JP3856729B2 - 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 layer, and more particularly to a silicon carbide semiconductor device for high current and high breakdown voltage and a method for manufacturing the same.
[0002]
[Prior art]
Silicon carbide (silicon carbide, SiC) is a semiconductor that is harder and has a wider band gap than silicon (Si), and is a material applied to power devices, environmental devices, high-temperature devices, high-frequency devices, etc. .
[0003]
As a power device, a switching element using Si is often used. When the switching element functions as a rectifying element, a pn diode is used because a withstand voltage is required. However, the pn diode has a large switching loss. For this reason, a Schottky diode with smaller switching loss is desirable. However, a desired breakdown voltage cannot be obtained when the Schottky diode is formed of Si due to the physical property limit of Si. Accordingly, SiC having a wide band gap has been attracting attention in order to realize a switching element with high breakdown voltage and low switching loss.
[0004]
FIG. 8 is a cross-sectional view of a general Schottky diode using SiC, which is a first conventional example representative of a switching element. As shown in FIG. 8, a Schottky diode 80 of the first conventional example includes an n-type 4H—SiC semiconductor substrate 81 and an n-type 4H—SiC layer epitaxially grown on the upper surface of the semiconductor substrate 81. 82, an ion implantation layer 83 implanted with boron, aluminum or the like, and a Schottky electrode 84 made of nickel, titanium, or the like, which is provided on the upper surface side of the substrate and forms a Schottky barrier between the 4H-SiC layer 82. And an ohmic electrode 85 made of nickel provided on the back side of the semiconductor substrate 81 and an insulator layer 86 surrounding the Schottky electrode 84.
[0005]
Here, the ion implantation layer 83 is necessary to form a guard ring structure that alleviates electric field concentration, and is in contact with a part of the Schottky electrode 84 at the interface 87. The ion implantation layer 83 has a function of relaxing electric field concentration when a high voltage is applied between the electrodes 84 and 85 so that the Schottky electrode 84 is negative and the ohmic electrode 85 is positive.
[0006]
FIG. 9 is a cross-sectional view of a general Schottky diode using SiC, which is a second conventional example representative of a switching element. As shown in FIG. 9, the Schottky diode 90 of the second example includes a semiconductor substrate 81 made of n-type 4H—SiC and an n-type 4H—SiC layer 82 epitaxially grown on the upper surface of the semiconductor substrate 81. A Schottky electrode 91 made of nickel, titanium or the like, which is provided on the upper surface side of the substrate and forms a Schottky barrier between the 4H-SiC layer 82 and the ion-implanted layer 83 into which boron or aluminum is implanted, In addition, an ohmic electrode 85 made of nickel provided on the back surface side of the semiconductor substrate 81 and an insulator layer 86 surrounding the Schottky electrode 91 are provided. Unlike the Schottky diode 80 of the first example, the Schottky electrode 91 of the Schottky diode 90 of the second example straddles the upper surface of the insulator layer 86.
[0007]
The ion implantation layer 83 is necessary to form a guard ring structure that reduces electric field concentration, and is in contact with a part of the Schottky electrode 91 at the interface 92. The ion implantation layer 83 has a function of relaxing electric field concentration when a high voltage is applied between the electrodes 85 and 91 so that the Schottky electrode 91 is negative and the ohmic electrode 85 is positive.
[0008]
Here, in the Schottky diodes 80 and 90 shown in FIG. 8 or 9, in order for the ion implantation layer 83 to function as a guard ring, it is necessary to activate the implanted impurities such as boron by high-temperature heat treatment. That is, in the manufacturing process of the Schottky diodes 80 and 90, before the Schottky electrodes 84 and 91 are formed, high-temperature heat treatment exceeding 1500 ° C. is required for the ion implantation layer 83.
[0009]
For example, as disclosed in the literature (Ito et al., IEEE Electron Device Letters, Vol. 17, No. 3 (1996) pp 139-141), the ion implantation layer 83 at a relatively low temperature (1050 ° C.). An example of heat-treating is also reported.
[0010]
In addition, in order to stabilize the characteristics of the Schottky electrodes 84 and 91, a heat treatment is performed, for example, at about 400 ° C. before or after the metal film constituting the Schottky electrodes 84 and 91 is patterned.
[0011]
[Problems to be solved by the invention]
However, in the conventional semiconductor device, as shown in FIGS. 8 and 9, in the region where the Schottky electrode 84 and the insulator layer 86 are in contact, and in the region where the Schottky electrode 91 and the insulator layer 86 are in contact, It has been found that altered layers 88, 93, 94 are formed, respectively. The deteriorated layers 88, 93, 94 are insulated from the metal constituting the Schottky electrodes 84, 91 and the insulating layer 86 in contact with the insulator layer 86 at the time of heat treatment of the Schottky electrodes 84, 91. It is formed by the reaction with the body material. If significant electric field concentration occurs in the portion where the altered layers 88 and 93 are in contact with the ion implantation layer 86, a leakage current may be induced or the diodes 80 and 90 may be destroyed in some cases.
[0012]
Further, in the manufacturing process of the conventional Schottky diode 80 or 90, if a high temperature heat treatment at 1500 ° C. or more is performed to activate the ion implantation layer 83, the surface of the 4H—SiC layer 82 is affected by the high temperature heat treatment. Roughness may occur, which may cause a leakage current in the Schottky diode 80 or 90 and may change various conditions in the manufacturing process due to loss of surface flatness. Further, when impurities in the furnace adhere to the surface of the 4H—SiC layer 82 during the high-temperature heat treatment, impurities are mixed at the interface between the 4H—SiC layer 82 and the Schottky electrode 84 or 91, thereby causing a leakage current of the Schottky barrier. May occur.
[0013]
In order to prevent such roughness and contamination of the surface of the 4H—SiC layer 82, it is preferable to perform a heat treatment in a state in which a protective film such as an oxide film is formed on the 4H—SiC layer 82. It is difficult to form a protective film that can withstand high-temperature heat treatment.
[0014]
Furthermore, when performing high-temperature heat treatment, a general-purpose apparatus cannot be used, and a special high-frequency induction heating apparatus such as a silicon carbide crystal growth apparatus must be used. When such a high-temperature heating furnace is used, an extra time is required for cooling, resulting in poor throughput and a disadvantage in terms of cost during mass production. Therefore, heat treatment at a lower temperature of the ion implantation layer 83 is preferable. However, since the surface layer of the epitaxial growth layer 82 is damaged along with the ion implantation, activation of the ion implantation layer 83 and recovery of the crystal structure are not possible when the ion implantation layer is heat-treated at a relatively low temperature. It is enough.
[0015]
A practical Schottky diode requires a large forward electrode current because it requires a forward current of several amperes or more. As a result, the area of the interface where the altered layers 88 and 93 and the ion implantation layer 83 are in contact with each other is inevitably large. Therefore, the probability of device destruction due to the influence of the altered layer of the Schottky diode is not low.
[0016]
In some cases, the insulator layer 86 does not exist in the structure shown in FIG. However, when the insulator layer 86 is not present, most of the ion implantation layer 83 is exposed to the outside, which causes a problem in the assembly process of the semiconductor device. For example, when a wire such as gold or aluminum is connected to the Schottky electrode 84, if the ion implantation layer 83 is exposed, the wire and the ion implantation layer 83 come into contact with each other, or the contact portion between the wire and the Schottky electrode 84 comes into contact. Therefore, wire metal and electrode metal may scatter in a minute amount. For this reason, there is a risk of unexpected leakage current and device destruction.
[0017]
An object of the present invention is to provide a semiconductor device that uses a silicon carbide layer and generates relatively little element breakdown or leakage current, and a method for manufacturing the same.
[0018]
[Means for Solving the Problems]
The semiconductor device of the present invention is formed on a semiconductor layer made of silicon carbide, an ion implantation layer formed by ion implantation into the semiconductor layer, and at least a region of the semiconductor layer excluding the ion implantation layer. The Schottky electrode and the Schottky electrode include an insulator layer formed on the ion implantation layer with a predetermined gap.
[0019]
As a result, since there is a gap between the Schottky electrode and the insulator layer, a structure in which there is no altered layer due to the reaction between the Schottky electrode and the insulator layer is realized. Therefore, it is possible to suppress the occurrence of leakage current due to the presence of the deteriorated layer in the semiconductor device, and thus it is possible to suppress the breakdown of the semiconductor device when a reverse bias is applied to the semiconductor device.
[0020]
The Schottky electrode may be formed across the region of the semiconductor layer excluding the ion implantation layer and the ion implantation layer.
[0021]
An upper metal electrode formed on the Schottky electrode and in contact with the Schottky electrode may be further provided.
[0022]
In that case, since the upper metal electrode covers at least a part of the insulator layer, the concentration of the electric field on the Schottky barrier is reduced, so that a slight leakage current of the guard ring is suppressed. Can do.
[0023]
Since the Schottky electrode is not in contact with the ion-implanted layer, the leakage current suppressing function can be remarkably exhibited.
[0024]
Since the Schottky electrode is heat-treated, formation of a Schottky barrier can be ensured.
[0025]
In the case where a substrate made of silicon carbide is further provided, the semiconductor layer is preferably epitaxially grown on the substrate.
[0026]
In the case where a substrate made of Si is further provided, the semiconductor layer is preferably epitaxially grown on the substrate.
[0027]
The semiconductor device preferably functions as a Schottky diode.
[0028]
A first method for manufacturing a semiconductor device of the present invention is a manufacturing process of a semiconductor device having a Schottky electrode in contact with a semiconductor layer made of silicon carbide, in which impurity ions serving as a dopant are implanted into the semiconductor layer, A step (a) of forming an ion implantation layer and a step (b) of forming an insulator layer on at least a part of the ion implantation layer, wherein the step (b) Performed at temperature.
[0029]
Since this method does not require high-temperature treatment, the surface of the semiconductor layer is prevented from being roughened, and the process can be simplified and the throughput can be improved.
[0030]
Before the step (b), it is possible to ensure the cleanliness of the surface of the semiconductor layer by further including a step of forming a protective film covering at least a region excluding the ion implantation layer in the semiconductor layer.
[0031]
The step of forming the protective film is preferably performed before the step (a), and the protective film is preferably a mask for ion implantation in the step (a).
[0032]
In the step (b), the insulator layer is formed in a high-temperature atmosphere containing oxygen, so that the ion implantation layer can be activated in the step (b).
[0033]
In the step (b), the insulator layer can be formed by a deposition method.
[0034]
A second method for manufacturing a semiconductor device according to the present invention is a method for manufacturing a semiconductor device having a Schottky electrode in contact with a semiconductor layer made of silicon carbide, the step of forming an ion implantation mask on the semiconductor layer ( a) a step (b) of implanting impurity ions as dopants into the semiconductor layer from above the ion implantation mask to form an ion implantation layer; and an insulator layer on the ion implantation layer. Forming step (c), forming a resist film having an opening in a region where a Schottky electrode is to be formed on the insulator layer, and using the resist film as a mask Removing the ion implantation mask by reactive etching and forming an opening larger than the opening of the resist film in the insulator layer; and from above the resist film After depositing the Shokumaku, by removing the resist film, and a step (f) to leave a Schottky electrode having a predetermined gap between the insulator layer.
[0035]
By this method, it becomes easy to form an insulator layer and a Schottky electrode that are opposed to each other with a gap therebetween by cell alignment.
[0036]
It is preferable to further include a step of performing a heat treatment at a temperature of 1200 ° C. or lower after the step (b) and before the step (d).
[0037]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is a cross-sectional view of the semiconductor device (Schottky diode) in the first embodiment. As shown in FIG. 1, the Schottky diode 10 of this embodiment includes a semiconductor substrate 11 made of n-type 4H—SiC, an n-type 4H—SiC layer 12 epitaxially grown on the upper surface of the semiconductor substrate 11, and A Schottky barrier between the ion implantation layer 13 formed by implanting boron into the 4H—SiC layer 12 and the 4H—SiC layer 12 provided on the upper surface side of the substrate and including a part of the ion implantation layer 13. A Schottky electrode 14 made of nickel, titanium, or the like, forming an ohmic electrode 15 made of nickel provided on the back side of the semiconductor substrate 11, and an insulator layer 16 made of a thermal oxide film surrounding the Schottky electrode 14. I have.
[0038]
Also in this embodiment, the ion-implanted layer 13 is necessary for forming a guard ring structure that relaxes electric field concentration, and is in contact with a part of the Schottky electrode 14. The ion implantation layer 13 has a function of relaxing electric field concentration when a high voltage is applied between the electrodes 14 and 15 so that the Schottky electrode 14 is negative and the ohmic electrode 15 is positive.
[0039]
Here, the main feature of the Schottky diode 10 of the present embodiment is that the Schottky electrode 14 and the insulator layer 16 are not in contact with each other.
[0040]
In the present embodiment, since the Schottky electrode 14 and the insulator layer 16 are not in contact with each other and the gap 17 is provided between them in this embodiment, the conventional Schottky diode shown in FIG. 8 or FIG. Altered layers 88, 93, 94 such as 80 or 90 do not occur. Therefore, the occurrence of leakage current can be suppressed by the Schottky diode 10 of the present embodiment.
[0041]
Next, the manufacturing process of the Schottky diode of this embodiment will be described with reference to FIGS.
[0042]
First, before the step shown in FIG. 2 (a), it is made of 4H—SiC having a diameter of 2 inches with the main surface being a surface inclined by 8 ° in the [1 1-2 0] direction from the (0 0 0 1) plane. A semiconductor substrate 11 is prepared. Then, the 4H—SiC layer 12 is epitaxially grown on the semiconductor substrate 11. This epitaxial growth is performed using propane as a carbon source, silane as a silicon source, hydrogen as a carrier gas, and nitrogen as a dopant. The 4H—SiC substrate 11 is n-type and has a resistivity of about 0.02 Ω · cm. The 4H—SiC layer 12 is n-type, and the carrier concentration is about 1 × 10 6. ¹⁶ cm ^-3 The film thickness is about 9 μm. At the end of the epitaxial growth, the surface treatment of the 4H—SiC layer 12 is performed in a high-temperature hydrogen atmosphere.
[0043]
Then, in the step shown in FIG. 2A, a SiON film having a thickness of about 800 nm is formed on the 4H—SiC layer 12. ₂ Deposit a film. Next, SiO is performed by a photolithography process. ₂ After forming a resist mask on the film, the resist mask is used to make SiO ₂ The film was etched with buffered hydrofluoric acid, and a 1 mm diameter SiO 2 serving as an implantation mask was formed on the 4H—SiC layer 12. ₂ A mask 21 is formed. Thereafter, the resist mask is removed.
[0044]
Next, in the step shown in FIG. ₂ From above the mask 21, boron ions (B ⁺ ) Injection. At this time, the ion implantation conditions are, for example, an inclination angle of 0 degree, an implantation energy of 30 keV, and a dose amount of 1 × 10. ¹⁵ / Cm ² The substrate temperature at the time of implantation is 500 ° C. Thereby, as shown in FIG.2 (b), the ion implantation layer 13 is formed. At this time, SiO ₂ Boron is also implanted into the mask 21, but SiO 2 ₂ In the mask 21, boron ions are SiO. ₂ It has a thickness that does not pass through the mask and reach the 4H—SiC layer 12 immediately below the mask.
[0045]
Next, in the step shown in FIG. ₂ With the mask 21 left, the substrate is introduced into a resistance heating furnace, and in the resistance heating furnace, heat treatment is performed in a nitrogen atmosphere at 1100 ° C. for 90 minutes to activate boron implanted into the ion implantation layer 13.
[0046]
Thereafter, the substrate was subjected to thermal oxidation treatment at 1100 ° C. for 60 minutes in an oxygen atmosphere containing water vapor. As a result, as shown in FIG. 2C, the surface portion of the ion implantation layer 13 is thermally oxidized, and a thermal oxide film 23 having a thickness of about 20 nm is formed on the ion implantation layer 13. At this time, SiO ₂ Since there is a mask 21, SiO 2 in the ion implantation layer 13 is used. ₂ The surface portion 24 in contact with the mask 21 is hardly affected by thermal oxidation and hardly oxidized.
[0047]
Next, a nickel film (Ni film) having a thickness of 400 nm is deposited on the back surface of the 4H—SiC substrate 11 in the step shown in FIG. The substrate on which the Ni film is deposited is heat-treated at 1000 ° C. for 5 minutes in a nitrogen atmosphere, thereby forming an ohmic electrode 15 made of Ni.
[0048]
Next, in the step shown in FIG. 2E, a photolithography step is performed to form a resist mask Re1 having an opening in a region where a Schottky electrode is to be formed on the thermal oxide film 23. The size of the opening of the resist mask Re1 is, for example, 1.04 mm in diameter, and SiO 2 ₂ It is made slightly larger than the mask 21.
[0049]
Next, in the step shown in FIG. 2 (f), SiO 2 is etched by wet etching with buffered hydrofluoric acid (BHF). ₂ The mask 21 is removed. At that time, the region near the edge of the opening of the resist film Re1 in the thermal oxide film 23 is also subjected to the etching action. Thereby, the thermal oxide film 23 is patterned to form the insulator layer 16 having an opening with a diameter of 1.041 mm, for example. That is, SiO ₂ By continuing the wet etching even after the mask 21 is removed, the insulator layer 16 having an opening larger than the opening (about 1.04 mm in diameter) of the resist mask Re1 is formed.
[0050]
Next, in the step shown in FIG. 2G, a Ni film 14x having a thickness of about 200 nm is deposited by electron beam evaporation from above the resist mask Re1. At this time, the Ni film 14x is deposited not only on the resist film Re1 but also on the 4H—SiC layer 12 and the ion implantation layer 13 in the opening of the resist mask Re1.
[0051]
Next, in the step shown in FIG. 2H, only the Ni film on the resist mask Re1 is removed by lift-off of the resist mask Re1, and the 4H-SiC layer 12 including a part of the ion implantation layer 13 is removed. Then, the Schottky electrode 14 is formed. At this time, an interval 17 of 0.5 μm exists between the insulator layer 16 and the Schottky electrode 14, and they are not in contact with each other. Thereafter, the substrate is heat-treated at 400 ° C. for 5 minutes in a nitrogen atmosphere, so that a Schottky barrier can be reliably formed between the Schottky electrode 14 and the 4H—SiC layer 12.
[0052]
Through the above steps, the Schottky diode 10 shown in FIG. 1 is formed.
[0053]
For example, the thermal oxide film 23 is patterned without forming the resist mask Re1 shown in FIG. ₂ Simultaneously with the removal of the mask 21, an insulator layer having a large opening is formed, and then a Ni film is deposited and patterned on the substrate to form a Schottky electrode smaller than the opening of the insulator layer. Is also possible. However, in that case, the size of the gap between the Schottky electrode and the thermal oxide film depends on the position due to the positional deviation between the mask for forming the Schottky electrode and the mask for patterning the thermal oxide film. It will vary.
[0054]
On the other hand, as shown in FIG. 2G, the manufacturing process of this embodiment easily forms a gap 17 having a substantially uniform size between the Schottky electrode 14 and the insulator layer 16 by self-alignment. be able to.
[0055]
In addition, SiO ₂ By forming the insulator layer 16 made of a thermal oxide film with the mask 21 left, SiO 2 ₂ The damage layer generated on the surface portion of the ion implantation layer 13 can be removed while maintaining the surface of the 4H—SiC layer 12 directly under the mask 21 clean. Moreover, since the oxidation is promoted by the presence of the damaged layer, a relatively thick thermal oxide film can be formed.
[0056]
-Experimental example-
Here, in order to confirm the effect of the Schottky diode of this embodiment, the following experiment was performed.
[0057]
For comparison, a conventional Schottky diode shown in FIG. 8 was also fabricated. The difference from the Schottky diode shown in FIG. 1 is that the insulator layer is made of SiO by plasma CVD. ₂ The use of a layer, and the condition that overetching is not performed during wet etching of the insulator, that is, the insulating layer 86 and the Schottky electrode 84 are in contact with each other while minimizing the etching time. . Hereinafter, the Schottky diode of the present embodiment is referred to as a diode A, and the conventional Schottky diode is referred to as a diode B.
[0058]
When the current-voltage characteristics (IV characteristics) of the diodes A and B were evaluated, there was almost no difference in the forward IV characteristics of the two diodes A and B. However, there was a large difference in the reverse direction IV characteristics between the two. In the diode A, 10% or less of the elements were destroyed when -600 V was applied as a reverse voltage. The cause of the breakdown is not due to the structure of the Schottky diode, but due to a defect in the crystal of the semiconductor substrate 11 or the 4H—SiC layer 12 which is an epitaxial growth layer.
[0059]
On the other hand, the leakage current of the diode B was slightly larger than that of the diode A, and most of them were destroyed when a reverse bias of −500 V or more was applied. The reason why the above difference occurs is considered as follows.
[0060]
In the diode B, since the activation temperature of the ion implantation layer is as low as 1100 ° C., damage due to the ion implantation remains in the ion implantation layer, and the crystal defects are not completely recovered. In this state, if the altered layer 88 as shown in FIG. 8 is in contact with the ion implantation layer 83, the electric field tends to concentrate on that portion, which may cause local leakage current and easily break down. On the other hand, in the diode A, since the insulating layer 16 and the Schottky electrode 14 are not in contact with each other as shown in FIG.
[0061]
However, also in the conventional Schottky diode 80, the ion implantation layer 83 can be sufficiently activated by the heat treatment at a higher temperature, in which case the probability of destruction is reduced. However, even when heat treatment is performed at a higher temperature, the structure without the deteriorated layer as in this embodiment has a smaller leakage current and a lower probability of destruction. In addition, if the surface becomes extremely rough due to the heat treatment at an excessively high temperature, the problem described in the section of the prior art is caused accordingly.
[0062]
-First Modification of Process of First Embodiment-
In the first embodiment, the thermal oxide film is formed after the ion implantation layer 13 is heat-treated at 1100 ° C., but the heat treatment step and the thermal oxidation step may be performed in the same apparatus. For example, as a first modification of the process of the first embodiment, after forming the ion implantation layer 13 as shown in FIG. 2B in the Schottky diode manufacturing process of the first embodiment, The substrate is introduced into a thermal oxidation furnace, an inert gas such as argon or nitrogen is introduced into the thermal oxidation furnace, the temperature is raised to 1100 ° C., and the ion implantation layer 13 is activated by heat treatment that is held for a certain period of time. Alternatively, the ion implantation layer 13 and the thermal oxide film 23 may be formed continuously by replacing the inert gas atmosphere with an oxygen-containing atmosphere and proceeding to the thermal oxidation process as it is. Thereby, the manufacturing process can be shortened.
[0063]
-Second modification of the process of the first embodiment-
In the first modification of the process of the first embodiment, the heat treatment step and the thermal oxidation step of the ion-implanted 4H—SiC layer are performed in the same apparatus, but the heat treatment step and the thermal oxidation step are performed simultaneously. Also good. For example, as a second modification of the process of the first embodiment, as shown in FIG. 2B in the Schottky diode manufacturing process shown in the first modification of the process of the first embodiment. In addition, after the ion implantation layer 13 is formed, the substrate is introduced into a thermal oxidation furnace, and heat treatment is performed as it is in an atmosphere containing oxygen at a desired temperature, whereby the activity of the ion implantation layer 13 by heating in the oxidation atmosphere is performed. The thermal oxidation film 23 may be formed at the same time. Of course, when the heat treatment time is insufficient, for example, the atmosphere containing oxygen may be replaced with an inert gas atmosphere, and the heat treatment time may be added. Thereby, the manufacturing process can be further shortened. However, when the heat treatment step and the thermal oxidation step are performed at the same time, the ion implantation layer 13 may be entirely thermally oxidized due to damage caused by the ion implantation in the ion implantation layer 13. Therefore, it is preferable that the ion implantation layer 13 is not thermally oxidized by increasing the implantation energy during ion implantation or by increasing the implantation depth of the ion implantation layer 13 by multi-stage implantation. .
[0064]
In the method for manufacturing a semiconductor device according to the present embodiment, the heat treatment temperature and thermal oxidation temperature after ion implantation are set to 1100 ° C. However, if a general-purpose resistance heating furnace, lamp annealing apparatus, or thermal oxidation furnace can be used, other In this sense, the heat treatment temperature and the thermal oxidation treatment temperature after ion implantation are desirably 1200 ° C. or lower.
-First and second modified examples of the structure of the first embodiment-
3A and 3B are cross-sectional views of the semiconductor device in the first and second modifications of the structure of the first embodiment.
[0065]
As shown in FIGS. 3A and 3B, in the first and second modifications, an upper metal electrode 31 is provided on the Schottky electrode 14. Since other elements in the Schottky diodes 30a and 30b of these modified examples are the same as those of the Schottky diode 10 of the first embodiment, the same reference numerals as those in FIG.
[0066]
As shown in FIG. 3A, in the Schottky diode 30a of the first modified example of the structure, the Schottky electrode 14 has a non-ion-implanted region of the 4H—SiC layer 12 as in the first embodiment. An upper metal electrode 31 is formed so as to straddle the ion implantation layer 13 and cover the Schottky electrode 14. Since other elements in the Schottky diode 30a of this modification are the same as those of the Schottky diode 10 of the first embodiment, the same reference numerals as those in FIG. In this modification, the Schottky electrode 14 is in contact with both the ion implantation layer 13 and the non-ion implantation region of the 4H—SiC layer 12, but the insulator layer 16 and the Schottky electrode 14 are not in contact with each other. The upper metal electrode 31 covers at least a part of the insulator layer 16. By previously heat-treating the Schottky electrode 14 at a desired temperature and then forming the upper metal electrode 31, a stable Schottky interface is formed at the interface between the 4H—SiC layer 12 and the Schottky electrode 14. Therefore, no special heat treatment is required after the upper metal electrode 31 is formed. Therefore, even if the upper metal electrode 31 enters the gap 17 between the Schottky electrode 14 and the insulator layer 16, an altered layer is hardly formed between the insulator layer 16 and the upper metal electrode 31.
[0067]
Further, since it is necessary to form a Schottky barrier between the 4H-SiC layer 12 and the type of metal material constituting the Schottky electrode 14 is limited to some extent, the metal material constituting the upper metal electrode 31 is limited. Since the type of is not particularly limited, a material that hardly forms a deteriorated layer with respect to the insulator layer 16 can be easily selected.
[0068]
In the first modification shown in FIG. 3A, the area of the contact portion 32 between the Schottky electrode 14 and the ion implantation layer 13 is preferably small. This is because a slight leakage current may be observed from the contact portion 32 when the heat treatment temperature of the ion implanted layer 13 is low. On the other hand, the area of the contact portion 33 between the upper metal electrode 31 and the insulator layer 16 is preferably large to some extent. Since the upper metal electrode 31 covers a part of the insulator layer 16, the contact portion 33 between the upper metal electrode 31 and the insulator layer 16 acts so as to alleviate electric field concentration. In addition, the presence of the insulator layer 16 makes it possible to further reduce the slight leakage current of the guard ring portion.
[0069]
In the Schottky diode 30b according to the second modification of the structure shown in FIG. 3B, the Schottky electrode 14 is in contact with only the non-ion implantation region of the 4H-SiC layer 12, and is in contact with the ion implantation layer 13. It is not configured. In the second modification, it is possible to more effectively reduce the leakage current.
[0070]
(Second Embodiment)
FIG. 4 is a cross-sectional view of the semiconductor device (Schottky diode) in the second embodiment. As shown in FIG. 4, the Schottky diode 40 according to the present embodiment includes an SiO layer formed by a thermal CVD method instead of the insulator layer 16 made of a thermal oxide film according to the first embodiment. ₂ An insulator layer 41 made of a film is provided. Since the other elements in the Schottky diode 40 of the present embodiment are the same as those of the Schottky diode 10 of the first embodiment, the same reference numerals as those in FIG.
[0071]
Also in this embodiment, the Schottky electrode 14 and the insulator layer 41 are not in contact with each other, and the gap 17 is provided between them, so that the conventional Schottky diode 80 or 90 shown in FIG. The altered layers 88, 93, and 94 are not generated. Therefore, the occurrence of leakage current can be suppressed by the Schottky diode 40 of the present embodiment.
[0072]
Next, the manufacturing process of the Schottky diode of this embodiment will be described with reference to FIGS.
[0073]
Since the processing in the steps shown in FIGS. 5A and 5B is the same as the processing shown in FIGS. 2A and 2B shown in the first embodiment, description thereof will be omitted.
[0074]
In the present embodiment, in the step shown in FIG. ₂ With the mask 21 left, the substrate is introduced into a resistance heating furnace, and in the resistance heating furnace, heat treatment is performed in a nitrogen atmosphere at 1100 ° C. for 90 minutes to activate boron implanted into the ion implantation layer 13.
[0075]
Then, using a CVD apparatus, as shown in FIG. 5C, the ion implantation layer 13 and SiO 2 are formed by thermal CVD. ₂ About 200 nm thick SiO 2 on the mask 21 ₂ A film 51 is deposited. During thermal CVD, silane gas and dinitrogen monoxide are used to maintain the substrate temperature at about 850 ° C.
[0076]
Next, a nickel film (Ni film) having a thickness of 400 nm was deposited on the back surface of the 4H—SiC substrate 11 in the step shown in FIG. The substrate on which the Ni film is deposited is heat-treated at 1000 ° C. for 5 minutes in a nitrogen atmosphere, thereby forming an ohmic electrode 15 made of Ni.
[0077]
Thereafter, in the step shown in FIG. 5E, a lift-off process similar to the steps shown in FIGS. 2E to 2H is performed, and the non-ion-implanted region and the ion-implanted layer 13 of the 4H—SiC layer 12 are performed. A Schottky electrode 14 is formed over the two. In addition, SiO ₂ The insulating layer 41 is formed by patterning the film 51. At this time, an interval 17 of 2 μm exists between the insulator layer 41 and the Schottky electrode 14, and they are not in contact with each other. Thereafter, the substrate is heat-treated at 400 ° C. for 5 minutes in a nitrogen atmosphere, so that a Schottky barrier is reliably formed between the Schottky electrode 14 and the 4H—SiC layer 12.
[0078]
According to the present embodiment, as in the first embodiment, the gap 17 between the insulator layer 41 and the Schottky electrode 21 by self-alignment can be ensured uniformly.
[0079]
-Experimental example-
Next, an experiment conducted for confirming the effect of the present embodiment will be described. In the following description, the Schottky diode in the second embodiment is abbreviated as diode C.
[0080]
The IV characteristics of the diode C were also evaluated. The forward direction IV characteristics of the diode C were hardly different from those of the diodes A and B. The reverse IV characteristic of the diode C was as excellent as that of the diode A, and 10% or less of the elements were destroyed when -600 V was applied as the reverse voltage. The cause of the breakdown is not due to the structure of the Schottky diode, but due to a crystal in the semiconductor substrate 11 or a defect in the 4H—SiC layer 12.
[0081]
In the diode B, since the activation temperature of the ion implantation layer is as low as 1100 ° C., damage due to the ion implantation remains in the ion implantation layer, and the crystal defects are not completely recovered. In this state, if the altered layer 88 as shown in FIG. 8 is in contact with the ion implantation layer 83, the electric field tends to concentrate on the portion, which may cause a local leakage current and easily break down. On the other hand, in the diode C, since the insulating layer 41 and the Schottky electrode 14 are not in contact with each other as shown in FIG.
[0082]
-First Modification of Process of Second Embodiment-
In the second embodiment, the ion-implanted layer 13 is heat-treated at 1100 ° C. and then the CVD apparatus is used for SiO 2. ₂ Although the film was formed, the heat treatment process and SiO ₂ The film forming step may be performed in the same apparatus. For example, as a first modification of the process of the second embodiment, after forming the ion implantation layer 13 as shown in FIG. 5B in the Schottky diode manufacturing process of the second embodiment, The substrate is introduced into a CVD apparatus, an inert gas such as argon or nitrogen is introduced into the CVD apparatus, the temperature is raised to 1100 ° C., and the ion-implanted layer 13 is activated by a heat treatment that is maintained for a certain period of time. Replace the active gas atmosphere with a reactive gas atmosphere containing silane or dinitrogen monoxide, and leave it as it is. ₂ By moving to the film formation process, the formation of the ion implantation layer 13 and the SiO 2 ₂ The formation of the film 51 may be performed continuously. Thereby, the manufacturing process can be shortened.
[0083]
-Second modification of the process of the second embodiment-
In the first modification of the manufacturing process of the second embodiment, the heat treatment process of the ion-implanted 4H—SiC layer and the SiO 2 ₂ The film formation process was performed in the same apparatus, but the heat treatment process and SiO ₂ You may perform a film formation process simultaneously. For example, as a second modification of the second embodiment, in the manufacturing process of the Schottky diode shown in the first modification of the process of the second embodiment, as shown in FIG. After forming the ion-implanted layer 13, the substrate is introduced into a CVD apparatus, and the SiO 2 is kept at a desired temperature in an atmosphere containing a reactive gas. ₂ By depositing the film, SiO ₂ Activation of ion-implanted layer 13 by heating for film formation and SiO ₂ The formation of the film 51 may be performed simultaneously. Thereby, the manufacturing process can be further shortened. Of course, if the heat treatment time is insufficient, for example, the reaction gas atmosphere may be replaced with an inert gas atmosphere, and further heat treatment time may be added. If the heat treatment temperature is too low, the heat treatment time is further increased to a desired temperature. Heat treatment may be performed.
[0084]
In the method for manufacturing a semiconductor device according to the present embodiment, the heat treatment temperature and thermal CVD temperature after ion implantation are set to 1100 ° C. and 850 ° C. However, if a general-purpose resistance heating furnace or lamp annealing device can be used, other special processes are possible. In this sense, the heat treatment temperature after ion implantation and SiO ₂ The film formation temperature is desirably 1200 ° C. or lower.
[0085]
In the first and second modifications of the second embodiment and process, the insulator layer is made of SiO. ₂ Although formed from a film, an insulator layer made of another insulating material may be formed.
[0086]
Further, in the second embodiment, SiO constituting the insulator layer. ₂ Although the film 51 is formed by a thermal CVD method, a plasma CVD method, a sputtering method, or other deposition methods may be used.
[0087]
-First and second modifications of the structure of the second embodiment-
6A and 6B are cross-sectional views of the semiconductor device according to the first and second modifications of the structure of the second embodiment.
[0088]
As shown in FIGS. 6A and 6B, in the first and second modifications, an upper metal electrode 61 is provided on the Schottky electrode 14. Since other elements in the Schottky diodes 60a and 60b of these modified examples are the same as those of the Schottky diode 40 of the second embodiment, the same reference numerals as those in FIG.
[0089]
As shown in FIG. 6A, in the Schottky diode 60a of the first modified example of the structure, the Schottky electrode 14 includes the 4H—SiC layer 12, the ion implantation layer 13, and the like, as in the second embodiment. The upper metal electrode 61 is formed so as to cover the Schottky electrode 14. In this modification, the Schottky electrode 14 is in contact with both the ion implantation layer 13 and the non-ion implantation region of the 4H—SiC layer 12, but the insulator layer 41 and the Schottky electrode 14 are not in contact with each other. The upper metal electrode 61 covers at least a part of the insulator layer 41. By previously heat-treating the Schottky electrode 14 at a desired temperature and then forming the upper metal electrode 61, a stable Schottky interface is formed at the interface between the 4H-SiC layer 12 and the Schottky electrode 14. Therefore, no special heat treatment is required after the upper metal electrode 61 is formed. Therefore, even if the upper metal electrode 61 enters the gap 17 between the Schottky electrode 14 and the insulator layer 41, an altered layer is hardly formed between the insulator layer 41 and the upper metal electrode 61.
[0090]
Further, since it is necessary to form a Schottky barrier between the 4H-SiC layer 12 and the type of metal material constituting the Schottky electrode 14 is limited to some extent, the metal material constituting the upper metal electrode 61 is limited. Since the type of is not particularly limited, it is possible to easily select a material that hardly forms a deteriorated layer with respect to the insulator layer 41.
[0091]
In the first modification shown in FIG. 6A, the area of the contact portion 62 between the Schottky electrode 14 and the ion implantation layer 13 is preferably small. This is because a slight leakage current may be observed from the contact portion 62 when the heat treatment temperature of the ion implanted layer 13 is low. On the other hand, the area of the contact portion 63 between the upper metal electrode 61 and the insulator layer 41 is preferably large to some extent. Since the upper metal electrode 61 covers a part of the insulator layer 41, the contact portion 63 between the upper metal electrode 61 and the insulator layer 41 acts so as to alleviate electric field concentration. In addition, the presence of the insulator layer 41 makes it possible to further reduce the slight leakage current of the guard ring portion.
[0092]
In the Schottky diode 60b according to the second modification of the structure shown in FIG. 6B, the Schottky electrode 14 is in contact with the 4H—SiC layer 12 and is not in contact with the ion implantation layer 13. Yes. In the second modification, it is possible to more effectively reduce the leakage current.
[0093]
In the semiconductor device and the manufacturing method thereof described in the first and second embodiments, the non-ion implantation region of the 4H—SiC layer 12 is a surface where the Schottky electrode is in contact with silicon carbide, and dust, impurities, etc. It is necessary to minimize the contamination of Therefore, in the semiconductor device manufacturing process, if the surface of the 4H-SiC layer 12 is covered with a protective layer before forming the Schottky electrode, the protective layer is removed immediately before the Schottky electrode forming step. Therefore, it is possible to remove dust and impurities mixed in the process. Therefore, in the first and second embodiments, in the step of forming the insulator layer, SiO, which is a protective film, is formed on the 4H—SiC layer 12 that is not ion-implanted. ₂ Since the mask 21 is provided, the cleanliness of the surface of the 4H—SiC layer 12 can be ensured.
[0094]
In particular, as in the manufacturing steps of the first and second embodiments, the protective film is SiO. ₂ Since the mask 21 functions as an ion implantation mask, the process can be simplified.
[0095]
In particular, in the first embodiment, when the thermal oxide film 23 to be the insulator layer 16 is formed, the protective film is formed on the 4H—SiC layer 12 that is not ion-implanted. ₂ The presence of the mask can suppress thermal oxidation of the surface portion of the 4H—SiC layer 12 in contact with the Schottky electrode 14. When the surface portion of the 4H—SiC layer 12 that is not ion-implanted is directly thermally oxidized, the thermal oxide film needs to be removed before the Schottky electrode 14 is formed. If there are significant defects such as the end of the micropipe, the defective portion is enlarged by removing the thermal oxide film. This defective portion may further cause a leakage current when a Schottky diode is formed later. Therefore, when the thermal oxide film is formed, the 4H—SiC layer 12 is preferably covered with a protective film.
[0096]
(Third embodiment)
FIG. 7 is a cross-sectional view of the semiconductor device (Schottky diode) in the third embodiment. As shown in FIG. 7, the ion implantation layer 71 of the Schottky diode 70 of the present embodiment has portions formed discretely below the vicinity of the central portion of the Schottky electrode 14. Since the other elements in the Schottky diode 70 of the present embodiment are the same as those of the Schottky diode 10 of the first embodiment, the same reference numerals as those in FIG.
[0097]
Also in this embodiment, since the Schottky electrode 14 and the insulator layer 16 do not contact each other and the gap 17 is provided between them, the conventional Schottky diode 80 or 90 shown in FIG. 8 or FIG. The altered layers 88, 93, and 94 are not generated. Therefore, the occurrence of leakage current can be suppressed by the Schottky diode 70 of the present embodiment.
[0098]
Also in this embodiment, the structure of a modified example in which the upper metal electrode 31 shown in FIGS. 3A and 3B is provided can be employed.
[0099]
(Other embodiments)
In the semiconductor device and the manufacturing method thereof described in the first and second embodiments, the 4H—SiC substrate is used as the semiconductor substrate, but a 6H—SiC substrate, a 15R—SiC substrate, or a Si substrate may be used. . Further, instead of the 4H—SiC layer, a 15R—SiC layer epitaxially grown on the 15R—SiC substrate or a 3C—SiC layer epitaxially grown on the Si substrate may be used as the semiconductor layer. Of course, other combinations may be used, and a laminated structure of two or more layers may be used. For example, a substrate including a SiC layer (semiconductor layer) epitaxially grown on an insulator substrate may be used. That is, the Schottky electrode only needs to be formed on the SiC layer.
[0100]
In the first and second embodiments, if the size of the gap 17 between the insulator layer 16 and the Schottky electrode 14 is about 0.1 μm or less, formation of a deteriorated layer can be reliably prevented. Since it becomes difficult, the thickness is preferably 0.1 μm or more, and more preferably 0.5 μm or more in order to more reliably prevent the formation of the deteriorated layer. On the other hand, in order to perform the lift-off process reliably, the gap 17 is preferably 20 μm or less, and more preferably 10 μm or less. Therefore, the dimension of the gap 17 is preferably in the range of 0.1 μm to 20 μm, and more preferably in the range of 0.5 to 10 μm.
[0101]
In the semiconductor device and the manufacturing method thereof described in the first and second embodiments, Ni is used as a material constituting the ohmic electrode and the Schottky electrode, but any material that can obtain ohmic characteristics and Schottky characteristics, respectively. Any material can be used.
[0102]
In the semiconductor device and the manufacturing method thereof described in the first and second embodiments, an electrode having a stacked structure may be provided as a Schottky electrode or an ohmic electrode instead of a single layer structure. Further, the size of the electrode is not particularly limited.
[0103]
In the semiconductor device and the manufacturing method thereof described in the first and second embodiments, the lift-off method is used as the method for forming the Schottky electrode. However, other methods may be used.
[0104]
Instead of the process conditions and gas types used in the manufacturing steps of the semiconductor device of the first and second embodiments, other conditions and gas types may be employed.
[0105]
In the semiconductor device and the manufacturing method thereof according to the first and second embodiments, boron is used as the ion implantation species. However, since the ion implantation layer only needs to be a high resistance layer, it is not an implantation species other than boron. But of course it does n’t matter.
[0106]
In the manufacturing process in the first and second embodiments, the heat treatment temperature and thermal oxidation treatment temperature after ion implantation are formed at 1200 ° C. or lower, but the insulator layer and the Schottky electrode are not in contact with each other. If it has a structure, it is possible to prevent formation of a deteriorated layer even if heat treatment after ion implantation is performed at a temperature exceeding 1200 ° C. For example, even if heat treatment is performed at a temperature of 1500 ° C. or higher after ion implantation, it is possible to prevent the formation of a deteriorated layer by the structures or manufacturing methods of the first and second embodiments.
[0107]
Furthermore, the semiconductor device of the present invention is not limited to a Schottky diode, and may be another element form such as a transistor as long as it has an electric field concentration relaxation structure by ion implantation.
[0108]
Further, the semiconductor device manufacturing method of the present invention can be applied to semiconductor devices having other configurations. For example, even when a semiconductor device having the conventional configuration shown in FIG. 9 is formed, the semiconductor device does not require high-temperature heat treatment by using the manufacturing methods of the first and second embodiments. The manufacturing process can be simplified and the throughput can be improved, and the leakage current can be reduced.
[0109]
【The invention's effect】
According to the semiconductor device or the manufacturing method thereof of the present invention, it is possible to provide a semiconductor device with a small leakage current and a large withstand voltage, or a manufacturing method thereof.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a Schottky diode according to a first embodiment.
FIGS. 2A to 2H are cross-sectional views illustrating manufacturing steps of the Schottky diode in the first embodiment. FIGS.
FIGS. 3A and 3B are cross-sectional views of a semiconductor device in first and second modifications of the structure of the first embodiment. FIGS.
FIG. 4 is a cross-sectional view of a Schottky diode according to a second embodiment.
FIGS. 5A to 5E are cross-sectional views illustrating manufacturing steps of a Schottky diode in the second embodiment. FIGS.
6A and 6B are cross-sectional views of a semiconductor device in first and second modifications of the structure of the second embodiment.
FIG. 7 is a cross-sectional view of a Schottky diode according to a third embodiment.
FIG. 8 is a cross-sectional view of a general Schottky diode using SiC, which is a first conventional example representative of a switching element.
FIG. 9 is a cross-sectional view of a general Schottky diode using SiC, which is a second conventional example representative of a switching element.
[Explanation of symbols]
10 Schottky diode
11 Semiconductor substrate
12 4H-SiC layer
13 Ion implantation layer
14 Schottky electrode
15 Ohmic electrode
16 Insulator layer
23 Thermal oxide film

Claims (11)

A semiconductor layer made of silicon carbide;
An ion implantation layer formed by ion implantation into the semiconductor layer;
A Schottky electrode formed on a region of the semiconductor layer excluding at least the ion implantation layer;
A semiconductor device comprising the Schottky electrode and an insulator layer formed on the ion implantation layer with a predetermined gap. The semiconductor device according to claim 1,
The Schottky electrode is formed over a region of the semiconductor layer excluding an ion implantation layer and the ion implantation layer. The semiconductor device according to claim 1 or 2,
A semiconductor device, further comprising an upper metal electrode formed on the Schottky electrode and in contact with the Schottky electrode. The semiconductor device according to claim 3.
The semiconductor device, wherein the upper metal electrode covers at least a part of the insulator layer. The semiconductor device according to claim 1 ,
The semiconductor device, wherein the Schottky electrode is not in contact with the ion implantation layer. In the semiconductor device according to any one of claims 1 to 5,
A semiconductor device, wherein the Schottky electrode is heat-treated. In the semiconductor device according to any one of claims 1 to 5,
Further comprising a substrate made of silicon carbide,
The semiconductor device, wherein the semiconductor layer is epitaxially grown on the substrate. In the semiconductor device according to any one of claims 1 to 5,
Further comprising a substrate made of Si,
The semiconductor device, wherein the semiconductor layer is epitaxially grown on the substrate. In the semiconductor device according to claim 1,
The semiconductor device functions as a Schottky diode. A method of manufacturing a semiconductor device having a Schottky electrode in contact with a semiconductor layer made of silicon carbide,
A step (a) of forming an ion implantation mask on the semiconductor layer;
(B) forming an ion implantation layer by implanting impurity ions serving as a dopant into the semiconductor layer from above the ion implantation mask;
A step (c) of forming an insulator layer on the ion implantation layer;
A step (d) of forming a resist film having an opening in a region where a Schottky electrode is to be formed on the insulator layer;
A step (e) of removing the ion implantation mask by isotropic etching using the resist film as a mask and forming an opening larger than the opening of the resist film in the insulator layer;
After the metal film is deposited from above the resist film, the resist film is removed to leave a Schottky electrode having a predetermined gap with the insulator layer (f). Method. The method of manufacturing a semiconductor device according to claim 1 0,
A method of manufacturing a semiconductor device, further comprising a step of performing a heat treatment at a temperature of 1200 ° C. or lower after the step (b) and before the step (d).

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