JP2004134419A - Method for manufacturing microwave semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a method for manufacturing a microwave semiconductor device which does not damage a microwave semiconductor element when a via hole is formed in a region of a semi-insulating board opposed to the microwave semiconductor element formed on the semi-insulating board. <P>SOLUTION: The method for manufacturing the microwave semiconductor device includes steps of forming an epitaxial layer 3 having different etching properties from those of the semi-insulating board 2 on the board 2, and further forming a PIN diode 4 on the layer 3. The via hole is formed by etching in the region of the substrate 2 directly under the PIN diode 4. The etching can be stopped from advancing by the layer 3, and the diode 4 is not damaged. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a microwave semiconductor device including a PIN diode and the like.
[0002]
[Prior art]
With the utilization of microwave and millimeter-wave bands, communication devices and the like using these bands include passive devices such as PIN diodes for microwave and millimeter-wave bands, active devices, monolithic integrated circuits, and transmission lines. Integrated microwave semiconductor devices have become widespread.
[0003]
Here, the PIN diode includes three layers in which an I layer which is a high resistivity region formed of an intrinsic semiconductor is disposed between a P-type semiconductor layer and an N-type semiconductor layer. This diode has extremely low series resistance at forward bias and extremely high series resistance at reverse bias, so it is used as a switching element with good on / off characteristics in the microwave / millimeter wave band, and as a microwave integrated circuit. Implemented with other microwave elements.
[0004]
FIG. 3 is a cross-sectional view illustrating an example of a method for manufacturing a conventional microwave semiconductor device including a PIN diode.
[0005]
In FIG. 3, a semi-insulating substrate 21 is, for example, gallium arsenide (GaAs). On this semi-insulating substrate 21, an N + layer 22, an I layer 23 and a P + layer 24 are sequentially laminated to form a PIN diode 20. You. Next, a via hole 25 is formed in a region directly below the PIN diode 20 by dry etching from below the semi-insulating substrate 21. A gold deposition film 26 is formed in the via hole 25, and the cathode side of the PIN diode 20 is directly connected to the lower side of the semi-insulating substrate 21. In a microwave band or a millimeter wave band, wiring over a short distance is indispensable in order to avoid the influence of the inductance of the wiring. Therefore, in this example, the via hole 25 is provided with a PIN diode so as to minimize the connection distance. It is formed in a region immediately below 20.
[0006]
[Problems to be solved by the invention]
However, in this method, when dry etching is performed from under the semi-insulating substrate 21 to form the via hole 25, the etching is stopped at the interface between the semi-insulating substrate 21 and the N + layer 22 of the PIN diode 20. It was difficult to set the etching conditions at the same time. Therefore, in many cases, the N + layer 22 of the PIN diode 20 is eroded by the etching for forming the via hole 25 as illustrated by way of example in FIG.
[0007]
In order to avoid this problem, a method is conceivable in which the position of the via hole 25 is formed not in the area directly below the PIN diode 20 but in a region of the semi-insulating substrate 21 far from the PIN diode 20, but in this case, the connection distance is long. And the influence of increase in lead inductance.
[0008]
The present invention has been made in order to solve the above-described problems, and when forming a via hole in a region of a semi-insulating substrate facing a microwave semiconductor device formed on the semi-insulating substrate, It is an object of the present invention to provide a method for manufacturing a microwave semiconductor device which does not damage a microwave semiconductor element.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a method for manufacturing a microwave semiconductor device according to the present invention includes a step of forming an epitaxial layer having a different etching property from that of the semi-insulating substrate on the semi-insulating substrate; Forming a microwave semiconductor element thereon, and selectively etching a region of the semi-insulating substrate facing the microwave semiconductor element with the epitaxial layer interposed therebetween with respect to the epitaxial layer, A step of forming a via hole in the insulating substrate; and a step of forming a metal film in contact with the epitaxial layer in the via hole.
[0010]
According to the method of manufacturing a microwave semiconductor device of the present invention, the epitaxial layer serves as a stopper for etching and can prevent damage to the microwave semiconductor element.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method of manufacturing a microwave semiconductor device according to the present invention will be described with reference to FIGS.
[0012]
1 and 2 are cross-sectional views showing a first step and a second step of a method of manufacturing a microwave semiconductor device including a PIN diode, respectively, according to an embodiment of the present invention in the order of steps.
[0013]
First, as shown in FIG. 1A, an epitaxial layer 3 having a different etching property from that of the semi-insulating substrate 2 is formed on the upper surface of the semi-insulating substrate 2. In the present embodiment, the material of the semi-insulating substrate 2 is gallium arsenide (GaAs). The material of the epitaxial layer 3 is aluminum gallium arsenide (AlGaAs), and the thickness of the layer is about 10 μm.
[0014]
Next, as shown in FIG. 2B, an N + layer 5a, an I layer 6a, and a P + layer 7a are further formed on the epitaxial layer 3 by epitaxial growth and stacked. In the present embodiment, the thickness of these layers is about 0.2 μm for the N + layer 5a, about 2 μm for the I layer 6a, and about 0.2 μm for the P + layer 7a.
[0015]
Further, as shown in FIG. 2 (c), a mask 11 is applied only to a portion where a PIN diode is to be formed on the P + layer 7a and wet etching is performed, thereby obtaining a semi-insulating substrate as shown in FIG. 2 (d). A PIN diode 4 having a three-layer structure of a P + layer 7, an I layer 6, and an N + layer 5 is formed on the epitaxial layer 3 formed on the layer 2. Then, by removing the mask 11, the upper surface of the P + layer 7 is exposed as shown in FIG.
[0016]
Next, as shown in FIG. 2 (f), a mask 12 is formed in an area directly below the PIN diode 4 on the lower surface of the semi-insulating substrate 2, and a reactive ion etching ( RIE) is performed to remove the semi-insulating substrate 2 at the opening of the mask 12 in a tapered shape.
[0017]
In this reactive ion etching, for example, a gas composition is silicon tetrachloride (SiCl ₄ ) and sulfur hexafluoride (SF ₆ ), and etching is performed at a pressure of 2 to 5 Pascal for about 3 minutes, thereby removing gallium arsenide (GaAs). The semi-insulating substrate 2 is selectively etched with respect to the epitaxial layer 3 made of aluminum gallium arsenide (AlGaAs).
[0018]
For this reason, the epitaxial layer 3 serves as a stopper layer for reactive ion etching, and as shown in FIG. 2G, the epitaxial layer 3 is exposed, but the etching does not proceed to the N + layer 5 on the cathode side of the PIN diode 4. . Therefore, the region of the semi-insulating substrate 2 facing the PIN diode 4 with the epitaxial layer 3 interposed therebetween is selectively removed without damaging the PIN diode 4 by etching. After that, the mask 12 is removed as shown in FIG.
[0019]
Next, a metal film 9 is formed from the periphery of the via hole 8 and the inner surface of the via hole 8 to the exposed surface of the epitaxial layer 3. In the present embodiment, the metal film 9 is formed by evaporating gold. Then, as shown in FIG. 2I, a via hole 8 can be formed in a region immediately below the PIN diode 4.
[0020]
As described above, according to the manufacturing method of the microwave semiconductor device of the embodiment of the present invention, the reactive ions are formed from the lower surface of the semi-insulating substrate 2 to form the via hole 8 in the region directly below the PIN diode 4. At the time of etching, selective etching is performed to remove only the semi-insulating substrate 2 made of gallium arsenide (GaAs), and the etching does not proceed to the epitaxial layer 3 made of aluminum gallium arsenide (AlGaAs). For this reason, the epitaxial layer 3 serves as a stopper layer, and can protect the N + layer 5 of the PIN diode 4 from etching.
[0021]
In addition, the thickness of the epitaxial layer 3 is sufficiently thin, about 10 μm, and has little effect on the conduction with the N + layer 5. be able to. Therefore, the via hole 8 as a cathode electrode can be formed in a region immediately below the PIN diode 4 without damaging the PIN diode 4.
[0022]
Further, since the via hole 8 is formed in a region immediately below the PIN diode 4, for example, the connection distance between the cathode side of the PIN diode 4 and an electrode provided on the lower surface of the semi-insulating substrate 2 can be reduced. In the microwave or millimeter wave band, the influence of the inductance due to the wiring can be minimized.
[0023]
【The invention's effect】
According to the present invention, a microwave semiconductor device is formed in a via hole without damaging the microwave semiconductor device in a region of the semi-insulating substrate facing the microwave semiconductor device formed on the semi-insulating substrate. It can be connected to a metal film to be formed.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a first-step process of a method for manufacturing a microwave semiconductor device according to an embodiment of the present invention.
FIG. 2 is a sectional view showing a second step of the method of manufacturing the microwave semiconductor device according to the embodiment of the present invention.
FIG. 3 is a sectional view showing an example of the structure of a microwave semiconductor device according to a conventional manufacturing method.
FIG. 4 is a cross-sectional view modeling an example of the structure of a microwave semiconductor device after an etching step according to a conventional manufacturing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Microwave semiconductor device 2 ... Semi-insulating substrate 3 ... Epitaxial layer 4 ... PIN diode 5, 5a ... N + layer 6, 6a ... I layer 7, 7a ... P + layer 8 ... Via hole 9 ... Gold vapor deposition layers 11, 12 …mask

Claims (2)

A step of forming an epitaxial layer having a different etching property from the semi-insulating substrate on the semi-insulating substrate;
Forming a microwave semiconductor device on the epitaxial layer;
Forming a via hole in the semi-insulating substrate by selectively etching a region of the semi-insulating substrate facing the microwave semiconductor element with the epitaxial layer interposed therebetween, with respect to the epitaxial layer;
Forming a metal film in contact with the epitaxial layer in the via hole. 2. The microwave semiconductor device according to claim 1, wherein in the step of forming the microwave semiconductor element, a PIN diode is formed by sequentially stacking an N layer, an I layer, and a P layer on the epitaxial layer. Manufacturing method.

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