JPH1090878A - Proximity effect correcting method and mask for pattern transfer used for the same method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the correcting method for proximity effect which can omit proximity effect correcting and exposing processes by wafers and form even a high-density pattern of about 0.2μm in minimum line width with high throughput. SOLUTION: A mask substrate which is already coated with resist is prepared (91), and on the resist of this substrate, a mask pattern is drawn (92) by electron beam(EB) drawing. Them a mask (whose forming method is described later) for proximity effect correction which is generated separately is used (94) to perform corrective exposure for a mask for pattern transfer (93). At this time, the pattern and exposure quantity of the correction mask are so determined that the pattern formed on the mask is corrected (overcorrected) in consideration of proximity effect at the time of EB transfer to the wafer. Then development (95) and etching (96) are performed to complete the mask for pattern transfer after proximity effect correction (97). This pattern transfer mask is used to perform EB transfer onto the wafer (98). At this time, exposure including proximity effect correction can be performed through single-time transfer and exposure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for correcting a proximity effect in EB transfer exposure on a semiconductor wafer and a mask for pattern transfer used in the method. In particular, the present invention relates to a proximity effect correction method capable of forming a high-density pattern having a minimum line width of 0.2 μm or less at a high throughput and a proximity effect correction exposure step for each wafer, and a pattern transfer mask used in the method. .

[0002]

2. Description of the Related Art When an electron beam (EB) exposure apparatus is used to perform electron beam drawing or electron beam exposure on a photosensitive substrate such as a mask substrate or a semiconductor wafer coated with an electron beam resist, a pattern is formed by a so-called proximity effect. May deviate from the design values. The main cause of the proximity effect is the backscattering of the electron beam incident on the photosensitive substrate. Therefore, in order to correct the proximity effect, the exposure amount of the photosensitive substrate by the backscattered electrons may be made substantially equal over the entire surface of the photosensitive substrate,
Conventionally, correction has been performed by, for example, the ghost method.

In the ghost method, an image of a reverse pattern of a pattern drawn or transferred on a photosensitive substrate is exposed on the same photosensitive substrate with an electron beam having a large blur, so that an exposure amount due to back scattering is made uniform. You. Conventionally, each electron beam lithography apparatus has a proximity effect correction function, and the apparatus itself corrects the proximity effect.

However, when the correction of the proximity effect is performed by the electron beam lithography apparatus itself as in the prior art, it is necessary to further perform the correction drawing of the inverted pattern using the machine time after drawing the original pattern. There is a disadvantage that the throughput is reduced by the amount corresponding to the correction drawing. Further, when the original pattern is a complicated pattern, it may be difficult to draw or expose an accurate inverted pattern.

In order to solve such a problem, the present inventor disclosed in Japanese Patent Application Laid-Open No. 5-175110, "Using a mask in which a large number of openings are formed at a pitch smaller than the spread radius of backscattered electrons in EB exposure. Proximity effect correction, which is based on the idea of "performing correction exposure on wafer".

FIG. 5 is a flowchart showing an outline of a lithography process using the proximity effect correction disclosed in Japanese Patent Application Laid-Open No. 5-175110. First, a mask substrate coated with a resist is prepared (101), and a mask pattern is drawn on the resist of the substrate by EB drawing (102). The mask substrate on which the mask pattern is drawn is developed (103) and etched (104) to complete a pattern transfer mask (1).
05). The pattern of this pattern transfer mask is
Basically, it is a pattern that is equal to a regular (design) pattern or is enlarged or reduced at a certain rate. The above 10
At the time of EB drawing of 2, the proximity effect correction by the ghost method or the like for correcting the proximity effect at the time of EB drawing is performed. In the present specification, the “regular pattern” means a pattern as designed (including a reduced and enlarged similar shape) desired to be finally obtained, that is, a pattern that is not distorted.

Next, EB transfer to the wafer is performed using this pattern transfer mask (106). If development is performed at this stage, the pattern obtained on the wafer will be distorted as a result of the proximity effect at the time of EB transfer. Then, without performing development, a correction exposure is performed for each wafer by using a correction mask (108) having a large number of openings prepared separately (107). As a result, the pattern on the wafer becomes a regular pattern after the proximity effect correction. That is, the proximity effect correction exposure is performed for each wafer.

[0008]

The above-mentioned Japanese Patent Application Laid-Open No. 5-17 / 1993
In the technique of No. 5110, since it was necessary to perform proximity effect correction exposure for each wafer, the wafer exposure process had two stages. The EB exposure has a serious problem to be overcome in that the throughput is lower than that of the ordinary light exposure. However, if such two-step exposure is performed, the throughput is further reduced, and other exposure techniques are used. Was to be less competitive.

The present invention has been made in view of such a conventional problem, and is a method for correcting a proximity effect in EB transfer exposure on a semiconductor wafer, wherein a proximity effect correction exposure step for each wafer is performed. Can be omitted, minimum line width is 0.2μ
An object of the present invention is to provide a proximity effect correction method capable of forming a high-density pattern of m or less with high throughput, and a pattern transfer mask used in the method.

[0010]

In order to solve the above-mentioned problems, a proximity effect correction method according to the present invention uses a pattern transfer mask which is manufactured by performing excessive proximity effect correction and in which the proximity effect correction has been incorporated in advance. EB (electron beam) transfer exposure is performed using the method.

According to one embodiment of the present invention, there is provided a proximity effect correcting method.
A method for correcting a proximity effect when performing EB exposure on a wafer by using a pattern transfer mask created through an EB exposure process itself; and forming a regular mask pattern on the pattern transfer mask substrate. In addition to the exposure for forming, the mask for pattern transfer is excessively corrected and exposed to the pattern transfer mask including the proximity effect that appears when performing EB exposure on the wafer, so that the proximity effect correction woven pattern transfer mask is incorporated. And performing EB transfer exposure on the wafer using the pattern transfer mask. In other words, the mask for transferring the pattern to the wafer itself is subjected to a treatment for correcting the proximity effect at the time of the transfer exposure to the wafer, and the pattern exposure and the correction exposure are performed only once for the wafer. They can do it at the same time.

A proximity effect correction method according to another aspect of the present invention is a method of correcting a proximity effect when performing EB exposure on a wafer using a pattern transfer mask formed by itself through an EB exposure step. Before or after performing exposure for forming a regular mask pattern on the pattern transfer mask substrate, correcting and exposing the pattern transfer mask substrate using a separately created proximity effect correction mask. A mask for pattern transfer in which the proximity effect correction weaving is performed, and performing EB transfer exposure on the wafer using the pattern transfer mask. Here, as a method of incorporating the proximity effect correction into the pattern transfer mask, the pattern transfer mask is additionally exposed using the proximity effect correction mask. This can also be expressed as an excessive "proximity effect correction" performed at the stage of the pattern transfer mask. As a correction method that does not use the proximity effect correction mask, there is a method of performing an inversion pattern by EB drawing with a blurred beam. However, it is preferable to use a proximity effect correction mask from the viewpoint of apparatus cost and throughput.

[0013] A proximity effect correction method according to another aspect of the present invention is a method of correcting a proximity effect when performing EB exposure on a wafer using a pattern transfer mask formed by itself through an EB exposure step. EB drawing of a mask pattern on a resist-coated mask substrate, and before or after EB drawing of the mask pattern, the mask pattern is drawn by using a separately created proximity effect correction mask. It is characterized in that the mask substrate is subjected to correction exposure, and EB transfer exposure is performed on the wafer using the pattern transfer mask obtained by incorporating the proximity effect correction thus obtained.

A proximity effect correction method according to another aspect of the present invention is a method of correcting a proximity effect when performing EB exposure on a wafer using a pattern transfer mask formed by itself through an EB exposure step. Dividing the area of the pattern transfer mask into areas having dimensions sufficiently smaller than the spread width of the backscattered electrons when the area is reduced by the reduction rate of the transfer apparatus, and in each area, Calculate the area of the pattern area, calculate the area of the difference obtained by subtracting the area of the non-pattern area in the area where the pattern is densest and finest from the area in each area, and calculate the amount of the difference in proportion to the area of the difference. Additional exposure is applied to each area to incorporate in advance the proximity effect correction into the pattern transfer mask, and EB transfer exposure is performed on the wafer using the pattern transfer mask. According to this aspect, there are advantages that the throughput of the correction exposure is high and that the mask can be easily formed.

According to another embodiment of the present invention, there is provided a proximity effect correction method, comprising: forming a pattern formed by an EB exposure step in a case where a current pattern is formed on a wafer on which a base pattern is already formed; A method of correcting a proximity effect when performing EB exposure on a wafer using a transfer mask; the spread of backscattered electrons when the area of the pattern transfer mask is reduced to a reduction rate of the transfer apparatus. The area is divided into areas having dimensions sufficiently smaller than the width, and in each area, the area Ssp of the inverted area of the logical sum of the base pattern and the current pattern is calculated. Similarly, the area Ss of the inverted area of the base pattern is calculated, The area with the highest density and the largest amount of backscattered electrons, that is, the area with the largest area of the underlying pattern in the memory cell portion is selected and its Ssp is set to Ss And m, the Ss S
sm, and for each area, (Ssp−Sspm) · β + (Ss−Ssm) · γ =
The modified non-pattern area area is calculated, where β is determined by actual measurement in the range of 0 <β ≦ 2.0, γ is determined by actual measurement in the range of 0 ≦ γ ≦ 1,
Providing an additional exposure in an amount proportional to the area of the modified non-pattern area to each area to incorporate the proximity effect correction into the pattern transfer mask in advance, and performing EB transfer exposure on the wafer using the pattern transfer mask. Features. Here, the memory cell portion is a memory cell portion in a DRAM or the like, and is a portion where the pattern density is usually the highest and the adverse effect of excessive correction is serious. By the above processing,
Appropriate proximity effect correction can be performed even on transfer to a wafer having a base pattern with significant backscattering.

Further, the pattern transfer mask of the present invention comprises:
A mask for EB transfer exposure, characterized in that a pattern that incorporates in advance the proximity effect correction manufactured by performing the proximity effect correction excessively is formed. The modes incorporating the proximity effect correction may include the above-described respective modes of the proximity effect correction.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle underlying the present invention will be described with reference to FIG. FIG. 1A is a plan view of a virtual pattern (regular pattern) to be formed on a wafer. FIG. 1B is a schematic graph showing the energy applied to the resist when the proximity effect correction is not performed, as viewed along the x-axis in FIG. Due to forward scattering of electrons in the resist, the dose distribution of each pattern is not rectangular but Gaussian, as shown in FIG. Further, the distribution is large due to the backscattering in the high density part and small in the low density part.

FIG. 1C is a graph showing the energy given to the resist when the correction exposure is performed. The solid line indicates the case where the correction is normally performed, and the dotted line indicates the case where the overcorrection (additional exposure) is performed. Is equivalent to In the case of a solid line, since the width of each pattern line at the threshold value of the resist is equal, a pattern (regular pattern) having an equal width is formed.

The dotted line in FIG. 1C shows the energy given to the resist when the correction exposure is performed at a dose 1.5 times the solid line. The total energy of the normal exposure and the correction exposure is as indicated by a dotted line, and under the developing condition determined by the threshold value, a pattern having a wide pattern width (a pattern that has been overcorrected) around the periphery shown in FIG. It is formed.
When a pattern is transferred onto a wafer by an electron beam using a pattern transfer mask (prepared under appropriate conditions) of the pattern shown in (d), a pattern having the same line width shown in (a) (regular pattern) ) Is formed on the wafer. That is, when the pattern transfer mask is formed by the exposure technique, correction for the proximity effect at the time of the subsequent transfer is also incorporated in advance (additionally, excessive correction is performed).

[0020]

FIG. 2 is a flowchart of a wafer exposure process incorporating a proximity effect correction method according to one embodiment of the present invention. First, a mask substrate coated with a resist is prepared (91), and a mask pattern is drawn on the resist of this substrate by EB drawing (92). At this time, the proximity effect at the time of EB drawing may be corrected by a ghost method or the like,
At the time of the next correction exposure (93), it is better to perform the proximity effect correction including the proximity effect at the time of the EB transfer exposure (collectively).

Next, using a proximity effect correction mask (preparation method described later) that has been separately prepared (94), a correction exposure of the pattern transfer mask is performed (93). At this time, the pattern of the correction mask and the pattern of the correction mask are adjusted so that the pattern formed on the mask is corrected (excessively corrected) by adding the proximity effect at the time of EB transfer to the subsequent wafer. Determine the amount of exposure. Thereafter, through development (95) and etching (96), a pattern transfer mask into which the proximity effect correction weaving has been completed is completed (97). Then, EB transfer onto the wafer is performed using this pattern transfer mask (98). In this case, the exposure including the proximity effect correction at the time of the EB transfer can be performed by one transfer exposure.

FIG. 3 is a view for explaining a method of forming a proximity effect correction mask according to one embodiment of the present invention. FIG. 3A shows a case in which transfer is performed by a transfer device having a reduction ratio of 1/4, and also shows a part of the mask pattern which is reduced by 1/4. Assuming that the accelerating voltage of the electron beam at the time of transfer is 100 kV, the spread of backscattered electrons is 30 μm.
It was divided into 3 μm × 3 μm regions as mR (dotted line breaks). Here, a large rectangular pattern 13 is on the right side, and a high-density linear pattern 11 is on the left side. The area of the non-pattern area is calculated for each area. The area of the non-pattern area is 0 in the areas indicated by 1 and 4, the area of the non-pattern area is the smallest in the fine pattern area of the area indicated by 2 and 3, and the area indicated by 5, 6, and 7 is , The area is the largest.

FIG. 3B shows the distribution of values (arbitrary units) obtained by subtracting the areas in a few areas from the above areas in each area. Negative values were obtained in the areas 1 and 4, but 0 was set in the negative areas. Proper proximity effect correction can be performed by performing correction exposure at a value proportional to this value so that the background level in an area where no pattern is present and the background level in a high-density area are equal. In the present invention, the appropriate exposure intensity of 1.2 to
Correction exposure was performed at an intensity of 1.8 times (magnification is determined by actual measurement). The result is, as shown in FIG.
The pattern (line width) is thicker around the high-density pattern,
In the center, it was formed to the correct dimensions.

When the pattern transfer mask thus prepared is transferred and exposed to a wafer using an electron beam reduction transfer apparatus, a pattern on which the proximity effect has been properly corrected can be obtained. The method of determining the appropriate exposure intensity based on the above actual measurement is as follows. First, JP-A-5
According to the method of No. 175110, a correction mask in which holes each having an area proportional to the value shown in FIG. 3B are provided in each area is formed, and correction exposure is performed by changing the exposure time by five steps. Various types of pattern transfer masks were obtained. EB transfer was performed using these five types of masks, and the optimum intensity of the correction exposure at the time of forming the pattern transfer mask was determined from the degree of correction of the proximity effect of the obtained five types of patterns.

A description will be given of a proximity effect correction method in the case where a pattern of a heavy metal such as Mo or W having a large backscattering coefficient has already been formed on a base, and a new pattern is to be formed on this pattern. In this case, first, proximity effect correction (additional) exposure when there is no Mo or W was performed by the above-described method, and additional correction exposure was performed by the following method to prepare a pattern transfer mask. .

FIG. 4 is an explanatory diagram of proximity effect correction in EB transfer onto a wafer having a heavy metal base pattern according to one embodiment of the present invention. Mo and W heavy metal base patterns 15 and 17 (bands extending vertically), horizontal lines 11 and rectangles 13 to be formed this time (same as FIG. 3)
Create overlapping patterns. As in the previous case, the mask area is divided into areas of about 3 μm × 3 μm, and in each area,
The area Ssp of the non-pattern area of the pattern common to the base pattern and the current pattern (the inverted pattern of the logical sum of the base pattern and the current pattern) (hatched portion at the upper right) and the area Ss of the non-pattern area of the base pattern (downward right) (Hatched area)
Are calculated respectively. These values Sspm and Ssm in the fine and dense areas 2 and 3 are also calculated. FIG. 4 (B)
Is (Ssp-Sspm) + (Ss-
2 shows the distribution of values of Ssm). Based on this, correction exposure was performed in each area with an exposure amount proportional to (Ssp−Sspm) β + (Ss−Ssm) γ.

[0027]

As is apparent from the above description, the present invention can omit the proximity effect correction exposure step for each wafer,
A proximity effect correction method capable of forming a high-density pattern having a minimum line width of 0.2 μm or less with high throughput, and a pattern transfer mask used in the method can be provided. When the pattern transfer mask is additionally exposed using the proximity effect correction mask as a method of incorporating the proximity effect correction into the pattern transfer mask, the mask itself can be produced with high efficiency. When the proximity effect correction is performed in consideration of the underlying pattern, a more accurate pattern can be realized on the wafer.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a proximity effect correction method according to the present invention. (A) is a pattern formed on a wafer,
(B) is a graph schematically showing the level of energy absorbed by the resist when no correction is made, (c) is the energy absorbed by the resist when proper correction is performed,
The dotted line is a graph schematically showing the level of energy absorbed by the resist when overcorrection is performed, and (d) is the pattern of the transfer mask when overcorrection is performed.

FIG. 2 is a flowchart of a wafer exposure process incorporating the proximity effect correction method according to one embodiment of the present invention.

FIG. 3 is a diagram for explaining a method of creating a proximity effect correction mask according to one embodiment of the present invention.

FIG. 4 is an explanatory diagram of a proximity effect correction in EB transfer onto a wafer having a heavy metal base pattern according to one embodiment of the present invention.

FIG. 5 is a flowchart of a wafer exposure process incorporating the proximity effect correction method disclosed in Japanese Patent Application Laid-Open No. 5-175110.

[Explanation of symbols]

11 Linear pattern 13 Rectangular pattern 15, 17 Strip base pattern

Claims (14)

[Claims] An EB (electron beam) transfer exposure is performed by using a pattern transfer mask, which is manufactured by excessively performing the proximity effect correction and in which the proximity effect correction is incorporated in advance. . 2. A method for correcting a proximity effect when performing EB exposure on a wafer by using a pattern transfer mask formed through an EB exposure process itself; Proximity effect correction is incorporated by exposing the mask substrate for pattern transfer excessively, including the proximity effect that appears when performing EB exposure on the wafer, in addition to the exposure for forming the regular mask pattern Forming a pattern transfer mask, and performing EB transfer exposure on the wafer using the pattern transfer mask. 3. A method for correcting a proximity effect when performing EB exposure on a wafer by using a pattern transfer mask formed by itself through an EB exposure step; Before or after performing exposure for forming a regular mask pattern, the proximity effect correction woven pattern transfer mask is obtained by correcting and exposing the pattern transfer mask substrate using a separately created proximity effect correction mask. A proximity effect correction method, comprising: performing EB transfer exposure on a wafer using the pattern transfer mask. 4. A method of correcting a proximity effect when performing EB exposure on a wafer by using a pattern transfer mask formed through an EB exposure process itself; Before or after performing EB drawing on the mask pattern and performing EB drawing on the mask pattern, the mask substrate on which the mask pattern is drawn is corrected and exposed using a separately prepared proximity effect correction mask. And performing EB transfer exposure on the wafer using a pattern transfer mask into which the proximity effect correction has been incorporated. 5. A method for correcting a proximity effect when performing EB exposure on a wafer by using a pattern transfer mask formed by itself through an EB exposure step; When the area is reduced to twice the reduction rate of the transfer apparatus, the area is divided into areas having dimensions sufficiently smaller than the spread width of the backscattered electrons, and in each area, the area of the non-pattern area in the area is calculated. From the area, the area of the difference obtained by subtracting the area of the non-pattern area in the area where the pattern is densest and finest is calculated. Effect correction method, wherein the EB transfer exposure is performed on a wafer by using the pattern transfer mask. 6. When forming a pattern this time by superimposing it on a wafer on which a base pattern has already been formed,
A method of correcting a proximity effect when performing EB exposure on a wafer using a pattern transfer mask created through an EB exposure process; reducing the area of the pattern transfer mask by a transfer apparatus. The area is divided into areas having dimensions sufficiently smaller than the spread width of the backscattered electrons when reduced by a factor of 2, and the area Ssp of the inversion area of the logical sum of the base pattern and the current pattern is calculated in each area. The area Ss of the inversion region of the underlying pattern is calculated, and the area with the highest density and the largest amount of backscattered electrons, that is, the area in the memory cell portion and the area of the underlying pattern that is the largest is selected, and the Ssp is defined as Sspm. Let Ss be Ssm, and for each area, (Ssp−Sspm) · β + (Ss−Ssm) · γ =
The corrected non-pattern area area is calculated, where β is determined by actual measurement in the range of 0 <β ≦ 2.0, γ is determined by actual measurement in the range of 0 ≦ γ ≦ 1, and is proportional to the corrected non-pattern area area. A proximity effect correction method comprising: applying an amount of additional exposure to each area to incorporate in advance a proximity effect correction into the pattern transfer mask; and performing EB transfer exposure on a wafer using the pattern transfer mask. 7. The proximity effect correction method according to claim 5, wherein the additional correction exposure is performed without multiplying the mask area by the reduction ratio. 8. A mask for EB transfer exposure, characterized in that a pattern in which proximity effect correction is incorporated in advance is formed by performing excessive proximity effect correction. 9. A pattern transfer mask formed through an EB exposure step, wherein the pattern transfer mask includes an exposure for forming a regular mask pattern on the pattern transfer mask substrate,
A pattern transfer mask characterized in that the proximity effect correction is incorporated by excessively correcting and exposing the pattern transfer mask substrate, including the proximity effect that occurs when performing EB exposure on a wafer. 10. A pattern transfer mask formed through an EB exposure step; a proximity effect separately formed before or after performing exposure for forming a regular mask pattern on the pattern transfer mask substrate. A pattern transfer mask, wherein proximity effect correction is incorporated by correcting and exposing the pattern transfer mask using the correction mask. 11. A pattern transfer mask formed through an EB exposure step, wherein the mask pattern is formed by EB drawing on a resist-coated mask substrate, and separately formed before or after performing the EB drawing of the mask pattern. A pattern transfer mask, wherein proximity effect correction is incorporated by correcting and exposing a mask substrate on which the mask pattern is drawn using the proximity effect correction mask. 12. A pattern transfer mask formed through an EB exposure step, wherein the area of the pattern transfer mask is sufficiently larger than the spread width of the backscattered electrons when the area of the pattern transfer mask is reduced by the reduction rate of the transfer apparatus. The area is divided into smaller-sized areas, the area of the non-pattern area in each area is calculated in each area, and the area obtained by subtracting the area of the non-pattern area in the area with the highest density of the pattern from the area in each area. A pattern transfer mask, wherein a proximity effect correction is incorporated in the pattern transfer mask in advance by calculating an area of the difference, and applying an additional exposure to each area in an amount proportional to the area of the difference. 13. A pattern transfer mask formed through an EB exposure step, which is used when a current pattern is formed on a wafer on which a base pattern is already formed; The area is divided into areas having dimensions sufficiently smaller than the spread width of the backscattered electrons when the area is reduced by the reduction rate of the transfer apparatus, and in each area, the area Ssp of the inversion area of the logical sum of the base pattern and the current pattern is calculated. Similarly, the area Ss of the inversion area of the base pattern is calculated, and the highest density area, that is, the area Ss of the above two forms is calculated.
The area where p and Ss are the smallest is selected and its Ssp is selected.
Is Sspm, and Ss is Ssm. For each area, (Ssp−Sspm) · β + (Ss−Ssm) · γ =
The corrected non-pattern area area is calculated, where β is determined by actual measurement in the range of 0 <β ≦ 2.0, γ is determined by actual measurement in the range of 0 ≦ γ ≦ 1, and is proportional to the corrected non-pattern area area. A pattern transfer mask characterized in that proximity effect correction is incorporated in said pattern transfer mask in advance by giving an amount of additional exposure to each area. 14. The pattern transfer mask according to claim 12, wherein the mask area is subjected to additional correction exposure without multiplying the mask area by a reduction ratio.