JPS5950091B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a planar semiconductor device using a semi-insulating semiconductor as a substrate.

In recent years, various semiconductor devices have been developed as semiconductor devices with a planar structure formed using a semi-insulating semiconductor as a substrate. In manufacturing a semiconductor device having a planar structure, one of the element electrodes of the formed semiconductor device is often short-circuited to a ground electrode. In such cases, bonding wires have usually been used, but due to the influence of mutual inductance, it is not easy to keep the grounding inductance below about 5oItI even if the number of bonding wires is increased. Decreasing the grounding inductance is the first step in manufacturing technology for planar elements.
・There were two major challenges.

In response to such demands, grounding methods using, for example, beam leads have been developed. In this method, for example, as shown in FIG. 1, beam leads 15 and 16 are drawn out from an electrode 14 to be grounded of a planar element 13 using a semiconductor crystal layer 12 on a semi-insulating substrate 11, and these beam leads are connected to a heat sink. Thermo-compression is applied to the ground electrode which also serves as a ground electrode. In this case, the ground is not a "wire" like a bonding wire.
Since this is done with "plane" metal, the grounding inductance is extremely reduced. However, there are drawbacks such as the need for skill in thermocompression bonding of the beam lead and the risk of the beam lead being bent during manufacturing, and the drawback is that it is not suitable for mass production in the manufacture of semiconductor devices. . SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a semiconductor device which eliminates the above-mentioned conventional drawbacks and is excellent in mass production.

According to the present invention, a method for manufacturing a semiconductor device includes forming a planar semiconductor device using a semi-insulating GaAs semiconductor as a substrate, and then short-circuiting at least one of the device electrodes and a ground electrode. After covering other parts of the formed planar semiconductor device with insulation 5 so as to constitute a continuous exposed surface connecting the element electrode to be grounded and the ground electrode, which of the element electrode and the ground electrode is The element is held so that one side is in contact with a conductive holder, and the element is inserted so as to be completely immersed in the plating solution, and electricity is applied to the conductive holder to perform electroplating. A method for manufacturing a semiconductor device is obtained, which is characterized in that an electrode and a ground electrode are short-circuited.

The present invention is a method for manufacturing a semiconductor device with excellent mass productivity, which utilizes a novel phenomenon discovered by the inventor of the present application.

In other words, the conventional electroplating method can only be applied to conductive materials, with a specific resistance of 103 to 10.
It was simply impossible to electroplate 10 ohm-cm semi-insulating semiconductor materials. However, according to a new phenomenon discovered by the inventor of the present application, when a semi-insulating semiconductor and a plating electrode provided on a part of the surface thereof are both immersed in a plating solution and the plating electrode is energized. In the conventional method in which the plating electrode is not immersed, almost no plating current flows, so plating can be performed under conditions where no plating is applied at all, such as at a set current density of 4 mA/Cnl and a liquid temperature of 60°C. A completely new phenomenon has been invented in which plating can be applied easily, and the speed at which plating progresses on the surface of a semi-insulating substrate is about 105 times faster than the speed at which plating grows in the thickness direction. . In addition, this phenomenon occurs when the surface of the insulating coating provided on the semi-insulating semiconductor surface is completely plated, and furthermore, the semi-insulating semiconductor surface is coated with the insulating coating on the exposed surface including the plating electrode and the exposed surface not including the plating electrode. When divided into exposed surfaces, plating is performed on the exposed surfaces containing the electrodes, and the plating does not progress past the insulating coating used for division to the exposed surfaces that do not contain the plating electrodes. Also, plating electrodes are not necessarily made of evaporated metal. It does not have to be a deposited electrode, but may be a semiconductor crystal or a conductor that simply contacts the surface of a semi-insulating semiconductor material. For example, plating can be carried out by simply pinching it with metal tweezers.

Below are books that utilize the newly discovered phenomenon mentioned above. As an embodiment of the invention, semi-insulating Ga is used as the semi-insulating semiconductor material.
A method for manufacturing a GaAs shot-barrier gate field effect transistor using an n-type GaAs crystal layer as an As crystal and a semiconductor crystal layer will be explained in detail by taking as an example.

A GaAs short-barrier gate field effect transistor (hereinafter referred to as GaAs SBFET) is a semi-insulating GaA
A source and an n-type GaAs crystal layer provided on the s-crystal surface
It is a three-terminal device consisting of an ohmic electrode called the drain and a gate electrode with a short barrier junction, and it has a high power gain, especially in high frequency bands above the X-band.
It is expected that the device will have better noise characteristics than conventional Si bipolar transistors.

Here, the present invention will be specifically explained using an example in which the source electrode of a GaAs SBFET is grounded.

In manufacturing the device, first, as shown in FIG. 2A, a carrier density of, for example, 1×10 17 /cm
After forming an n-type GaAs crystal layer having a thickness of, for example, 0.25 μm, a mesa-shaped operating region 12 is obtained by etching away the remaining region except for a region that will become an operating region. Next, a source 21. Gate 22, drain 2
3 to obtain the original form of GaAsSBFET. Here, the gate length is, for example, 1μ, the source-drain distance is, for example, 4μ, and the gate width is, for example, 300μ. Also the gate,
The source (drain) material should be changed each evening, e.g. aluminum (
A1), a gold (Au)-germanium (Ge) alloy. Next, a SiO2 film (thickness: 0.5 μm, for example) is formed on the entire surface of the wafer by, for example, a thermal decomposition method, and after a suitable photoresist mask is provided, SiO2 film 74 is formed on the portions corresponding to the gate, source, and drain electrodes. remove the membrane,
Further, the wafer is cut and separated to obtain pellets as shown in FIG. 2A. Next, a semi-insulating substrate and Si
If plating is performed on the surface of the operating region not covered with the O2 film at a current density of, for example, 4 mA/Crff and a liquid temperature of, for example, 50°C, the source electrode 22 will be made of gold (A) as shown in FIG. 2B.
u) A plating layer results in an element short-circuited to the back side of the substrate. Next, some examples of specific plating methods will be shown. First, the source electrode 21 or drain electrode 23 shown in FIG. 2A can be used as the plating electrode. In this case, gold (Au) is applied to the semi-insulating substrate 11.
) The plating progresses from the source electrode end 25 and covers the back surface of the substrate. In this case, the gold (Au) plating film is directly attached to the back side of the substrate, so if the adhesion of the film is a problem when soldering the element, the back side 2 of the pellet should be removed.
A metal such as chromium (Cr) and gold (Au) may be deposited on the layer 6, and in this case, the chromium and gold deposited film can be used as a plating electrode.

On the other hand, when performing electroplating, it is necessary to apply a plating voltage to the plating electrode of each element, but in this case it is extremely inefficient to provide a lead wire for each element. Yes, it is not suitable for mass production. Therefore, as shown in FIG. 3A, plating can be carried out by using a metal basket 34 and placing pellets 33 in the basket. FIG. 3B shows a case where a metal plate 35 is used as a lead wire.
In FIG. 3, a metal basket 34 and a metal plate 35 are used to apply a plating voltage to the plating electrode of each pellet, but the surface of the basket or plate is connected to the plating electrode. Even in the case of contact with the surface of a semi-insulating substrate without contact, plating progresses from the contact portion, and it is possible to obtain an element in which the source electrode and the back surface of the pellet are short-circuited, as shown in FIG. 2B. In the embodiment explained in FIGS. 2 and 3, the wafer is cut and separated into pellets, but in the method of the present invention, the wafer is not completely pelletized and each element is separated as shown in FIG. 41 is, for example, a plated heat sink.
This can also be applied to the case where they are formed separately from each other on the 42.

In the device shown in FIG. 4, the device is formed using an n-type active layer on a semi-insulating substrate in the same manner as explained in FIG.
u) forming a film (plated heat sink) 92, for example by gold (Au) plating, and then covering the active area surface with a suitable photoresist mask and selectively chemically etching the substrate; However, when applying the plating method according to the present invention to such an element, electroplating may be performed using the plated heat sink as a plating electrode. In this case, the north electrode and the plated heat sink are shorted by a gold (Au) layer plated on the side of the semi-insulating substrate. As described above, if the device manufacturing method of the present invention is used, the electrode to be grounded and the back surface of the device pellet are short-circuited by the metal film, so it is possible to manufacture a device with small grounding inductance.

Furthermore, in the device manufactured by this method, when the device is soldered to the heat sink, the device is automatically grounded, so there is an advantage that the bonding step for grounding can be omitted.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a method of grounding a planar type element using a beam lead, and Figs. 2, 3, and 4 are diagrams showing grounding when the plating method of the present invention is applied to grounding of a planar type element. Give an example. In the figure, 11... semi-insulating GaAs substrate,
12... N-type GaAs crystal layer, 13...
...Planar type element, 14... Electrode to be grounded, 15, 16... Beam lead, 21...
... Source electrode, 22 ... Gate electrode, 23.
...Drain electrode, 24...SiO.

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor device, which comprises forming a planar semiconductor device on a semi-insulating GaAs substrate, and then short-circuiting at least one of the electrodes of the device to be grounded and a ground electrode on the back surface of the substrate. , after insulating other parts so as to form a continuous exposed surface connecting the electrode to be grounded and the grounding electrode, a holding table in which at least one of the electrode to be grounded and the grounding electrode is conductive; The electrode to be grounded is held in contact with the electrode, completely immersed in a plating solution, and electrically applied to the exposed surface by energizing the conductive holding base. A method for manufacturing a semiconductor device, comprising short-circuiting a ground electrode.