Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
2002-07-03
2003-06-17
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C257S080000, C257S081000, C257S098000, C257S099000, C257S432000, C257S433000, C385S049000, C372S096000
Reexamination Certificate
active
06579737
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to an optical semiconductor module having an optical semiconductor element which is resin-sealed to improve moisture resistance, its manufacture method, a reflection film, its manufacture method, and laser and optical devices using reflection films.
b) Description of the Related Art
With the advent of multimedia societies, subscriber networks are now vigorously changed to optical networks. In order to prevail optical fibers to subscriber networks, it is necessary to lower the cost of optical components, particularly optical semiconductor modules which have a large influence upon the total cost.
Conventional low price optical semiconductor modules have been manufactured by a simple coupling method of coupling an optical semiconductor element and an optical waveguide such as an optical fiber on an Si platform or by a simple sealing method of sealing an optical semiconductor element by directly potting resin. These methods can reduce the number of components and lower the cost. Conventional solder sealing has been replaced by cheap resin sealing to lower the cost required for protecting an optical semiconductor element from external moisture.
Epoxy resin transparent to reception/emission light has been used as sealing resin. The publication of JP-A-HEI-8-18163 discloses a double sealing structure which covers an optical semiconductor element with silicon resin having rubber elasticity and also covers the silicon resin coated the optical semiconductor element with epoxy resin which shields sun light and water contents.
Although epoxy resin has a high moisture resistance, it has a large coefficient of linear expansion so that the optical semiconductor element may be damaged by a resin volume change to be caused by a temperature change. When LSI using Si or other components is resin-sealed, epoxy resin is mixed with filler such as silica in order to relax thermal stress to be applied to the semiconductor element. However, when an optical semiconductor element is resin-sealed, the resin cannot be mixed with filler because it is necessary to provide optical coupling between the optical semiconductor element and an optical fiber.
If silicon resin is used as the sealing resin, thermal stress applied to an optical semiconductor element can be relaxed because it has rubber elasticity. However, since silicon resin has higher moisture permeability than epoxy resin, it is difficult to ensure a sufficient moisture resistance of an optical semiconductor module.
Double sealing with silicon resin and epoxy resin can relax thermal stress while the moisture resistance is retained. It is, however, necessary to perform at least two resin curing processes because the curing conditions of two types of resin are different. This increases the number of manufacture processes, and contradicts the demands of low cost. An insufficient strength of uncured resin is likely to occur.
Next, issues regarding resin sealing will be described by paying attention to an optical viewpoint.
A reflection film of a multi-layer structure is know which is a lamination of two or more thin films having an optical film thickness of a quarter wavelength of light to be reflected. If this reflection film of the multi-layer structure is formed on the facets of an optical resonator of a laser diode, the laser diode can have a low threshold current, a high output, and the like.
The fundamental parameters as indices of the laser characteristics of a semiconductor laser device having a pair of resonator facets include a threshold gain, an external differential quantum efficiency, a front/back ratio, and a slope efficiency. The threshold gain is defined by:
g
th
=&agr;
i
+(1
/L
)
ln
(1/(
R
f
R
r
)
½
)
where &agr;
i
is an internal loss of an optical resonator, L is a resonator length, R
f
and R
r
are reflectivities at the front and back facets.
The external differential quantum efficiency &eegr;
d
is defined by:
&eegr;
d
=&eegr;
i
×ln
(1
/R
)/(&agr;
i
L+ln
(1
/R
))
where &eegr;
i
is an internal quantum efficiency and an assumption of R=R
f
=R
r
is incorporated.
The front/back ratio r is defined by:
r
=((1
−R
f
)/(1
−R
r
))×(
R
r
/R
f
)
½
.
The slope efficiency S
d
is defined by:
S
d
=1.24×&eegr;
d
/&lgr;
where &lgr; is an oscillation wavelength.
As seen from the above definition equations, as the reflectivities R
f
and R
r
lower, the threshold gain g
th
lowers although the external differential quantum efficiency &eegr;
d
and slope efficiency S
d
become high. Namely, the threshold current increases. An increase of the threshold current may degrade the optical output characteristics, particularly under the high temperature operation environment.
Evaluation of the laser diode characteristics is generally performed in the atmospheric air or in an inert gas atmosphere. In actual operation, a laser diode is mounted on a substrate and thereafter covered with resin or the like. As the reflection facet of an optical resonator is covered with resin, the reflectivity lowers and the threshold gain g
th
increases. Therefore, it is difficult to evaluate the optical output characteristics under the actual operation conditions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical semiconductor module having a sufficient moisture resistance and is easy to be made low in cost, and its manufacture method.
It is another object of the present invention to provide a reflection film, its manufacture method, and a semiconductor laser device, capable of evaluating the characteristics of the semiconductor laser device under the conditions approximate to the actual operation conditions.
According to one aspect of the present invention, there is provided an optical semiconductor module comprising: a platform having a support surface; an optical semiconductor element disposed on the support surface of the platform; an optical element disposed on the support surface of the platform and having an optical coupling facet, the optical element being optically coupled to the optical semiconductor element at the optical coupling facet; and a protective member made of gel acrylic modification resin, covering the optical semiconductor element, and being disposed at least in a light transmission area in a space between the semiconductor element and the optical coupling facet of the optical element.
Since the protective member is made of gel resin, a thermal stress applied to the optical semiconductor element can be reduced. Since the acrylic modification resin has a low moisture permeability and moisture absorption, it is possible to prevent water contents from invading into the optical semiconductor element.
According to another aspect of the present invention, there is provided a method of manufacturing an optical semiconductor module comprising the steps of: disposing an optical semiconductor element and an optical element on a support surface of a platform so as to optically coupling the optical semiconductor device and the optical element; placing the platform on an inner surface of an outer frame, with ultraviolet curing type adhesive being interposed between the platform and the inner surface; disposing an acrylic modification resin composition covering the semiconductor element on the platform and being filled in a light transmission area between the optical semiconductor element and the optical element, the acrylic modification resin composition being cured upon radiation of ultraviolet rays and becoming gel; and curing the adhesive and the acrylic modification resin composition by radiating ultraviolet rays.
Both the adhesive and acrylic modification resin composition can be cured at the same time by one ultraviolet ray radiation process, so that the number of manufacture processes can be reduced.
According to another aspect of the present invention, there is provided a method of manufacturing a reflection film comprising the step of prepar
Fukushima Akira
Shoji Hajime
Soda Haruhisa
Yoneda Yoshihiro
Armstrong Westerman & Hattori, LLP
Fujitsu Limited
Nelms David
Tran Mai-Huong
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