Stock material or miscellaneous articles – Three dimension imitation or 'treated' natural product – Flora
Reexamination Certificate
1999-08-31
2001-09-25
Chaudhuri, Olik (Department: 2814)
Stock material or miscellaneous articles
Three dimension imitation or 'treated' natural product
Flora
C385S088000
Reexamination Certificate
active
06294232
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser diode chip (an LD chip), and to a method for mounting this semiconductor laser diode chip onto a substrate. In particular, the present invention relates to an LD chip and its mounting method suitable for a passive alignment technique without performing optical coupling to an optical waveguide and an optical fiber by emitting light from the LD chip.
2. Description of the Related Art
An LD chip is, conventionally, optically coupled to an optical waveguide formed on a substrate, or to an optical fiber arranged on the substrate by monitoring intensity of light outputted from the optical fiber in an oscillating state of the LD chip, and performing a positioning operation such that the light intensity is maximized. However, it is necessary to flow an electric current through the LD chip to oscillate the LD chip. Further, productivity is low since it is also necessary to make a position adjustment while the light intensity outputted from the optical fiber is monitored. In particular, when the LD chip is optically coupled to the optical waveguide and an adjusting mechanism is arranged, the structure becomes complicated and it is difficult to monitor in advance light outputted from the optical waveguide.
Therefore, mainly in a module in which the LD chip and the optical waveguide are optically coupled to each other, the consideration of an assembly technique called a passive alignment mounting technique is forwarded instead of the above method to reduce the number of assembly works. For example, a construction described in U.S. Pat. No. 5,414,787 is known as a construction relative to positioning of the LD chip and its mounting method by the passive alignment technique. In the passive alignment technique, a coupling technique of the LD chip and the optical fiber is constructed by fixedly mounting a semiconductor laser and the optical fiber at respective predetermined positions, and it is not necessary to adjust an optical axis. Accordingly, it is not necessary to oscillate the LD chip in the passive alignment technique, either. However, in any technique, it is normally necessary to perform a mounting operation with sub-&mgr;m accuracy to couple with sufficient efficiency the semiconductor laser and the optical fiber to each other.
In the LD chip used in the mounting method using the conventional passive alignment technique, a positioning mark is formed on a substrate-side face of the LD chip. This mark is normally formed of a metallized layer. In the mounting method of the LD chip using the passive alignment technique, it is necessary to accurately recognize the position of an active layer buried in a semiconductor laser body to mount the LD chip to the substrate with high accuracy.
No active layer can be normally confirmed directly by its outward appearance. Therefore, a positioning mark is formed on a surface of the LD chip body. The LD chip is positioned by confirming the positioning mark. Accordingly, relative position accuracy of the positioning mark to the active layer is very important in the passive alignment.
However, at a position facing the active layer, it is necessary to perform solder joining to a heat sink such as a silicon (Si) substrate in order to radiate heat. Accordingly, an Au metallized layer
2
for the solder joining is formed in the position facing the active layer. Therefore, it is difficult to pattern a mark requiring a certain wide area such as the positioning mark. Accordingly, in the conventional LD chip, the distance between the positioning mark and the active layer is as far as 50 &mgr;m to 100 &mgr;m.
A method of directly measuring position accuracy by observing a section of the LD chip body is most accurate to confirm the relative positions of the active layer of the LD chip and the positioning mark of the LD chip. However, in the conventional LD chip, since the distance between the positioning mark and the active layer is 50 &mgr;m to 100 &mgr;m, a measurement error in measuring the relative position accuracy of the positioning mark to the active layer is as large as 2 to 3 &mgr;m, or more. Therefore, no sufficient recognizing accuracy can be obtained with respect to mounting using the passive alignment technique requiring sub-&mgr;m accuracy.
SUMMARY OF THE INVENTION
An object of a mounting method of an LD chip of the present invention is to make it possible to mount the LD chip to a substrate with high positioning accuracy by a passive alignment technique.
To achieve the above object, in a mounting method of an LD chip in the present invention, a positioning mark is formed in a predetermined position with respect to an active layer on the surface of an LD chip body in which the active layer is buried. In the LD chip, a mark for measuring relative position of the active layer to the positioning mark is positioned in the vicinity of the active layer on the body surface with respect to the positioning mark in a metallic layer.
More concretely, in the mounting method of the LD chip for mounting the semiconductor laser diode chip (LD chip) having the active layer to a substrate in its predetermined position, the semiconductor laser diode has a mark for measurement (first mark) formed in the vicinity of the active layer and a mark for positioning (second mark) that is provided for positioning with respect to the substrate. On the other hand, the substrate has a substrate-side positioning mark in a position opposed to the mark for measurement when the LD chip is arranged at the predetermined position. A position relation between the active layer and the mark for measurement of the LD chip is made clear by measurement in advance. Next, the LD chip is arranged on the substrate so that the mark for measurement and the substrate side mark are opposed to each other. The LD chip is fixed to the substrate while correcting a position of the LD chip on the basis of the above position relation.
Here, the mark for measurement may be arranged just above the active layer, or may be arranged just above the active layer and may be formed to have approximately the same width as that of the active layer. Otherwise, the mark for measurement may be constructed by forming a metallic layer, etc. in plural thin parallel straight lines. Further, a pair of positioning marks may be arranged in predetermined positions between which the active layer is located, and a pair of marks for measurement may be arranged with respect to the pair of positioning marks.
The positioning mark may be constructed by a mark for mounting in the passive alignment technique, or may be constructed by a mark formed by a metallic layer for solder joining, etc.
In the above mounting method, the substrate has a V-groove the center of which coincides with the central axis of the active layer. The LD chip and an optical fiber can be optically coupled to each other on the substrate with high efficiency by arranging the optical fiber in this V-groove.
REFERENCES:
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patent: 5790737 (1998-08-01), Aoyagi et al.
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Lee et al., Quantitative Evaluation of Passive-Aligned Laser Diode-to-Fiber Coupling, 1998 Electronic Component and Technology Conference, pp. 1459-1463.*
European Search Report dated Mar. 6, 2000.
Lee S H et al, Quantitative Evaluation of Passive-Aligned Laser Diode-To-Fiber Coupling, 1998 Electronic Components and Technology Conference, pp. 1459-1463.
Tanaka K et al, “High Optical Coupling Scheme In LD Modules with Silicon Platform Technology” pp. 107-111, Jan. 1997.
Chaudhuri Olik
McGinn & Gibb PLLC
NEC Corporation
Wille Douglas A.
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