|Publication number||USRE41509 E1|
|Application number||US 11/207,203|
|Publication date||Aug 17, 2010|
|Filing date||Aug 18, 2005|
|Priority date||Dec 7, 2000|
|Also published as||DE10196990T0, DE10196990T1, US6608350, US20020070418, WO2002047171A1|
|Publication number||11207203, 207203, US RE41509 E1, US RE41509E1, US-E1-RE41509, USRE41509 E1, USRE41509E1|
|Inventors||Daniel M. Kinzer, Srikant Sridevan|
|Original Assignee||International Rectifier Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Non-Patent Citations (2), Referenced by (7), Classifications (18), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to semiconductor devices and more specifically relates to novel vertical conduction superjunction type devices and their methods of manufacture.
Superjunction semiconductor devices are well known and generally provide plural layers of P and N regions connected between a source and drain region. In order to turn the device on in a forward conduction direction, current flow can proceed, for example, through the N type regions, which have a relatively high N type concentration. Thus, the device has a relatively low on resistance per unit area, or RDSON. To turn the device off, the adjacent P and N regions are caused to fully deplete, thus blocking current flow and turning the device off.
Superjunction devices of these types are shown in U.S. Pat. Nos. 5,216,275 and 4,754,310, and are also shown in copending application Ser. No. 60/113,641, filed Dec. 23, 1998 (IR-1676 Prov) in the name of Boden, and assigned to the assignee of the present invention.
The present invention provides a novel superjunction structure capable of blocking very high voltages, while having an ultra low on-resistance in the conduction mode.
In accordance with a first feature of the invention a plurality of deep P-type regions are shorted to the ground terminal placed within the N-type drift regions to assist in the depletion of these N-type regions during the blocking mode and to allow the use of even higher doping in the N-type regions. This further reduces the on-resistance contribution of the drift region, which is the principal source of on-resistance in devices in a high voltage range. The deep P-type regions are formed by etching deep trenches and doping the trench sidewalls with the appropriate P-type dose. The use of trench gates further allows increased density and reduced on-resistance.
In accordance with a second feature of the invention, the deep trenches are lined with an oxide film and then filled with a SIPOS (semi-insulating polysilicon) layer which is shorted to the drain through an opening in the oxide liner. The SIPOS is also shorted to the source at the top of the structure. This provides a highly resistive leakage path between source and drain causing the potential distribution to be uniform, thus reinforcing the RESURF effect of the trench sidewall doping.
In accordance with a third feature of the invention, the oxide used to fill the trench is replaced by alternate layers of oxide (SiO2) and nitride (Si3N4). The thermal coefficient of expansion of the nitride layer is greater than that of the oxide and of the parent silicon so that when the dielectric deposit cools, it shrinks as much as the silicon, reducing the material stress that would otherwise be present, had the dielectric had a different expansion coefficient from that of the silicon.
Referring first to
The side walls and bottoms of each of trenches 3 are doped P type, by any suitable process, and are shown as P layer 4 which lines each groove 3. P regions 4 electrically contact P base 13 while the mesa shaped region of epi 2 between the trenches 3 remains of the N type. The doses in N− epi layer 2 and P region 4 can be varied, or tailored, to obtain desired switching characteristics.
The trenches 3 are then filled with a dielectric material 6, which may be a single dielectric or a combination of two or more dielectric media as later described in FIG. 3.
Shallow trenches such as trench 12 are then etched through P base layer 13, and into region 2, between pairs of trenches 4. A gate oxide 7 is then grown over and lines the interior of trenches 12, and a conductor material 8, for example, conductive polysilicon, fills the trenches 12, forming the gate electrode of the final device. The conductivity of region 13 adjoining gate insulation 7 can now be conventionally modulated by the application of bias voltage to gate electrode 8.
High dose, low energy implants of a suitable N type species are then applied to the top surface of the device to form shallow, high concentration and low resistivity N+ source regions 9.
Shallow trenches 9a are then etched through source regions 9 and into the P base on opposite sides of gate 8, and a source contact metal 11 is applied to the device surface, making contact to N+ sources 9 and P bases 13. Note that an insulation oxide 15 insulates gate 8 from source 11.
In making the device of
The base 13, source regions 9, gate oxide 7 and gate 8 form together a MOSgate type structure for controlling the conduction and blocking of the semiconductor device.
The operation of the device of
Considering next operation in the conduction mode, with the application of a bias to the gate electrode 8 and the grounding of the source 9, an N-type channel is formed on the channel surface between base 13 and gate oxide 7. The device can now conduct current and the application of a small bias to the drain will cause a current to flow in the device with ultra low RDSON.
The use of deep trenches 3 to form the P-type regions 4 allows the use of lower resistivity N-type drift conduction regions 2 than would be allowed by conventional devices. Further, the use of vertical trenches as opposed to successive horizontal epitaxial layers as in the prior art allows higher device density (by a factor of at least 30-40%) and further reduces the conduction losses in the device.
Referring next to the embodiment of
As a result, the SIPOS bodies provide a highly resistive leakage current path between source 9 and drain (2/1/11), forcing a uniform potential distribution along the length of the trenches 3, thus reinforcing the RESURF effect of the trench sidewall doping.
That is, during blocking, when the gate 8 is grounded with respect to the source 10 and a high relative bias applied to the drain 11, the regions 5 and 4 deplete out allowing an almost uniform electric field distribution in the region between the trenches 3. The topping in the regions 4 and 5 must be carefully controlled to obtain optimal blocking performance. The highly resistive leakage path between source 10 and drain 11 through the SIPOS film 20 reinforces this almost uniform electric field distribution due to the resistive potential distribution along the SIPOS. Further, use of the SIPOS reinforces the RESURF effect of the P-type sidewalls and reduces the effect of variations in the P-type sidewall does and epi resistivity. The SIPOS film 20 however does not affect operation in the forward conduction mode.
Referring next to
The fan phenomenon is caused when hot oxide is grown or deposited into deep trenches in any silicon trench-type device. Thus, when cooling, the oxide does not shrink as much as the silicon so that, when cool, the oxide tends to spread apart the trench. This effect is magnified in a product having many parallel trenches, all filled at the same time, causing the silicon to warp and sometimes fracture.
In accordance with the invention, and in the step following the formation of P diffusion 4, the trench 3 is first partly filled, along its height, with an initial thin oxide liner 30. The remainder of the trench 3 is then filled with nitride (Si3O4) 31 which has a temperature coefficient of expansion which is greater than that of both silicon and oxide. Consequently, upon cooling, the total lateral dimension change of the oxide and nitride layers 30 and 31 is more closely matched to that of the silicon 2 to avoid or reduce stress on the silicon 2.
While oxide and nitride are described, other insulation materials may be selected, and may be applied in a reversed sequence. Further, a plurality of interleaved pairs of diverse insulation layers can be used.
Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.
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|U.S. Classification||257/341, 257/331, 257/E29.201, 257/339|
|International Classification||H01L21/76, H01L21/336, H01L29/06, H01L29/78|
|Cooperative Classification||H01L29/0653, H01L29/7813, H01L29/408, H01L29/1095, H01L29/0634, H01L29/405, H01L29/41766|
|European Classification||H01L29/06B3C2, H01L29/78B2T, H01L29/06B2B3R2|
|Feb 22, 2011||FPAY||Fee payment|
Year of fee payment: 8
|Feb 19, 2015||FPAY||Fee payment|
Year of fee payment: 12