Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1999-12-08
2004-08-17
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S087000, C257S753000, C257S759000
Reexamination Certificate
active
06778572
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electrode structure, a process for fabricating the electrode structure and a semiconductor light-emitting device, more specifically an electrode structure having a parasitic capacity reduced with respect to a lower layer, a process for fabricating the electrode structure and a semiconductor light-emitting device.
These days, optical communication using semiconductor lasers, which enable high-speed and large-capacity information transmission, having been noted. A semiconductor laser generally has a structure including electrodes formed respectively on the upper sides and the back sides of the devices. Bonding pads are connected to the electrodes on the upper sides, and bonding wires are connected to the bonding pads. Modulation signals are supplied to the modulator region of the semiconductor laser.
Recently, further increase of the communication speed is required to meet larger capacities for information processing amounts. For higher communication speed it is necessary to use signal of radio-frequencies as the modulation signals.
However, in order that the modulation signals further have radio-frequencies, parasitic capacities between the bonding pads and the lower layer must be decreased. Delays in rises and falls of waveforms are caused corresponding to parasitic capacities between the bonding pads and the lower layer. In a case that the modulation signals have radio-frequencies, response delays due to parasitic capacities between the bonding pads and the lower layer become unnegligible.
In order to decrease parasitic capacities between the bonding pads and the lower layer it is proposed that the bonding pads have small areas. The bonding pads have small areas, whereby parasitic capacities between the bonding pads and the lower layer can be small.
However, there is a limitation to decreasing the bonding pad area. That is, the bonding pads requires a certain area for the bonding wires to be jointed to the bonding pads. When an area for the bonding is taken into account, the bonding pads cannot be made smaller than a certain area. Resultantly, parasitic capacities between the bonding pads and the lower layer cannot be decreased to about 1 pF. In a case of 1 pF, a modulation frequency could be increased to only about 2.5 GHz. Recently, the modulation speed is required to be increased to about 10 GHz. However, the modulation speed increase to about 10 GHz cannot be attained by decreasing the bonding pad area.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an electrode structure which enables decrease of parasitic capacities with respect to a lower layer, a process for fabricating the electrode structure and a semiconductor light-emitting device using radio-frequencies.
In order to make a parasitic capacity between the bonding pads and a lower layer small it is proposed that a thick insulation film is formed below the bonding pads.
However, in a case that silicon oxide film or others is formed thick below the bonding pads, the silicon oxide film or others is broken due to a force applied upon the bonding, and the bonding pad peel off.
Then, it is proposed that polyimide layer, which is not broken easily even by a strong force and can be formed thick is formed below the bonding pads. It is considered that the polyimide layer will not be broken by impacts applied upon the bonding because polyimide is a material having high flexibility. A semiconductor laser including a polyimide layer formed thick below the bonding pads will be explained with reference to FIG.
14
.
As shown in
FIG. 14
, a silicon nitride film
134
is formed on a substrate
110
. A thick polyimide layer
136
is formed on the silicon nitride film
134
. A silicon nitride film
138
is formed on the upper surface and the side surface of the polyimide layer
136
.
In the semiconductor laser shown in
FIG. 14
, the silicon nitride films
134
,
138
cover the backside surface, the side surface and the upper surface of the polyimide layer
136
because the polyimide layer
136
has low adhesion to the lower layer and has high hygroscopicity. In the semiconductor laser shown in
FIG. 14
, the polyimide layer
136
has the back side surface, and side surface and the upper surface covered with the silicon nitride films
134
,
138
, whereby the polyimide layer
136
can have good adhesion to the lower layer, and the polyimide layer
136
can be prohibited from absorbing water. A bonding pad
124
is formed on the silicon nitride film
138
.
However, in a case that the polyimide layer
136
is formed below the bonding pad
124
as shown in
FIG. 14
, the polyimide layer
136
is distorted due to an impact which is as large as, e.g., 500 kg/cm
2
applied to the polyimide layer
136
upon the bonding. The silicon nitride film
138
is accordingly broken. Good adhesion cannot be obtained any more between the broken silicon nitride film
138
and the bonding pad
124
. As a result, the bonding pad
124
peels off the silicon nitride film
138
. Thus, simply forming the thick polyimide layer
136
below the bonding pad
124
cannot make the semiconductor laser reliable.
Then, the inventors of the present application made earnest studies and have obtained an idea of art that the polyimide layer formed thick can stand impacts applied upon the bonding.
The above-described object is achieved by an electrode structure including a conductive film formed on a base substrate through an insulation film, the insulation film comprising a plurality of poles of polyimide, a first film formed on side surfaces of the poles and formed of an insulation material having a higher hardness than polyimide, and a second film of polyimide buried among said a plurality of poles with the first film formed on the side surfaces thereof. Because of the first film of an insulation material having high hardness formed on the side surfaces of the poles of polyimide, even when a strong force is applied upon the bonding, the poles are prevented from being distorted, and the conductive film is protected from peeling off. Because of the thick polyimide layer below the conductive film, a parasitic capacity between the conductive film and the lower layer can be small, whereby radio-frequency signals can be used.
The above-described object is achieved by an electrode structure including a conductive film formed on a base substrate through an insulation film, the insulation film comprising a first film of polyimide having a plurality of openings which reach the base substrate, a second film formed on inside walls of the openings and formed of an insulation material having a higher hardness than polyimide, and a plurality of poles of polyimide buried in the openings with the second film formed on the inside walls thereof. Because of the second film of an insulation material of a high hardness is formed on the inside walls of the openings formed in the first film of polyimide, even when a strong force is applied upon the bonding, the first film are prevented from being distorted, and the conductive film is protected from peeling off. Because of the thick polyimide layer below the conductive film, a parasitic capacity between the conductive film and the lower layer can be small, whereby radio-frequency signals can be used.
The above-described object is achieved by a semiconductor light-emitting device having an electrode structure including a conductive film formed on a base substrate through an insulation film, the insulation film comprising a plurality of poles of polyimide, a first film formed on side surfaces of the poles and formed of an insulation material having a higher hardness than polyimide, and a second film of polyimide buried among said a plurality of poles with the first film formed on side surfaces thereof. Because of the first film of an insulation material of a high hardness formed on the side surfaces of the poles of polyimide, even when a strong force is applied upon the bonding, the poles are prevented from being distorted, and the conductive film is prote
Domoto Shinichi
Ohsaka Shigeo
Okada Nobumasa
Armstrong Kratz Quintos Hanson & Brooks, LLP
Fujitsu Quantum Devices Limited
Menefee James
Wong Don
LandOfFree
Electrode structure, process for fabricating electrode... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrode structure, process for fabricating electrode..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrode structure, process for fabricating electrode... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3362309