JPH09232255A - Compound semiconductor device and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compound semiconductor element having an electrode structure which can come into ohmic contact with the element always stably by a method wherein a first metal layer is formed by a resistance heating vapor deposition system and a second metal layer, in then formed on the first metal layer by an EB vapor deposition system. SOLUTION: The surface of a wafer 4 is cleaned, and the wafer and a vapor deposition material are set on a vapor deposition machine which is provided with both mechanisms as, a resistance heating system and an EB vapor deposition system. Then, an AuBe material which contains 1wt.% of Be is set on a boat for resistance heating, and an Au material in a prescribed amount required for one vapor deposition is set on a berth for an EB vapor deposition. At this time, the AuBe material is used up in every batch. In this state, an AuBe layer 61 is formed by the resistance heating system by an automatic vapor deposition. Then, an Au layer 62 is vapor-deposited continuously on the layer 61 by the EB vapor deposition system under a high vacuum. Then, a photolithographic process is performed to obtain an anode electrode in a prescribed shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a compound semiconductor device, and more particularly to a method for forming an electrode of a compound semiconductor device and an electrode structure obtained thereby.

[0002]

2. Description of the Related Art A conventional method for manufacturing a compound semiconductor device will be described with reference to FIG. 3 (a) to 3 (g)
FIG. 4 is a manufacturing process diagram of a compound semiconductor device according to a conventional example.
FIG. 3A shows a state of a wafer 4 in which an n-type GaP epitaxial layer 2 and a p-type GaP epitaxial layer 3 are sequentially grown on an n-type GaP substrate 1.

Next, as shown in FIG. 3 (b), after controlling the wafer thickness (back lapping step), an Au alloy layer is formed on the back surface side of the n-type GaP substrate 1 as shown in FIG. 1 (c). After the formation, the cathode electrode 5 is formed by etching.

Next, as shown in FIG. 3D, p-type GaP
The anode electrode layer 6 is formed on the upper surface of the epitaxial layer 3 by EB.
(ELECTRON BEAM: hereinafter simply referred to as EB) It is formed by a vapor deposition method. The lower layer of the anode electrode layer 6 is, for example, Au.
The Be layer and the upper layer are composed of the Au layer. Here, the thickness of the anode electrode layer 6 is usually about 1.5 to 2.0 μm.

Next, as shown in FIG. 3 (e), a normal photolithography process is performed. That is, the photomask 7 is placed on the wafer.
Then, the unnecessary portion is removed by etching as shown in FIG. 3 (f) to obtain the anode electrode 6 '.

Finally, as shown in FIG. 3 (g), the wafer 4
Is divided into each element (dicing step) to obtain a final element.

[0007]

By the way, in the above-mentioned conventional example, the anode electrode 6'having the AuBe / Au structure is formed by the EB vapor deposition method. In this case, the Be concentration in the AuBe ingot is Au and Be. Due to the difference in vapor pressure, it tends to decrease with each vapor deposition.

Further, since the Be element is small and light (B
The atomic weight of e is 197, the atomic weight of Au is 9), and there are many Be elements that cannot reach the wafer due to the influence of the EB electromagnetic field.
Therefore, even if the AuBe material is replenished each time the vapor deposition is performed, the Be concentration in the formed AuBe layer decreases with the number of vapor depositions, making it difficult to form a stable AuBe layer.

As a result, a good ohmic contact cannot be stably obtained, and the contact resistance at the interface between the electrode 6'and the wafer is increased or it becomes non-ohmic.

Further, conventionally, the anode electrode 6'has a thick Au cap layer (for example, 0.5 .mu.m to 2 .mu.m) in order to improve the wire bonding, and the total thickness of the anode electrode 6'is 1.5. Although about 2.0 μm is formed, the tensile stress increases as the electrode thickness increases. Further, when the electrode shape is, for example, a quadrangular shape, stress is likely to be concentrated on the corner portion, and particularly, as shown in FIG. 4 which is an enlarged view of a portion A of FIG.
If the peripheral lower P portion is roughened to improve the light extraction efficiency, the stress causes the defect that the wafer crystal of the electrode lower surface layer 3 is broken.

Further, when forming the anode electrode 6'having an AuBe / Au structure, as described above, a usual photolithography process, that is, a photomask arranged so that only the electrode portion is covered on the AuBe / Au layer 6 is formed. Chemical etching is performed via 7. Here, as the etching solution, an ammonium iodide-based Au etchant is used. At this time, the etching does not partially proceed at the interface between the AuBe layer and the Au layer, and the outer periphery of the Au layer is overetched. There were cases.

Therefore, an object of the present invention is to realize a compound semiconductor device having an electrode structure capable of always providing a stable ohmic contact with the device, and to perform etching for forming an electrode smoothly to provide a stable electrode shape. Another object of the present invention is to provide a method for producing a compound semiconductor device which can obtain

[0013]

In order to achieve the above-mentioned object, the first aspect of the present invention has an electrode structure comprising a first metal layer and a second metal layer laminated on the first metal layer. A method of manufacturing a compound semiconductor device, comprising the steps of forming the first metal layer by resistance heating vapor deposition, and then forming the second metal layer by EB vapor deposition on the first metal layer. Is characterized by.

According to a second aspect of the present invention, in the method of manufacturing a compound semiconductor device according to the first aspect, the resistance heating vapor deposition and the EB vapor deposition are performed in the same vapor deposition apparatus.

According to a third aspect of the present invention, in the method of manufacturing a compound semiconductor device according to any one of the first or second aspects,
The electrode structure is characterized in that the first metal layer and the second metal layer are AuBe / Au electrodes including an AuBe layer and an Au layer, respectively.

According to a fourth aspect of the present invention, in the method for manufacturing a compound semiconductor device according to the third aspect, a step of forming an AuBe layer by resistance heating vapor deposition and then an Au layer by EB vapor deposition on the AuBe layer. Forming step and the AuBe /
The Au layer is characterized in that an AuBe / Au electrode is obtained by selectively etching the Au layer with an ammonium iodide-based Au etchant mixed with buffered hydrofluoric acid.

According to a fifth aspect of the present invention, there is provided a compound semiconductor device obtained by the manufacturing method according to any one of the third and fourth aspects, wherein the surface of the device is roughened.
The Be / Au electrode has a thickness of 1.0 to 1.5 μm.

According to a sixth aspect of the present invention, there is provided a compound semiconductor device obtained by the manufacturing method according to the third or fourth aspect, wherein the surface of the device is roughened.
The Be / Au electrode is characterized in that the outer periphery of the Be / Au electrode in a top view is curved.

The operation of each claim will be described below.

According to the first aspect of the present invention, the first metal layer is formed by resistance heating vapor deposition instead of EB vapor deposition, and the processing material is used up for each batch. Therefore, each element constituting the first metal layer is formed. The concentration of is always stable,
An electrode structure with excellent ohmic properties can be realized.

According to the second aspect of the present invention, since the formation of the first metal layer and the subsequent formation of the second metal layer by EB vapor deposition are also performed in the same vapor deposition apparatus, not only the vapor deposition process can be performed smoothly, but also The adhesion of both layers can also be guaranteed.

An example of an actual electrode structure according to claim 1 is an AuBe / Au layer as shown in claim 3, and the present invention is effective in such a structure. In particular, in the case of this structure, the Be concentration was unstable according to the conventional EB deposition, but according to the method of the present invention, a very stable Be concentration can be secured and a stable ohmic contact can be guaranteed. Can be realized.

According to the invention of claim 4, AuBe / Au
A step of selectively etching the layer is performed with an etchant in which a buffered hydrofluoric acid is mixed in an ammonium iodide-based Au etchant. Thus, by mixing buffered hydrofluoric acid into the etchant, AuB
Since the oxide film formed on the e layer can be removed, smooth etching can be performed from the AuBe layer to the Au layer.

By adopting the electrode thickness according to claim 5 and the electrode shape according to claim 6, the adhesion between the element and the electrode can be improved. Conventionally, the element surface may be roughened in order to improve the light extraction efficiency. However, in this structure, since the lower part of the electrode is also roughened, problems such as electrode peeling are likely to occur. On the other hand, this problem can be solved by the invention as claimed in claim 5 or 6.

[0025]

1 is a block diagram of an embodiment of the present invention.
This will be described with reference to FIG. 1A to 1F are process diagrams showing a method of manufacturing a compound semiconductor device according to this embodiment. Here, the process up to the formation of the cathode electrode is the same as the conventional one, and therefore the description thereof is omitted. It should be noted that the same functional parts as those in FIG. 3 are denoted by the same symbols.

First, in the state of FIG. 1A, the surface of the wafer 4 is cleaned with a sulfuric acid + hydrogen peroxide type etchant as a pretreatment for forming electrodes.

Then, the wafer and the vapor deposition material are set in the vapor deposition machine having both the resistance heating system and the EB vapor deposition system. Here, the AuBe material containing 1 wt% of Be is set in a W boat for resistance heating, and the Au material is set in a hearth for EB vapor deposition in a predetermined amount required for one vapor deposition. Here, the AuBe material is used up for each batch.

In this state, as shown in FIG. 1B, the AuBe layer 61 is formed by a resistance heating method by automatic vapor deposition. Then, as shown in FIG. 1C, the AuBe layer 61 is formed.
The Au layer 62 is continuously vapor-deposited thereon by the EB method under high vacuum. Here, the thickness of each layer is controlled by the film formation controller that controls the frequency of the crystal unit.
The thickness of the AuBe layer 61 was set to 200 nm, and the thickness of the Au layer 62 was set to 1100 nm (total electrode thickness: 1300 nm).

Next, a photolithography process is performed to obtain an anode electrode having a predetermined shape. First, as shown in FIG. 1D, an electrode pattern protective film is formed by a photoresist 7 serving as a photomask. The outer peripheral shape of an electrode pattern 6 ′ finally obtained by this is a curved surface shape without corners. Here, the circular shape shown in the top view of FIG. 2 is used.

Then, the photoresist is removed into a shape of an electrode by a chemical solution. Here, AuBe
As an etchant for the / Au layer, a conventional Au etchant in which iodine + ammonium iodide + ethanol + DIW (DE-IONIZED WATER: pure water) is mixed with BHF (buffered hydrofluoric acid: ammonium fluoride) as a main component. Hereinafter, a mixture of about 10% BHF) is used.

By mixing BHF with the etchant as described above, there is a problem in the case where the conventional Au etchant is used, that is, the progress of etching is partially stopped at the AuBe layer-Au interface, in particular, in the side portion of the Au layer. The phenomenon of being over-etched can be eliminated.

The action of this BHF is as follows.

That is, the reason why the progress of etching is partially stopped in the conventional manufacturing method is that the AuBe layer 62 is formed.
It is thought that this is due to the oxide film formed on the surface of.
Therefore, in order to remove this oxide film, BH is used in the present invention.
I try to mix F with the etchant.

By using the etchant mixed with BHF as described above, the AuBe layer 61 to the Au layer 6 are used.
Smooth etching that is continuous to 2 is possible.

Next, after the electrode etching is completed, as shown in FIG.
As shown in (e), the resist 7 is removed and alloying is performed to obtain an anode electrode 6'having a good ohmic contact.

The wafer thus obtained is shown in FIG.
As shown in (f), the PN junction is divided by dicing to form an element for each chip.

Finally, after etching with a sulfuric acid-based etchant to remove a damaged layer on the dicing surface after dicing, roughening treatment is performed with a boiling hydrochloric acid to increase the light extraction efficiency to obtain a final device.

As described above, in the present embodiment, the vapor deposition apparatus capable of carrying out both the resistance heating method and the EB method is used, and the AuBe layer is subjected to the resistance heating method and Au.
Since the layers are continuously formed by the EB method, AuBe layer, Au
The electrode layer can be formed without impairing the adhesion strength of the layer. Here, since the AuBe layer is formed by the resistance heating method, only the necessary amount of AuBe material is set in each batch and used up each time, which is different from the method using the EB method ingot. Therefore, it is possible to always form an AuBe layer having a stable Be concentration. As a result, the anode electrode 6'can make a stable ohmic contact with the device.

The Au layer 62 needs to have a layer thickness of 1 μm or more in order to improve the wire bonding. However, the resistance heating method usually limits the amount of material set, so that a thick film can be formed. Since it is not suitable, it is formed by EB evaporation as usual.

Further, in the final step, a roughening treatment is carried out in order to improve the light extraction efficiency. In this step, the lower part around the electrode is also roughened, so that it is clear from FIG. Moreover, it is vulnerable to external force and stress, and the lower part of the electrode may be crystallized.

However, in this embodiment, as described above, the electrode film thickness is formed to be 1300 nm, which is thinner than that of the conventional structure, and the electrode shape is circular, so that electrode peeling or the like is less likely to occur. And highly reliable. Here, the relationship between the electrode forming method, the electrode film thickness, the electrode shape, and each evaluation item, which are clarified as a result of the experiment, is shown in the following table.

[0042]

[Table 1]

As described above, the electrode film thickness is 1.
It was found that the electrode peeling can be prevented by setting the thickness to 0 μm to 1.5 μm.

[0044]

As described above, according to the manufacturing method of the present invention, it is possible to realize a compound semiconductor device having an electrode capable of always making stable ohmic contact with the device. In addition, etching for electrode formation can be smoothly performed, and a stable electrode shape can be obtained.

Further, the electrode structure has excellent adhesion to the element, does not cause a problem such as peeling, and is highly reliable.

[Brief description of drawings]

1A to 1F are process diagrams showing a method for manufacturing a compound semiconductor device according to an embodiment of the present invention.

FIG. 2 is a top view of a photoresist used in the process of FIG.

3A to 3G are process diagrams showing a method for manufacturing a compound semiconductor device according to a conventional example.

FIG. 4 is an enlarged view of part A of FIG.

[Explanation of symbols]

 6'Anode electrode 61 First metal layer 62 Second metal layer 7 Photoresist

Claims (6)

[Claims] 1. A method of manufacturing a compound semiconductor device having an electrode structure comprising a first metal layer and a second metal layer laminated on the first metal layer, wherein the first metal layer is formed by resistance heating vapor deposition. Forming, and then EB on the first metal layer
And a step of forming the second metal layer by vapor deposition. 2. The method for producing a compound semiconductor element according to claim 1, wherein the resistance heating vapor deposition and the EB vapor deposition are performed in the same vapor deposition apparatus. 3. The method of manufacturing a compound semiconductor device according to claim 1, wherein the electrode structure is an AuBe / Au electrode in which the first metal layer and the second metal layer are an AuBe layer and an Au layer, respectively. And a method for manufacturing a compound semiconductor device. 4. The method of manufacturing a compound semiconductor device according to claim 3, wherein a step of forming an AuBe layer by resistance heating vapor deposition is performed, and then Au is deposited by EB vapor deposition on the AuBe layer.
A compound semiconductor device comprising: a step of forming a layer; and a AuBe / Au electrode is obtained by selectively etching the AuBe / Au layer with an etchant in which a buffered hydrofluoric acid is mixed in an ammonium iodide-based Au etchant. Manufacturing method. 5. A compound semiconductor device obtained by the manufacturing method according to claim 3, wherein the device surface is roughened, and the AuBe / Au electrode has a thickness of 1.0 to 1 A compound semiconductor device characterized by being set to 0.5 μm. 6. A compound semiconductor device obtained by the manufacturing method according to claim 3, wherein the device surface is roughened, and the AuBe / Au electrode has a curved outer peripheral surface in a top view. A compound semiconductor device characterized in that