JPH0587189B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high voltage shot barrier semiconductor device.

[Prior Art and Problems to be Solved by the Invention] A shotgun barrier diode is widely used in high-frequency rectifier circuits and the like, taking advantage of its high-speed response (high-speed switching characteristics) and low loss. However, shot barrier diodes have a problem in that the peripheral breakdown voltage (withstand voltage around the shot barrier) is significantly lower than the bulk breakdown voltage (breakdown voltage at the center of the shot barrier), making it difficult to increase the breakdown voltage.

Providing a field plate or a guard ring in order to solve this problem is known, for example, in "Physics of Semiconductor Devices", 2nd edition, written by SMM, USA. Additionally, the use of both field plates and guard rings has already been practiced.

A shot barrier diode with a field plate structure consists of an n ⁺ type semiconductor region, an n type semiconductor region formed on this, and a metal electrode (hereinafter referred to as barrier metal) capable of forming a shot barrier formed on this n type semiconductor region. an insulating layer formed on the n-type semiconductor region so as to surround the barrier metal electrode; a field plate provided on the insulating layer and connected to the barrier metal ^electrode ; and an ohmic electrode connected to a semiconductor region. When a reverse voltage is applied between the barrier metal electrode and the ohmic electrode, a depletion layer is generated between the barrier metal electrode and the n-type semiconductor region, and
A depletion layer is also generated in the n-type semiconductor region under the field plate due to the field effect of the field plate, which alleviates the concentration of the electric field around the barrier metal electrode and improves the peripheral breakdown voltage of the shotgun barrier. However, it has been practically difficult to satisfactorily alleviate the concentration of the electric field and significantly improve the withstand voltage.

On the other hand, a shot barrier diode with a guard ring structure has a guard ring that is connected to the periphery of a barrier metal electrode in plan view and is made of a p ⁺ -type semiconductor region that is arranged so as to surround the barrier metal electrode. The p ⁺ type semiconductor region of the guard ring forms a pn junction with the n type semiconductor region, and when a reverse voltage is applied to this pn junction, the depletion layer expands more effectively than the periphery of the Schottky barrier. As a result,
The peripheral breakdown voltage of the barrier metal electrode can be improved. However, the shotgun barrier diode and
Since it has a structure in which a pn junction diode is placed in parallel, when a forward voltage is applied and a forward current flows,
Injection of minority carriers occurs at the p-n junction, and the high-speed response, which is one of the characteristics of shotgun barrier diodes, deteriorates. Further, although the guard ring structure is widely used in combination with the field plate structure, it is still difficult to significantly increase the withstand voltage.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a shot barrier semiconductor device that is capable of increasing withstand voltage and has high stability.

[Means for Solving the Problems] The present invention for achieving the above object includes a semiconductor region and a barrier metal formed on the semiconductor region so as to create a shot barrier between the semiconductor region and the semiconductor region. an electrode, disposed on the semiconductor region so as to surround the barrier metal electrode, electrically connected to the barrier metal electrode, and having a sheet resistance greater than that of the barrier metal electrode; and a thin layer of titanium oxide formed to cover the thin layer and coated with plasma CVD or photoresist.
The present invention relates to a shot barrier semiconductor device characterized by comprising an insulating layer made of a silicon oxide film formed by CVD. In the above invention, the sheet resistance of the thin layer is 10kΩ/□~
It is preferable to set it to 5000MΩ/□.

[Operation] In the above invention, when a reverse voltage is applied between the barrier metal electrode and the semiconductor region, a depletion layer based on the shot barrier between the barrier metal electrode and the semiconductor region, and the titanium oxide thin layer and the semiconductor region are formed. A depletion layer is generated based on the shotgun barrier between the Since the titanium oxide thin layer surrounds the barrier metal electrode, when the titanium oxide thin layer surrounds and adjoins the barrier metal electrode, the depletion layers based on these layers are continuous with each other, and as will be described later. When a guard ring of the p ⁺ type region is provided to surround the barrier metal electrode as shown in the modification example, the titanium oxide thin layer and the barrier metal electrode are connected to each other through a depletion layer based on the pn junction of this guard ring. The depletion layer is continuous. Both the barrier metal electrode and the titanium oxide thin layer create a shot barrier between themselves and the semiconductor region, and since the titanium oxide thin layer is a resistor, the titanium oxide thin layer is A potential gradient is created in which the potential gradually changes towards the end. As a result, the depletion layer is expanded so that the electric field is not concentrated at the peripheral edge of the barrier metal electrode, and the withstand voltage is significantly improved.

Since the silicon oxide film produced by plasma CVD or photo-CVD does not interfere with the high breakdown voltage effect based on the titanium oxide thin layer, it is possible to provide a high breakdown voltage shot barrier semiconductor device. In addition, plasma CVD
Alternatively, the photo-CVD silicon oxide film stably maintains the high breakdown voltage effect based on the titanium oxide thin layer over a long period of time. Therefore, plasma CVD or optical
The CVD silicon oxide film is suitable as a protective film for the titanium oxide thin layer.

In a preferred embodiment of the present invention, when a reverse voltage is applied, breakdown occurs in a minute region at the outer peripheral edge of the titanium oxide thin layer, and based on this, a reverse current flows through the titanium oxide thin layer. Since the titanium oxide thin layer is a resistor, the reverse current due to this minute breakdown is suppressed and does not become very large. When a current flows from the outer circumferential edge of the titanium oxide thin layer toward the inner circumferential edge, a potential gradient occurs because the titanium oxide thin layer is a resistor, and a depletion layer is obtained that satisfactorily alleviates electric field concentration.

In addition, the sheet resistance of the thin layer is 10kΩ/□~
If it is in the range of 5000MΩ/□, high voltage resistance can be effectively achieved.

[Example] A shot barrier diode and its manufacturing method according to the first example of the present invention are shown in Figs.
This will be explained based on FIGS. 2 and 3. First, as shown in FIG. 1A, a semiconductor substrate 21 made of GaAs (gallium arsenide) is prepared. Semiconductor substrate 2
1 has a thickness of approximately 300 μm and an impurity concentration of 0.5 to 2×10 ¹⁸ cm
An n ^- type region 23 having a thickness of 10 to 20 μm and an impurity concentration of 1 to 2×10 ¹⁵ cm ⁻³ is epitaxially grown on the −3 n + type region 22 ^.

Next, as shown in FIG. 1B, a thin layer 24 of Ti (titanium), that is, a Ti thin film, is formed on the entire upper surface of the n-type region 23 made of n-type GaAs by vacuum evaporation, and then Al ( A layer 25 (aluminum) is successively vacuum deposited. The thickness of the Ti thin layer 24 is 50 Å to 200
It is extremely thin with a thickness of Å (0.005 to 0.02 μm). The thickness of the Al layer 25 is about 2 μm, which is more than 100 times that of the thin Ti layer 24. Furthermore, Au (gold)-Ge is added to the lower surface of the n ⁺ type region 22.
An ohmic contact electrode 26 made of a (germanium) alloy is formed by vacuum evaporation, and then
Heat treatment at ℃ for 10 seconds.

Next, as shown in FIG. 1C, a part of the Al layer 25 is removed by photo-etching,
The Al layer 25a is left in a region corresponding to a region where a shot barrier serving as a main forward current path is to be formed.
Furthermore, by photoetching,
Remove the Ti thin layer 24 and remove the Ti layer 24 below the Al layer 25a.
The Ti thin layer 24a and the Ti thin layer 24b surrounding it adjacently remain. The Ti thin layer 24b is a resistive layer with a sheet resistance of 20 to 400 Ω/□ because Ti itself is an extremely thin film even though it is a conductor.
It has an order of magnitude higher resistance than 5a.

Next, heat treatment is performed in air at 300°C for 5 to 30 minutes. As a result, as shown in Figure 1D, Al
The thin Ti layer 24b not covered by the layer 25a is oxidized to a thin layer 28 of titanium oxide,
The Ti thin layer 24a below the Al layer 25a is
It is not oxidized because it is masked by a. Al and
Since both Ti and GaAs are metals that form a shot barrier, they will be collectively referred to as a barrier metal electrode 27. Ti thin layer 24a
Since these are extremely thin films, it is not necessarily clear how the thin Ti layer 24a and the Al layer 25a are each involved in forming the shot barrier. Note that, in addition to forming a shot barrier, the Ti thin layer 24a contributes to improving the adhesion of the Al layer 25a to the n-type region 23, and also serves as a titanium oxide thin layer surrounding the barrier metal electrode 27 in a ring shape. Contributes to electrical connection between layer 28 and Al layer 25a.
It is desirable that the sheet resistance of the barrier metal electrode 27 is 1Ω/□ or less, and in this embodiment, it is approximately 1Ω/□ or less.
It is 0.05Ω/□. As shown in FIG. 1D and FIG. 2, the titanium oxide thin layer 28 according to the present invention, provided so as to surround the Al layer 25a,
It is a semi-insulating high-resistance layer with an estimated thickness of 75 Å to 300 Å, which is greater than that of 4b, and a sheet resistance of 50 M to 500 MΩ/□. That is, the titanium oxide thin layer 28 is not TiO ₂ (titanium dioxide), which can be considered a perfect insulator, but a so-called oxygen-poor titanium oxide TiOx, which contains less oxygen than TiO ₂ (however, x is 2).
It is considered that the value is smaller than the above.

Next, as shown in FIG. 1E, the titanium oxide thin layer 28 is covered with an insulating layer 29 to complete a semiconductor chip having a shottling barrier, that is, a power shottling barrier diode chip. Note that the insulating layer 29 is formed by plasma CVD (chemical vapor deposition).
It consists of a silicon oxide film formed by a deposition method.

Plasma CVD is a method in which a raw material gas is brought into a low-temperature plasma state to promote a chemical reaction, and a thin film, which is a reaction product of the raw material gas, is deposited on a substrate. This method is different from conventional normal pressure or reduced pressure because ions, radicals (active species), etc. that are chemically very active are created under plasma conditions.
Compared to CVD methods, thin films can be created at significantly lower temperatures. There are several methods for plasma CVD, but
High-frequency discharge plasma CVD, which uses high-frequency discharge to generate plasma, is the most common.

Next, a method for forming the insulating layer 29 by plasma CVD will be described with reference to a conceptual diagram of a high frequency discharge plasma CVD apparatus shown in FIG. A source gas is supplied to the space 43 between the parallel plate electrodes 41 and 42.
A mixed gas of SiH ₄ (monosilane) and N ₂ O (nitrous oxide) is introduced. The gas inflow rates (converted to 1 atm) were 3.3 cc/min for SiH ₄ and 98 cc/min for N ₂ O. The space 43 is maintained at a reduced pressure of 0.5 torr by exhaustion using a vacuum pump (not shown). Between the electrodes 41 and 42, a high frequency power source 44
13.56MHz, 150W high frequency power is supplied. The semiconductor substrate 21 in the state shown in FIG.
It is heated to ℃. The source gas is excited to a plasma state, and an insulating layer 29 made of a silicon oxide film is deposited on the semiconductor substrate 21. The thickness of insulating layer 29 is approximately 6000 Å after 7 minutes of growth. Thereafter, a portion of the insulating layer 29 is removed by photoetching to form the insulating layer 29 as shown in FIG. 1E.

The insulating layer 29 can be replaced with a silicon nitride film formed by plasma CVD or photo CVD, a polyimide resin film formed by coating, etc., but a silicon oxide film formed by plasma CVD or photo CVD is preferable. It was hot. Although not shown in the figure, for example, a Ti layer and an Au layer are formed on the upper surface of the Al layer 25a.
Usually, the layers are sequentially provided and used as connection electrodes for the lead member.

Examples of dimensions of each part in FIG. 2 are as follows. The width a of the barrier metal electrode 27 is about 900 μm, the width b of the thin titanium oxide layer 28 is about 150 μm, and the width c between the thin titanium oxide layer 28 and the edge of the n-type region 23 is about 150 μm.

In this shotki barrier diode,
Between the barrier metal electrode 27 and the n-type region 23, a first
Not only a second shot barrier is created, but a second shot barrier is created between the thin titanium oxide layer 28 and the n-type region 23. Titanium oxide thin layer 28
It was confirmed that a shot barrier occurs between the capacitor and the n-type region 23 based on the rectification characteristics, capacitance characteristics, saturation current characteristics, etc. of the shot barrier diode. For example, when the area of the titanium oxide thin layer 28 is increased from zero, the saturation current Is becomes smaller than the titanium oxide thin layer 28.
8 and the area of the barrier metal electrode 27. It has been confirmed that this proportional relationship is obtained at various temperatures of the shotgun barrier diode. Saturation current with respect to the sum area of the titanium oxide thin layer 28 and the barrier metal electrode 27
The fact that Is changes approximately proportionally means that a reverse current flows through the titanium oxide thin layer 28 at approximately the same current density as the barrier metal electrode 27. This phenomenon occurs because the titanium oxide thin layer 28
This clearly shows that a shot barrier having a barrier height φ _B that is approximately the same as that of 7 is formed.

The solid line characteristic curve in FIG. 3 shows the reverse voltage-reverse current characteristics of the shot barrier diode of FIG. 3 shows the reverse voltage-reverse current characteristics of a shotgun barrier diode having a structure in which the titanium oxide thin layer 28 is removed from the structure shown in FIG. 2
As is clear from the comparison of the two characteristic curves, the breakdown voltage of the shotgun barrier diode with the thin titanium oxide layer 28 according to the invention is approximately 250 V.
The breakdown voltage of the conventional shotgun barrier diode without the titanium oxide thin layer 28 is approximately 60V, and it is clear that the titanium oxide thin layer 28 is responsible for the significant improvement in the breakdown voltage. Ru. The breakdown voltage value (approximately 250 V) of the shotgun barrier diode having the titanium oxide thin layer 28 is considered to have reached a level approximately equal to the bulk breakdown voltage (the breakdown voltage at the center of the barrier metal electrode 27).

Next, the reverse voltage-reverse current characteristics of the shotgun barrier diode according to the present invention will be explained in more detail.
When the reverse voltage applied to the shotgun barrier diode is gradually increased from zero volts, the third
As shown in region I of the figure, the saturation current is extremely small.
Is flows. At this time, a reverse current flows through the first shottock barrier based on the barrier metal electrode 27 and also flows through the second shottock barrier based on the thin titanium oxide layer 28. The reverse voltage application circuit is connected to the barrier metal electrode 27, ie, the anode, and the ohmic electrode 26, ie, the cathode, and is not directly connected to the titanium oxide thin layer 28. Therefore, the current flowing through the thin titanium oxide layer 28 flows into the barrier metal electrode 27. Area I in Figure 3
In this case, since the value of the current flowing through the titanium oxide thin layer 28 is small, the potential difference between a point of the titanium oxide thin layer 28 near the barrier metal electrode 27 and a point far from the barrier metal electrode 27 is not very large. That is, the potential gradient in the lateral direction of the titanium oxide thin layer 28 is small, and the potential of each part of the titanium oxide thin layer 28 is approximately equal to the potential of the barrier metal electrode 27.

If you further increase the reverse voltage to about 60 to 100V,
Breakdown occurs in a plurality of minute regions at the outer periphery of the titanium oxide thin layer 28, and the reverse current increases in a stepwise manner as shown in the region of FIG. One step of this staircase corresponds to breakdown of one outer peripheral edge of the thin titanium oxide layer 28. In conventional shotgun barrier diodes, a large reverse current flows due to breakdown in a minute region, but in the shotgun barrier diode according to the present invention, no large reverse current flows. That is, titanium oxide thin layer 2
Since 8 is a semi-insulating high resistance layer, the current is limited by the resistance of the titanium oxide thin layer 28, and a large increase in reverse current is suppressed. At the end of the region, the barrier metal electrode 2 of the thin titanium oxide layer 28
7 and the inner circumferential end P ₁ and the barrier metal electrode 27
As a result, the potential difference between the peripheral edge ₂ of the titanium oxide thin layer ₂₈ and the ohmic electrode 26 increases as the applied reverse voltage increases. Even if you don't let it grow, it won't increase much. Therefore, no new breakdown occurs at the peripheral edge _P2 . However, the breakdown that has already occurred at the peripheral edge P ₂ is maintained, and the reverse current based on this breakdown continues to flow through the titanium oxide thin layer 28. In the region, the first shot barrier based on the barrier metal electrode 27 and the thin titanium oxide layer 28 decrease as the reverse voltage increases, since no new breakdown occurs at the peripheral edge P ₂ of the thin titanium oxide layer 28. The reverse current through the second shot barrier based on .

If the titanium oxide thin layer 28 is replaced with a resistor layer that does not form a shot barrier, reverse current (leakage current) will increase as the reverse voltage increases.
becomes significantly larger, and as a result, the withstand voltage also becomes lower. The thin titanium oxide layer 28 according to the invention not only has a high resistance but also forms a shot barrier, so that the leakage current suppression effect is greater than in the case of the resistor layer described above.

Since a voltage is applied not only to the barrier metal electrode 27 but also to the titanium oxide thin layer 28, the depletion layer 30 schematically shown in FIG. occurs in region 23.
The potential difference between the titanium oxide thin layer 28 and the n ⁺ type region 22 decreases from the inner circumferential end _P1 to the outer circumferential end _P2 , so the spread (vertical thickness) of the depletion layer 30 increases. also becomes smaller toward the outer peripheral end _P2 . Further, the surface of the n-type region 23 from the barrier metal electrode 27 to the titanium oxide thin layer 28 is continuous as a shot barrier. As a result of these,
A gentle depletion layer 30 that can alleviate electric field concentration is obtained, and the electric field is no longer concentrated at the peripheral edge of the barrier metal electrode 27. Therefore, as shown in , even if the reverse voltage applied between the pair of electrodes 26 and 27 increases, there is a wide region in which no breakdown occurs.

When the reverse voltage becomes 250V, the barrier metal electrode 27
A critical electric field is created between the periphery of the ohmic electrode 26 and the ohmic electrode 26.
Breakdown occurs when Ecrit is exceeded, and the reverse current increases as shown in the area.

For comparison, the Ti thin layer 2 shown in FIG.
When the reverse voltage-reverse current characteristics were measured before oxidizing the Ti layer 24b, it was found that the Ti thin layer 24b had not become a sufficiently high-resistance layer, so the reverse current was suppressed as shown in the area shown in Figure 3. This resulted in a breakdown as shown by the broken line, similar to the conventional method.

When the shot barrier diode of this example was used as a rectifier diode of a switching regulator with a switching frequency of 500KHz,
Rectification operation with extremely low noise generation was confirmed. Note that no decrease in switching speed (high-speed response) was observed due to the provision of the titanium oxide thin layer 28. In addition, even after long-term use, the shotgun barrier diode's breakdown voltage characteristics were stable.

The advantages of this embodiment are summarized as follows.

(1) Since the titanium oxide thin layer 28 is both a resistor and an object capable of generating a shot barrier, it can effectively generate a depletion layer that alleviates the concentration of electric field at the periphery of the barrier metal electrode 27, thereby significantly increasing the withstand voltage. I can do it.

(2) Better high-speed response than conventional shotgun barrier diodes with guard rings.

(3) The thermal instability of characteristics observed in conventional shotgun barrier diodes having a field plate through an insulating layer has been eliminated.

(4) Since the titanium oxide thin layer 28 is obtained by oxidizing the Ti thin layer 24b, which is an extension of the Ti thin layer 24a provided directly under the Al layer 25a, it is easy to form the desired titanium oxide thin layer 28. can be obtained.
Further, electrical connection between barrier metal electrode 27 and titanium oxide thin layer 28 can be easily and reliably achieved.

(5) By providing the insulating layer 29 made of a silicon oxide film by plasma CVD, the withstand voltage characteristics etc. will not be deteriorated, and the titanium oxide thin layer 2
It is possible to maintain the high pressure resistance effect based on 8. In addition, an insulating layer 29 made of a silicon oxide film
Shock barrier diodes that have been packaged with this method have high reliability, with little deterioration in withstand voltage characteristics due to long-term use.

[Second Embodiment] Next, a shot barrier diode according to a second embodiment of the present invention shown in FIG. 6 will be described. However, in FIG. 6 and FIGS. 7 to 11 showing third to seventh embodiments, which will be explained later, parts common to those in FIG. Omitted.

The shotgun barrier diode shown in Figure 6 is
Similar to Figure E, a Ti thin layer 24a is placed on the n-type region 23.
, an Al layer 25a, and a titanium oxide thin layer 28. However, the titanium oxide thin layer 28
It is not directly connected to the Al layer 25a, but is connected via the Ti thin layer 24c. This Ti thin layer 2
4c, the Al layer 2 is formed by photoetching after the oxidation treatment step to obtain the titanium oxide thin layer 28.
Obtained by removing part of 5a. The Ti thin layer 24c is continuous with the Ti thin layer 24a, and the n-type region 2
Since a shot barrier is formed between the metal electrode 3 and the metal electrode 3, this is also included as a part of the barrier metal electrode 27. Providing the Ti thin layer 24c in this manner further increases the breakdown voltage. That is, the Al layer 25a and the n-type region 2
3 are mutually different objects, so the Al layer 25a
The stress concentration point 31 based on the provision of the Al layer 2
It occurs at the lower part of the periphery of 5a. This stress concentration point 31
The critical electric field Ecrit that causes breakdown in is lower than in other parts. Therefore, if the electric field concentrates on this stress concentration point 31, breakdown is more likely to occur. Therefore, in this example,
By providing the Ti thin layer 24c, the inner peripheral end of the titanium oxide thin layer 28 is separated from the stress concentration point 31. In the case of Fig. 1E, the barrier metal electrode 2
The electric field was concentrated at the lower part of the boundary between 7 and the thin titanium oxide layer 28, which is different in nature, but in FIG. An electric field concentration point 32 occurs at the lower part of the boundary with 28. Since the electric field concentration point 32 is separated from the stress concentration point 31, breakdown is less likely to occur and the withstand voltage is higher than in the shotgun barrier diode having the structure shown in FIG. 1E.

[Third Example] In the shot barrier diode of the third example shown in FIG. Ti thin layer 24d, second titanium oxide thin layer 28b, second potential equalization Ti thin layer 24e, third
The titanium oxide thin layers 28c are sequentially arranged in a ring shape and are electrically connected to each other. Al for potential equalization on the Ti thin layers 24d and 24e
The layers 25b and 25c are formed by leaving a portion of the Al layer 25. That is, the Al layer 25 shown in FIG.
When photoetching, the Ti thin layer 24d in Fig. 7,
Al layers 25b and 25c remain corresponding to 24e, and are used as masks for preventing oxidation of the Ti thin layers 24d and 24e.

Ti thin layers 24d, 24e and Al layers 25b, 25
Since the annular region consisting of c has high conductivity, it can serve as an equipotential distribution region. As a result, it is possible to correct the non-uniformity of the potential distribution seen in a plan view on the surface of the n-type region 23, form a uniform depletion layer, and improve the breakdown voltage. Note that the Ti thin layers 24d, 24
Since e has higher conductivity than the titanium oxide thin layers 28a, 28b, and 28c, it exhibits the potential equalization effect even when it is alone, so the Al layers 25b and 25c may be removed. Alternatively, the equipotential region may be formed only by using a titanium oxide thin layer in the Ti thin layers 24d and 24e and a conductor provided in the portions corresponding to the Al layers 25b and 25c. Further, a p ⁺ -type region similar to a guard ring may be formed under the Ti thin layers 24d and 24e as an independent or auxiliary potential equalization region.
Furthermore, the equipotential regions may be provided in one layer or three or more layers.

[Fourth embodiment] The shotgun barrier diode shown in FIG.
Substantially similar to FIG. 6, a ring-shaped titanium oxide thin layer 28a, 28b and a Ti thin layer 24d are provided around a barrier metal electrode 27 consisting of an Al layer 25a and Ti thin layers 24a, 24c. , has a shorting electrode 33 connecting the second titanium oxide thin layer 28b and the n-type region 23. This shorting electrode 33 is made of Au
-A Ni (nickel) layer and an Au layer are sequentially stacked on a Ge alloy layer, and are in ohmic contact with an n-type region 23 made of GaAs.

When the short-circuit electrode 33 is provided in this way, the potential at the outer periphery of the titanium oxide thin layer 28b becomes substantially the same as that of the n-type region 23 when a reverse voltage is applied, so breakdown occurs at this outer periphery. do not. Therefore, the noise that occurs when the shot barrier diode of FIG. 1E operates in the region of FIG. 3 does not occur in the diode of FIG. 8. Since the periphery of the titanium oxide thin layer 28b is connected to the n-type region 23 by the electrode 33, current can flow therethrough relatively easily. Therefore, a current corresponding to the current in the area shown in FIG. be able to.

[Fifth Example] The shot barrier diode of the fifth example shown in FIG. It has thin layers 28d, 28e, 28f and ring-shaped potential equalizing Ti thin layers 24h, 24i.
Upper titanium oxide thin layer 28d, 28e, 28f
is obtained by oxidizing the Ti thin layer that was continuous with the Ti thin layers 24g, 24h, and 24i. The lower titanium oxide thin layer 28g is equal to the upper titanium oxide thin layer 2.
The thicknesses of 8d, 28e, and 28f are almost the same, but the degree of oxidation is different from that of the upper titanium oxide thin layer 28.
d, 28e, and 28f, the sheet resistance is greater than that of the upper titanium oxide thin layers 28d, 28e, and 28f. Therefore, the current passing through the upper titanium oxide thin layer 28d, the Ti thin layer 24h, the titanium oxide thin layer 28e, the Ti thin layer 24i, and the titanium oxide thin layer 28f is transferred to the lower titanium oxide thin layer 2.
8g, and the potential gradient is determined primarily by the upper layer. Since the lower titanium oxide thin layer 28g has a high barrier height _φB , it is possible to provide a shot barrier diode with a small saturation current Is.
In other words, the reverse current level in the regions , , , in FIG. 3 can be reduced.

Although a portion of the upper titanium oxide thin layer 28f is in contact with the n-type region 23, it may not be in contact therewith. In addition, the lower titanium oxide thin layer 28
Ti thin layers 24d and 24e for potential equalization as shown in FIGS. 7 and 8 may also be provided on the electrodes g. Also,
7 and 8 on the Ti thin layers 24h and 24i.
The Al layer may remain as shown in the figure.

[Sixth Embodiment] The shot barrier diode of the sixth embodiment shown in FIG. 10 has an electrode layer formed by vacuum evaporation on the barrier metal electrode 27 and the insulating layer 29 having the same structure as in FIG. 6. 34. This electrode layer 3
Since the peripheral edge portion 34a of No. 4 faces the n-type region 23 via the insulating layer 29 and the titanium oxide thin layer 28, it functions as a field plate. As a result, both the breakdown voltage improvement effect based on the titanium oxide thin layer 28 and the breakdown voltage improvement effect based on the field plate can be obtained. In addition, plasma CVD
Insulating layer 2 made of silicon oxide film formed by
In No. 9, no particular problem was observed in making the peripheral portion 34a of the electrode layer 34 function as a field plate.

[Seventh Example] The insulating layer 29 in the first to sixth examples is a silicon oxide film formed by plasma CVD. In order to confirm that the silicon oxide film formed by plasma CVD and the silicon oxide film formed by photoCVD have similar effects, the insulating layer 2 of the first to sixth embodiments was
A shotgun barrier diode corresponding to No. 9 was replaced with a silicon oxide film formed by photo-CVD. Note that the manufacturing method for the parts other than the insulating layer 29 is the same as in the first to sixth embodiments.

The optical CVD according to this embodiment is a method in which a raw material gas is irradiated with a high energy force (ultraviolet light, ultraviolet laser, etc.) to excite it, and a thin film, which is a reaction product of the raw material gas, is deposited on a substrate. . In this method, too, radicals are created by photoexcitation and chemical reactions are promoted, so thin films can be formed at significantly lower temperatures. Optical CVD is plasma CVD
Although the growth rate is significantly lower than that of plasma CVD, the temperature can be lowered even more than plasma CVD, and since almost no ions are generated, there is less damage to the substrate. Therefore, it is possible to obtain characteristics that are substantially equivalent to or better than those of a shotgun barrier diode having a silicon oxide film formed by plasma CVD.

Next, referring to the conceptual diagram of the ultraviolet-excited optical CVD apparatus in FIG.
I will explain the method in detail. A space 47 between the upper wall 45 and the lower window 46 of the envelope is filled with Si ₂ as a raw material gas.
A mixed gas of H ₆ (disilane) and N ₂ O (nitrous oxide) is introduced. Gas inflow amount (converted to 1 atm)
are Si ₂ H ₆ 2.5 cc/min and N ₂ O 50 cc/min.
The space 47 is maintained at a reduced pressure of 0.5 torr by exhaustion using a vacuum pump (not shown). Window section 46
is made of transparent quartz, and a 500W low-pressure mercury lamp 48 is placed below it. On the upper wall 45 there is a mark shown in Figure 1D.
The semiconductor substrate 21 in this state is attached and heated to 300° C. by a heater (not shown).
The source gas is irradiated with ultraviolet light 49 (1849 Å and 2537 Å spectral lines) emitted from a low-pressure mercury lamp 48 and excited to an active state. the result,
An insulating film 29 consisting of a silicon oxide film is deposited on the semiconductor substrate 21 . The thickness of the insulating film 29 at this stage was about 1000 Å after 1 hour of growth. You can make it thicker if you take more time, but
Here, approximately 600Å
An insulating film 29 was formed by overlapping a silicon oxide film with a thickness of about 1000 Å by photo-CVD. After that, the insulating film 2 is etched by photo-etching.
9 is removed, and the insulating film 29 is removed as shown in FIG. 1E.
was formed.

[Modifications] The present invention is not limited to the above-mentioned embodiments, but
For example, the following transformations are possible.

(1) The effective range of the sheet resistance of the titanium oxide thin layers 28, 28a to 28f varies depending on the semiconductor chip structure and size, but is from 10 kΩ/□ to
5000MΩ/□, preferably 10MΩ/□～
It should be selected as 1000MΩ/□.

(2) By increasing the width b of the titanium oxide thin layer to approximately 10 μm or more, the effect of improving the breakdown voltage appears;
It has been confirmed that the effect becomes more pronounced when the thickness is 30 μm or more. However, in order to increase the yield at which the specified withstand voltage can be obtained,
It is even more desirable to design the above. Width b
Even if the thickness is set to 500 μm or larger, a sufficient effect of improving the breakdown voltage can be obtained. Therefore, although there is no upper limit to the width b, even if the width b is set to 500 .mu.m or more, a proportional increase in breakdown voltage cannot be expected, and the problem arises that the semiconductor chip becomes larger. Therefore, it is desirable that the width b is in the range of 30 to 500 μm.

(3) The thickness of the Ti thin layer 24 in FIG.
The thickness should be 20 Å or more in consideration of oxidation temperature, oxidation time, etc. As for the upper limit, there is no limit as long as the above prescribed sheet resistance can be obtained, but when forming a titanium oxide thin layer by thermally oxidizing a Ti thin layer, the upper limit is 300 Å, taking into account the oxidation temperature and oxidation time.
It should be: If strong oxidation such as plasma oxidation is used, this upper limit can be further expanded.

(4) The oxidation temperature when oxidizing the Ti thin layer 24a to obtain the titanium oxide thin layer 28 is preferably 500°C or lower, and 380°C when using an Au-based electrode.
The following shall apply. The lower limit of the oxidation temperature is 200° C. or higher when thermal oxidation is used, but it can be lower than room temperature when plasma oxidation is used. The oxidation time is the thickness of the Ti thin layer 24,
The oxidation time varies depending on the oxidation temperature and oxidation atmosphere, but is preferably within the range of 5 seconds to 2 hours.

(5) It corresponds to the titanium oxide thin layers 28, 28a to 28g, and may be formed by vapor deposition or sputtering of titanium oxide.

(6) The Ti thin layer 24 and the titanium oxide thin layer 28 are In
It may also be one to which Sn or the like is added.

(7) If you want to further improve the withstand voltage and reverse surge resistance, you can also combine it with a guard ring consisting of a p ⁺ type region. Generally, when combined with a guard ring, there is a disadvantage in terms of high-speed response, but this disadvantage can be overcome by using the following structure. That is, to explain using the example of FIG. 6, the p ⁺ type region is formed at a position from the Ti thin layer 24c to the titanium oxide thin layer 28 corresponding to the electric field concentration point 32,
It is spaced apart from the Al layer 25a. If you do this,
Due to the resistance of the Ti thin layer 24c, forward current hardly flows into the p ⁺ type region, and high-speed response does not deteriorate. In this case, the titanium oxide thin layer 28 and the barrier metal electrode 27
Although no shot barrier is formed between the guard ring and the guard ring consisting of the p ⁺ type region, a depletion layer is formed based on the pn junction between the p ⁺ type region of the guard ring and the n type region 23 of the substrate 21, and this pn
The depletion layer of the titanium oxide thin layer 28, the barrier metal electrode 27, and the depletion layer are connected through the depletion layer of the junction, resulting in an effect of improving the breakdown voltage.

(8) It is also applicable to shot barrier semiconductor devices that use − group compounds such as InP (indium phosphide) or silicon instead of GaAs.

(9) When forming a shot barrier semiconductor device in an integrated circuit, a planar structure is used in which the n ⁺ -type region 22 is provided so as to surround the n-type region 23 in an island shape, and the ohmic electrode 26 is provided on the surface side of the n-type region 23 . It may also be a structure.

(10) The n-type region 23 and the n ⁺ -type region 22 can be replaced with a p-type region.

(11) The method of plasma CVD or photoCVD for forming the insulating film 29 made of a silicon oxide film is not limited to the method of the embodiment. For example, a plasma CVD method that generates optically excited plasma by irradiating a powerful ultraviolet laser can also be applied.

[Effects of the Invention] As described above, according to the present invention, by providing a thin layer of titanium oxide and a silicon oxide film formed by plasma CVD or photo-CVD, a high-voltage, high-speed, and highly reliable shot barrier semiconductor can be obtained. equipment can be provided. Further, by setting the sheet resistance of the thin layer to 10 kΩ/□ to 5000 MΩ/□, a high breakdown voltage can be effectively achieved.

[Brief explanation of the drawing]

1 is a cross-sectional view showing the shot barrier diode according to the first embodiment of the present invention in the order of manufacturing steps, FIG. 2 is a plan view showing the state shown in FIG. 1D, and FIG.
The figure is a reverse voltage-reverse current characteristic diagram of the shot barrier diode shown in Figure 1E, Figure 4 is a partially enlarged sectional view of the shot barrier diode schematically showing the depletion layer, and Figure 5 is a diagram showing the plasma CVD equipment. A cross-sectional view showing,
6 is a sectional view showing a shot barrier diode of the second embodiment, FIG. 7 is a sectional view of a shot barrier diode of the third embodiment, and FIG. 8 is a sectional view of a shot barrier diode of the fourth embodiment. 9 is a sectional view showing the shot barrier diode of the fifth embodiment, FIG. 10 is a sectional view showing the shot barrier diode of the sixth embodiment, and FIG. 11 is the light FIG. 2 is a cross-sectional view showing a CVD device. 22...n ⁺ type area, 23...n type area, 24
a... Ti thin layer, 25a... Al layer, 26... Ohmic electrode, 27... Barrier metal electrode, 28...
Titanium oxide thin layer, 29...insulating layer.

Claims (1)

[Scope of Claims] 1. a semiconductor region; a barrier metal electrode formed on the semiconductor region so as to be able to generate a shot barrier between the semiconductor region; and a barrier metal electrode formed on the semiconductor region so as to surround the barrier metal electrode. disposed on the semiconductor region, electrically connected to the barrier metal electrode, having a sheet resistance greater than the barrier metal electrode, and capable of creating a shot barrier between the semiconductor region and the semiconductor region. A shot protection barrier comprising: a thin layer of titanium oxide; and an insulating layer formed to cover the thin layer and made of a silicon oxide film formed by plasma CVD or photoCVD. Semiconductor equipment. 2 The thin layer has a sheet resistance of 10 kΩ/□~
2. The shot barrier semiconductor device according to claim 1, wherein the film is 5000 MΩ/□.