KR102329192B1 - Silicon carbide shottky diode forward chracteristic is improved and manufacturing method thereof - Google Patents

Abstract

The present invention provides a silicon carbide Schottky diode with improved forward characteristics and a method for manufacturing the same, comprising: forming a metal layer in which a Schottky metal layer-diffusion barrier metal layer-pad metal layer is laminated on an epitaxial layer; etching the metal layer; It is a technical gist to include the step of heat-treating the etched metal layer. Thereby, the diffusion barrier metal layer is formed between the pad metal layer and the Schottky metal layer, thereby preventing the Schottky metal layer from penetrating into the pad metal layer during heat treatment. In addition, it is possible to reduce the interfacial resistance and improve the Schottky bonding properties through high-temperature heat treatment.

Description

Silicon carbide shottky diode forward chracteristic is improved and manufacturing method thereof

The present invention relates to a silicon carbide Schottky diode with improved forward characteristics and a method for manufacturing the same, and more particularly, it prevents the Schottky metal layer from penetrating into the pad metal layer during heat treatment, reduces the interface resistance through high temperature heat treatment, and Schottky The present invention relates to a silicon carbide Schottky diode having improved junction characteristics and improved forward characteristics, and a method for manufacturing the same.

A Schottky diode is a semiconductor device formed by using a junction between a metal and a semiconductor. When a voltage is supplied to a metal (+) and a semiconductor (-), electrons are injected from the semiconductor. Since the Schottky diode uses only electrons with a large number of carriers, the reverse maximum current is smaller and the reverse recovery time is shorter than the PN structure diode that uses both electron-holes as carriers. Have. Despite these advantages, it was not easy to manufacture a Schottky diode having a breakdown voltage of more than 200V because the Schottky diode was made of silicon as a power semiconductor in the existing power system. To this end, due to the development of 4H-silicon carbide (4H-SiC) material technology, which has a bandgap 3 times and a critical electric field strength 10 times larger than that of silicon, 4H-SiC Schottky diodes to which it is applied have been commercialized and power system. is being used in

1 is a schematic diagram of a conventional diode used in the field of power electronics as an electrical equivalent model. A diode can be expressed by an ideal diode (D) and a series resistance component (R _{s ) present inside and outside the diode.} In small-signal models other than power electronics, the series resistance component can be neglected, but in power electronics applications dealing with large currents, the series resistance component directly affects the forward loss. In particular, since the ideal diode current is exponentially affected by the voltage drop applied to the anode and the anode, the current magnitude is also exponentially affected by a small change in the series resistance component. .

2 is a graph showing the current-voltage characteristic with respect to the change in the magnitude of the series resistance component, and shows the current-voltage characteristic of an ideal diode having a series resistance component of 0Ω, and the current-voltage characteristic when the series resistance component is 0.01Ω and 0.05Ω. If the rating of the diode is 10A, when the series resistance component is 0Ω, 0.01Ω and 0.05Ω, respectively, the forward voltage drop of the diode becomes 1V, 1,1V, and 1.5V, respectively. If this is converted into diode forward loss, it means that the voltage of a diode with a series resistance component of 0.05Ω is increased by 50% compared to an ideal diode. Therefore, in order to reduce the loss of the diode, the series resistance must be reduced.

FIG. 3 shows the structure of a conventional 4H-SiC Schottky diode 10 and the resistance of the parasitic series component present inside the Schottky diode 10. As shown in FIG. In the structure of the Schottky diode 10 , an n-type substrate 11 and an n-type epitaxial layer 12 for withstanding a breakdown voltage are formed on the n-type substrate 11 . A Schottky metal layer 13 for forming a Schottky junction and a pad metal layer 14 for wire bonding are sequentially stacked on the n-type epitaxial layer 12 . Here, a p-type junction is constituted. In the p-type junction, a termination structure 15 is formed on the n-type epitaxial layer 12 to prevent electric field concentration occurring at the edge of the metal electrode, and the frame and contact resistance are lowered for the package. An ohmic bonding layer 16 is stacked under the n-type substrate 11 so as to In addition to this, a junction barrier structure in which a p-type junction is inserted under the Schottky metal layer 13 may be included in order to reduce leakage current, which is the biggest drawback of the Schottky diode. The series resistance component formed in such a Schottky diode includes the Schottky metal layer 13, the pad metal layer 14 and the resistive components 21 and 22 by their interfaces, and the n-type epitaxial layer 12 for supporting the breakdown voltage. ), the resistive component 24 of the n-type substrate 11, is formed Among these resistive components, the remaining resistive components 23, 24, 25 except for the Schottky metal layer 13, the pad metal layer 14, and the resistive components 21 and 22 formed by their interfaces are the n-type substrate 11 and the n-type substrate 11 and the n-type substrate. It is determined by the selection of the type epitaxial layer 12 and the manufacturing process of the ohmic layer 16 .

In the conventional Schottky diode 10 , the upper metal layer is mainly composed of a Schottky metal layer 13 and a pad metal layer 14 . In the process of manufacturing such a Schottky diode 10, a Schottky metal layer 13 is laminated on top of the epitaxial layer 12, and then heat treatment is performed to improve the Schottky bonding characteristics, and then the pad metal layer 14 ) are stacked. This is because the melting point of aluminum (Al), which is mainly used as the pad metal layer 14, is low, and when heat treatment is performed after laminating the pad metal layer 14, the molten aluminum penetrates the Schottky metal layer 13 and the epi layer 12. This is to prevent the formation of a direct junction with

However, if the pad metal layer 14 is laminated after the Schottky metal layer 13 is heat treated in this way, the Schottky metal layer 13 may be oxidized in the process of laminating the pad metal layer 14, and the metal layer due to the intervention of foreign substances. (13, 14) The resistance of the interface may increase. In addition, the resistance may vary depending on the quality of the pad metal layer 14. In particular, in the case of a deposition condition in which the grain boundary of the pad metal layer 14 is small, the resistance may increase, and the final result due to the metal layer and the interface resistance. Therefore, there is a problem that the series resistance component may increase.

US 0237608 US 0327017

Therefore, it is an object of the present invention to form a diffusion barrier metal layer between the pad metal layer and the Schottky metal layer to provide a 4H-silicon carbide Schottky diode with improved forward properties for preventing the Schottky metal layer from penetrating into the pad metal layer during heat treatment and a method for manufacturing the same will provide

Another object of the present invention is to provide a 4H-silicon carbide Schottky diode with improved forward characteristics, which reduces the interface resistance through high-temperature heat treatment and improves the Schottky junction characteristics, and a method for manufacturing the same.

The above object comprises the steps of: forming a metal layer in which a Schottky metal layer-diffusion barrier metal layer-pad metal layer is laminated on the epitaxial layer; etching the metal layer; It is achieved by a method of manufacturing a silicon carbide Schottky diode with improved forward characteristics, characterized in that it comprises the step of heat-treating the etched metal layer.

Here, the diffusion barrier metal layer is formed of a metal material or a conductive ceramic material having a melting point of 1000° C. or higher, and the metal material is tungsten (W), nichrome (NiCr), tantalum (Ta), hafnium (Hf), and vanadium (V). ) and mixtures thereof, and the conductive ceramic material is preferably selected from the group consisting of tantalum nitride (TaN), titanium nitride (TiN), titanium tungsten (TiW), and mixtures thereof.

In addition, the heat treatment step is preferably made at 400 to 600 ℃.

The above object is also a Schottky metal layer-a silicon carbide Schottky diode including a pad metal layer, wherein a diffusion barrier metal layer is formed between the Schottky metal layer and the pad metal layer. Silicon carbide Schottky with improved forward characteristics This is also achieved by diodes.

According to the above-described configuration of the present invention, the diffusion barrier metal layer is formed between the pad metal layer and the Schottky metal layer to prevent the Schottky metal layer from penetrating into the pad metal layer during heat treatment.

In addition, it is possible to reduce the interfacial resistance and improve the Schottky bonding properties through high-temperature heat treatment.

1 is an electrical equivalent model of a power diode composed of an ideal diode and a series resistance component,
2 is a graph showing the forward current and voltage characteristics of the diode according to the change in the magnitude of the series resistance component;
3 is a cross-sectional view of a conventional diode in which an equivalent model of parasitic components is displayed;
4 is a flowchart of a method for manufacturing a Schottky diode according to the present invention;
5 is a cross-sectional view of a Schottky diode according to the present invention;
6 is a flowchart showing the manufacturing steps of FIG. 5,
7 is a graph showing the resistance of the Schottky diode according to the heat treatment temperature.

Hereinafter, a method for manufacturing a 4H-silicon carbide (4H-SiC) Schottky diode with improved forward characteristics according to an embodiment of the present invention will be described in detail with reference to the drawings. In some cases, a Schottky diode may be manufactured by using 6H-SiC and 3C-SiC in addition to 4H-SiC.

4 to 6 , first, a p-type semiconductor 120 is formed on the epitaxial layer 110 ( S1 ).

The 4H-SiC Schottky diode 100 includes an n-type substrate 130 and an epitaxial layer 110 formed on the n-type substrate 130 . In order to implement a termination structure in the epitaxial layer 110 , an ion implantation mask 200 having a desired termination structure pattern is disposed on the epitaxial layer 110 as shown in FIG. 6A . Thereafter, ion impurities are implanted into the epitaxial layer 110 using ion implantation to form the p-type semiconductor 120 having a terminal structure. Since most 4H-SiC Schottky diodes 100 are manufactured in the n-type epitaxial layer 110 , the termination structure is composed of the p-type semiconductor 120 having the opposite polarity to the epitaxial layer 110 . desirable.

Here, the thickness and concentration of the epitaxial layer 110 and the depth, concentration, and spacing between the rings of the p-type semiconductor 120 have an absolute influence on the breakdown voltage of the device, and therefore, it should be appropriately designed to suit them. However, since the p-type semiconductor 120 greatly affects the breakdown characteristic of the Schottky diode 100, it is necessary to inject more than a specific concentration, and it is preferable to ^{doping with 5×10 18} cm ^-3 or more. If necessary, an ohmic junction layer 140 may be formed under the high-concentration n-type substrate 130 stacked together with the EPIC layer 110 as shown in FIG. 6B .

A Schottky metal layer 150-diffusion barrier metal layer 160-pad metal layer 170 is formed on the epitaxial layer 110 (S2).

As shown in FIG. 6c , a Schottky metal layer 150 is deposited on the epitaxial layer 110 on which the p-type semiconductor 120 is formed to form a Schottky junction, and a diffusion barrier is formed on the Schottky metal layer 150 . A metal layer 160 and a pad metal layer 170 are formed. The diffusion barrier metal layer 160 is laminated on top of the Schottky metal layer 150 to improve the Schottky bonding characteristics, and heat treatment is performed to reduce the resistance between the pad metal layer 170 and the Schottky metal layer 150 that are subsequently laminated. In this case, it is possible to prevent diffusion of the pad metal layer 170 . When the schottky metal layer 150 and the pad metal layer 170 are laminated in a state in which the diffusion barrier metal layer 160 is not formed and then heat treatment is performed, the pad metal layer 170 is diffused into the schottky metal layer 150. problems will arise.

In general, the pad metal layer 170 mainly uses aluminum (Al) because it has a low melting point and exhibits excellent ohmic properties even at a low temperature. In particular, when the p-type semiconductor 120 having a terminal structure is formed through aluminum implantation, lattice defects exist and exhibit ohmic characteristics even at a low temperature, which is advantageous for forming an ohmic junction. However, since aluminum has a low melting point, the pad metal layer 170 is diffused into the Schottky metal layer 150 when heat treatment is performed after being directly laminated on the Schottky metal layer 150 . In order to solve this problem, conventionally, a method of laminating the pad metal layer 170 after heat-treating the Schottky metal layer 150 is also used. Since this is high, there exists a possibility that the interface resistance may increase. Therefore, in order to prevent this, the diffusion barrier metal layer 160 is laminated between the Schottky metal layer 150 and the pad metal layer 170 .

Here, the Schottky metal layer 150 uses a material selected from the group consisting of titanium (Ti), platinum (Pt), nickel (Ni), molybdenum (Mo), and mixtures thereof, and other metals or alloys other than this are also available. . In addition, the diffusion barrier metal layer 160 is a metal having a high melting point using a material selected from the group consisting of tungsten (W), nichrome (NiCr), tantalum (Ta), hafnium (Hf), vanadium (V), and mixtures thereof; It is preferable to use a conductive ceramic selected from the group consisting of tantalum nitride (TaN), titanium nitride (TiN), titanium tungsten (TiW), and mixtures thereof. That is, the melting point of the diffusion barrier metal layer 160 is preferably 1000° C. or higher. This is to prevent the diffusion barrier metal layer 160 from melting and penetrating into the Schottky metal layer 150 when heat treatment is performed at a high temperature.

The metal layers 150 , 160 , and 170 are etched using the photoresist 300 ( S3 ).

A positive photoresist 300 is laminated on the Schottky metal layer 150 - the diffusion barrier metal layer 160 - the pad metal layer 170 in an area not to be etched as shown in FIG. 6C. Thereafter, light is applied to etch regions of the metal layers 150 , 160 , and 170 except for regions where the positive photoresist 300 is stacked. Here, both dry etching and wet etching are possible, but wet etching is more preferable.

A heat treatment is performed on the metal layers 150 , 160 , and 170 ( S4 ).

As shown in FIG. 6D , a process of applying heat to the Schottky metal layer 150 - the diffusion barrier metal layer 160 - the pad metal layer 170 is performed. The heat treatment process improves the Schottky bonding characteristics and the interfacial characteristics of the metal layers 150 , 160 , and 170 , and increases the grain boundary of the metal layers 150 , 160 , 170 to lower the series resistance. Therefore, it is desirable to increase the crystal boundary to lower the resistance.

At this time, the heat treatment temperature is suitable for the pad metal layer 170 to penetrate the Schottky metal layer 150 and to 400 to 600° C. in which a spike that forms a junction with the epitaxial layer 110 does not occur and the Schottky bonding characteristic does not deteriorate. . When the expansion barrier metal layer 160 is not present, it is not recommended to heat treatment at 400° C. or higher due to the low melting point of aluminum, which is the generally used pad metal layer 170 . However, in the present invention, since the expansion barrier metal layer 160 is present, it is possible to heat treatment at 400° C. or higher, and depending on the type of the diffusion barrier metal layer 160 or if the thickness is increased, it is expected that 600° C. or higher is possible. However, when the heat treatment temperature is too high, as mentioned above, there is a possibility that the Schottky bonding characteristics may be deteriorated, so 400 to 600° C. is most preferable. A more preferable temperature is 450 to 550° C., which is less likely to deteriorate the Schottky junction characteristics, and can lower the series resistance component without causing spikes. Such heat treatment may be performed in an argon (Ar), nitrogen (N ₂ ), or hydrogen (H ₂ ) atmosphere, and may be performed under other atmospheres in addition to this.

A passivation layer 180 is formed on the top of the Schottky diode 100 (S5).

As shown in FIG. 6E , passivation is performed by forming the passivation layer 180 on the top of the Schottky diode 100 in order to protect the characteristics of the Schottky diode 100 . Such a step may be formed before step S4 if the passivation layer 180 is not deteriorated by the heat treatment temperature of step S4. If the passivation layer 180 is a polymer-based polyimide (Polyimide), benzocyclobutene (BCB), silicon rubber (Si rubber), etc., when heat of 300 ° C or higher is applied, the properties may deteriorate, so in step S5 The passivation layer 180 is formed, and in the case of a silicon dioxide film or a silicon nitride film, heat treatment may be performed after being formed before step S4. When a silicon oxide film or a silicon nitride film is used as the passivation layer 180, heat treatment can be performed after the passivation, so that thermal stability can be secured and defect healing can be performed at the same time, which is more preferable.

7 shows the series resistance characteristics with respect to the heat treatment temperature of the Schottky diode 100 manufactured through steps S1 to S5. This can be confirmed through the graph. As-dep indicates no heat treatment, and it can be seen that as the heat treatment temperature increases, the dispersion decreases and the average and median values of series resistance decrease compared to when no heat treatment is performed. In particular, it can be seen that the series resistance is reduced by 50% in the case of heat treatment at 550 °C compared to the temperature without heat treatment.

Conventional Schottky diodes heat-treat the Schottky metal layer to improve the Schottky junction characteristics. When the pad metal layer is formed after the Schottky metal layer is heat-treated, there is a risk that foreign substances may be inserted into the metal layer interface or the Schottky metal layer may be oxidized. . In addition, when heat treatment is performed after laminating the Schottky metal layer and the pad metal layer, there is a problem in that the pad metal layer is impregnated into the Schottky metal layer. Therefore, even after heat treatment, it could not be done at high temperature. To this end, in the present invention, a diffusion barrier metal layer 160 is formed between the Schottky metal layer 150 and the pad metal layer 170, and the Schottky metal layer 150-diffusion barrier metal layer 160-pad metal layer 170 is formed. Even after sequential lamination and heat treatment at high temperature, the pad metal layer 170 was not impregnated into the Schottky metal layer 150 . In addition, it was confirmed that the performance of the Schottky diode 100 was improved by reducing the resistance due to the heat treatment at a high temperature.

10, 100: Schottky diode
11, 130: n-type substrate
12, 110: epi layer
13, 150: Schottky metal layer
14, 170: pad metal layer
15: longitudinal structure
16, 140: ohmic bonding layer
21, 22, 23, 24, 25: resistant component
120: p-type semiconductor
160: diffusion barrier metal layer
180: passivation layer
200: ion implantation mask
300: photoresist

Claims (8)

In the method for manufacturing a silicon carbide Schottky diode with improved forward characteristics,
depositing a Schottky metal layer on top of the epitaxial layer;
depositing a diffusion barrier metal layer on the Schottky metal layer;
depositing a pad metal layer on the diffusion barrier metal layer;
etching the metal layer formed by laminating the Schottky metal layer, the diffusion barrier metal layer, and the pad metal layer; and
Including; heat-treating the etched metal layer;
In the heat treatment step, the silicon carbide Schottky diode manufacturing method with improved forward characteristics, characterized in that the crystal boundary of the metal layer increases. The method of claim 1,
The diffusion barrier metal layer is a silicon carbide Schottky diode manufacturing method with improved forward characteristics, characterized in that the melting point is formed of a metal material or a conductive ceramic material of 1000 ℃ or more. 3. The method of claim 2,
The metal material is silicon carbide Schottky with improved forward properties, characterized in that it is selected from the group consisting of tungsten (W), nichrome (NiCr), tantalum (Ta), hafnium (Hf), vanadium (V), and mixtures thereof. Diode manufacturing method. 3. The method of claim 2,
The conductive ceramic material is a silicon carbide Schottky diode manufacturing method with improved forward characteristics, characterized in that selected from the group consisting of tantalum nitride (TaN), titanium nitride (TiN), titanium tungsten (TiW), and mixtures thereof. The method of claim 1,
The heat treatment step is a silicon carbide Schottky diode manufacturing method with improved forward characteristics, characterized in that made at 400 to 600 ℃. The method of claim 1,
A method of manufacturing a silicon carbide Schottky diode having improved forward characteristics, characterized in that it comprises the step of forming a passivation layer before or after the heat treatment step. A silicon carbide Schottky diode manufacturing method with improved forward characteristics according to any one of claims 1 to 6,
Silicon carbide Schottky diodes with improved forward characteristics. delete

Images