Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Reexamination Certificate
2000-06-26
2001-11-20
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
Reexamination Certificate
active
06320195
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus, a method of making the apparatus, an exposure method, and a device and a manufacturing method of the device. More particularly, the invention relates to an exposure apparatus used in a lithographic process, a method of making the apparatus, an exposure method used in a lithographic process, and a device manufactured by the use of the exposure method, and a manufacturing method of the device.
2. Description of the Related Art
Various exposure apparatus are conventionally used in a lithographic process for the manufacture of micro-devices such as integrated circuits. As this exposure apparatus, an optical exposure apparatus such as a step-and-repeat type reducing projection exposure apparatus (known as a stepper) is mainly used. Though within a limited range of fields, there is also utilized a charged particle beam exposure apparatus performing exposure by the use of a charged particle beam such as an electron beam or an ion beam for forming an extra-fine circuit pattern on a substrate such as a wafer. An electron beam exposure apparatus (known also as an EB exposure apparatus) is a typical example of the charged particle beam exposure apparatus.
FIG. 9
schematically illustrates an example of the conventional electron beam exposure apparatus. The electron beam exposure apparatus
110
shown in
FIG. 9
comprises a base plate
103
horizontally supported on a plurality of vibration isolators
102
, a vacuum chamber
104
of a high degree of vacuum provided adjacent to the base plate
103
, a pre-stage chamber of a slightly lower degree of vacuum than in the vacuum chamber
104
, an electron beam barrel
108
fixed to an upper portion of the vacuum chamber
104
and having the lower end thereof inserted into the vacuum chamber
104
, and a stage
106
housed in the vacuum chamber
104
and moving two-dimensionally while holding a wafer W on the base plate
103
.
In this apparatus, it is possible to change the irradiation point on the wafer W by a slight amount by deflecting the electron beam EB emitted from an electron gun
109
and to the right by means of a deflection electrode (not shown in Figs.). A large change of the irradiation point of the electron beam EB relative to the wafer W has however been accomplished through two-dimensional movement of the stage
106
.
In the conventional electron beam exposure apparatus, a medium-acceleration type electron beam barrel accelerating an electron beam by a voltage within a range of 30 to 50 kV has mainly been used, taking into account the thickness and the sensitivity of the resist layer used. When carrying out exposure with such a medium-acceleration type electron gun barrel, however, it is necessary to conduct ghost exposure (double exposure) to avoid an adverse effect of back scattered electron, and a Coulomb blur has caused a decrease in resolution.
For the purpose of solving these problems, an electron beam exposure apparatus was recently developed, which eliminated the necessity of the above-mentioned ghost exposure, and particularly, adopted an electron beam barrel performing high-voltage (for example, 50 to 100 kV) acceleration to prevent a decrease in resolution caused by the Coulomb blur and improve the throughput. With such an apparatus, however, the exposing efficiency of the resist relative to the energy necessary for acceleration of the electron beam is reduced to a lower level than in the use of medium-acceleration electron beam. The electron beam barrel is required to be larger, to such a level that the height reaches a value within a range of 150 to 200 cm.
In the conventional electron beam exposure apparatus, as described above, a structure in which a wafer stage making a two-dimensional movement was adopted because of the necessity to adopt a large-scale electron beam barrel including the case of the medium acceleration. With this apparatus, however, the footprint (floor area occupied by the apparatus) of the main body of the apparatus becomes larger along with the tendency toward a large diameter of wafers. More specifically, in order to achieve exposure of the entire surface of a wafer in an apparatus of this type, the stage must provide a movement stroke twice as large as the wafer diameter. In order to expose the entire surface of a 12-inch wafer(a wafer having a diameter of 300 mm), which is likely to become available in the near future, the stage must have a stroke of at least ±300 mm around the barrel, as a result the footprint requires over 600 mm square. Actually, it is necessary to provide a vacuum chamber and a wafer introduce/removal mechanism, resulting in a scale twice as large.
In the electron beam exposure apparatus, the exposing speed is lower compared with the optical exposure apparatus. That is, the number of wafers capable of being fabricated in a unit time is small. As a result, when carrying out exposure in the mix-and-match manner with an optical exposure apparatus, i.e., when exposing a layer by optical means and exposing another layer with an electron beam, it becomes necessary to use electron beam exposure apparatus in a number several times as large as that of optical exposure apparatus. For example, while an optical exposure apparatus can expose 80 12-inch wafers per hour, a high-acceleration electron beam exposure apparatus has a throughput of only about five to ten wafers per hour. In order to achieve the same throughput, electron beam exposure apparatus in a number even eight times as large as that of an optical exposure apparatus are necessary. If, in the case, an optical exposure apparatus and an electron beam exposure apparatus are designed with a same concept, and the footprint is designed to be equal between the two, the electron beam exposure apparatus may require a larger footprint due to the area occupied by a vacuum chamber. This result in the necessity of a very large clean room, leading to a very high cost.
SUMMARY OF THE INVENTION
The present invention was developed under the circumstances as described above, and has an object to provide an exposure apparatus and an exposure method, which permit reduction of the footprint.
A lower acceleration voltage to a charged particle beam leads in general to a higher response of a resist and a shallower resist penetration depth. The resist film on an object to be exposed is therefore limited to thinner ones. Therefore, in order to use a low-acceleration charged particle beam while keeping a resist film thickness necessary for a conventional manufacturing process of semiconductor devices, it has so far been necessary to adopt a special resist such as a surface-reactive resist or the double-layer resist method. When such a process is adopted, the resist coating step has caused a cost problem. In the conventional charged particle beam exposure apparatus, therefore, a medium-acceleration or a high-acceleration charged particle beam barrel has been employed. Recently, however, improvement of the process technology (wafer flattening technique) is making it possible to reduce the film thickness, even with the use of an ordinary resist by flattening the wafer surface by the application of, for example, CMP (chemical & mechanical polishing). As a result, the use of a low-acceleration charged particle beam barrel with a high resist response performance has become a practical choice. In the case of an electron beam exposure apparatus, the progress made in the resist technology now makes it possible to use a low-acceleration electron beam barrel even when the film is somewhat thick. The low-acceleration charged particle beam barrel can easily be downsized and made movable. The present invention was developed with these points in view.
According to a first aspect of the invention, there is provided an exposure apparatus comprising a substrate holder holding a substrate; and a charged particle beam barrel movable along a plane parallel to the surface of the substrate to expose the substrate by irradiating a charged particle beam o
Nguyen Kiet T.
Nikon Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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