X-ray or gamma ray systems or devices – Specific application – Lithography
Reexamination Certificate
2002-03-29
2004-06-22
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Lithography
Reexamination Certificate
active
06754302
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an X-ray exposure apparatus for manufacturing devices such as microdevices by transferring a pattern from a reticle such as a mask to a substrate such as a wafer using X-rays as the exposure light.
BACKGROUND OF THE INVENTION
Semiconductor exposure apparatus of a variety of forms are in use in order to manufacture microdevices such as IC and LSI devices. Such a semiconductor exposure apparatus has an exposure light source specific to the apparatus and is so adapted that a circuit pattern written on a mask or reticle is burned into a wafer, which has been coated with a photoresist, by light emitted from the exposure light source.
It is required that the exposure light source have a short wavelength in order to raise the scale of integration of the microdevices. An X-ray light source has been proposed and developed as one candidate for a short-wavelength exposure light source.
X-ray light sources well known in the art include one using a synchrotron ring and one (referred to as a “point-source X-ray source” below) in which a target substance is irradiated with laser-light pulses to generate a plasma, and the plasma is used to produce X-rays.
The synchrotron ring is advantageous in that the X-rays generated exhibit a high intensity. A disadvantage of the synchrotron ring is its large size. This apparatus is inefficient in terms of cost and installation space unless the apparatus is provided with 10 to 20 ports per light source and an exposure apparatus is connected to each port. The point-source X-ray source, on the other hand, generates X-rays of comparatively low intensity, bit is small in size and generally is used by connecting one exposure apparatus per light source.
Various X-ray generating mechanisms have also been proposed for the point-source X-ray source. All of the point-source X-ray sources are such that radial X-rays having a certain solid angle are emitted from the X-ray source. In order for the point-source X-ray source to be used for the exposure of microdevices, it is desired that the X-rays that are projected upon the mask and wafer be parallel. To achieve this, an implementation has been considered in which the X-rays emitted from the point-source X-ray source are introduced to the exposure apparatus upon having their angle of divergence reduced using an X-ray optics element referred to as a collimator.
FIG. 11
is a schematic view illustrating an example of the structure of an X-ray exposure apparatus having a point-source X-ray source according to the prior art. In the X-ray exposure apparatus shown in
FIG. 11
, X-rays emitted from a point-source X-ray source
901
at a certain solid angle are introduced into a collimator
902
. The latter is designed in conformity with the solid angle of the X-rays introduced. X-rays output from the collimator
902
are introduced into an exposure unit
903
. The design is such that the angle of all X-rays output from the collimator
903
will be approximately perpendicular to the surface direction of a mask within the exposure unit
903
. An example of the structure of the collimator
903
is one in which a number of capillary tubes are shaped in accordance with the angle of the X-rays on the input and output sides and are bundled together. The exit of the point-source X-ray source
901
, the collimator
902
and an X-ray window
906
are constructed in the form of a chamber in which a gas can be sealed. In order to suppress attenuation of the X-rays, highly pure helium gas is sealed within the chamber as the atmosphere and the interior of the chamber is held at atmospheric pressure or lower. Though
FIG. 11
is an example by which the point-source X-ray source
901
and the collimator
902
are configured in an X-ray introduction chamber
905
, several other examples of implementation are available.
X-rays are introduced into the exposure unit
903
from the X-ray introduction chamber
905
through the X-ray window
906
. The latter is used as an X-ray introducing portion that serves also as a pressure partition if the pressure on the side of the X-ray introduction chamber
905
differs from that within the exposure unit
903
. An example of the X-ray window
906
known in the art is a thin film obtained by forming beryllium to a thickness of several microns to several tens of microns. The exposure unit
903
is constructed to suppress attenuation of the X-rays, highly pure helium gas is sealed within the chamber of the exposure unit
903
as the atmosphere and the interior of the chamber is held at atmospheric pressure or lower. If the gas purity and pressure in the X-ray introduction chamber
905
are the same as those in the chamber of the exposure unit
903
, the X-ray window
906
can be eliminated.
With regard to the exposure unit
903
, a mask
904
is carried in and out by a mask transport device, which is not shown. The mask
904
is held by a mask chuck (not shown) in order that exposure may be performed.
A wafer
903
is carried in and out by a wafer transport device, which is not shown. The wafer
907
is held by a wafer chuck
909
mounted on a wafer stage
908
in order that exposure may be performed. The wafer stage
908
has a precision positioning mechanism for positioning an exposure area on the wafer
907
with respect to the mask
904
.
X-rays introduced into the exposure unit
903
have their intensity measured by an X-ray sensor
910
outside the exposure area. On the basis of the measured X-ray intensity, the exposure unit
903
controls the X-ray source device in such a manner that the optimum amount of exposure will be obtained. For example, in the case of an X-ray source device that generates X-rays in a pulsed form, the amount of exposure is controlled by commanding the number of pulses generated and the intensity of each pulse.
However, in a case wherein the point-source X-ray source according to the prior art is such that one collimator is combined with one point-source X-ray source, a problem which arises is that a large part of the energy radiated from the light source is not utilized.
In
FIG. 11
, only area B is utilized in exposure; other areas A and C represent dead space. In order to facilitate an understanding of the concept,
FIG. 11
is drawn in such a manner that all X-rays emanate from the X-ray emission point of the point-source X-ray source. In actuality, however, emission of unnecessary X-rays is undesirable and, therefore, X-rays are shielded in the point-source X-ray source or exterior thereto. In either case, it can be construed that the efficiency with which all of the radiated energy of the light source is utilized is poor owing to the placement of various devices.
In order to solve the foregoing problem, the area of the collimator opening should be enlarged relative to the X-rays that emanate from the point-source X-ray source. However, if is it attempted to merely enlarge the single collimator, an angular disparity with respect to the emission angle of the collimator will grow larger as the periphery of the collimator is approached. This makes designing the apparatus extremely difficult.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been proposed to solve the foregoing problems of the prior art, and has as its object to provide an X-ray exposure apparatus in which the efficiency of utilization of all the radiant energy possessed by X-rays is raised over that of the prior art. The present invention adopts a creative approach wherein use is made of a plurality of collimators of a number that lend itself to actual design and one exposure unit is connected to each collimator.
Specifically, according to the present invention, the foregoing object is attained by providing an X-ray exposure apparatus comprising: an X-ray source for generating pulsed X-rays; first to nth exposure means which use X-rays emitted from the X-ray source, wherein the exposure means project patterns of first to nth masks onto respective ones of first to nth substrates that are to be exposed.
Here, “n” represents an integer of 2 or great
Canon Kabushiki Kaisha
Church Craig E.
Fitzpatrick ,Cella, Harper & Scinto
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