Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1998-12-24
2003-04-29
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S322000, C382S144000
Reexamination Certificate
active
06555273
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a glass substrate which is mainly used for an electron device and which is capable of patterning with high accuracy, a photomask blank and a photomask using the glass substrate.
The known photolithography method is generally used to form a fine pattern in a step for fabricating a semiconductor integrated circuit and a photomask.
For instance, the pattern is transferred on a transparent substrate by the use of the photomask. Herein, the transparent substrate is finished to a mirror surface by accurately polishing it. Further, the photomask is made by forming the pattern thereon by the use of a light shielding film, such as, a chromium film.
Recently, strict condition has been required for fine defects (contaminant on a surface, flaw, and stain) with respect to the mirror-finished transparent substrate which is polished with high accuracy and high density.
An inspecting method for removing the fine defects from the transparent substrate has been suggested in Japanese Unexamined Patent Publication No. Sho 58-162038 (thereinafter, referred to as a conventional reference).
In this conventional reference, a light beam is focused into a fine region on a pattern surface. In this condition, a surface state of the substrate is inspected by comparing a reflected output with a transmitted output from the pattern surface.
However, in the conventional reference, only when the light beam is irradiated to a constant direction, the inspection is carried out by comparing the reflected output with the transmitted output.
In consequence, it is difficult to accurately detect a fine flaw having a specific polarity on the surface of the glass substrate even when the latest inspection apparatus is used. Further, the defect, such as the stain, inside the glass substrate can not be detected at all.
In this case, the flaw having the specific polarity is formed via a trace through which an undesirable contaminant passes by mixing the contaminant during a polishing step of the glass substrate. Alternatively, the flaw may be formed when the glass substrate is inserted into a supporting case during moving the glass substrate.
Further, the flaw may be also formed when the glass substrate is handled after the polishing step. In this event, it is difficult to detect the flaw by the normal inspecting method or apparatus disclosed in the conventional reference.
Moreover, it is assumed that the size of the flaw having the specific polarity on the surface of the glass substrate is represented by a length of a major axis direction and a length of a minor axis direction perpendicular to the major axis direction.
In this condition, the flaw having the length of the minor axis direction of 1 &mgr;m on a surface in which the flaw is cut by a cross sectional plane perpendicular to the surface can not be accurately detected in the conventional reference.
Herein, it is to be noted that when a size of a concave portion on a principal surface is hereinafter described, the size is represented by (the length of the major axis direction and the minor axis direction perpendicular to the major axis direction), and each length of the major axis direction and the minor axis direction indicates the length on the principal surface when the concave portion is cut by a cross sectional plane perpendicular to the principal surface.
In this case, it is assumed that the surface state of the glass substrate is inspected by the conventional reference, and the photomask and the phase shift mask are manufactured by the use of the inspected glass substrate.
Under this circumstance, even when the glass substrate, in which no defect is detected in the inspection, is used, the desired pattern can not be obtained when the pattern is transferred to a substance to be transferred because of pattern breakage (or clear extension). This problem takes place by the following reason.
Namely, when the defect, such as, the flaw on the surface of the substrate has dependency for a moving direction of an inspection light beam, the defect has polarity of a constant direction. Consequently, the defect may be not detected in accordance with an incident direction of the inspection light beam.
Further, when the defect, such as, the stain exists inside the substrate, the reflected output is not almost detected in the conventional reference. From these reasons, it is accidentally judged that the glass substrate has no defect in the conventional reference.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a glass substrate for an electron device, a photomask blank and a photomask which are capable of performing patterning and projection lithography with high accuracy.
In a glass substrate for an electron device which is selected based upon a predetermined reference set value using a method for detecting a defect for the glass substrate in accordance with optical change of an inspecting light beam, the defect for the glass substrate has no dependency for a moving direction of the inspecting light beam.
Conventionally, the inspecting light beam is introduced into a constant direction. The glass substrate is inspected by comparing the reflected output with the transmitted output. In this condition, the defect (for example, the flaw on the surface of the substrate) which has dependency in the moving direction of the inspecting light beam can not be accurately detected and removed.
Namely, the reflected output is not detected at all in many cases because only a light beam of a constant direction passes for the flaw.
In contrast, in the case of an inspecting method for inspecting non-uniformity of a translucent substance disclosed in Japanese Patent Application No. Hei 9-192763 (thereinafter, will be referred to as a related reference and will be described in more detail), the light beam is irradiated from an inner portion of the substrate toward the surface thereof in all directions for the flaw.
Thereby, even when the defect has dependency in the moving direction of the inspecting light, the defect can accurately be detected and removed.
In consequence, the pattern defect does not take place in the etching process during the patterning. As a result, the patterning can be carried out with high accuracy. Further, the exposure can be suitably performed by the use of the photomask and the phase shift mask using the glass substrate.
Herein, the optical change means that optical characteristic, such as, optical quantity, the moving direction of the light beam is varied.
Further, the reference set value means optical information (image information, light quantity, brightness, and strength distribution and the like) which is obtained in accordance with a permissible defect (having non-uniformity) for the glass substrate, and means a threshold value which is flexibly set by a user.
The inspecting light beam is introduced into the glass substrate so that the light beam transmits by repeating total reflection on the surface of the glass substrate when a light path of the glass substrate is optically uniform.
Namely, the light beam which satisfies all reflected condition is introduced into the glass substrate. Thereby, when the light path is optically uniform inside the glass substrate, the light beam covers the entire surface of the substrate in all directions.
As a result, even when the concave portion (the flaw) having the specific polarity exists on the surface of the glass substrate or the defect, such as, the stain exists inside of the glass substrate, the defect can be accurately detected with high accuracy and high speed.
The inspecting light beam is a laser light beam. Further, the surface of the glass substrate includes at least a pair of principal surfaces parallel to each other, at least a pair of side surfaces perpendicular to the principle surfaces, and a chamfered surface interposed between the principal surface and the side surface. With such a structure, the introduced laser light beam transmits inside the glass substrate so that the total reflection is carried out through the princi
Hoya Corporation
Huff Mark F.
Mohamedulla Saleha R.
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