JPH0261143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming bump electrodes on each Zener diode of a semiconductor wafer on which a large number of Zener diodes having a low Zener voltage are formed.

A Zener diode generally has an element structure shown in FIG. In the figure, 1 is an N-type region,
A P type region 2 is selectively formed within this N type region 1. 3 is PN junction. 4 is an insulating film such as an oxide film. Reference numeral 5 denotes an anode electrode, which is formed of a gold vapor-deposited film 6 and silver bumps 7 thereon. 8 is a cathode electrode, which has a gold vapor deposited film 9 and a silver plating film 10 thereon.
It is formed of.

This type of Zener diode is manufactured as follows. First, an N-type semiconductor wafer (hereinafter simply referred to as wafer) 1 is prepared, an insulating film 4 such as a thermal oxide film is formed on both main surfaces, and a large number of windows are drilled in the insulating film 4 on only one main surface. Then, P-type impurities are selectively diffused through this window hole to form P-type region 2. Next, a window hole is made again in the insulating film 4 on the P-type region 2, and gold vapor deposited films 6, 9 are formed on the P-type region 2 exposed through the window hole and on the N-type region 1 on the back surface. Next, a silver plating film 10 is applied on the gold vapor deposited film 9 on the back side.
is formed to obtain the wafer 100. After this, as shown in FIG. 2, the silver electrode plate 11 and the wafer 10 are
0 are immersed in a plating solution at a predetermined interval and placed facing each other, and a forward voltage is applied to the PN junction 3 between the silver electrode plate 11 and the wafer 100, that is, the positive electrode of the DC plating power source 12 is connected to the silver electrode. The negative electrode is connected to the plate 11 and the cathode electrode 8 of the wafer 100, and silver bumps 7 are plated on the gold vapor deposited film 6 on the surface to form the anode electrode 5.
Thereafter, by cutting and separating each Zener diode element, a Zener diode as shown in FIG. 1 is obtained.

By the way, in the step of forming the bumps 7 shown in FIG. 2 above, if all the PN junctions 3 are normal, each bump 7 can be formed to approximately the same height.
If some of the PN junctions 3a are short-circuited, the plating current will concentrate and flow in this defective element portion, causing abnormal growth of the bumps 7a. For this reason, the plating current of the surrounding normal elements decreases, and the height of the bump 7 becomes insufficient in the normal plating time. become longer. Furthermore, if an abnormal bump 7a is formed, there are problems such as the probe getting caught on the abnormal bump 7a during a characteristic check, damaging the characteristic checking device, and furthermore, making it difficult to cut and separate each element. It was hot.

Various methods have been proposed to solve the above drawbacks. First, the first method is to perform a characteristic check after forming the gold vapor deposited films 6 and 9, and then deposit an insulating film on the gold vapor deposited film 6a of the defective element. This method is complicated because it requires a characteristic check step and an insulating film formation step. The second method is
This utilizes the voltage versus current characteristics of a Zener diode. In other words, the Zener diode is
As shown in Fig. 3, it conducts at a low threshold voltage V _S with respect to a forward voltage, but conducts at a Zener voltage V _Z1 with respect to a reverse voltage.
V _S <V _Z1 . Therefore, when forming the bump 7, as shown in FIGS. 3 and 4A, a forward voltage higher than the threshold voltage V _S is applied.
V ₁ is applied, but if this is done suddenly, if a defective PN junction 3a occurs, an abnormal bump 7a will be formed as described above. Therefore, the second method, as shown in FIG. 4B, is to first apply a voltage V ₂ lower than the Zener voltage V _Z1 ,
A reverse current is applied only to the defective PN junction 3a to selectively dissolve and remove only the gold vapor deposited film 6a of the defective element by electrolytic action, and then a forward voltage _V1 is applied to remove the good PN junction 3. In this method, bumps 7 are formed only on non-defective devices that have the same characteristics. The third method is
As shown in FIG. 4C, the forward voltage is increased for time T1.
This is a method of repeating plating with V ₁ and applying a reverse voltage V ₂ for a time T 2 to dissolve and remove the bumps 7a on the defective elements. These second and third methods are very clever methods and are very good when the Zener voltage V _Z is relatively large, but when the Zener voltage V _Z becomes about several volts, the There is a problem that the gold vapor deposited film 6 and the bumps 7 are also dissolved. That is, the low Zener voltage V _Z2 (2~
6V) Zener diode is in the N-type region 1
Since the P-type region 2 is manufactured with a high impurity concentration, the specific resistance of the wafer 100 is reduced, and an inversion layer (channel) is easily formed directly under the insulating film 4. , the voltage vs. current characteristics are as shown in FIG.
For this reason, the reverse voltage smaller than the Zener voltage V _Z2
Even if V ₃ is applied, leakage current I ₀ flows, so in the second method, the gold vapor deposited film 6 on the defective PN junction 3a is
In addition to a, the gold vapor deposited film 6 on the normal PN junction 3
Also, in the third method, not only the abnormal bump 7a but also a part of the normal bump 7 is dissolved, so in order to form the bump 7 of a predetermined height, the plating time is extremely long. There was a problem that it could not be adopted.

Therefore, the main object of the present invention is to provide a method for plating good bumps on each element of a wafer on which a large number of Zener diode elements with low Zener voltage are formed.

In summary, the present invention is characterized in that after a bump is first formed with a predetermined forward voltage, a reverse voltage lower than the reverse breakdown voltage, such as a Zener voltage, is applied to dissolve the abnormal bump.

The above objects and other objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 6 is a diagram showing the relationship between plating time and applied voltage according to the present invention, and FIG. 7 is a diagram showing the state during plating. In the figure, Figures 2 and 4
Parts that are the same as those in the figures have the same reference numerals. In FIG. 7, 13 is a changeover switch, which has a common terminal 14a connected to the silver electrode plate 11, a common terminal 14b connected to the cathode electrode 8 of the wafer 100, and a voltage
Switching terminal 15a connected to the positive pole of the V ₁ DC plating power supply 12, switching terminal 15b connected to the negative pole
, a switching terminal 17a connected to the positive electrode of the DC electrolytic power supply 16 of voltage _V3 , and a switching terminal 17b connected to the negative electrode.

First, as shown in FIG.
When applied to the switching terminals 15a and 15b, the silver electrode plate 11 is connected to the positive electrode of the DC plating power supply 12, and the cathode electrode 8 of the wafer 100 is connected to the negative electrode, so that a threshold voltage is applied to the PN junction 3 of the wafer 100. A forward voltage V ₁ larger than V _S is applied, and bumps 7 are formed on the gold vapor deposited film 6 on the surface. Here, if the PN junction 3 includes a part of the defective PN junction 3a, the current will concentrate on the element including the defective PN junction 3a, and the abnormal bump 7
As mentioned above, a is formed.

Next, the changeover switch 13 is connected to the changeover terminals 17a, 1
Insert it into the 7b side. Then, the cathode electrode 8 of the wafer 100 is connected to the positive electrode of the DC electrolytic power source 16, and the silver electrode plate 11 is connected to the negative electrode, so that the wafer 10
A reverse voltage V ₃ lower than the Zener voltage V _Z2 is applied to the PN junction 3 of 0. However, if the Zener voltage V _Z2 is low, as shown in Figure 5, the normal
Leakage current I ₀ also flows through PN junction 3, but the defective PN
A larger current flows through junction 3a. As a result, the bumps 7 of the element with the normal PN junction 3 are also slightly dissolved by the electrolytic action, but the abnormal bumps 7a of the element with the defective PN junction 3a are more significantly dissolved. In this way, when the abnormal bump 7a reaches a height that will not damage the characteristic check device, the changeover switch 13 is returned to the neutral state and the electrolytic action is stopped.
Thereafter, by cutting and separating each element, a Zener diode as shown in FIG. 1 is obtained.

Note that in the above embodiment, a P-type region 2 is provided within an N-type region 1.
We explained the case where is formed by selective diffusion, but
A P-type polycrystalline region doped with a P-type impurity may be formed on the N-type region 1. An N-type region may be selectively diffused in or on the P-type region, or an N-type polycrystalline region may be formed. Furthermore, the present invention can also be applied to devices having bumps on both principal surfaces, such as a temperature-compensated Zener diode.

Furthermore, when forming the bumps 7, the silver electrode plate 1
In addition to the case where the wafer 1 and the wafer 100 are immersed in a plating liquid and placed facing each other, jet plating may be adopted.

As described above, the present invention provides a method for plating bump electrodes on each semiconductor element of a semiconductor wafer on which a large number of semiconductor elements having PN junctions are formed, in which a forward voltage is first applied to the PN junction. After forming bump electrodes on each semiconductor element, a reverse voltage smaller than the reverse breakdown voltage is applied to the PN junction to dissolve the abnormal bump electrodes. Therefore, even in a Zener diode with a low Zener voltage, This has the effect that a good bump electrode can be formed in a short time.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of an example of a Zener diode which is the background of this invention, Fig. 2 is a schematic cross-sectional view for explaining the conventional manufacturing method of the diode shown in Fig. 1, and Fig. 3 is a comparison of Zener voltages. Figures 4A to 4C are voltage vs. current characteristic diagrams when the target is large;
The figure is a voltage vs. current characteristic diagram when the Zener voltage is relatively small, FIG. 6 is a voltage application characteristic diagram illustrating the manufacturing method according to the present invention, and FIG. 7 is a schematic diagram illustrating one embodiment of the method of the present invention. It is a configuration sectional view. 3... (good product) PN junction, 3a... (defective)
PN junction, 5... anode electrode, 7... bump,
8... Cathode electrode, 11... Silver electrode plate, 12...
...DC plating power supply, 13...Selector switch, 16
...DC electrolytic power supply, 100...semiconductor wafer,
V ₁ ...Forward voltage, V _Z2 ...Reverse breakdown voltage, V ₃
...Reverse voltage.

Claims (1)

[Claims] 1. In a method of plating bump electrodes on each semiconductor element of a semiconductor wafer on which a large number of semiconductor elements having PN junctions are formed, a predetermined forward voltage is first applied to the PN junctions, and each After forming bump electrodes on the semiconductor element,
A method of manufacturing a semiconductor device, comprising applying a reverse voltage to the PN junction to dissolve the abnormal bump electrode.