Patent Application
20210313466
The present invention relates to a semiconductor device and a method for manufacturing the same.
In order to achieve a high withstand voltage and a low on-resistance, a semiconductor device with a super junction (SJ) structure has been developed (see Patent Literature 1). The SJ structure is a structure in which n-type drift regions and p-type column regions are arranged alternately with each other to periodically form pn junctions. In the semiconductor device with the SJ structure, even if a concentration of N-type impurities in the drift regions through which a main current flows is increased to lower the on-resistance, the withstand voltage thereof can be kept high since the drift regions are depleted at the time of reverse bias by depletion layers which extend from the pn junction.
[Patent Literature] Japanese Patent Laid-Open Publication No. 2002-319680
However, there has been a problem that the withstand voltage of the semiconductor device decreases by the fact that an electric field concentrates to boundaries between the drift regions and the column regions at the time of reverse bias.
The present invention has been made in consideration of the above-described problem, and has an object to provide a semiconductor device that has a super junction structure and is capable of suppressing the decrease of the withstand voltage and to provide a method for manufacturing the semiconductor device.
A semiconductor device according to an aspect of the present invention includes, in at least a part between a drift region and a column region which constitute a super junction structure, an electric field relaxation region that is either a low-concentration region in which an impurity concentration is lower than in a same conductivity-type adjacent region or a non-doped region.
A method for manufacturing a semiconductor device according to another aspect of the present invention includes forming a drift region and a column region by ion-implanting impurities into a substrate, wherein an electric field relaxation region that is either a low-concentration region in which an impurity concentration is lower than in a same conductivity-type adjacent region or a non-doped region is formed in at least part between the drift region and the column region.
According to the present invention, a semiconductor device that has a super junction structure and is capable of suppressing the decrease of the withstand voltage and a method for manufacturing the semiconductor device can be provided.
Hereinafter, a description will be given of embodiments with reference to the drawings. In the description of the drawings, the same reference numerals are assigned to the same portions, and a description thereof is omitted. However, the drawings are schematic, and relationships between thicknesses and plane dimensions, ratios of thicknesses of the respective layers, and the like include portions different from actual ones. Moreover, between the drawings, portions where dimensional relationships and ratios therebetween are different from each other are also included.
As illustrated in
The semiconductor layer 20 includes: a first conductivity-type drift region 21 through which the main current flows; and second conductivity-type column regions 22 and electric field relaxation regions 23, which are disposed inside the drift region 21. Each of the electric field relaxation regions 23 is disposed in at least a part between the drift region 21 and the column region 22. The column regions 22 extend in parallel to the current path. An SJ structure is composed of the drift regions 21 and the column regions 22. The electric field relaxation regions 23 are low-concentration regions in which an impurity concentration is lower than in adjacent regions with the same conductivity type, or non-doped regions which are not intentionally doped with impurities. In the semiconductor device illustrated in
The first conductivity type and the second conductivity type are conductivity types opposite to each other. That is, if the first conductivity type is the n type, then the second conductivity type is the p-type, and the first conductivity type is the p-type, then the second conductivity type is the n type. Hereinafter, a description will be given of the case where the first second conductivity type is the n-type and the second conductivity type is the p-type.
The semiconductor layer 20 illustrated in
Moreover, the semiconductor device illustrated in
A plurality of gate trenches are formed so as to reach the substrate 10. Opening portions of the gate trenches lie astride upper surfaces of the source region 25, the column regions 22 and the well region 24. The gate insulating films 60 are disposed on inner wall surfaces of the gate trenches, and the control electrodes 50 are disposed inside the gate trenches so that a periphery thereof is surrounded by the gate insulating films 60. Between the gate trenches, the drift region 21 and the well region 24 connect to each other, and the well region 24 and the source region 25 connect to each other. At the time of an on-operation, an inversion layer is formed in a channel region of the well region 24, which contacts the gate insulating films 60.
The semiconductor device illustrated in
Further, in the semiconductor device illustrated in
Note that, when the drift region 21 is of the n-type, and the electric field relaxation regions 23 is of the p-type, then the impurity concentration of the electric field relaxation regions 23 may be higher than that of the drift region 21. Moreover, when the column regions 22 are of the p-type, and the electric field relaxation regions 23 are of the n-type, then the impurity concentration of the electric field relaxation regions 23 may be higher than the column regions 22.
Hereinafter, a description will be given of basic operations of the semiconductor device illustrated in
In an on-operation, a potential of the control electrodes 50 is controlled in a state in which a positive potential is applied to the second main electrode 40 while taking a potential of the first main electrode 30 as a reference, whereby the semiconductor device operates as a transistor. That is, a voltage between the control electrodes 50 and the first main electrode 30 is set to a predetermined threshold voltage or more, whereby inversion layers are formed in channel regions of the well region 24 on side surfaces of the control electrodes 50. Thus, the semiconductor device turns to an on-state, and the main current flows between the first main electrode 30 and the second main electrode 40.
Meanwhile, in an off-operation, the voltage between the control electrodes 50 and the first main electrode 30 is set equal to or less than the predetermined threshold voltage. Thus, the inversion layer disappears, and the main current is shielded.
In an off-state, the depletion layers spread from the interfaces between the drift region 21 and the column regions 22, and when the reverse voltage increase to some extent, the drift region 21 and the column regions 22 turn to a pinch-off state. Thus, an electric field intensity of the drift region 21 and the column regions 22 forms a uniform rectangular distribution, and a maximum electric field applied to the semiconductor device decreases greatly. Thus, the withstand voltage of the semiconductor device improves.
In order to obtain a high withstand voltage by completely depleting the SJ structure in the off-state, it is required to set, to approximately 1, a ratio of a total amount of n-type impurities of the n-type semiconductor region and a total amount of p-type impurities of the p-type semiconductor regions. Therefore, the concentration Nd of the n-type impurities of the drift region 21, the concentration Na of the p-type impurities of the column regions 22, a width Wn of the drift region 21, and a width Wp of the column regions 22 are set so as to satisfy the following Equation (1).
Na×Wp=Nd×Wn (1)
The width Wn and the width Wp are widths in a direction where the drift region 21 and the column regions 22 are arranged alternately with each other.
The impurity concentrations of the drift region 21 and the column regions 22 are set so as to satisfy Equation (1), whereby the drift region 21 and the column regions 22 are depleted by the depletion layers which extend from the pn junctions. Therefore, the withstand voltage of the semiconductor device is high. In addition, a resistance value of the drift region 21 can be reduced.
However, at the time of reverse bias, the electric field is likely to concentrate on the pn junctions in the interfaces between the drift region 21 and the column regions 22. This is because the relationship of Equation (1) is not established in regions close to the pn junctions, and electric charges in the n-type semiconductor region and the p-type semiconductor regions are not balanced. The withstand voltage of the semiconductor device decreases when the electric field concentrates on the pn junctions.
In contrast, in the semiconductor device illustrated in
The model illustrated in
As illustrated in
As described above, the electric field is concentrated on the region between each column region 22 and the second main electrode 40. Therefore, though the electric field relaxation region 23 is disposed on the entire region of the boundary between the drift region 21 and the column region 22 in the semiconductor device illustrated in
However, the concentration of the electric field also occurs in the boundary region where the drift region 21 and the column region 22 face each other, the boundary region being parallel to the current path.
As described above, in accordance with the semiconductor device according to the first embodiment of the present invention, the electric field relaxation region 23 is disposed on at least a part between the drift region 21 and the column region 22, whereby the concentration of the electric field is relaxed. As a result, the decrease of the withstand voltage of the semiconductor device having the SJ structure can be decreased.
For the substrate 10, a semi-insulating substrate and an insulating substrate are suitably used. Thus, an element separation process at the time of integrating a plurality of semiconductor devices on the same substrate 10 can be simplified. Moreover, at the time of mounting the semiconductor device on a cooler, it is possible to omit an insulating substrate placed between the substrate 10 and the cooler. Here, the insulating substrate refers to a substrate with resistivity of several kΩ·cm or more.
For example, a silicon carbide (SiC) substrate having insulating properties is used for the substrate 10. SiC has some polytypes (crystal polymorphisms), and an SiC substrate with typical 4H can be used for, the substrate 10. The SiC substrate is used for the substrate 10, whereby the insulating properties of the substrate 10 can be increased, and thermal conductivity thereof can be increased. Therefore, the back surface of the substrate 10 can be directly attached to a cooling mechanism, and the semiconductor device can be cooled efficiently. In accordance with this structure, since thermal conductivity of the SiC substrate is large, heat generated by the main current can be radiated efficiently when the semiconductor device is in the on-state. Moreover, SiC is a wide band gap semiconductor in which the number of intrinsic carriers is small, and accordingly, easily achieves high insulating properties. Therefore, use of the SiC substrate makes it possible to achieve a semiconductor device with a high withstand voltage.
Hereinafter, a method for manufacturing the semiconductor device according to the first embodiment of the present invention will be described with reference to the drawings. Note that the method for manufacturing a semiconductor device, which will be mentioned below, is merely an example, and the semiconductor device is achievable by a variety of manufacturing methods other than this mentioned method, the manufacturing methods including modified examples thereof. Hereinafter, a description will be given of the case of using a non-doped SiC substrate for the substrate 10.
First, as illustrated in
As a general mask material, a silicon oxide film can be used, and as a deposition method, a thermal CVD method or a plasma CVD method can be used. As a patterning method, a photolithography method can be used. That is, the mask material is etched by using a patterned photoresist film as a mask. As an etching method, wet etching using hydrofluoric acid and dry etching such as reactive ion etching can be used. Thereafter, the photoresist film is removed by oxygen plasma, sulfuric acid or the like. In this way, the mask material is patterned.
Next, the column regions 22 which extend in parallel to the drift region 21 are formed inside the drift region 21 so as to form the electric field relaxation regions 23 in at least a part between the drift region 21 and the column regions 22 themselves. That is, as illustrated in
Thereafter, as illustrated in
In the ion implantation, for example, nitrogen (N) is used as the n-type impurities, and aluminum and boron are used as the p-type impurities. Note that a crystal defect can be suppressed from occurring in ion-implanted regions by performing the ion implantation in a state of heating the substrate 10 to a temperature of approximately 600° C. Then, the ion-implanted impurities are activated by being subjected to heat treatment. For example, heat treatment at approximately 1700° C. is performed in an argon atmosphere or a nitrogen atmosphere.
The impurity concentrations of the column regions 22 and the drift region 21 are, for example, approximately 1E15/cm3 to 1E19/cm3. However, the impurity concentrations of the drift region 21 and the column regions 22 are set so as to satisfy the relationship of Equation (1) so that the drift region 21 and the column regions 22 are depleted by the depletion layers generated between the drift region 21 and the column regions 22 in an off-state.
An impurity concentration of the well region 24 is, for example, approximately 1E15/cm3 to 1E19/cm3. Moreover, an impurity concentration of the source region 25 is, for example, approximately 1E18/cm3 to 1E21/cm3.
Note that manufacturing cost can be reduced in the case of ion-implanting impurities into the substrate 10 to form the drift region 21 and the column regions 22 more than in the case forming the drift region 21 and the column regions 22 by epitaxial growth.
Next, as illustrated in
Thereafter, the gate insulating films 60 are formed on inner wall surfaces of the gate trenches 500. A method for forming the gate insulating films 60 may by either a thermal oxidation method or a deposition method. As an example, in the case of the thermal oxidation method, the substrate is heated to a temperature of approximately 1100° C. in an oxygen atmosphere. Thus, a silicon oxide film is formed on all portions where the substrate contacts oxygen.
After the gate insulating films 60 are formed, annealing treatment at approximately 1000° C. may be performed in an atmosphere of nitrogen, argon, N2O or the like in order to reduce an interface state on interfaces between the well region 24 and the gate insulating films 60. Moreover, thermal oxidation in an atmosphere of rigid NO or N2O is also possible. A temperature in that case is suitably 1100° C. to 1400° C. A thickness of the gate insulating films 60 is about several ten nanometers.
Next, the gate trenches 500 are embedded to form the control electrodes 50. A general material of the control electrodes 50 is polysilicon films, and a description will be given here of the case of using the polysilicon films for the control electrodes 50.
A reduced pressure CVD method or the like can be used as the deposition method of the polysilicon films. For example, a thickness of the polysilicon films to be deposited is set to a value larger than a half of a width of each of the gate trenches 500, and the gate trenches 500 are embedded with the polysilicon films. Since the polysilicon films are formed from the inner wall surfaces of the gate trenches 500, the gate trenches 500 can be completely embedded with the polysilicon films by setting the thickness of the polysilicon films as described above. For example, when the width of the gate trenches 500 is 2 μm, the polysilicon films are formed so that a film thickness thereof becomes thicker than 1 μm. Moreover, after the polysilicon films are deposited, annealing treatment at 950° C. is performed in phosphorus oxychloride (POCl3), whereby n-type polysilicon films are formed to impart conductivity to the control electrodes 50.
Next, as illustrated in
Thereafter, the first main electrode 30 and the second main electrode 40, which face each other with the semiconductor layer 20 sandwiched therebetween, are formed separately from each other on the substrate 10 along a direction where the drift region 21 extends. For example, the first main electrode 30 and the second main electrode 40 are formed on predetermined regions formed by selectively etching the substrate 10 by using an etching mask patterned by a photolithography technology and the like. Thus, the semiconductor device illustrated in
As a material of the first main electrode 30 and the second main electrode 40, there can be used metal materials such as titanium (Ti), nickel (Ni) and molybdenum (Mo) and laminated films of Ti/Ni/Ag and the like. For example, after such a metal material is entirely deposited by a sputtering method, an EB evaporation method or the like, the metal material is etched by dry etching using a patterned photoresist film as a mask, and each of the first main electrode 30 and the second main electrode 40 is formed. Alternatively, the first main electrode 30 and the second main electrode 40 may be formed by a plating process.
In accordance with the method for manufacturing a semiconductor device, which is described above, the electric field relaxation regions 23 are formed between the drift region 21 and the column regions 22. Therefore, the concentration of the electric field at the time of reverse bias is relaxed, and the decrease of the withstand voltage of the semiconductor device having the SU structure can be suppressed.
Note that, in the above, the description is given of the case of forming the electric field relaxation regions 23 as non-doped semiconductor regions by leaving a part of the non-doped substrate 10 between the drift region 21 and the column regions 22. However, the electric field relaxation regions 23 are not limited to the non-doped regions. That is, the electric field relaxation regions 23 may be either n-type semiconductor regions formed by doping the substrate 10 with n-type impurities or p-type semiconductor regions formed by doping the substrate 10 with p-type impurities.
For example, when the drift region 21 is an n-type semiconductor region, and the column regions 22 are p-type semiconductor regions, then the electric field relaxation regions 23 may be set to be n-type semiconductor regions having a lower impurity concentration than the drift region 21. Alternatively, the electric field relaxation regions 23 may be set to be p-type semiconductor regions having a lower impurity concentration than the column regions 22.
In the above, the description is given of the example of using an SiC substrate for the substrate 10; however, a semi-insulating substrate or an insulating substrate other than the SiC substrate may be used for the substrate 10. For example, a GaN substrate, a diamond substrate, a zinc oxide (ZnO) substrate, an AlGaN substrate and the like, which are wide band gap substrates, may be used for the substrate 10.
Moreover, a wide band gap semiconductor may be used for the semiconductor layer 20. Thus, it is possible to increase the impurity concentration while keeping on maintaining the withstand voltage to be high. Therefore, the withstand voltage of the semiconductor device can be increased, and the on-resistance can be reduced.
Further, the semiconductor layer 20 in, which the respective regions are made of the same material is used, whereby active regions of the semiconductor device are formed of the same semiconductor material. Thus, a malfunction caused by an occurrence of a defect due to junction of different types of semiconductor materials can be eliminated, and reliability of the semiconductor device can be improved.
Note that, in the above, the description is given of the example of using the first conductivity-type polysilicon films for the control electrodes 50; however, second conductivity-type polysilicon films may be used for the control electrodes 50. Moreover, other semiconductor materials may be used for the control electrodes 50, or other conductive materials such as metal materials may be used. For example, second conductivity-type poly silicon carbide, SiGe, Al and the like can be used for the materials of the control electrodes 50.
Further, though the example of using the silicon oxide films for the gate insulating films 60 is described, silicon nitride films may be used for the gate insulating films 60. Moreover, laminated films of the silicon oxide films and the silicon nitride films may be used for the gate insulating films 60. Isotropic etching in the case of using the silicon nitride films for the gate insulating films 60 can be performed by washing using hot phosphoric acid at 160° C.
A semiconductor device according to a modified example of the first embodiment of the present invention further includes an electric field relaxation electrode disposed so as to cover at least a part of the region where the drift region 21 and the column regions 22 face each other. In the semiconductor device according to the modified example, which is illustrated in
A conductor film such as a metal film is used for the electric field relaxation electrode 70. The electric field relaxation electrode 70 and the second main electrode 40 may be formed integrally with each other, for example, by using the same material as the second main electrode 40. For example, an insulating film such as a silicon oxide film is used for the interlayer insulating film 80.
In the semiconductor device illustrated in
Note that, though
In a semiconductor device according to a second embodiment of the present invention, as illustrated in
Hereinafter, a method for manufacturing the semiconductor device according to the second embodiment of the present invention will be described with reference to the drawings. Note that the method for manufacturing a semiconductor device, which will be mentioned below, is merely an example, and the semiconductor device is achievable by a variety of manufacturing methods other than this mentioned method, the manufacturing methods including modified examples thereof.
First, as illustrated in
Subsequently, as illustrated in
Next, as illustrated in
Thereafter, as illustrated in
Next, as illustrated in
After the gate insulating films 60 are formed on the inner wall surfaces of the gate trenches 500, as illustrated in
Thereafter, the first main electrode 30 and the second main electrode 40, which face each other with the semiconductor layer 20 sandwiched therebetween, are formed separately from each other on the substrate 10. In such a way as described above, the semiconductor device illustrated in
In the semiconductor device illustrated in
In
As described above, in accordance with the semiconductor device according to the second embodiment of the present invention, a decrease of the withstand voltage of the semiconductor device can be reduced, the semiconductor device having the SJ structure in which the drift regions 21 and the column regions 22 are arranged alternately with each other along the thickness direction of the substrate 10. Others are substantially similar to those of the first embodiment, and a duplicate description will be omitted.
In a semiconductor device according to a third embodiment of the present invention, as illustrated in
Also in the semiconductor device illustrated in
Moreover, in accordance with the semiconductor device illustrated in
As illustrated in
In an on-operation, a low voltage (forward voltage) is applied to the second main electrode 40 while the first main electrode 30 is being set to a reference potential, whereby an energy barrier between the well region 24 and the drift region 21 lowers. Therefore, electrons come to flow from the drift region 21 to the well region 24, and a forward current flows between the first main electrode 30 and the second main electrode 40. In an off-operation, a high voltage (reverse voltage) is applied to the second main electrode 40 while the first main electrode 30 is being set to the reference potential, whereby the energy barrier between the well region 24 and the drift region 21 rises. Therefore, the electrons come not to flow from the drift region 21 to the well region 24.
Also in the semiconductor device having such a diode structure illustrated in
Moreover, as illustrated in
In the semiconductor device illustrated in
As above, the present invention has been described by the embodiments; however, it should not be understood that the description and the drawings, which form a part of this disclosure, limit the present invention. For those skilled in the art, varieties of alternative embodiments, examples and application technologies will be obvious from this disclosure.
For example, in the above, the description is given of the case where the semiconductor device that operates as a transistor is a MOSFET. However, the semiconductor device may be a transistor with another structure. For example, the present invention is also applicable to a bipolar transistor in which the first main electrode 30 is an emitter electrode, the second main electrode 40 is a collector electrode, and the control electrode 50 is a base electrode.
As described above, it is natural that the present invention incorporates a variety of embodiments which are not described herein.
The semiconductor device of the present invention and the method for manufacturing the semiconductor device are usable for an electronic device industry including manufacturers which manufacture the semiconductor device having the SJ structure.
10 Substrate
20 Semiconductor layer
21 Drift region
22 Column region
23 Electric field relaxation region
24 Well region
25 Source region
30 First main electrode
40 Second main electrode
50 Control electrode
60 Gate insulating film
70 Electric field relaxation electrode
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2018/001002 | 7/27/2018 | WO | 00 |
