JPH09134875A - Exposure method and system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a projection optical system in resolution exceeding its intrinsic resolution limit by a method wherein a contrast enhancing layer is separated from a photosensitive material after exposure is carried out by projection, then the enhancing layer is applied again, and then a different pattern is projected onto the photosensitive material for exposure. SOLUTION: A resist 2 is applied onto a substrate 1, and a contrast enhancing layer CEL 3 is applied thereon. The contrast enhancing layer CEL 3 is formed of light discoloring composition and kept low in light transmission before light rays impinge on it, then increased in light transmission with an increase in incident light volume, and reaches to 100% light transmission when an incident light volume reaches to a certain value. A latent image of density corresponding to a transmitted light volume is formed in the resist 2 through a first exposure. Then, the contrast enhancing layer CEL 3 is separated from the resist 2, and another contrast enhancing layer CEL 3 of the same material is applied on the resist 2 as thick as the former. A second exposure pattern which is of the same strength and period P of a resolution limit with the first exposure pattern and deviates from the first exposure pattern by half a period is used. A pattern of period 1/2 P of resolution limit is formed, and when the resist 2 is dipped into developing solution, a pattern beyond the resolution limit of an optical system can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus and an exposure method used for manufacturing a semiconductor.

[0002]

2. Description of the Related Art With the progress of semiconductor manufacturing technology, the degree of integration of semiconductor integrated circuits has been improved. In order to improve the degree of integration, it is necessary to increase the resolution of projection exposure. As a method of increasing the resolution, it is conceivable to shorten the exposure wavelength of the projection exposure apparatus or increase the numerical aperture of the projection exposure apparatus. At present, the exposure wavelength of the projection exposure apparatus reaches the excimer laser region, and the numerical aperture is about 0.5.

[0003]

However, neither of the methods was able to obtain a resolution exceeding the resolution limit of the optical system. An object of the present invention is to provide a technique for improving resolution by exceeding the resolution limit of a projection optical system, which has been impossible in the past.

[0004]

In order to solve the above problems, the present invention provides an exposure method in which a pattern on an original plate is projected and exposed on a predetermined photosensitive material by a projection optical system.
A contrast-enhancing layer whose transmittance changes according to the amount of light is applied to the projection-exposed side of the light-sensitive material, and the pattern is exposed once to the light-sensitive material coated with the contrast-enhancing layer, and then the contrast-enhancing layer. Is peeled off from the photosensitive material, the contrast enhancing layer is applied again to the side of the photosensitive material to be projected and exposed, and a pattern different from that at the time of the exposure is projected and exposed on the photosensitive material to solve the projection optical system. Provided is an exposure method characterized by forming a high-resolution pattern exceeding the image limit.

Further, according to the present invention, in an exposure apparatus for projecting a predetermined pattern of an original onto a predetermined photosensitive material by a projection optical system, a contrast whose transmittance changes according to the amount of light on the projection exposed side of the photosensitive material. A coating means for coating the enhancement layer and a peeling means for peeling the contrast enhancement layer from the photosensitive material after each exposure, and the pattern of the original plate projected on the photosensitive material is different for each exposure. There is also provided an exposure apparatus characterized by forming a latent image density distribution of a pattern finer than the predetermined pattern.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A method of forming a resolution pattern on a resist which exceeds the resolution limit of a projection optical system will be described below with reference to embodiments. FIG. 1 is a schematic cross-sectional view of an exposed body in an example in which a diazonium salt is used as a contrast enhancing layer, which will be described with reference to FIG. A resist 2 is applied on a substrate 1, and a contrast enhancing layer (hereinafter referred to as CEL in English because it is called Contrast Enhancing Layer) 3 is further applied thereon. Hereinafter, such a laminated body will be referred to as an exposed body.

[0007] In this embodiment, the substrate is a silicon wafer for manufacturing semiconductor devices, resist using an i-ray resist of novolak with linear sensitivity characteristics, CEL before
As described above, the main component is a diazonium salt. Actually, as CEL, there are documents (resist materials and process technologies issued by the Institute of Technology Information) and documents (Makoto Nakase et al. Technical Report of the Institute of Electronics and Communication Engineers, Vol. 84, No. 241, SSD84-97 A.
Characteristic evaluation of CEL by BC model) and literature (BFGrif
fing and PRWest IEEE Electron Devices Letters, V
ol. EDL-4, No. 1, JANUARY 1983, p14-16) can be used. In particular, nitrone, polysilane, styrylpyridinium salt and the like can be mentioned as the substance names other than the diazonium salt.

CEL is a compound that uses a photobleaching compound and has a low light transmittance before the incidence of light. However, the light transmittance increases as the amount of incident light increases.
It has the characteristic of reaching a transmittance close to 100% with a certain amount of light. CEL containing a diazonium salt as a main component decomposes into a transparent substance and nitrogen by the photochemical reaction shown below.

[0009]

Embedded image

As parameters that characterize common resists including CEL, the coefficients of A, B and C and the thickness d
There is. The meaning of these parameters can be found in the literature (FHD
ill, WP Hornberger, PS Hauge, JM Shaw, IEE
E Transactions of Electron Devices, Vol. ED-22, N
o. 7, July 1975, p445-452). In the CEL used in this example, A = 11.1 μm ⁻¹ , B
A CEL of = 0.192 μm ⁻¹ , C = 0.033 cm ² / mJ and d = 0.5 μm was used.

A simulation was performed to calculate how the transmittance T of the CEL under these conditions changes depending on the exposure amount I · t (I is the light intensity and t is the exposure time). The result is shown in FIG. Looking at FIG. 2, the exposure amount is 100 mJ / c
The curve rises from around m ² and the exposure dose is 300 mJ / c
It can be seen that the value saturates at a constant value near m ² . When exposed through such a CEL, the amount of light transmitted through the resist D
Is

[0012]

(Equation 1)

Is given by FIG. 3 shows the relationship between the exposure amount I · t on the CEL and the transmitted light amount D to the resist in this embodiment. This is the result obtained by simulation from the relationship of FIG. At this time, the latent image density is formed in the resist in proportion to the transmitted light amount D on the vertical axis. As can be seen from FIG. 3, the light does not reach the resist at the exposure amount up to a certain threshold value, and when it exceeds the threshold value, the transmitted light amount D suddenly starts to increase. In order to express this relationship by a power polynomial of the exposure dose, a polynomial of the fifth degree is approximately required. That is, fifth-order nonlinearity is realized in this embodiment.

In such a situation, first, the first pattern is exposed using the above-mentioned exposed body. CEL on top
Then, a pattern close to the resolution limit of the projection optical system is exposed.
Assuming that the wavelength used for projection exposure is λ and the numerical aperture of the projection optical system is NA, the period P of the resolution limit pattern is P = λ / 2N
A. In this embodiment, λ = 365 nm and NA = 0.6,
P = 304 nm. When an ideal phase shift mask is used, this diffraction-limited pattern has the exposure intensity I as a function of the position x.

[0015]

## EQU2 ## It can be expressed as I (x) = I ₀ (1 + cos (2πx / P)). In this example, I ₀ = 50 mW / c
m ² . Using the exposure light of this intensity, 3
Expose for 2 seconds. (In Expression 1, a = 3.) Here, the exposure amount distribution of the exposure amount I · t to the CEL is shown in FIG.
It becomes as shown in. Although FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8 and FIG. 11 which will be shown below are not scaled, all the positions x on the horizontal axis in these figures are the same.

When this exposure amount distribution reaches the resist through the CEL, the transmitted light amount D to the resist is given by FIG. 5 using the relationship of FIG. In the distribution shown in FIG. 5, the valley portion of the exposure amount distribution shown in FIG. 4 is approximately flattened. By this first exposure, the density of the latent image proportional to D is formed in the resist. Next, the CEL of the exposed body is peeled off. Since the resist is insoluble in water but the CEL is soluble, it is possible to remove only the CEL while holding the resist by showering pure water.

Subsequently, the CEL made of the same material and having the same thickness is again used.
Is applied. After that, the second exposure is performed. The second exposure uses a pattern having the resolution limit period P and the same intensity as the first exposure pattern, but uses a pattern shifted by a half period from the first exposure. In the formula,

[0018]

It is given in the form of I ₂ (x) = I ₀ (1-cos (2πx / P)). The amplitude I _{0 of the} exposure intensity is 50 mW / cm ² which is the same as the first time. The exposure time is also 3 seconds, which is the same as the first exposure. The exposure amount distribution of the exposure amount I ₂ · t on the CEL in the second exposure is shown in FIG. In FIG. 6, the cycle is shifted by half compared to FIG. 4.

Similar to the first exposure, C shown in FIG. 3 is used.
Due to the effect of EL, the distribution of the transmitted light amount of the second exposure on the resist is as shown in FIG. 7, and the density of the latent image proportional to this transmitted light amount is formed on the resist. The pattern of the total amount of light to the resist given by the first and second exposures is the sum of the amounts of transmitted light shown in FIGS. 5 and 7, and is as shown in FIG. The latent image density is proportional to this total light amount. The contrast of the latent image density pattern is 0.68.

According to the method of this embodiment, as can be seen from FIG. 8, a pattern having a period half the period P of the resolution limit pattern is formed. After the second exposure is completed, only the CEL is peeled off again by showering with pure water and immersed in the developing solution. Next, an embodiment different from the above embodiment will be described.

With the same structure and the same material as in the above embodiment, CE
An exposed body in which the thickness of L is changed to 0.8 μm is used. exposure
The intensity distribution is the same, the exposure time of the first and second exposure
For 4 seconds. In this case, the change in transmittance of CEL
The conversion is as shown in FIG. Looking at FIG. 9, the exposure amount 2
00mJ / cm^TwoThe curve rises from the vicinity and the exposure amount is 3
50 mJ / cm ^TwoIt turns out that it saturates to a certain value in the vicinity
You. In addition, the exposure amount It · t on the CEL and
The relationship of the transmitted light amount D is given in FIG. Exposure 250
mJ / cm^TwoFrom around, the amount of transmitted light D suddenly started to increase.
You.

The density pattern of the latent image after the exposure is performed twice as in the above embodiment is as shown in FIG. In this embodiment, the contrast is 0.925.
When a resist (second-order non-linear resist) that forms a latent image density proportional to the square of the intensity of incident light is used as the resist, the relationship between the exposure amount and the latent image density is shown in FIG. 3 is the square of the vertical axis, and the first exposure and the second
The latent image pattern formed by the second exposure becomes clearer. As a result, the contrast of the pattern finally obtained after multiple exposure (exposure of the same resist more than once) is increased.

In the case of performing multiple exposure using a linear resist as well as in the case of performing multiple exposure using a secondary non-linear resist, multiple exposure using only the secondary non-linear resist without using CEL It is possible to obtain a contrast larger than the contrast value of 0.33 in the case of performing. In the above, the CEL containing the diazonium salt as the main component was used, but an example of using the CEL containing nitrone as the main component will be described below. CE containing nitrone as a main component
L is disclosed in JP-A-59-104642, and CEM388WS (trademark of Shin-Etsu Chemical) is available. When nitrone is used, it undergoes the photochemical reaction shown below and changes into a substance called oxaziridine.

[0024]

Embedded image

When the nitrone is used, the exposed body is shown in FIG.
The structure is as shown in. That is, the resist 2 is coated on the substrate 1, the binder 4 is coated thereon, and the CEL 3 is further coated thereon. The reason why such a structure is adopted is that the CEL3 itself using nitrone penetrates water but is insoluble in water. But binder 4
Is soluble in water, it becomes possible to separate CEL3 from resist 2 by dissolving binder 4 after water permeates CEL3. At this time, as the binder 4, pullulan and polyvinylpyrrolidone can be used.

The first exposure and the second exposure are performed in the same manner as CEL containing a diazonium salt as a main component. After the second exposure, the CEL 3 is peeled off from the resist 2 again by the above-mentioned method and immersed in a developing solution to obtain a pattern exceeding the resolution limit of the optical system. FIG. 12 shows a schematic configuration of an exposure apparatus for performing a plurality of exposures with different light intensity distributions by using an exposed body of CEL containing a diazonium salt as a main component. The illumination light flux from the light source 11 is condensed by the elliptical mirror 12, guided to the collimator lens 14 by the mirror 13, becomes a substantially parallel light flux, and enters the fly-eye integrator 15. The light flux emitted from the fly-eye integrator 15 is reflected by the mirror 16 to the main condenser 17
Is guided to uniformly illuminate the reticle 18a as the original plate. A predetermined pattern on the original 18a is projected and exposed on the exposure body 20 by the projection optical system 19. The exposed body 20 is
The CEL is applied in advance by the CEL applicator 24, which is the application means. Here, the reticle 18a
After exposure, the reticle 18b having a different pattern is exchanged by the reticle loader 21 after the exposure. The exposed body 20 is also brought to the shower 23, which is a peeling means, by the wafer loader 22, and the CEL is peeled off by the shower of pure water. After that, it is returned to the CEL coating machine 24, and CEL is coated again.
The exposed body thus completed is returned to the original position and the second exposure is performed.

Instead of exchanging different patterns by the reticle loader 21, the reticle 18a is moved to the optical axis Ax of the projection optical system 19 after the first exposure by the reticle 18a.
Alternatively, the second exposure may be performed by moving in the vertical direction by a predetermined amount. Needless to say, in the case of exposing the same reticle pattern a plurality of times, instead of moving the reticle, the exposure body itself may be moved for every plurality of exposures.

For the alignment between a plurality of exposures, so-called latent image alignment is effective in which the latent image is observed and aligned. When CEL containing nitrone as a main component is used, the binder is applied by the binder application unit before the CEL is applied by the CEL applicator 24. Other steps and the like are the same as in the case of using CEL containing a diazonium salt as a main component.

[0029]

As described above, according to the present invention, the resolution can be improved by exceeding the resolution limit of the projection optical system.

[Brief description of the drawings]

FIG. 1 is a CEL containing a diazonium salt as a main component.
It is a schematic cross section which shows the structure of the exposure body at the time of using.

FIG. 2 is a graph showing the exposure amount to CEL and C in the example.
It is a graph which shows the relationship with EL transmittance.

FIG. 3 is a graph showing the exposure amount to CEL and C in the example.
7 is a graph showing the relationship of the amount of transmitted light that reaches the resist through EL.

FIG. 4 is a graph showing the distribution of the exposure amount on the CEL at the time of the first exposure in the example.

FIG. 5 is a graph showing the distribution of the amount of transmitted light reaching the resist during the first exposure in the example.

FIG. 6 is a graph showing the distribution of the exposure amount to the CEL at the time of the second exposure in the example.

FIG. 7 is a graph showing the distribution of the amount of transmitted light that reaches the resist during the second exposure in the example.

FIG. 8 is a graph showing a density distribution of a latent image formed in a resist after a total of two exposures in the example.

FIG. 9 is a graph showing the relationship between the exposure amount of CEL and the transmittance of CEL in another example.

FIG. 10 is a graph showing the relationship between the exposure amount to the CEL and the amount of transmitted light reaching the resist through the CEL in another example.

FIG. 11 is a graph showing a density distribution of a latent image formed in a resist after a total of two exposures in another example.

FIG. 12 is a diagram showing an embodiment of the device according to the present invention.

FIG. 13 is a schematic cross-sectional view showing the structure of an exposed body when a CEL containing nitrone as a main component is used.

[Explanation of main symbols]

 1 substrate 2 photosensitive material 3 CEL 4 binder 23 shower 24 CEL coating machine

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 21/30 565 573

Claims (13)

[Claims] 1. An exposure method in which a pattern on an original plate is projected and exposed on a predetermined photosensitive material by a projection optical system, and a contrast enhancing layer whose transmittance changes according to the amount of light is provided on the side of the photosensitive material to be projected and exposed. After the coating, the pattern is exposed once to the photosensitive material coated with the contrast enhancing layer, then the contrast enhancing layer is peeled off from the photosensitive material, and the contrast enhancing layer is again exposed to the contrast enhancing layer. An exposure method characterized by forming a high-resolution pattern that exceeds the resolution limit of a projection optical system by applying a layer and projecting and exposing a pattern different from that at the time of the exposure onto the photosensitive material. 2. The exposure method according to claim 1, wherein the contrast enhancing layer is a substance containing nitrone as a main component. 3. Before applying the contrast enhancing layer,
3. A binder is applied, wherein the binder is applied.
Exposure method according to the above. 4. The contrast enhancing layer is a substance containing a diazonium salt as a main component.
Exposure method according to the above. 5. The exposure method according to claim 1, wherein the photosensitive material has a linear sensitivity characteristic. 6. The exposure method according to claim 1, wherein the photosensitive material has a non-linear sensitivity characteristic. 7. An exposure apparatus for projecting a predetermined pattern of an original plate onto a predetermined photosensitive material by a projection optical system, wherein a contrast enhancing layer whose transmittance changes according to the amount of light is applied to the projection exposed side of the photosensitive material. Coating means and a peeling means for peeling the contrast enhancing layer from the photosensitive material after each exposure, and the pattern of the original plate projected on the photosensitive material is different for each exposure. An exposure apparatus that forms a latent image density distribution that is finer than a pattern. 8. The exposure apparatus according to claim 7, further comprising a binder coating unit for coating a binder between the contrast enhancing layer and the photosensitive material. 9. An exposure apparatus for projecting a predetermined pattern of an original plate onto a predetermined photosensitive material by a projection optical system, wherein a contrast enhancing layer whose transmittance changes according to the amount of light is applied to the projection exposed side of the photosensitive material. A first original plate having a first pattern and a second original plate having a second pattern as the original plate, and a peeling unit for peeling the contrast enhancing layer from the photosensitive material after each exposure. The photosensitive material is subjected to a second exposure by the second original plate after a first exposure by the first original plate, thereby forming a finer pattern than the first pattern and the second pattern on the photosensitive material. An exposure apparatus which forms a latent image density distribution. 10. The exposure apparatus according to claim 9, further comprising a binder coating unit for coating a binder between the contrast enhancing layer and the photosensitive material. 11. The first original plate and the second original plate have different patterns, and after the first exposure, the first original plate is replaced with the second original plate to perform the second exposure. The exposure apparatus according to claim 9 or 10. 12. The first original plate and the second original plate are the same, and after the first exposure, the first original plate is moved by a predetermined amount in a direction perpendicular to the optical axis of the projection optical system to obtain a second original plate. The exposure apparatus according to claim 9 or 10, which performs exposure. 13. The first original plate and the second original plate are the same, and a photosensitive material coated with a contrast enhancing layer after the first exposure is moved by a predetermined amount in a direction perpendicular to the optical axis of the projection optical system. The exposure apparatus according to claim 9, wherein the second exposure is performed.