Patent Application
20150263145
The present disclosure relates to insulated gate bipolar transistor (IGBT) devices and structures.
The insulated gate bipolar transistor (IGBT) is a semiconductor device that combines many of the desirable properties of a field-effect transistor (FET) with those of a bipolar junction transistor (BJT). An exemplary conventional IGBT device 10 is shown in
Each one of the junction implants 24 is generally formed by an ion implantation process, and includes a base well 30, a source well 32, and an ohmic well 34. Each base well 30 is implanted in the first surface 26 of the IGBT stack 12, and extends down towards the injector region 20 along a lateral edge 36 of the IGBT stack 12. The source well 32 and the ohmic well 34 are formed in a shallow portion on the first surface 26 of the IGBT stack 12, and are surrounded by the base well 30. A JFET gap 38 separates each one of the junction implants 24, and defines a JFET gap width WJFET as the distance between each one of the junction implants 24 in the conventional IGBT device 10.
A gate oxide layer 40 is positioned on the first surface 26 of the IGBT stack 12, and extends laterally between a portion of the surface of each one of the source wells 32, such that the gate oxide layer 40 partially overlaps and runs between the surface of each source well 32 in the junction implants 24. The gate contact 16 is positioned over the gate oxide layer 40. The emitter contact 18 is a “U” shape, and includes two portions in contact with the first surface 26 of the IGBT stack 12. Each portion of the emitter contact 18 on the first surface 26 of the IGBT stack 12 partially overlaps both the source well 32 and the ohmic well 34 of one of the junction implants 24, respectively, without contacting the gate contact 16 or the gate oxide layer 40.
A first junction J1 between the injector region 20 and the drift region 22, a second junction J2 between each base well 30 and the drift region 22, and a third junction J3 between each source well 32 and each base well 30 are controlled to operate in one of a forward-bias mode of operation or a reverse-bias mode of operation based on the biasing of the conventional IGBT device 10. Accordingly, the flow of current between the collector contact 14 and the emitter contact 18 is controlled.
The conventional IGBT device 10 has three primary modes of operation. When a positive bias is applied to the gate contact 16 and the emitter contact 18, and a negative bias is applied to the collector contact 14, the conventional IGBT device 10 operates in a reverse blocking mode. In the reverse blocking mode of the conventional IGBT device 10, the first junction J1 and the third junction J3 are reverse-biased, while the second junction J2 is forward biased. As will be understood by those of ordinary skill in the art, the reverse-biased junctions J1 and J3 prevent current from flowing from the collector contact 14 to the emitter contact 18. Accordingly, the drift region 22 supports the majority of the voltage across the collector contact 14 and the emitter contact 18.
When a negative bias is applied to the gate contact 16 and the emitter contact 18, and a positive bias is applied to the collector contact 14, the conventional IGBT device 10 operates in a forward blocking mode. In the forward blocking mode of the conventional IGBT device 10, the first junction J1 and the third junction J3 are forward biased, while the second junction J2 is reverse-biased. As will be understood by those of ordinary skill in the art, the reverse-bias of the second junction J2 generates a depletion region, which effectively pinches off the JFET gap 38 of the IGBT device 10 and prevents current from flowing from the collector contact 14 to the emitter contact 18. Accordingly, the drift region 22 supports the majority of the voltage across the collector contact 14 and the emitter contact 18.
When a positive bias is applied to the gate contact 16 and the collector contact 14, and a negative bias is applied to the emitter contact 18, the conventional IGBT device 10 operates in a forward conduction mode of operation. In the forward conduction mode of operation of the conventional IGBT device 10, the first junction J1 and the third junction J3 are forward-biased, while the second junction J2 is reverse-biased. Accordingly, current can flow from the collector contact 14 to the emitter contact 18. Specifically, the positive bias applied to the gate contact 16 generates an inversion channel on the first surface 26 of the IGBT stack 12, thereby creating a low-resistance path for electrons to flow from the emitter contact 18 through each one of the source wells 32 and each one of the base wells 30 into the drift region 22. As electrons flow into the drift region 22, the potential of the drift region 22 is decreased, thereby placing the first junction J1 in a forward-bias mode of operation. When the first junction J1 becomes forward-biased, holes are allowed to flow from the injector region 20 into the drift region 22. The holes effectively increase the doping concentration of the drift region 22, thereby increasing the conductivity thereof. Accordingly, electrons from the emitter contact 18 may flow more easily through the drift region 22 and to the collector contact 14.
The IGBT stack 12 of the conventional IGBT device 10 is Silicon (Si), the advantages and shortcomings of which are well known to those of ordinary skill in the art. In an attempt to further increase the performance of IGBT devices, many have focused their efforts on using wide band-gap materials such as Silicon Carbide (SiC) for the IGBT stack 12. Although promising, conventional IGBT structures such as the one shown in
The present disclosure relates to insulated gate bipolar transistor (IGBT) devices and structures. According to one embodiment, an IGBT device includes an IGBT stack, a collector contact, a gate contact, and an emitter contact. The IGBT stack includes an injector region, a drift region over the injector region, a spreading region over the drift region, and a pair of junction implants in the spreading region. The spreading region provides a first surface of the IGBT stack, which is opposite the drift region. The pair of junction implants is separated by a JFET gap, and extends from the first surface of the IGBT stack along a lateral edge of the IGBT stack towards the drift region to a first depth, such that the thickness of the spreading region is at least one and a half times greater than the first depth. By including the spreading layer that is at least one and a half times thicker than the depth of each junction implant, the ON resistance RON and front-side injection capabilities of the IGBT device may be improved.
According to various embodiments, the thickness of the spreading layer is at least 2 to 4 times greater than that of the first depth of the junction implants.
According to one embodiment, the IGBT stack is formed of a wide band-gap semiconductor material. For example, the IGBT stack may be a Silicon Carbide (SiC) substrate.
According to one embodiment, the drift region is a lightly doped N region, the injector region is a highly doped P region, and the spreading region is a highly doped N region.
According to one embodiment, an IGBT device includes an IGBT stack, a collector contact, a gate contact, and an emitter contact. The IGBT stack includes an injector region, a drift region over the injector region, a spreading region over the drift region, and a pair of junction implants in the spreading region. The spreading region provides a first surface of the IGBT stack, which is opposite the drift region. The pair of junction implants are separated by a JFET gap, and extend from the first surface of the IGBT stack along a lateral edge of the IGBT stack towards the drift region to a first depth, such that the spreading region extends at least 1.5 μm beyond the first depth so that at least 1.5 μm of the spreading region exists between the bottom of each junction implant and the drift region. As discussed above, by including the spreading layer that extends at least 1.5 μm beyond the depth of each junction implant, the ON resistance RON and front-side injection capabilities of the IGBT device may be improved.
According to various embodiments, the spreading region is from at least 2.0 μm to at least 10.0 μm thicker than the first depth of each junction implant.
Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.
The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Turning now to
Each one of the junction implants 58 may be formed by an ion implantation process, and may include a base well 64, a source well 66, and an ohmic well 68. Each base well 64 is implanted in the first surface 60 of the IGBT stack 44, and extends down towards the injector region 52 along a lateral edge 70 of the IGBT stack 44 to a first depth (DB). Notably, the first depth (DB) represents the portion of each junction implant 58 that is closest to the drift region 54, which is substantially less than the thickness (TS) of the spreading region 56, thereby leaving a spreading layer buffer 72 between each one of the junction implants 58 and the drift region 54 in order to mitigate the effects of one or more damaged regions located below the junction implants 58, as discussed in further detail below. The thickness of the spreading layer buffer 72 is the thickness (TS) of the spreading region 56 less the first depth (DB) of the base well 64. The source well 66 and the ohmic well 68 are formed in a shallow portion of the first surface 60 of the IGBT stack 44, and are surrounded by the base well 64. A JFET gap 74 separates each one of the junction implants 58, and defines a JFET gap width WJFET as the distance between each one of the junction implants in the IGBT device 42. An additional junction field-effect transistor (JFET) implant 76 may be provided in the JFET gap 74, as discussed in further detail below.
According to one embodiment, the thickness (TS) of the spreading region 56 is between about 1.5 μm to 10 μm. The first depth (DB) of the base well 64 may be between about 0.5 μm to 1.5 μm. As discussed in further detail below, the thickness (TS) of the spreading region 56 is substantially greater than the first depth (DB) of the base well 64 of each junction implant 58 in order to provide the spreading layer buffer 72, which mitigates the effects of one or more damaged regions located below the junction implants 58. For example, the thickness (TS) of the spreading region 56 may be between one and a half to four times greater than the first depth (DB) of each one of the base wells 64. As an additional example, the thickness (TS) of the spreading region 56 may be at least 1.5 μm to 10.0 μm greater than the first depth (DB) of the base wells 64, such that the spreading layer buffer 72 is at least 1.5 μm to 10.0 μm.
A gate oxide layer 78 may be positioned on the first surface 60 of the IGBT stack 44, and may extend laterally between a portion of the surface of each one of the source wells 66, such that the gate oxide layer 78 partially overlaps and runs between the surface of each source well 66 in the junction implants 58. The emitter contact 50 may be a “U” shape, and may include two portions in contact with the first surface 60 of the IGBT stack 44. Each portion of the emitter contact 50 on the first surface 60 of the IGBT stack 44 may partially overlap both the source well 66 and the ohmic well 68 of one of the junction implants 58, respectively, without contacting the gate contact 48 of the gate oxide layer 78.
A first junction J1 between the injector region 52 and the drift region 54, a second junction J2 between each base well 64 and the drift region 54, and a third junction J3 between each source well 66 and each base well 64 are controlled to operate in one of a forward-bias mode of operation or a reverse-bias mode of operation based on the biasing of the IGBT device 42. Accordingly, the flow of current between the collector contact 46 and the emitter contact 50 is controlled.
According to one embodiment, the injector region 52 is a highly doped P region 52 with a doping concentration between 1E16 cm−3 to 1E21 cm−3. The drift region 54 may be a lightly doped N region with a doping concentration between 1E13 cm−3 to 1E15 cm−3. In some embodiments, the drift region 54 may include a notably light concentration of dopants, in order to improve one or more performance parameters of the IGBT device 42 as discussed in further detail below. The spreading region 56 may be a highly doped N region with a doping concentration between 5E15 cm−3 to 5E16 cm−3. Further, in some embodiments, the spreading region 56 may include a graduated doping concentration, such that as the spreading region 56 extends away from the first surface 60 of the IGBT stack 44, the doping concentration of the spreading region 56 gradually decreases. For example, the portion of the spreading region 56 directly adjacent to the first surface 60 of the IGBT stack 44 may be doped at a concentration of about 5E16 cm−3, while the portion of the spreading region directly adjacent to the drift region 54 may be doped at a concentration of about 5E15 cm−3. The JFET region 76 may be also be a highly doped N region with a doping concentration between 1E16 cm−3 to 1E17 cm−3. Further, the base well 64 may be a P doped region with a doping concentration between 5E17 cm−3 and 1E19 cm−3, the source well 66 may be a highly doped N region with a doping concentration between 1E19 cm−3 and 1E21 cm−3, and the ohmic well 68 may be a highly doped P layer with a doping concentration between 1E19 cm−3 and 1E21 cm−3.
The injector region 52 may be doped aluminum, boron, or the like. Those of ordinary skill in the art will appreciate that many different dopants exist that may be suitable for doping the injector region 52, all of which are contemplated herein. The drift region 54, the spreading region 56, and the JFET region 76 may be doped with nitrogen, phosphorous, or the like. Those of ordinary skill in the art will appreciate that many different dopants exist that may be suitable for doping the drift region 54, the spreading region 56, and the JFET region, all of which are contemplated herein.
According to one embodiment, the injector region 52 is generated by an epitaxy process. According to an additional embodiment, the injector region 52 is formed by an ion implantation process. Those of ordinary skill in the art will appreciate that numerous different processes exist for generating the injector region 52, all of which are contemplated herein. The spreading region 56 and the JFET region 76 may similarly be formed by either an epitaxy process or an ion implantation process. Those of ordinary skill in the art will appreciate that numerous different processes exist for generating the spreading region 56 and the JFET region 76, all of which are contemplated herein.
According to one embodiment, the IGBT stack 44 is a wide band-gap semiconductor material. For example, the IGBT stack 44 may be Silicon Carbide (SiC). As discussed above, manufacturing limitations inherent in current SiC technologies will generally result in a diminished carrier lifetimes and/or carrier concentration in the injector region of a SiC IGBT device. As a result, SiC IGBT devices generally suffer from a reduced amount of “backside injection”, which results in poor conductivity modulation and an increased ON resistance (RON) of the SiC IGBT device. Further, in attempting to design a wide band-gap IGBT device, it was discovered by the inventors that damaged regions below each one of the junction implants of a SiC IGBT device result in a significantly degraded carrier lifetime at or near these damaged regions. These so-called “end-of-range” defects effectively prevent the modulation of current in the upper portion of the drift layer in a SiC IGBT device, which in turn significantly increases the resistance in this area. As a result of the increased resistance in the upper portion of the drift region, current flow in the SiC IGBT device may be significantly reduced, and may even be cut off altogether. The spreading region 56 of the IGBT device 42 is therefore provided to bypass the damaged regions below each one of the junction implants 58, thereby improving the performance of the SiC IGBT device 42.
By bypassing the damaged regions below each one of the junction implants 58, electrons from the emitter contact 50 are delivered directly to a region of high conductivity modulation in the drift region 54. Accordingly, electrons easily pass into the drift region 54 and to the collector contact 46 of the IGBT device 42. Those of ordinary skill in the art will recognize that the ON resistance (RON) is significantly reduced in the IGBT device 42, thereby improving the performance thereof.
While the spreading region 56 effectively reduces the ON resistance (RON) of the IGBT device 42, the introduction of the spreading region 56 also results in a decrease in the blocking voltage (VBLK) of the IGBT device 42. In order to compensate for this fact, the doping concentration in the drift region 54 may be decreased, such that the doping concentration in the drift region 54 is exceptionally light, as discussed above. Accordingly, a balance between the on resistance (RON) and the blocking voltage (VBLK) of the IGBT device 42 may be struck.
In addition to the advantages described above, the IGBT device 42 further benefits from the predominant use of “front-side” injection. That is, the IGBT device 42 shown in
Further, providing the spreading region 56 also allows the JFET gap width (WJFET) and the overall device width (WD) to be significantly reduced when compared to conventional IGBT devices. For example, the JFET gap width (WJFET) of the IGBT device 42 may be between 1 μm to 4 μm, and the overall device width (WD) of the IGBT device 42 may be between 5 μm to 15 μm.
Finally, providing the spreading region 56 results in desirable thermal properties of the IGBT device 42. As will be appreciated by those of ordinary skill in the art, conventional IGBT devices generally suffer from a significant amount of temperature dependence. That is, the performance characteristics of a conventional IGBT generally change with temperature. Specifically, as the temperature of an IGBT device increases, so does the lifetime of carriers in the drift region, thereby resulting in increased current flow through the device. This can result in a dangerous cycle, in which increased current flow through the IGBT device further raises the temperature of the device, until the IGBT device can no longer handle the amount of current through the device and fails. By providing the spreading region 56 in the IGBT device 42, a large unmodulated region is generated below the first surface 60 of the IGBT stack 44, as discussed above. As will be appreciated by those of ordinary skill in the art, this unmodulated region has an inverse relationship between the current flow therein and temperature. By carefully choosing the dimensions of the drift region 54 and the spreading region 56, a designer can thus effectively cancel the effects of temperature on current flow in the IGBT device 42, thereby significantly increasing the performance thereof.
FIGS. 3 and 4A-4I illustrate a method for manufacturing the IGBT device 42 shown in
The JFET region 76 is then provided in the channel 74 between the junction implants 58 (step 108 and
Although the process illustrated in FIGS. 3 and 4A-4I is illustrated in a particular number of discrete steps, which are arranged in a particular order, the present disclosure is not so limited. Each illustrated step may in fact comprise one or more steps, and may be accomplished in any order with respect to the other steps without departing from the principles described herein.
FIGS. 6 and 7A-7F illustrate a method for manufacturing the IGBT device 42 shown in
The JFET region 76 is then provided in the channel 74 between the junction implants 58 (step 206 and
Although the process illustrated in FIGS. 6 and 7A-7F is illustrated in a particular number of discrete steps, which are arranged in a particular order, the present disclosure is not so limited. Each illustrated step may in fact comprise one or more steps, and may be accomplished in any order with respect to the other steps without departing from the principles described herein.
Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.
