot remove the bulge generated in the transfer pattern. This limits the miniaturization of the pattern.

In view of the above problems, an object of the present invention is to provide a mask, a method of making the same, and a charged particle beam, which can sufficiently and easily correct the proximity effect without lowering the throughput of the exposure apparatus. An object is to provide an exposure method.

[0009]

In the mask making method according to the first invention, a pattern similar to a desired transfer pattern is divided into first rectangles, and second rectangles are formed in each first rectangle. , For each second rectangle, the amount of the proximity effect from itself and the surrounding second rectangle is calculated, and the size of the second rectangle is corrected according to the amount to form the third rectangle. Create a mask to be a transmission hole. The mask according to the second invention has a transmission hole having a shape obtained by the method described above.

In the charged particle beam exposure method according to the third aspect of the invention, the cross section of the charged particle beam is shaped by the mask and reduced projection exposure is performed on the exposure object. According to the first to third aspects of the present invention, the proximity effect in each part is corrected by the size of the third rectangle, so that the proximity effect correction becomes sufficient.
It is possible to reduce the bulge as shown in. Further, since it is not necessary to use both the positive pattern and the reverse pattern and to reduce the block pattern for the proximity effect correction, it is possible to prevent the throughput of the exposure apparatus from being lowered.
Further, since there is no step of attaching the wire mesh, the mask can be easily manufactured.

In the first aspect of the first aspect of the invention, the direct exposure amount of the resist by the charged particle beam passing through the second rectangle, and the charged particles passing through the second rectangle itself and the second rectangle around the second rectangle itself. The third rectangle is formed by correcting the size of the second rectangle so that the sum of the direct exposure amount and the exposure amount added based on the proximity effect of the beam is substantially the same for each second rectangle. To do.

According to the first aspect, the proximity effect correction becomes more sufficient. In the second aspect of the first invention, the pattern similar to the desired transfer pattern is a rectangular pattern, the first rectangles have the same size in the rectangular pattern, and the second rectangle in the rectangular pattern. They are the same size as each other. According to this second aspect,
Since the correction for the second rectangle is easy, the mask can be easily created.

In the third aspect of the first aspect of the present invention, the reference lengths in the X direction and in the Y direction orthogonal thereto are Mx and My, respectively, and the length Nx in the X direction of the first rectangle and the Y direction orthogonal thereto. Ny = Lx / [Lx / Mx], N
The second aspect is implemented by determining as y = Ly / [Ly / My], where Lx and Ly are the lengths of the rectangular pattern in the X and Y directions, and [] rounds up the fractional part. Means to be an integer.

According to the third aspect, it is possible to easily make the size of the first rectangle within an appropriate range for the proximity effect correction for any of the above patterns. First
In the fourth aspect of the invention, the maximum size of the third rectangle is made equal to that of the second rectangle. According to the fourth aspect, since the minimum value of the interval between the adjacent third rectangles is determined before the correction, it becomes easy to create an appropriate mask.

In the fifth aspect of the first invention, the length Ux of the third rectangle in the X direction and the length Uy in the Y direction perpendicular to the length Ux.
, Ux = (Q / Qmax) ^1/2 · SxUy = (Q / Qma
x) ^1/2 · Sy, where Sx and Sy are the lengths of the second rectangle in the X and Y directions, respectively, and Q = 1 / (1 + C · η) , C is a constant, η is a value approximately proportional to the amount of proximity effect from the second rectangle itself to be corrected and the second rectangle around it, and Qmax is the maximum value of Q.

According to the fifth aspect, since the correction for the second rectangle is easy, the mask can be easily made. Third
In the first aspect of the invention, in the mask, the one having the largest size among the third rectangles is equal to the second rectangle, and the appropriate exposure amount is approximately E0. (Nx / Sx). (Ny / Sy). E0 is an appropriate exposure amount when a mask is formed with a pattern similar to the desired transfer pattern, and Nx and Ny are the X direction of the first rectangle and this, respectively. Is a length in the Y direction perpendicular to, and Sx and Sy are the lengths in the X direction and the Y direction of the second rectangle, respectively.

According to the eighth aspect, the exposure amount can be easily determined.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] A mask forming method according to the first embodiment will be described with reference to FIG. This mask is used for block exposure in a charged particle beam exposure apparatus. A large number of block patterns that are repeatedly used are formed on the mask.By irradiating the selected block pattern with a charged particle beam to shape the beam cross section, the block pattern is exposed on the object to be exposed in one shot. For example, a resist on a semiconductor wafer is subjected to reduction projection exposure.

The first design pattern 40 for the block pattern is a pattern similar to the desired transfer pattern, and the outer shapes of the regions 41 to 44 are the transmission holes 1 shown in FIG.
It is equal to the outer shape of 1-14. Next, the regions 41 to 44 are divided into rectangles 45 of the same size. Next, FIG.
As shown in (B), the separation rectangles 46 having the same size are formed in the division rectangle 45.

Separation rectangle 46 for area of division rectangle 45
Let k be the ratio of the areas and the appropriate exposure amount in the case of FIG. 7 be E0. A mask having the separating rectangle 46 as a transmission hole is formed, and a charged particle beam is irradiated on the mask to set the exposure amount to E = E0.
By setting / k, it is possible to form almost the same transfer patterns 31 to 33 shown in FIG. 7 which are not subjected to proximity correction. The portion of the resist film corresponding to the adjacent divided rectangles 45 is exposed by the diffraction of the charged particle beam passing through the transmission hole and the scattering shown in FIG. 8 in the resist film.

Next, for each separation rectangle 46, the exposure amount of scattered electrons from the other separation rectangle 46 is calculated, and the larger the value, the smaller (corrected) the size of the separation rectangle 46 is. However, the size of the separation rectangle 46 that minimizes the exposure amount due to scattered electrons does not change. Next, as shown in FIG. 2, the transmission hole 56 having the corrected size is formed on the Si substrate by, for example, the photolithography technique to form the mask 50. Although many block patterns are actually formed on the mask 50, in FIG.
Only one (block mask) is shown.

Each transmission hole 56 along the line BB in FIG.
The exposure amount on the exposure target that has passed through is as shown by the alternate long and short dash line. Curve 60 is a superposition of these. Transfer patterns 71 to 71 obtained by developing the exposed object
The proximity effect 74 is corrected to have a desired value. In each of the regions 41 to 44, the proximity effect in each part is corrected by the size of the transmission hole 56, so that the proximity effect correction is sufficient and the swelling as shown in FIG. 7 can be reduced. Further, since it is not necessary to use both the positive pattern and the reverse pattern and to reduce the block pattern for the proximity effect correction, it is possible to prevent the throughput of the exposure apparatus from decreasing. Further, since there is no step of attaching the wire mesh, the mask can be easily manufactured.

[Second Embodiment] FIG. 3 shows a transfer pattern to be formed, which is a block 8 separated by an alternate long and short dash line.
It is formed by a block mask corresponding to 0, B1 to B8. FIG. 4A is an enlarged view of the block 80 in FIG. The hatched portion is required to have an exposure amount necessary for development. When forming such a transfer pattern, since the hollow portions 81 to 84 and A1 to A5 are present, when the transmission hole is formed by the conventional method of FIG. 7, the portion on the mask corresponding to the hollow portion falls off. However, I cannot support this part.

However, if the method of the first embodiment is used, a mask having hatched portions as transmission holes 86 as shown in FIG. 4B corresponding to FIG. The parts corresponding to 81 to 84 are supported. Further, the throughput is higher than that of the method of exposing each of the two partial patterns as in Japanese Patent Publication No. 63-11657.

The preferred pattern to be formed on the block mask is different depending on the transfer pattern around it even if the corresponding transfer patterns are the same, so it is necessary to form it according to the transfer pattern on the periphery. , Block exposure is used for repetitive patterns, so
The utility value of the present invention is high. [Third Embodiment] Generally, since all the exposure patterns can be decomposed into rectangular patterns, a general method of forming the above-mentioned divided patterns for the rectangular patterns is important.
Next, this will be described with reference to FIGS.

As shown in FIG. 5A, a rectangular pattern 90
Let Lx and Ly be the lengths of the X direction and the Y direction, respectively, and let Mx and My be the reference lengths for rectangle division in the X direction and the Y direction, respectively. The lengths Nx and Ny of the divided rectangles in the X and Y directions are calculated by the following equation. Nx = Lx / [Lx / Mx] (1) Ny = Ly / [Ly / My] (2) where [] means an integer value rounded up after the decimal point. .

As shown in FIG. 5B, a rectangular pattern 90
Is divided into rectangles 95 having lengths Nx and Ny in the X and Y directions. Within the divided rectangle 95, the length in the X direction Sx = Nx
-2dx, a separation rectangle 96 having a length Sy = Ny-2dy in the Y direction is formed. Here, 2dx is the X of the separation rectangle 96.
2dy is an adjacent interval in the Y direction of the divided rectangle 95. 2dx and 2dy are determined so as to satisfy the following two conditions.

(1) Due to the diffraction of the charged particle beam passing through the separation rectangle 96 and the proximity effect in the resist on the object to be exposed, the resist in the portion corresponding to the interval is exposed and the transfer pattern is continuous. (2) The mask having the divided rectangle 95 as a transmission hole has sufficient strength. The appropriate exposure time E after the proximity effect correction is approximately calculated as E = E0 · (Nx / Sx) · (Ny / Sy) (3). Here, E0 is a conventional appropriate exposure time in which the entire rectangular pattern 90 is used as a transmission hole.

Next, in order to easily calculate the proximity effect correction amount, as shown in FIG. 6A, one side of the X direction and the Y direction of the pattern to be exposed (for example, 1/100 of the mask size) is exposed. Rectangle 9 of length Tx and Ty respectively
Divide by 7. Tx and Ty are, for example, one rectangle 9
7 is a size that can be sufficiently corrected by considering the proximity effect only from the eight rectangles 97 around it, and rotation including the proximity effect when one point is irradiated with the charged particle beam. The target exposure amount (dose amount) distribution f (r), where r is the distance from the point, f (R) / f
(0) = equal to a predetermined value, for example, a distance R that becomes 1/8. f (r) is approximately: f (r) = a · exp {-(r / b) ² } + c · exp
It is known to be represented by {-(r / d) ² }. Here, a to d are constants.

For each rectangle 97, the ratio λ of the area inside the rectangle 97 of the rectangle pattern 90 to the area of the rectangle 97 is determined. The numerical value in the parentheses in the figure indicates this area ratio. Figure 6
In (A), only the area ratio is shown around the rectangular pattern 90. The following correction count Q is calculated for each rectangle 97. Q = 1 / (1 + C · η) (4) η = Σλi · Tx · Tyf (ri) (5) where C: constant η: rectangle of interest 97 (i = 0) Approximate proximity effect amount Σ: i = 0 to 8 from itself and eight surrounding rectangles 97 (i = 1 to 8) to the focused rectangle 97 (i = 0) Symbol λi: Area ratio of the rectangle 97 (i) ri: Distance between the center of gravity of the rectangle 97 (i) and the center of gravity of the rectangle 97 (i = 0) For example, if the value of η of the rectangle 97 including the upper right corner of the rectangular pattern 90 is Tx = Ty = 1, then η = 0.8f (0) + (0.8 + 0 + 0 + 0.8) f (1) + (0. 4 + 0 + 0.2 + 0.8) f (2 ^1/2 ) = 0.8f (0) + 1.6f (1) + 1.4f (2 ^1/2 ).

Sx and Sy are corrected by the following equations to obtain Ux and Uy, respectively. Uxi = (Qi / Qmax) ^1/2 * Sx ... (6) Uyi = (Qi / Qmax) ^1/2 * Sy ... (7) Here, Qi is Q of the i-th rectangle 97. , Qmax
Is the maximum value among all Qi in one block pattern which is an exposure unit of one shot, and Uxi and Uyi are Ux and Uy in the i-th rectangle 97.

From equations (4) to (6), the relation Uxi · Uyi (1 + C · ηi) = constant is obtained for all i. Where ηi is the i-th rectangle 9
7 is η. From this relational expression, expressions (4) to (7) are
It can be seen that this is a first-order approximation correction formula for the proximity effect.

As described above, the mask pattern for forming the rectangular transfer pattern, which has the hatched portion as the transmission hole 106, is designed as shown in FIG. 6B. To be precise, ηi is obtained by dividing the above f (r) by the area. Further, in the formulas (1) and (2), when Nx and Ny are too small, dx and dy are too small,
If it is too large, the proximity effect correction will be insufficient, so there is an appropriate range. Therefore, Mx and My are preferably set to approximately the upper limit values for sufficient proximity effect correction. In this way, Nx obtained from equations (1) and (2)
And Ny are appropriate values.

Specific examples of the size are as follows. Mask: Si having a thickness of 20 μm Mx = My = 8 μm 2dx = 2dy = 2 μm Tx = Ty = 1 to 4 μm C = 0.5 to 1.0 The present invention includes various modifications other than the above.

For example, in FIG. 6A, the rectangle 97 may be made smaller, and Q may be calculated for 8 rectangles around the rectangle 97 and 16 rectangles around the rectangle 97. Further, the above Q or η may be modified based on the actually obtained transfer pattern. Further, in the above-described first to third embodiments, the case where the size of the separation rectangle is corrected by correcting the separation rectangle has been described. Of course, you can do that.

Further, the sizes of the divided rectangles 96 do not have to be the same, and a divided rectangle having a size larger than the periphery thereof may be formed in the central portion of the rectangular pattern 90.

[0037]

As described above, according to the mask, the method for making the same, and the charged particle beam exposure method according to the first to third inventions, the proximity effect in each portion of the exposure pattern is the third.
Since it is corrected by the size of the rectangle, the proximity effect correction will be sufficient and the bulge of the rectangular pattern can be reduced. Moreover, both the positive pattern and the inverted pattern can be used, or the proximity effect correction can be performed. Since it is not necessary to reduce the block pattern, it is possible to prevent the throughput of the exposure apparatus from being lowered, and further, since there is no process such as attaching a wire mesh, the mask can be easily manufactured, which is an excellent effect.

According to the first aspect of the first aspect of the invention, there is an effect that the proximity effect correction becomes more sufficient. According to the second aspect of the first aspect of the present invention, the correction of the second rectangle is facilitated, so that the mask can be easily produced. According to the third aspect of the first aspect of the invention, it is possible to easily make the size of the first rectangle within an appropriate range for the proximity effect correction for any of the above patterns.

According to the fourth aspect of the first invention, before correction,
Since the minimum value of the interval between the adjacent third rectangles is determined, there is an effect that it is easy to create a proper mask.
According to the fifth aspect of the first aspect of the invention, the correction of the second rectangle is facilitated, so that the mask can be easily produced. According to the first aspect of the third aspect of the invention, there is an effect that the determination of the exposure amount becomes easy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a mask forming method according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a mask, an exposure amount, and a transfer pattern according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a transfer pattern according to a second embodiment of the present invention.

4 is a diagram showing an enlarged transfer pattern of a block 80 in FIG. 4 and a mask for forming the transfer pattern.

FIG. 5 is an explanatory diagram of a mask rectangular pattern forming method according to a third embodiment of the present invention.

FIG. 6 is an explanatory diagram of a mask rectangular pattern forming method according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating a problem of the conventional technique.

FIG. 8 is an explanatory diagram of a proximity effect.

[Explanation of symbols]

 10, 50 Masks 11-14, 56, 86, 106 Transmission holes 31-33, 71-74, 80 Transfer pattern 40 Design pattern 41-44 Region 45, 95 Dividing rectangle 46, 96 Separation rectangle 81-84 Hollowing part 90 Rectangular pattern

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Satoru Satoru Satoru Satoru Satoshi Aichi Prefecture Kozoji-cho 2-chome 1844-2 Kasugai City, Aichi Prefecture (72) Inventor Kiichi Sakamoto 1015 Kamitadanaka, Nakahara-ku, Kanagawa Incorporated (72) Inventor Hiroshi Yasuda 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited

Claims (9)

[Claims] 1. A pattern similar to a desired transfer pattern is divided into first rectangles, a second rectangle is formed in each first rectangle, and for each second rectangle, the second rectangle around itself and the second rectangle. The mask making method is characterized in that the amount of the proximity effect is calculated, and the size of the second rectangle is corrected according to the amount to form a third rectangle, and a mask having the third rectangle as a transmission hole is created. . 2. The direct exposure dose to the resist by the charged particle beam that has passed through the second rectangle and the proximity effect due to the charged particle beam that has passed through the second rectangle itself and its surroundings. The third rectangle is formed by correcting the size of the second rectangle such that the sum of the direct exposure amount and the exposure amount added is substantially the same for each second rectangle. The mask making method according to claim 1. 3. The pattern similar to the desired transfer pattern is a rectangular pattern, the first rectangles have the same size in the rectangular pattern, and the second rectangles have the same size in the rectangular pattern. There is, The mask making method according to claim 1 or 2 characterized by things. 4. The reference lengths in the X direction and in the Y direction perpendicular thereto are Mx and My, respectively, and the length Nx in the X direction of the first rectangle and the length Ny in the Y direction perpendicular thereto are Nx.
= Lx / [Lx / Mx], Ny = Ly / [Ly / My]
The Lx and Ly are the lengths of the rectangular pattern in the X direction and the Y direction, and [] means that the fractional part is rounded up to an integer. How to make a mask. 5. The mask making method according to claim 4, wherein the maximum size of the third rectangle is made equal to that of the second rectangle. 6. The length Ux in the X direction of the third rectangle and the length Uy in the Y direction perpendicular to the X direction are: Ux = (Q / Qmax) ^1/2 · Sx Uy = (Q / Qmax) ^{1 / 2} · Sy, where Sx and Sy are the lengths of the second rectangle in the X and Y directions, respectively, and Q = 1 / (1 + C · η), and C is a constant. And η is a value substantially proportional to the amount of proximity effect from the second rectangle itself to be corrected and the second rectangle around it, and Qmax is the maximum value of Q. How to make. 7. A mask having a transmission hole having a shape obtained by the method according to any one of claims 1 to 6. 8. A charged particle beam exposure method, which comprises shaping the cross section of a charged particle beam with the mask according to claim 7 and performing reduction projection exposure on an exposure object. 9. The mask has the largest size among the third rectangles equal to the second rectangle, and the appropriate exposure amount is E0. (Nx / Sx). (Ny / Sy).
Where E0 is an appropriate exposure amount when a mask is formed with a pattern similar to the desired transfer pattern, and N0 is
And Ny are the lengths of the first rectangle in the X direction and the Y direction perpendicular thereto, respectively, and Sx and Sy are the lengths of the second rectangle in the X direction and the Y direction, respectively. The charged particle beam exposure method described.