JPS6146983B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a thyristor, and more particularly to a method for manufacturing a thyristor with improved switching performance.

Thyristors often have a turn-on amplification function by introducing an auxiliary thyristor structure to improve di/dt tolerance, reduce turn-on loss, speed up turn-on, and increase pulse current carrying capacity or high frequency current carrying capacity. It is used.

FIG. 1 is a schematic perspective view showing a typical example of a thyristor having an auxiliary thyristor along with a cross section. This thyristor 1 is a thyristor wafer in which a P-type first emitter (P _E ) layer 2, an N-type first base (N _B ) layer 3, and a P-type second base (P _B ) layer 4 are sequentially formed. 5, P _B
An annular N-type second emitter (N
_E ) A layer 6 and a third N-type emitter layer 7 formed in a small annular shape inside the annular layer 6. Then, the first main surface 8 of the thyristor wafer 5 on the N _E layer 6 side
Above are a cathode electrode 9 electrically connected to the N _E layer 6, an auxiliary thyristor electrode 10 electrically connected across the third emitter layer 7 and the P _B layer 4 on its outer periphery; 3 A control electrode 11 electrically connected to the P _B layer 4 surrounded by the emitter layer 7 is formed, and the P of the thyristor wafer 5 is
An anode electrode 13 is formed on the second main surface 12 on the _E layer 2 side and electrically connected to the P _E layer 2 . From the cathode electrode 9, control electrode 11, and anode electrode 13, a cathode electrode terminal K, a control electrode terminal G, and an anode electrode terminal A (hereinafter abbreviated as "K,""G," and "A," respectively) are connected. It's being pulled out. This thyristor wafer 5 is divided into a main thyristor region consisting of an annular portion corresponding to the N _E layer 6 and an auxiliary thyristor region surrounded by the main thyristor region.

Now, as is well known, the turn-on switching operation of this thyristor 1 is such that a voltage with positive polarity on the A side is applied between A and K, and a voltage with positive polarity on the G side is applied between G and K. When the voltage is applied, a control current i _G flows between G and K, and the auxiliary thyristor region consisting of four layers, P _E layer 2, N _B layer 3, P _B layer 4, and third emitter layer 7, is turned on. Anode electrode 13-P _E layer 2-N _B layer 3-P _B layer 4-third emitter layer 7-auxiliary thyristor electrode 10-P _B layer 4
An auxiliary thyristor current i _A that is ten times or more the control current i _G flows through the path of -N _E layer 6 - cathode electrode 9 -K, and this current i _A turns on the main thyristor region. A-Anode electrode 1
A main thyristor current i _M flows through the path of 3-P _E layer 2-N _B layer 3-P _B layer 4-N _E layer 6-cathode electrode 9-K. In this way, the control current i _G is amplified to become the auxiliary thyristor current i _A , which turns on the main thyristor region, so that the initial turn-on region becomes the inner junction surface 1 of the annular third emitter layer 7.
From the vicinity of 4, the inner joint surface 15 of the annular N _E layer 6
As mentioned above, the turn-on switching performance of this thyristor 1 is significantly improved.

Another example of a thyristor structure for further increasing such an auxiliary thyristor function is shown in FIG. In the thyristor 1a of this example, the auxiliary thyristor electrode 10a has a finger-like shape inserted into the cathode electrode 9a, and the inner joint surface 15a of the annular N _E layer 6a is provided long along the finger-like shape. ing. Accordingly, since the initial turn-on region described in connection with FIG. 1 is widened along this finger-like shape, the turn-on switching performance is further improved compared to that of the structure of FIG.

However, a thyristor having such an auxiliary thyristor function causes the following problem at turn-off. Figure 3 is a current and voltage waveform diagram when the thyristor is turned off. A current (peak value _ID ) is passed between A and K from time t ₀ to time t ₁ , and commutated by an external circuit at time t ₁ . When the on-current is cut off at time _t2 , the thyristor receives a reverse voltage V
_R is applied. Next, the time is determined by an external circuit.
Off voltage from _t3 (rise rate dv/dt, peak value V _D )
Apply. At this time, if the reverse voltage application time T _p is long enough, the thyristor will maintain the off state and turn-off switching operation will be achieved, but if the time T _p is shorter than the predetermined time T _q , the thyristor will fail to turn off. does not enter the off state. The predetermined time _Tq required for this turn-off switching operation is called a turn-off time. by the way,
The off-voltage rise rate dv/dt is determined in order to simplify the circuit and reduce the size and weight when applying the thyristor.
It is desirable to make it higher. However, this rate of increase
When the value of dv/dt exceeds 100V/μs, there is a problem that the turn-off time T _q becomes long.Moreover, in a thyristor having an auxiliary thyristor structure as described above, the off-voltage increase rate dv of the turn-off time T _q increases. It was found that the dependence on /dt was even stronger. The solid curve in FIG. 4 is a characteristic curve showing an example of this dependence. In this dependence characteristic, as the ratio of the area of the auxiliary thyristor region (including the finger-shaped portion in the case of FIG. 2) to the area of the main thyristor region increases, the turn-off time T _q at a high dv/dt value increases. It has been experimentally found that it is longer.

The solid curve in FIG. 5 is a characteristic curve showing the relationship between the turn-off time T _q and the area ratio. According to this, for example, the area of the auxiliary thyristor region is made 20% of the area of the main thyristor region to improve turn-on switching characteristics (di/dt withstand capacity: 1000A/
(μs or more) Thyristors have the disadvantage that the turn-off time when the dv/dt is as high as 400V/μs is longer by about 15 μs than when the area ratio is 5%. Note that both Fig. 4 and Fig. 5 are measurements taken on a thyristor with an outer diameter of 40 mm and a withstand voltage of 1500 V class.

Here, some consideration will be given to the dependence of turn-off time _Tq on dv/dt. In FIG. 1, when an off voltage with a voltage increase rate dv/dt is applied at turn-off, in the main thyristor region, the N _B layer 3,
Current i _r due to accumulated carriers in P _B layer 4 and N _B
Displacement current i _d due to junction J ₂ between layer 3 and P _B layer 4
and flows. On the other hand, in the auxiliary thyristor area,
A displacement current i _d ' mainly due to the junction J ₂ flows. This displacement current i _d ' is transmitted from the auxiliary thyristor electrode 10 to P
via _{the B} layer 4 to the inner joint surface of the N _E layer 6 (hereinafter referred to as “N
15 (referred to as _"E junction"). Therefore, as the area of the auxiliary thyristor region increases, the displacement current i _d ' increases proportionally, and the N _E junction 1
The injection current in the vicinity of 5 is increased, and the main thyristor is able to satisfy the turn-on condition at this portion, failing to complete turn-off.

This invention was made in view of the drawbacks of the conventional device and the above consideration, and the carrier injection efficiency of the N _E junction 15 is compared to the inner junction surface of the third emitter layer 7 (hereinafter referred to as "third emitter junction") 14. It is an object of the present invention to provide a method of manufacturing a thyristor in which the influence of the off-voltage rise rate on the turn-off time is small by making the auxiliary thyristor smaller by making it smaller, without impairing the amplification function of the auxiliary thyristor.

FIG. 6 is a schematic perspective view showing a cross section of a thyristor manufactured by a method according to an embodiment of the present invention. Obtained by FZ method, resistivity 50Ω-cm, diameter 40
A thyristor wafer 5b having a main thyristor region and an auxiliary thyristor region with a PNPN four-layer structure is prepared using a well-known diffusion technique on an n-type silicon wafer with a thickness of 350 μm and an anode electrode 13 made of a molybdenum plate is formed thereon. A cathode electrode 9, an auxiliary thyristor electrode 10, and a control electrode 11 made of an aluminum vapor-deposited layer are formed using metallization technology. Here, the area ratio between the auxiliary thyristor region and the main thyristor region can be easily set by changing the dimensions of the pattern of the diffusion photomask.

Now, the exposed portion of the inner bonding 15 of the annular _NE layer 6 to the main surface 8 of the wafer 5b is sandwiched and the main surface 8 is selectively sandblasted into a band shape. The cross-hatched numeral 16 in the figure indicates this sandblasting section. In this sandblasting process, for example, No. 200 alumina powder is sprayed through a metal mask that has a window only in the sprayed area. A construction depth of 5 to 10 μm is sufficient.

The dependence of the turn-off time _Tq of the thyristor 1b on the off-voltage increase rate dv/dt obtained by the method of this embodiment is shown by a broken line in FIG. When compared with the characteristics of the conventional device shown by the solid line in Figure 4, the improvement is obvious, and the off-state voltage increase rate dv/dt is 500V/
Even if it reaches a high value of μs, the turn-off time T _q
The increase is about 5 μs at most.

Next, regarding the system obtained by the method of this example, the ratio of the area of the auxiliary thyristor region to the area of the main thyristor region and the turn-off time T
The relationship between _q and
In order to ensure a large di/dt tolerance such as A/μs, a thyristor with an auxiliary thyristor having an area ratio of 10 to 20% can be realized without increasing the turn-off time _Tq .

The reason for the above effects is that the sandblasting increases the surface leakage current per unit length of the N _E layer junction 15, and the auxiliary emitter junction 14 increases.
This is because it is larger than the surface leakage current per unit length.

It goes without saying that the present invention can be applied in the same manner even if the P-type part and the N-type part are reversed in the above embodiment.

As detailed above, in the present invention, in a thyristor having an auxiliary thyristor structure, the surface near the exposed part of the junction of the second emitter layer of the main thyristor is sandblasted, and the carrier injection efficiency of the third emitter layer is 2nd main thyristor
Since the carrier injection efficiency of the emitter junction is lowered, the dependence of the turn-off time of this thyristor on the off-voltage rise rate can be reduced without impairing the function of the auxiliary thyristor.

[Brief explanation of the drawing]

Fig. 1 is a schematic perspective view showing a conventional example of a thyristor having an auxiliary thyristor along with a cross section, Fig. 2 is a schematic perspective view showing an example of a conventional thyristor with a further expanded function of the auxiliary thyristor along with a cross section, and Fig. 3 is a schematic perspective view showing a thyristor with a cross section. 4 is a characteristic curve showing the dependence of the turn-off time on the off-voltage rise rate of the conventional thyristor and the thyristor of the present invention, and FIG. 5 is the auxiliary thyristor region of the turn-off time. FIG. 6 is a schematic perspective view showing a cross section of a thyristor manufactured by a method according to an embodiment of the present invention. In the figure, 1, 1a, 1b are thyristors, 2
is the first emitter layer ( _PE layer) of the first conductivity type, 3 is the first base layer ( _NB layer) of the second conductivity type, 4 is the second base layer ( _PB layer) of the first conductivity type, 5, 5a, 5b are thyristor wafers, 6, 6a are second conduction type second
Emitter layer ( _NE layer), 7 is the third emitter layer of the second conductivity type, 9, 9a are the second main electrodes (cathode electrodes), 10, 10a are the auxiliary thyristor electrodes, 11
13 is a control electrode, 13 is a first main electrode (anode electrode), 14 is a third emitter junction, 15 and 15a are second emitter junctions, and 16 is a sandblasting section. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A first emitter layer of a first conductivity type, a first base layer of a second conductivity type, and a second base layer of a first conductivity type are formed so as to be in contact with each other in this order, a second emitter layer of a second conductivity type formed on a part of the surface part of the base layer; and a third emitter layer of a second conductivity type formed on another part of the surface part of the second base layer. , a first main electrode electrically connected to the first emitter layer, a second main electrode electrically connected to the second emitter layer, and a third emitter layer and the third emitter layer in the vicinity thereof. an auxiliary thyristor electrode electrically connected to the second base layer and provided to sandwich the junction of the second emitter layer between the second main electrode and the second base layer; a control electrode connected to the auxiliary thyristor electrode so as to sandwich the junction of the third emitter, and corresponding to the main thyristor region corresponding to the second emitter layer forming part and the remaining part. When manufacturing a thyristor comprising an auxiliary thyristor region, sandblasting is performed on the surface near the exposed portion of the junction of the second emitter layer, and
The carrier injection efficiency of the junction of the emitter layer is
A method for manufacturing a thyristor, characterized in that the carrier injection efficiency is lower than that of the junction of the emitter layer. 2. The method for manufacturing a thyristor according to claim 1, characterized in that the sandplast is applied to a depth of 5 to 10 μm. 3. The method of manufacturing a thyristor according to claim 1 or 2, characterized in that the area of the auxiliary thyristor region is 10% or more of the area of the main thyristor region.