JPH097935A - Resist exposure method - Google Patents

Abstract

(57) [Summary] [Object] To provide a resist exposure method capable of manufacturing an IC having a high degree of integration. [Structure] A thin film 5 whose light transmittance increases according to the intensity of incident light is coated on a resist 6, and the thin film 5 is irradiated with a light spot to locally increase the light transmittance of the thin film 5. The light transmittance increasing portion 5a of the thin film 5 is formed into a desired pattern by relatively scanning the spot and the resist 6, and the resist 6 is exposed through the light transmittance increasing portion 5a of the thin film 5. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of exposing a resist provided on a semiconductor substrate.

[0002]

2. Description of the Related Art Conventional exposure processes in IC manufacturing include reduction projection type exposure method and close-type exposure (proximity).
Methods, contact-type exposure (contact printing) methods and the like have been used.

[0003]

Among the above-mentioned conventional techniques, the reduction projection type exposure method has the highest resolution at present. However, in this method, since exposure is performed with an optically formed reticle image, there is an upper limit of resolution due to the diffraction limit, and the resolution is limited to about the wavelength of light used for projection. In the close-contact exposure method, the space between the mask and the resist cannot be unnecessarily reduced, so that the resolution is generally inferior to that in the reduced projection exposure method. Moreover, since the space between the mask and the resist has a great influence on the resolution, extremely strict specifications are required for the flatness of the mask, which is a major factor that hinders the high resolution. In the contact type exposure, there is no diffraction limit in principle, but since the mask is contacted, scratches and stains on the resist cannot be ignored, and it is not practical for an IC having a high degree of integration. Therefore, the present invention is a highly integrated IC.
It is an object of the present invention to provide a method for exposing a resist capable of producing

[0004]

The present invention has been made to achieve the above object, that is, a thin film whose light transmittance increases according to the intensity of incident light is applied onto a resist, and the thin film is applied. The light transmittance of the thin film is locally increased by irradiating the film with a light spot, and the light transmittance increasing portion of the thin film is formed into a desired pattern by relatively scanning the light spot and the resist. It is a resist exposure method of exposing a resist through a transmittance increasing portion. At that time, an opaque thin film having a fixed melting point or sublimation point is used as the thin film, and the light spot locally increases the temperature of the thin film to exceed the melting point or sublimation point, thereby increasing the light transmittance of the thin film. it can.

[0005]

[Function] The property that the light transmittance changes depending on the light intensity is generally treated as a nonlinear optical effect of a substance.
For simplicity, first, an opaque thin film having a constant melting point will be described. When such a thin film is scanned by a laser scanning type exposure device, the temperature of the opaque thin film rises in the portion hit by the laser spot. However, as shown in FIG. 1, since the light intensity distribution of the laser spot generally has a Gaussian distribution, the temperature distribution of the thin film 5 also has a substantially Gaussian distribution.
Therefore, by adjusting the laser power, it is possible to set the temperature only in the region w, which is much narrower than the laser spot size φ, to the melting point or higher. In this region w, the thin film 5 melts above its melting point, and the melted portion 5a allows light to pass therethrough. Therefore, for example, when a laser spot is scanned linearly, the laser spot size φ on the opaque thin film 5 is
It is possible to form the linear light transmitting portion 5a having a width w much narrower than that. The width w of the light transmitting portion 5a of the opaque thin film 5 thus obtained can be reduced, and when a plurality of linear light transmitting portions 5a are formed at regular intervals, the period is optically cut off. It can be much smaller than the diffraction limit determined by the frequency. Therefore, the pattern formed by the light transmitting portion 5a of the opaque thin film 5 is basically not limited in resolution due to light diffraction.

However, no matter how fine the pattern 5a can be formed on the opaque thin film, it is meaningless unless it is exposed to the resist 6. The present invention makes this possible by using evanescent light for this exposure. In general,
Of the spatial frequency components of the object, the band that exceeds the optical cutoff frequency is converted to an evanescent wave instead of a traveling wave as a result of diffraction. Since the evanescent wave stays near the object and does not propagate in the space, it is impossible to extract the information of the evanescent wave using the imaging optical system. However, according to the method of the present invention, as described above, the opaque thin film 5 having the fine pattern 5a exceeding the optical cutoff frequency is formed.
Since the resist 6 is coated on the resist 6, all the evanescent light generated as a result of the diffraction of the light by the fine pattern 5a can also contribute to the exposure of the resist 6. Therefore, the fine pattern 5a formed on the opaque thin film 5 is exposed to the resist 6 without the limit of diffraction.

The same is basically true when considering a thin film having a nonlinear optical effect such that the light transmittance increases depending on the intensity of incident light as the opaque thin film. When the light transmittance of the thin film is uniform without depending on the incident light intensity, the intensity distribution of the laser light transmitted through this thin film is naturally the original distribution, that is, it is proportional to the first power of the original distribution. When the light transmittance is proportional to the incident light intensity, the intensity distribution of the laser light transmitted through this thin film is proportional to the square of the original distribution. Generally, when the light transmittance is proportional to the nth power of the incident light intensity, the laser spot intensity distribution transmitted through this thin film is the n + 1th power of the original distribution, and the larger n is, the smaller the spot is. Therefore, as shown in FIG. 2, it is preferable that the light transmittance with respect to the incident light intensity has a threshold value so that the light transmittance changes abruptly at a certain incident light intensity. According to Fourier optics, when the spot intensity distribution is the n + 1th power in the normal case, the cutoff frequency of the optical image obtained by scanning the spot is n + 1 times the normal case. When n is too large, the light transmitted through the thin film is partially converted into evanescent light.
In the method of the present invention, since exposure including evanescent light is performed, there is no problem.

[0008]

Embodiments of the present invention will be described with reference to the drawings. FIG. 3 shows a first embodiment of the present invention, in which the laser light source 1 is controlled by a light source control device 8, and the laser light emitted from the laser light source 1 is converted into parallel light by a condenser lens 2. The parallel light is incident on the XY two-dimensional optical scanning device 3, and thus the laser light is formed so as to be scanned by the two-dimensional scanning device 3 in a plane direction orthogonal to the optical axis. As the two-dimensional optical scanning device 3, a pair of galvano mirrors, polygon mirrors, acousto-optic elements, etc. can be used. The laser light emitted from the two-dimensional scanning device 3 is condensed by a projection lens 4, which forms a minute laser spot on an opaque thin film 5 coated on a resist 6 on a wafer 7. It is arranged to.

This embodiment is formed as described above.
The opaque thin film 5 is locally heated by the heat generated by the laser, and as a result, the thin film 5 is locally melted and partially punctured. Examples of the thin film having such characteristics include tellurium oxide, which is known as a recording material for write-once type optical disks. Light is transmitted from the pierced portion of the opaque thin film 5 to the resist 6, so that the light transmitting portion of the opaque thin film 5 has a desired pattern.
The laser spot is moved by the two-dimensional scanning device 3, and at the same time, the output of the light source 1 is controlled by the light source control device 8. Thereby, the resist 6 can be exposed to a desired pattern. At this time, the diameter of the light transmitting portion of the opaque thin film 5 can be made much smaller than the diameter of the laser spot, and is not limited by the diffraction limit. Further, since the resist 6 is in close contact with the opaque thin film 5, all the diffracted waves including the evanescent wave contribute to the exposure. Therefore, according to this embodiment, it is possible to expose a fine pattern exceeding the diffraction limit.

Although the laser beam is scanned in the above embodiment, the beam may be fixed and the stage (not shown) on which the wafer 7 is mounted may be scanned. Further, the thin film 5 coated on the resist 6 preferably has a property of being peeled off at the time of development. Further, the evanescent light generated by the diffraction in the opaque thin film 5 is rapidly attenuated in the optical axis direction in the resist 6, and the faster the evanescent light transmitting a high spatial frequency is, the faster the evanescent light is. It is preferable to use.

In the above embodiment, the patterning of the thin film 5 and the exposure of the resist 6 were carried out at the same time.
Since it is considered that the hole once opened will not be closed again, it is possible to pattern only the thin film 5 first and then expose the resist 6 collectively. At that time, for example, the projection lens 4 may be removed when the resist 6 is collectively exposed. It is more preferable to perform the patterning of the thin film 5 and the exposure of the resist 6 separately in order to make the illumination intensity uniform.

Next, FIG. 4 shows a second embodiment of the present invention. In the first embodiment, the light source 1 serves both for patterning the opaque thin film 5 and for exposing the resist 6, but in the second embodiment, a light source for scanning for patterning the opaque thin film 5. 10 and a light source 1 for exposing the resist 6
It is equipped with 1 and each independently. Light emitted from the exposure light source 11 passes through the lens 12 and the two-dimensional scanning device 3
And the projection lens 4 are interposed between the half mirror 13
And is projected onto the opaque thin film 5 through the projection lens 4. As the half mirror 13, when the scanning light source 10 and the exposure light source 11 have different wavelengths, a wavelength selection mirror may be used, and of course, a detachable mirror may be used. Since the projection lens 4 merely functions as an illumination lens for the exposure light source 11, the aberration needs to be corrected only for the wavelength of the scanning light source 10.

The light source 11 for exposure as in the second embodiment
, The scanning light source 10 is used only for patterning the opaque thin film 5, and the resist 6 is used.
It becomes easy to collectively perform the actual exposure of (3) after patterning the opaque thin film 5. However, by arranging the two-dimensional scanning device 3 and the half mirror 13 interchangeably, the opaque thin film 5 is patterned by the scanning light source 10, and simultaneously with this patterning, the exposure light source 11 is formed.
The resist 6 can also be exposed by.

Next, in each of the above embodiments, the temperature of the opaque thin film 5 applied on the resist 6 was raised by a laser spot so as to partially exceed the melting point thereof. Can also use a non-linear optical thin film whose light transmittance increases depending on the intensity of incident light. This is generally a thin film that exhibits the characteristics of saturated absorption in the nonlinear optical effect. Also in this case, the same light source 1 can be used to perform thin film patterning and resist exposure, or the scanning light source 10 and the exposure light source 11 can be provided separately. However, when the scanning light source and the exposure light source are separately provided, it is necessary to select the wavelength of the exposure light source 11 while paying attention to the wavelength dependence of the light transmittance.

In any case, the light transmittance of the thin film increased by the laser light from the laser light source 1 or the scanning light source 10 maintains the increased light transmittance even after the laser light is removed. In this case, the resist can be collectively exposed after patterning the thin film. However, it should be noted that when performing the collective exposure, the cutoff frequency of the optical image is only n times, not n + 1 times. On the other hand, when the light transmittance of the thin film returns to the original value when the light from the laser light source 1 or the scanning light source 10 is removed, the thin film patterning and the resist exposure may be performed at the same time.

[0016]

As described above, according to the present invention, it is possible to expose a fine pattern on a resist without being limited by the diffraction limit, so that an IC having a high degree of integration can be manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the principle of the present invention when utilizing the melting point of a thin film.

FIG. 2 is an explanatory diagram showing the principle of the present invention when utilizing the light transmittance characteristics of a thin film.

FIG. 3 is a schematic configuration diagram showing an apparatus according to a first embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing an apparatus of a second embodiment.

[Explanation of symbols]

1 ... Laser light source 2 ... Condenser lens 3
2D scanning device 4 Projection lens 5 Thin film 5
a ... Light transmittance increasing portion 6 ... Resist 7 ... Wafer 8
Light source control device 10 Scanning light source 11 Exposure light source 1
2 ... Lens 13 ... Half mirror

Claims (6)

[Claims] 1. A thin film, whose light transmittance increases according to the intensity of incident light, is coated on a resist, and the thin film is irradiated with a light spot to locally increase the light transmittance of the thin film. A method of exposing a resist, wherein the light transmittance increasing portion of a thin film is formed into a desired pattern by relatively scanning a spot and the resist, and the resist is exposed through the light transmittance increasing portion of the thin film. 2. The thin film is an opaque thin film having a constant melting point or sublimation point, and the light transmittance increases when the temperature of the thin film locally exceeds the melting point or sublimation point by the light spot. The method for exposing a resist according to claim 1, which is a one. 3. The resist exposure method according to claim 1, wherein the resist is exposed using the same light source as the light source for irradiating the thin film with the light spot. 4. The resist exposure method according to claim 1, wherein the resist is exposed by using a light source provided separately from a light source for irradiating the thin film with the light spot. 5. The resist exposure method according to claim 3, wherein the step of locally increasing the light transmittance of the thin film and the exposure of the resist are performed simultaneously. 6. The resist is exposed after the step of locally increasing the light transmittance of the thin film.
A method for exposing a resist as described.