JP3890311B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device such as a Schottky barrier diode using a silicon carbide semiconductor substrate and a manufacturing method thereof.
[0002]
[Prior art]
The structure of a Schottky barrier diode using a silicon carbide (SiC) semiconductor substrate is as shown in FIG. SiC semiconductor substrate 100 has a silicon surface 110 on one surface and a carbon surface 120 on the other surface. A SiC epitaxial layer 101 is formed on the silicon surface 110 side.
[0003]
For example, a titanium (Ti) metal layer 30 is formed on the silicon surface 110, and a Schottky junction is formed at the interface between the silicon surface 110 and the Ti metal layer 30. Also, for example, an Al surface electrode 50 is formed on the surface of the Ti metal layer 30 in order to ensure good connectivity with a metal wire such as aluminum (Al) for connection with an external electrode. Yes.
On the other hand, for example, a nickel (Ni) metal layer 20 is formed on the carbon surface 120, and an ohmic junction is formed at the interface between the carbon surface 120 and the Ni metal layer 20. Further, for example, a silver (Ag) back electrode 40 is formed on the surface of the Ni metal layer 20 in order to satisfactorily connect the Schottky barrier diode onto an external substrate having copper (Cu) wiring, for example.
[0004]
In manufacturing the Schottky barrier diode, first, as shown in steps T1 and T2 of FIG. 9A and FIG. 10, a Ni metal layer is formed on the carbon surface 120 of the SiC semiconductor substrate 100 having the epitaxial layer 101 on the silicon surface 110. 20 is deposited (step T1). Then, in order to form a good ohmic junction at the interface between the carbon surface 120 and the Ni metal layer 20, the Ni metal layer 20 is heat-treated at 1000 ° C. for 20 minutes (step T2).
[0005]
Next, as shown in step T3 of FIG. 9B and FIG. 10, the Ti metal layer 30 is formed on the silicon surface 110 of the SiC semiconductor substrate 100 (step T3). Thereafter, as shown in steps T4 and T5 of FIG. 9C and FIG. 10, after the resist 60 is applied to the surface of the Ti metal layer 30 and patterning is performed (step T4), the Ti metal layer 30 is etched. (Step T5).
Then, after the resist 60 is removed, in order to form a good Schottky junction with the SiC semiconductor substrate 100, as shown in step T6 of FIG. 9D and FIG. 30 heat treatment is performed (step T6). Thereafter, the Al surface electrode 50 and the Ag back electrode 40 are formed on the surfaces of the Ti metal layer 30 and the Ni metal layer, respectively (step T7), and the Schottky barrier diode shown in FIG. 9E is formed.
[0006]
[Patent Document 1]
JP 2000-164528 A
[Non-Patent Document 1]
Shigeyuki Somiya and Yoshizo Inomata, “New Material Series Silicon Carbide Ceramics”, Semiconductor Device Research and Development Department, ROHM Co., Ltd., Uchida Otsukuru, September 15, 1988, p. 177-182
[0007]
[Problems to be solved by the invention]
As described above, the Ni metal layer 20 and the Ti metal layer 30 are individually formed during the manufacturing process (steps T1 and T3) and individually heat-treated (steps T2 and T6). Therefore, since at least two heat treatments are required, there is a problem that it is difficult to shorten the manufacturing process.
Further, since the Ni metal layer 20 is used as an ohmic electrode, the Ni metal layer 20 and the carbon surface of the SiC semiconductor substrate 1 are not subjected to heat treatment at a high temperature of about 1000 ° C. as shown in Step T2 of FIG. A good ohmic junction cannot be formed at the interface with 120. Therefore, there is a possibility that the operating characteristics of the semiconductor device may be adversely affected by the heat treatment during the manufacturing process, and there is a problem that the manufacturing yield is poor.
[0008]
Accordingly, an object of the present invention is to provide a semiconductor device and a method for manufacturing the same that can shorten the manufacturing process.
Another object of the present invention is to provide a semiconductor device and a method for manufacturing the semiconductor device in which the operating characteristics are not adversely affected by the heat treatment during the manufacturing process.
[0009]
[Means for Solving the Problems and Effects of the Invention]
  In order to achieve the above object, the invention according to claim 1 provides:Having a silicon surface (11) and a carbon surface (12)Silicon carbide semiconductor substrate (1) and the silicon carbide semiconductor substrateCarbon aboveOhmic joined to the surface,Alloy of molybdenum or at least one metal selected from the group comprising molybdenum, titanium, chromium, manganese, zirconium, tantalum and tungstenAnd an ohmic metal layer (2).
[0010]
  The numbers in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.
  According to this configuration,An ohmic metal layer made of molybdenum or an alloy of molybdenum and at least one metal selected from the group including titanium, chromium, manganese, zirconium, tantalum, and tungsten, in ohmic contact with the carbon surface of the silicon carbide semiconductor substrate. It is formed. The above metal materials areThe free energy of formation of silicide and the free energy of formation of carbideIn addition, even at the temperature at the time of heat treatment for bringing the ohmic metal layer into ohmic contact with the carbon surface of the silicon carbide semiconductor substrate,Both negative valuesThe Therefore, a good ohmic junction can be formed. Moreover,The metal material as described above is subjected to heat treatment at a relatively low temperature (for example, 300 ° C. to 500 ° C., preferably a temperature equal to or higher than the temperature of the silicon carbide semiconductor substrate during operation of the semiconductor device). A good ohmic junction is formed at the interface. Therefore, it is possible to eliminate the adverse effect on the operating characteristics due to the heat treatment.
[0012]
The invention according to claim 2 is the above-mentioned silicon carbide semiconductor substrate.carbonThe carrier concentration in the semiconductor layer (1) on the surface side is 10 ¹⁸ -10 ¹⁹ / Cm^Three ofClaims that fall within the scope1It is a semiconductor device of description.
[0013]
  According to this configuration, the ohmic metal layer is bonded to the surface of the silicon carbide semiconductor substrate with a low resistance because the carrier concentration of the semiconductor layer in contact with the ohmic metal layer is sufficiently high. Thereby, a favorable ohmic junction can be formed.
  Claim3The described invention further includes a multilayer metal structure (2, 4) in which another metal layer (4) made of a metal material different from the ohmic metal layer is formed on the surface of the ohmic metal layer. 1.Or 2It is a semiconductor device of description.
[0014]
  If a metal material having good adhesion to a metal wire (bonding wire) such as aluminum or gold is used as the other metal layer, the element can be externally connected.
  For example, when the semiconductor device is mounted on a package provided with an external connection electrode (external electrode), the external electrode and the ohmic metal layer can be satisfactorily connected using a metal wire or a lead frame. For example, when the metal wire connected to the external electrode is an aluminum wire, the ohmic metal layerUpIt is preferable to form a metal layer of aluminum (Al), an alloy of aluminum and silicon (Al / Si), or an alloy of aluminum, silicon and copper (Al-Si-Cu). When the external electrode and the ohmic metal layer are directly connected, that is, for example, when the ohmic metal layer side is die-bonded to the lead frame, for example, silver (Au) or gold (on the surface of the ohmic metal layer) It is preferable to form a metal layer of Ag). Thereby, for example, the ohmic metal layer can be connected to the external substrate made of copper (Cu) wiring formed on the external substrate with good adhesion.
[0015]
  Two or more metal layers may be provided on the surface of the ohmic metal layer.
For example,An example outside the scope of the present invention,Ohmic metal layerTheTitanium metal layerWhen configuring withAlternatively, a multilayer metal structure in which a molybdenum metal layer is laminated on the titanium metal layer and an aluminum metal layer or an Al—Si alloy metal layer is laminated on the molybdenum metal layer may be used. In other words, aluminum and Al—Si alloy have not very good adhesion to the titanium metal layer, but by interposing the molybdenum metal layer between them, a good adhesion state can be obtained at the interface between each metal layer, and reliability A highly reliable semiconductor device can be manufactured.
[0016]
  Claim4The invention described is the above-described silicon carbide semiconductor substrate.carbonsurfaceSideThe carrier concentration in the first semiconductor layer (1) is that of the silicon carbide semiconductor substrate.SiliconSurface (11)SideHigher than the carrier concentration in the second semiconductor layer (10),siliconA Schottky metal layer (3) made of the same material as that of the ohmic metal layer, which is Schottky bonded to the surface, is further included.3A semiconductor device according to any one of the above.
[0017]
With this configuration, a SiC semiconductor Schottky barrier diode can be obtained. Since metal layers of the same metal material are formed on both sides of the silicon carbide semiconductor substrate, even if one metal layer is formed after the other metal layer is formed, one metal layer is contaminated. Absent.
In addition, the metal materials constituting the ohmic metal layer and the Schottky metal layer are both metal materials in which the free energy of formation of silicide and the free energy of formation of carbide have negative values. An ohmic junction can be formed. Therefore, when a relatively low temperature heat treatment is performed after forming the ohmic metal layer and the Schottky metal layer, the ohmic metal layer in contact with the first semiconductor layer having a relatively high carrier concentration is satisfactorily connected to the first semiconductor layer. The Schottky metal layer that is in contact with the second semiconductor layer having a relatively low carrier concentration forms a good Schottky junction with the second semiconductor layer. In this manner, a Schottky barrier diode having good characteristics can be manufactured by a single heat treatment at a relatively low temperature.
[0018]
  According to the experiment by the present inventor, it has been found that the Schottky barrier diode having the above configuration has a good breakdown voltage. In addition, since the metal layers of the same metal material are formed on both surfaces of the SiC semiconductor substrate, the heat treatment on both surfaces of the substrate can be combined at one time, so that the manufacturing process can be shortened.
  Claim5In the described invention, the carrier concentration of the first semiconductor layer is 10. ¹⁸ -10 ¹⁹ // cm^Three ofWithin the range, the carrier concentration of the second semiconductor layer is 10 ¹⁵ -10¹⁶/ Cm^Three ofClaims that fall within the scope4It is a semiconductor device of description.
[0019]
  According to this configuration, an ohmic metal layer that satisfactorily ohmic-joins with the first semiconductor layer can be formed, and a Schottky metal layer that satisfactorily Schottky-joins with the second semiconductor layer can be formed.
  Claim6The described inventionHaving a silicon surface (11) and a carbon surface (12)Of silicon carbide semiconductor substrate (1)To contact the carbon surface,The carbon surface side made of molybdenum or made of an alloy of molybdenum and at least one metal selected from the group comprising titanium, chromium, manganese, zirconium, tantalum and tungstenDeposit metal layer (2)Carbon surface side metal layerFilm formation process and thisCarbon surface side metal layerAfter the film formation process,Carbon sideOn the metal layerPredetermined temperatureHeat treatment of the aboveCarbon sideOf the metal layer and the silicon carbide semiconductor substrate.Carbon aboveA heat treatment step for forming an ohmic junction with the surfaceIncludeThis is a method for manufacturing a semiconductor device.
[0020]
  According to the present invention, the heat treatment of the silicon carbide semiconductor substrate is performed by heat treatment in a temperature range of relatively low temperature (300 ° C. to 500 ° C., preferably higher than the temperature of the silicon carbide semiconductor substrate during operation of the semiconductor device).carbonA metal layer (ohmic metal layer) that makes ohmic contact with the surface can be formed. Thereby, a silicon carbide semiconductor device having good characteristics can be manufactured..
[0021]
Claim7The described inventionThe silicon carbide substrate is the carbonThe carrier concentration in the first semiconductor layer (1) on the surface side isSiliconIt is higher than the carrier concentration in the second semiconductor layer (10) on the surface sideIs a thing,the aboveSilicon surfaceContactThe silicon surface side made of the same material as the carbon surface side metal layerDeposit metal layer (3)Silicon side metal layerFilm formation processThe heat treatment step further includes:the aboveCarbon surface side metal layerFilm formation process and aboveSilicon sideAfter the film formation process,Carbon sideMetal layer andSilicon sideMetal layer simultaneouslythe aboveBy heat treatment at a predetermined temperature, the aboveCarbon sideWhile forming an ohmic junction between the metal layer and the first semiconductor layer,Silicon sideForming a Schottky junction between the metal layer and the second semiconductor layer;WorkAboutIsIt is characterized byClaim 6A method for manufacturing a semiconductor device.
[0022]
  In addition,Silicon sideIf patterning of the metal layer is required,Silicon sideThe metal layer is deposited first, thenCarbon sideA metal layer may be formed.
  By this method, a Schottky barrier diode using a silicon carbide semiconductor substrate can be manufactured. In this case, in the first semiconductor layer having a relatively high carrier concentration by one heat treatment,Carbon surfaceOn the surface of the second semiconductor layer where the side metal layer can be ohmic-bonded and the carrier concentration is relatively lowSilicon sideThe metal layer can be Schottky bonded. In this way, since the heat treatment for forming the ohmic metal layer and the Schottky metal layer can be performed simultaneously, the manufacturing process can be shortened.
[0023]
  Claim8The invention described in the above is characterized in that the heat treatment step is a heat treatment step within a temperature range of 300 ° C to 500 ° C.6 or 7It is a manufacturing method of the semiconductor device of description.
  In this method, since the heat treatment is performed in a low temperature range of 300 ° C. to 500 ° C., the device characteristics are not deteriorated by the heat treatment.
  In addition, if heat treatment is performed at a temperature of 300 ° C. or less, there is a possibility that a good ohmic junction cannot be formed, and the time required for the heat treatment becomes long. Cause a decline. On the other hand, when heat treatment is performed at a temperature of 500 ° C. or higher, there is a possibility that the interface that should be Schottky bonded becomes ohmic bonding. Therefore, if heat treatment is performed within a temperature range of 300 ° C. to 500 ° C., there is no possibility that the manufacturing process takes a long time, and a good ohmic junction and Schottky junction can be formed.
[0025]
  The upper limit of the temperature at which the Schottky junction at the interface between the silicon carbide semiconductor substrate and the metal layer in contact with the silicon carbide semiconductor substrate becomes an ohmic junction is about 500 ° C., and therefore within a temperature range of 350 ° C. to 450 ° C. It is preferable that the heat treatment step is performed. As a result, there is no possibility that the operating characteristics of the semiconductor device will be affected by the heat treatment temperature during the manufacturing process, and the manufacturing yield can be improved.
  The aboveCarbon surface side metal layerAfter the film formation process,Carbon sideThis on the metal layerCarbon sideA film forming step of forming another metal layer made of a metal material different from the metal material constituting the metal layer is performed, andSilicon side metal layerAfter the film formation process,Silicon sideThis on the metal layerSilicon sideWhile performing the film-forming process which forms another metal layer which consists of metal materials different from the constituent material of a metal layer, the above-mentioned heat treatment process is the above-mentionedCarbon sideMetal layer and aboveSilicon sideIt is preferable to carry out after forming the above-mentioned separate metal layers on the metal layer.
[0026]
  This makes the aboveCarbon sideMulti-layer metal structure on the metal layer side and aboveSilicon sideHeat treatment for the multilayer metal structure on the metal layer side can be performed at once. By this heat treatment,Carbon sideAn ohmic junction is formed at the interface between the metal layer and the silicon carbide semiconductor substrate,Silicon sideA Schottky junction is formed at the interface between the metal layer and the surface of the silicon carbide semiconductor substrate. With that,Carbon sideThe interface between the metal layer and other metal layers on its surface, andSilicon sideThe adhesion at the interface between the metal layer and the other metal layer on the surface can also be improved.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a sectional view schematically showing the structure of a semiconductor device according to an embodiment of the present invention. This semiconductor device is, for example, a Schottky Barrier Diode, and as a semiconductor substrate, for example, an N-type SiC semiconductor substrate having a plane orientation of {0001} and an off-angle of 8 ° (for example, 4H-SiC epiwafer) 1 is used, and an edge termination 15 is formed on the SiC semiconductor substrate 1 by boron implantation and annealing at a relatively low temperature (about 1000 ° C.).
[0028]
SiC semiconductor substrate 1 has a silicon surface 11 on one surface and a carbon surface 12 on the other surface.
On the silicon surface 11 side, the thickness is about 10 μm and the carrier concentration is 4.0 × 10.¹⁵/ Cm^Three~ 8.0 × 10¹⁵/ Cm^ThreeN-type SiC semiconductor epitaxial layer 10 is formed. Thereby, on the silicon surface 11 side, the carrier concentration in the SiC semiconductor substrate 1 is relatively lower than that on the carbon surface 12 side, and on the carbon surface 12 side, the carrier concentration in the SiC semiconductor substrate 1 is relatively silicon. It is higher than the surface 11 side. Specifically, the carrier concentration on the silicon surface 11 side is 10¹⁵-10¹⁶/ Cm^ThreeAnd the carrier concentration on the carbon surface 12 side is 10¹⁸-10¹⁹/ Cm^ThreeWithin the range.
[0029]
  On the silicon surface 11 side, the surface molybdenum metal layer 3(Silicon surface side metal layer)Is formed. The surface molybdenum metal layer 3 covers a predetermined region (region surrounded by the edge termination 15) of the silicon surface 11, and the surface molybdenum metal layer 3 and the surface molybdenum metal layer 3 are in contact with the silicon surface 11 A Schottky junction is formed at the interface.
  A surface metal layer 5 made of a metal other than molybdenum metal is formed on the surface of the molybdenum metal layer 3 as a surface electrode. The surface metal layer 5 is formed of a metal having good adhesion to the surface molybdenum metal layer 3.
[0030]
For example, when the aluminum (Al) wire extending from the external electrode and the surface molybdenum metal layer 3 side are wire-bonded, the surface metal layer 5 is made of, for example, aluminum (Al), an alloy of aluminum and silicon (Al-Si) or aluminum It is preferably formed of an alloy of silicon and copper (Al—Si—Cu) or the like (metal showing good adhesion to aluminum). As a result, the surface molybdenum metal layer 3 and the Al wire are well electrically connected via the surface metal layer 5.
[0031]
  On the other hand, the back surface molybdenum metal layer 2 is formed on the carbon surface 12 side.(Carbon surface side metal layer)Is formed. The back surface molybdenum metal layer 2 covers the entire carbon surface 12, and an ohmic junction is formed at the interface between the back surface molybdenum metal layer 2 and the carbon surface 12 in contact with the back surface molybdenum metal layer 2.
  Further, on the surface of the back surface molybdenum metal layer 2, a back surface metal layer 4 made of a metal other than molybdenum metal is formed as a back surface electrode. The back surface metal layer 4 is formed of a metal having good adhesion to the back surface molybdenum metal layer 2.
[0032]
For example, when the copper (Cu) wiring formed on the wiring board is connected to the back surface molybdenum metal layer 2 side, the back surface metal layer 4 is made of, for example, gold (Au) or silver (Ag) (adhesion with copper). The metal is preferably made of a metal having good properties. Thereby, the back surface molybdenum metal layer 2 and the Cu wiring are well electrically connected via the back surface metal layer 4.
FIG. 2 is a schematic cross-sectional view showing the manufacturing process of the Schottky barrier diode having the above-described configuration in the order of steps, and FIG. 3 is a flowchart showing the manufacturing process.
[0033]
2A and 3, first, on the silicon surface 11 of the SiC semiconductor substrate 1 (after the formation of the edge termination 15) having the epitaxial layer 10 formed on the silicon surface 11 side. Then, after surface cleaning with RCA or the like, surface molybdenum metal layer 3 is formed by cleaning with dilute hydrofluoric acid (step S1). The surface molybdenum metal layer 3 is formed by sputtering by causing argon ions to collide with a molybdenum target. The degree of vacuum in the sputtering chamber before introducing argon gas is, for example, 10^-3-10^-FourPa.
[0034]
When the film formation of the surface molybdenum metal layer 3 is completed, a metal layer made of a metal other than molybdenum is formed on the surface of the surface molybdenum metal layer 3 by sputtering as shown in step S2 of FIG. 2B and FIG. Filming is performed (step S2), and the surface metal layer 5 is formed. The surface metal layer 5 is formed (step S2) in the same processing chamber as that in which the surface molybdenum metal layer 3 is formed (step S1). This is performed by so-called continuous sputtering processing performed by exchanging the target. At this time, there is a possibility that the IV characteristic will be deteriorated once the atmospheric state is reached without continuous sputtering (forward rising voltage V_FEtc.).
[0035]
Next, as shown in step S3 of FIG. 2C and FIG. 3, in order to pattern the surface molybdenum metal layer 3 and the surface metal layer 5, a photolithography process such as application of a resist 6 or an exposure process is performed. (Step S3). After completion of the photolithography process, as shown in step S4 of FIG. 2D and FIG. 3, the surface molybdenum metal layer 3 and the surface metal layer 5 are etched together using the resist 6 as a mask, thereby performing edge termination. After patterning the region surrounded by 15 (step S4), the resist 6 is removed.
[0036]
Thereafter, after cleaning with dilute hydrofluoric acid, as shown in step S5 of FIG. 2 (e) and FIG. 3, the back surface molybdenum metal layer 2 is formed on the carbon surface 12 of the SiC semiconductor substrate 1 by sputtering (step). S5). At this time, it is preferable to perform reverse sputtering that applies a reverse voltage before applying a forward voltage at the time of sputtering so that the interface between the back surface molybdenum metal layer 2 and the carbon surface 12 is a good ohmic junction. Thereby, the surface of carbon surface 12 of SiC semiconductor substrate 1 is irradiated with argon ions, and an undesired oxide film on carbon surface 12 is removed.
[0037]
When the film formation of the back surface molybdenum metal layer 2 is completed, a metal layer made of a metal other than molybdenum is formed on the surface of the back surface molybdenum metal layer 2 by sputtering, as shown in step S6 of FIG. 2 (f) and FIG. Filmed (step S6), the back metal layer 4 is formed. The back surface metal layer 4 is formed in the same processing chamber as that in which the back surface molybdenum metal layer 2 is formed (step S5), and the target is exchanged while keeping the inside of the chamber in an atmosphere of high vacuum. This is performed by so-called continuous sputtering. At this time, once the atmospheric state is reached without continuous sputtering, the IV characteristics may be deteriorated (forward rising voltage V_FEtc.).
[0038]
Thus, surface molybdenum metal layer 3 and surface metal layer 5 are formed by being laminated on the silicon surface 11 side of SiC semiconductor substrate 1, and back surface molybdenum metal layer 2 and back surface metal layer 4 are formed on the carbon surface of SiC semiconductor substrate 1. After being laminated on the 12th side, for example, heat treatment is performed at 400 ° C. for 20 minutes (step S7). By this one-time heat treatment, a good Schottky junction is formed at the interface between the silicon surface 11 and the surface molybdenum metal layer 3 formed on the silicon surface 11, and the surface molybdenum metal layer 3 and the surface metal layer 5 are bonded together. The adhesion of the interface is increased. At the same time, a good ohmic junction is formed at the interface between the carbon surface 12 and the back surface molybdenum metal layer 2 formed on the carbon surface 12, and the adhesion at the interface between the back surface molybdenum metal layer 2 and the back surface metal layer 4. Is increased.
[0039]
That is, heat treatment for the two molybdenum metal layers 2 and 3 and the two metal layers 4 and 5 is performed at once by unifying the metal that is Schottky-bonded to the silicon surface and the metal that is ohmic-bonded to the carbon surface into molybdenum. Can do. Thereby, the manufacturing process of a Schottky barrier diode can be remarkably shortened.
The heat treatment temperature is set within a temperature range of 300 ° C to 500 ° C (for example, 350 ° C to 450 ° C). As a result, the heat treatment at a temperature much lower than the heat treatment at 1000 ° C., which has been necessary in the case of using a Ni metal layer in the past, is sufficient, and the heat treatment temperature during the manufacturing process adversely affects the operating characteristics of the Schottky barrier diode. Manufacturing yield can be improved.
[0040]
Here, for example, if heat treatment is performed at a temperature of 300 ° C. or less, a good ohmic junction cannot be formed at the interface between the carbon surface 12 and the back surface molybdenum metal layer 2 formed in contact with the carbon surface 12, Furthermore, the manufacturing process takes a long time, resulting in a decrease in manufacturing efficiency. If heat treatment is performed at a temperature of 500 ° C. or higher, the Schottky junction at the interface between the silicon surface 11 and the surface molybdenum metal layer 3 formed in contact with the silicon surface 11 becomes an ohmic junction. Therefore, if the heat treatment is performed within a temperature range of 300 ° C. to 500 ° C., there is no possibility that the time of the manufacturing process becomes long, and the interface between the carbon surface 12 and the back surface molybdenum metal layer 2 formed in contact with the carbon surface 12. A good ohmic junction can be formed. At the same time, a good Schottky junction can be formed at the interface between the silicon surface 11 and the surface molybdenum metal layer 3 formed in contact with the silicon surface 11.
[0041]
Since the upper limit of the temperature at which the Schottky junction at the interface between the silicon surface 11 and the surface molybdenum metal layer 3 formed in contact with the silicon surface 11 becomes an ohmic junction is 500 ° C., the temperature range is 350 ° C. to 450 ° C. More preferably, a heat treatment step is performed.
The Schottky barrier diode manufactured in this way has a reverse breakdown voltage of 600 V to 1000 V and a forward rise voltage of 1.3 V / 1 A, and exhibits good operating characteristics. Thereby, even if the molybdenum metal layers 2 and 3 are commonly used on both surfaces of the SiC semiconductor substrate 1 and the manufacturing process is shortened, a Schottky barrier diode that can be sufficiently put into practical use can be manufactured.
[0042]
Schottky barrier diodes with similar characteristics are made of titanium (Ti), chromium (Cr), manganese (Mn), zirconium (Zr), tantalum (Ta) or tungsten (W) instead of molybdenum (Mo). An alloy of two or more selected metals can be used in common as the material of the metal layers 2 and 3 for forming an ohmic junction and a Schottky junction. The same applies to molybdenum, but these metals exhibit a reaction according to the following chemical reaction formula with SiC.
[0043]
SiC + M → M_xSi_y+ M_mC_n
However, M represents a metal. x, y, m, and n are natural numbers.
That is, the metal as described above reacts with both Si and C in SiC, and as a result, an ohmic junction is easily formed at the interface with SiC.
On the other hand, metals such as iron (Fe), nickel (Ni), copper (Cu) and lead (Pb)
SiC + M → M_xSi_y+ C
It reacts only with C in SiC. Aluminum (Al) etc.
SiC + M → M_mC_n+ Si
It reacts only with Si in SiC.
[0044]
That is, metals such as iron, nickel, copper, lead, and aluminum react only with either C or Si in SiC, so that it is difficult to form an ohmic junction at the interface with SiC.
Molybdenum, titanium, chromium, manganese, zirconium, tantalum, and tungsten have silicide free formation energy (Gibs formation free energy ΔG) of less than zero (negative value) and their metals. The free energy of formation of carbide is also less than zero. The smaller the free energy of formation, the easier the chemical reaction to occur. When the value is negative, the chemical reaction proceeds spontaneously. When the value is positive, the chemical reaction proceeds to generate the product. Therefore, it is necessary to give energy from the outside.
[0045]
Therefore, the above metal group in which the free energy of formation of silicide and the free energy of formation of carbide are both negative values easily reacts with both Si and C in SiC to form a good ohmic junction. It can be said that.
FIG. 4 shows the free energy of formation of silicides of molybdenum, titanium and nickel. FIG. 4 shows that molybdenum, titanium, and nickel all take negative values for the free energy of formation of silicide in the temperature range of 400 ° C. to 1000 ° C.
[0046]
FIG. 5 is a diagram showing the free energy of formation of carbides of molybdenum, titanium, nickel and aluminum. From FIG. 5, it can be seen that aluminum, molybdenum, and titanium have negative values for the free energy of formation of carbides in the temperature range of 400 ° C. to 1000 ° C. In contrast, Ni, which is a carbide of nickel_ThreeThe free energy of formation of C takes a positive value in the temperature range of 400 ° C to 1000 ° C. From this, it is understood that even if a nickel metal film is formed on the surface of the SiC semiconductor substrate, it is difficult to obtain a good ohmic junction.
[0047]
Although not appearing in FIG. 4, aluminum does not react with Si to form silicide, and therefore the free energy of formation of silicide is so large that it cannot be shown in FIG. 4. Therefore, even if an aluminum metal layer is formed on the surface of the SiC semiconductor substrate, a good ohmic junction cannot be obtained.
In order to form a good ohmic junction on the surface of the SiC semiconductor substrate, the lower the free energy of formation of carbides and silicides, the better. Therefore, a better ohmic junction can be formed using titanium than molybdenum.
[0048]
4 and FIG. 5 are prepared based on the description of Non-Patent Document 1. According to the description of Non-Patent Document 1, zirconium is further silicided and carbide than titanium. The free energy of formation is low. Therefore, it is considered that a better ohmic junction can be formed by using zirconium than titanium.
The inventor of the present application relates to a Schottky barrier diode fabricated by bonding molybdenum metal layers 2 and 3 to both surfaces of a SiC semiconductor substrate 1. The interface between the silicon surface and the carbon surface and the metal layers 2 and 3 is measured with a transmission electron microscope. Observation was performed with (Transmission Electron Microscope: TEM).
[0049]
As a result, on the carbon surface 12, it was confirmed that a region having a thickness of about 30 mm thought to be a quasicrystal maintaining a periodic crystal structure was formed at the SiC crystal interface. That is, it was confirmed that molybdenum metal was sufficiently diffused on the surface of the SiC semiconductor substrate 1 and a good ohmic junction was obtained.
On the other hand, on the silicon surface 11, it was confirmed that an amorphous alloy region having a thickness of about 10 mm was formed at the interface between the molybdenum metal layer 3 and the SiC semiconductor substrate 1. Thereby, it can be said that a good Schottky junction is formed on the silicon surface.
[0050]
Further, the inventor of the present application analyzes the amorphous alloy region at the interface between the silicon surface 11 and the molybdenum metal layer 3 by energy dispersive X-ray spectroscopy (Energy Disperse X-ray: EDX). According to the analysis result, it has been confirmed that the amorphous alloy region contains oxygen atoms.
Similarly, the inventor of the present application has conducted an EDX analysis of the interface between the carbon surface 12 and the molybdenum metal layer 2, and as a result, oxygen in the SiC / Mo diffusion region that seems to form a quasicrystal. It has been confirmed that atoms exist.
[0051]
Thus, it is considered that oxygen atoms are also present in the ohmic junction on the carbon surface 12 of the SiC semiconductor substrate 1 as a result of performing a cleaning process in the air. Forms of Schottky barrier diodes have been confirmed to exhibit good characteristics.
That is, FIG. 6 shows the forward voltage V in the Schottky barrier diode._FForward current I_FIn comparison with the conventional SiC Schottky barrier diode (Ni using ohmic electrode and Ti using Schottky electrode) shown by curve L1, molybdenum metal layers 2 and 3 are bonded to carbon surface 12 and In the SiC Schottky barrier diode according to the above-described embodiment that is commonly applied to the silicon surface 11, a favorable rising characteristic of the forward current was obtained as shown by the curve L2. That is, the forward rising voltage V_FWas able to be lowered.
[0052]
Further, when a metal layer made of an alloy of titanium and molybdenum (Ti-Mo) is applied to the carbon surface and the silicon surface of the SiC semiconductor substrate, as shown by a curve L3, the metal layer further includes a molybdenum metal layer. Good forward rise characteristics were obtained.
A curve L0 indicates the characteristics of a Schottky barrier diode using a Si semiconductor substrate.
[0053]
FIG. 7 shows the on-resistance characteristics of the SiC Schottky barrier diode. A curve L11 indicates a limit value of on-resistance in the silicon semiconductor device, and a curve L12 indicates a limit value of on-resistance in the 4H-SiC semiconductor device.
The Schottky barrier diode of the above embodiment in which the molybdenum metal layer was formed on the carbon surface and the silicon surface of the SiC semiconductor substrate showed extremely low on-resistance as indicated by point P1. Further, if a titanium metal layer is applied to both surfaces of the SiC semiconductor substrate, it is expected that an on-resistance characteristic near the region A can be obtained.
Note that the on-resistance characteristic of a conventional product (using Ni for the ohmic electrode and Ti for the Schottky electrode) is indicated by a point P10.
[0054]
FIG. 8 is a schematic cross-sectional view showing a structural example in the case where a Schottky barrier diode is formed by forming a titanium metal layer on both surfaces of a SiC semiconductor substrate. In this structural example, a molybdenum metal layer is formed on the surfaces of the titanium metal layers on both sides of the SiC semiconductor substrate 1, and on the Schottky electrode side, an Al—Si alloy layer having excellent adhesion to an aluminum wire on the molybdenum metal layer. Is formed. In addition, a metal layer made of gold (Au), silver (Ag), or an alloy of gold and silver (Au—Ag) is formed on the molybdenum metal layer on the ohmic electrode side, so that it is good for a lead frame or the like. Die bonding is possible.
[0055]
As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, an example in which a Schottky barrier diode is configured by forming a metal layer made of molybdenum or the like on both surfaces of a SiC semiconductor substrate has been described. However, the present invention relates to a junction field effect using a SiC semiconductor substrate. Arbitrary junction electrodes (source electrodes, drain electrodes, etc.) that require ohmic contact with the surface of the SiC semiconductor substrate, such as transistors (Junction field effect transistors), MOS field effect transistors (MOSFETs), and integrated circuit elements It can be applied to SiC semiconductor devices.
[0056]
  In the above embodiment, an example using an N-type SiC semiconductor substrate has been described. However, when a P-type SiC semiconductor substrate is used, a SiC semiconductor device such as a Schottky barrier diode can be manufactured in the same manner..
[0057]
In addition, various modifications can be made within the scope of the matters described in the claims.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing the structure of a semiconductor device according to an embodiment of the present invention.
FIG. 2 is an illustrative view showing a manufacturing process of the Schottky barrier diode according to one embodiment of the present invention in the order of steps;
FIG. 3 is a flowchart showing manufacturing steps of the Schottky barrier diode according to one embodiment of the present invention in order of steps.
FIG. 4 is a diagram showing free energy of formation of silicide.
FIG. 5 is a diagram showing the free energy of formation of carbides.
FIG. 6 is a diagram showing forward voltage versus forward current characteristics of a Schottky barrier diode.
FIG. 7 is a graph showing on-resistance characteristics of a Schottky barrier diode.
FIG. 8 is a schematic sectional view showing a structural example of a Schottky barrier diode in which a titanium metal layer is formed on both surfaces of a silicon carbide semiconductor substrate.
FIG. 9 is an illustrative view showing a conventional Schottky barrier diode manufacturing process in order of process;
FIG. 10 is a flowchart showing a manufacturing process of a conventional Schottky barrier diode in order of processes.
[Explanation of symbols]
1 Silicon carbide semiconductor substrate
2 Molybdenum metal layer on the back side
3 Surface molybdenum metal layer
4 Back metal layer
5 Surface metal layer
11 Silicon surface
12 Carbon surface

Claims (8)

A silicon carbide semiconductor substrate having a silicon surface and a carbon surface ;
An ohmic junction made of molybdenum or an alloy of molybdenum and at least one metal selected from the group including titanium, chromium, manganese, zirconium, tantalum and tungsten , ohmic-bonded to the carbon surface of the silicon carbide semiconductor substrate A semiconductor device comprising a metal layer. 2. The semiconductor device according to claim 1 , wherein a carrier concentration in the semiconductor layer on the carbon surface side of the silicon carbide semiconductor substrate is in a range of 10 ¹⁸ to 10 ¹⁹ / cm ³ . 3. The semiconductor device according to claim 1, further comprising a multilayer metal structure in which another metal layer made of a metal material different from the ohmic metal layer is formed on the surface of the ohmic metal layer. . The carrier concentration in the first semiconductor layer on the carbon surface side of the silicon carbide semiconductor substrate is higher than the carrier concentration in the second semiconductor layer on the silicon surface side of the silicon carbide semiconductor substrate,
The silicon surface is Schottky junction, the semiconductor device according to any one of claims 1 to 3, further comprising a Schottky metal layer of the same material as the ohmic metal layer. The carrier concentration of the first semiconductor layer is in the range of 10 ¹⁸ to 10 ¹⁹ / cm ³ ;
5. The semiconductor device according to claim 4 , wherein the carrier concentration of the second semiconductor layer is in a range of 10 ¹⁵ to 10 ¹⁶ / cm ³ . At least one selected from the group consisting of molybdenum or molybdenum and titanium, chromium, manganese, zirconium, tantalum and tungsten so as to contact the carbon surface of the silicon carbide semiconductor substrate having a silicon surface and a carbon surface A carbon surface side metal layer forming step of forming a carbon surface side metal layer made of an alloy with a metal ;
After the carbon surface-side metal layer forming step, forming an ohmic junction between the heat-treated at a predetermined temperature on the carbon surface-side metal layer, the carbon surface-side metal layer and the above carbon face of the silicon carbide semiconductor substrate A method for manufacturing a semiconductor device, comprising: a heat treatment step. The silicon carbide substrate, the carrier concentration in the first semiconductor layer of the carbon surface side are those higher than the carrier concentration of the second semiconductor layer of the silicon surface,
So as to be in contact with the silicon surface, further comprising a silicon surface-side metal layer forming step of forming a silicon surface-side metal layer made of the same material as the carbon surface-side metal layer,
The heat treatment step, after the carbon surface-side metal layer forming step and the silicon surface film forming step, by heat-treating the carbon surface-side metal layer and the silicon surface-side metal layer simultaneously at the predetermined temperature, the carbon wherein the to form the ohmic contact between the surface-side metal layer and the first semiconductor layer is higher Engineering form a Schottky junction between the silicon surface-side metal layer and the second semiconductor layer A method for manufacturing a semiconductor device according to claim 6 . 8. The method of manufacturing a semiconductor device according to claim 6 , wherein the heat treatment step is a step of heat treatment within a temperature range of 300.degree. C. to 500.degree.

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