Phase shift mask and manufacturing the same

Details Phase shift mask and manufacturing the same Phase shift mask and manufacturing the same

2001-03-08

2003-05-06

Rosasco, S. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

Reexamination Certificate

active

06558855

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photo mask, more particularly to a halftone phase shift mask suitable for manufacturing fine devices such as a semiconductor device, a semiconductor integrated circuit device, a superconductor device, a micromachine, and electronic devices, in particular suitable for forming very fine patterns, and a production method of the same.
2. Description of the Prior Art
In the manufacturing of semiconductor integrated circuit (IC) devices, a technique known as lithography is used for transferring very fine circuitry patterns onto a semiconductor wafer. The lithograph technique needs in general a projection exposure apparatus, which loads a photomask and transfers the patterns drawn on the photomask thus loaded onto a semiconductor wafer to form patterns of devices thereon. Since the exposure area of an exposure apparatus with a higher resolution is smaller in size than the area of the wafer
21
to be projected, a wafer surface plane figure will be divided into a plurality of “shots” as is shown in
FIG. 2
, and will be fed in stepping or scanning by one area after another to expose a plurality of chips
22
thereon. At the exposure, a scribing area
23
for separating chips each other will be provided around each chip.
In recent years, the patterns have been made finer than ever for accommodating the requirement of large-scale, high-integration of devices as well as improved device operation speed. Under such circumstances, the wavelength of the exposing light emitted from the exposure apparatus for use in the pattern formation is being shortened. As an alternative, an exposure technique known as halftone phase shifting is also used. The halftone phase shifter mask is a mask having a translucent film (referred to as a halftone film) formed on a transparent plate for attenuating the exposing light and shifting the phase. The transmissivity of the exposure light through the film is, in general, thought desirable in the range between approximately 1% and 25%. The light transmitted through this film is adjusted so as to have-certain phase difference from the light, that does not pass through the film. The best phase difference for achieving the highest resolution is at 180 degrees and the odd multiples thereof. However, the resolution will be more or less improved when the phase is approximately in 180 degrees ±90 degrees. It is known in general that the resolution may be improved by approximately 5% to 20% when using a halftone mask.
In the chip exposure, a certain part of outer frame area belonging to the adjacent shot may be overlapped to the pattern formed. When a photo mask is provided with a shade film having a sufficient shading (shielding) performance such as made of Cr or the like, the light transmitted through the outer frame area may cause probably no problem since its amount is sufficiently small. However, when using a halftone mask, the outer frame area is also a part of the halftone mask and therefore is not a perfect shield. The light transmitted through the outer frame area, which may be attenuated but not shut off, will be superposed on the pattern to be formed. The area having exposed to the superposed light will have such a problem as the thickness loss of the resist to be exposed or the decreased resolution. In accordance with the prior art technique, a shade film made of Cr was formed on the outer frame area to solve this problem. The shading film made of Cr is referred to as ‘Cr shade band’
An exemplary structure of a mask having the Cr shade band is shown in FIG.
3
. In the figure, FIG.
3
(
a
) is a plan view of a mask, and FIG.
3
(
b
) is a cross-sectional of the mask taken along with the line A-A′. A desired pattern
31
to be delineated is placed on a chip field
32
made from a halftone film (the chip field is a pattern forming area, corresponding to a circuit pattern area in manufacturing semiconductor devices). On the entire outer field surrounding the chip field
32
, a Cr shade film
33
is deposited. In this figure, the reference numeral
36
designates a transparent plate.
The pattern on this chip field
32
will be delineated on the wafer by exposing it to form a chip
22
shown in FIG.
2
. If the Cr shade film
33
is not deposited, the exposure will be superposed on the area
34
in the vicinity of the outer periphery of the chip field. This may happen because of foggy effect by exposure in the peripheral region. Although, in general, the exposure apparatus has a masking blade for adjusting the area size of exposure field, the precision of position alignment is as low as on the order of about 50 micrometers, and in addition, the inherent lack of sufficient sharpness of shielding characteristics of the masking blade cause the foggy effect. The multiple exposures on the outer periphery of the chip field may result in a poor resolution. On the other hand, when a Cr shade film
33
is applied to the entire surface area of the peripheral region as shown in
FIG. 3
, such problems may not happen as the exposure light will be shielded with a sufficient sharpness at the border.
As an alternative to the use of Cr shade band, a halftone shade band method has been proposed, in which a dense grating pattern or a checker pattern may be cut on the halftone film, the pattern being finer than the resolution of the exposure apparatus used in order to well decrease the transmissivity of the exposure light passing through the patterned area by making use of the diffraction. The method above is disclosed in the Japanese Unexamined Patent Publication No. Hei 06-175347.
References on the halftone phase shift include the Japanese Unexamined Patent Publication No. Hei 05-181257, which disclosure is incorporated herein as a reference.
Now referring to
FIG. 4
, the procedural steps of producing a halftone phase shift mask with a Cr shade band is shown according to a prototype experiment conducted by the inventors of the present invention. As shown in FIG.
4
(
a
), on a quartz glass plate
40
a halftone film
41
, a Cr film
42
, and a resist film
43
in the order were sequentially deposited prior to exposing a desired pattern (
44
). It is to be noted here that the Cr film
42
was formed by the sputter technology. Then the plate was developed to form a resist pattern
43
′ shown in FIG.
4
(
b
). Then, the exposed Cr film
42
and halftone film
41
were etched successively to develop Cr pattern
42
′ and halftone film pattern
41
′ as shown in FIG.
4
(
c
). Next, after removing the resist
43
′ as in FIG.
4
(
d
), resist
45
was again applied thereto as shown in FIG.
4
(
e
) and the chip field was exposed (
46
). Then the development lead to the resist pattern
45
′ formed as shown in FIG.
4
(
f
), while Cr film remaining on the surface unmasked by the resist was removed by etching to form the Cr pattern
42
″ as shown in FIG.
4
(
g
). Finally the resist
45
′ was removed to obtain the halftone phase shifting mask as shown in FIG.
4
(
h
) (which corresponds to FIG.
3
(
b
)).
The inventors of the present invention have found that, after the experimental production cited above, there exist problems as follows. As the halftone phase shift mask using the Cr shade band has a structure in which the Cr film is deposited thereon in addition to the halftone film, (1) there are required a number of steps in manufacturing the mask, causing the high cost; (2) in addition to the considerable number of steps, the process contains such steps as sputtering and etching of the Cr film, which may often cause some defects by a particle, resulting in a lower yield of mask manufacturing; (3) in the process steps from FIGS.
4
(
f
) to (
g
), the decreased phase controllability of the halftone film may be resulted by partly inhomogeneous etch during the removal of the Cr film that covers the fine-patterned halftone phase shift mask, as well as the accuracy of sizing the patterns may be decreased; (4) a material for the halftone mask should

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