JPH11354423A - Method for correcting proximity effect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently correcting a proximity effect caused when electron beam transfer exposure is performed on a substrate, where a base material layer has been already formed. SOLUTION: The region of a pattern transfer mask is subdivided into sections 51-57 of small dimensions, and for each section an area S1 of a region with no base material patterns 66 and 67 and an area S2 of current non-exposed region are calculated. In addition, the value K1S1+S2 (where K1 represents a factor) is calculated for all sections. Then, with the value in the section comprising a non-exposed part of minimum line thickness where this value is minimum is get as Smin , and expression (K1S1+S2)-Smin = correction reference area is calculated for each section. Using a proximity effect correcting mask provided with an opening of an area corresponding to that correction reference area, the mask is exposed for correction excessively, before or after an electron beam exposure process for the pattern transfer mask.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting a proximity effect in transferring and exposing a circuit pattern on a semiconductor wafer by using an electron beam. In particular, the present invention relates to a proximity effect correction method capable of omitting a correction exposure step for each wafer and forming a high-density pattern having a minimum line width of 0.2 μm or less with high throughput.

[0002]

2. Description of the Related Art When an electron beam exposure is performed on a sensitive substrate such as a mask substrate or a semiconductor wafer coated with an electron beam resist, the line width of a pattern may deviate from a design value due to a so-called proximity effect. The main cause of the proximity effect is
When the accelerating voltage of the electron beam is 50 kV or more, it is the back scattering of the electron beam incident on the sensitive substrate. In such a case, the proximity effect can be corrected by making the exposure amount of the substrate by the backscattered electrons substantially equal over the entire surface of the substrate. Conventionally, the correction has been performed by, for example, a ghost method.

In the ghost method, an image of a reverse pattern of a pattern drawn or transferred on a sensitive substrate is exposed (corrected exposure) on the same substrate with an electron beam having a large blur, so that exposure by back scattering of electrons is performed. The amount is equalized. Such a function for the correction exposure is provided in each of the conventional electron beam writing apparatuses, and the apparatus itself corrects the proximity effect.

However, when the correction of the proximity effect is performed by the electron beam writing apparatus itself as in the prior art, it is necessary to further perform the correction writing of the inverted pattern using the machine time after the writing of the original pattern is completed. There is an inconvenience 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 an accurate inverted pattern.

On the other hand, when the pattern is transferred by the electron beam, the pattern size changes due to the proximity effect. Therefore, the mask pattern is deformed in advance so that the transfer pattern has the correct size due to the proximity effect. The idea of resizing has been proposed. However, the method of calculating the amount of change according to this proposal requires an enormous amount of calculation, is not practical, and has not been corrected with an actual pattern until now. Further, in order to correct correctly, the deformed pattern becomes a pattern including an oblique line having an arbitrary inclination, and it is difficult to form a mask.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and there is no need to perform a complicated correction pattern calculation for correcting the proximity effect, and a mask is used when a regular pattern to be transferred does not include oblique lines. It is an object of the present invention to provide a proximity effect correction method that does not require the formation of a diagonal line pattern at the time of manufacturing. In addition, the proximity effect can be corrected without increasing the number of patterns at the time of pattern formation. In addition, the proximity effect at the time of electron beam exposure in the pattern transfer mask manufacturing process and the transfer exposure to a wafer using the pattern transfer mask are performed. An object of the present invention is to provide a proximity effect correction method capable of correcting the proximity effect at a time.

Another object of the present invention is to provide a method for efficiently correcting a proximity effect that occurs when an electron beam transfer exposure is performed on a substrate patterned with a material having a large backscattering electron coefficient. It is another object of the present invention to provide a method for efficiently correcting a proximity effect affected by the density of a distant pattern peculiar to a high acceleration voltage electron beam.

[0008]

In order to solve the above problems, the proximity effect correction method according to the first aspect of the present invention incorporates the proximity effect correction in advance by excessively performing the proximity effect correction. When performing electron beam transfer exposure using a mask for pattern transfer, the pattern formation of the mask is performed by a pattern drawing apparatus having a resolution lower than the beam resolution of the transfer exposure or a lower acceleration voltage. . The operation of this embodiment will be described later.

A proximity effect correction method according to a second aspect of the present invention comprises:
In the case where a pattern is formed this time on a wafer on which an underlayer pattern made of a material having a different backscattering electron coefficient from the substrate material is already formed, the pattern transfer mask itself is manufactured through an electron beam exposure process A method for correcting a proximity effect when performing electron beam reduction transfer exposure on a wafer using: a backscatter at the time of pattern transfer when the area of the pattern transfer mask is reduced to the reduction rate of the transfer. It is divided into areas having dimensions sufficiently smaller than the electron spread width, and in each area, the area S ₁ of the area without the underlying pattern and the area S ₂ of the non-exposed part are calculated, and (K ₁ S ₁ + S ₂ ) the values calculated for the whole area (K ₁ is a coefficient), the value of and in the region where the value is minimized in the region and S _min containing unexposed portion of the minimum line width in each zone (K ₁ S ₁ + S ₂₎ -S _min = calculates a correction reference area, corresponding to the correction reference area (e.g., proportional)
Producing a proximity effect correction mask provided with an opening having an area having a predetermined area, and using the proximity effect correction mask before or after the electron beam exposure step of the pattern transfer mask, excessively correcting and exposing the pattern transfer mask It is characterized by doing.

In the second aspect of the present invention, as a method of correcting the proximity effect of the pattern transfer mask, the pattern transfer mask is corrected and exposed using the proximity effect correction mask. Then, the amount of the correction exposure is adjusted in advance to compensate for the proximity effect at the time of the transfer exposure so that a normal pattern can be obtained on the wafer when the transfer exposure is performed on the wafer using the pattern transfer mask. I have. Further, the correction mask is provided with a correction exposure opening that also takes into account the areas of the underlying patterns having different backscattered electron coefficients already formed on the wafer.

Here, the value of K ₁ is, for example, 0.1 to
It can be 0.7. T with high backscattered electron coefficient
When a base pattern such as a or Mo and a base pattern of Si having the same coefficient coexist, the value of K ₁ is about 0.6,
The value of K ₁ If the same material of the base pattern and the underlying Si pattern substantially Si and backscattered electron coefficient coexists as l is about 0.1. Further, if the acceleration voltage is high when 0.5 the value of K _1, when the acceleration voltage is low, the value of K ₁ is 0.6.

[0012] A proximity effect correction method according to a third aspect of the present invention comprises:
In the case where a pattern is formed this time on a wafer on which an underlayer pattern made of a material having a different backscattering electron coefficient from the substrate material is already formed, the pattern transfer mask itself is manufactured through an electron beam exposure process A method for correcting a proximity effect when performing electron beam reduction transfer exposure on a wafer using: a backscatter at the time of pattern transfer when the area of the pattern transfer mask is reduced to the reduction rate of the transfer. In addition to dividing into areas with dimensions sufficiently smaller than the spread of the electrons, the surrounding area is set around each area by removing the area from a circle having a radius smaller than the spread radius of the backscattered electrons. the area S ₁ of no base pattern area, and the area S ₂ of this non-exposed portion, and the area ratio R ₃ of the no base pattern of the peripheral region area, surrounding territory And of calculating the area ratio R ₄ of the non-exposed _{portion, (K 2 S 1 + S} 2 + S 0 R 3 K 3 + S 0 R 4 K
₄ ) is calculated for each area (K ₂ , K ₃ and K ₄ are coefficients,
S ₀ is the area of the above-mentioned area), the area including the non-exposed portion having the minimum line width and the area where the above-mentioned value becomes the minimum is represented by S ′ _min
And (K ₂ S ₁ + S ₂ + S ₀ R ₃ K ₃ + S
₀ R ₄ K ₄ −S ′ _min ) (correction reference area), and
Producing a proximity effect correction mask provided with an opening having an area proportional to (corresponding to) the correction reference area, and excessively correcting and exposing the pattern transfer mask using the proximity effect correction mask. I do.

In this aspect, the correction dose is determined in consideration of the influence of backscattered electrons entering the wafer area to be calculated from the peripheral region. That is, in order to improve the calculation accuracy of the correction exposure aperture, the influence of not only the above-mentioned area but also the peripheral part of the area is efficiently calculated.

Here, as an example of the value of each constant, K ₂ is set to 0.
1 to 0.7, K ₃ is 0.05 to 0.35, K ₄ 0.2
０．５0.5. The concept of selecting this value is as follows. K ₂ : Decrease when the backscattering coefficient of the underlying pattern is close to Si, and increase when the backscattering coefficient of the underlying pattern is large. K ₃ : Increase when the backscattering coefficient of the underlying pattern is large or when the peripheral region is reduced, and decrease when the backscattering coefficient of the underlying pattern is close to Si or when the peripheral region is widened. K ₄ : Increase when the peripheral area is reduced, and decrease when the peripheral area is wide.

Various numerical processes such as determining the opening area of the correction mask by multiplying the entire calculation area by a correction coefficient or a function can also be performed. Alternatively, the test correction exposure may be actually performed with a different dose, and the correction dose may be measured at what correction dose the proximity effect is most appropriately corrected. Further, the correction dose may be determined by computer simulation.

The basic principle of the present invention will be described with reference to FIG. FIG. 1A is a plan view of a certain pattern (regular pattern) to be formed on a wafer. The pattern consists of seven lines 1-1 to 7 to be exposed. Each line has the same length and width and is arranged in parallel at equal intervals. FIG.
FIG. 1B is a schematic graph showing the distribution of the dose given to the resist when the pattern of FIG. 1A is transferred and exposed and the proximity effect correction is not performed, as viewed along the x-axis in FIG. is there. Because of the forward scatter of electrons in the resist,
The dose distributions 2-1 to 7 of each pattern are not rectangular but Gaussian. The background dose 3 is high in the central part where the density of the line pattern is high, and low in the peripheral part where the pattern density is low.

FIG. 1C is a graph showing a dose distribution given to the resist when the correction exposure is performed. A solid line 4 indicates a conventional proximity effect correction exposure dose, and the dose 4 indicates a total dose added to the dose of FIG. At the total dose 5 as a result of the correction exposure, the width of each of the pattern lines 7-1 to 7 at the threshold value 6 of the resist is equal, so that a pattern having the same width is formed.

The dotted line in FIG. 1C shows the dose given to the resist when the correction exposure is performed with a 1.5 times excess dose. Dotted line 8 shows the dose distribution of the correction exposure, and dotted line 9 shows the total dose with the pattern transfer exposure dose. In the total dose 9 (showing the distribution of the line pattern 1 in the width direction) as a result of the overcorrection exposure, the width of each of the pattern lines 9-1 to 7 at the resist threshold value 6 becomes almost a regular line pattern at the center. Equally, the line width is large in the peripheral portion.
Similarly, in the longitudinal direction of the pattern, since the correction exposure dose at the peripheral portion is high, each pattern has the minimum size at the central portion as shown in FIG. 1D, and the line width gradually increases as approaching the edge. Become.

When a pattern transfer mask having the pattern shown in FIG. 1D is used to transfer a pattern onto the wafer with an electron beam, a pattern (regular pattern) having the same line width as shown in FIG. Formed on top. That is, when the pattern transfer mask is formed by the electron beam exposure technique, correction for the proximity effect at the time of the subsequent transfer is also incorporated in advance (additionally, excessive correction is performed).

Here, it is a necessary condition that proper correction can be performed so that the pattern thickness at the time of mask fabrication and the pattern narrowing at the time of electron beam transfer onto a wafer match. For this purpose, it is desirable that the slope Δθ (FIG. 1B) at the pattern edge of the dose distribution at the time of mask pattern drawing be (1 / reduction rate) times the slope of the dose distribution at the time of pattern transfer. The slope Δθ of the dose distribution is determined by the square root of the sum of squares of the beam resolution of the pattern drawing apparatus and the equivalent blur of the beam due to the scattering (forward scattering) of the electron beam in the resist.

On the other hand, the slope of the dose distribution at the time of pattern transfer generally has almost no forward scattering when an electron beam having a high accelerating voltage is used, and is almost determined by the beam resolution. Therefore, in the case of 縮小 reduction, the value of Δθ may be four times as large as Δθ of the transfer device. Therefore, assuming that the beam resolution of the electron beam transfer device is Δ, the most appropriate correction can be made if the beam resolution of the mask pattern drawing device is M · Δ. However, even if it is not exactly M · Δ, the same correction can be performed by controlling the beam resolution of the mask pattern drawing apparatus to a value lower than the resolution of the transfer apparatus and controlling the degree of overcorrection exposure.

FIG. 2 is a flow chart of a method of fabricating a pattern transfer mask incorporating the proximity effect correction method according to one embodiment of the present invention and a wafer transfer exposure using the same mask. First, a resist-coated mask substrate is prepared (3.
1) A mask pattern is drawn on the resist of this substrate by electron beam drawing (32).

Next, using a proximity effect correction mask (34, a preparation method described later) prepared separately (34), the pattern transfer mask is corrected and exposed (33). At this time, the pattern of the correction mask is corrected so that the pattern formed on the mask is corrected (excessively corrected) by adding the proximity effect at the time of electron beam transfer to the subsequent wafer. And the exposure amount. Then, develop (3
5) After etching (36), a pattern transfer mask incorporating the proximity effect correction weave is completed (37). Then, the electron beam is transferred onto the wafer using the pattern transfer mask (38). With this single transfer exposure, exposure including proximity effect correction during mask drawing and electron beam transfer can be performed.

FIG. 3 is a diagram for explaining a method of forming a proximity effect correction mask used in one embodiment of the present invention.
(A) is a plan view of a pattern, and (b) shows a correction reference area of each area. Assuming that the accelerating voltage of the electron beam at the time of transfer is 100 kV, the spread width of the backscattered electrons is 6
It was set to 0 μm. Then, the mask was divided into 5 μm × 5 μm areas indicated by dashed lines. In this pattern, there is a large rectangular pattern 63 on the right side, and a high-density linear pattern 61 on the left side. Also, the 50 nm M
The base patterns 65 and 67 of o (a strip extending vertically) are formed. The area of the non-exposed area in each area is 51, 54
In the area indicated by, the area of the non-exposed portion is 0. 55, 5
In the areas indicated by 6 and 57, the area of the non-exposed portion is the maximum.

In each area, S ₁ : the area of a region without a base pattern (for example, a hatched portion falling to the lower right in the figure), and S ₂ : the area of a non-exposed portion (a hatched portion to the lower left in the figure) are calculated for all the areas. , (S ₁ K ₁ + S ₂ ) were calculated. Here K ₁ is set to 0.5. A value of 0.6 was obtained in the area (52 and 53 in the figure) including the pattern of the minimum line width and having the minimum value of (S ₁ K ₁ + S ₂ ). (S _{1 in} each area
The value obtained by subtracting 0.6 from the value of (K ₁ + S ₂ ) is shown in (b). For example, in the areas 51 and 54, it becomes 0.2, and when 0.6 is subtracted, it becomes -0.4. Producing a proximity effect correction mask in which an opening having a size proportional to such a number is provided in the center of each area, and using this mask, a beam having a blur that is about the extent of backscattered electrons spreading during transfer is used for transfer. Correction exposure was performed on the mask.

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, according to the method disclosed in Japanese Patent Application Laid-Open No. 5-175110, a correction mask in which holes having areas proportional to the values shown in FIG. Exposure,
Five types of pattern transfer masks were obtained. Electron beam transfer was performed using these five types of masks, and from the degree of correction of the proximity effect of the obtained five types of patterns, the optimum intensity of the correction exposure at the time of preparing the pattern transfer mask was obtained.

Next, a description will be given of an embodiment in which the influence of backscattered electrons from the periphery of each area is taken into account when calculating the opening of the correction exposure mask. FIG. 4 shows a peripheral area having a spread of about half the spread of the backscattered electrons of the beam at the time of transfer outside the area, and shows a more accurate opening area of the proximity effect correction mask than the case of FIG. FIG.

In this semiconductor device, two tungsten base patterns 85 and 87 extending on the left and right sides of the drawing on the Si wafer as shown by dense hatching downward to the right.
Are formed. Tungsten pattern thickness is 10
0 nm. Other parts are Si layers. in addition,
The two patterns 81 and 8 extending upward and downward in the figure, as shown by rough hatching in the lower left, which are the exposure patterns this time.
Form 3

Hereinafter, a method of determining the width of the correction exposure opening of the correction mask will be described. Base W pattern 85, 8
The radius of the backscattering spread of electrons from 7 is 3R _bm ,
In the present embodiment, the range of the radius R _bm up to 1/3 of the range is set as a correction target.

The area of the opening for correction exposure in each area is calculated by the following method. A circle having a radius of R _bm is considered from the center of the area aceg, and the following area or area ratio is obtained inside the circle. Note that the consecutive letters of the alphabet indicate the area of the drawing surrounded by the dots of the alphabet shown in the drawing. Area S ₁ : addha (Area of area where W base pattern does not exist in area) Area S ₂ : bcefb (Area of non-exposed area in area) Area ratio R ₃ : Inside and area of the circle Area ratio of the portion where the W base pattern does not exist outside = (ABCDA + OE)
FGNO + MHIJKLM-abcdha) ÷ (πR _bm
²⁻ acega) Area ratio R ₄ : Area ratio of non-exposed portion inside the circle and outside the area = (PLMMNOP + BCJKB + FGHIF−b)
cdefb) ÷ (πR _bm ² −acega) S = K ₂ S ₁ + S ₂ + K ₃ × R ₃ × acega + K ₄ ×
Calculate R ₄ × acega. Next, the value of S in an area where S has the minimum value in an area including the non-exposed portion having the minimum line width is defined as S ′ _min . SS ′ _min was _defined as the area of the correction exposure opening in each area of the correction mask.

When a pattern to be transferred is divided into small areas (main field and sub-field) on a pattern transfer mask, and a non-pattern area is provided between the small areas, the peripheral area of each of the above-mentioned areas must be divided. , A region when the non-pattern region is removed. As a result, an appropriate opening area of the proximity effect correction mask can be set.

[0032]

As is apparent from the above description, according to the present invention, the following effects can be obtained as compared with the conventional method of correcting the proximity effect by distorting the pattern size. A huge calculation for changing the pattern size is not required. It is possible to prevent an increase in the number of rectangles during pattern formation (in the case of a variable shaped beam) and the occurrence of oblique lines. It is possible to correct a difference in beam resolution between pattern formation and transfer and a difference in pattern magnification. Correction can be performed in consideration of the difference in the spread of backscattered electrons during pattern formation and transfer.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the basic principle of the present invention.

FIG. 2 is a flowchart of a process for producing a pattern transfer mask incorporating a proximity effect correction method according to an embodiment of the present invention and wafer transfer exposure using the same mask.

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

FIG. 4 takes into account a peripheral area outside the area which has a spread of about half that of the backscattered electrons of the beam during transfer,
FIG. 4 is an explanatory diagram of a method of obtaining an opening area with higher accuracy than the case of FIG. 3.

[Explanation of symbols]

1 Line Pattern 2 Dose 3 Background Dose 4 Proximity Effect Correction Exposure Dose 5 Total Dose 6 Threshold 7 Line Pattern Dose 8 Overcorrection Exposure Dose 9 Line Pattern Dose 10 Line Pattern on Pattern Transfer Mask 51-57 Area 61 Line Pattern 63 Rectangular pattern 65, 67 Base pattern 81, 83 Pattern 85, 87 Base pattern

Claims (7)

[Claims] When performing electron beam transfer exposure using a pattern transfer mask in which proximity effect correction has been incorporated in advance by excessively performing proximity effect correction, a resolution lower or better than the beam resolution of the transfer exposure. A proximity effect correction method, wherein a pattern of the mask is formed by a pattern writing apparatus having a low acceleration voltage. 2. The method according to claim 1, wherein the beam resolution at the time of pattern formation of the mask is such that the beam resolution is deteriorated on the lower surface of the resist as a result of scattering of the electron beam in the resist during the transfer exposure. Item 6. The proximity effect correction method according to Item 1. 3. The method according to claim 1, wherein the reduction ratio of the transfer exposure is 1 / M, and the beam resolution of the exposure is Δ, and the beam resolution at the time of pattern formation of the pattern transfer mask is approximately M · Δ. The proximity effect correction method according to claim 1. 4. When forming a pattern this time by superimposing a base pattern made of a material having a backscattering electron coefficient different from that of a substrate material on an already formed wafer, the pattern itself is manufactured through an electron beam exposure step. Correcting the proximity effect when performing electron beam reduction transfer exposure on a wafer using a pattern transfer mask; wherein the pattern transfer mask area is reduced when the transfer reduction ratio is doubled. The area is divided into areas having dimensions sufficiently smaller than the spread width of the backscattered electrons at the time of transfer, and in each area, the area S ₁ of the area without the base pattern and the area S ₂ of the non-exposed part this time are calculated, and (K ₁ The value of (S ₁ + S ₂ ) is calculated for all areas (K ₁
Is a coefficient), the above-mentioned value in the area including the non-exposed part having the minimum line width and the above-mentioned area where the above-mentioned value is the minimum is defined as S _min, and (K ₁ S ₁ + S ₂ ) −S _min = correction reference area Calculating a proximity effect correction mask provided with an opening having an area corresponding to the correction reference area, and using the proximity effect correction mask before or after the electron beam exposure step of the pattern transfer mask. A proximity effect correction method, wherein the pattern transfer mask is subjected to excessive correction exposure. 5. The method according to claim 1, wherein the degree of overcorrection exposure of the pattern transfer mask is determined by performing a transfer experiment using an actually manufactured mask with a variable dose during correction exposure or by computer simulation. The proximity effect correction method according to claim 4, wherein 6. When forming a pattern this time by superimposing a base pattern made of a material having a backscattering electron coefficient different from that of a substrate material on an already formed wafer, the pattern itself is produced through an electron beam exposure step. Correcting the proximity effect when performing electron beam reduction transfer exposure on a wafer using a pattern transfer mask; wherein the pattern transfer mask area is reduced when the transfer reduction ratio is doubled. In addition to dividing into areas with dimensions sufficiently smaller than the spread width of the backscattered electrons at the time of transfer, a surrounding area is set around each area except for a circle with a radius smaller than the spread radius of the backscattered electrons. in each zone, the area S ₁ of the region with no underlying pattern, the area S ₂ of this non-exposed portion, the area ratio of no base pattern in the peripheral region region R ₃ and the area ratio R of the non-exposed portion in the peripheral region
₄ is calculated, and the value of (K ₂ S ₁ + S ₂ + S ₀ R ₃ K ₃ + S ₀ R ₄ K ₄ ) is calculated in each area (K ₂ , K ₃ , K ₄ are coefficients, and S ₀ is the above area) The value of the area including the non-exposed portion having the minimum line width and the area where the above value is minimum is defined as S ′ _min, and (K ₂ S ₁ + S ₂ + S ₀ R ₃ K ₃ + S) ₀ R ₄ K
_4- S ' _min ) (correction reference area), and a proximity effect correction mask having an opening having an area corresponding to the correction reference area is manufactured. A proximity effect correction method, which comprises subjecting a mask to excessive correction exposure. 7. When a pattern to be transferred is divided into small areas (main field of view and sub-field of view) on a pattern transfer mask and a non-pattern area is provided between each of the small areas, a peripheral area of each of the areas is defined as 7. The proximity effect correction method according to claim 6, wherein the non-pattern area is set as an area obtained by removing the non-pattern area.