Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-11-20
2003-11-04
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S322000, C430S396000, C430S397000, C355S053000
Reexamination Certificate
active
06641981
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method, exposure apparatus, and device manufacturing method and, more particularly, to an exposure method and apparatus used in a lithography process for manufacturing a semiconductor device, liquid crystal display device, image pick-up device (such as a CCD), thin-film magnetic head, or the like and a device manufacturing method using the exposure method and apparatus in the lithography process.
2. Description of the Related Art
Conventionally, in a lithography process for manufacturing semiconductor devices and the like, various types of exposure apparatuses designed to form predetermined patterns on a substrate such as a wafer or glass plate (to be referred to as a “wafer” or “substrate” hereinafter, as needed). Recently, with increases in the degree of integration of semiconductor devices, the following exposure apparatuses are mainly used: a step-and-repeat type reduction projection exposure apparatus (so-called stepper) capable of transferring fine patterns formed on a mask or reticle (to be generically referred to as a “reticle” hereinafter) onto a plurality of shot areas on a wafer coated with a photoresist through a projection optical system with a relatively high throughput and high precision and a sequential moving type projection exposure apparatus such as a step-and-scan type scanning exposure apparatus (so-called scanning stepper) obtained by improving the above stepper.
The resolution of the projection optical system of such a projection exposure apparatus can be expressed by R=k
1
·&lgr;/N.A., as is well-known as the Rayleigh formula, where R is the resolution of the projection optical system, &lgr; is the wavelength of exposure light, N.A. is the numerical aperture of the projection optical system, and k
1
is a constant determined by the resolution of a photoresist and other processes. To improve the resolution of the projection optical system, therefore, the numerical aperture N.A. may be increased.
A depth of focus DOF of the projection optical system is expressed by DOF=k
2
·&lgr;/(N.A.)
2
where k
2
is a proportional constant. If, therefore, the numerical aperture N.A. is simply increased, the depth of focus DOF may become too small. It is known that when periodic lattice patterns like patterns for memory circuit portions are to be exposed, the depth of focus can be substantially increased, with the resolution being improved, by a so-called modified illumination method of tilting the principal ray of exposure light from an illumination optical system.
It is also known that when isolated patterns such as contact hole patterns are to be exposed, the depth of focus of the projection optical system can be substantially (apparently) increased by a so-called FLEX method, DP exposure method, CDP exposure method, or the like in which the positional relationship between a wafer and the imaging plane of the projection optical system in the optical axis direction of the projection optical system is continuously or intermittently changed according to a desired procedure so that an irradiation area on the wafer surface which is irradiated with exposure light through the projection optical system is always located in a range having a predetermined width in the optical axis direction, which includes the imaging plane, and the distribution of light amounts supplied onto the wafer, corresponding to the relative positions of the imaging plane and wafer surface, becomes a predetermined distribution. Exposure methods of substantially increasing the depth of focus of the projection optical system by continuously or intermittently changing the positional relationship between the imaging plane and the wafer in the optical axis direction of the projection optical system according to the desired procedure will be generically referred to as a progressive focus exposure method hereinafter. For example, the progressive focus exposure method used by a static exposure apparatus such as a stepper is disclosed in, for example, Japanese Patent Laid-Open Nos. 63-42122 and 5-13305. The progressive focus exposure method used by a scanning exposure apparatus such as a scanning stepper is disclosed in, for example, Japanese Patent Laid-Open Nos. 4-277612 and 6-314646.
In the conventional progressive focus exposure method disclosed in each of the above references, when patterns such as contact hole patterns are to be transferred onto a plurality of shot areas on a wafer, exposure is performed under the same conditions (e.g., the relative moving range (so-called Z swing width) of the wafer surface with datum to an imaging plane, light amount) for each shot area.
According to the principle of resist coating by a coater (resist coating unit), the thickness of a photosensitive agent (resist) layer formed on the wafer varies from a central portion to peripheral portion of the wafer. In addition, the thickness distribution of the resist layer on the wafer is unique to each resist coating unit. Conventionally, such variations in resist layer thickness have hardly raised problems. With further increases in the degree of integration of semiconductor devices, accompanied with a reduction in circuit pattern size, and an increase in wafer size, variations in the shapes of isolated pattern images, mainly contact hole pattern images, among shot areas due to variations in resist layer thickness cannot be neglected.
Semiconductor devices will further increase in the degree of integration in the future, and wafers tend to further increase in size. It is therefore expected that variations in the shapes of isolated pattern images such as contact hole pattern images due to the above variations in resist layer thickness will further become noticeable.
In a liquid crystal exposure apparatus or the like, patterns having different shapes are transferred onto a plurality of shot areas on the same substrate with relatively high frequency. Such operation is sometimes performed in a semiconductor exposure apparatus. In such a case, patterns having different shapes are formed in shot areas on the respective layers on the substrate. For this reason, when overlay exposure is performed on a subsequent layer, detection light from a focus sensor for detecting the position (focus position) of the substrate in the optical axis direction of the projection optical system may be affected by stepped portions on the surface due to the shapes of patterns that have already been formed on the substrate or the difference in thickness between resist layers, resulting in a detection error. As in the above case, a plurality of patterns transferred onto the respective shot areas may not be formed in desired shapes with high precision owing to variations in resist layer thickness. When the target value of the focus sensor is fixed, in particular, an actual pattern shape tends to differ from a desired pattern shape. Even if the above progressive focus exposure method is used under the same conditions (e.g., the relative moving range of the wafer surface with datum the imaging surface, so-called Z swing width, light amount, and the like), shape differences occur more or less. The above shape differences inevitably occur almost especially when patterns requiring predetermined shapes in the depth direction such as pixel patterns in a liquid crystal display device and contact hole patterns and other patterns requiring no predetermined shapes in the depth direction such as line-and-space patterns are to be formed on the same layer on the same substrate by exposure.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its first object to provide an exposure method and apparatus which can suppress variations in the shapes of pattern images transferred/formed on a substrate.
It is the second object of the present invention to provide an exposure method and apparatus which can transfer all patterns having different shapes onto the same substrate with high precision in desired shap
Fujitsuka Seiji
Kaneko Kenichirou
Morioka Toshinobu
Huff Mark F.
Nikon Corporation
Sagar K
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