JPH0385543A - Exposure mask, exposure method, and projection exposure device - Google Patents

Abstract

PURPOSE:To obtain a high resolving power by providing a first pattern and a second pattern obtained by white/black inversion of the first pattern with respect to mask pattern. CONSTITUTION:An exposure mask 1 consists of a first area R1 where a desired circuit pattern is formed with a light shielding pattern 2 made of a chromium thin film and a second area R2 where a pattern obtained by white/black inversion of the circuit pattern. An exposure device consists of a light source L, a mask 1, a projection lens 3, a quartz plate 4 which is arranged between the mask 1 and the projection lens 3 and functions as a phase shifter to shift the phase by lambda/2, and a shielding plate 5 which shields light to prevent the light from a half area of the exposure mask from reaching a body to be exposed, and the pattern is transferred to the surface of a silicon substrate 5 coated with resist. Thus, a resolving power higher than the resolving power determined by the wavelength of the light source, the numerical aperture of an image forming element, a process parameter, or the like is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an exposure method, an exposure apparatus, and an exposure mask, and particularly relates to lithography technology used in manufacturing semiconductor devices.

(Prior Art) In the field of manufacturing semiconductor devices such as VLSIs, there is a technology in which light is irradiated onto a substrate through a lens system and a mask formed with a desired light-shielding pattern, and a fine pattern is transferred by reduction projection exposure. is widely used.

By the way, the resolving power of a projection exposure apparatus is designed so that the imaging element has almost no aberration, so it depends on the numerical aperture (NA) of the imaging element such as the lens system used and the wavelength λ of the light used for exposure.
Depends on.

In other words, the minimum resolvable line width (L) is L=λ/NA
■ It can be expressed as. Here, k is a proportionality constant, and is usually about 0.8. That is, the smaller the wavelength and the larger the numerical aperture, the better the resolution.

By the way, in recent years, lens development has progressed rapidly and the NA has increased, and G1! By shortening the wavelength from <436 nm) to IL (365 nm), the resolution has improved year by year, and by using exposure using an excimer laser (194 nm), the prospect of reaching a region of about 0.3μ milk is being drawn. There is.

However, there is a limit to the use of short wavelength light sources because it is very difficult to secure glass materials for lenses.

On the other hand, another means to improve resolution is to increase the numerical aperture, but it is possible to use an imaging element such as a lens system with a high numerical aperture that has no aberrations while ensuring a large exposure area necessary for an exposure device. It is very difficult to design and manufacture a child.

Therefore, in an exposure method using an imaging system, it is not possible to obtain a resolution better than that of a -window by simply improving the resolution by wavelength or numerical aperture, and it is necessary to reduce the proportionality constant k. Although various efforts have been made to improve photosensitive resins, they are reaching their limits.

(Problem to be solved by the invention) As described above, in the projection exposure method, the resolution is determined by the wavelength of the light source, the numerical aperture, and the photosensitive material, and it is impossible to obtain a resolution higher than a fixed i1. .

The present invention has been made in view of the above-mentioned circumstances, and the present invention provides a projection exposure method and a projection exposure method for obtaining high resolution that has not been previously possible even if the wavelength of the light source, the numerical aperture of the optical system, and the photosensitive material are determined. The purpose of the present invention is to provide an exposure apparatus and a mask structure.

[Structure of the invention]

(Means for solving the TI problem) Therefore, in the present invention, a mask pattern and an inverted pattern that is black and white reversed with respect to the mask pattern are projected and exposed with a slightly blurred and weakened intensity onto the same exposure area. It is a feature.

Further, in the exposure mask of the present invention, a first mask pattern and a second mask pattern whose black and white are reversed with respect to the first mask pattern are provided.
It is designed to have a mask pattern.

Further, the projection exposure apparatus of the present invention is provided with a phase shift means which is detachably mounted on the optical path and shifts the phase of light.

Furthermore, the projection exposure apparatus of the present invention is provided with a shielding means for shielding light from a part of the exposure mask from reaching the object to be exposed.

(Function) By the way, when an image of a so-called sine wave chart, which repeats brightness and darkness in a sinusoidal manner, is created using a lens, the contrast (MT l": modular tra
nsfer function) and place @ (P T
F: phase transfer function
ion) are expressed as numbers between spatial frequencies, and these functions are called optical transfer functions (OTF).

MTF is often used to discuss the resolving power of an imaging element, and MTF is expressed by the following equation (2).

MTF = image contrast/mask contrast... ■In other words, if MTF is 1, it means that the mask pattern can be transferred onto the substrate as a complete image, and M
This shows that if TF is O, no transfer is possible.

Further, the MTF is a function of the spatial frequency, and an example when the object is in focus is shown in FIG. 4.

Here, S is the normalized spatial frequency s=(λ/NA
) tJ...■, and the relationship between the normalized spatial frequency and MTF is shown.

On the other hand, FIG. 5 shows an example of the MTF when there is a defocus of λ/2. Here, the fact that the MTF is negative in FIG. 5 indicates that the contrast is negative, that is, black and white are inverted at that spatial frequency.

Therefore, when exposure is performed under the same conditions as shown in Figure 5 using a mask with negative contrast, that is, black and white are reversed, the MTF at this time becomes as shown in curve a in Figure 6. ing. Furthermore, if we expose a little weakly based on such MTF, M
The TF decreases as shown in track IIAb in FIG.

Furthermore, when the curve in FIG. 6 and the curve in FIG. 4 are superimposed, the result is as shown in FIG. 7.

Therefore, the MTF is high at high spatial frequencies, and high resolution can be obtained during pattern transfer.

Furthermore, the decrease in MTF near the spatial frequency of 0 can reduce the pattern dimension change vJI due to the size of the transferred pattern dimension.

In this way, the present invention exposes the same exposure area by projecting a mask pattern and an inverted pattern obtained by reversing black and white with respect to the mask pattern, which is slightly blurred and weakened in intensity, and by overlapping these, a high space is created. The main idea is to increase the MTF at the frequency, thereby improving the solution By using a second mask pattern that is black and white inverted with respect to the first mask pattern, the above exposure method can be realized without replacing the mask, and the time required for mask alignment can be reduced. The scale can easily perform high-resolution exposure in a short time.

Furthermore, as an exposure apparatus for realizing such an exposure method, a phase shift means for shifting the phase of light is removably mounted on the optical path. In this state, the first pattern is exposed, and with the phase shift means installed on the optical path, the second pattern is exposed.
By exposing the pattern, high-resolution exposure can be performed extremely easily.

Furthermore, since the projection exposure apparatus of the present invention is equipped with a shielding means for shielding light from a part of the exposure mask from reaching the exposed object, 11 mask patterns and the first When performing exposure using a second mask pattern that is black and white inverted with respect to the mask pattern, the above exposure method can be realized without replacing the mask, and the time required for mask alignment is reduced. It is possible to easily perform high-resolution exposure in a short time.

(Example) Next, an example of the present invention will be described in detail with reference to the drawings.

Example 1 FIG. 1 is an explanatory diagram schematically showing an exposure method according to a first example of the present invention.

Here, the exposure mask 1 is a first mask formed by forming a desired circuit pattern with a light-shielding pattern 2 made of a thin chromium film.
, and a second region R formed by forming a black and white inversion pattern of the circuit pattern. This circuit pattern, that is, the first and second regions R1 and R2 has dimensions of 25 ms x 25 ms on the mask, and both head regions are arranged adjacent to each other.

This exposure apparatus includes a light source, a mask 1, a projection lens 3, and a quartz plate 4 as a phase shifter disposed between the mask 1 and the projection lens 3 to shift the phase by λ/2. , and a shielding plate 5 that blocks light from a half area of the exposure mask from reaching the exposed object, and is designed to transfer a pattern onto the surface of a resist-coated silicon substrate 5. be.

Here, this projection exposure apparatus uses a wavelength of 2480 as a light source.
Using a KrF excimer laser of A, the numerical aperture of the lens system is N.
A one-fifth reduction exposure device with A of 0.42 was used.

Next, the process of performing pattern exposure using this exposure apparatus will be explained with reference to the flowchart of FIG.

First, a positive photoresist is applied to the surface of the silicon substrate to a thickness of 0.5 μm, and the shielding plate 5 is placed at a position corresponding to the second area, and with the focus set,
Under an energy condition of 250 mJ/cj, the substrates were sequentially transferred and exposed using a step-and-repeat method, and exposure was performed at 52 locations on - silicon substrates 6 (wafers) using the first region R1 of the exposure mask 1. I went (Step 1
).

Next, the shielding plate 5 is installed at a position corresponding to the first area, and the lens system is left as is, and the quartz plate 4 is installed on the optical path with the focus adjusted.
The silicon substrate 6 (
Exposure was performed using the second region R2 of the exposure mask 1 so as to overlap the circuit pattern exposure regions of the 52 first regions on the wafer (Step 2). Note that during the two exposures, the stage 7 on which the silicon substrate 6 is placed is
A position measuring device using a laser interferometer attached to the laser interferometer ensures that the exposed areas are accurately overlapped.

Finally, development (step 3) is performed to transfer the circuit pattern to the resist on the silicon substrate.

When the resist pattern thus formed was observed using an electron microscope, a good pattern 7 of 0.27 μml/S could be obtained.

In contrast, according to the conventional exposure method, when a projection exposure apparatus with the same resist and the same lens system is used, the
With pattern dimensions of mL/S or less, dimensional controllability was extremely poor.

In addition, in this example, the overlapping of two exposures is as follows:
Alignment was performed using only the values of the laser interferometer on the stage, but it is also possible to set alignment marks on the wafer in advance and perform alignment using these alignment marks during the second exposure. good.

In addition, when alignment is performed using alignment marks in this way, a large number of wafers are placed on a stage one after another, and only the first circuit pattern is transferred to these wafers while being replaced, and then an exposure mask is applied. The second circuit pattern, which is an inverted pattern, may be transferred onto these wafers again by replacing the shielding plate or by moving the position of the shielding plate. Therefore, in this case, the first pattern and the second pattern and may be formed on separate exposure masks. This is effective when the pattern area is large.

Furthermore, either the first exposure or the second exposure may be performed first.

Furthermore, the projection exposure apparatus of the second embodiment of the present invention is
As shown in the figure. In this apparatus, an exposure mask 10 forms a first region R10 in which a desired circuit pattern is formed by a light-shielding pattern 2 made of a chrome film, and a black and white inverted pattern of the circuit pattern, and also forms an upper layer of this light-shielding pattern. A second region R20 includes a phase shifter layer 21 made of a PMMA pattern. This circuit pattern, that is, the first and second regions R10°R2
0 is the size on the mask of 25 cm as in the previous example.
x25■, and the circumferential regions are arranged adjacent to each other. Here, the film thickness of the phase shifter layer 21 is determined by the wavelength of light used as a light source, but here the shift amount is λ/2.
It is determined that

This projection exposure apparatus also enables highly accurate pattern transfer as in the first embodiment.

Further, the materials of the light-transmitting substrate and the light-shielding film are not limited to the examples, and can be changed as appropriate.

In addition, the present invention is not limited to the first and second embodiments, and the ratio of the exposure amount and the shift amount of the focal position between the first exposure and the second exposure are determined depending on the purpose. It can be modified as appropriate depending on the solution f11 degrees and dimensional controllability,
Modifications may be made without departing from the gist of the water-saturated invention.

(Effects of the Invention) As described above, according to the present invention, a mask pattern and a reversal pattern obtained by reversing black and white with respect to the mask pattern, which is slightly blurred and whose intensity is weakened, are projected onto the same exposure area. As a result, it is possible to achieve a resolution higher than that determined by the wavelength of the light source, the number of frontages of the imaging element, process parameters, etc., and it is also possible to improve the dimensional controllability of fine patterns. can.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a projection exposure apparatus according to a first embodiment of the present invention, FIG. 2 is a diagram showing a 70-chip exposure process using the same projection exposure apparatus, and FIG. 3 is a diagram showing a projection exposure apparatus according to a first embodiment of the present invention. FIGS. 4 to 7 are diagrams showing the relationship between MTF and spatial frequency for explaining the principle of the exposure method of the present invention. 1.10... Exposure mask, 2... Light shielding film pattern,
R1, R10...first region, R2, R20...second region, 3...projection lens, 4...phase shifter,
5... Shielding plate,... Light source, 6... Silicon substrate, 7... Stage, 21... Phase shifter layer. 2nd figure S = Possible U 4th figure S - 翫U Figure S 7th procedure Nem positive cause (self Te) 1. Display of the incident 1999 special rFI! 1m223661 No. 12, Name of the invention Exposure mask, exposure method and projection exposure device 3, Relationship with the person making the correction case (307) Co., Ltd.

Claims (5)

[Claims] (1) In an exposure mask comprising a light-transmitting substrate and a mask pattern made of a light-blocking material disposed on the light-transmitting substrate, the mask pattern includes a first pattern, and the first pattern. 1. An exposure mask comprising: a second pattern in which black and white are reversed; (2) The exposure mask according to claim 1, wherein the second pattern includes a phase shift layer that slightly shifts the phase of light transmitted through the first pattern. (3) In an exposure method in which lithography light is transmitted through an exposure mask and a pattern is transferred onto a substrate to be processed, a first exposure step in which projection exposure is performed through a first mask pattern; and a second exposure step in which the area exposed in the first exposure step is exposed by projection through a second pattern in which black and white is reversed and the phase is slightly shifted. exposure method. (4) In a projection exposure apparatus comprising a light source, an exposure mask, and an optical system that guides light from the light source onto the substrate via the exposure mask, the light from the light source is directed onto the substrate via the exposure mask. 1. A projection exposure apparatus comprising, on an optical path leading upward, a removable phase shift means for slightly shifting the phase of light transmitted through an exposure mask pattern. (5) In a projection exposure apparatus comprising a light source, an exposure mask, and an optical system that guides light from the light source onto the substrate via the exposure mask, the light from the light source is directed onto the substrate via the exposure mask. 1. A projection exposure apparatus, comprising a removable shielding means for shielding light transmitted from a part of an exposure mask pattern on an optical path leading upward.