JP3623638B2 - Optical semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical semiconductor device, and more particularly to a structure of a waveguide type light receiving diode and a manufacturing method thereof.
[0002]
[Prior art]
In an optical communication system, a waveguide type light receiving diode is used as a light receiving element for converting a high frequency optical signal of gigahertz into an electric signal. In order to obtain good high-frequency characteristics of the light-receiving diode, it is necessary not only to finely process the semiconductor portion, but also to reduce the contact resistance between the electrode and the semiconductor, the stray capacitance of the wiring, and the like as much as possible.
[0003]
Here, a manufacturing method of a conventional InP-based waveguide type light-receiving diode having an air bridge wiring structure will be described with reference to a manufacturing process sectional view of FIG. 4 is a front sectional view, and the right column is a side sectional view.
[0004]
First, as shown in FIG. 4A, an n-type InP ohmic layer 2 is formed on a semi-insulating InP substrate 1 by a crystal growth method such as an MBE (Molecular Beam Epitaxy) method or a MOCVD (Metal Organic Chemical Vapor Deposition) method. The n-type InGaAsP cladding layer 3, the non-doped InGaAs light absorption layer 4, the p-type InGaAsP cladding layer 5, and the p-type InP ohmic layer 6 are sequentially deposited, and then a mask pattern 7 is formed by photolithography.
[0005]
Next, as shown in FIG. 4B, the p-type InP ohmic layer 6, the p-type InGaAsP cladding layer 5, the non-doped InGaAs light absorbing layer 4, and the n-type InGaAsP cladding layer 3 are sequentially etched by the mask pattern 7. A ridge-type waveguide shape 9 is obtained. Similarly, after patterning the n-type InP ohmic layer 2 by photolithography and etching to form the n-type ohmic region 10, an insulating film 11 is deposited on the entire device surface.
[0006]
Next, as shown in FIG. 4C, a resist opening is formed on the n-type ohmic region 10 by photolithography and mask alignment, and an n-electrode 12 is formed by etching of the insulating film, vapor deposition of ohmic metal, and lift-off. Form. Similarly, a p-electrode 13 is formed on the p-type InP ohmic layer 6 in the top surface of the waveguide shape 9.
[0007]
Next, as shown in FIG. 4D, a wiring base resist 14 is formed by an air bridge by a photolithography method.
[0008]
Next, as shown in FIG. 4E, an n-electrode wiring 15 is formed by vapor deposition of photolithography and wiring metal.
[0009]
Next, as shown in FIG. 4 (f), the wiring base resist 14 is dissolved and removed to form the air bridge wiring 16.
[0010]
Finally, the semiconductor is cleaved at the position shown in FIG. 4F to obtain a waveguide element. Incident light is absorbed by the InGaAs light absorption layer 4 from the direction of the arrow and converted into an electrical signal.
[0011]
[Problems to be solved by the invention]
In order to operate the light receiving element at a high frequency, it is important to reduce as much as possible the series resistance, inductance, and parasitic capacitance connected to the element. However, the dimensions of the ridge-type waveguide shape 9 of the high-frequency waveguide-type light-receiving element are designed to be very small with a width of 4 to 6 μm, a length of 10 to 20 μm, and a height of 2 to 3 μm.
[0012]
In FIG. 4C, in order to reliably form the p-electrode 13 in the top surface of the ridge-type waveguide shape 9, the width of the p-electrode 13 is set to a ridge-type from the limit of mask alignment accuracy in the photolithography process. The width of the top surface of the waveguide shape 9 is usually required to be 2 to 3 μm smaller. For this reason, when the top surface width is 4 μm, the width of the p-electrode 13 becomes about 1 μm, and there is a drawback that the ohmic contact area is reduced and the contact resistance is increased.
[0013]
Similarly, also in the wiring steps in FIGS. 4D to 4F, for the same reason as described above, the wiring width of the ridge-type waveguide shape 9 becomes as thin as about 1 μm, so that inductance and wiring resistance are reduced. There was a drawback of becoming larger.
[0014]
An object of the present invention is to eliminate the above-mentioned problems and to provide an optical semiconductor element excellent in high frequency characteristics and a method for manufacturing the same, by reducing series resistance, inductance, and parasitic capacitance connected to the element as much as possible.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
In the optical semiconductor device having (1) ridge, and having a shape larger than the width of the electrode width is the ridge top surface of the ohmic electrode with ohmic electrodes of the ridge upper face side is full contact with the upper surface of the ridge-side The ohmic electrode on the upper surface side of the ridge has a shape that is drawn out to the pad portion outside the ridge at the same time in the form of an air bridge .
[0016]
[ 2 ] In a method of manufacturing an optical semiconductor device having a ridge shape, a step of obtaining a ridge-type waveguide shape, a step of forming a resist so as to cover the ridge-type waveguide shape, and ashing the entire semiconductor substrate And a step of obtaining a resist pattern in which the top surface of the ridge-type waveguide shape is exposed, and a step of forming a new resist pattern having an opening width larger than the ridge-type waveguide shape. A wiring having a shape in which an ohmic electrode and an ohmic electrode on the ridge upper surface side are simultaneously drawn out in an air bridge shape to a pad portion outside the ridge by a wiring metal that is in ohmic contact with the top surface of the ridge-type waveguide shape. And a forming step.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0018]
FIG. 1 is a front sectional view of a semiconductor light receiving element showing an embodiment of the present invention, FIG. 2 is a side sectional view of the semiconductor light receiving element, and FIG. 3 is a manufacturing process sectional view of the semiconductor light receiving element showing an embodiment of the present invention. . 3 is a front sectional view, and the right column is a side sectional view.
[0019]
As shown in FIGS. 1 and 2, the semiconductor light receiving device of this embodiment has an n-type InP ohmic layer 22, an n-type InGaAsP cladding layer 23, a non-doped InGaAs light absorbing layer 24, on a semi-insulating InP substrate 21. It has a ridge-type waveguide shape composed of a p-type InGaAsP cladding layer 25 and a p-type InP ohmic layer 26, and ohmic electrodes 32 are formed on both sides of the ridge-type waveguide shape, and an n-type InP ohmic layer 22 is connected.
[0020]
Furthermore, an ohmic electrode 35 having a width wider than that of the p-type InP ohmic layer 26 is formed on the top of the ridge-type waveguide shape. Further, as shown in FIG. 2, the ohmic electrode 35 is connected to a pad portion 37 on the semi-insulating InP substrate 21 by a wiring 36 that is integrally connected to the ohmic electrode 35. Reference numeral 38 denotes a cleavage plane on which the incident light 39 is incident.
[0021]
A method for manufacturing the semiconductor light receiving element of this embodiment will be described below with reference to FIG.
[0022]
(1) As in the conventional process, first, as shown in FIG. 3A, an n-type InP ohmic layer 22, an n-type InGaAsP cladding layer 23, a non-doped layer are formed on a semi-insulating InP substrate 21 by crystal growth. After sequentially depositing the InGaAs light absorbing layer 24, the p-type InGaAsP cladding layer 25, and the p-type InP ohmic layer 26, a mask pattern 27 is formed by photolithography.
[0023]
(2) Next, as shown in FIG. 3B, the p-type InP ohmic layer 26, the p-type InGaAsP cladding layer 25, the non-doped InGaAs light absorption layer 24, and the n-type InGaAsP cladding layer 23 are sequentially formed by the mask pattern 27. Etching is performed to obtain a ridge-type waveguide shape 29. Similarly, after patterning the n-type InP ohmic layer 22 by photolithography and etching to form the n-type ohmic region 30, an insulating film 31 is deposited on the entire device front surface.
[0024]
(3) Next, as shown in FIG. 3C, after forming the ohmic electrode 32 for the n-type ohmic region 30, a resist pattern 33 is formed so as to include the ridge-type waveguide shape 29. Here, the resist pattern 33 has the same effect even when a normal resist material or a resin such as polyimide is used. Further, when a liquid resin material is applied on the unevenness, the liquid resin material is thinly deposited on the convex portion due to its viscosity, so that it is particularly thin on the top surface of the ridge-type waveguide shape 29.
[0025]
(4) Next, as shown in FIG. 3D, the entire semiconductor substrate is ashed (resin ashing by oxygen plasma) to remove the resist 33, and the top surface of the ridge-type waveguide shape 29 is formed. A resist pattern 33 'is exposed. Next, a new resist pattern 34 having an opening width larger than the ridge-type waveguide shape 29 is formed.
[0026]
(5) Next, as shown in FIG. 3 (e), the ohmic electrode 35 and the ohmic electrode 35 are formed by vapor deposition / lift-off of a wiring metal (for example, Ti / Pt / Au structure) in ohmic contact with the p-type InP ohmic layer 26. A wiring 36 to be connected is formed. In this step, the wiring metal may be deposited after the insulating film 31 is etched after the wiring photolithography. Here, as can be seen from the front sectional view of FIG. 3 (e), the electrode width of the ohmic electrode 35 is widely formed so as to include the ridge-type waveguide shape 29, and the ohmic electrode 35 of FIG. 3 (e). As can be seen from the side sectional view, the ridge-type waveguide shape 29 is formed so as to be connected to the pad portion 37 on the semi-insulating InP substrate 21 from the top surface.
[0027]
Finally, as shown in FIG. 3 (f), the resist pattern 33 'is removed and then cleaved to obtain a waveguide type light receiving element. Here, the resist pattern 33 may be made of a resin material such as polyimide and may not be finally removed, and at this time, the pad portion 37 may be formed on the polyimide.
[0028]
As described above, according to the present embodiment, as shown in FIG. 3C, the entire top of the ridge-type waveguide shape 29 and the wiring metal can be in ohmic contact without using precise mask alignment of photolithography. Therefore, the contact resistance can be greatly reduced with good reproducibility. In addition, since the wiring resist pattern 34 is formed on the resist pattern 33 ′, the electrode width of the ohmic electrode 35 at the top of the ridge-type waveguide shape 29 is set to the width of the top of the ridge-type waveguide shape 29. There is an advantage that it can be made larger than the width and the conductance of the wiring 36 can be reduced.
[0029]
Furthermore, since the ohmic electrode 35 at the top of the ridge-type waveguide shape 29 can be formed on the overhang, it does not contact the side surface of the ridge-type waveguide shape 29, that is, between the upper wiring and the semiconductor element. There is no risk of increasing the parasitic capacitance. Further, since the wiring in this embodiment is formed integrally with the ohmic electrode 35, the process can be simplified.
[0030]
As described above, according to the present embodiment, there is an advantage that a semiconductor light-receiving element having excellent high-frequency characteristics can be easily manufactured with high reproducibility such that series resistance and wiring inductance are small without increasing parasitic capacitance.
[0031]
The present invention has the following usage forms.
[0032]
In the above embodiment, the waveguide type light receiving element in which light is incident from the crystal side surface has been described. However, the present invention relates to a waveguide type optical semiconductor element, and has an ohmic electrode on the upper surface side that is simple and highly reproducible. It is formed with low contact resistance and low inductance, and at the same time, the wiring can be drawn out to the pad portion. That is, it goes without saying that the present invention can be applied not only to a light receiving element but also to an optical semiconductor element such as a waveguide type laser diode or an optical modulator operating at a high frequency.
[0033]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0034]
【The invention's effect】
As described above in detail, according to the present invention, the following effects can be obtained.
[0035]
(1) According to the first aspect of the present invention, an optical semiconductor element having excellent high-frequency characteristics is provided while reducing the series resistance, inductance, and parasitic capacitance connected to the element as much as possible , and at the same time, the wiring is drawn out to the pad portion. be able to.
[0036]
(2) According to the second aspect of the present invention, a semiconductor light receiving element having a small series resistance and a small wiring inductance and excellent in high frequency characteristics can be manufactured easily and with high reproducibility without increasing the parasitic capacitance.
[Brief description of the drawings]
FIG. 1 is a front sectional view of a semiconductor light receiving element according to an embodiment of the present invention.
FIG. 2 is a side sectional view of a semiconductor light receiving element showing an embodiment of the present invention.
FIG. 3 is a cross-sectional view of a manufacturing process of a semiconductor light receiving element showing an embodiment of the present invention.
FIG. 4 is a manufacturing process cross-sectional view of a conventional semiconductor light receiving element.
[Explanation of symbols]
21 Semi-insulating InP substrate 22 n-type InP ohmic layer 23 n-type InGaAsP clad layer 24 non-doped InGaAs light absorption layer 25 p-type InGaAsP clad layer 26 p-type InP ohmic layer 27 mask pattern 29 ridge-type waveguide shape 30 n-type Ohmic region 31 Insulating film 32, 35 Ohmic electrode 33, 33 ', 34 Resist pattern 36 Wiring 37 Pad part 38 Cleaved surface 39 Incident light

Claims (2)

In an optical semiconductor element having a ridge shape,
The ohmic electrode on the upper surface side of the ridge is in complete contact with the upper surface side of the ridge, and the electrode width of the ohmic electrode is larger than the width of the upper surface of the ridge. An optical semiconductor element having a shape that is drawn out in an air bridge shape to an external pad portion . In the method of manufacturing an optical semiconductor element having a ridge shape,
(A) obtaining a ridge-type waveguide shape;
(B) forming a resist so as to cover the ridge-type waveguide shape;
(C) ashing the entire semiconductor substrate to remove the resist, and obtaining a resist pattern in which the top surface of the ridge-type waveguide shape is exposed;
(D) forming a new resist pattern having an opening width larger than that of the ridge-type waveguide;
(E) The wiring metal in ohmic contact with the top surface of the ridge-type waveguide shape has a shape in which the ohmic electrode and the ohmic electrode on the ridge upper surface side are simultaneously drawn out in an air bridge shape to the pad portion outside the ridge. And a step of forming a wiring.

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