Photomask having patterns to reduce power of a stepper

An energy-saving photomask comprises: at least one first pattern region in which a light can penetrate through the photomask without diffraction; and a second pattern region in which a plurality of fine patterns are formed in such a way to serve as slits through which the light is diffracted to increase the energy of the light irradiated relative to the first pattern region and diffracted to an extent that it comes to have an insufficient energy for the development of all photosensitive film except below the first pattern region. By virtue of the auxiliary patterns, the energy of the light incident on the photosensitive film can be rich at the auxiliary patterns contributes intensity of light to the desired portions without seriously affecting other portions. Because of a reduction of processing time, the photomask prolongs the lifetime of a light lamp in the stepper, as well as allows usage of a stepper with low power.

BACKGROUND OF THE INVENTION 
1. Field of the invention 
The present invention relates, in general, to a photomask useful to the 
exposure of a photosensitive film of a semiconductor device to a light 
and, more particularly, to a photomask capable of accomplishing the 
exposure with a small amount of energy, thereby saving the energy. 
2. Description of the Prior Art 
Generally, in order to form a predetermined pattern, a series of processes 
must be carried out, that is, coating a photosensitive film on a wafer, 
exposing it to a light along with a photomask and developing it. When a 
contact hole is to be formed, a greater energy of irradiating light is 
required than when other patterns are to be formed. 
In order to better understand the background of the present invention, 
description for a conventional photomask will be given next with reference 
to some figures. 
First, referring to FIG. 1, there is a plan view showing a photomask 
according to a conventional technique. In this photomask, a region for the 
exposure of photosensitive film to a light by which a contact hole will be 
formed is made of a non-chrome material 3, and the other regions are 
formed of a chrome layer 2. 
Referring to FIG. 2, there is shown a result of the exposure to a light 
using the conventional photomask of FIG. 1. As shown in these figures, on 
being irradiated on the conventional photomask in a stepper, a light is 
blocked in the regions of chrome layer 2 atop a quartz substrate 4, 
whereas it penetrates through the quartz substrate below the non-chrome 
region and reaches predetermined portions of a photosensitive film 7 
placed on a wafer 9. The irradiated, predetermined portions of the 
photosensitive film 7 are eliminated in a subsequent developing process. 
FIG. 3 shows the intensity of the light irradiated over the photosensitive 
film, indicating that the non-chrome region has higher intensities than 
the other regions. 
As will be expected, the exposure to a light using the conventional 
photomask is problematic in that if the chrome layer occupies a greater 
part of the photomask, like a contact hole mask, a greater energy for the 
exposure is required. In addition, in case of using a stepper with a low 
power, a high degree of resolution is difficult to obtain with the 
conventional photomask. 
SUMMARY OF THE INVENTION 
Therefore, an object is to overcome the aforementioned problems encountered 
in the prior art and to provide an energy-saving photomask designed to 
diffract an incident light at a plurality of auxiliary patterns, thereby 
forming a desired pattern on a wafer with less energy and hence saving the 
energy. 
In accordance with the present invention, the above object can be 
accomplished by a provision of an energy-saving photomask, comprising: at 
least one of first pattern region in which a light can penetrate through 
the photomask without diffraction; and a second pattern region in which a 
plurality of fine patterns are formed in such a way to serve as slits 
through which the light is diffracted to increase the energy of the light 
irradiated to the first pattern region and diffracted to an extent that it 
comes to have an insufficient energy to the development of all 
photosensitive film except below the first pattern region.

DETAILED DESCRIPTION OF THE INVENTION 
Hereinafter, the preferred embodiment of the present invention will be in 
detail described with reference to the accompanying drawings. 
To begin with, the technical principle of the present invention is 
introduced. A light with a constant wavelength shows various degrees of 
diffraction in dependence with a size of a slit. An auxiliary pattern 
which is greater than the wavelength of the light used in a stepper and 
capable of controlling the degree of the diffraction of the light can be 
utilized to form a pattern on a wafer. That Is, the images of the 
auxiliary pattern is not transferred to the wafer because of the large 
degree of diffraction. In addition, the intensity of the diffractive light 
is added to the intensity of the image resulting from a mask pattern, so 
that a predetermined pattern can be accurately formed on the wafer with 
less irradiation energy. 
A photomask to accomplish the principle of the present invention is shown 
in FIG. 4. As shown in this figure, besides main non-chrome regions 23, a 
plurality of fine auxiliary patterns 23' are formed of a non-chrome 
material in such a way to play a role as slits for the light irradiated 
over a chrome layer 22. The fine auxiliary pattern 23' is so sized as to 
have a shortest length therein longer than the wavelength of an 
irradiating source and a longest length shorter than three times of the 
wavelength. 
Referring now to FIG. 5, there is shown the procedure of lithography using 
the photomask of the present invention. As shown in these figures, a light 
irradiated over the photomask reaches a photosensitive film 27 (in this 
case, positive photosensitive film) atop a wafer 29 through a quartz 
substrate 24 straightly or in diffraction. 
The light incident over the photosensitive film formed on the wafer 29 is 
largely grouped into two: one comes from through the main non-chrome 
regions 23 which has great influence on the formation of a pattern of 
photosensitive film; the other comes from the diffraction by the slits, 
the auxiliary patterns, which distributes the light over wide ranges. In 
the meanwhile, the photosensitive film is exposed to a weak light, the 
diffracted light, at some predetermined portions 27 and to a more strong 
light, the sum of the vertically incident light through the non-chrome 
region and the diffracted light, at other predetermined portions 28 
(positive photosensitive film). 
Accordingly, as shown in FIG. 6, the distribution of energy 26 in the light 
incident on the photosensitive film results from the sum of the 
distribution of energy 6', formed in the absence of the auxiliary patterns 
23', and the distribution of energy 26" due to the auxiliary patterns 23' 
which is constant over all of the photosensitive film. Consequently, the 
more strengthened light is irradiated to the predetermined portions 28 of 
the photosensitive film, so that the pattern of the photosensitive film 
can be formed with less energy. In this connection, a mask manufacturer 
may control the distribution of energy in the incident light through the 
density and the proper arrangement of the auxiliary patterns 23'. 
Referring to FIG. 7, there is plotted the thickness of the photosensitive 
film left after the development with regard to the energy of the light. 
Developing the exposed photosensitive film leaves only the predetermined 
regions 22 eliminating the positive photosensitive film 28. For a certain 
amount (Ei) of energy necessary to remove the photosensitive film cannot 
be obtained with the diffracted light by the auxiliary pattern 23'. 
As described hereinbefore, a high energy distribution of an irradiating 
light over a predetermined portion can be obtained only by an appropriate 
rearrangement of the auxiliary patterns without increasing the intensity 
of light source, in accordance with the present invention. Therefore, the 
present invention can effect the reduction of processing time and prolong 
of the life time of a light lamp in the stepper as well as the utilization 
of the stepper with a low power. 
Other features, advantages and embodiments of the invention disclosed 
herein will be readily apparent to those exercising ordinary skill after 
reading the foregoing disclosures. In this regard, while specific 
embodiments of the invention have been described in considerable detail, 
variations and modifications of these embodiments can be effected without 
departing from the spirit and scope of the invention as described and 
claimed.