JP2000114169A - Pattern-forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve dimentional accuracy of a pattern by containing a process drawing a pattern only in the outside of a region to be exposed where a resist film is exposed, at scanning with an electron beam in an alignment mark detecting process, in an electron beam exposure process. SOLUTION: To a resist film, which is formed on a substrate and becomes an object of pattern formation, only a region where a distance from a position 32 which is scanned with an electron beam is irradiated with an electron beam in order to detect a mark exceeds the maximum exposure radius rx. That is, a pattern is drawn by having an electron beam irradiated only in the outside of a region 33 to be exposed, where a resist film is exposed with a third exposure light source, when scanning with an electron beam is performed in order to detect an alignment mark 31. Then the resist film subjected to electron beam has been irradiation is developed, an unwanted part of the resist film is selectively removed, and a resist pattern is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pattern forming method using an electron beam exposure method.

[0002]

2. Description of the Related Art An electron beam exposure method is a method of drawing or transferring a desired pattern by irradiating a resist film formed on a substrate and having a high sensitivity to an electron beam with an electron beam at a high speed. It is.

[0003] When the electron beam exposure method is used, 0.1 μm
A pattern having the following width dimensions can be drawn with high resolution, and highly accurate alignment and overlay exposure can be performed. For this reason, the electron beam exposure method has conventionally been used for ultrafine processing such as pattern formation of a photomask or the like or wiring formation of a semiconductor device.

In the electron beam exposure method, electrons incident on a resist film formed on a substrate collide with atoms such as carbon having a small atomic weight constituting the resist film and scatter forward, and after passing through the resist film, The electrons incident on the substrate collide with the atoms of the substrate, such as silicon, having a large atomic weight and are back-scattered. As a result, the periphery of the electron beam irradiation region in the resist film is exposed by the forward-scattered or back-scattered electrons, thereby causing a proximity effect that the dimensional accuracy of the pattern is deteriorated.

Therefore, in order to improve the dimensional accuracy of a pattern in the electron beam exposure method, the proximity effect correction is performed by adjusting the exposure amount of the electron beam in consideration of the influence of the proximity effect before irradiating the electron beam. There is a need.

Hereinafter, the above-mentioned forward scattering and back scattering, and
The conventional proximity effect correction method shown in J. Appl. Phys., Vol. 50, No. 6, June 1979, pp.
This will be described with reference to (a) and (b).

FIG. 5A shows one track of an electron which is scattered forward in the resist film and then scattered back in the substrate.

In FIG. 5A, 1 is a substrate, 2 is a resist film formed on the substrate 1, 3 is an incident electron incident on the resist film 2, and 4 is a forward scattered electron which is scattered forward in the resist film 2. 5 indicates the trace of backscattered electrons scattered backward in the substrate 1, 6 indicates the spread of the trace of forward scattered electrons in the resist film 2, and 7 indicates the spread of the trace of backscattered electrons in the resist film 2.

FIG. 5B shows the distribution of the spread 6 of the track of forward scattered electrons and the spread 7 of the track of backscattered electrons.

In FIG. 5B, reference numeral 8 denotes a first Gaussian distribution indicating the distribution of the track spread 6 of the forward scattered electrons, 9 denotes a second Gaussian distribution indicating the distribution of the track spread 7 of the backscattered electrons, beta _f is a forward scattering radius is the standard deviation of the first Gaussian distribution 8, beta _b is the maximum value of the spread 7 of track of the second back scattering radius is the standard deviation of the Gaussian 9, r _b is backscattered electrons It shows a certain backscattered electron arrival radius. In this case, the distance from the incident point of the incident electron 3 in the resist film 2 is at a position beyond the backscattered electrons reach the radius r _b, never backscattered electrons reach.

[0011] forward scattering radius beta _f, the magnitude of backscatter radius beta _b and backscattered electrons reach the radius r _b, the acceleration voltage of the electron beam, but varies according to the material or the like of the material or the resist film 2 of the substrate 1, When a silicon substrate is used as the substrate 1 and a normal resist having a carbon skeleton is used as the resist film 2 and the resist film 2 is irradiated with an electron beam having an acceleration voltage of 70 KV, the forward scattering radius β _f is about 0.0
5 μm, the backscattering radius β _b is about 20 μm,
Backscattered electrons reach the radius r _b is about 35 [mu] m.

When the resist film 2 is irradiated with an electron beam,
Since the energy of the forward scattered electrons and the back scattered electrons is absorbed by the resist film 2, the intensity distribution of the energy absorbed by the resist film 2 around the incident point of the incident electrons 3, that is, the absorption energy intensity distribution is The first absorption energy intensity distribution, which is the intensity distribution centered on the incident point of the incident electrons 3 of the energy of the forward scattered electrons absorbed by the resist film 2, and the incidence of the incident electrons 3 of the energy of the backscattered electrons absorbed by the resist film 2 The second is the intensity distribution centered on the point
With the absorbed energy intensity distribution of

The first distribution of the intensity of the absorbed energy due to the forward scattered electrons can be approximated to a first Gaussian distribution 8 having a standard deviation of the forward scattering radius β _f shown in FIG. second absorption energy intensity distribution by electrons can be approximated to the second Gaussian distribution 9, backscattering radius beta _b standard deviation shown in Figure 5 (b).

The intensity of the energy of the forward scattered electrons absorbed by the incident point of the incident electrons 3 in the resist film 2 is as follows:
This is several hundred times the energy intensity of the backscattered electrons 5 absorbed by the incident point of the incident electrons 3 on the resist film 2.

The conventional proximity effect correction method includes a forward scattering radius β _f and a back scattering radius β _b , a first absorption energy intensity distribution due to forward scattered electrons, and a second absorption energy intensity due to back scattered electrons by experiments or simulations. A step of obtaining a distribution or the like, and approximating the first absorbed energy intensity distribution to a first Gaussian distribution 8 having a forward scattering radius β _f as a standard deviation, and converting the second absorbed energy intensity distribution to a back scattering radius β _b . A step of approximating the second Gaussian distribution 9 as a standard deviation, a function representing the sum of the approximated first absorbed energy intensity distribution and the approximated second absorbed energy intensity distribution, and an arbitrary function of the resist film 2 Is convolved with a predetermined value of the exposure amount at the position, that is, a function representing the exposure pattern, so that the energy accumulated at an arbitrary position of the resist film 2 is obtained. And a step of correcting a function representing an exposure pattern so that the stored energy intensity distribution becomes a desired distribution. The proximity effect correction corrects the electron beam. After adjusting the exposure amount, a pattern is drawn by irradiating the resist film 2 with an electron beam, and thereafter, the unnecessary portion of the resist film 2 is selectively developed by developing the resist film 2 irradiated with the electron beam. Removal forms a resist pattern.

Incidentally, in order to improve the accuracy of correction in the conventional proximity effect correction method, the proximity effect is taken into consideration by considering the effect of secondary electrons generated when electrons incident on the substrate 1 collide with atoms constituting the substrate 1. Effect correction may be performed.
However, since the secondary electrons are relatively slow and the trace of the secondary electrons in the resist film 2 spreads out on the order of several hundredths of the backscattering radius β _b , the secondary electrons absorbed by the resist film 2 Even if the intensity distribution centered on the incident point of the incident electrons 3 of energy is considered, the accuracy of the proximity effect correction will not be significantly improved.

Many of the conventionally proposed proximity effect correction methods relate to an approximation method or the like used for calculating the convolution integral at a higher speed, as well as forward scattered electrons and backward scattered electrons in electron beam exposure. It is assumed that the resist film 2 is exposed by scattered electrons.

[0018]

The electron beam exposure method using the conventional proximity effect correction method has been used when the electron beam acceleration voltage is 50 KV or less, but the resolution of the electron beam exposure method will be increased in the future. In order to improve the acceleration, the acceleration voltage of the electron beam needs to be 50 KV or more.

However, in the conventional electron beam exposure method using the proximity effect correction method, the acceleration voltage of the electron beam is set to 50K.
When the voltage is V or more, the accuracy of the proximity effect correction deteriorates with an increase in the acceleration voltage, so that there is a problem that the dimensional accuracy of the pattern deteriorates.

In view of the above, according to the present invention, the acceleration voltage is 50K.
In a pattern forming method using electron beam exposure of V or more, an object is to improve the dimensional accuracy of a pattern by improving the accuracy of proximity effect correction.

[0021]

SUMMARY OF THE INVENTION The present inventor has found that in the electron beam exposure method using the conventional proximity effect correction method, when the acceleration voltage of the electron beam is set to 50 KV or more, the accuracy of the proximity effect correction deteriorates. In order to investigate the cause of the deterioration of the dimensional accuracy of the pattern, the resist film was subjected to electron beam exposure using the line and space pattern shown in FIG.

In FIG. 6, L is a line portion exposed by the electron beam (hatched portion in FIG. 6), S is a space portion between the line portions L, s is an interline distance which is a distance between the line portions L, β _b backscatter radius, is r _b represents the backscattered electrons reach radius. Incidentally, the Monte Carlo simulation backscattering radius beta _b and backscattered electrons reach the radius r _b is as reported conventionally [K. Murata, Electron Beam Interactio
n With Solids, pp.311-329, SEM, Inc., AMF O'Hare (Ch
icago), IL 60666, USA].

As shown in FIG.
The area with the pace pattern is A₁From A_nUp to vertical
Is set to In addition, the distance s between the lines is directed rightward.
Once s = 2β_b, 2 (β_b+ △ β_b),···like
It is set to gradually increase and the final
(Right end) distance s between lines is s> 2r_bSet to be
Is defined. Also, all the line parts in one area
L is exposed at the same exposure amount,
Amount is area A₁In D₁, Area A_TwoIn
D_Two, ..., area A_nIn D_nIs set to
And, for example, D_n= D₀eⁿ△^D, D_n= ΑⁿD₀or
Is D_n= D₀+ N △ D, etc.₁ To D_n
It is set to gradually increase until.

FIG. 7 shows how the inter-line distance s changes in the line-and-space pattern shown in FIG. 6 and how the back-scattered electron reaching area, which is the area where the back-scattered electrons can reach, in the resist film. (A) ~
This will be described with reference to FIG. 7 (a) to 7 (c), the backscattered electron reaching region is indicated by a thick line.

As shown in FIG. 7 (a) and (b), if the line spacing s is less than twice the back-scattered electrons reach the radius r _b, the rear when irradiated with electron beam in the line portion L The scattered electron reach regions overlap. However, as shown in FIG. 7 (c), the line spacing s is backscattered electrons reach the radius r _b
When the electron beam is applied to the line portion L, the backscattered electron reaching regions do not overlap each other, so that the center of the space portion S of the resist film is not exposed by the backscattered electrons. Therefore, when the line spacing s is greater than twice the back-scattered electrons reach the radius r _b,
When the center of the space S of the resist film is exposed,
It can be assumed that the cause is an effect of the third exposure source other than the forward scattered electrons or the back scattered electrons.

The present inventor first uses the line and space pattern shown in FIG. 6 to apply an accelerating voltage of 70 to only the line portion L of the resist film formed on the silicon substrate.
An electron beam of kV was applied while changing the exposure amount. Threshold sensitivity about 5μC for resist film
/ Cm ² of a negative electron beam resist NEB-22 manufactured by Sumitomo Chemical Co., Ltd. on a silicon substrate.
One coated at 5 μm was used.

Next, after developing the resist film irradiated with the electron beam, the maximum value of the line-to-line distance s at which the center of the space S of the resist film starts to remain is measured. When the maximum exposure radius r _X was determined by dividing the maximum value of s by 2, it was about 70 μm.
Meanwhile, approximately the radius of the area forward scattered electrons and backscattered electrons only by the resist film that is the subject of a conventional proximity effect correction method is exposed equally to the backscattered electron reaches the radius r _b 35
μm.

Accordingly, it has been found that when electron beam exposure at a high accelerating voltage is used, the radius of the region where the resist film is exposed is about twice as large as that assumed in the conventional proximity effect correction method.

In the future, electron beam exposure at a high accelerating voltage is expected to form a finer pattern. In this case, it is necessary to perform the proximity effect correction in consideration of the effect of exposing the resist film by the third exposure source other than the forward scattered electrons or the back scattered electrons.

The present inventor has further studied the third exposure source. As a result, it was found that an X-ray or the like generated from inside the substrate by electrons incident on the substrate was assumed as the third exposure source.

Hereinafter, the reason why the above-mentioned X-ray is assumed as the third exposure source will be described.

Since the electrons incident on the substrate excite the atoms constituting the substrate, the excited atoms emit characteristic X-rays, and the electrons incident on the substrate are scattered by the nuclei of the atoms constituting the substrate. Therefore, continuous X-rays are emitted from the scattered electrons.

In order to improve the resolution of the electron beam exposure method, it is necessary to increase the acceleration voltage of the electron beam. On the other hand, it is known that the X-ray intensity increases as the acceleration voltage of the electron beam increases. Eugene P. B
ertim, Introduction to X-Ray Spectrometric Analysi
s, Plenum Press].

Further, since X-rays easily transmitted through the substrate as compared to electron, with distance from the irradiation point of the electron beam in the resist film to reach the X-ray to a point beyond the back-scattered electrons reach the radius r _b In addition, as the acceleration voltage of the electron beam increases, the collision cross section where electrons interact with the constituent atoms of the resist film to cause a chemical reaction decreases, and the sensitivity of the resist to the electron beam decreases. Therefore, when an electron beam with a high accelerating voltage is used, the effect of exposure of the resist film by X-rays cannot be ignored, so that the conventional method presumes that the resist film is exposed only by forward scattered electrons and back scattered electrons. It is considered that the accuracy of the proximity effect correction method deteriorates.

In order to improve the throughput of the electron beam exposure method, it is necessary to increase the sensitivity of the resist. On the other hand, as the resist becomes more sensitive to electron beams, it becomes more sensitive to X-rays. become. Therefore, when using an electron beam with a high acceleration voltage together with a highly sensitive resist,
The dimensional accuracy of the pattern formed by the electron beam exposure method using the conventional proximity effect correction method is further deteriorated.

Therefore, when an electron beam with a high acceleration voltage is used, it is necessary to perform proximity effect correction in consideration of the effect of exposing the resist film with X-rays.

The present invention has been made based on the above findings. More specifically, the first pattern forming method according to the present invention provides a method of forming a resist on a film to be processed formed on a substrate. A resist film deposition step of depositing a film, a registration mark detection step of scanning an electron beam to detect a registration mark formed on a substrate, and drawing a pattern by irradiating the resist film with an electron beam. An electron beam exposing step, and a pattern forming step of developing a resist film irradiated with the electron beam to form a resist pattern. The electron beam exposing step scans the electron beam in the alignment mark detecting step. A step of drawing a pattern only in a region outside a region to be exposed to which the resist film is exposed.

According to the first pattern forming method of the present invention, when the electron beam exposure step scans the electron beam in the alignment mark detection step, the pattern is formed only in the area outside the exposure area where the resist film is exposed. Since the drawing step is included, it is possible to prevent the resist film from being exposed when the electron beam is scanned in the alignment mark detecting step, thereby preventing the dimensional accuracy of the pattern from deteriorating.

The second pattern forming method according to the present invention comprises:
A resist film depositing step of depositing a resist film on a film to be processed formed on a substrate; an alignment mark detecting step of scanning an electron beam to detect an alignment mark formed on the substrate; An electron beam exposure step of drawing a pattern by irradiating the resist film with a resist pattern, and a pattern forming step of developing the resist film irradiated with the electron beam to form a resist pattern. Sets the exposure amount of the electron beam in the exposed region where the resist film is exposed when scanning the electron beam in the alignment mark detection step, smaller than the exposure amount of the electron beam in the region outside the exposed region. It is characterized by including a step.

According to the second pattern forming method of the present invention, when the electron beam exposure step scans the electron beam in the alignment mark detection step, the exposure amount of the electron beam in the exposed area where the resist film is exposed is In order to include a step of setting the exposure amount of the electron beam in the region outside the exposure region to be smaller than the total exposure amount of the electron beam in the exposure region, the exposure amount of the electron beam in the region outside the exposure region Can be about the same.

In the first or second pattern forming method of the present invention, the resist film is made of a negative resist, and the exposed area has a line-to-line distance, which is the distance between the line portions.
From the value of not more than twice the backscattering radius, which is the standard deviation of the Gaussian distribution representing the spread of the backscattered electrons in the resist film, to twice the backscattered electron arrival radius, which is the maximum value of the backscattered electrons. The electron beam is applied to a plurality of line groups of the test resist film having the same specifications as the resist film while changing the exposure amount. When the maximum exposure radius is set to 1/2 of the maximum value of the distance between the lines at which the center of the space portion between the line portions of the test resist film begins to develop, the electron beam is detected in the alignment mark detection step. It is preferable that the distance from the scanning position is within the maximum exposure radius.

In the first or second pattern forming method of the present invention, the resist film is made of a positive resist, and the region to be exposed has a line-to-line distance that is a distance between line portions.
From the value of not more than twice the backscattering radius, which is the standard deviation of the Gaussian distribution representing the spread of the backscattered electrons in the resist film, to twice the backscattered electron arrival radius, which is the maximum value of the backscattered electrons. The electron beam is applied to a plurality of line groups of the test resist film having the same specifications as the resist film while changing the exposure amount. When the maximum exposure radius is set to 1/2 of the maximum value of the distance between the lines at which the center of the space between the line portions of the test resist film begins to disappear after development, the electron beam is used in the alignment mark detection step. It is preferable that the distance from the scanning position is within the maximum exposure radius.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, a pattern forming method using an electron beam exposure method according to a first embodiment of the present invention will be described with reference to FIG.
In the first embodiment, the third resist absorbed in the resist film by irradiating the test resist film with the same specifications as the resist film to be patterned with the electron beam.
A third absorption energy intensity distribution, which is an intensity distribution centered on the electron beam irradiation point of the energy of the exposure source, is obtained, and the result is used for proximity effect correction.

In FIG. 1, reference numeral 11 denotes a first normalized absorption energy intensity distribution by forward scattered electrons, 12 denotes a second normalized absorption energy intensity distribution by back scattered electrons, and 13 denotes a third exposure source. 3 shows a third normalized absorbed energy intensity distribution according to the present invention.

[0045] First, by experiment or simulation or the like are conventionally known, is a forward scattering electrons of energy absorbed irradiation point of the electron beam in the backward scattering radius beta _b, backscattered electrons reach the radius r _b and the resist film with obtaining the forward scattering energy E _f, backscatter is absorbed by the first absorbent energy intensity distribution and the resist film is an intensity distribution centered on the irradiation point of the electron beam energy of the forward scattered electrons absorbed in the resist film A second absorption energy intensity distribution, which is an intensity distribution centered on the electron beam irradiation point of the electron energy, is obtained.

Next, using a line and space pattern as shown in FIG. 6, for example, an electron beam is applied to a line portion L of a test resist film having the same specification as the resist film to be formed. Irradiation while changing.

[0047] Specifically, as also shown in FIG. 6 and means for solving the problems, the region having the same line-and-space pattern is set in the vertical direction from A ₁ to A _n. The line spacing s is to the right direction _{s = 2β b, 2 (β} b + △ β b), with are set so as to gradually increase as ..., final (rightmost)
Line spacing s of is set to be s> 2r _b. Also, with all of the line portion L in one region are exposed at the same exposure amount, the exposure amount for each area D ₁ in the area A _1, in the area A ₂ D _2, · · ·
Together it is set to D _n in the region A _n, for example, ^{_{D n = D 0 e n △}} D, D n = α n D 0 or D _n = D ₀ +
It is set so as to gradually increase from D ₁ to D _n according to equation such as n △ D.

Next, when a negative resist is used as the test resist film, the first exposure amount is the minimum exposure amount at which the center of the line portion L of the test resist film begins to develop by developing the test resist film. the second exposure amount is the minimum amount of exposure which the center starts to remaining of the space portion S of the exposure dose D _f and testing resist film, obtaining the function D (s) to the line spacing s variable.

When a positive resist is used as the test resist film, the first exposure, which is the minimum exposure amount at which the center of the line portion L of the test resist film begins to disappear by developing the test resist film. the second exposure amount is the minimum amount of exposure which the center begins to disappearance of the space portion S of the amount D _f and testing resist film, obtaining the function D (s) to the line spacing s variable.

At this time, as shown in FIG. 1, the vertical axis is log (D _f / D (s)) indicating the absorbed energy intensity standardized so that the maximum value is 0 (= log 1), and the horizontal axis is The first, second, and third normalized absorption energy intensity distributions 11, 12, and 13 can be obtained by plotting s / 2 indicating the distance from the electron beam incident point. The distance s / 2 from the electron beam incident point
There is normalized absorbed energy intensity distribution between 0~β _b, the first absorption energy intensity distribution and the second absorption energy intensity distribution that is calculated in advance the maximum value 0 (= log
It is standardized to satisfy 1).

Using a line and space pattern shown in FIG. 6, a threshold sensitivity of about 5 μm was formed on a silicon substrate.
When a resist film formed by applying a 0.5 μm-thick negative electron beam resist NEB-22 manufactured by Sumitomo Chemical Co., Ltd. having C / cm ² was irradiated with an electron beam having an acceleration voltage of 70 kV, A normalized absorbed energy intensity distribution as shown in FIG. 2 was obtained. In FIG. 2, a is a first normalized absorbed energy intensity distribution due to forward scattered electrons, b is a second normalized absorbed energy intensity distribution due to back scattered electrons, and c is a third normalized absorbed energy intensity distribution due to a third exposure source.
2 shows a normalized absorption energy intensity distribution of the above.

Next, the third absorption energy intensity distribution, which is the intensity distribution centered on the irradiation point of the electron beam at the energy of the third exposure source absorbed by the resist film, is represented by (D _f / D
(S)) × E _f .

In this embodiment, s / 2 indicating the distance from the electron beam incident point is the backscattered electron arrival radius r.
_A third absorption energy intensity distribution is obtained in a region exceeding _b , that is, in a region outside the backscattered electron reaching region which is a region where the backscattered electrons can reach in the resist film.

Next, after approximating the first, second and third absorption energy intensity distributions to Gaussian distributions respectively, a function representing the sum of the approximated first, second and third absorption energy intensity distributions is obtained. By convoluting and integrating a predetermined value of the exposure amount at an arbitrary position on the resist film to be patterned, that is, a function representing the exposure pattern, energy stored at an arbitrary position on the resist film to be patterned can be obtained. Is calculated, that is, the accumulated energy intensity distribution is calculated, and then the function representing the exposure pattern is corrected so that the accumulated energy intensity distribution becomes a desired distribution.

Next, after adjusting the exposure amount of the electron beam by the above-described proximity effect correction, a pattern is drawn by irradiating the resist film, which is formed on the substrate and which is to be patterned, with the electron beam. Thereafter, by developing the resist film irradiated with the electron beam, unnecessary portions of the resist film are selectively removed to form a resist pattern.

According to the first embodiment, in addition to the first and second absorption energy intensity distributions due to the forward scattered electrons and the back scattered electrons, the third absorption energy intensity distribution due to the third exposure source is used. Since the effect correction is performed, the accuracy of the proximity effect correction can be improved when a highly sensitive resist is irradiated with an electron beam of a high acceleration voltage, so that the dimensional accuracy of the pattern can be improved.

Further, according to the first embodiment, the test resist film having the same specification as the resist film to be patterned is irradiated with the electron beam, so that the third absorption energy by the third exposure source is obtained. Since the intensity distribution is obtained, the third absorption energy intensity distribution can be obtained with high accuracy, so that the accuracy of the proximity effect correction can be further improved.

According to the first embodiment, the sensitivity is 2
The acceleration voltage is 5 for a resist film of 0 μC / cm ² or less.
When irradiating an electron beam of 0 kV or more, the dimensional accuracy of the pattern is remarkably improved as compared with a conventional pattern forming method using an electron beam exposure method.

In the first embodiment, the first absorption energy intensity distribution due to the forward scattered electrons, the second absorption energy intensity distribution due to the back scattered electrons, and the third absorption energy intensity distribution due to the third exposure source. Although used for the proximity effect correction, in addition to the first, second and third absorption energy intensity distributions, the electron beam irradiation causes
A fourth absorption energy intensity distribution, which is an intensity distribution centered on the irradiation point of the electron beam of the energy absorbed by the resist film among the energies of the secondary electrons, may be used for the proximity effect correction.

(Second Embodiment) Hereinafter, a pattern forming method using an electron beam exposure method according to a second embodiment of the present invention will be described with reference to FIG. The second
In the embodiment, the X-ray generated in the substrate by the electron beam is regarded as the third exposure source, and the intensity distribution of the energy of the X-ray absorbed by the resist film around the irradiation point of the electron beam is considered as the center. A third absorption energy intensity distribution is obtained by calculation, and the result is used for proximity effect correction.

FIG. 3 schematically shows one track of scattered electrons incident on the substrate after passing through the resist film and scattered, and one path of X-rays generated in the substrate by the electron beam. .

In FIG. 3, reference numeral 21 denotes a substrate; 22, a resist film; 23, incident electrons incident on the substrate 21 after passing through the resist film 22; 24, tracks of scattered electrons scattered in the substrate 21; , 26 represents the center of X-ray generation. In FIG. 3, l is a first distance from the incident point of the incident electrons 23 on the substrate 21 to the arrival point of the X-ray on the resist film 22, and R is the distance from the X-ray generation center 26 to the resist film 22. A second distance from the X-ray arrival point, d represents a third distance from the surface of the substrate 21 to the X-ray generation center 26, and θ represents a radiation angle of the X-ray.

[0063] First, the Monte Carlo simulation or the like which have been conventionally known, forward scattering radius beta _f, with obtaining a backscattering radius beta _b and backscattered electrons reach the radius r _b, the forward scattered electrons are absorbed in the resist film 22 A first absorption energy intensity distribution, which is an intensity distribution centered on the irradiation point of the electron beam of energy, and a first absorption energy intensity distribution, which is centered on the irradiation point of the electron beam, of the energy of the backscattered electrons absorbed by the resist film 22. 2 is obtained.

Next, the average depth of the scattered electrons is determined from the scattered electron tracks 24 obtained by Monte Carlo simulation or the like. Since X-rays are generated when electrons are scattered in the substrate 21, the third distance d representing the depth of the X-ray generation center 26 is equal to the average depth of the scattered electrons. As described above, when the value of the third distance d is obtained, an arbitrary first distance l
, The value of the second distance R is uniquely determined by using the relational expression of R ² = l ² + d ² .

Next, when irradiating a target having the same specifications as the substrate 21 with an electron beam using the same acceleration voltage applied to the incident electrons 23 incident on the substrate 21, the irradiation of the electron beam per unit current is performed. The intensity distribution I (λ, θ) of X-rays generated by the method is experimentally or theoretically calculated [Ludwig Reimer, Sc
anning Electron Microscopy, Spriger-Verlag, pp158-
169]. Here, λ represents the wavelength of the X-ray, and θ represents the radiation angle of the x-ray. Further, the radiation angle θ is uniquely determined by using a relational expression of tan θ = d / l for an arbitrary value of the first distance l.

Next, the number n of electrons per unit time contained in the electron beam per unit current is obtained by using the relational expression of n = 1 / elementary charge. The intensity distribution of the generated X-rays is obtained as I (λ, θ) / n. At this time, immediately below the incident point of the incident electrons 23 on the substrate 21, the range in which a large amount of X-rays is generated is X
Since the region is considered to be sufficiently narrow compared to the range reached by the rays, the source of X-rays can be regarded as a point light source.
An X-ray point light source having an intensity of (λ, θ) / n
And the substrate 21 just below the incident point of the incident electrons 23
At a position where the depth from the surface is equal to the third distance d, ie, X
It can be assumed that it is located at the line origin 26.

Next, assuming that the transmittance of the conventionally known X-ray of the wavelength λ to the substrate 21 is a (λ),
The intensity of the X-ray when the line reaches the resist film 22 located at the second distance R from the X-ray generation center 26 is calculated as exp (−R / a (λ)) × I (λ , θ) / n × Δλ
Asking. Next, the ratio of the energy that the conventionally-known unit intensity X-rays accumulates in the resist film 22 is expressed by g
As (λ), the intensity at which the resist film 22 is exposed to X-rays having a wavelength λ is represented by g (λ) × exp (−R / a (λ)) × I (λ
, θ) / n × Δλ. Next, by integrating this intensity with respect to the wavelength λ of the X-ray, the resist film 22
The third absorption energy intensity distribution, which is the intensity distribution centered on the irradiation point of the electron beam with the energy of the X-ray absorbed by, is expressed as Σ [g (λ) × exp (−R / a (λ)) × I (λ, θ)
/ N × Δλ].

In the present embodiment, the first distance l
There in a region beyond the backscattered electrons reach the radius r _b, i.e., in the outer region of the back scattered electrons reach the region is a region that can reach the backscattered electrons in the resist film 22, obtains the third absorption energy intensity distribution.

Next, after the first and second absorption energy intensity distributions obtained in advance are approximated to Gaussian distributions, respectively, the approximated first and second absorption energy intensity distributions and third absorption energy intensity distributions are approximated. And a function that represents the sum of
By convolving and integrating the exposure amount at an arbitrary position of the resist film 22, that is, the function representing the exposure pattern,
After calculating the intensity distribution of energy stored at an arbitrary position on the resist film 22, that is, the stored energy intensity distribution,
The function representing the exposure pattern is modified so that the stored energy intensity distribution becomes a desired distribution.

Next, after adjusting the exposure amount of the electron beam by the above-described proximity effect correction, a pattern is drawn by irradiating the resist film 22 formed on the substrate 21 with the electron beam. Is developed to selectively remove unnecessary portions of the resist film 22 to form a resist pattern.

According to the second embodiment, in addition to the first and second absorption energy intensity distributions due to forward scattered electrons and back scattered electrons, the third absorption energy intensity due to X-rays regarded as a third exposure source Since the proximity effect correction is performed using the distribution, the accuracy of the proximity effect correction can be improved when a highly sensitive resist is irradiated with an electron beam of a high accelerating voltage. Can be.

Further, according to the second embodiment, since the third absorbed energy intensity distribution can be obtained by simple numerical calculation, the proximity effect correction can be easily performed.

(Third Embodiment) A pattern forming method using an electron beam exposure method according to a third embodiment of the present invention will be described below with reference to FIG. The third
In the embodiment, the resist film is exposed by a third exposure source as shown in FIG. 4 by irradiating an electron beam to a test resist film having the same specification as the resist film to be patterned. A region to be exposed is obtained, and the result is used for pattern formation in the peripheral portion of the alignment mark.

FIG. 4 is a diagram showing the alignment mark formed on the substrate and its peripheral portion as viewed from directly above the substrate.

In FIG. 4, 31 is an alignment mark,
Numeral 32 denotes a position where an electron beam is scanned for detecting a mark, 3
3 the area to be exposed to the resist film is exposed by the third exposure source, the maximum pattern drawn on the inside of the exposure region 33, the pattern 35 is drawn to the outside of the exposure region 33, r _X 34 Represents the exposure radius. As the alignment mark 31, a step formed by performing etching on the substrate, or a convex mark formed on a substrate made of silicon or the like and having a larger atomic number than silicon or the like, for example, made of tungsten or the like is used. Can be

Although not shown in FIG. 4, a resist film is formed on the substrate together with the alignment mark 31.

[0077] First, the backscattering radius beta _b and backscattered electrons reach the radius r _b by Monte Carlo simulation.

Next, using a line-and-space pattern as shown in FIG. 6, for example, an electron beam is applied to a line portion L of a test resist film having the same specifications as the resist film to be patterned. Irradiation while changing.

[0079] Specifically, as also shown in FIG. 6 and means for solving the problems, the region having the same line-and-space pattern is set in the vertical direction from A ₁ to A _n. The line spacing s is to the right direction _{s = 2β b, 2 (β} b + △ β b), with are set so as to gradually increase as ..., final (rightmost)
Line spacing s of is set to be s> 2r _b. In addition, all the line portions in one area are exposed with the same exposure amount, and the exposure amount for each area is the area A
D ₁ in _1, D ₂ in the area A _2, together with the set to D _n in the ... area A _n, for example, ^{_{D n = D 0 e n △}} D, D n = α n D 0, Or D _n = D ₀
+ Are set so as to gradually increase as the formula n △ D, etc. from D ₁ to D _n.

Next, when a negative resist is used as the test resist film, the test resist film is developed to obtain the maximum value of the line-to-line distance s at which the center of the space S of the test resist film starts to remain. .

When a positive resist is used as the test resist film, the test resist film is developed to measure the maximum value of the line-to-line distance s at which the center of the space S of the test resist film starts to disappear. .

Next, the maximum exposure radius r _X is obtained by dividing the measured maximum value of the line-to-line distance s by two.

Using the line and space pattern shown in FIG. 6, a threshold sensitivity of about 5 μm was formed on a silicon substrate.
An electron beam having an acceleration voltage of 70 kV is applied to a test resist film formed by applying a 0.5 μm-thick negative electron beam resist NEB-22 manufactured by Sumitomo Chemical Co., Ltd. having C / cm ^2. As a result, the maximum exposure radius r _X was determined to be about 70 μm.

Next, as shown in FIG. 4, the distance from the electron beam scanning position 32 for mark detection to the resist film formed on the substrate and subject to pattern formation is the maximum exposure. only in the region beyond the radius r _X, namely the electron beam only in the outer region of the exposure area 33 where the resist film is exposed by the third exposure source when scanning electron beam for detecting the alignment mark 31 The pattern is drawn by irradiation.

Next, by developing the resist film irradiated with the electron beam, unnecessary portions of the resist film are selectively removed to form a resist pattern.

According to the third embodiment, since the pattern is drawn only in the region outside the exposed region 33 where the resist film is exposed by the third exposure source, the electron beam is scanned when detecting the mark. It is possible to prevent the dimensional accuracy of the pattern from deteriorating due to the exposure of the resist film by the third exposure source.

When it is necessary to draw the pattern 34 in the exposed area 33, the exposure amount used to draw the pattern 35 in the area outside the exposed area 33 is smaller
By irradiating the area 33 to be exposed with an electron beam using an exposure amount smaller than the exposure amount on the resist film when the electron beam is scanned for mark detection, the pattern 3 is obtained.
4 is preferably drawn. In this way, the dimensional accuracy of the pattern 34 in the exposed region 33 can be made substantially equal to the dimensional accuracy of the pattern 35 in the region outside the exposed region 33.

[0088]

According to the first pattern forming method of the present invention, it is possible to prevent the resist film from being exposed when the electron beam is scanned in the alignment mark detecting step, thereby preventing the dimensional accuracy of the pattern from deteriorating.

According to the second pattern forming method of the present invention, the total exposure amount of the electron beam in the region to be exposed can be made substantially equal to the exposure amount of the electron beam in the region outside the region to be exposed. The dimensional accuracy of the pattern in the region to be exposed can be made comparable to the dimensional accuracy of the pattern in the region outside the region to be exposed.

In the first or second pattern forming method of the present invention, the resist film is made of a negative resist, and the region to be exposed has a line-to-line distance that is a distance between line portions.
From the value of not more than twice the backscattering radius, which is the standard deviation of the Gaussian distribution representing the spread of the backscattered electrons in the resist film, to twice the backscattered electron arrival radius, which is the maximum value of the backscattered electrons. The electron beam is applied to a plurality of line groups of the test resist film having the same specifications as the resist film while changing the exposure amount. When the maximum exposure radius is set to 1/2 of the maximum value of the distance between the lines at which the center of the space portion between the line portions of the test resist film begins to develop, the electron beam is detected in the alignment mark detection step. If the distance from the scanning position is within the maximum exposure radius, the maximum exposure radius can be determined with high accuracy by using the test resist film. It can be determined with high accuracy.

In the first or second pattern forming method of the present invention, the resist film is made of a positive resist, and the region to be exposed has a line-to-line distance that is a distance between line portions.
From the value of not more than twice the backscattering radius, which is the standard deviation of the Gaussian distribution representing the spread of the backscattered electrons in the resist film, to twice the backscattered electron arrival radius, which is the maximum value of the backscattered electrons. The electron beam is applied to a plurality of line groups of the test resist film having the same specifications as the resist film while changing the exposure amount. When the maximum exposure radius is set to 1/2 of the maximum value of the distance between the lines at which the center of the space between the line portions of the test resist film begins to disappear after development, the electron beam is used in the alignment mark detection step. If the distance from the scanning position is within the maximum exposure radius, the maximum exposure radius can be determined with high accuracy by using the test resist film. It can be determined with high accuracy.

[Brief description of the drawings]

FIG. 1 shows a method for forming a pattern using an electron beam exposure method according to a first embodiment of the present invention;
FIG. 9 is a diagram illustrating a normalized absorption energy intensity distribution by backscattered electrons and a third exposure source.

FIG. 2 is a diagram illustrating a method of forming a pattern using an electron beam exposure method according to the first embodiment of the present invention; FIG. 9 is a diagram showing a normalized absorption energy intensity distribution by a third exposure source.

FIG. 3 shows one trace of scattered electrons incident on a substrate after passing through a resist film and generated in the substrate and in the substrate in the pattern forming method using the electron beam exposure method according to the second embodiment of the present invention. FIG. 3 is a diagram showing one path of an X-ray to be emitted.

FIG. 4 is a diagram showing a positioning mark formed on a substrate and a peripheral portion thereof viewed from directly above in a pattern forming method using an electron beam exposure method according to a third embodiment of the present invention.

FIG. 5 (a) is a diagram showing one track of electrons that are scattered forward in a substrate after being scattered forward in a resist film;
(B) is a diagram showing how the spread of the track of forward scattered electrons and the spread of the track of back scattered electrons are distributed.

FIG. 6 is a diagram showing a line and space pattern used to check the accuracy of proximity effect correction in the electron beam exposure method.

FIGS. 7A to 7C are diagrams showing a change in a backscattered electron reaching region when an electron beam is irradiated on a line portion while changing the distance between the line portions.

[Explanation of symbols]

β _f Forward scattering radius β _b Back scattering radius r _b Back scattered electron arrival radius r _X Maximum exposure radius L Line part S Space part s Distance between lines D _f First exposure amount D (s) Second exposure amount line Function having the distance s as a variable a First normalized absorbed energy intensity distribution b Second normalized absorbed energy intensity distribution c Third normalized absorbed energy intensity distribution l Incident point of incident electrons Distance from X-ray generation center to X-ray arrival point d Distance from substrate surface to X-ray generation center θ Radiation angle of X-ray 1 Substrate 2 Resist film 3 Injection Electrons 4 Traces of forward scattered electrons 5 Traces of back scattered electrons 6 Spread of tracks of forward scattered electrons 7 Spread of tracks of back scattered electrons 8 First Gaussian distribution 9 Second Gaussian distribution 11 First normalized absorption Energy intensity Cloth 12 Second normalized absorbed energy intensity distribution 13 Third normalized absorbed energy intensity distribution 21 Substrate 22 Resist film 23 Incident electrons 24 Trace of scattered electrons 25 One path of X-ray 26 Generation of X-ray Center 31 Alignment mark 32 Electron beam scanning position for mark detection 33 Exposed area 34 Pattern 35 Pattern

Claims (4)

[Claims] A resist film depositing step of depositing a resist film on a film to be processed formed on a substrate; and an alignment mark for scanning an electron beam to detect an alignment mark formed on the substrate. A detecting step, an electron beam exposure step of drawing a pattern by irradiating the resist film with an electron beam, and a pattern forming step of developing the resist film irradiated with the electron beam to form a resist pattern. In the pattern forming method, the electron beam exposure step is a step of drawing the pattern only in a region outside the exposed region where the resist film is exposed when scanning the electron beam in the alignment mark detection step. A pattern forming method comprising: 2. A resist film depositing step of depositing a resist film on a film to be processed formed on a substrate, and an alignment mark for detecting an alignment mark formed on the substrate by scanning an electron beam. A detecting step, an electron beam exposure step of drawing a pattern by irradiating the resist film with an electron beam, and a pattern forming step of developing the resist film irradiated with the electron beam to form a resist pattern. In the pattern forming method, the electron beam exposure step includes: setting an exposure amount of the electron beam in an exposure area where the resist film is exposed when scanning the electron beam in the alignment mark detection step; A step of setting the exposure amount of the electron beam to be smaller than an exposure amount of an electron beam in a region outside the pattern. . 3. The resist film is made of a negative type resist, and the exposed region has a Gaussian distribution standard in which the distance between lines, which is the distance between line portions, represents the spread of tracks of backscattered electrons in the resist film. The deviation gradually decreases from a value equal to or less than twice the backscattering radius to a value exceeding twice the radius of arrival of the backscattered electrons, which is the maximum value of the spread of the tracks of the backscattered electrons, and the resist film and After irradiating a plurality of line groups of the test resist film of the same specification with an electron beam while changing the exposure amount, the test resist film is developed and a gap between the line portions of the test resist film is developed. When a half of the maximum value of the distance between lines at which the center of the base portion starts to remain is set as the maximum exposure radius, from the position where the electron beam is scanned in the alignment mark detection step, 3. The pattern forming method according to claim 1, wherein the distance is a region within the maximum exposure radius. 4. 4. The resist film is made of a positive resist, and the exposed region has a Gaussian distribution standard in which the distance between lines, which is the distance between line portions, indicates the spread of tracks of backscattered electrons in the resist film. The deviation gradually decreases from a value equal to or less than twice the backscattering radius to a value exceeding twice the radius of arrival of the backscattered electrons, which is the maximum value of the spread of the tracks of the backscattered electrons, and the resist film and After irradiating a plurality of line groups of the test resist film of the same specification with an electron beam while changing the exposure amount, the test resist film is developed and a gap between the line portions of the test resist film is developed. When a half of the maximum value of the distance between lines at which the center of the base portion starts to disappear is set as the maximum exposure radius, the position of the electron beam scanning in the alignment mark detecting step is determined. 3. The pattern forming method according to claim 1, wherein the distance is a region within the maximum exposure radius. 4.