Phase-shifting mask with multiple phase-shift regions

Details Phase-shifting mask with multiple phase-shift regions Phase-shifting mask with multiple phase-shift regions

2000-06-30

2001-08-28

Huff, Mark F. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

Reexamination Certificate

active

06280888

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a phase-shifting mask and a method of manufacturing an electronic device using the mask. More particularly, it relates to formation of contact holes arranged at a high density in manufacturing a semiconductor integrated circuit device.
A dynamic random access memory (hereinafter referred to as the DRAM) functioning as a technology driver for a semiconductor integrated circuit device has played a significant role in promoting refinement and high integration of elements in a semiconductor integrated circuit device. Now, mass production of a DRAM of 64 Mbits designed in accordance with a 0.25 &mgr;m rule has been realized. Furthermore, production of a DRAM of 1 Gbit designed in accordance with a 0.18 &mgr;m rule has been expected.
In a DRAM of 1 Gbit, it is necessary to form each memory cell in an area of approximately 0.3 &mgr;m
2
, and hence, there is a demand for a cell pitch of 0.4 &mgr;m. A memory cell of an 8F
2
structure used in a memory includes one storage node contact in each cell. Therefore, it is necessary to adopt a technique to form a contact hole with a diameter of approximately 0.2 &mgr;m with a pitch of 0.4 &mgr;m or less.
As a technique to improve resolution in patterning contact holes through exposure, an attenuated phase-shifting mask is proposed. In this technique, a semi-transparent film is formed in a field region of a photomask, thereby shifting the phase of the field region by 180° from the phase of a transmitting hole region. Thus, interference is caused between transmitted light of these regions, so as to sharply define a pattern edge. By adopting this technique, an isolated contact hole with a diameter of approximately 0.2 &mgr;m can be formed. In this technique, however, it is difficult to separate contact holes from one another when the pitch therebetween is smaller than approximately 0.5 &mgr;m.
Therefore, use of an alternating phase-shifting mask having a higher degree of interference has been proposed for formation of contact holes with a smaller pitch (Japanese Laid-Open Patent Publication No. 62-50811). An alternating phase-shifting mask is a photomask provided with a phase shifter to every other transmitting areas for defining contact holes to be formed, so that a phase difference of 180 degrees can be caused between light transmitted by adjacent patterns. Such a phase shifter is generally formed by etching a photomask plate. By adopting this technique, a contact hole with a pitch of approximately 0.3 &mgr;m can be formed.
The aforementioned phase-shifting mask is effective in forming a contact hole array where contact holes are periodically two-dimensionally arranged in an array of rows and columns. However, it is difficult to apply the phase shifting mask to contact holes to be formed in positions shifted from the regular matrix positions.
When a DRAM memory cell with an area of 0.3 &mgr;m
2
or smaller is to be formed, it is preferred that metal plugs are formed in a storage node contact hole and a bit line contact hole as is disclosed in, for example, IEDM '96 Technical Digest, p. 593. When these two types of contact holes are to be simultaneously formed, the storage node contact holes are regularly arranged in an array of rows and columns, but the bit line contact holes are disposed in positions shifted by a ½ pitch. Accordingly, it is difficult to form these contact holes at the same time by using the alternating phase-shifting mask. Therefore, after the storage node contact holes are formed by using the alternating phase-shifting mask, the bit line contact holes are required to be separately formed by using an attenuated phase-shifting mask or the like. As a result, discrepancy in locations of these contact holes, i.e., relative placement errors, cannot be avoided, which obstructs the development of refined memory cells.
SUMMARY OF THE INVENTION
The phase-shifting mask of this invention comprises a transparent photomask plate, an opaque portion formed in the transparent photomask plate and transmitting portions formed in the transparent photomask plate, and the transmitting portions include plural first transmitting areas periodically arranged along a first direction and a second direction different from the first direction; and at least one second transmitting area provided in an area surrounded with adjacent four first transmitting areas among the plural first transmitting areas, a phase difference of substantially 180 degrees in exposure light is caused between adjacent two first transmitting areas among the plural first transmitting areas, and a phase difference of substantially 90 degrees in the exposure light is caused between the second transmitting area and the four first transmitting areas surrounding the second transmitting area.
Preferably, a surface of at least a part of the plural first transmitting areas is positioned at a different level from a main surface of the transparent photomask plate.
Preferably, a surface of at least a part of the plural first transmitting areas is recessed to be lower than the main surface of the transparent photomask plate.
Preferably, a surface of the second transmitting area is positioned at a different level from surfaces of the plural first transmitting areas.
Preferably, the surface of the second transmitting area is positioned at the same level as the main surface of the transparent photomask plate.
Preferably, the phase difference caused between adjacent two first transmitting areas among the plural first transmitting areas is in a range between 160 degrees and 200 degrees.
Preferably, the phase difference caused between the second transmitting area and the four first transmitting areas is in a range between 70 degrees and 110 degrees.
In one aspect of the phase-shifting mask, the first direction can be perpendicular to the second direction.
In another aspect of the phase-shifting mask, each of the plural first transmitting areas has a shape for forming a hole.
In still another aspect of the phase-shifting mask, the second transmitting area has a dimension larger than a dimension of each of the first transmitting areas.
In still another aspect of the phase-shifting mask, a pitch of the first transmitting areas measured along the first direction is approximately twice as large as a pitch of the first transmitting areas measured along the second direction.
Preferably, a dimension of each of the first transmitting areas measured along the second direction is smaller than a dimension thereof measured along the first direction.
In the method of manufacturing an electronic device of this invention, a phase-shifting mask including a transparent photomask plate, an opaque portion formed in the transparent photomask plate and transmitting portions formed in the transparent photomask plate is used, the transmitting portions of the phase-shifting mask includes plural first transmitting areas periodically arranged along a first direction and a second direction different from the first direction; and at least one second transmitting area provided in an area surrounded with adjacent four first transmitting areas among the plural first transmitting areas, a phase difference of substantially 180 degrees in exposure light is caused between adjacent two first transmitting areas among the plural first transmitting areas, and a phase difference of substantially 90 degrees in the exposure light is caused between the second transmitting areas and the four first transmitting areas surrounding the second transmitting area, and the method comprises the steps of forming a resist layer on a film used for forming a part of the electronic device; irradiating the resist layer with the exposure light through the phase-shifting mask; developing the resist layer; and patterning the film partially covered with the resist layer.
In the method of manufacturing an electronic device, the electronic device can be a semiconductor integrated circuit device, and the first transmitting areas and the second transmitting area of the phase-shifting mask can de

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