JP4942255B2 - Silicon carbide semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device using a silicon carbide semiconductor material (hereinafter referred to as “silicon carbide semiconductor device”) and a method for manufacturing the same.
[0002]
[Prior art]
An example of a silicon carbide semiconductor device is a Schottky barrier diode. A Schottky barrier diode is a diode that uses the rectifying action of a Schottky junction. In the conventional Schottky barrier diode, in order to alleviate electric field concentration at the outer peripheral edge of the Schottky barrier electrode, the structure of the outer peripheral edge region of the Schottky barrier electrode is a p-type region formed by ion implantation, or a high resistance. Area is being used. For example, as shown in Material Science Forum Vols. 338-342 (2000) pp. 1167-1170, a conventional Schottky barrier diode has a structure with a guard ring of an Al injection region around the Schottky barrier electrode. have. In this structure, the position where the electric field is maximized is the pn junction surface formed at the boundary between the guard ring and the drift region, and the electric field concentration at the end of the Schottky barrier electrode is alleviated.
[0003]
(Conventional example 1)
(Constitution)
FIG. 9 is a cross-sectional view of a main part of a conventional Schottky barrier diode. On the upper surface of the n-type SiC substrate 1, an SiC drift layer 2 having n-type conductivity with a low impurity concentration is formed by epitaxial growth. A p-type conductive guard ring region 3 is formed by ion implantation from the upper surface of the drift layer 2 to the inside of the drift layer 2. A Schottky barrier electrode 4 is formed on the drift layer 2, and an end 5 of the Schottky barrier electrode 4 is located on the upper surface of the p-type conductive guard ring region 3. On the other hand, a back electrode 6 is formed on the back side of SiC substrate 1 as an n-side electrode. A pn junction surface 7 is formed at the interface between the p-type conductive guard ring region 3 and the drift layer 2. When a negative voltage is applied to the Schottky barrier electrode 4, electrons are blocked by the potential barrier formed on the lower surface of the Schottky barrier electrode 4, thereby applying a negative voltage to the depletion layer formed in the drift layer 2. And exhibits rectification characteristics as a diode. At this time, since the p-type conductive guard ring region 3 is formed as a guard ring below the end 5 of the Schottky barrier electrode 4, no electric field concentration occurs at the end 5 of the Schottky barrier electrode. The position at which becomes the maximum is the pn junction surface 7 formed at the boundary between the guard ring and the drift region, and the electric field concentration is alleviated.
[0004]
(Production method)
Next, a method for manufacturing this semiconductor device will be described. A conventional Schottky barrier diode as shown in FIG. 9 is manufactured as follows, for example. On the SiC substrate 1, a drift layer 2 having a low impurity concentration and having an n-type conductivity is epitaxially grown by, for example, a thickness of 10 μm by a CVD (Chemical Vapor Deposition) crystal growth method. Next, a mask for selective ion implantation is formed on the surface, and Al ions are implanted as an acceptor impurity. Next, in order to repair crystal damage caused by ion implantation and activate the impurity as an acceptor, for example, annealing is performed at 1700 ° C. for about 1 hour in an Ar atmosphere to form the p-type conductive guard ring region 3. Next, nickel is formed as a back electrode 6 on the back surface of the SiC substrate 1 by a thickness of 0.5 μm by sputtering, and then annealed at 950 ° C. for 1 minute, for example, in order to form an ohmic electrode. Subsequently, after the SiC surface is cleaned and treated to form a good Schottky barrier, titanium is deposited as a Schottky barrier electrode 4, for example. The Schottky barrier electrode 4 is formed by normal patterning.
[0005]
(Conventional example 2)
(Constitution)
Furthermore, as another example of a conventional Schottky barrier diode, a Schottky barrier diode using a so-called high resistance SiC region formed by ion implantation as a guard ring region is shown. FIG. 10 is a cross-sectional view of the main part of the Schottky barrier diode. The SiC substrate 1, the drift layer 2, the Schottky barrier electrode 4, and the back electrode 6 have the same structure as the previous example. In this example, a high resistance guard ring region 8 is formed as a guard ring instead of the p-type conductive guard ring region 3. The high resistance guard ring region 8 is a region formed by damaging a crystal by ion implantation of Ar or the like, for example. When a negative voltage is applied to the Schottky barrier electrode 4, since the high resistance guard ring region 8 is formed below the end 5 of the Schottky barrier electrode 4, the potential is the resistance of the high resistance guard ring region 8. Divided by. For this reason, the electric field concentration at the end 5 of the Schottky barrier electrode 4 is alleviated.
[0006]
(Production method)
Next, a manufacturing method will be described. The manufacturing process of the conventional Schottky barrier diode as shown in FIG. 10 is the same as that shown in FIG. 9 until the manufacturing process of the mask for ion implantation. For example, Ar ions are ion-implanted with an energy of 300 keV for the purpose of damaging defects and forming a high-resistance region by ion implantation. The subsequent steps are the same as those shown in FIG.
[0007]
[Problems to be solved by the invention]
In a semiconductor device using a silicon carbide semiconductor material, a guard ring region formed by ion implantation has been used as a structure for relaxing electric field concentration at the end of a conventional Schottky barrier electrode. However, expensive equipment is required for ion implantation, which increases the manufacturing cost of the semiconductor device. Further, for example, in a guard ring structure by p-type implantation, activation annealing after implantation is performed at a high temperature of 1500 ° C. to 1800 ° C., so that the surface of the drift layer where the Schottky barrier should be formed is altered or shaped. There is a problem that it becomes difficult to obtain a good Schottky barrier due to unevenness. Further, not only in the case of low-temperature annealing conditions, but also in the case of high-temperature annealing conditions, the implantation damage is not necessarily completely repaired, and the damage due to the implantation remains, and a leakage current is generated at the pn junction surface, resulting in Schottky. There has been a problem that the reverse leakage current characteristic of the barrier diode is deteriorated. In the guard ring region having a pn junction surface, the electric field concentration at the end of the Schottky barrier electrode is alleviated. On the other hand, the pn junction surface formed by ion implantation, particularly the pn junction surface, has a convex shape. There is a problem that electric field concentration occurs in the portion, and as a result, the reverse breakdown voltage of the Schottky barrier diode is lowered.
[0008]
Further, for example, in a structure using a high resistance region as a guard ring region by Ar ion implantation or the like, the high resistance region is realized by a deep level due to defect damage, and by recombination in the guard ring region. There is a problem that the leakage current becomes large and the reverse leakage current characteristics of the Schottky barrier diode are deteriorated.
[0009]
The present invention has been made to solve these problems, and an object thereof is to provide a semiconductor device having a low reverse leakage current at low cost.
[0010]
[Means for Solving the Problems]
To achieve the above object, a silicon carbide semiconductor device according to the present invention includes a substrate made of a silicon carbide semiconductor material, a drift layer made of a silicon carbide semiconductor material formed on an upper surface of the substrate, and a contact with the drift layer. A Schottky barrier electrode disposed so as to cover a partial region of the upper surface of the drift layer and functioning as an Schottky barrier at an interface in contact with the drift layer, and an outer peripheral edge region of the Schottky barrier electrode , A guard ring is interposed between the drift layer and the Schottky barrier electrode, and the Schottky barrier electrode is lifted by the guard ring. By adopting this configuration, when a negative voltage is applied to the Schottky barrier electrode, a guard ring is formed under the end of the Schottky barrier electrode, so the electric field concentration at the end of the Schottky barrier electrode is The pressure resistance is improved. Moreover, the guard ring is not provided in the same layer as the drift layer, but is configured so that the Schottky barrier electrode is lifted by the guard ring. This eliminates the need for ion implantation and other methods that have been problematic in the past.
[0011]
Preferably, in the above invention, the guard ring has a shape in which the film thickness becomes thinner from the outside to the inside of the Schottky barrier electrode. By adopting this configuration, the structure does not change discontinuously at the boundary between the region where the Schottky barrier electrode directly contacts the drift layer and the region where the guard ring is interposed, and the thickness of the guard ring gradually increases. It has a structure. Therefore, electric field concentration at this boundary does not occur. For this reason, the problem that a reverse breakdown voltage falls does not arise.
[0012]
Preferably, in the above invention, the guard ring is made of a material different from that of the drift layer, and is higher than a resistance value when the forward voltage is applied to the drift layer and higher than a resistance value when the reverse voltage is applied to the drift layer. Includes materials with low resistance. By adopting this configuration, the potential is divided by the resistance of the high resistance guard ring 18. For this reason, the electric field concentration at the end of the Schottky barrier electrode is relaxed, and the pressure resistance is improved.
[0013]
Preferably, in the above invention, the guard ring is a metal oxide layer formed by oxidizing the outer end of the Schottky barrier electrode. By adopting this configuration, since the guard ring is a metal oxide layer formed by oxidation of the Schottky barrier electrode, there is no structurally discontinuous change between the Schottky barrier electrode and the guard ring. Concentration does not occur. Further, since the guard ring is formed by oxidation of the electrode, problems such as defects at the interface between the Schottky barrier electrode and the high resistance layer are reduced. Further, it is not necessary to form the guard ring using a separate process.
[0014]
Preferably, in the above invention, the Schottky barrier electrode includes titanium, and the metal oxide layer includes titanium oxide. By adopting this configuration, a low-loss Schottky barrier diode can be realized. This is because titanium is suitable as a rectifying element having a Schottky barrier with respect to 4H—SiC of about 1 eV and about 1 kV. Titanium oxide serves as a high resistance layer and functions as a guard ring.
[0015]
Preferably in the above invention, the guard ring includes a semi-insulating silicon carbide semiconductor layer grown on the drift layer. By adopting this configuration, a guard ring can be obtained by growth. In this case, since there is no damage due to implantation and no deterioration of the surface due to annealing, a good Schottky barrier diode can be realized.
[0016]
In the above invention, preferably, the guard ring and the drift layer have different conductivity types, and the guard ring forms a pn junction surface at the interface with the drift layer. By adopting this configuration, the Schottky barrier electrode is lifted by the guard ring and does not require ion implantation to form the guard ring, but a pn junction is formed between the guard ring and the drift layer. Therefore, there is an effect that the reverse leakage current can be reduced as compared with a guard ring formed by ion implantation.
[0017]
Preferably, in the above invention, the drift layer has a concave slope, and the guard ring is formed to cover the slope. By adopting this configuration, it is possible to increase the radius of curvature at the portion where the pn junction surface is convex, so that the electric field concentration on the pn junction surface is reduced. In this way, electric field concentration can be alleviated and the reverse breakdown voltage of the Schottky barrier diode can be improved.
[0018]
In order to achieve the above object, a method for manufacturing a silicon carbide semiconductor device according to the present invention includes a drift layer forming step of forming a drift layer made of a silicon carbide semiconductor material on an upper surface of a substrate made of a silicon carbide semiconductor material, and the drift An electrode material film forming step of forming an electrode material film made of a Schottky barrier electrode material for causing the interface in contact with the layer to function as a Schottky barrier so as to contact the drift layer and cover the upper surface of the drift layer; and An etching process that removes other parts from the electrode material film while leaving a desired part, and an oxidation process that oxidizes a part of the electrode material film to form a guard ring made of a metal oxide layer, and the etching process, The oxidation step is performed in parallel. By employing this method, a Schottky barrier electrode can be formed by etching, and at the same time a guard ring can be obtained, and the number of steps can be reduced.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
(Constitution)
With reference to FIG. 1, the silicon carbide semiconductor device in Embodiment 1 based on this invention is demonstrated. FIG. 1 is a cross-sectional view of a Schottky barrier diode as an example of a silicon carbide semiconductor device. On the upper surface of the n-type SiC substrate 1, an SiC drift layer 2 having n-type conductivity with a low impurity concentration is formed by epitaxial growth. Schottky barrier electrode 4 is formed so as to directly cover a part of the upper surface of drift layer 2. A high resistance guard ring 18 is formed on the upper side of the drift layer 2 so as to surround a region directly covered with the Schottky barrier electrode 4 on the upper surface of the drift layer 2. Schottky barrier electrode 4 is made of, for example, titanium. However, the “high resistance” of the high resistance guard ring 18 means that the resistance value is higher than the resistance value when the forward voltage is applied to the drift layer 2 and lower than the resistance value when the reverse voltage is applied to the drift layer 2. Shall mean. Here, the high resistance guard ring 18 is made of, for example, titanium oxide. In the outer peripheral edge region of the Schottky barrier electrode 4, the Schottky barrier electrode 4 extends above the high resistance guard ring 18. The end 5 of the Schottky barrier electrode 4 is located above the high resistance guard ring 18. As a result, as shown in FIG. 1, in the outer peripheral edge region of the Schottky barrier electrode 4, the portion including the end 5 of the Schottky barrier electrode 4 is lifted by the high resistance guard ring 18. . That is, the high resistance guard ring 18 is interposed between the drift layer 2 and the Schottky barrier electrode 4. On the other hand, a back electrode 6 is formed on the back side of SiC substrate 1 as an n-side electrode.
[0020]
When a negative voltage is applied to the Schottky barrier electrode 4, electrons are blocked by the potential barrier formed on the lower surface of the Schottky barrier electrode 4, thereby applying a negative voltage to the depletion layer formed in the drift layer 2. And exhibits rectification characteristics as a diode.
[0021]
(Production method)
The Schottky barrier diode shown in this embodiment can be manufactured as follows, for example. On the SiC substrate 1, a drift layer 2 having an n-type conductivity having a low impurity concentration is epitaxially grown by a CVD crystal growth method, for example, by a thickness of 10 μm. As the back electrode 6, nickel is formed on the back surface of the SiC substrate 1 by a thickness of 0.5 μm by sputtering, and then annealed in a vacuum at 950 ° C. for 1 minute, for example, to form an ohmic electrode.
[0022]
As a material layer for forming the high resistance guard ring 18 on the surface of the drift layer 2, titanium oxide is formed to a thickness of 0.5 μm by sputtering film formation. The high resistance guard ring 18 is formed in an annular shape when viewed from above by a normal patterning method and an etching method. As an electrode material film to be a material for the Schottky barrier electrode 4, titanium is formed by a thickness of 0.5 μm by a sputtering film forming method, and then the Schottky barrier electrode 4 is formed by a normal patterning method and an etching method.
[0023]
(Action / Effect)
In the silicon carbide semiconductor device in the present embodiment, when a negative voltage is applied to Schottky barrier electrode 4, high resistance guard ring 18 is formed under end 5 of Schottky barrier electrode, so that the potential is high. It is divided by the resistance of the resistance guard ring 18. For this reason, the electric field concentration at the end 5 of the Schottky barrier electrode 4 is relaxed, and the pressure resistance is improved.
[0024]
Here, an example in which titanium oxide is used as the material of the high resistance guard ring 18 is described, but other materials may be used as long as the material satisfies the definition of high resistance described above.
[0025]
(Embodiment 2)
(Constitution)
With reference to FIG. 2, the silicon carbide semiconductor device in Embodiment 2 based on this invention is demonstrated. FIG. 2 is a cross-sectional view of a Schottky barrier diode as an example of a silicon carbide semiconductor device. The characteristics of SiC substrate 1, drift layer 2, Schottky barrier electrode 4, and back electrode 6 are the same as in the first embodiment. The material of the high resistance guard ring 18 is the same as that of the first embodiment. However, in the present embodiment, the thickness of the high resistance guard ring 18 becomes thinner from the outside to the inside of the Schottky barrier electrode 4. The rectifying function of the diode and the function of the guard ring are the same as in the first embodiment.
[0026]
(Production method)
The Schottky barrier diode in the present embodiment can be manufactured as follows, for example. The processes up to the formation of the back electrode 6 and the annealing are the same as those already described in the first embodiment.
[0027]
Next, 0.5 μm of titanium oxide is formed as a material layer for the guard ring region 18 on the surface of the drift layer 2 by a sputtering film forming method. The high resistance guard ring 18 is formed in an annular shape when viewed from above by a normal patterning method and an etching method. When the high resistance guard ring 18 is formed, the outer peripheral edge region of the Schottky barrier electrode 4 is directed from the outside to the inside as shown in FIG. 2 by a gentle slope forming process utilizing the recession of the etching film. As the film thickness decreases, the film thickness decreases.
[0028]
This gentle slope forming process will be described with reference to FIGS. First, as shown in FIG. 3A, a resist mask 31 is formed in a shape having a slope on the material film 38 to be the high resistance guard ring 18. Such a shape can be realized by manipulating the exposure and development conditions of the resist mask 31. In dry etching, the thickness of the resist mask 31 also decreases at a certain rate. Therefore, the resist mask 31 disappears from the thin portion at the end of the resist mask 31, and the underlying material film 38 is gradually exposed. . FIGS. 3B and 3C show how the dry etching proceeds. Finally, as shown in FIG. 3D, after the resist mask 31 is completely removed, a part of the material film 38 remains in a form having a slope. This becomes the high resistance guard ring 18.
[0029]
After the high resistance guard ring 18 is formed in this manner, the Schottky barrier electrode 4 is formed. The process for forming the Schottky barrier electrode 4 is the same as that in the first embodiment. In this way, the structure shown in FIG. 2 is obtained.
[0030]
(Action / Effect)
In the silicon carbide semiconductor device in the present embodiment, the structure does not change discontinuously at the boundary between the region where Schottky barrier electrode 4 is in direct contact with drift layer 2 and the region where the guard ring is interposed, and the guard is gradually increased. The structure increases the thickness of the ring. Therefore, electric field concentration at this boundary does not occur. For this reason, the problem that a reverse breakdown voltage falls does not arise. As a result, a silicon carbide semiconductor device including a Schottky barrier diode having an ideal reverse breakdown voltage, which is limited by the material properties of the silicon carbide semiconductor, can be realized.
[0031]
In the description of the manufacturing method according to the present embodiment, an example in which the recess of the etching mask is used as the gentle slope forming process of the guard ring is shown. However, if the method can form the gentle slope, isotropic etching is used. Other methods such as a method using undercut under the mask may be used.
[0032]
(Embodiment 3)
(Constitution)
With reference to FIG. 4, the silicon carbide semiconductor device in Embodiment 3 based on this invention is demonstrated. FIG. 4 is a cross-sectional view of a Schottky barrier diode as an example of a silicon carbide semiconductor device. The characteristics of SiC substrate 1, drift layer 2, Schottky barrier electrode 4, and back electrode 6 are the same as in the first embodiment. The material of the high resistance guard ring 18 is the same as that of the first embodiment. However, in the present embodiment, the high resistance guard ring 18 is composed of a metal oxide layer formed by partial oxidation of the outer peripheral portion of the Schottky barrier electrode 4 made of titanium. The diode rectification function and the guard ring function are the same as in the first and second embodiments.
[0033]
(Production method)
The Schottky barrier diode in the present embodiment can be manufactured as follows, for example. The processes up to the formation of the back electrode 6 and the annealing are the same as those already described in the first embodiment.
[0034]
Next, titanium is formed to a thickness of 0.5 μm on the surface of the drift layer 2 as an electrode material layer that becomes the material of the Schottky barrier electrode 4 by a sputtering film forming method. Next, an etching mask for the Schottky barrier electrode 4 is formed by a normal patterning method. Next, for example, the Schottky barrier electrode 4 is formed by etching with diluted hydrofluoric acid. At the same time, a part of the periphery of the Schottky barrier electrode 4 is oxidized to form the high resistance guard ring 18 made of titanium oxide so as to have an annular shape when viewed from above. In this case, since the oxidation reaction tends to proceed rapidly at the interface between SiC and titanium, the thickness of the high resistance guard ring 18 increases from the outside to the inside of the Schottky barrier electrode 4 as shown in FIG. A thinning shape can also be obtained.
[0035]
(Action / Effect)
In the silicon carbide semiconductor device in the present embodiment, high resistance guard ring 18 is a metal oxide layer formed by oxidation of Schottky barrier electrode 4, and therefore, between Schottky barrier electrode 4 and high resistance guard ring 18. There is no structurally discontinuous change and no electric field concentration occurs. Further, since the high resistance guard ring 18 is formed by oxidation of the electrode, problems such as defects at the interface between the Schottky barrier electrode and the high resistance layer are reduced. Further, it is not necessary to form the guard ring using a separate process. Thus, a silicon carbide semiconductor device including a Schottky barrier diode excellent in reverse breakdown voltage can be easily realized.
[0036]
In the first to third embodiments, the example in which titanium is used as the Schottky barrier electrode 4 is shown. However, depending on the specifications of the forward voltage and the reverse leakage current, gold, nickel, platinum, Copper or the like can be used as a metal forming the Schottky barrier. In the above embodiment, an example in which titanium oxide is used as the high resistance guard ring has been described. However, other metal compounds such as other nitrides as well as other metal oxide films exhibiting high resistance, and other high resistances are used. A material exhibiting properties can also be used.
[0037]
In the third embodiment, an example in which diluted hydrofluoric acid is used as an etchant that oxidizes a part of the outer peripheral portion of the Schottky barrier electrode 4 is shown. Is possible.
[0038]
(Embodiment 4)
(Constitution)
With reference to FIG. 5, the silicon carbide semiconductor device in Embodiment 4 based on this invention is demonstrated. FIG. 5 is a cross-sectional view of a Schottky barrier diode as an example of a silicon carbide semiconductor device. The characteristics of SiC substrate 1, drift layer 2, Schottky barrier electrode 4, and back electrode 6 are the same as in the first embodiment. This Schottky barrier diode includes a semi-insulating guard ring 28 made of semi-insulating SiC formed by crystal growth instead of the high-resistance guard ring 18 as in the previous embodiments as a guard ring. The inner end of the semi-insulating guard ring 28 is the Schottky barrier end 15.
[0039]
In this example, the semi-insulating guard ring 28 is formed in the outer peripheral edge region of the Schottky barrier electrode 4 so that the film thickness decreases from the outside toward the inside as shown in FIG. You may form in the shape like the high resistance guard ring 18 shown in FIG. 1, FIG.
[0040]
The rectifying function of the diode and the function of the guard ring are the same as in the first embodiment.
[0041]
(Production method)
The Schottky barrier diode shown in this embodiment can be manufactured as follows, for example. A drift layer 2 having n-type conductivity with a low impurity concentration is epitaxially grown on the SiC substrate 1 by, for example, a thickness of 10 μm by a CVD crystal growth method.
[0042]
Next, similarly, as an impurity, for example, organic vanadium is introduced into the growth chamber, and a layer serving as a material of the semi-insulating guard ring 28 made of SiC having semi-insulating conductivity is grown. Next, back electrode 6 is formed by the same method as in the first embodiment.
[0043]
Next, the semi-insulating guard ring 28 is formed on the upper surface so as to have an annular shape when viewed from above by a normal patterning method and an etching method. At the time of this formation, as described in the second embodiment, if a gentle slope forming process by dry etching using the recession of the etching mask is used, the outer peripheral portion of the Schottky barrier electrode 4 as shown in FIG. A shape in which the film thickness of the semi-insulating guard ring 28 becomes thinner from the outside toward the inside can also be formed. The subsequent formation process of the Schottky barrier electrode 4 is the same as that of the first embodiment.
[0044]
(Action / Effect)
In the present embodiment, an expensive apparatus is required as a process for obtaining a high-resistance SiC layer, and a crystal growth process is used instead of an ion implantation process that causes defect damage to the crystal. By using a crystal growth apparatus used for producing the drift layer in combination, a semi-insulating silicon carbide semiconductor layer made of the growth layer can be obtained at a low cost. The semi-insulating silicon carbide semiconductor layer formed by the growth layer is free from damage due to implantation and surface deterioration due to annealing, so that a good Schottky barrier diode can be realized. Further, since the drift layer and the guard ring are made of the same material and there is no discontinuity at the boundary, there is an effect that there is no electric field concentration and no increase in leakage current.
[0045]
Further, as exemplified in the present embodiment, when the thickness of the semi-insulating guard ring 28 is reduced from the outside toward the inside, the Schottky barrier electrode 4 serving as the end 15 of the Schottky barrier There is no structural discontinuity at the boundary of the semi-insulating guard ring 28, and no electric field concentration occurs at this point. For this reason, the problem that a reverse breakdown voltage falls does not arise. Therefore, a silicon carbide semiconductor device including a Schottky barrier diode having an ideal reverse breakdown voltage that is limited by the material properties of the silicon carbide semiconductor can be realized.
[0046]
(Embodiment 5)
(Constitution)
With reference to FIG. 6, the silicon carbide semiconductor device in Embodiment 5 based on this invention is demonstrated. FIG. 6 is a cross-sectional view of a Schottky barrier diode as an example of a silicon carbide semiconductor device. The characteristics of SiC substrate 1, drift layer 2, Schottky barrier electrode 4, and back electrode 6 are the same as in the first embodiment. This Schottky barrier diode includes a p-type conductive guard ring 23 formed by crystal growth instead of the high resistance guard ring 18 and the semi-insulating guard ring 28 as in the previous embodiments as a guard ring. . The inner end of the p-type conductive guard ring 23 is the Schottky barrier end 15.
[0047]
In this example, the p-type conductive guard ring 23 is formed in the outer peripheral edge region of the Schottky barrier electrode 4 so that the film thickness decreases from the outside toward the inside as shown in FIG. 1 and 4 may be formed into a shape like the high resistance guard ring 18 shown in FIGS.
[0048]
The rectifying function of the diode and the function of the guard ring are the same as in the first embodiment.
[0049]
(Production method)
The Schottky barrier diode shown in this embodiment can be manufactured as follows, for example. The process up to the epitaxial growth of the drift layer 2 is the same as that described in the fourth embodiment.
[0050]
Next, similarly, for example, organic aluminum is introduced into the growth chamber as an impurity, and a layer serving as a material of the p-type conductive guard ring 23 having p-type conductivity is grown. Next, back electrode 6 is formed by the same method as in the first embodiment.
[0051]
Next, the p-type conductive guard ring 23 is formed on the upper surface so as to have an annular shape when viewed from above by a normal patterning method and an etching method. At this time, in the same manner as in the fourth embodiment, the outer peripheral portion of the Schottky barrier electrode 4 is formed with a shape in which the film thickness of the p-type conductive guard ring 23 becomes thinner from the outside toward the inside as shown in FIG. You can also The subsequent formation process of the Schottky barrier electrode 4 is the same as that of the first embodiment.
[0052]
(Action / Effect)
In this example, since the grown SiC layer is used as the guard ring, in addition to having the same effect as in the fourth embodiment, the pn junction is formed by crystal growth, so that it is formed by ion implantation. Compared to the guard ring, the reverse leakage current can be reduced.
[0053]
(Embodiment 6)
(Constitution)
With reference to FIG. 7, the silicon carbide semiconductor device in Embodiment 6 based on this invention is demonstrated. FIG. 7 is a cross-sectional view of a Schottky barrier diode as an example of a silicon carbide semiconductor device. On the upper surface of the n-type SiC substrate 1, an SiC drift layer 2 having n-type conductivity with a low impurity concentration is formed by epitaxial growth. A concave gentle slope 19 is provided on the upper surface of the drift layer 2, and the guard ring is formed so as to cover the slope 19. This guard ring is a p-type conductive guard ring 23 formed by crystal growth. The pn junction surface 27 is formed on the slope 19. The Schottky barrier electrode 4 extends away from the drift layer 2 on the p-type conductive guard ring 23 outside the Schottky barrier end 15. The end 5 of the Schottky barrier electrode 4 is located above the p-type conductive guard ring 23.
[0054]
The rectifying function of the diode and the function of the guard ring are the same as in the fifth embodiment.
[0055]
(Production method)
The Schottky barrier diode shown in this embodiment can be manufactured as follows, for example. The process up to the epitaxial growth of the drift layer 2 is the same as that described in the fourth embodiment.
[0056]
With reference to FIGS. 8A to 8D, a process for forming the p-type conductive guard ring 23 will be described. First, as shown in FIG. 8A, a concave portion having a shape corresponding to the shape of the Schottky barrier electrode 4 is formed in the SiC drift layer 2 by a normal patterning method and an etching method. However, in forming the concave portion, as described in the second embodiment, the inner surface of the concave portion becomes a gentle slope 19 by using a gentle slope forming process by dry etching utilizing the recession of the etching mask. . The depth of the recess is, for example, 0.55 μm. Hereinafter, description will be made on the assumption that the depth of the recess is 0.55 μm.
[0057]
Next, as shown in FIG. 8B, a material film 33 serving as a material for the p-type conductive guard ring 23 is formed on the entire surface including the recesses of the drift layer 2 with a thickness of 0. Grows by 5 μm. This can be done as a subsequent regrowth with the drift layer 2 grown. Next, as shown in FIG. 8C, a resist mask 32 is formed. As shown in FIG. 8D, using the resist mask 32, the SiC layer is etched again by a normal patterning method and an etching method to a depth of 0.6 μm, and viewed from above. The p-type conductive guard ring 23 is formed so as to have an annular shape. Also at this time, a gentle slope forming process by dry etching utilizing the recession of the etching mask is used. The remaining resist mask 32 is removed. Next, back electrode 6 and Schottky barrier electrode 4 are formed by the same method as in the first embodiment. In this way, the structure shown in FIG. 7 is obtained.
[0058]
(Action / Effect)
In the present embodiment, in addition to the effects described in the fifth embodiment, the radius of curvature at the portion where the pn junction surface 27 is convex is increased, so that the electric field concentration at the pn junction surface 27 is reduced. In this way, electric field concentration can be alleviated and the reverse breakdown voltage of the Schottky barrier diode can be improved.
[0059]
In the fifth and sixth embodiments, aluminum is used as an impurity for crystal growth of p-type conductivity. However, an impurity that becomes another acceptor such as boron may be used. In the fourth embodiment, vanadium is used as an impurity for semi-insulating crystal growth. However, other deep level impurities can naturally be used.
[0060]
In each of the above-described embodiments, an example of a silicon carbide semiconductor device formed from a single Schottky barrier diode has been described. However, the present invention relates to a semiconductor device in which a pn diode and a Schottky barrier diode are combined, a switch element, and a Schottky barrier diode. The present invention can also be applied to a silicon carbide semiconductor device combined with a key barrier diode.
[0061]
In addition, the said embodiment disclosed this time is an illustration in all the points, Comprising: It is not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and includes all modifications within the scope and meaning equivalent to the terms of the claims.
[0062]
【Effect of the invention】
According to the present invention, when a negative voltage is applied to the Schottky barrier electrode, since the high resistance guard ring is formed under the end of the Schottky barrier electrode, the potential is divided by the resistance of the high resistance guard ring. As a result, the electric field concentration at the end of the Schottky barrier electrode is relaxed, and the pressure resistance is improved. Moreover, the guard ring is not provided in the same layer as the drift layer, but is configured so that the Schottky barrier electrode is lifted by the guard ring. This eliminates the need for ion implantation and other methods that have been problematic in the past.
[Brief description of the drawings]
FIG. 1 is a cross sectional view of a silicon carbide semiconductor device in a first embodiment based on the present invention.
FIG. 2 is a cross sectional view of a silicon carbide semiconductor device in a second embodiment based on the present invention.
FIGS. 3A to 3D are explanatory views of a gentle slope forming process in Embodiment 2 based on the present invention. FIGS.
4 is a cross sectional view of a silicon carbide semiconductor device in a third embodiment based on the present invention. FIG.
FIG. 5 is a cross sectional view of a silicon carbide semiconductor device in a fourth embodiment based on the present invention.
FIG. 6 is a cross sectional view of a silicon carbide semiconductor device in a fifth embodiment based on the present invention.
FIG. 7 is a cross sectional view of a silicon carbide semiconductor device in a sixth embodiment based on the present invention.
FIGS. 8A to 8D are explanatory diagrams of a p-type conductive guard ring forming step according to the sixth embodiment of the present invention.
FIG. 9 is a cross-sectional view of a silicon carbide semiconductor device based on a conventional technique.
FIG. 10 is a cross-sectional view of a silicon carbide semiconductor device based on a conventional technique.
[Explanation of symbols]
1 SiC substrate, 2 drift layer, 3 p-type conductive guard ring region, 4 Schottky barrier electrode, 5 edge (of Schottky barrier electrode), 6 back electrode, 7, 27 pn junction surface, 8 high resistance guard ring region , 15 (Schottky barrier) edge, 18 high resistance guard ring, 19 slope, 23 p-type conductive guard ring, 28 semi-insulating guard ring, 31, 32 resist mask, 33 (p-type conductive guard ring) Material film, 38 Material film (of high resistance guard ring).

Claims (3)

A substrate made of a silicon carbide semiconductor material;
A drift layer made of a silicon carbide semiconductor material formed on the upper surface of the substrate;
A Schottky barrier electrode disposed so as to be in contact with the drift layer and covering a partial region of the upper surface of the drift layer, and for causing the interface in contact with the drift layer to function as a Schottky barrier;
In the outer peripheral edge region of the Schottky barrier electrode, a guard ring is interposed between the drift layer and the Schottky barrier electrode, and the Schottky barrier electrode is lifted by the guard ring. And
The guard ring has a shape in which the film thickness becomes thinner from the outside to the inside of the Schottky barrier electrode,
The guard ring is made of a material different from that of the drift layer, and has a resistance value higher than a resistance value when a forward voltage is applied to the drift layer and lower than a resistance value when a reverse voltage is applied to the drift layer. Including
The silicon carbide semiconductor device, wherein the guard ring is a metal oxide layer formed by oxidizing an outer end portion of the Schottky barrier electrode.   The silicon carbide semiconductor device according to claim 1, wherein the Schottky barrier electrode includes titanium, and the metal oxide layer includes titanium oxide. A drift layer forming step of forming a drift layer made of a silicon carbide semiconductor material on an upper surface of a substrate made of a silicon carbide semiconductor material;
An electrode material film forming step for forming an electrode material film made of a Schottky barrier electrode material for causing the interface in contact with the drift layer to function as a Schottky barrier so as to be in contact with the drift layer and to cover the upper surface of the drift layer; ,
An etching step of removing other parts from the electrode material film while leaving a desired portion;
An oxidation step of oxidizing a part of the electrode material film to form a guard ring made of a metal oxide layer,
The etching step and the oxidation step are performed in parallel.
A method for manufacturing a silicon carbide semiconductor device.

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