JPH0324767A - Semiconductor rectifier - Google Patents

Abstract

PURPOSE:To cut down the inverse recovery time for accelerating the title rectifier with the gentle slope of current during the inverse recovery time kept as it is by a method wherein p<-> type semiconductor regions in specific intervals and width are intermittently formed in the surface region of n<-> type semiconductor region provided on n type semiconductor region. CONSTITUTION:The title semiconductor rectifier is composed af p<-> type semiconductor regions 13 intermittently arranged on anode side as well as a Schottky diode in short inverse recovery time trr laid between pn junction diodes. Accordingly, the inverse recovery time trr can be cut down to accelerate the rectifier moreover enabling the total impurity amount of the whole anode to be reduced without lowering the impurity concentration in the p<-> type semiconductor regions 13 so that the inverse recovery time trr may be cut down with the gentle slope of current di/dt2 during the inverse recovery time kept as it is. Through these procedures, the said characteristics can be notably enhanced by equally setting up the individual width w1 of the p<-> type semiconductor regions 13 and the width w2 between the p<-> type semiconductor regions 13.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a semiconductor rectifier, and in order to shorten the reverse recovery time and increase speed while maintaining a gentle slope of current during reverse recovery, the present invention relates to a semiconductor rectifier. n” type semiconductor region provided on the
By intermittently forming p-type semiconductor regions of a predetermined width at predetermined intervals on the surface region of the type semiconductor region, p-n junction portions and Schottky junction portions are arranged alternately on the anode side. It is something.

[Industrial application field]

The present invention relates to a semiconductor rectifier, and particularly to an improvement in a so-called pin diode in which a semiconductor region with a low impurity concentration is interposed between a P-type and an N-type semiconductor region.

[Prior Art] FIG. 4 shows a cross-sectional structure of a semiconductor rectifier having a conventional pin structure.

In the same figure, the impurity concentration is 5 x 10 "cm-"
An n'' type semiconductor region (i region) 2 with a low impurity concentration of about I x 101 cm-'' is formed on an n type semiconductor substrate l with a thickness of about 40 cm by epitaxial elongation.
A p'' type semiconductor region 3 with a surface impurity concentration of about 2×1016 CI11-3 is formed in the surface region by impurity diffusion to a depth of about 5 to 6 μm. On top of the type semiconductor region 3, an AI
! ．． A metal electrode 4 made of, for example, is formed by vacuum evaporation or the like.

When the diode having such a structure is switched from being forward biased to reverse biased, a current waveform as shown in FIG. 5, for example, is obtained at 1M. That is, first, the forward current IF rapidly decreases, and then the current reaches zero and the reverse current begins to flow. Then, after reaching the maximum reverse current value IPR, the reverse current begins to decrease and finally settles to zero current. In the same figure, trr is 10% of the maximum value IPII after the reverse current starts flowing.
di/dt2 is the time required for the reverse current to recover from the maximum value ipt+ to zero (hereinafter referred to as reverse recovery time), and di/dt2 is the slope of the current when the reverse current recovers from the maximum value ipt+ to zero. [Problems to be Solved by the Invention] In semiconductor rectifiers, there is generally a demand for higher frequencies, and for this purpose, reverse recovery times t, . ．． needs to be shortened.

Conventionally, methods for this purpose include, for example, Au or PT.
There are known methods to control the lifetime of carriers by diffusing heavy metals such as metals, etc., or irradiating them with electron beams or protons. However, when such lifetime control is performed, there is a problem that the forward voltage VF increases and the leakage current also increases.
Therefore, in order to increase the speed without performing lifetime control, the impurity concentration of the p-type semiconductor region 3 in FIG. Therefore, the reverse recovery time t, . ．． Attempts are being made to shorten the .

However, it has been empirically confirmed that if an attempt is made to shorten the reverse recovery time trr in this manner, the slope di/dt2 of the current during reverse recovery inevitably increases. When ai,/tit2 increases, the inductance L existing in the circuit incorporating this semiconductor rectifier increases
As a result, a large electromotive force of -Ldi/dt2 is generated, which causes spike noise generation and element destruction.

The present invention has been made in view of the above conventional problems, and its purpose is to reduce the current slope d i / d during reverse recovery.
It is an object of the present invention to provide a semiconductor rectifier that can achieve high speed by shortening the reverse recovery time trr while keeping tz moderate.

[Means to solve the problem]

The semiconductor rectifier of the present invention includes an n-type semiconductor region, a low impurity concentration n-type semiconductor region formed on the n-type semiconductor region, and a surface region of the n-type semiconductor region intermittently at predetermined intervals. a p-type semiconductor region with a low impurity concentration formed in
On the p-type semiconductor region and on the n''-type semiconductor region exposed between the p-type semiconductor regions, there is an orthogonal contact with the p-type semiconductor region and with the n-type semiconductor region. has a metal electrode formed in Schottky contact;
The width between the p-type semiconductor regions is less than or equal to the distance that depletion layers extending from both sides reach each other when a reverse bias is applied, and the width of each of the p-type semiconductor regions is equal to the width between the p-type semiconductor regions. It is characterized in that it is made to be almost equal.

[For production]

According to the above structure, firstly, the p-type semiconductor region on the anode side is formed intermittently, compared to the conventional structure in which it is formed continuously (see FIG. 4). , it becomes possible to reduce the total amount of impurities in the entire anode without changing the average impurity concentration. Second, the anode side has a structure in which Schottky junctions are interposed between intermittently formed pn junctions, so overall, a Schottky diode with a small reverse recovery time trr can be used. The structure is built between pn junction diodes. From the above points, the semiconductor rectifier of the present invention has a reverse recovery time t
The short rr makes it possible to increase the speed, and since it is not necessary to lower the impurity concentration of the p-type semiconductor region too much, the slope d i /d t 2 of the current during reverse recovery can be kept gentle. And these properties are p” as above
It has been confirmed through experiments that the method is good when the width of each of the p-type semiconductor regions is equal to or almost equal to the width between the p-type semiconductor regions.

In addition, the width between the p-type semiconductor regions is set to be less than the distance that allows the depletion layers extending from both sides of the p-type semiconductor region to reach each other when a reverse bias is applied, so even if a Schottky diode portion exists, Regardless, sufficient reverse withstand voltage can be obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor rectifier according to an embodiment of the present invention, and FIG. 2 is a diagram showing an impurity profile along the line A-A.

In FIG. 1, the impurity concentration is 5×10”cm−
' on the n-type semiconductor substrate 11 with an impurity concentration lxlQ
An n-type semiconductor region (i region) 12 having a low impurity concentration of about +4 cm -3 is deposited to a thickness of about 40 μm by ebitaxial deposition. In the surface region of the n-type semiconductor region 12, p-type semiconductor regions l3 each having a width w of about 20 μm and a depth d of about 5 μm are disposed intermittently at a predetermined width Wz of about 20 μm. It is formed. This p-type semiconductor region l3 is formed by, for example, implanting ions of B (boron) or the like at a dose of about 5XIO12Cll1-'' and diffusing it to a depth of about 5 μm, thereby reducing the impurity concentration at the surface. IXIO”
It is formed so that it is about cm-3. Further, in the surface region of the n-type semiconductor region l2, a p-type semiconductor region l
A plurality of field limiting rings 14 are formed so as to surround the entirety of the p-type semiconductor region 13 by a process simultaneous with the formation of the p-type semiconductor region 13.

Furthermore, an oxide film 1 is formed on the field lifting ring 14.
5, and also on the p-type semiconductor region 13,
AN(
A surface electrode 16 made of (aluminum) is formed by vacuum deposition or the like. Here, the Af surface electrode 16 is in ohmic contact with the p-type semiconductor region 13 and in Schottky contact with the n-type semiconductor region 13. On the other hand, on the back surface of the n-type semiconductor substrate l1, a back electrode I7 having a 3N structure is formed by laminating Cr (chromium), Ni (nickel), and Au (gold) in this order from the back surface side.

In the semiconductor rectifier of this embodiment having the above-mentioned structure, by disposing the p-type semiconductor regions 13 intermittently on the anode side, a Schottky diode with a small reverse recovery time trr is inserted between the pn junction diodes. It is a mediated precept. Therefore, the reverse recovery time trr can be shortened and the speed can be increased, and moreover, the p-type semiconductor region l
Since the total amount of impurities in the entire anode can be lowered without significantly lowering the impurity concentration in step 3, the reverse recovery time tr can be reduced while keeping the current slope at/atz during reverse recovery gentle.
y can be shortened. It has been experimentally shown that these characteristics are extremely good by setting the individual widths W of the p-type semiconductor regions 13 and the width W2 between the p-type semiconductor regions 13 to be equal as described above. was confirmed. The current waveform (solid line) obtained in this experiment when applying a reverse bias is
FIG. 3 shows a comparison with the current waveform (broken line) obtained from the conventional semiconductor rectifier shown in the figure. As is clear from the figure, the reverse recovery time trr is 350 nS in the conventional model.
In contrast, in this example, it is as short as 290 ns, and the current slope di/dt2 is 66.7 A in the conventional one.
/μS, whereas in this example it is 28.3A/μS (
! : Becomes gradual.

In addition, in this embodiment, the width W2 between the p-type semiconductor regions l3
is set to 20 μm, and this distance is less than or equal to the distance at which depletion layers extending from adjacent p-type semiconductor regions 13 can reach each other when a reverse bias is applied. Therefore, sufficient reverse breakdown voltage can be obtained despite the presence of the Schottky diode portion. Moreover, the surface electrode 1
By forming 6 with Al and providing a finyl limiting ring 14 in the peripheral region, it was possible to obtain a very large reverse breakdown voltage of 548V. Furthermore, due to the presence of the Schottky diode part, 165A/af
It was also found that a small forward voltage of 1.02 V can be obtained at a large current density of 1.

In addition, in the above embodiment, the width Wl of the p'' type semiconductor region l3
and the width W2 between them are set equal, but they do not necessarily have to be completely equal; for example, Wl - 1Bμm, W2
=22, as in czm, w+/(w+10W2) is 0.
It is sufficient if they are set approximately equal within a range of 4 to 0.5.

Furthermore, the impurity concentration on the surface of the p-type semiconductor region 13 is not limited to the above-mentioned 1×1016 CII1-3, but may be set within the range of 5×10” to l×IQ”cm−3. It is desirable that

〔Effect of the invention〕

According to the invention, the reverse recovery time t, . It becomes possible to shorten the current speed and increase the speed, and also to maintain a gentle current slope di/dt2, which has a trade-off relationship with the reverse recovery time Lrr, and to obtain a sufficient reverse breakdown voltage. can.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a semiconductor rectifier according to an embodiment of the present invention, Figure 2 is a diagram showing an impurity profile along line A-A in Figure 1, and Figure 3 is a current waveform during reverse recovery. FIG. 4 is a cross-sectional view of a conventional semiconductor rectifier, and FIG. 5 is a diagram showing a typical current waveform during reverse recovery in a semiconductor rectifier. DESCRIPTION OF SYMBOLS 11... N-type semiconductor substrate, 12... N-type semiconductor region, l3... P-type semiconductor region, l4... Field lying ξ ring, 15...
Oxide film, 16... Surface electrode, 17... Back electrode.

Claims (1)

[Claims] An n-type semiconductor region, and a low impurity concentration n^- formed on the n-type semiconductor region.
a p^- type semiconductor region with a low impurity concentration formed intermittently at predetermined intervals on the surface region of the n^- type semiconductor region, and on the p^- type semiconductor region and the p^- type semiconductor region. a metal electrode formed on the n-type semiconductor region exposed between the n-type semiconductor regions so as to be in ohmic contact with the p^-type semiconductor region and in Schottky contact with the n^-type semiconductor region; The width between the p^- type semiconductor regions is set to be less than or equal to the distance that the depletion layers extending from both sides thereof reach each other when a reverse bias is applied, and the width of each of the p^- type semiconductor regions is equal to or less than the width of the p^- type semiconductor regions. 1. A semiconductor rectifying device characterized in that the width is equal to or almost equal to the width between semiconductor regions.