JPS6018138B2 - Method for forming metal electrodes on semiconductor substrates - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming electrodes on a semiconductor substrate in a semiconductor device.

Conventionally, in a semiconductor device including a pn junction, many methods of forming a resistance junction electrode have been proposed and put into practical use in order to extract power from the semiconductor device more efficiently.

However, there have been very few inexpensive methods for selectively forming electrodes on predetermined portions of a semiconductor substrate.

Especially recently, by forming a groove in a part of a silicon wafer that has a pn junction and covering the pn junction surface exposed on the groove surface with inorganic glass, the pn junction is inactivated and stabilized.
Although a so-called glass passivation technology that can obtain a bonding surface has been established, there is almost no inexpensive method of forming metal electrodes on silicon wafers using this glass passivation. Figure 1 shows the conventional glass passivation method. FIG. 3 is a diagram showing a state in which metal electrodes are formed on a wafer subjected to this process. That is, a groove 1 is formed in a silicon wafer 100 having a pn junction, the pn junction surface exposed in the groove part is covered with an inorganic glass 2, and then A-Ni-Cr-A or A-Mo- FIG. 2 is a cross-sectional view of a wafer on which a multilayer metal electrode 3 such as Nj-Au is formed. In the silicon pellet 101 obtained from such a silicon wafer, a silver-plated copper lead wire or the like can be soldered to the resistance-bonded metal electrode 3 in order to flow a relatively large current of several amperes or more. Nickel or gold is often used on the top surface of the metal electrode, as shown in FIG. By the way, as a method for forming metal electrodes to obtain these resistance junctions, after glass passivation is applied to silicon substrate, 1×10
A commonly used method is to heat each pure metal placed in a melter with an electron beam in a high vacuum of less than -5 centimeters to vaporize each metal one after another, thereby performing vacuum deposition.

As shown in FIG. 2, a method for selectively forming metal electrodes only on predetermined portions is as follows: a shielding plate 4 is placed over the portion where metal is not desired to be deposited, and then the metal is deposited on the portion where the metal is not desired to be deposited. There is a method of removing the shielding plate 4 to obtain a predetermined metal electrode. However, this method is not suitable for forming fine metal electrodes because the shielding plates cannot be placed in precise alignment. Furthermore, as shown in FIG. 3, metal is deposited on the entire surface of the silicon wafer 100, and then a predetermined metal electrode as shown in FIG. 1 is obtained by photolithography and metal etching technology. It is often used in

However, in this method, in order to form a multilayer metal electrode, several types of metals must be vapor-deposited, and photolithography and metal etching must also be performed. For this metal etching, it is necessary to use an etching solution suitable for the metal of each layer, so generally it is necessary to use two or more types of etching solutions, and in the end, the above-mentioned method as shown in Figure 3 is required. The method of forming metal electrodes in this method has the disadvantage that it requires a very large number of steps and cannot form metal electrodes at low cost. In addition, as a method for forming metal electrodes that can be soldered and at low cost, as shown in FIG.
This nickel 5 is subjected to electroless plating, then sintered with nickel plating in an inert gas at a temperature of 700 to 800°C for about 15 to 60 minutes, and then nickel plated again. Perform gold plating 6,
Methods of forming metal electrodes are also well known.

However, in this method, since nickel is electrolessly plated directly onto the silicon wafer, for example, if a nickel plating solution based on nickel chloride is used, the nickel chloride reacts violently and is firmly attached to the silicon surface. Generally, it is devised to be plated. For this reason, in the case of such nickel plating, as shown in Figure 4, nickel 5 also adheres to the glass 2 for glass passivation, and this nickel 5 melts into the glass 2, resulting in significant damage. Degrading the electrical characteristics of semiconductor devices; in other words, nickel 5 enters the stable lead glass or zinc glass that is commonly used as glass 2, changing the properties of the lead glass or zinc glass, which should be protected. This often causes deterioration of the PN junction of the semiconductor substrate, particularly the breakdown voltage of the PN junction. Furthermore, if the above-mentioned nickel plating is performed in the case of a diode with one pn junction as in the case of FIG.
If so, the leakage current of the diode in the reverse voltage blocking state increases significantly, and the diode may even lose its function. A further inconvenience is that after nickel plating, the silicon wafer is placed in an inert gas or reducing gas for 7 days in order to firmly adhere the silicon wafer.
It is necessary to heat the glass to a high temperature of 0.00 to 800 qo, but by heating to this high temperature, the glass 2, which had been in a stable state due to mottled glass, changes in quality and becomes frothed on the groove surface.
The disadvantage is that the effect of glass passivation, which inactivates the n-junction surface and stabilizes the electrical characteristics of the diode, is lost, resulting in a diode of poor quality. Therefore, an object of the present invention is to improve the shortcomings of the conventional method of forming electrodes by resistance bonding on glass passivated silicon wafers, and to provide a method for forming metal electrodes using good resistance bonding, which is solderable and inexpensive. We aim to provide the following.

Examples of the present invention will be described in detail below.

As shown in FIG. 5, aluminum 7
selectively attached. Thereafter, aluminum sintering is performed at about 450 to 550° C. for about 15 to 60 minutes in an inert gas. Next, this wafer is immersed in a galvanizing solution for several tens of seconds, and the zinc 8 is scooped onto the aluminum 7.
Electroless tsutaki. Next, this zinc is further lightly etched with acid, and then zinc plating is performed once again in the same manner as above. Then, when nickel plating is performed using a nickel plating solution that has a mild decomposition reaction of nickel salts,
Nickel 9 is easily and strongly plated on the zinc plating, but the glass 2 portion is not plated with nickel. Furthermore, if necessary, even if gold plating is performed after the nickel plating, the gold plating will be deposited only on the nickel plating, so the gold plating will be deposited on the glass 2. There isn't. After the nickel plating or gold plating described above, heating the above-described silicon wafer at 350 to 500°C for about 15 to 60 minutes in an inert gas will cause the metal electrode to be more firmly attached to the silicon wafer. You can get it. As is clear from the above description, the fact that no nickel or gold is deposited on the glass 2 and that the heating temperature in inert gas for sintering after aluminum deposition and after nickel plating or after gold plating is at most 550q0 Since the sintering temperature is relatively lower than the conventional sintering temperature, the glass 2 used for glass passivation does not change in quality, and therefore the leakage current of the diode shown in FIG. 5, which is an embodiment of the present invention, is very small. , exhibits excellent electrical characteristics as a diode.

The aluminum evaporation method used in the present invention does not require the use of an expensive deposition method in which aluminum placed in a melt is evaporated using an electron beam. By passing a current through the thin tungsten or tantalum wire, the tungsten or tantalum pongee wire is heated, and the heat evaporates the aluminum, making it easy to deposit aluminum onto the silicon wafer.

After vapor deposition of aluminum, conventional methods continue to
Nickel was vacuum-deposited, but in the present invention, metal electrodes are formed by zinc plating on aluminum and then nickel plating.

When using the plating method, a large amount of objects can be processed in a much shorter time than when using the vacuum evaporation method, so the economic effect is greater. Furthermore, it has the advantage that the electrical characteristics of the semiconductor device do not deteriorate even if nickel plating is applied. As described above, the metal electrode forming method of the present invention can firmly plate a nickel plating layer without adversely affecting the PN junction of a semiconductor substrate, and has an extremely excellent effect on semiconductor device manufacturing. Note that the above-mentioned semiconductor substrate includes not only a semiconductor substrate cut out from a single crystal, but also a semiconductor material in which a single crystal is produced by liquid phase growth or vapor phase growth on a semiconductor substrate cut out from a single crystal. That is clear.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a silicon wafer with metal electrodes formed on a glass-passivated silicon wafer, and Figure 2 is a cross-sectional view of a silicon wafer with glass passivation on which metal electrodes are selectively formed by using a shielding plate. FIG. 3 is a sectional view showing a method of forming a glass passivation plate
A cross-sectional view of a silicon wafer for explaining the conventional method of forming metal electrodes on a silicon wafer that has been subjected to
FIG. 4 is a cross-sectional view of a silicon wafer to show the disadvantages that occur when metal electrodes are selectively formed on a glass-passivated silicon wafer by a conventional method.
FIG. 5 is a cross-sectional view of a silicon wafer which has been subjected to the metal electrode forming method of the present invention on a silicon wafer which has been subjected to glass passivation. /Throughout each figure, if the same parts are the same, the corresponding parts are given the same symbols, 1 is the groove,
indicates glass, 7 indicates aluminum, 8 indicates zinc, and 9 indicates nickel. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 On a semiconductor substrate with glass passivation,
A step of selectively depositing aluminum; for the sintering of the aluminum, the semiconductor substrate is
a step of heating to 50° C.; a step of electrolessly plating zinc as a plating base on the aluminum layer; a step of plating the galvanized layer with nickel as an electrode or an electrode base; and sintering the nickel plating. , a method for forming metal electrodes on a semiconductor substrate, comprising the step of heating the semiconductor substrate to 350 to 500°C.