Patent Application
20090127661
1. Field of the Invention
The present invention relates to nitride semiconductor devices and methods of manufacturing the same.
2. Description of the Background Art
Conventional semiconductor devices, in particular nitride semiconductor devices for use in the manufacture of laser diodes, in many cases adopt what is called a “ridge structure” in which an electrode is formed via an insulation film formed on a ridge side wall. However, insufficient adhesion between the insulation film and an electrode material can possibly cause peeling-off of the electrode from the insulation film, and consequently, peeling-off of the electrode from a semiconductor layer. This peeling-off of the electrode can further cause an increase in the operating voltage for driving the laser diodes or variations in the properties due to heat generation during operation, thus accompanying a problem of difficulty in providing stable operation output within a specified temperature range.
In view of the above problems, for example, Japanese Patent Application Laid-open No. 2005-51137 discloses a technique for obtaining good electrode adhesion by forming an adherence layer of a heat-treated platinum metal between an electrode and an insulation film on the ridge side wall. Furthermore, Japanese Patent Application Laid-open No. 2007-134445 discloses a technique for forming a protection film of zirconium oxide or the like, which has a density or surface roughness that meets certain requirements, between the ridge side wall and an electrode.
The technique disclosed in Japanese Patent Application Laid-open No. 2005-51137, however, has a drawback that a great difference in material between the insulation film and the adherence layer can complicate device manufacturing processes or can have an adverse effect on the optical properties of a device, which may lead to a reduction in yield. The technique disclosed in Japanese Patent Application Laid-open No. 2007-134445 also has the drawback of increased complexity of device manufacturing processes.
It is an object of the invention to provide a nitride semiconductor device that prevents peeling-off of the electrode, and at the same time reduces the complexity of processes and a reduction in yield.
According to an aspect of the invention, the nitride semiconductor device includes a P-type semiconductor layer, an insulation film, an adherence layer, and an electrode. The P-type semiconductor layer has a ridge on its surface. The insulation film covers at least a side face of the ridge. The adherence layer is formed on a surface of the insulation film and composed mainly of silicon. The electrode is formed on an upper surface of the ridge and on a surface of the adherence layer.
According to another aspect of the invention, the nitride semiconductor device includes a P-type semiconductor layer, an insulation film, an adherence layer, and an electrode. The P-type semiconductor layer has a ridge on its surface. The insulation film covers at least a side face of the ridge. The adherence layer is formed on a surface of the insulation film and composed mainly of Ti or Al. The electrode is formed on an upper surface of the ridge and on a surface of the adherence layer.
According to still another aspect of the invention, the nitride semiconductor device includes a P-type semiconductor layer, an insulation film, and an electrode. The P-type semiconductor layer has a ridge on its surface. The insulation film is formed of a silicon oxide film which covers at least a side face of the ridge, and the silicon composition of which is nonuniform along the film thickness. The electrode is formed on an upper surface of the ridge and on a surface of the insulation film.
The invention is also directed to a method of manufacturing a nitride semiconductor device. The nitride semiconductor device includes a P-type semiconductor layer, an insulation film, and an electrode. The P-type semiconductor layer has a ridge on its surface. The insulation film is formed of a silicon oxide film which covers at least a side face of the ridge, and the silicon composition of which is nonuniform along the film thickness. The electrode is formed on an upper surface of the ridge and on a surface of the insulation film. The silicon composition of the insulation film increases toward the surface of the insulation film. The method includes the step of forming the insulation film by sputtering silicon so that a mixture ratio of oxygen gas to argon gas is changed such that the oxygen gas content is reduced from a high level to a low level.
The formation of the adherence layer on the surface of the insulation film on the side face of the ridge can prevent peeling-off of the electrode, thus stabilizing the formation of a low-resistance electrode, and can reduce the operating voltage of a semiconductor device such as a laser diode. This allows a reduction of heat generation during operation, thereby providing high-power and stable operation. Besides, composing the adherence layer mainly of silicon can avoid the problem that the insulation film and the adherence layer have a great difference in material. This prevents peeling-off of the electrode on the ridge while preserving the properties without any great change in the manufacturing processes and in the device configuration, thus reducing the complexity of processes and a reduction in yield.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
Referring now to the drawings, preferred embodiments of the invention is described in detail.
Next is described a method of manufacturing the essential parts of the nitride semiconductor device according to the present preferred embodiment.
First, a resist pattern (not shown) is formed by transferring on the surface of the P-type nitride semiconductor layer 1 in
After the formation of the ridge 2, as shown in
Examples of the processes for forming the SiO2 film 3 include evaporation, sputtering, and CVD (chemical vapor deposition). The thickness of the SiO2 film 3 is determined according to the optical properties of the device, but it must be on the order of, for example, 200 nm. Although SiO2 (silicon oxide) is desirable from the viewpoint of device manufacture, any other insulation film such as Si3N4 (silicon nitride) or SiON (silicon oxynitride) may be used as long as it can meet optical property requirements.
Similarly, the Si adherence layer 4 can also be formed on this SiO2 film 3 by evaporation, sputtering, CVD, or the like. The use of the same technique as used for the SiO2 film 3 will allow successive formation of the SiO2 film 3 and the Si adherence layer 4 by one operation, and on the other hand, the use of different techniques is also possible. The Si adherence layer 4 should desirably have such a thickness that can improve adhesion without exerting any effect on the device properties. For example, it may preferably be 50 nm or less, and more preferably 25 nm or less. The thickness of 25 nm or less will not affect not only the device properties, but also the processes in device manufacture.
Since the Si adherence layer 4 is used for improving the adhesion of the SiO2 film 3 to the P-type electrode 5, the thickness of the Si adherence layer 4 may be uniform, or may be nonuniform within a range that can provide good adhesion. The Si adherence layer 4 may be of single crystalline silicon or amorphous silicon. If the processes permit, similar effects can also be attained by forming a metal such as Ti or Al, instead of silicon. The SiO2 film 3 and the Si adherence layer 4 formed in this way are then selectively removed by a lift-off or etch-back process so as to be formed on the side face of the ridge 2 and on the upper surface of the P-type semiconductor layer 1 joined to the bottom edge of the ridge side face.
After the formation of the SiO2 film 3 and the Si adherence layer 4, as shown in
Referring to the formation of the P-type electrode 5, an electrode material is first deposited using a technique, such as evaporation or sputtering, and then selectively formed by a lift-off process on the top of the ridge 2 and on the surface of the Si adherence layer 4 on the side face of the ridge 2. The P-type electrode 5 may be made of any material that can establish an ohmic contact with the P-type nitride semiconductor layer 1; for example, it is preferably made of a material containing palladium (Pd), and more preferably, a material containing palladium (Pd) and tantalum (Ta). Furthermore, applying an organic coating material containing silicon as pretreatment prior to the formation of a P-type electrode material can also lead to an improvement in adhesion. For example, the use of a material such as hexamethyldisilazane (HMDS) allows selective formation of the P-type electrode 5 on the SiO2 film 3, thus further improving adhesion without deteriorating the properties of the P-type electrode 5. In addition, performing heat treatment in an atmosphere containing oxygen after the formation of the P-type electrode 5 can provide an ohmic contact.
According to the invention, the formation of the P-type electrode 5 via the Si adherence layer 4 on the SiO2 film 3 on the side face of the ridge 2 can prevent peeling-off of the electrode, thus stabilizing the formation of the low-resistance electrode, and can reduce the operating voltage of the semiconductor device. This allows a reduction of heat generation during operation, thus providing high-power and stable operation. It is also possible to avoid the problem that the insulation film and the adherence layer has a great difference in material. This preventing peeling-off of the electrode on the ridge 2 while preserving the properties without any great change in the manufacturing processes and in the device configuration, thus reducing the complexity of processes and a reduction in yield.
In the example shown, the silicon composition of the SiO2 film 16 is controlled so as to be nonuniform along the film thickness.
Next is described a method of manufacturing the nitride semiconductor device in
Referring to the formation of the SiO2 film 16, for example silicon is subjected to sputtering so that a mixture ratio of oxygen gas to argon gas is changed such that the oxygen gas content is reduced from a high level to a low level. This changes the concentration of oxygen within the film, allowing the control of the composition of the film deposited. Other features, such as the formation of the ridge 2 and the P-type electrode 5, are the same as those described in the first preferred embodiment 1, so the detailed description thereof is omitted herein.
According to the invention, making the silicon composition of the SiO2 film 16 to increase toward the surface of the SiO2 film 16 can prevent peeling-off of the electrode, thus stabilizing the formation of the low-resistance electrode, and can reduce the operating voltage of the semiconductor device. This allows a reduction of heat generation during operation, thus providing high-power and stable operation.
While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-300004 | Nov 2007 | JP | national |
