Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-03-30
2001-11-20
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S022000
Reexamination Certificate
active
06319638
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Related Art
The present invention relates to manufacture of a semiconductor device, and particularly to a method of performing alignment in the case of exposure.
2. Description of the Invention
In manufacturing processes of a semiconductor laser, each chip is separated by cleavage. The semiconductor laser forms a resonator using a cleavage plane as a Miller plane. Thus, it is important to form an optical waveguide in the direction vertical to the cleavage plane (parallel to a crystallographic axis).
On the other hand, stripe width control of an active region is very important in order to improve controllability and uniformity of characteristics of the semiconductor laser, and use of patterning by stepper exposure has effective in the control. Also, in manufacture of a DFB (Distributed Feedback) type laser, it is significant to control a shape and a period of a diffraction grating, and use of patterning by EB (Electron Beam) exposure has effective in the control.
As a result of this, when the semiconductor laser is manufactured using an aligner, the crystal direction of a semiconductor must be accurately aligned with the direction of a marker pattern for aligning in the case of exposure.
As a method of performing this, a manufacturing method of a semiconductor device and an alignment method for providing a mark for alignment in a mask for exposure and performing alignment by this mark are disclosed in Japanese Patent Unexamined Publication No. 323575 of 1993.
In the manufacturing method disclosed in Japanese Patent Unexamined Publication No. 323575 of 1993, however, no consideration is given to accuracy in position within a substrate plane of the marker pattern, with the result that the marker pattern cannot be always formed in the same position of a substrate. Because of this, in the stepper exposure or the EB exposure, it is necessary to search the position of a stepper marker or an EB marker in manual operations, and thus, it is lacking in productivity.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of forming markers in manufacture with excellent productivity of a semiconductor device capable of forming the markers accurately aligned with the crystal direction in the same position of a semiconductor crystal substrate.
A method of manufacturing a semiconductor device according to the present invention comprises the steps of providing a semiconductor crystal substrate having a cleavage orientation flat; providing a mask for exposure in which an alignment pattern is formed, the alignment pattern comprising a segment-shaped pattern which is a chord joining two points on a circular arc matching with an outer peripheral circle of the semiconductor crystal substrate and corresponds to the cleavage orientation flat; aligning the mask for exposure with the semiconductor crystal substrate so as to match the cleavage orientation flat with the segment-shaped pattern; and transferring the pattern formed in the mask for exposure on the semiconductor crystal substrate.
Also, an alignment method according to the present invention comprises the steps of forming an alignment pattern in a mask for exposure, the alignment pattern comprising a segment-shaped pattern which is a chord joining two points on a circular arc matching with an outer peripheral circle of a semiconductor crystal substrate having a cleavage orientation flat and corresponds to the cleavage orientation flat; and aligning the mask for exposure with the semiconductor crystal substrate so as to match the cleavage orientation flat with the segment-shaped pattern.
According to the present invention, using a semiconductor crystal substrate (wafer) having an orientation flat formed by cleavage, the cleavage orientation flat is utilized as alignment standards of patterning. That is, a segment-shaped pattern with the same length as the cleavage orientation flat is formed in a mask for exposure and alignment is performed so as to match the segment-shaped pattern with the cleavage orientation flat.
When the cleavage orientation flat with a length of L is formed in the wafer with a diameter of D, a length R of a perpendicular extending to the cleavage orientation flat from the center of this wafer is given by an expression of R=SQRT {(D/2)
2
−(L/2)
2
}, where SQRT indicates square root. Thus, when using a predetermined wafer, the distance R is uniquely determined by the length L of the cleavage orientation flat.
Using this, an alignment pattern comprising segments with the same length as the cleavage orientation flat is formed in the mask for exposure and alignment is performed so as to match them, and thereby a transfer pattern (such as stepper markers) can be always formed in the same position of the wafer. That is, the stepper markers can be aligned with the crystal axis with high accuracy.
Also, in consideration of change in length of the cleavage orientation flat due to variation of machining, it is effective to form an alignment pattern comprising plural segment-shaped patterns with different lengths changed according to the distance from the center of the wafer. By performing alignment according to the best matching segment-shaped pattern, measures can be effectively taken even in the presence of the variation of machining. In this case, the plural segment-shaped patterns have to be accurately set according to the above R. That is, the mask for exposure has the plural segment-shaped patterns which are a chord joining two points on a circular arc matching with an outer peripheral circle of the semiconductor crystal substrate (wafer) and are parallel one another.
When the stepper markers are formed on the semiconductor crystal substrate in such a manner, various patternings necessary in using a stepper aligner with an automatic alignment function can be performed. Further, similar effect can be obtained in an EB aligner with an automatic alignment function.
REFERENCES:
patent: 5-323575 (1993-12-01), None
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Young Christopher G.
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