JP2934606B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-speed diode having a small reverse recovery current.

[0002]

2. Description of the Related Art FIG. 7 shows current and voltage waveforms when a general rectifier diode changes its state from flowing a current in the forward direction to a blocking state in the reverse direction. Current density J _{F in} forward direction
When a reverse bias voltage is applied at the next moment, a reverse recovery current flows. At this time, a peak value J _RP of the current causes a power loss in proportion to the peak value J _RP , and thus it is necessary to reduce the peak value as much as possible. In addition, the _JRP becomes a noise source and causes a circuit using the diode, particularly an integrated circuit, to malfunction. From such a viewpoint, the structure shown in FIG. 8 is used as a diode for reducing the J _RP in 1987, IEE, International, Electron, Devices, Meeting (1987, IEEE International).
al Electron Devices Meeting) Pages 658 to 66
Discussed on page 1. In this structure, for example, n
⁺ P layer 113 is formed separately in n layer 112 formed on one side of substrate 111 by crystal growth or the like. The electrode 121 makes ohmic contact with the p-layer 113 and the p-layer 11
A Schottky junction is formed with the n − layer 112 exposed on the surface between the three layers. Further, the electrode 121 is formed so as to protrude on the oxide film 131 in the periphery,
It plays the role of a field plate that alleviates the surrounding electric field. The electrode 122 has low resistance contact with the n ⁺ layer 111. When a current flows from the electrode 121 to the electrode 122 in this diode, the pn junction, ie, the p
Holes are injected into the layer, and excess carriers are accumulated in the n ~ layer.
Holes are hardly injected into 12. Therefore, the carrier concentration accumulated near the interface between the pn junction and the Schottky junction is smaller than that of a conventional pn junction alone. As a result, as can be seen from FIG. 7, since the J _RP generated at the moment when the reverse bias voltage is applied is generated by the accumulated carriers near the pn junction, the diode of FIG. 8 is effective in reducing the J _RP . Have. In the reverse blocking state, the p layer 113 and the n１１３ layer 1 on both sides of the Schottky junction are connected.
12, a depletion layer extending from a pn junction formed between
Since reach-through is performed under the Schottky junction, the electric field applied to the Schottky junction can be reduced. For this reason, it has the feature that the leakage current can be reduced as compared with a conventional diode having only a Schottky junction.

Meanwhile, the diode of Figure 9 is shown in JP-A-58-60577 as a structure for reducing the J _RP. P in the diode, n ~ layer 112 surface between the p ⁺ layer 113 ⁺
8 in that a p-layer 114 having a lower carrier concentration than the layer 113 is provided. Thereby, in the forward direction, the pn of the p-layer 114 and the n-
Since a current flows through the junction, the p ⁺ layer 113 and the n ~ layer 112
It has the feature that the forward voltage drop can be reduced as compared with a diode consisting of only the junction. Also, the p layer 114
Since the carrier concentration is low, it is possible to reduce the amount of injected carriers from the p layer 114, also has features that can reduce the J _RP. Furthermore, since an interface between a metal and a semiconductor such as a Schottky junction is not used, the semiconductor device is less susceptible to contamination of the semiconductor surface and has stable characteristics. Of course, as in FIG. 8, the depletion layer extending from the deep p ⁺ layer 113 and the n −
There is also an effect that the electric field applied to the pn junction of No. 12 can be reduced and the leakage current can be reduced.

[0004]

The diode shown in FIG. 8 has a problem that the leakage current is increased and the breakdown voltage is deteriorated by bonding the wire 141 to the electrode 121. The cause is presumed as follows.

When bonding the wire 141 to the electrode 121, a pressure is applied between the electrode 121 and the wire 141, and this pressure causes a defect at the interface between the electrode 121 and the n− layer 112. This defect constitutes the recombination center,
Electrons in the conduction band flow into the defect and the leakage current increases. In particular, when a reverse bias state occurs and the electric field applied to the interface between the electrode 121 and the n ~ layer 112 increases, the thickness of the Schottky barrier decreases, and the probability that electrons transition to the recombination center as a tunnel current increases. As a result, it is considered that the leakage current further increases, and as a result, the breakdown voltage decreases.

Further, the diode shown in FIG. 9 has a problem that the _JRP is increased because carriers are injected from the p-layer 114 as compared with the diode shown in FIG. Therefore, it is disclosed that the carrier concentration of the p-layer 114 is reduced in order to further reduce the J _RP . However, if the carrier concentration of the p-layer 114 is too low, there is a problem that the breakdown voltage is reduced.
This is because if the concentration of the p-layer 114 is too low,
It is considered that the depletion layer punches through at 1 and the breakdown voltage decreases. Further, as compared with the diode of FIG.
There is a problem that the number of manufacturing processes for forming No. 4 increases.

[0007] As described above, no consideration is for the decrease in breakdown voltage in a structure to achieve a small J _RP in the prior art, both to ensure the reduction and breakdown voltage of the J _RP is a problem that it is difficult been filed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor device which has a small J _RP and a stable breakdown voltage, is easy to manufacture, and has excellent stability.

[0009]

SUMMARY OF THE INVENTION The features of the semiconductor device of the present invention are described below.
The feature is that the first semiconductor region has one conductivity type,
Forming a pn junction with the first semiconductor region;
A second half of the other conductivity type having a higher impurity concentration than the semiconductor region.
The conductor region is a diode region where current flows in the forward direction.
Ri, and amount of impurities in the second semiconductor region is 1 cm ² per
It should be less than × 10 14 powers. Furthermore, if more detail, the forward voltage V _F when a forward current flows through the current density J _F above the diode region from 0.1 (V) 0.3
In the range of (V),

[0010]

(Equation 3)

Is that it holds.

According to the present invention, the impurity in the second semiconductor region is improved.
Physical quantity must be 1 × 10 14 or less per 1 cm ²
Suppresses carrier injection from the second semiconductor region
Can be Therefore, _JRP can be reduced.

Further, by setting the n value to 1.00 ≦ n ≦ 1.15, the injection of carriers from the second semiconductor region can be suppressed, so that excess carriers accumulated at the pn junction interface can be reduced. , _JRP can be reduced.

[0014]

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments.

FIG. 2 is a sectional view and a plan view showing one embodiment of the diode portion of the semiconductor device of the present invention. In the figure, reference numeral 1 denotes a pair of main surfaces 11, 1 located on opposite sides of each other.
In the semiconductor substrate having a 2, and n ⁺ layer 13 adjacent to one main surface 11, and the n ~ layer 14 of low impurity concentration than the n ⁺ layer 13 adjacent to the n ⁺ layer 13 and the other main surface 12, the other A p-layer 15 having a higher impurity concentration than the n- layer 14 extending into the n- layer 14 from a plurality of selected portions of the main surface 12 of the p-layer 15;
The p-layer 16 has a higher impurity concentration than the n- layer 14 and is thinner than the p-layer 15 and extends between the other main surface 12 and the n- layer 14 between the main surfaces 12. The p layer 15 includes a plurality of small regions 151 and an annular region 152 surrounding them. 2 is an n ⁺ layer 13 on one main surface 11
The other main electrode 3 which makes ohmic contact with the p layer 15 on the other main surface 12 and forms a Schottky barrier with the p layer 16 at the other main surface 12, and the other 4 In the periphery, n ~ layer 14 and p layer 1
The other main electrode 3 is an oxide film formed on the oxide film 4.
Extending above. Thereby, between a pair of main surfaces,
A first diode consisting of n ⁺ layer 13, n ~ layer 14 and p layer 15 and a second diode consisting of n ⁺ layer 13, n ~ layer 14, p layer 16 and a Schottky barrier are arranged in parallel. A diode having the structure is obtained.

The diode shown in FIG. 2 differs from the conventional diode shown in FIG. 9 in that a Schottky barrier is provided between the p layer 16 and the main electrode 3. The effect of the present invention will be described with reference to FIG. (A) shows an electrode 121 in FIG.
The energy band structure of the Schottky barrier region of the n ~ layer 112, and (b) shows the main electrode 2 in FIG.
The energy band structure of the Schottky barrier region of the p layer 16 and the nｎ layer 14 is shown. In the conventional structure (a), as described above, if a defect occurs at the Schottky barrier interface, for example, by wire bonding, electrons in the conduction band flow to the recombination center where the defect has occurred at the time of reverse bias, and the leakage current increases. It is considered that the breakdown voltage decreases. On the other hand, in the present invention (b), even if a defect occurs at the Schottky barrier interface, the width W of the barrier can be increased by the p-layer 16, so that
The probability that electrons in the conduction band transition to defects by tunnel current or the like is significantly reduced. For example, if the width of the p layer 16 is 100 °
Above this level, electrons hardly transition. Therefore,
Leakage current is reduced, and higher breakdown voltage can be achieved. And p
Since a Schottky barrier is formed between the layer 16 and the main electrode 3, the breakdown voltage does not deteriorate as in the diode of FIG. . Of course, the p-layer 15 is
6, it is needless to say that the depletion layer extending from the pn junction of the p layer 15 has the effect of reducing the electric field applied to the pn junction of the p layer 15.
Further, supply of holes to the p layer 16 can be suppressed by the barrier φ _BP for holes in the p-type Schottky barrier. Therefore, in a diode in which the p-layer 114 and the electrode 121 are in ohmic contact as shown in FIG. 9, holes are supplied from the electrode 121 to the p-layer 114, and holes are injected from the p-layer 114 to the n-layer 112. On the other hand, in the diode of FIG. 2, the supply of holes to the p layer 16 is suppressed by φ _BP , so that the injection of holes from the p layer 16 to the n − layer 14 can be reduced. As a result, accumulated carriers near the pn junction can be reduced, and J _RP can be reduced.
More preferably, if the p layer 16 is depleted due to the potential difference between the pn junction and the Schottky barrier, the injection of holes can be extremely reduced, so that the J _RP can be further reduced.

FIG. 4 shows experimental results at room temperature in which the electrical characteristics of the diode of FIG. 2 having various P layers 16 were examined in detail. The horizontal axis, in that which causes a forward current density J _F to the diode, in the range forward voltage V _F is about 0.1～0.3V, relationship V _F and l _n J _F becomes substantially straight In the area

[0019]

(Equation 4)

[0020] shows the relationship between the value and J _RP / J _F. The value of n indicates that the closer to 1, the majority carrier occupies the main current, and the closer to 2, the greater the recombination current with the injected minority carrier. Result of examining the ratio J _RP / J _F forward current density J _F and reverse recovery current density J _RP, it was found that there is a relation of FIG. The value of n is 1.00
If during the 1.15 was found to be reduced J _RP / J _F, which is also provided with a p-layer 16, if reducing injection of minority carriers (smaller n), the J _RP It shows that it can be made smaller. As a condition of the p-layer 16, for example, when the p-layer 16 is formed by ion implantation of B (boron), the ion implantation amount is desirably set to about 1 × 10 14 or less per 1 cm ² . If the number is about 1 × 10 14 or more per cm ² , the p-layer 16 and the main electrode 2 approach an ohmic junction, and the p-layer 16 has a high concentration.
This is because holes can be easily injected from No. 6 into the n ~ layer 14 and _JRP increases.

FIG. 5 shows a preferred method of manufacturing the semiconductor device of FIG. First, an n ~ layer 14 having a specific resistance and a thickness necessary to obtain a desired breakdown voltage is prepared, and a p-type impurity is partially introduced from one surface thereof by ion implantation or diffusion. Here, a p-layer impurity is diffused by heat treatment to 1 to 10 μm in a diode having a desired depth of, for example, 600 V to form a p-layer 15 (a). Next, the electrode 3 containing a p-type impurity
From the surface of the p-layer 15 and the n ~ layer 14 surrounded by the p-layer 15
(B). Here, heat treatment is performed to diffuse the p-type impurity in the electrode 3 to the surface of the nｎ layer 14 to form a p-layer. By doing so, the step of forming the p-layer 16 using the ion implantation or the like required in FIG. 9 can be omitted. In this case, since the junction depth of the p layer 16 is extremely thin, about 100 nm or less, it is desirable to connect the p layer 15 at the final end in order to alleviate the electric field in the periphery and secure the withstand voltage. The effect of the present invention can be obtained even if the plane shape of the p-layer 15 in the meantime is rod-shaped, circular, or polygonal. Of course, the electrode forming the Schottky barrier and the electrode forming the ohmic junction may be made of different materials, and both electrodes may be electrically short-circuited.

FIG. 6 shows the results of an experiment on a more preferable main electrode 3. The case where a material containing aluminum is used for the main electrode 3 is shown. As a result of experiments by the present inventors, it has been found that when the heat treatment temperature is higher than 430 ° C., the p layer 14 is formed. However, if the eutectic temperature of aluminum and silicon is set to 577 ° C. or higher, aluminum is condensed, and disconnection of the main electrode 3 and unevenness of the p-layer 14 occur. From this result, it is possible to apply aluminum added with silicon, which is widely used in a semiconductor process, to the main electrode 3, which has an effect that the main electrode 3 can be adapted to a semiconductor manufacturing process.

FIG. 1 shows the diode and power MO shown above.
FIG. 3 is a schematic cross-sectional view showing an embodiment of a semiconductor device of the present invention in which SFETs are combined in antiparallel. The power MOSFET is n ~ layer 1
4, a p-type well layer 17, an n-type source layer 18 formed in the well layer 17, a gate electrode 4, a main electrode 2,
3 is formed by extending the drain electrode and the source electrode. Reference numeral 6 denotes a bonding wire provided on the main electrode 3 of the diode. As a result, the power MOSFET becomes n ⁺
Since the main current can be passed through the built-in diode composed of the layer 13, the n layer 14, the p layer 15, and the p layer 16, the wire 6
Can prevent withstand voltage deterioration due to bonding of
J _RP can be reduced.

In the above-described semiconductor device of the present invention, it is needless to say that the lifetime of minority carriers may be shortened by electron beam irradiation or the like, and the same effect can be obtained by replacing the p-type and n-type semiconductor layers. No.

[0025]

According to the semiconductor device of the present invention, the reverse recovery current can be reduced, the deterioration of the breakdown voltage can be prevented, and the manufacturing process can be simplified, so that the effects such as low noise, high reliability, and easy manufacturing can be obtained. There is.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of a semiconductor device of the present invention.

FIG. 2 is a schematic sectional view and a plan view showing one embodiment of a diode applied to the present invention.

FIG. 3 is an explanatory diagram showing an effect of the diode shown in FIG.

FIG. 4 is a schematic diagram showing a relationship between a ratio between a forward current density and a reverse recovery current density of the diode shown in FIG. 2 and a forward voltage drop.

FIG. 5 is a process chart showing a method for manufacturing the diode shown in FIG.

FIG. 6 is an explanatory diagram showing manufacturing conditions of the diode shown in FIG.

FIG. 7 is an explanatory diagram of a reverse recovery characteristic of a diode.

FIG. 8 is a cross-sectional view illustrating an example of a conventional semiconductor device.

FIG. 9 is a sectional view showing another example of a conventional semiconductor device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor base, 2,3 ... Main electrode, 13 ... N ⁺ layer, 14
... n ~ layers, 15, 16 ... p layers.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naoki Sakurai 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hidetoshi Arakawa 3-10-2 Bentencho, Hitachi City, Ibaraki Prefecture Haramachi Electronics Co., Ltd. (72) Inventor Hiroshi Owada 3- 10-2 Bentencho, Hitachi City, Ibaraki Pref. Tachihara Town Electronics Co., Ltd. (56) References JP-A-56-37683 58-60577 (JP, A) JP-A-3-248563 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 29/861 H01L 29/78 H01L 29/872

Claims (3)

(57) [Claims] A first semiconductor region of one conductivity type, a pn junction with the first semiconductor region, and a first semiconductor region;
Region of the other conductivity type having a higher impurity concentration than that of the second semiconductor region
When a first electrode in contact with the first semiconductor region, and a second electrode contacting the second semiconductor region includes a first semiconductor region and the second semiconductor region, conductive in the forward direction
And a second semiconductor region having an impurity amount of 1 × 10 / cm ^2.
14 or less, and the second electrode contains aluminum.
Only, the second semiconductor region contains aluminum as an impurity
A semiconductor device characterized by the above-mentioned. 2. A semiconductor device comprising: a first semiconductor region of one conductivity type; and a pn junction formed with the first semiconductor region.
Region of the other conductivity type having a higher impurity concentration than that of the second semiconductor region
A first electrode in contact with the first semiconductor region and a second semiconductor
And a second electrode in contact with the body region , wherein the first semiconductor region and the second semiconductor region are forwardly charged.
And a second semiconductor region having an impurity amount of 1 × 10 / cm ^2.
14 or less, and the forward current of the current density JF between the first electrode and the second electrode
Is applied, the forward voltage VF changes from 0.1 (V) to 0.3.
In the range of (V), A semiconductor device characterized by the following. 3. A first semiconductor region of one conductivity type, and a pn junction with the first semiconductor region are formed, and the first semiconductor region is formed.
Region of the other conductivity type having a higher impurity concentration than that of the second semiconductor region
A first electrode in contact with the first semiconductor region and a second semiconductor
And a second electrode in contact with the body region , wherein the first semiconductor region and the second semiconductor region are forwardly charged.
And a second semiconductor region having an impurity amount of 1 × 10 / cm ^2.
14 or less, and the second semiconductor region and the second electrode form a Schottky junction.
A semiconductor device characterized by being formed.