Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Having diverse electrical device
Reexamination Certificate
2001-06-07
2003-09-30
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Having diverse electrical device
C065S017300, C065S030100, C359S335000, C438S022000, C438S023000
Reexamination Certificate
active
06627468
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing an optical element, an optical element, an optical system using the optical element, an optical apparatus and exposure apparatus using the optical system, and a method for manufacturing a device. In particular, the present invention relates to a diffractive optical element suitable for semiconductor equipments and a method for manufacturing the diffractive optical element, an optical system and optical instrument using the diffractive optical element, and a device and a method for manufacturing the device.
2. Description of the Related Art
Refractive optical elements such as a lens and prism are frequently used for optical systems constituting optical instrument. Particularly, the diffractive optical element has been used as an optical element for converting a incident wavefront into a desired wavefront. This diffractive optical element has characteristics that are not found in the refractive optical element such that, for example, it has an inverse dispersion value to that of the refractive optical element, and the optical system can be compactly arranged.
The diffractive optical element has been manufactured by mechanical grinding, or by using a mold manufactured by mechanical grinding. However, the optical element is desirably manufactured with pitches as fine as possible, in order to endow the diffractive optical element with a large power as an optical element. Accordingly, applying a semiconductor manufacturing process has been considered.
A semiconductor manufacturing technology is usually applicable when the diffractive optical element assumes a binary shape. This technology enables fine pitches to be manufactured with high precision as compared with conventional mechanical grinding method. Consequently, a binary type diffractive optical element in which blazed shapes are approximated by stepped shapes has been actively studied in recent years.
The binary optics will be described in detail hereinafter with reference to
FIGS. 7A
,
7
B and
8
.
In
FIG. 7
, the reference numeral
50
denotes a Fresnel lens, the reference numeral
51
denotes a blazed shape, the reference numeral
52
denotes a binary optics, and the reference numeral
53
denotes a stepped shape. In
FIG. 8
, the reference numeral
55
shows a whole view of the diffractive optical element.
Ideally, the Fresnel lens
50
as a diffractive optical element should have a cross section of the blazed shape
51
as shown in
FIG. 7A
, which enables light diffraction ratio against the design wavelength to reach almost 100%. However, since machining into a perfect blazed shape
51
is actually difficult, the blazed shape
51
is approximated by quantization to form a binary optics
52
having a stepped cross section
53
as shown in FIG.
7
B. Although the binary optics
52
is an approximation of the Fresnel lens
50
, it ensures a diffraction efficiency of the primary diffraction light of 90% or more.
The minimum line width of the diffractive optical element should be as fine as possible in order to enhance the degree of approximation and to endow the diffractive optical element with high power as an optical element. Accordingly, a lithography process that has been experienced in the production of semiconductors is used for obtaining a high performance diffractive optical element.
The semiconductor manufacturing apparatus as used herein is designed on the premise that a wafer with a thickness of less than 1 mm is handled. Consequently, the diffractive optical element manufactured by using the semiconductor lithography process is formed as a wafer-shaped optical member.
Assume that the diffractive optical element obtained by the manufacturing method as described above is employed as the optical system of a semiconductor exposure apparatus using an eximer laser such as a KrF, ArF or F2 laser.
FIG. 4
shows a schematic drawing of the exposure apparatus for manufacturing semiconductors.
In
FIG. 4
, the letter A denotes a light source of an eximer laser such as a KrF, ArF or F2 laser. A light flux C from the light source is guided to an illumination optical system D by a mirror B, and the light flux after passing through the illumination optical system illuminates the surface of a reticle E as a first block. The light flux carrying a line of reticle information is projected onto a light-sensitive substrate (a wafer) G through a reductive projection optical system F. The letter H denotes a wafer stage, which adjust the wafer G at a focal point by means of the wafer stage H.
While an oxide such as alumina and silica glass, or a fluoride such as calcium fluoride and magnesium fluoride may be used as a material of the optical element using a light source of the eximer laser such ad KrF, ArG or F2 laser, silica glass is mainly used since it is suitable for machining, homogeneous and has a low thermal expansion coefficient. As disclosed in Japanese Patent Publication No. 6-48734, the concentrations of OH group and hydrogen molecules are further controlled in a high purity synthetic silica glass (synthetic silica glass) prepared by controlling the content of impurities in order to use the material as silica glass on which a laser beam having a wavelength of 300 nm or less is irradiated from the eximer laser source such as the KrF, ArF or F2 laser, thereby permitting such silica glass to be used as a material having high resistivity against a long term laser irradiation.
However, the quality of silica glass as disclosed in Japanese Patent Publication No. 6-48734 has been controlled on the premise that it is used for a refractive optical element commonly called as a lens. Japanese Patent Laid-Open No. 10-330120 discloses a method for controlling the hydrogen concentration in the silica glass for irradiating with the eximer laser by annealing, wherein discussions have been mainly related to the silica glass having a minimum thickness of 10 mm or more by adjusting the thickness of the silica glass before annealing to be larger than 10 mm or more as compared with the finally required thickness.
In manufacturing the diffractive optical element through the lithography process, the semiconductor manufacturing apparatus to be used for this purpose is designed within a range of the standard of the wafer, and the highest accuracy is obtained within the range. While a variety of standards of the wafer are known, the outer diameter is defines to be 150 mm (6 inches), 200 mm (8 inches) and 300 mm (12 inches), and the range of thickness is also defined depending on each size. The thickness of the wafer is 1 mm or less, forming a substrate far more thinner than the conventional optical elements. However, remodeling of the semiconductor manufacturing apparatus so as to be used out of the Si wafer standard makes it difficult to maintain its accuracy.
Resist patterning and etching steps are included in the detailed lithography process. In the resist patterning steps, an organic resist is coated, the coating pattern is exposed to a light through a reticle on which a planar shape to be printed is formed, and a resist pattern having a desired planar shape is formed after baking and development steps. Since an apparatus called a spinner, which allows the substrate to rotate at a high speed to coat the resist with a uniform film thickness, is used for coating the resist, the heavier substrate gives so much load on the spinner that control of rotation turns out to be difficult.
While a hot plate is used in the baking step with a strict temperature control in a unit of second, temperature control of a substrate such as silica glass having a low heat conductivity and large thickness is quite difficult. Meanwhile, although the substrate is etched with chemicals using the resist pattern as a mask, or the substrate is processed with a dry etching machine using a plasma, the dry etching method is mainly used since its accuracy is high. While the dry etching machine requires a device for cooling the substrate, temperature control of a sub
Berry Renee R.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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