JPH07211924A - Schottky diode and its manufacture - Google Patents

Abstract

PURPOSE:To form a guard ring by self-alignment by forming a void between a Schottky metal and insulating film and a groove below the void and filling the void and groove with an insulator. CONSTITUTION:After etching an insulating film 4 with a hydrofluoric acid-based etchant from an opening 50 by using a photoresist 5 as a mask, a metallic layer 60 (Schottky metal 6) composed of titanium is formed. As a result, a void 7 is formed between the side wall of the insulating film 4 forming the opening 50 and that of the metallic 6 formed in the opening 50. Then a groove 8 is formed by performing reactive ion etching through the void 7 and a polyimide resin 90 is applied to the surface of the insulating film 4 until the surface of the resin 90 becomes flat so as to fill up the groove with the resin 90. The filling of the fine groove 8 with the resin 90 is performed in such a way that, after applying the resin 9, the periphery of the groove 8 is evacuated to a vacuum so as to remove air from the groove 8, and then, the periphery is returned to the atmospheric pressure. Then, the resin 90 is removed by oxygen ashing until the metal 6 is exposed. As a result, a guard ring 9 can be formed by using the resin 90 filling the groove 8 as an insulator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Schottky diode having a guard ring structure and a manufacturing method thereof.

[0002]

2. Description of the Related Art In order to precisely form a guard ring for improving the characteristics of a Schottky diode with respect to a Schottky electrode, a method of providing this by self-alignment is disclosed in JP-A-59-94462 and JP-A-58-66366. It is disclosed in Japanese Patent Publication No. In order to form a Schottky diode by the method shown here, thermal oxidation step 2 times, photolithography step 2 times, etching step 6 times, silicon nitride film forming step 1 time, ion implantation step 1 time, after ion implantation Heat treatment process 1 time, metal deposition process 3 times, post-deposition annealing (50
A total of 17 steps are required, one step at 0 ° C.

The heat treatment temperature after the above-mentioned ion implantation is usually required to be as high as 700 ° C. or higher. In the above literature, it is a Schottky diode using silicon. The case where this method is applied to the production of a GaAs Schottky diode which is superior in high frequency characteristics will be considered.

In the case of GaAs, since an oxide film is not formed by thermal oxidation, it is necessary to form it by the CVD method or the like. In this case, selective oxide film formation cannot be formed only in the opening portion as shown in FIG. 2 (d) of JP-A-59-94462. Therefore, in GaAs, the self-aligned process is interrupted here, and the self-aligned process cannot be performed. Further, since GaAs is decomposed at the high temperature required for the heat treatment after the ion implantation, it is necessary to form and remove the cap layer (silicon nitride film or the like) to prevent the decomposition. Therefore, this method further increases the number of steps.

Further, the ion implantation apparatus is a fairly large-scale apparatus and requires a large amount of cost for equipment. These points are problems in forming a self-aligned GaAs Schottky diode with a guard ring by the method shown in the related art.

A method has also been proposed in which the Schottky electrode itself is used as a mask and ion implantation is performed through a gap with the side-etched insulating film (JP-A-58-66366). Using this concept, the guard ring can be formed by self-alignment even in the case of GaAs. If the method of "implanting ions into the substrate through the gap of the side-etched insulating film using the Schottky electrode itself as a mask" is applied to GaAs, it will be as shown in FIG.

First, the oxide film 4 is formed on the n-GaAs 2 ((1) in FIG. 5), the resist 5 is patterned, and the opening 50 is formed.
Are formed ((2) in FIG. 5). Next, after etching (side etching) the oxide film 4 through the opening 50, an electrode metal is deposited ((3) in FIG. 5). Next, this is immersed in an organic solvent to remove unnecessary resist and unnecessary metal together with the resist by lift-off, and then ion implantation of impurities that form p-type through the voids 7 in the oxide film 4 and the Schottky electrode 6 (FIG. 5). (4)). Next, this is covered with a protective film for preventing GaAs decomposition and heat-treated to remove the protective film again ((5) in FIG. 5).

[0008]

According to this method, since the Schottky electrode is also used as a mask for ion implantation, the number of steps can be reduced as compared with the case of JP-A-59-94462. On the other hand, since the Schottky electrode is exposed to the heat treatment after ion implantation, a metal that does not change the Schottky characteristics even when exposed to a high temperature of 700 ° C. or higher is required. As such a metal, one having a high melting point such as molybdenum, tungsten, tantalum or tungsten silicide is known. However, when the refractory metal is vapor-deposited, since the heat radiation is large and the substrate temperature rises, there is a problem that the resist pattern forming the minute Schottky electrode collapses and the shape is deformed, or lift-off cannot be performed. Occur. Further, the problems associated with the ion implantation as described above still remain.

The present invention has been made to solve the above problems, and an object of the present invention is to improve the breakdown voltage of a Schottky diode and facilitate its manufacture.
Particularly, by forming the guard ring by self-alignment without performing the ion implantation that causes the high temperature process, the withstand voltage is improved and the manufacturing is facilitated.

Another object of the present invention is to facilitate the production of a GaAs Schottky diode by forming a guard ring at a low temperature.

[0011]

The structure of the invention for solving the above-mentioned problems is, in a Schottky diode formed by providing a metal forming a Schottky barrier on a semiconductor and an insulating film around the metal, a Schottky metal A void is formed between the insulating films, and an insulator is filled in the void and a groove formed under the void.

The invention of claim 2 is characterized in that the semiconductor is GaAs.

The invention of claim 3 is characterized in that the insulating material filled in the groove is made of resin.

Further, the invention of claim 4 is the invention of a manufacturing method, wherein in the method of manufacturing a Schottky diode comprising a Schottky metal forming a Schottky barrier on a semiconductor and an insulating film around the Schottky metal, An air gap is formed between the key metal and the insulating film by side etching of the insulating film, and the Schottky metal and the insulating film are used as a mask to pass through the air gap to form a groove in the semiconductor below the air gap. It is characterized in that the object is filled.

[0015]

In the present invention, the guard ring is
It is formed by a gap formed between the Schottky metal and the insulating film and an insulator filled in a groove formed under the gap. That is, the insulator is embedded in the semiconductor portion immediately below the peripheral portion of the Schottky metal that is directly joined to the semiconductor. Therefore, the insulating layer is provided immediately below the peripheral portion of the Schottky metal where the electric field strength is maximum, so that dielectric breakdown is prevented.

Since the high temperature heat treatment after the ion implantation is not required unlike the conventional case, the filling of the insulating material can be performed without heating the semiconductor substrate to a high temperature. As a result, it is particularly effective to use this structure for a GaAs Schottky diode which undergoes thermal decomposition when subjected to high temperature treatment. That is, since the heat treatment is not required, the steps of forming and removing the protective film against thermal decomposition are not required, which facilitates the manufacturing.

Further, by using a resin as the insulator to be filled in the groove, the filling process is facilitated and the filling process can be performed at a relatively low temperature. As a result, there is no need to use a refractory metal as the Schottky metal, the substrate does not reach a high temperature due to heat radiation during metal deposition, and the resist pattern is prevented from collapsing, so that a fine pattern is possible.

Further, in the invention of the manufacturing method, a void is formed between the Schottky metal and the insulating film by side etching of the insulating film, the Schottky metal and the insulating film are used as a mask to pass through the void, and a space below the void is formed. Since the method is to form a groove in a semiconductor and fill the groove and the void with an insulating material, the filling of the groove and the insulating material can be realized in a self-aligned manner using the Schottky metal as a mask. Becomes extremely easy.

[0019]

EXAMPLES The present invention will be described below based on specific examples. First Embodiment FIG. 1 and FIG. 2 show the manufacturing process of the Schottky diode of the present invention. First, as shown in (1) of FIG. 1, n ⁺ -GaAs doped with an impurity concentration of 2 × 10 ¹⁸ cm ^-3
N-Ga doped with an impurity concentration of 5 × 10 ¹⁶ cm ^-3 on the substrate 1
The As layer 2 is formed to a thickness of 1 μm. The impurity concentration of the n ⁺ -GaAs substrate 1 is preferably as high as possible in order to reduce the resistance.

The impurity concentration of the n-GaAs layer 2 depends on the required breakdown voltage. The theoretical breakdown voltage in the case of 5 × 10 ¹⁶ cm ⁻³ shown here is about 23 V, and the depletion layer width at this time is 0.8 μm. Here, the thickness is set to 1 μm with some allowance. The impurity concentration and the thickness of the n-GaAs layer 2 are appropriately determined according to the required breakdown voltage.

Next, on the back surface of the n ⁺ -GaAs substrate 1, Au
An ohmic electrode 3 made of -Ge / Ni / Au was formed by vapor deposition. Next, on the n-GaAs layer 2, an insulating film 4 made of a SiO ₂ film is formed.
Was formed to a thickness of 300 nm by, for example, the plasma CVD method. FIG. 1A shows the structure formed up to this step.

Next, as shown in FIG. 1B, the insulating film 4
Photoresist 5 was uniformly applied on the resist, exposed to a predetermined pattern, and then treated with monochlorobenzene and developed to form resist openings 50 having overhangs in the regions where Schottky electrodes were formed.

Next, as shown in FIG. 1C, the photoresist 50 is used as a mask to etch the insulating film 4 from the opening 50 using a hydrofluoric acid-based etching solution, and then the film is made of titanium by vacuum evaporation. The metal layer 60 was formed uniformly. The metal layer 60 directly bonded to the surface of the n-GaAs layer 2 in the opening 50 becomes the Schottky metal 6. The thickness of this Schottky metal 6 is 300 nm. Here, titanium is used as the Schottky metal 6, but any metal such as gold or aluminum that forms a Schottky junction may be used.

The hydrofluoric acid type etching solution etches the insulating film 4, but does not attack GaAs. By utilizing this property and lengthening the etching time, the etching proceeds only in the lateral direction, and the insulating film 4 below the edge portion of the resist 5 can be etched. As a result, a gap 7 is formed between the side wall of the insulating film 4 forming the opening 50 and the side wall of the Schottky metal 6 formed in the opening 50. As the etching liquid, other etching liquids can be used as long as they do not attack GaAs but etch the insulating film 4. Next, the metal layer 60 deposited on the photoresist 5 was removed by a lift-off method of removing the photoresist 5 using an organic solvent.

Next, as shown in FIG. 1 (4), a groove 8 having a depth of 900 nm was formed by reactive ion etching through the void 7. This etching is not limited to the dry method, but may be the wet method. Next, as shown in (5) of FIG. 1, the polyimide resin 9 was applied to the surface of the insulating film 4 and planarized, so that the groove 8 was filled with the polyimide resin 90. In order to fill the inside of the fine groove 8 with the resin 90, the surrounding air was evacuated after application of the resin to evacuate the inside air, and then the atmospheric pressure was returned to fill the inside of the fine groove 8. The resin 90 was cured at about 150 ° C.

Next, as shown in FIG. 1 (6), the resin 90 was removed by oxygen ashing until the Schottky metal 6 was exposed. As a result, the resin 9 filled in the groove 8
0 serves as a guard ring 9 as an insulator.

Next, as shown in FIG. 2, a wiring metal 12 made of gold was selectively formed on the Schottky metal 6, the guard ring 9 and a part of the insulating film 4 by a lift-off method. In this way, a Schottky diode was manufactured.

As described above, in the present invention, since the ion implantation is not used, the maximum temperature in the process after the formation of the Schottky metal 6 is 150 ° C. at the time of curing the resin 90, and at this temperature. If so, the characteristics will not be deteriorated without using a refractory metal for the Schottky metal 6.

Further, the number of steps here is the oxide film forming step 1
Times, photolithography process 2 times, etching process 3
11 steps including a metal vapor deposition step, a resin deposition step, and a resin thermosetting step, a total of 11 steps, which are more than the 17 steps of the conventional manufacturing method described in JP-A-59-94462. It turns out to be simple.

The function of this structure as a guard ring will be described below. In the structure without the guard ring shown in FIG. 6, the potential gradient becomes largest at the part of d ₂ where the width of the depletion layer is smallest, so that this part causes breakdown. However, in the Schottky diode of the present invention, since the resin 90 as an insulator is present in this d ₂ portion, it cannot serve as a current path, and breakdown at this portion can be prevented. This state is shown in FIG. The breakdown of this Schottky diode is shown in Fig. 3.
Of the depletion layer d ₁ , but the potential gradient here is smaller than the portion of d ₂ in FIG. 6, so that it does not break down to a higher voltage. That is, the breakdown voltage can be improved.

In this structure, as shown in, for example, Japanese Patent Laid-Open Nos. 59-94462 and 58-66366, the conventional guard ring has a polarity opposite to that of the semiconductor operation layer (for example, n-type). In contrast to being formed of a semiconductor (for example, p-type), the present invention is different in that the guard ring 9 is formed of a resin 90 which is an insulator.

Second Embodiment Next, a second embodiment of the present invention will be shown. The first embodiment has a vertical structure in which the ohmic electrode 3 is provided on the back side, whereas the present embodiment has a planar structure in which the ohmic electrode 3 and the Schottky electrode 6 are provided on the same surface, which is integrated. Suitable for conversion. This structure is shown in FIG.

The n ⁺ -GaAs layer 2 is formed on the semi-insulating GaAs substrate 21.
2 and the n-GaAs layer 2 are laminated. The n-GaAs layer 2 was removed by etching at the peripheral portion of this device, and the exposed n ⁺ -GaA
The ohmic electrode 3 is formed on the s layer 22. Further, in the central part, by the same method as the method shown in the first embodiment,
A guard ring 9 made of resin and a Schottky electrode 6 are formed. Since the formation of the ohmic electrode 3 requires heat treatment at about 350 ° C., it is performed before the formation of the Schottky electrode 6. Since the Schottky electrode 6 has the same structure as that of the first embodiment, the breakdown voltage is improved by the guard ring 9 which is an insulator.

[0034]

MODIFICATION OF THE INVENTION In the first and second embodiments described above,
Although the polyimide resin is used as the insulator filled in the groove 8, other thermosetting resin can be used. In the case of a thermosetting resin, it is easy to fill the groove 8 with an insulating material because it is hardened by a low temperature heat treatment after filling the groove 8. If a coating device is considered, a thermoplastic resin can also be used.
An oxide insulator such as SOG (spin on glass) may be used as the insulator other than the resin. The depth of the groove 8 may be deeper than the depth d ₁ of the depletion layer directly below the Schottky metal 6 as shown in FIG. Although the cross-sectional shape of the groove 8 is shown as a rectangle, it may be a triangle whose cross-sectional area decreases in the depth direction as in the case of wet etching. The present invention may be formed as an individual element of a Schottky diode or as an element on an integrated circuit. The present invention is effective in an integrated circuit because fine processing is possible. When the Schottky diode of the present invention is made of GaAs, it can be used as a rectifying element for receiving microwaves and converting the microwaves into energy. For example, in order to drive a micro robot arranged in a metal pipe, power is supplied by microwaves using the metal pipe as a waveguide, and the microwave is rectified by a Schottky diode to obtain a high voltage. To be According to the Schottky diode of the present invention, not only is it easy to manufacture, but also the breakdown voltage is improved, so that it can be used as a rectifying element that requires a high voltage.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a manufacturing process of a Schottky diode according to a first embodiment of the present invention.

2 is an explanatory view following the manufacturing process of the Schottky diode according to the first embodiment, following FIG. 1. FIG.

FIG. 3 is an explanatory view for explaining improvement of breakdown voltage of the Schottky diode according to the first embodiment.

FIG. 4 is an explanatory view showing the structure of a Schottky diode according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a process when the conventional method is applied to the manufacture of a GaAs Schottky diode.

FIG. 6 is an explanatory diagram illustrating the breakdown voltage of a conventional Schottky diode.

[Explanation of symbols]

1 ... n ⁺ -GaAs substrate 2 ... n-GaAs layer 3 ... Ohmic electrode 4 ... Insulating film 5 ... Photoresist 6 ... Schottky metal 7 ... Void 8 ... Groove 9 ... Guard ring 12 ... Wiring metal 50 ... Opening 90 ... Polyimide resin

Claims (4)

[Claims] 1. A Schottky diode comprising a Schottky metal forming a Schottky barrier on a semiconductor and an insulating film surrounding the Schottky metal, wherein a void is formed between the Schottky metal and the insulating film. A Schottky diode characterized in that an insulating material is filled in a groove formed in a lower portion of the void. 2. The Schottky diode according to claim 1, wherein the semiconductor is GaAs. 3. The Schottky diode according to claim 1, wherein the insulator filled in the groove is a resin. 4. A method of manufacturing a Schottky diode comprising a Schottky metal forming a Schottky barrier on a semiconductor and an insulating film surrounding the Schottky metal, wherein a gap is provided between the Schottky metal and the insulating film. And forming a groove in the semiconductor below the void through the void using the Schottky metal and the insulating film as a mask, and filling the trench and the void with an insulator. Schottky diode manufacturing method.