JP2002134808A - Indium phosphorus gunn diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat dissipation, yields, and mountability on a plane circuit, etc., of an indium phosphorus Gunn diode. SOLUTION: Boron ions are implanted into a multilayer semiconductor section 13 and 14 to form a high resistance region 17 to separately form a section working as a Gunn diode, and a low resistance layer section working as a path for applying voltage to a first contact layer 12 of the Gunn diode section from outside. Electrodes 15 and 16 for applying voltage to the section working as a Gunn diode are provided on the upper face of a second contact layer 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an indium phosphide (InP) gun diode used for microwave or millimeter wave oscillation, and more particularly to improvement of heat radiation, improvement of yield, ease of mounting on a planar circuit, and the like. The present invention relates to an indium phosphorus gun diode realizing the above.

[0002]

2. Description of the Related Art A gun diode for oscillating microwaves or millimeter waves is usually formed of a compound semiconductor such as gallium arsenide (GaAs) or indium phosphide (InP).
In these compound semiconductors, the mobility of electrons is as high as several thousand cm ² / V · sec in a low electric field, but when a high electric field is applied, the accelerated electrons transition to a band with a large effective mass and the mobility is increased. And negative differential mobility occurs in the bulk, resulting in a negative differential conductance of the current-voltage characteristic,
Thermodynamic instability occurs. For this reason, a domain is generated and travels from the cathode side to the anode side. As a result of repeating this, an oscillating current (oscillation) is obtained.

In the microwave region, the oscillation frequency f
t is obtained from the traveling distance L and the average drift velocity Vd of electrons, and ft = Vd / L. In the millimeter wave band, the energy relaxation time, which is the time required for electrons to increase or decrease the energy in the valley, is the main factor that determines the upper limit of the oscillation frequency. The relaxation time constant of gallium arsenide is twice that of indium phosphide, and the cutoff frequencies of gallium arsenide and indium phosphide are 100 GHz and 200 G, respectively.
Hz (MAdi Forte-Poisson e
tal .: Proc. IPRM'89, p. 551 (1989)). The upper limit of the oscillation frequency of gallium arsenide gun diode is 60G at practical level
Hz to 70 GHz, and an indium phosphorus gun diode is suitable for a high frequency band such as a 77 GHz band used for automotive radar.

In the case of a millimeter-wave gun diode, it is necessary to make the traveling distance of the domain as short as 1 to 2 μm. Moreover, in order to obtain a sufficient oscillation efficiency, it is necessary to set the product of the impurity concentration and the thickness of the traveling space (active layer) of the domain to a predetermined value (for example, 1 × 10 ¹² / cm ² ). Since the oscillation frequency is uniquely determined by the thickness of the active layer, the impurity concentration of the active layer is considerably high in a high frequency band such as a millimeter wave. The current density in the operating state is determined by the product of the impurity concentration of the active layer and the saturation electron velocity. In the millimeter wave band, the temperature of the active layer increases due to the increase in the current density, and the oscillation efficiency decreases.

In order to solve such a problem, a conventional millimeter-wave gun diode employs a mesa structure to reduce the size of an element including an active layer to several tens.
It was formed in a pill-shaped package having a very small diameter of about 0 μm and provided with a heat-dissipating portion made of copper or the like having good heat-dissipating efficiency, which has a great influence on the heat-generating efficiency that determines the most important figure of merit.

FIG. 9 is a cross-sectional view of a conventional indium phosphorus gun diode 100 having a mesa structure. Semiconductor substrate 10 made of n + type (n type high concentration, hereinafter the same) indium phosphide
1, a first contact layer 102 made of n + -type indium phosphide, an active layer 103 made of n-type (n-type low concentration, the same applies hereinafter) indium phosphide, and a second contact made of n + -type indium phosphide by MOCVD. The layers 104 are sequentially stacked, and have a mesa structure in order to reduce the area of the electron traveling space.

After that, the back surface of the semiconductor substrate 101 is thinned, and the cathode electrode 105 is formed on the back surface of the semiconductor substrate 101.
Is formed, and an anode electrode 106 made of AuGe-based metal is formed on the surface of the second contact layer 104, followed by element isolation to complete a Gunn diode element.

The thus formed Gunn diode 10
0 is assembled in a pill package 110 as shown in FIG. The pill type package 110 includes a radiation base electrode 111 and a cylinder 112 made of glass or ceramic as an envelope surrounding the gun diode 100.
The cylinder 112 has a structure in which the heat radiation base electrode 111 is hard-brazed. Gun diode 100
Is electrostatically attracted by a bonding tool such as a sapphire material (not shown), and is adhered to the radiation base electrode 111.

Further, the gun diode 100 and the metal layer provided at the tip of the cylinder 112 are connected by a gold ribbon 113 by thermocompression bonding or the like. After the connection of the gold ribbon 113, the lid-shaped metal disk 114 is brazed onto the cylinder 112, and the assembly into the pill type package 110 is completed.

[0010]

However, the conventional indium phosphorus gun diode 100 is usually formed by a chemical wet etching method using a photoresist as an etching mask in order to obtain the aforementioned mesa structure. However, in this etching method, etching proceeds simultaneously not only in the depth direction but also in the lateral direction, and it is very difficult to control the electron traveling space (active layer). There has been a problem that device characteristics vary.

In addition, since the mesa surface of indium phosphide is unstable, there is also a problem that a current concentration on the mesa surface may cause burnout of the gun diode.

Further, when assembling into the pill type package 110, the gun diode 10
When bonding 0, the bonding tool obstructs the field of view, making it difficult to directly see the radiation base electrode 111, and there is also a problem that the efficiency of assembly work is very poor.

An object of the present invention is to provide an indium phosphorus gun diode which has solved the above-mentioned problems in manufacturing, reliability, assembly, and mounting.

[0014]

For this purpose, a first aspect of the present invention is to provide a first semiconductor layer made of high-concentration n-type indium phosphide and an active layer made of low-concentration n-type indium phosphide on a semiconductor substrate made of indium phosphide. A first electrode and a second electrode separated from each other on an upper surface of the second semiconductor layer in an indium phosphorus gun diode in which a layer and a second semiconductor layer made of high-concentration n-type indium phosphorus are sequentially stacked; From the upper surface of the separation region between the two electrodes, at an arbitrary depth until the minimum depth reaches the active layer and the maximum depth reaches the first semiconductor layer,
Forming a high resistance region by ion implantation and making the first electrode approximately 15 μm or slightly smaller in diameter;
The second electrode was configured to have a larger area than the first electrode.

According to a second aspect, in the first aspect, the second semiconductor layer is replaced with a semiconductor layer made of high-concentration n-type indium gallium arsenide.

In a third aspect based on the first aspect, a third semiconductor layer made of high-concentration n-type indium gallium arsenide is further laminated on the second semiconductor layer, The first electrode and the second electrode are formed on the upper surface of the substrate.

According to a fourth aspect, in any one of the first to third aspects, the first semiconductor layer is replaced with a semiconductor layer made of high-concentration n-type indium gallium arsenide.

[0018]

FIG. 1 is a view showing the structure of an indium phosphorus gun diode 10A according to an embodiment of the present invention.
(a) is a plan view, and (b) is a cross-sectional view. FIG. 2 is a manufacturing process diagram.

First, the manufacturing process will be described with reference to FIG. On a semiconductor substrate 11 made of n + -type indium phosphide having an impurity concentration of 3 to 8 × 10 ¹⁸ atom / cm ^2, an n-type semiconductor having an impurity concentration of 2 × 10 ¹⁸ atom / cm ² and a thickness of 0.5 μm is formed by MOCVD.
A first contact layer (first semiconductor layer) 12 made of + -type indium phosphorus, an active layer 13 made of n-type indium phosphorus having an impurity concentration of 1.5 × 10 ¹⁶ atom / cm ² and a thickness of 1.3 μm, and an impurity concentration A semiconductor substrate is prepared in which a second contact layer (second semiconductor layer) 14 of 2 × 10 ¹⁸ atom / cm and a thickness of 0.3 μm made of n + -type indium phosphide is sequentially laminated (see FIG. 2).
(a)).

Next, a photoresist is patterned on the second contact layer 14 so as to open regions where cathode electrodes and anode electrodes are to be formed, and AuGe, Ni, Au or the like which makes ohmic contact with the second contact layer 14 is formed. A metal film (underlying electrode layer) is deposited. After removing the photoresist, heat treatment (annealing) is performed to form a cathode electrode 15 and an anode electrode 16 on the second contact layer 14 in a form separated by D = 10 μm (FIG. 2).
(B)). Here, the diameter of the cathode electrode 15 is approximately 15
μm or slightly smaller. In addition, as shown in FIG. 1, the planar shape of the anode electrode 16 is a square edge, and the planar shape of the cathode electrode 15 is a circle. However, an elliptical shape, a substantially square shape, or the like can be selected. The number of cathode electrodes 15 may be two or more as shown in the figure in order to obtain a desired current.

Next, using the cathode electrode 15 and the anode electrode 16 as masks,
At 0 and 200 KeV, the dose amount is 7 × 1 respectively.
Boron (B) is implanted under the conditions of 0 ¹² , 1 × 10 ¹³ and 2 × 10 ¹³ / cm ² , and the region from the top surface of the second contact layer 14 to the bottom surface of the active layer 13 is raised by heat treatment at 400 ° C. High resistance area (insulation area) by resistance (insulation) 1
7 is formed (FIG. 2C). The high resistance region 17 is formed by the gap D between the cathode electrode 15 and the anode electrode 16 described above.
= 10 μm. Instead of boron (B), oxygen (O), iron (Fe), hydrogen (H), or the like may be ion-implanted to increase the resistance.

Next, a photoresist is patterned so that a part of the surface of each of the cathode electrode 15 and the anode electrode 16 is opened, and the cathode electrode 15 and the anode electrode are formed in the openings by electrolytic plating or electroless plating. Using the electrode 16 as a base electrode, a cathode bump 18 and an anode bump 19, which are conductive projections made of Au or the like, are deposited and formed (FIG. 2 (d)).

Active layer 13 to which cathode electrode 15 is connected
(The area of the cathode electrode 16) is set to an area (cross-sectional area in the lateral direction) where a predetermined operating current as a Gunn diode can be obtained. In other words, the area is set to an area that can function as a gun diode. As described above, the diameter of the cathode electrode 15 is approximately 15 μm or slightly smaller, and if a desired current cannot be obtained, the cathode electrode 1
5 are provided. On the other hand, the area of the active layer 13 to which the anode electrode 16 is connected is sufficiently larger than the area of the active layer 13 to which the cathode electrode 15 is connected.
The electrical resistance of the semiconductor lamination below 6 is reduced by the cathode electrode 15.
By making the electrical resistance sufficiently lower than the lower semiconductor laminated portion, this portion does not function as a Gunn diode, but functions as a substantially low-resistance portion, and the anode electrode 16 is substantially directly connected to the first electrode. It is connected to the contact layer 12.

Next, the back surface of the semiconductor substrate 11 is polished and thinned so that the entire gun diode has a thickness of about 100 μm in accordance with the usual manufacturing process of a gun diode. Thereafter, if necessary, AuGe, Ni, Au, which is in ohmic contact with the semiconductor substrate 11,
A metal film (metal) 20 made of Ti, Pt, etc. is deposited,
A heat treatment (annealing) is performed ((d) in FIG. 2). Although the metal film 20 formed on the back surface of the semiconductor substrate 11 is not always necessary, the electric resistance of the semiconductor laminated portion below the anode electrode 16 can be further reduced.

In the Gunn diode 10A of the present embodiment formed as described above, the active region 13 made of indium phosphide, which functions as a Gunn diode, is not formed by mesa formation by etching but by high resistance by ion implantation. Since they are formed independently of each other, the conventional mesa-type problem that the gun diode is burned out due to current concentration on the mesa surface because the surface is unstable does not occur.

FIG. 3 shows that the Gunn diode 10A of FIG. 1 in which the cathode bump 18 of the cathode electrode 15 is formed at the center and the anode bump 19 of the anode electrode 16 is formed on both sides is mounted on the flat circuit board 31 constituting the microstrip line 30. It is a figure which shows an example of the structure made. A signal electrode 32 is provided on the surface of a semi-insulating flat substrate 31 having a specific resistance of at least 10 ⁶ Ω · cm and a thermal conductivity of at least 170 W / mK, such as aluminum nitride (AlN), and a ground electrode on the entire back surface. 33 are formed. Numeral 34 denotes a via hole filled with tungsten, which electrically connects the ground electrode 33 on the back surface to the front ground electrode 35 formed on the front surface.

In the gun diode 10A, the central cathode bump 18 is bonded to the central signal electrode 32, and the anode bumps 19 of the anode electrodes 16 on both sides are bonded to the surface ground electrodes 35 on both sides. 32A is Gunn diode 10
B is a bias electrode for supplying a bias voltage to A, 32B is an electrode constituting a microstrip line resonator including the Gunn diode 10A, and 32C is a microstrip line signal output electrode.

When the resonator length (length of the electrode 32B) is 400 μm, the oscillator constituted by the Gunn diode 10A and this mounting structure has an oscillation frequency of 77 GHz and a frequency of 60 GHz.
An output power of mW is obtained.

In this mounting structure, the gun diode 10A
In a face-down position, the cathode bump 18 is used as the signal electrode 32, and the anode bump 19 is used as the surface ground electrode 35.
And no gold ribbon is used, so that the occurrence of the parasitic inductance caused by the connection of the gold ribbon is eliminated, and an oscillator with less variation in characteristics can be realized.

Further, since the heat generated in the gun diode 10A is dissipated to the substrate 31 functioning as a heat sink via the cathode bumps 18 and the anode bumps 19, the heat radiation effect is enhanced. Further, in such a mounted state of the gun diode 10A, since the anode bumps 19 of the anode electrode 16 are located on both sides of the cathode bumps 18 of the cathode electrode 15, it is possible to prevent an excessive load from being applied to the cathode electrode 15 having a small area. Is done.

Further, the gun diode 10 of the present embodiment
A can prevent the breakdown by making the diameter of the cathode electrode 15 approximately 15 μm or slightly smaller. FIG. 4 shows that the diameter of the cathode electrode 15 is 46
The current-voltage characteristics when changing to μm, 33 μm, 23 μm, 19 μm, and 15 μm are shown. For example, 77 GHz
When oscillating in the band, the bias voltage is about 6 V.
It can be seen that it is necessary to be less than or equal to μm. This is presumably because the current flowing through the deep level and the surface pinning level generated after the ion implantation is reduced.

FIG. 5 shows a gun diode 10 according to another embodiment.
4B is a diagram showing a cross section of the second contact layer 14, wherein the second contact layer 14 is replaced with an n + -type In _0.53 Ga _0.47 As having a thickness of 0.1 _mm .
The second contact layer 14 'made of 2 μm indium gallium arsenide (InGaAs) is used, and operates similarly to the Gunn diode 10A of FIG.

FIG. 6 also shows a gun diode 10 according to another embodiment.
FIG. 4C is a diagram showing a cross section of the first contact layer 12, which is made of n + -type In _0.53 Ga _0.47 As instead of the first contact layer 12.
The first contact layer 12 'of 5 μm indium gallium arsenide (InGaAs) is used, and operates similarly to the Gunn diode 10A of FIG.

FIG. 7 also shows a Gunn diode 10 according to another embodiment.
FIG. 4D is a diagram showing a cross section of FIG. 3D, in which an upper surface of the second contact layer 14 is made of n + -type In _0.53 Ga _0.47 As and has a thickness of 0.
A third contact layer 14 ″ of 2 μm indium gallium arsenide (InGaAs) is laminated, and operates similarly to the Gunn diode 10A of FIG.

FIG. 8 also shows a gun diode 10 according to another embodiment.
FIG. 4E is a diagram showing a cross section of FIG. 4C, in which the depth of the high-resistance region 17 by boron (B) ion implantation reaches the upper surface of the active layer 13, and thus at least the second contact layer 14 is formed. By forming the high resistance region 17 having a high resistance by ion implantation up to the depth of the interface of the active layer 13, the portion functioning as a Gunn diode is partitioned by the cathode electrode 15.

[0036]

As described above, in the Gunn diode of the present invention, the active region made of indium phosphide, which functions as a Gunn diode, does not form a mesa by etching.
Since it is separated and formed by the high resistance region, it is possible to prevent burning due to current concentration on the mesa surface.

Further, since the ion-implanted region in forming the high-resistance region is determined in a self-aligned manner using the cathode electrode and the anode electrode as masks, variations in the characteristics of the Gunn diode can be reduced.

The diameter of the cathode electrode is approximately 15 μm.
Or, by making it slightly smaller, breakdown during operation can be prevented.

Further, since the cathode electrode and the anode electrode are provided on the same surface, when the bumps are provided thereon, the heights of the bumps can be set to the same level.
The mounting posture can be realized face down. For this reason, it is not necessary to assemble into a conventional pill type package, and it is easy to assemble on a flat board, which has a great advantage in assembling.

Further, since it is not necessary to connect the micro-electrodes with a gold ribbon or the like at the time of mounting, no parasitic inductance is generated, and variations in circuit characteristics due to variations in the length of the gold ribbon can be eliminated.

Further, by arranging the cathode electrode, which substantially functions as a Gunn diode, into a plurality of parts, the heat radiation efficiency is remarkably improved, and the oscillation efficiency and oscillation power can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a view showing an indium phosphorus gun diode according to an embodiment of the present invention, wherein (a) is a plan view and (b) is a cross-sectional view.

FIG. 2 is an explanatory diagram of a method of manufacturing the indium phosphorus gun diode of FIG.

FIG. 3 is a perspective view of a mounting structure of the indium phosphorus gun diode of FIG. 1;

4 is a current-voltage characteristic diagram when the diameter of a cathode electrode of the indium phosphorus gun diode of FIG. 1 is changed.

FIG. 5 is a sectional view of a modified example of the indium phosphorus gun diode of FIG. 1;

FIG. 6 is a sectional view of a modified example of the indium phosphorus gun diode of FIG. 1;

FIG. 7 is a sectional view of a modified example of the indium phosphorus gun diode of FIG. 1;

FIG. 8 is a sectional view of a modified example of the indium phosphorus gun diode of FIG. 1;

FIG. 9 is a sectional view of a conventional indium phosphorus gun diode having a mesa structure.

FIG. 10 is a cross-sectional view in which the indium phosphorus gun diode having the mesa structure of FIG. 9 is incorporated in a pill type package.

[Explanation of symbols]

10A, 10B, 10C, 10D, 10E: indium phosphorus gun diode 11: semiconductor substrate, 12: first contact layer, 13:
Active layer, 14: second contact layer, 15: cathode electrode, 16: anode electrode, 17: high resistance region by ion implantation, 18: cathode bump, 19: anode bump, 20: metal film 30, microstrip line, 3
1: plate substrate, 32: signal electrode, 33: ground electrode, 3
4: Via hole, 35: Surface ground electrode 100: Conventional Gunn diode, 101: Semiconductor substrate,
102: first contact layer, 103: active layer, 10
4: second contact layer, 105: cathode electrode, 10
6: anode electrode 110: pill type package, 111: heat dissipation base electrode, 1
12: cylinder, 113: gold ribbon, 114: metal disk

Claims (4)

[Claims] A first semiconductor layer made of high-concentration n-type indium phosphide, an active layer made of low-concentration n-type indium phosphide, and a second semiconductor layer made of high-concentration n-type indium phosphide. In an indium phosphorus gun diode in which semiconductor layers are sequentially stacked, a first electrode and a second electrode are formed on an upper surface of the second semiconductor layer so as to be separated from each other by a minimum depth from an upper surface of a separation region between the two electrodes. Forming a high resistance region by ion implantation at an arbitrary depth before reaching the active layer and reaching a maximum depth to the first semiconductor layer, and forming the first electrode at approximately 15 μm or more. An indium phosphorus gun diode having a slightly smaller diameter and a second electrode having a larger area than the first electrode. 2. The indium phosphorus gun diode according to claim 1, wherein said second semiconductor layer is replaced with a semiconductor layer made of high-concentration n-type indium gallium arsenide. 3. A third semiconductor layer made of high-concentration n-type indium gallium arsenide is further laminated on the second semiconductor layer, and the first electrode and the first electrode are formed on an upper surface of the third semiconductor layer. The indium phosphorus gun diode according to claim 1, wherein a second electrode is formed. 4. The indium phosphorus gun diode according to claim 1, wherein said first semiconductor layer is replaced with a semiconductor layer made of high-concentration n-type indium gallium arsenide.