CN107799610A - A kind of Schottky diode and preparation method - Google Patents

Abstract

The invention provides a Schottky diode and a preparation method thereof. The Schottky diode includes: a metal layer; an N-type substrate located on the metal layer; an N-type epitaxial layer located on the N-type substrate; at least one The groove filled with the first metal is located on the first end face of the N-type epitaxial layer, and the first end face of the N-type epitaxial layer is the surface away from the end of the N-type substrate; the low-barrier metal layer composed of the second metal, Covering the first end face of the N-type epitaxial layer and the first metal in the trench; wherein, the potential barrier of the first metal is higher than the potential barrier of the second metal; the junction of the first metal and the N-type epitaxial layer is formed The first Schottky junction; the junction of the low barrier metal layer and the N-type epitaxial layer forms a second Schottky junction. The invention solves the problem that the Schottky diode has a relatively large leakage current and poor reverse blocking ability.

Description

A kind of Schottky diode and preparation method thereof

technical field

The invention relates to the technical field of semiconductors, in particular to a Schottky diode and a preparation method.

Background technique

Power diodes are key components of circuit systems, and are widely used in various advanced weapon control systems and instrumentation equipment such as high-frequency inverters, digital products, generators, televisions, and other civilian products, satellite receivers, missiles, and aircraft. . At present, power diodes are expanding in two important directions: (1) to tens of millions or even tens of thousands of amperes, which can be applied to high-temperature arc wind tunnels, resistance welding machines and other occasions; (2) reverse recovery time is getting shorter and shorter , showing the direction of ultra-fast, ultra-soft, and ultra-durable, so that it is not only used in rectification occasions, but also has different functions in various switching circuits.

In order to meet the application requirements of low power consumption, high frequency, high temperature, and miniaturization, the requirements for withstand voltage, on-resistance, turn-on voltage drop, reverse recovery characteristics, and high-temperature characteristics of power diodes are getting higher and higher.

Commonly used power diodes include ordinary rectifier diodes, Schottky diodes, and PIN diodes. Schottky diodes have been widely used because of their low on-state voltage drop and almost zero reverse recovery time. However, Schottky diodes have a large leakage current, that is, when the PN junction is off A very small current flows, and the reverse blocking ability is poor.

Contents of the invention

The invention provides a Schottky diode and a preparation method thereof, and aims to solve the problems that the Schottky diode has a large leakage current and poor reverse blocking ability.

In order to achieve the above object, an embodiment of the present invention provides a Schottky diode, the Schottky diode includes:

metal layer;

N-type substrate, located on the metal layer;

The N-type epitaxial layer is located on the N-type substrate;

At least one groove filled with the first metal is located on the first end face of the N-type epitaxial layer, and the first end face of the N-type epitaxial layer is the surface away from the end of the N-type substrate;

A low-barrier metal layer composed of a second metal covering the first end face of the N-type epitaxial layer and the first metal in the trench;

Wherein, the potential barrier of the first metal is higher than the potential barrier of the second metal;

A first Schottky junction is formed at the junction of the first metal and the N-type epitaxial layer; a second Schottky junction is formed at the junction of the low barrier metal layer and the N-type epitaxial layer.

Preferably, the first Schottky junctions are respectively located at the sidewall and the bottom of the trench.

Preferably, the thickness of the low-barrier metal layer is between 0.1 microns and 4 microns.

Preferably, the trench is filled with the first metal.

In order to achieve the above object, the present invention also provides a method for preparing a Schottky diode, comprising:

Fabricate an N-type epitaxial layer on an N-type substrate;

Making at least one groove on the first end face of the N-type epitaxial layer, the first end face of the N-type epitaxial layer is the surface away from the end of the N-type substrate;

filling the trench with a first metal and performing thermal annealing to form a first Schottky junction;

Cover the second metal on the first end surface of the N-type epitaxial layer and the first metal to form a low-barrier metal layer, and perform thermal annealing on the second metal, at the junction of the low-barrier metal layer and the N-type epitaxial layer forming a second Schottky junction; wherein the potential barrier of the first metal is higher than the potential barrier of the second metal;

On the N-type substrate, one end away from the N-type epitaxial layer is covered with a metal layer.

Preferably, the step of filling the trench with the first metal and performing thermal annealing includes:

filling the trench with the first metal;

Etching the first end face of the N-type epitaxial layer to remove the first metal on the surface;

Thermal annealing is performed on the first metal within the trench.

Preferably, the step of forming at least one trench on the first end face of the N-type epitaxial layer includes:

Using the photoresist as a mask, dry etching is performed on the first end face of the N-type epitaxial layer to form at least one groove.

Preferably, the first Schottky junctions are respectively located at the sidewall and the bottom of the trench.

Preferably, the thickness of the low-barrier metal layer is between 0.1 microns and 4 microns.

Above-mentioned scheme of the present invention comprises following beneficial effect at least:

The Schottky diode and the preparation method provided by the present invention form a high barrier Schottky junction at the sidewall and bottom of the trench, and form a low barrier Schottky junction at the junction of the low barrier metal layer and the N-type epitaxial layer Base junction, when the Schottky diode is forward-conducting, since the high-barrier Schottky junction is not turned on, the conduction current provided by it can be ignored, and the forward current is mainly conducted by the low-barrier Schottky junction; When the Schottky diode is reverse biased, because the high barrier Schottky junction in the trench has a suppressive effect on the electric field strength between the trenches, the electric field strength on the surface of the Schottky diode is reduced. value, which plays a role in suppressing the leakage current of the device and improves the reverse blocking ability of the device; the invention solves the problem that the Schottky diode has a relatively large leakage current and poor reverse blocking ability.

Description of drawings

Fig. 1 represents the schematic cross-sectional view of the Schottky diode that the first embodiment of the present invention provides;

Fig. 2 represents the basic step flowchart of the preparation method of the Schottky diode that the second embodiment of the present invention provides;

FIG. 3 shows one of the schematic diagrams of the manufacturing method of the Schottky diode provided by the second embodiment of the present invention;

FIG. 4 shows the second schematic diagram of the manufacturing method of the Schottky diode provided by the second embodiment of the present invention;

FIG. 5 shows the third schematic diagram of the manufacturing method of the Schottky diode provided by the second embodiment of the present invention;

FIG. 6 shows the fourth schematic diagram of the manufacturing method of the Schottky diode provided by the second embodiment of the present invention;

FIG. 7 shows the fifth schematic diagram of the manufacturing method of the Schottky diode provided by the second embodiment of the present invention.

Explanation of reference signs:

1. Metal layer; 2. N-type substrate; 3. N-type epitaxial layer; 4. Trench; 5. Low barrier metal layer.

Detailed ways

In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will describe in detail with reference to the drawings and specific embodiments.

Aiming at the existing problems, the invention provides a Schottky diode and a preparation method. Among them, the Schottky Barrier Diode (SBD) is a diode made of the metal-semiconductor junction principle formed by the contact between the metal and the semiconductor. Therefore, the SBD is also called a metal-semiconductor diode or a surface barrier diode. carrier diode.

first embodiment

Referring to Fig. 1, the first embodiment of the present invention provides a Schottky diode, comprising:

Metal layer 1; wherein, the metal layer 1 is located at the bottom of the Schottky diode.

N-type substrate 2, located on the metal layer 1;

The N-type epitaxial layer 3 is located on the N-type substrate 2 ; wherein, the N-type epitaxial layer 3 is formed by doping ions on the N-type substrate 2 .

At least one groove 4 filled with the first metal is located on the first end face of the N-type epitaxial layer 3, and the first end face of the N-type epitaxial layer 3 is the surface away from the end of the N-type substrate 2; wherein, in FIG. 1 Taking three trenches 4 as an example, the trenches 4 are located on the surface of the end of the N-type epitaxial layer 3 away from the N-type substrate 2 , and the trenches 4 are filled with the first metal.

The low-barrier metal layer 5 made of the second metal covers the first end surface of the N-type epitaxial layer 3 and the first metal in the trench 4; Both the end face and the first metal in the trench 4 are in contact.

Among them, the potential barrier of the first metal is higher than the potential barrier of the second metal; among them, the potential barrier is the space region where the potential energy is higher than that of the nearby potential energy, and the potential barrier formed by the space region where the first metal is located is higher than that of the first metal. The potential barrier formed by the space region.

The junction of the first metal and the N-type epitaxial layer 3 forms a first Schottky junction; wherein, the first Schottky junction is a high-barrier Schottky junction, and the first Schottky junctions are respectively located on the sides of the trench 4 At the wall and the bottom, the high barrier Schottky junction determines the reverse characteristics of the Schottky diode, which can inhibit the electric field intensity between the trenches 4, thereby reducing the electric field intensity value on the surface of the Schottky diode , reducing the on-state voltage drop.

The junction of the low barrier metal layer 5 and the N-type epitaxial layer 3 forms a second Schottky junction, the second Schottky junction is a low barrier Schottky junction, and the low barrier Schottky junction determines the Schottky junction. The forward characteristics of the diode, when the Schottky diode is forward-conducting, since the high-barrier Schottky junction is not turned on, the conduction current provided by it can be ignored, and the forward current is mainly carried by the low-barrier Schottky junction conduction.

Preferably, the thickness of the low-barrier metal layer 5 is between 0.1 microns and 4 microns. It can be understood that the optimal thickness range of the low barrier metal layer 5 is 0.1 micron-4 microns, and other thicknesses are also possible.

Preferably, the trench 4 is filled with the first metal to ensure the formation of a high barrier Schottky junction.

In the above embodiments of the present invention, a high barrier Schottky junction is formed at the sidewall and bottom of the trench 4, and a low barrier Schottky junction is formed at the junction of the low barrier metal layer 5 and the N-type epitaxial layer 3. Junction, when the Schottky diode is forward-conducting, since the high-barrier Schottky junction is not turned on, the conduction current provided by it can be ignored, and the forward current is mainly conducted by the low-barrier Schottky junction; and When the Schottky diode is reverse biased, because the high barrier Schottky junction in the trench 4 has a suppressive effect on the electric field intensity between the trenches 4, thereby reducing the electric field on the surface of the Schottky diode The strength value plays a role in suppressing the leakage current of the device and improves the reverse blocking ability of the device; the invention solves the problem that the Schottky diode has a relatively large leakage current and the reverse blocking ability is poor.

second embodiment

Referring to Fig. 2, the second embodiment of the present invention provides a method for preparing a Schottky diode, comprising:

Step 201 , fabricating an N-type epitaxial layer 3 on an N-type substrate 2 .

Optionally, as shown in FIG. 3 , the N-type epitaxial layer 3 can be formed by ion diffusion.

Step 202 , making at least one trench 4 on the first end surface of the N-type epitaxial layer 3 , the first end surface of the N-type epitaxial layer 3 being the surface away from the end of the N-type substrate 2 .

Preferably, step 202 includes:

Using photoresist as a mask, dry etching is performed on the first end surface of the N-type epitaxial layer 3 to form at least one trench 4 .

Specifically, photoresist is a light-sensitive mixed liquid composed of three main components: photosensitive resin, sensitizer (see spectral sensitizing dye) and solvent. Using photoresist as a mask, dry etching etch to form grooves 4 on the surface of the silicon wafer, as shown in FIG. 4 .

Step 203 , filling the first metal in the trench 4 and performing thermal annealing to form a first Schottky junction.

Preferably, the first Schottky junctions are respectively located at the sidewall and the bottom of the trench 4 . Wherein, the first Schottky junction is a high-barrier Schottky junction, and the high-barrier Schottky junction determines the reverse characteristics of the Schottky diode, which can inhibit the electric field intensity between the trenches 4, thereby The value of the electric field intensity on the surface of the Schottky diode is reduced, and the on-state voltage drop is reduced.

As shown in FIG. 5 , the trench 4 is filled with the first metal. In order to ensure that the first metal fills the trench 4 , the first metal should cover the first end surface of the N-type epitaxial layer 3 .

Preferably, step 203 includes:

filling the trench 4 with the first metal;

Etching the first end face of the N-type epitaxial layer 3 to remove the first metal on the surface;

Thermal annealing is performed on the first metal in the trench 4 .

Wherein, after the trench 4 is filled with the first metal, etching is first performed to remove the first metal of the N-type epitaxial layer 3, and the first metal in the trench 4 is retained; then thermal annealing is performed, heated to an appropriate temperature, and Maintain a certain heat preservation time, and then slowly cool down, so that the internal structure of the first metal reaches or approaches the equilibrium state, and a high barrier Schottky junction is formed on the side wall and bottom of the trench 4 .

Step 204, cover the second metal on the first end surface of the N-type epitaxial layer 3 and the first metal to form the low barrier metal layer 5, and perform thermal annealing on the second metal, and form the low barrier metal layer 5 and the N The junction of the type epitaxial layer 3 forms a second Schottky junction; wherein, the potential barrier of the first metal is higher than the potential barrier of the second metal.

Among them, the second Schottky junction is a low-barrier Schottky junction, and the low-barrier Schottky junction determines the forward characteristics of the Schottky diode. When the Schottky diode is conducting forward, due to the high barrier The Schottky junction is not turned on, and the conduction current provided by it can be ignored, and the forward current is mainly conducted by the low barrier Schottky junction.

As shown in FIG. 6, the first end surface of the N-type epitaxial layer 3 and the first metal are covered with a second metal to form a low barrier metal layer 5, and the second metal is heated to an appropriate temperature by thermal annealing and maintained at a certain temperature. the holding time, and then slowly cool, so that the internal structure of the second metal reaches or approaches the equilibrium state, and the second Schottky junction is formed at the junction of the low barrier metal layer 5 and the N-type epitaxial layer 3, and the first metal The potential barrier is higher than that of the second metal.

Step 205 , covering the end of the N-type substrate 2 away from the N-type epitaxial layer 3 with the metal layer 1 .

As shown in Figure 7; preferably, the thickness of the low-barrier metal layer 5 is between 0.1 micron-4 microns, it can be understood that the optimal thickness range of the low-barrier metal layer 5 when 0.1 micron-4 microns is also But other thicknesses.

In the above embodiments of the present invention, a high barrier Schottky junction is formed at the sidewall and bottom of the trench 4, and a low barrier Schottky junction is formed at the junction of the low barrier metal layer 5 and the N-type epitaxial layer 3. Base junction, when the Schottky diode is forward-conducting, since the high-barrier Schottky junction is not turned on, the conduction current provided by it can be ignored, and the forward current is mainly conducted by the low-barrier Schottky junction; When the Schottky diode is reverse biased, because the high potential barrier Schottky junction in the trench 4 has an inhibitory effect on the electric field intensity between the trenches 4, thereby reducing the surface of the Schottky diode. The electric field strength value plays a role in suppressing the leakage current of the device and improves the reverse blocking ability of the device; the invention solves the problem that the Schottky diode has a relatively large leakage current and the reverse blocking ability is poor.

The above description is a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (9)

1. A kind of 1. Schottky diode, it is characterised in that including：

   Metal level；

   N-type substrate, on the metal level；

   N-type epitaxy layer, on the N-type substrate；

   At least one groove for being filled with the first metal, positioned at the first end face of the N-type epitaxy layer, the N-type epitaxy layer First end face is the surface of one end away from the N-type substrate；

   The low barrier metal layer being made up of the second metal, is covered in the first end face and the groove of the N-type epitaxy layer First metal on；

   Wherein, the potential barrier of first metal is higher than the bimetallic potential barrier；

   First metal and the intersection of the N-type epitaxy layer form the first schottky junction；The low barrier metal layer and institute The intersection for stating N-type epitaxy layer forms the second schottky junction.
2. 2. Schottky diode according to claim 1, it is characterised in that first schottky junction is respectively positioned at described At the side wall of groove and bottom.
3. 3. Schottky diode according to claim 1, it is characterised in that the thickness of the low barrier metal layer is 0.1 Between -4 microns of micron.
4. 4. Schottky diode according to claim 1, it is characterised in that the groove is full of first metal.
5. A kind of 5. preparation method of Schottky diode, it is characterised in that including：

   N-type epitaxy layer is made in N-type substrate；

   At least one groove is made in the first end face of the N-type epitaxy layer, the first end face of the N-type epitaxy layer is away from institute State the surface of one end of N-type substrate；

   The first metal is filled in the groove and carries out thermal annealing, forms the first schottky junction；

   The second metal is covered on the first end face of the N-type epitaxy layer and first metal, forms low barrier metal Layer, and thermal annealing is carried out to second metal, the is formed in the intersection of the low barrier metal layer and the N-type epitaxy layer Two schottky junctions；Wherein, the potential barrier of first metal is higher than the bimetallic potential barrier；

   One end covering metal level away from the N-type epitaxy layer in the N-type substrate.
6. 6. the preparation method of Schottky diode according to claim 5, it is characterised in that described to be filled out in the groove The step of filling the first metal and carrying out thermal annealing, including：

   Full first metal is filled in the groove；

   The first end face of the N-type epitaxy layer is performed etching, removes first metal on surface；

   Thermal annealing is carried out to first metal in the groove.
7. 7. the preparation method of Schottky diode according to claim 5, it is characterised in that described in the N-type extension The first end face of layer makes the step of at least one groove, including：

   Using photoresist as mask, dry etching is carried out in the first end face of the N-type epitaxy layer, makes at least one ditch Groove.
8. 8. the preparation method of Schottky diode according to claim 5, it is characterised in that first schottky junction point Not Wei Yu the groove side wall and bottom at.
9. 9. the preparation method of Schottky diode according to claim 5, it is characterised in that the low barrier metal layer Thickness is between 0.1 micron -4 microns.