Microbench and producing method therefor, and optical...

Details Microbench and producing method therefor, and optical... Microbench and producing method therefor, and optical...

2001-01-10

2002-11-05

Healy, Brian (Department: 2874)

Optical waveguides

With optical coupler

Particular coupling structure

C385S052000, C385S088000, C385S092000, C385S136000, C385S137000

Reexamination Certificate

active

06477302

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microbench, which is used to optically couple an optical fiber and an optical semiconductor device, and a manufacturing method therefor, and an optical semiconductor module, which is constituted using same.
2. Description of the Related Art
A substrate having V-groove thereon, such as that shown in
FIG. 11
, has been used as a self-alignment mechanism for the optical coupling of an optical fiber to an optical fiber, or an optical fiber to an optical semiconductor device (Japanese Patent Laid-open No. H5-21817). In the figure,
1
is a silicon (Si) substrate,
2
is back surface metallization,
3
are metallized interconnects,
4
is silica insulation,
5
is a AuSn deposited die area,
6
is an alignment mark,
7
is a V-groove, and
8
is a dicing line. Actually, as long as the substrate has a groove shape, it is possible to affix an optical fiber to the substrate, and a trapezoid or rectangular groove would also be capable of fully performing this function, but because V-shaped processing has been accurate in the past, a V-groove
7
has come to be used most often. Ceramics substrates and Si substrates
1
have been used as this substrate having a V-groove (Japanese Patent Laid-open No. 7-174941). The former has primarily been processed a dicing process, and the latter has been processed via a dicing process, and anisotropic etching with potassium hydroxide (KOH).
A substrate, which has this V-groove
7
, and optically couples an optical semiconductor device and an optical fiber in a compact fashion by the V-groove
7
is called a microbench. Among these microbenches, those that make use of Si are called Si microbenches, and to date there have been numerous inventions that put an Si microbench into practice (Refer to “Packaging Technology in Lightwave Communication” Japan Institute of Electronics Packaging Society publication Vol. 1, No. 2, 1998).
A semiconductor laser device (laser diode (LD)) will be used as a typical example of an optical semiconductor device, and will be explained. An LD is lined up with an alignment mark on an Si microbench, and is die bonded, using an AuSn or other soldering material, to a junction down package, which provides light-emitting, light-receiving layers on the substrate side. The facet of an optical fiber is either used as-is, or is used by processing the end into a lens to enhance optical coupling efficiency. Further, there are also cases in which a non-reflective coating is applied to avoid the noise of mode disturbance resulting from reflected light. This optical fiber is affixed in a groove with either plastic or soldering material. With such a simple process, it has become possible to eliminate the time consuming, and costly laser beam welding-based aligning process that had been deemed necessary to date (“Packaging Technology in Lightwave Communication” Japan Institute of Electronics Packaging Society publication Vol. 1, No. 2, 1998).
This Si microbench is manufactured using the following process. (1) A photomask is manufactured using sub-micron order precision. The shape of this photomask is designed so that the center point of an optical fiber, which is a cylindrical shape, is on the substrate surface because of taking into account the KOH-based anisotropic etching of Si. (2) After etching, a dicing line is formed so as to form an optical semiconductor device mounting portion that is orthogonal to the groove. This is because in anisotropic etching, the vicinity of the LD mounting portion is etched in the shape of a triangular pole, and in the state following etching, the distance between the LD and the optical fiber cannot be made shorter, and the purpose is for the dicing line to bring the optical fiber right near the semiconductor device. (3) Since the Si substrate is conductive, silica glass is formed as an insulating layer on parts, which are to be electrically isolated from the semiconductor device, and thereafter, metallization is performed for the interconnects. (4) Metallization and the vapor deposition of an AuSn or other solder are carried out on the semiconductor device mounting portion (die bonding area).
An optical semiconductor module is manufactured by combining the skeletal structure, resulting from the Si microbench, LD and optical fiber, together with ceramics, a leadframe, and a plastic body, and forming an electrical connection (Refer to Japanese Patent Laid-open No. H9-223806, and Japanese Patent Laid-open No. H10-200155).
In the field of optical communications, there has been a tendency to develop large-capacity, high-speed communications in line with the popularization of the Internet and other means of multimedia communications. However, in general, there is a tendency for noise to increase when the telecommunications rate is raised, and a more excellent signal-to-noise (S/N) ratio than in the past is required for telecommunications systems. Meanwhile, lowering the junction temperature of a LD and enhancing light output has the advantage of improving the S/N ratio of a signal. For this reason, there is a need for a semiconductor system with good heat-radiating characteristics,,and a high light output LD device that makes use the system.
In the meantime, in the field of the information industry, even higher speed, higher density recording/playback capabilities are needed. In general, a blue or other such short wavelength LD required in a high-density system still has low light emitting efficiency, necessitating the improvement of the S/N ratio here as well, and to enhance the light output of such LD, there is a need for a high light output LD device that makes use of a system having good heat-radiating characteristics. In particular, even higher light output is required in a recording system than in a playback system.
High speed is a performance capability demanded of an LD. Operating an LD at the high speed of 10 gigabits per second (Gbps) will make it possible to increase capacity four-fold compared to the conventional 2.5 Gbps. For this reason, the capacitance between the substrate and the interconnects, and the inductance of the interconnects themselves, as well as interconnect resistance must be lowered. Because silica is utilized in the insulating film for a Si microbench, the thickness of the film cannot be increased. The problem is that reducing inductance increases the capacitance of the interconnects. According to the disclosure in The Proceedings of the 1995 Electronics Society Conference of IEICE on the Characteristic of High Speed Electrical Circuit on PLC-Platform, on a Study on a Compact Package for Multichannel Multigigabit Optical Interconnection C179, with the object of reducing interconnect capacitance, a thick polyimide sheet was purposely formed on top of an Si microbench, and metallization for the interconnects was formed thereupon. However, in this method, in addition to the fact that polyimide formation had to be carried out with precision thickness, the polyimide foamed during the die bonding of the semiconductor device due to the pressure of absorbed water and caused open circuits and the like, deteriorating the yield of optical semiconductor modules.
Further, because the LD discussed here is a mass production type, which is utilized in ordinary homes, costs must also be lowered. The most costly part of a LD is the Si microbench. In a case in which anisotropic etching was performed on an Si substrate, the situation was such that etching unevenness occurred on the inner surface, making it almost impossible to achieve an uniform anisotropic etching surface. This was a problem in that the optical coupling of the optical fiber and LD could not be accomplished satisfactorily. In Japanese Patent Application Laid-open No. H9-90173, there is disclosed a microbench, which is constituted by forming a plastic using a metal, or a metal and ceramics as filler to reduce the costs thereof. The problem here is that in a case in which a metal was used, interconnect capacitance increased, a polyimide sheet proces

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