JPH05259437A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor device having an extremely small reverse leakage current, a low loss, high withstand voltage and high speed. CONSTITUTION:This semiconductor device is so constituted that, if the shortest distance of one-conduction type semiconductor 1 (for instance N) sandwiched by a pair of reverse conduction type semiconductor regions 6 (for instance P+) is WN, and if the depletion layer width having zero potential to be decided by specific resistance of the regions of a one-conduction type semiconductor and a reverse conduction type semiconductor is Wbi, it is to be 0<WN<=2Wbi, further, the one-conduction type semiconductor of the part to come in contact with an electrode A is made a second one-conduction type semiconductor 8 having a different resistant value from one-conduction type semiconductor of the other part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a semiconductor device.

[0002]

2. Description of the Related Art As is well known, development has been advanced to improve the characteristics of semiconductor devices, in particular, the forward characteristics, the backward characteristics, and the switching characteristics (2), and various structures have been proposed. ..

FIG. 1 shows a cross-sectional structural view of a known Schottky barrier type semiconductor device. 1 is a one conductivity type semiconductor (eg N type), 1'is a high concentration one conductivity type semiconductor (eg N + type), 2
Is a guarding region (for example, P + type), 3 is an insulating film, 4
Is an electrode, and 5 is an ohmic electrode. In such a structure, the breakdown voltage is increased by forming the guard ring region 2, but the reverse leakage current at the central portion of the contact between the electrode 4 and the one conductivity type semiconductor 1 is not reduced. Further, in order to improve the conventional structure shown in FIG. 1, Japanese Patent Publication No. 59-35183 and the like have been proposed.

[0004]

SUMMARY OF THE INVENTION In utilizing a semiconductor device,
There is a demand for a semiconductor device having a reverse leakage current smaller than that of the conventional structure described above, and more improved forward characteristics and switching characteristics than those of the PN junction structure.

[0005]

A plurality of opposite conductivity type semiconductor regions are formed on the surface of a one conductivity type semiconductor, and electrodes are provided on the surface of the one conductivity type semiconductor sandwiched between the opposite conductivity type semiconductor regions.
When the shortest distance between one conductivity type semiconductors sandwiched between a pair of opposite conductivity type semiconductor regions is WN and the zero potential depletion layer width determined by the specific resistance between the one conductivity type semiconductor and the opposite conductivity type semiconductor regions is Wbi, 0 < Basically, it is configured such that WN ≦ 2Wbi, and the one-conductivity-type semiconductor in contact with the electrode is a second one-conductivity-type semiconductor having a resistance value different from that of the other-part one-conductivity-type semiconductor. It is a feature and solves the above problems.

[0006]

(3) FIG. 2 and FIG. 3 are sectional structural views showing an embodiment of the present invention, in which the same reference numerals as those in FIG. In a
In addition, FIG. 3 shows an example in which unevenness is provided.

The main structural feature of the present invention is that, firstly, a reverse conductivity type semiconductor region 6 (for example, P + type) is formed and is determined by the specific resistance of the one conductivity type semiconductor 1 and the reverse conductivity type semiconductor region 6. When the depletion layer of zero potential is Wbi, the shortest distance WN of the one conductivity type semiconductor 1 sandwiched between the pair of opposite conductivity type semiconductor regions 6
Is in the relation of 0 <WN ≦ 2Wbi, and secondly, the second one conductivity type semiconductor 8 having a resistance value different from that of the one conductivity type semiconductor 1 is brought into contact with the electrode 4. A general means for forming the second one-conductivity-type semiconductor 8 having a different resistance value can be obtained by setting the impurity concentration to be higher or lower than the impurity concentration of the one-conductivity-type semiconductor 1.

A Schottky barrier semiconductor device having the structure of the present invention using a well-known barrier metal as the electrode 4 is manufactured and shown in FIG.
A reverse characteristic diagram is shown in FIG. 5, a forward characteristic diagram is shown in FIG. 5, and a switching characteristic diagram is shown in FIG. 6, respectively, and the excellent characteristics of the structure of the present invention are compared with those of the conventional structure. In both cases, the curves of a and b show the characteristics according to the structure of the present invention.
For comparison, the structure of FIG. 1 and the structure of FIG. 2, in which the relationship between the shortest distance WN of one conductivity type semiconductor 1 and the depletion layer width Wbi at zero potential is WN> 2Wbi are shown. ..

The electrodes 4 of FIGS. 2 and 3 are provided over the surface of the second semiconductor 8 of one conductivity type and the surface of the semiconductor region 6 of opposite conductivity type. However, depending on the embodiment, it is not always necessary to provide them. However, it suffices that it exists at least on the surface of the second one conductivity type semiconductor 8 and the surface of the pair of opposite conductivity type semiconductor regions 6.

The material of the electrode 4 does not have to be a barrier metal which makes Schottky contact, but may be any material capable of forming an electrode (4) such as an ohmic metal or other conductive material.

Next, the operation of the structure of the present invention will be described based on a specific embodiment. FIG. 7 is an electronic potential diagram, and the curves of the structure of the present invention are shown in a and b. That is, a is the second one-conductivity type semiconductor 8 having a thickness of 0.7 μm and a specific resistance of 0.5 Ω · cm, and b is the second one-conductivity type semiconductor 8 having a thickness of 0.7 μm and a specific resistance of 8 Ω · cm was formed by known epitaxial silicon deposition. The contact potential of the second N-type semiconductor 8 and the Schottky barrier metal 4 is 0.5 eV, and the resistance of the N-type semiconductor 1 is 5Ω.
cm resistivity, WN 0.5 μm, P + semiconductor region 6 has an impurity surface concentration of 1 × 10 ²⁰ Atoms / cm 3, Side Dif
fusion rate 0.1, P + semiconductor region 6 diffusion depth 2 μm, P
2 shows the electronic potential from the center point O of the shortest distance WN of the pair of P + semiconductor regions 6 to the distance X in the depth direction of the N-type semiconductor 1 when the width of the + semiconductor region 6 is 2 μm. As shown in FIG. 7, a phenomenon of lifting of the electronic potential, which was not seen in the conventional structure of WN> 2Wbi, occurred.

That is, the Schottky contact potential φM by the second N-type semiconductor 8 and the electrode 4, the conduction band potential φX in the N-type semiconductor 1 sandwiched between the P + semiconductor regions 6, the N-conductivity type semiconductor and the electrode as shown in FIG. N caused by only 4 configurations
When the conduction band potential in the conductivity type semiconductor 1 is φN, φM ≧ φX> φN according to the a curve, or φM according to the b curve.
A state of ≦ φX can be formed.

The shortest distance WN and the zero potential depletion layer width Wb
From the relationship of i, when WN> 2Wbi, the potential distribution of the characteristic curve of FIG. 1 is obtained, and the potential on the center line of WN is the height of the conduction band and valence band of the original N-type semiconductor. Thus, when WN = 2Wbi, the conduction band potential at the position of x on the centerline OX of the potential extending from the P + semiconductor region coincides with φN. Also, WN
<2Wbi, the potential on the center line OX is φN
At the higher position (5), the potentials extending from the two P + semiconductor regions intersect. Therefore, as shown in FIGS. 7A and 7B, by manipulating the impurity concentration of the second N-type semiconductor 8 in contact with the electrode 4 and further making the distance between the adjacent P + semiconductor regions close, Can be adjusted. This means that the pseudo P region in which the potential φX can be adjusted is formed.

According to the structure of the present invention, the conduction band potential φX in the N-type semiconductor 1 sandwiched between the P + semiconductor regions 6 by the formation of the pseudo P region is φM ≧ φX> φN or φM ≦ φX.
Can change to the state of.

When φM ≧ φX> φN in which a high-concentration layer is formed as the second one-conductivity-type semiconductor 8, the forward characteristic is shown by the curve a in FIG. 5, and is mainly determined by the height of φM. Further, since the effective φM is smaller and the series resistance is smaller than when the second one-conductivity-type semiconductor 8 in contact with the electrode 4 has the same impurity concentration as the one-conductivity-type semiconductor 1, the forward resistance is reduced. The properties are further improved. For reverse characteristics, φM
Not only is determined by, but also the electrode 4 and the second N formed by φX.
The electric field strength E at the junction surface of the type semiconductor 8 is higher than that of the structure of FIG. 1 and the structure of WN> 2Wbi.
The electric field strength E is reduced by the increase in φX due to the formation of the region. Therefore, the reverse leakage current decreases as is clear from the known reverse leakage current formula, the voltage dependence also decreases, and excellent characteristics are shown as the curve a in FIG. When .phi.M = .phi.X, the electric field strength E across the junction is almost zero, and the reverse leakage current has a minimum saturation current value as a Schottky barrier diode determined by the barrier metal.

When φM ≦ φX in which a low-concentration layer is formed as the second one-conductivity-type semiconductor 8, the forward and reverse characteristics are not governed by the height of the Schottky contact potential φM, but are governed by the height of φX. It will be the characteristic that is. That is, the reverse leakage current becomes smaller than the minimum saturation current value described above, and becomes like the curve b in FIG. Further, since φX can be made higher than when the second conductive semiconductor 8 (6) contacting the electrode 4 has the same impurity concentration as the conductive semiconductor 1, the reverse leakage current becomes small. However, the forward characteristic requires a threshold voltage commensurate with φX, and
Therefore, the forward voltage drop VF as a diode has to be slightly large as shown by the curve b. However, it becomes smaller than the threshold voltage of the PIN junction.

Next, the switching characteristic diagram of FIG. 6 will be described. trr is a so-called reverse recovery time from when the forward current is applied to when the carrier is switched to the opposite polarity and disappears. For example, as the N-type high resistance layer, 5Ω · c
175 Amp for a PIN junction in which a P + type high-concentration layer having a surface concentration of 1 × 10 ²⁰ Atoms / cm 3 and a junction depth of 3 μm and a junction area of 1 cm 2 are formed on silicon with a thickness of 30 μm and a thickness of 30 μm.
When a reverse voltage of 50 V is applied after the forward current of / cm2 is applied, a trr of about 400 nsec is required.

When 0 <WN ≦ 2Wbi in the structure of the present invention, the Ti metal and the N-type semiconductor are in Schottky contact, and the P + semiconductor region is in ohmic contact.
If it is equal to N, trr is 50 ns as shown in FIG.
It could be less than ec.

The mechanism is represented by φM ≧ φX> of the structure of the present invention.
Description will be given separately for two embodiments of φN and φM ≦ φX. When the second one-conductivity-type semiconductor 8 has a high-concentration layer of φM ≧ φX> φN, the influence of φM is large as can be seen from the potential distribution in FIG. 7, and the injection of the Ti Schottky minority carrier itself. 1 and a relatively wide WN, a short trr equivalent to that of a simple Schottky junction as shown in FIG. 1, that is, a high speed of several nsec to 20 nsec is obtained.

The second one conductivity type semiconductor 8 has a low concentration of φM ≦.
In the case of φX, as shown in the electron potential diagram of FIG. 8, even if no external voltage is applied, the conduction band EC in the depth formation region of the P + semiconductor (7) region has a bump shape higher in energy level than φM. Potential is formed. Further, since the upper end of the bump-like potential of the valence band EV approaches the valence band of the P + semiconductor region as much as possible, a hole is accumulated in the bump-like potential forming portion during the conduction of the forward current. As a result, the WN distance is sufficiently smaller than 2 Wbi, and a large amount of holes are accumulated in the hump-shaped potential forming portion, while facilitating the formation of the pseudo P region, while the depletion distance is to be completely depleted. The pseudo P region is formed in the N type semiconductor immediately below the electrode provided on the surface of the second N type semiconductor 8 sandwiched between the P + semiconductor regions. Moreover, since the conditions for electrical neutrality are satisfied, electrons having the same concentration as that of the holes are present in the conduction band of the bump-like potential forming portion, and a strong potential gradient (internal electric field) is obtained toward the Schottky contact. ing.

The reverse recovery time at the time of switching operation in the structure of the present invention simply moves the holes to the cathode side and the electrons to the anode side as in the conventional structure due to the formation of the hump-like potential due to the pseudo P region. By doing so, it was discovered that the phenomenon is shortened by a unique phenomenon rather than the phenomenon of disappearing.

That is, each of the carriers accumulated in the conduction band EC and the valence band EV in the depth formation region of the P + semiconductor region has a strong internal electric field within a few nsec immediately after switching to the opposite polarity. The electrons are attracted and the electrons flow toward the Schottky metal electrode against the external electric field, and the holes move to P +.
It flows from the semiconductor region into the Schottky metal electrode. That is, unlike the conventional structure, there is a period in which both holes and electrons flow in the electrode metal in the same direction. Then, electrons and holes are recombined and disappear in the Schottky contact electrode metal. This operation is difficult to observe with an ammeter attached to the electrode metal, and can be observed due to the behavior of charges in the P + semiconductor region.

The above phenomenon occurs in the range (0) where the shortest distance WN of one conductivity type semiconductor (N) sandwiched between the opposite conductivity type semiconductor regions (P +) of the present invention is 0 <WN ≦ 2Wbi. This is due to the lifting phenomenon of the conduction band and valence band. Therefore, by designing and distributing in the range of 0 <WN ≦ 2Wbi, the reverse recovery time trr can be adjusted and designed at a high speed within the range of the normal Schottky contact region to about ⅛ or less of the PIN junction. As described above, there is no need to diffuse the lifetime killer due to the heavy metal used for shortening the reverse recovery time.

As another embodiment of the structure of the present invention, FIG. 9 is a sectional structural view of a high breakdown voltage transistor, and FIG. 10 is a SIT gate.
The cross-sectional structural drawing of a toe part is shown, and the same code | symbol represents the same part. In addition, it can be used for various semiconductor devices such as IGBT.

Any modification, addition, conversion or other change is included in the scope of the present invention as long as it satisfies the structural requirements of the present invention including the equivalent conversion of conductivity type.

[0026]

As described above, the semiconductor device of the present invention can obtain the characteristics of low loss, high breakdown voltage and high speed, and is a rectifying element used for various industrial equipment including power applications. It can be widely applied as a semiconductor device such as a transistor and a switching element, and its effect is extremely great.

[Brief description of drawings]

FIG. 1 is a cross-sectional structural diagram of a conventional semiconductor device.

FIG. 2 is a sectional structural view showing an embodiment of the present invention.

FIG. 3 is a sectional structural view showing another embodiment of the present invention.

FIG. 4 is a reverse characteristic diagram. (9)

FIG. 5 is a forward characteristic diagram.

FIG. 6 is a switching characteristic diagram.

[Figure 7]

FIG. 8 is an electronic potential diagram.

FIG. 9 is a cross-sectional structure diagram in which the present invention is applied to a high breakdown voltage transistor.

FIG. 10 is a cross-sectional structure diagram in which the present invention is applied to a gate portion of a SIT.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 One conductivity type semiconductor (for example, N type) 1'High concentration one conductivity type semiconductor (for example, N + type) 2 Guarding region (for example P +) 3 Insulating film 4 Electrode 5 Ohmic electrode 6 Reverse conductivity type Semiconductor region (for example, P + type) 7 Recessed portion 8 Second conductive type semiconductor (for example, N + type or N− type) having a resistance value different from that of the one conductive type semiconductor 1 A Anode C Cathode WN 6 The shortest distance of 1 Wbi The Schottky contact potential due to the zero potential depletion layer width φM 1 and 4 which is determined by the specific resistance of 6 and N 4 The conduction band potential within 1 which is caused by the configuration of φN 1 and 4 Conduction band potential (10) VF forward voltage IF forward current VR reverse voltage IR reverse current a φM ≧ 8 in the embodiment of the present invention when 8 is a high concentration layer
Characteristic curve of φX> φN b φM ≦ φX when 8 is low concentration in the embodiment of the present invention
Characteristic curve of Ec conduction band EV valence band

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 29/73 29/804

Claims (4)

[Claims] 1. A pair of opposite conductivity type semiconductors, wherein a plurality of opposite conductivity type semiconductor regions are formed on the surface of one conductivity type semiconductor, and electrodes are provided on the surface of the one conductivity type semiconductor sandwiched between the opposite conductivity type semiconductor regions. The shortest distance of one conductivity type semiconductor sandwiched between regions is W
N, 0 <WN ≦ 2, where Wbi is the width of the depletion layer at zero potential determined by the specific resistances of the one conductivity type semiconductor and the opposite conductivity type semiconductor region.
In a semiconductor device configured to be Wbi, a semiconductor of one conductivity type in a portion in contact with the electrode is a second semiconductor of one conductivity type having a resistance value different from that of one semiconductor in another portion. apparatus. 2. An electrode is provided straddling the surface of the second one conductivity type semiconductor and the opposite conductivity type semiconductor region, and the electrode forms Schottky contact or ohmic contact with the surface of the second one conductivity type semiconductor. The semiconductor device according to claim 1, wherein an ohmic contact is formed with the opposite conductivity type semiconductor region. 3. The height of the electronic potential generated in a semiconductor of one conductivity type sandwiched between a pair of semiconductor regions of opposite conductivity type is:
3. The semiconductor device according to claim 1, wherein the height of the electronic potential generated by only the surface of the second one conductivity type semiconductor and the electrode is higher than the height of the electronic potential. 4. The one-conductivity-type semiconductor has an uneven surface shape, and a reverse-conductivity-type semiconductor region is formed on the bottom surface or side surface of the recess or both surfaces thereof. Item 3. The semiconductor device according to item 3.