Active solid-state devices (e.g. – transistors – solid-state diode – Alignment marks
Reexamination Certificate
2000-01-27
2004-08-17
Baumeister, Bradley (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Alignment marks
C257S618000, C257S620000, C257S622000, C428S064100, C428S066700
Reexamination Certificate
active
06777820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor wafer formed with dot marks used in fabrication history or product control in semiconductor fabrication steps, further particularly to a semiconductor wafer having dot marks which are formed at a region least influential on reading accuracy at and after semiconductor wafer and device fabrication steps and effecting no influence on electric properties of the wafer per se and produced by laser irradiation ensuring a desired amount of information.
2. Description of the Related Art
Conventionally, in makers of wafers and devices of semiconductors, with an object of process control or production control, a surface of a wafer is marked by bar codes, characters or numerical characters as a clue for finding processing conditions, fabrication history or electric properties up to the occasion. A laser marker is frequently used as an apparatus of making these. According to marking operation by a laser marker, laser beam emitted from a laser oscillator is condensed via an optical system and at the same time, a predetermined region on a surface of a wafer is scanned with laser beam by a beam scanning apparatus to thereby locally melt the surface of the wafer to form a recessed and projected surface and inscribe desired information.
Generally, the marking region is a portion of a wafer at a vicinity of an orientation flat face or a specific wafer surface region in the case of a wafer maker and a portion of a rear face or a mounting face of the substrate constituting a chip in the case of a device maker. However, in carrying out laser marking at these marking regions, regardless of a wafer or a chip substrate, a dead space for marking is needed and the yield is deteriorated. Further, since the mark is formed by melting a portion of the wafer surface, there is a concern of producing particles in melting thereof and by forming irregularities at the surrounding of the mark, there is pointed out a drawback in which a smooth face is deteriorated when a fine pattern is formed at high accuracy.
Hence, conventionally, in order to avoid such a drawback, there have been trials of executing laser marking on an outer peripheral face (side face) of a semiconductor wafer as disclosed in, for example, Japanese Patent Laid-Open No. 23512/1984 and Japanese Patent Laid-Open No. 175154/1990. That is, according to a laser marking method disclosed in Japanese Patent Laid-Open No. 23512/1984, laser beam emitted from a laser oscillator is reflected by two sheets of mirrors orthogonal to each other and deflecting an angle of deviation in accordance with marking characters and irradiated to an outer peripheral side face of a wafer via a condensing lens to thereby continuously inscribe characters. Meanwhile, according to a laser marking method disclosed in Japanese Patent Laid-Open No. 175154/1990, after vacuuming to suck a rear face center of a semiconductor wafer by a vacuum chuck, an original point is determined by an orientation flat detecting mechanism, while rotating a pulse motor by a predetermined angle, a shutter is opened and closed in cooperation with rotation and stop of the pulse motor and laser beam emitted from a laser oscillator is condensed on an outer peripheral side face of an intermittently rotating wafer to heat a spot thereof thereby forming dot marks.
Further, other than the above-described publications, for example, according to Japanese Patent Laid-Open No. 256105/1998, a total peripheral face of a semiconductor wafer in a circular disk shape is chamfered by mirror finish and the chamfered portion is inscribed with a laser mark for determining crystal orientation and a laser mark for specification, product number or wafer ID, etc.
Meanwhile, in carrying out process control in a silicon maker, particularly in order to efficiently carry out wafer production, it is preferable to attach a number to every wafer from the following reason.
It is generally difficult to summarizingly control a plurality of sheets of wafers in a state in which the wafers are contained in wafer cassettes in polishing steps or heat treatment steps of the wafer. At every processing, the plurality of sheets of wafers contained in the wafer cassettes are discharged from the cassettes and are contained again in the cassettes after the individual processings. Further, in the discharging operation, transferring among respective steps or in the containing operation to the cassettes, cracking or chipping is liable to be produced by mechanical interference between the wafers and peripheral members. When laser marking is carried out on the peripheral side face of a semiconductor wafer as disclosed in the above-described publications, the marks are lost by cracking or chipping.
Further, semiconductor wafers need to be classified to respective grades at each occasion according to modes of causing cracking or chipping or a result of inspecting electric properties etc. inspected at every processing step. And also in the classifying operation, wrong classification is liable to cause by mistake of an operator. Further, in the classifying operation, the specification significantly differs depending on users and complicated classification is needed.
Hence, when readable marking can be inscribed on the wafer surface even after having been processed in steps, easy mistake can be prevented from causing in the classifying operation. However, when laser marking is carried out on the wafer surface, as mentioned above, there poses a problem in which particles are produced thereby, the flatness of the wafer is obliged to sacrifice or the marked portion may constitute an onset of crystal strain. Hence, conventionally, wafers are not controlled individually but controlled in a unit of lot or controlled in a unit of wafer cassette.
On the other hand, according to a size of a dot mark formed on the wafer surface by normal laser marking, a limit of its diameter is 15 &mgr;m and the dot mark cannot be downsized to less than the limit. Therefore, in marking a peripheral side face of a wafer by the laser marking methods disclosed in the respective publications, mentioned above, when a desired amount of information is to be inscribed, most of the peripheral side face is needed. In order to find necessary information from the pieces of information, the necessary information needs to search by rotating the wafer. In the case of the semiconductor wafer disclosed in the above-described respective publications, in a state in which the semiconductor wafer is contained in a wafer cassette, desired laser marking cannot be inscribed and naturally, these marks cannot be read.
SUMMARY OF THE INVENTION
The invention has been carried out in order to resolve these problems and it is an object of the invention to provide a semiconductor wafer having laser marks in which specifically, at a time point as early as possible in steps of fabricating a semiconductor wafer, a writable and readable region is selected in an individual wafer in a state in which the regions are mostly difficult to lose and the wafers are contained in wafer cassettes and information such as an identification number or electric properties is written to the region to thereby enable to grasp past history by a unit of wafer at and after processing steps or semiconductor fabrication steps.
In order to achieve such an object, the inventors have carried out an investigation from various angles. First, the first angle resides in selecting a region of a semiconductor wafer in which the above-described problems are not posed even by laser marking of the semiconductor wafer and marks are difficult to lose even having been processed in various fabrication steps in fabrication steps of the wafer and fabrication steps of semiconductor. The second angle resides in whether the region is provided with an area enough for sufficiently writing a necessary amount of information. Further, the third angle resides in whether the marking region is a region capable of writing and reading marks to and from the wafer while t
Chiba Teiichirou
Satou Etsurou
Tajika Jun
Baumeister Bradley
Chu Chris C
Komatsu Electronic Metals Co. Ltd.
Varndell & Varndell PLLC
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