This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2011-273275, filed Dec. 14, 2011; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate to a semiconductor device and a method for manufacturing the same.
Semiconductor devices as represented by a metal-oxide-semiconductor field-effect transistor (MOSFET), are widely used in applications such as power control. In order to reduce power loss, both the on-resistance, and the input capacitance, need to be small. However, the values of on-resistance and input capacitance commonly are dictated by design and material considerations which make it difficult to reduce both of them at the same device. As a result, a semiconductor device that having a trench gate structure with field plates has been pursued.
An example of related art includes Patent Reference of JP-A-2011-159763.
In general, according to one embodiment, the following paragraphs explain the embodiment, in part with reference to the drawings. Elements of the embodiments are explained in referring to the related reference numbers that appear in the drawings in order to provide a detailed and concise explanation. In addition, Cartesian coordinates, XYZ, are used in the figures, but solely for purposes of explanation and not to limit the embodiments to particular two- or three-dimensional embodiments. In the following embodiment explanation, n-type refers to the first conductivity type, and p-type refers to the second conductivity type. Please note that this does not limit the embodiments to a particular dopant paradigm, as it is also acceptable to reverse the dopant paradigm, using a p-type dopant for the first conductivity type and an n-type dopant for the second. Also, silicon wafer is used as an example of a semiconductor layer, but other compound semiconductors such as gallium nitride (GaN) and silicon carbide (SiC) are also applicable. As for the insulator film, silicon oxide is specified as an example; of course, it is also possible to use other insulators, such as silicon nitride or silicon oxy-nitride.
According to one embodiment, there is provided a semiconductor device having both reduced on-resistance and input capacitance, and a method of manufacturing the device is also provided.
The semiconductor device in this embodiment provides the semiconductor layer of the first conductivity type; on this layer is the first region of the second conductivity type; on this first region is the second region of the first conductivity type, which had been selectively prepared; then, still on this first region, the third region of the second conductivity type, which had also been selectively prepared, is joined to the second region. Then, from the first side of the second region, the first control electrode will be formed inside a trench that reaches an even deeper position than the first region mentioned above. The first part, which is opposed to the first and the second regions, will be separated by the first insulator, while the second part, which is opposed to the semiconductor layer, is separated by the second insulator, which is even thicker than the first one. Between the first control electrode and the interior bottom of the trench, the second control electrode is formed, opposed to the semiconductor layer separated by the third insulator, which is even thicker than the second. In addition, this first main electrode, which is electrically connected to the semiconductor layer, then to the second and the third regions, is electrically connected to the second main electrode.
P-type base region 3 is provided on the n-type drift layer 1, while n-type source region 5 is selectively provided on top of the p-type base region 3, some of which extends into the upper surface of the p-type base region 3. P-type contact region 7 is adjoined to the n-type source region 5 and is also selectively prepared on top of the p-type base region 3. P-type contact region 7 can also be formed in the bottom of the trench, from the surface 2a (the first side) on top of the n-type source region 5 in the direction of the rear surface 2b (the second side) of the n-type drift layer 1 (direction Z).
In addition gate electrode 13, which is the first control electrode, is formed inside trench 11, which extends from the surface 2a of the n-type source region 5 to terminate within the n-type drift layer 1 at trench bottom 11a. Trench 11 also extends in the Y direction (into or out of the plane of
Gate electrode 13 includes a first part 13a, which is opposed to n-type source region 5 and p-type base region 3 and separated therefrom by gate insulator 17 (the first insulator), and a second part 13b, which is opposed to n-type drift layer 1 and separated therefrom by field plate insulator 21 (the second insulator), which is thicker from the edge of gate electrode 13 to the n-type drift layer than is gate insulator 17 extending between gate electrode and adjacent portions of the n-type source region 5 and p-type base region 3.
Field plate electrode 15 is opposed to n-type drift layer 1, and separated therefrom by field plate insulator 23 (the third insulator), which is thicker than field plate insulator 21 in the lateral direction from the side of the field plate electrode 15 to the adjoining drift layer 1. In the bottom of trench 11, field plate electrode 15 is opposed to n-type drift layer 1 separated by field plate insulator 25 (the fourth insulator), which is thinner in span to the adjacent drift layer than field plate insulator 23.
Field plate electrode 15 is opposed to, and disposed inwardly of the trench than, gate electrode 13 and separated therefrom by insulator 27, which is the fifth insulator. In addition, the area of the part where field plate electrode 15 is opposed to gate electrode 13 is smaller than the thickness of the other areas where gate electrode 13 faces field plate electrode 15.
Gate insulator 17, field plate insulators 21, 23, and 25, and insulator 27 are preferably configured as a continuous layer of silicon oxide material with intervening materials within the trench 11.
The semiconductor device 100 also includes a n-type drain layer 31 connected to the rear surface 2b of the n-type drift layer 1, to form a drain electrode 33 (the first main electrode), which is electrically connected to n-type drift layer 1.
Furthermore, the semiconductor device 100 provides source electrode 35 (the second main electrode) on the surface 2a of n-type source region 5 and p-type contact region 7; n-type source region 5 and p-type contact region 7 are electrically connected to source electrode 35.
P-type contact region 7 electrically connects p-type base region 3 and source electrode 35; so the holes that have been accumulated in p-type base region 3 are discharged into source electrode 35. In addition, field plate electrode 15 is held to the same potential because it is electrically connected (connection not shown) to source electrode 35.
Next, the method of manufacturing a semiconductor device according to the present embodiment is explained by referring to
As shown in
N-type layer 2 is, for example, an epitaxial layer formed on the surface of a silicon wafer (not shown in the figure). Then, n-type drain layer 31 can be formed between n-type layer 2 and silicon wafer, or the silicon wafer itself can turn out to be n-type drain layer 31. The carrier density of n-type layer 2 can be, for example, 1-4×1016 atoms/cm3, while its thickness can be 4-11 micrometers (μm). Also, the carrier density of n-type drain layer 31 can be, for example, 2-8×1019 atoms/cm3.
The aperture 19a is formed in a stripe-shaped pattern that extends indirection Y, and thus is deeper in the direction in and out of the Fig. (Y direction) than to the right and left (X-direction)in the Fig. to form an elongated trench. The opening side lib of trench 11, for example, equals the size of the opening side 19a of the etching mask; the width in direction X is 1-2 μm. The depth of trench 11 in direction Z equals the depth across p-type base region 3, for example, 4-6 μm.
Next, as shown in
The formation of lowermost field plate insulator 25, i.e., that which extends between the base of the field plate electrode 15 and the underlying drift layer 2 as shown in
Now, as shown in
For example, a CVD technique is used to generate a polycrystalline silicon stud or plug over the field insulating layer 23 within the trench as shown in
Next, as shown in
For example, a selective wet-etching technique, which etches the field plate insulator film 23 without significantly effecting the silicon oxide layer 19 such that silicon oxide 19 remains on the surface of n-type layer 2, is used. Etching is terminating while a thin layer of field plate insulator film 23 on the upper side wall of trench 11 remains after etching.
Next, as shown in
Now, as shown in
Next, as shown in
Then, as shown in
Conditions of anisotropic etching of RIE are used, for example, in order to etch the gate electrode 13 material to form the gate electrode as shown in
Next, as shown in
The edge of the gate electrode 13 adjacent to the open-end of trench 11 extends upwardly, to overlap, in the z direction, the terminus of the n- type source region 5 inwardly of the base region 3, the p type base region 3 extends partially below, in the z direction, the n-type source region, and the electrode 13 extends further inwardly to extend adjacent to a portion of drift region 1. As a result, portions of gate electrode are opposed to n-type drift layer 1, p-type base region 3, and n-type source region 5 across gate insulator 17. As a result of the MOS channel that has been formed between p-type base region 3 and gate insulator 17, it is possible to control the drain current that flows from n-type drift layer 1 to n-type source region 5.
Now, as shown in
The process is continued, as shown in
In this embodiment of semiconductor device 100, on-resistance and input capacitance are reduced, which also enables power loss reduction. For example, most power loss in a MOSFET results from conduction loss due to on-resistance (RON) or from switching loss at power-on. In order to reduce power loss, it is good to reduce RON and input capacitance (CISS). CISS is the sum of gate-to-source capacitance (CGS) and gate-to-drain capacitance (CGD).
With semiconductor device 100, by reducing the capacity between field plate electrode 15, which is connected to the source electrode and gate electrode 13, CGS will be reduced and so will be CISS. More precisely, field plate electrode 15 is opposed to the lower part 13c of gate electrode 13 across the edge 15b of a thin insulator 27, as compared to other insulator 27 thicknesses between the electrodes 13, 15 and adjacent doped drain region 1. Also, the area of the edge 15b of field plate electrode 15 is smaller, as compared to the opposed or facing area of the lower part 13c of gate electrode 13. As a result, it is possible to reduce gate-to-source capacitance inside trench 11.
In addition, referring again to
For example,
In the example shown in
More precisely, the drain-source breakdown voltage can be improved by reducing the thickness in direction X of field plate insulator 21 to make it thinner than the thickness in direction X of field plate insulator 23, as well as by reducing the thickness in direction Z of field plate insulator 25 to make it thinner than the thickness in direction X of field plate insulator 23. As a result, by maintaining the prescribed breakdown voltage and by increasing the carrier density of n-type drift layer 1, it is possible to reduce the resistance, including the on-resistance (RON).
In addition, the cross-sectional area of gate electrode 13 becomes wider, because it includes the second part 13b, which extends to the bottom side of trench 11. This enables the reduction of the gate resistance.
As shown in
Inside each trench 41, a field plate electrode 15 is provided within field plate insulator 23. Field plate electrode 15 is opposed to, or adjacent to, the n-type layer 2, separated therefrom by field plate insulator 23. In addition, field plate insulator 21 is formed on the opening side of field plate insulator 23, by, for example, forming an insulator layer to line the trench 41, etching a trench shaped aperture into the insulator material, depositing the field plate electrode 15 material into the trench shaped aperture and etching it back to a desired depth in the trench shaped aperture, and then wet etching the insulating material to form a thinner region thereof (as compares to field plate insulator 23, to become field plate insulator 21, without significantly etching the field plate insulator 23 while exposing the uppermost portions of the side walls of the trench 21. The manufacturing process in
Next, as shown in
FIG. GC shows the process to continue to etch back gate electrode 13 and remove the portion of the material deposited to form the gate electrode from the surface 2a of n-type layer 2 and a portion of the gate insulator 17 closest to the opening of the trenches 41. As a result, inside trench 41, the first part 13a of gate electrode 13 and the second part 13b are formed.
In this embodiment, because the width in direction X of opening side 41b is narrow, it is possible to flatten the surface of gate electrode 13, which is embedded in trench 41. Therefore, to etch back gate electrode 13, it is possible to use an isotropic etching technique such as the CDE (chemical dry etching) technique.
Next, as shown in
Now, as shown in
Even in the case of this modified structure, the thickness in direction X of field plate insulator 21, which is sandwiched between the second part 13b of gate electrode 13 and n-type drift layer 1, is thinner compared to that of field plate insulator 23, which is sandwiched between field plate electrode 15 and n-type drift layer 1. Also, the thickness in direction Z of field plate insulator 25, which is formed in the bottom of trench 41, is thinner compared to the thickness in direction X of field plate insulator 23. As a result, it is possible reduce on-resistance (RON) by increasing the carrier density of n-type drift layer 1.
In addition, the area of the edge 15b of field plate electrode 15, which is opposed to the lower part 13c of gate electrode 13, is narrower compared to the area of the lower part 13c of gate electrode 13. This enables the reduction in gate-to-source capacitance.
Also, in this embodiment, by using a simple manufacturing method, it is possible to achieve the trench gate structure, which includes field plate electrode 15, which is opposed to n-type drift layer 1, through different thicknesses of field plate insulators as well as the second part 13b of gate electrode 13. More precisely, by etching field plate insulator 23, which is provided inside the trench, field plate insulator 21, which is the second insulator, is formed. Then, the conductivity layers embedded inside the trench are the only two layers suitable for field plate electrode 15 and gate electrode 13. As a result, it is possible to achieve the semiconductor device with reduced on-resistance (RON) and input capacitance (CISS) at low cost.
The semiconductor device 300 provides n-type base layer 51, which is the semiconductor layer of the first conductivity type, p-type base region 53, which is the first region of the second conductivity type, n-type emitter region 55, which is the second region of the first conductivity type, and p-type contact region 57, which is the third region of the second conductivity type.
P-type base region 53 is provided on the top of n-type base layer 52. N-type emitter region 55 is selectively provided on p-type base region 53; one part of this invades the interior of p-type base region 53. P-type contact region 57 is selectively provided after adjoining n-type emitter region 55 to the top of p-type base region 53.
Gate electrode 13 which is the first control electrode is provided inside trench 11, which is formed by n-type base layer 51. Trench 11 is provided, for example, by a stripe that extends vertically in direction Y on side XZ; the depth in direction Z is deeper compared to that of p-type base region 53. Then, between the bottom 11a of trench 11 and gate electrode 13, field plate electrode 15, which is the second control electrode, is provided.
Gate electrode 13 includes the first part 13a and the second part 13b. The first part 13a is opposed to p-type base region 53 and n-type emitter region 55, separated by gate insulator 17 (the first insulator). The second part 13b is opposed to n-type base layer 51, separated by field plate insulator 21 (the second insulator), which is even thicker than gate insulator 17.
Field plate electrode 15 is opposed to n-type base layer 51, separated by field plate insulator 23 (the third insulator), whose thickness in direction X is thicker compared to that of field plate insulator 21. Also, field plate electrode 15 is opposed to n-type base layer 52, separated by field plate insulator 25 (the fourth insulator) in the bottom of trench 11. The thickness in direction Z of field plate insulator 25 is thinner than that of field plate insulator 23 in direction X.
Field plate electrode 15 is opposed to gate electrode 13, separated by insulator 27, which is the fifth insulator. And the area of the part that is opposed to gate electrode 13 to field plate electrode 15 is smaller compared to the entire area where gate electrode 13 and field place electrode 15 face each other.
The semiconductor device 300 includes p-type collector layer 61, which is connected to the back side 2b of n-type base layer 51. Then, collector electrode 63 (the first main electrode), which has been electrically connected to p-type collector layer 61, is prepared. Also, the semiconductor device 300 provides emitter electrode 65 (the second main electrode), which has been electrically connected to p-type contact region 57 and n-type emitter region 55 on the surface 2a of p-type contact region 57 and n-type emitter region 55.
The semiconductor device 300 includes the first part 13b of gate electrode 13, which is opposed to n-type base layer 51 across field plate insulator 21. The thickness indirection Z of field plate electrode insulator 25 from the bottom of trench 41 is thinner compared to the thickness in direction X of field plate insulator 23. This enables a higher carrier density of n-type base layer 51 to be set in order to reduce on-resistance (RON). Also, reducing the capacity between field plate electrode 15 and gate electrode 13 enables the reduction of switching loss.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the embodiments. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the embodiments. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the embodiments.
Number | Date | Country | Kind |
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2011-273275 | Dec 2011 | JP | national |