JPH05315219A - Reduction projection exposure method - Google Patents

Abstract

PURPOSE:To easily manufacture a photomask for phase-shifting exposure use by a method wherein a light-shielding pattern and a phase shifter are formed on separate substrates. CONSTITUTION:A prescribed pattern composed of a light-shielding material 4 such as chromium or the like is formed on a transparent substrate 2 such as quartz or the like; a first photomask 1 is prepared. In addition, a phase shifter 6 which corresponds to the pattern composed of the light-shielding material 4 is formed on a transparent substrate 5 which is different from said transparent substrate 3; a second photomask 2 is prepared. The first photomask 1 is bonded to the second photomask 2; a photomask for phase-shifting exposure use is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduction projection exposure method used in a semiconductor device manufacturing process, and more particularly to a reduction projection exposure method using a phase shift method.

[0002]

2. Description of the Related Art Optical integration and density increase of semiconductor integrated circuits are progressing year by year, and the design rule thereof is close to 0.5 μm. Due to such miniaturization, in optical sography, reduction projection exposure apparatuses have been made to have higher NA and shorter wavelength.

However, in the reduction projection exposure apparatus, although the resolution is improved by increasing the NA of the lens, the depth of focus is decreased conversely. Therefore, from the viewpoint of the depth of focus, it is difficult to improve the resolution by increasing the NA of the lens beyond this.

Therefore, in recent years, called the phase shift method,
A method has been proposed in which the resolution is improved by selectively reversing the phase of light passing through a mask.

The phase shift method and its photomask will be briefly described below. FIG. 3A shows a sectional view of a general phase shift mask. A predetermined pattern is formed by a light shielding material 22 such as chrome on a transparent substrate 21 such as quartz. A transparent film pattern called a phase shifter 23 is formed on one of the adjacent openings.
A material such as SOG or SiO ₂ is usually used for the phase shifter 23, and its thickness t is selected so that t = λ / (n−1). Where λ is the wavelength of the exposure light and n
Is the refractive index of the phase shifter material. Using such a phase shift mask, reduction projection exposure is performed on a semiconductor substrate coated with a photoresist. At this time, the phases of the light transmitted through the two openings in the figure differ from each other by 180 °,
On the semiconductor substrate, a light amplitude distribution as shown in FIG. 3B is obtained. The light intensity given by the square of the amplitude is as shown in FIG. 3C, and the two apertures are separated and resolved.

[0006]

In this conventional reduction projection exposure method of the phase shift method, since the photomask has the light-shielding pattern and the phase shifter formed on the same transparent substrate, the photomask is manufactured and inspected / corrected. There was a problem that it was difficult.

For example, when forming a light-shielding pattern of chromium on a quartz substrate and then forming a phase shifter of SOG, there is a problem that the coating film thickness of SOG becomes non-uniform due to the step of the underlying layer. Further, there are problems that the light-shielding pattern is deteriorated by the heat treatment of SOG, and the light-shielding pattern is displaced due to the stress during the heat treatment.

[0008]

In the reduction projection exposure method of the present invention, a pattern of a light-shielding material and a phase shifter corresponding thereto are formed on different transparent substrates, and these two photomasks are overlapped to perform reduction projection exposure. .

[0009]

The present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a photomask according to an embodiment of the present invention. Light-shielding material 4 such as chrome on a transparent substrate 3 made of quartz
And a second photomask 2 having a phase shifter 6 corresponding to the pattern of the first photomask 1 formed on the transparent substrate 5 by SOG or the like is fixed in proximity to several μm. . Here, the second photomask 2
A layer slightly higher than the internal phase shifter 6 is formed in the periphery of the phase shifter 6 so that the phase shifter 6 and the pattern of the light shielding material 4 of the first photomask 1 do not come into contact with each other. After that, these two photomasks may be placed on a stepper, which is a reduction projection optical system, and exposed in the same manner as in the prior art.

Next, a second embodiment of the reduction projection exposure method of the present invention will be described with reference to the drawings. FIG. 2 is a diagram showing a second embodiment of the present invention. In this embodiment,
The first photomask 11 having a light-shielding pattern and the second photomask 12 having a phase shifter are separated. Second
The pattern of the photomask 12 is projected on the first photomask 11 by the lens system 13 by transillumination. Then, the first photomask 11 is illuminated with the light whose phase is selectively inverted by the second photomask 12, and the lens system 14
Then, reduction projection exposure is performed on the semiconductor substrate 15 coated with the photoresist. In this embodiment, since the first photomask 11 and the second photomask 12 are separated from each other, there is an advantage that there is no risk of accidentally making contact with each other and damaging the photomask.

[0011]

As described above, according to the present invention, the light-shielding pattern and the phase shifter of the photomask to be used are formed on different transparent substrates, respectively, which facilitates the manufacture of the respective products and allows the inspection to be sufficiently performed by the conventional technique. Become so. Further, the phase shifter is more easily damaged than the light-shielding pattern, but even in this case, only the phase shifter can be replaced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating a second embodiment of the present invention.

FIG. 3 is a vertical sectional view of a conventional phase shift mask.

[Explanation of symbols]

 1 1st photomask 2 2nd photomask 3 Transparent substrate 4 Light-shielding material 5 Transparent substrate 6 Phase shifter 11 1st photomask 12 2nd photomask 13 Lens system 14 Lens system 15 Semi-moving body substrate 21 Transparent substrate 22 Light-shielding material 23 Phase Shifter

Claims (1)

[Claims] 1. A photomask in which an original image pattern is formed of a light-shielding film on an optically transparent substrate, and a phase shift layer for changing the phase of illumination light is provided in a specific opening, and the photomask is mounted, and a desired mask is mounted. In a reduction projection exposure method using a stepper for reducing and projecting a pattern on a semiconductor wafer, the light shielding film and the phase shift layer are formed on different transparent substrates, respectively, and the light shielding film and the phase shift layer are A reduction projection exposure method in which a transparent substrate on which only the light-shielding film is formed and a transparent substrate on which only the phase shift layer is formed are used at the same time, and exposure is performed by the stepper.