Super junction MOS bipolar transistor having drain gaps

Abstract

Methods and designs are provided for a vertical power semiconductor switch having an IGBT-with-built-in-diode bottom-side structure combined with a SJMOS topside structure in such a way as to provide fast switching with low switching losses (MOSFET), low on-resistance at low currents (SJMOS), low on-resistance at high currents (IGBT), and high current-density capability (IGBT).

Claims

1. A super junction metal oxide semiconductor bipolar transistor comprising: a source terminal; a gate terminal; a source portion connected to the source terminal; a body contact portion adjacent the source terminal; an extended p-column beneath the body contact portion; a first n-column adjacent a first side of the extended p-column; a second n-column adjacent a second side of the extended p-column; an n-drift region beneath the extended p-column, the first n-column and the second n-column; an n-type field stop layer beneath the n-drift region; a P+collector layer beneath the n-type field stop; an N+drain gap in the P+collector layer; a drain contact beneath the N+drain gap; and, whereby the N+drain gap enables low R.sub.ds(on) unipolar conduction at a low current density and bipolar conduction at a high current density.

2. The super junction metal oxide semiconductor bipolar transistor of claim 1 wherein: the extended p-column has a doping of about 710.sup.15 atoms/cm.sup.3; the first n-column and the second n-column having dopings of about 710.sup.15 atoms/cm.sup.3; and, the n-drift region has a doping of about 710.sup.14 atoms/cm.sup.3.

3. The super junction metal oxide semiconductor bipolar transistor of claim 2 wherein the n-type field stop layer has a doping of between about 10.sup.15 and about 10.sup.17 atoms/cm.sup.3.

4. The super junction metal oxide semiconductor bipolar transistor of claim 3 wherein: the P+collector has a doping of between about 10.sup.17 and about 10.sup.19 atoms/cm.sup.3; and, the N+drain gap has a doping of between about 10.sup.14 and about 10.sup.16 atoms/cm.sup.3.

5. The super junction metal oxide semiconductor bipolar transistor of claim 2 wherein the N+drain gap is positioned beneath the second N-column.

6. The super junction metal oxide semiconductor bipolar transistor of claim 1 wherein the extend p-column has a depth of between about 35 m to about 45 m and a width of about 3 m.

7. The super junction metal oxide semiconductor bipolar transistor of claim 6 wherein the N+drain gap within about 1 to 2 m of the n-type field stop layer has a doping of between about 10.sup.14 and about 10.sup.17 atoms/cm.sup.3.

8. The super junction metal oxide semiconductor bipolar transistor of claim 1 wherein the Ndrift region depth of between about 4 m and about 10 m.

9. The super junction metal oxide semiconductor bipolar transistor of claim 1 wherein the n-type field stop has a depth of about 2.5 m.

10. The super junction metal oxide semiconductor bipolar transistor of claim 1 wherein the P+collector layer has a depth of between about 0.1 m and about 5 m.

11. The super junction metal oxide semiconductor bipolar transistor of claim 1 wherein the N+drain gap has a depth of between about 1 m and about 5 m and has a width of between about 0.5 m to about 8 m.

12. A super junction metal oxide semiconductor bipolar transistor comprising: a set of source portions; a set of body contact portions, each body contact portion of the set of body contact portions adjacent a corresponding source portion of the set of source portions; a set of extended p-columns, each P-column of the set of P-columns beneath a corresponding body contact portion of the set of body contact portions; a set of Ncolumns, each Ncolumn of the set of Ncolumns adjacent one extended Pcolumn of that set of extended Pcolumns; an Ndrift region beneath the set of extended Pcolumns and the set of N columns; an Ntype field stop layer beneath the Ndrift region; a P+collector layer beneath the Ndrift region; a set of N+drain gaps in the P+collector layer; and, whereby the set of N+drain gaps enable a transition of unipolar conduction to bipolar conduction at a pre-determined current density.

13. A super junction metal oxide semiconductor bipolar transistor of claim 12 wherein one N+drain gap of the set of N+drain gaps is positioned beneath one Ncolumn of the set of Ncolumns.

14. A super junction metal oxide semiconductor bipolar transistor of claim 12 wherein one drain gap of the set of drain gaps is positioned beneath every other Ncolumn of the set of Ncolumns.

15. A super junction metal oxide semiconductor bipolar transistor of claim 12 wherein one drain gap of the set of drain gaps is positioned beneath every tenth Ncolumn of the set of Ncolumns.

16. A vertical semiconductor device comprising: a top surface; a bottom surface; a super junction metal oxide semiconductor field effect transistor (SJMOSFET) in the top surface; a P+collector region formed in the bottom surface; an N+field stop region adjacent the P+collector region; a plurality of N+drain gaps, in the P+collector region; and, whereby the plurality of N+drain gaps enables unipolar conduction at a low current density and bipolar conduction at a high current density.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A shows a cross-section of a super junction metal oxide semiconductor bipolar transistor (SJMOSBT) structure.

(2) FIG. 1B shows a cross-section of a backside of an SJMOSBT structure.

(3) FIG. 1C shows a cross-section of a topside of an SJMOSBT structure.

(4) FIG. 1D shows a cross-section of an SJMOSBT structure with a 1 to 1 column to gap ratio.

(5) FIG. 1E shows a cross-section of an SJMOSBT structure with a 2 to 1 column to gap ratio.

(6) FIG. 1F shows a cross-section of an SJMOSBT structure with a 10 to 1 column to gap ratio.

(7) FIG. 2 is a plot of R.sub.ds(on) versus Current Density for IGBT, SJMOS, and SJMOSBT.

(8) FIG. 3 is a plot that illustrates R.sub.ds(on) vs. Current Density for various SJMOSBT design variations vs. IGBT.

(9) FIG. 4A is a plot that illustrates the current switching waveforms for an IGBT.

(10) FIG. 4B is a plot that illustrates the current switching waveforms for a first SJMOSBT design.

(11) FIG. 4C is a plot that illustrates the current switching waveforms for a second SJMOSBT design.

(12) FIG. 4D is a plot that illustrates the current switching waveforms for a third SJMOSBT design.

(13) FIG. 4E is a plot that illustrates the current switching waveforms for a fourth SJMOSBT design.

(14) FIG. 4F is a plot that illustrates the current switching waveforms for a fifth SJMOSBT design.

(15) FIG. 5A is a plot that illustrates voltage switching waveforms for an IGBT.

(16) FIG. 5B is a plot that illustrates voltage switching waveforms for a first SJMOSBT design variation.

(17) FIG. 5C is a plot that illustrates voltage switching waveforms for a second SJMOSBT design variation.

(18) FIG. 5D is a plot that illustrates voltage switching waveforms for a third SJMOSBT design variation.

(19) FIG. 5E is a plot that illustrates voltage switching waveforms for a fourth SJMOSBT design variation.

(20) FIG. 5F is a plot that illustrates voltage switching waveforms for a fifth SJMOSBT design variation.

(21) FIG. 6 is a bar chart that illustrates the Switch Energy Loss for various SJMOSBT design variations vs. IGBT.

(22) FIG. 7A is a flow chart of a preferred embodiment of a process for creating a vertical semiconductor device.

(23) FIG. 7B is a flow chart of a preferred embodiment of a method for processing a wafer.

(24) FIG. 7C is a flow chart of a preferred embodiment of a method for processing a topside of the wafer.

(25) FIG. 7D is a flow chart of a preferred embodiment of a method for processing a backside of the wafer.

DETAILED DESCRIPTION

(26) A preferred embodiment of the disclosed device is a vertically conducting FET-controlled power device with unipolar conduction at low current densities that transitions to bipolar conduction at high current densities. Bipolar conduction switches on after the unipolar conduction turns on. Unipolar conduction takes place in a highly-doped, charge-balanced drift region, thereby enabling faster switching due to the reduction in minority carrier tail current due to the enhanced recombination of minority carriers in the highly-doped charge-balance regions. Bipolar conduction switches off before the unipolar conduction switches off. These characteristics enable the device to switch faster because of a reduction in minority carrier tail current due to minority carriers starting recombination in the interval between bipolar conduction switch off and unipolar conduction switch off.

(27) Referring to FIG. 1A, a partial cross-section of vertical semiconductor device 100 is shown. Vertical semiconductor device 100 is a SJMOSBT formed on wafer 102. Wafer 102 includes topside 104 and backside 106. In a preferred embodiment, many identical devices are formed on the same wafer and may be sectioned into parts that also contain many devices to enable high current capacity.

(28) In a preferred embodiment, vertical semiconductor device 100 is a vertical insulated gate bipolar transistor (IGBT) that includes a topside charge balanced metal oxide semiconductor field effect transistor (MOSFET) and a set of N+drain gaps 144 in P+collector 140 of the IGBT. The gaps enable unipolar operation of the apparatus so that the apparatus is enabled for both unipolar and bipolar operation.

(29) Vertical semiconductor device 100 includes P+columns 110 and 111 and Ncolumns 112, 113 and 115. The Pcolumns and Ncolumns are arranged in a regular alternating pattern, so as to create a charge balance between them. The Pcolumns and Ncolumns extend into the wafer by depth 170. In a preferred embodiment, depth 170 can range between about 35 m and about 45 m (10%). P+columns 110 and 111 each have width 177. In a preferred embodiment, width 177 is on average about 3.0 m (10%). Doping of the Pcolumns is about 710.sup.15 atoms/cm.sup.3 (10%). Ncolumn 113 has typical width 179. In a preferred embodiment, width 179 is about 3.0 m (10%). Doping of the Ncolumns is about 710.sup.15 atoms/cm.sup.3 (10%). The overlapping intersections between the Pcolumns and the Ncolumns form PN junctions 180, 182, 184 and 186.

(30) Vertical semiconductor device 100 includes Ndrift region 154 formed below P+columns 110 and 111. Ndrift region 154 is constructed of Ntype material with doping 1-2 orders of magnitude below the surrounding material. In one embodiment, doping of the Ndrift region is about 710.sup.14 atoms/cm.sup.3 (10%). In a preferred embodiment, Ndrift region 154 has depth 173. In one embodiment, depth 173, that is, the distance between the bottom of the Pcolumns and the Ntype field stop is approximately 7 m (10%). In a typical embodiment, the depth may range from about 4 m (10%) to about 10 m (10%).

(31) Referring to FIG. 1B, Ntype field stop 138 is formed as a layer below the Ndrift region. Ntype field stop 138 has depth 175, which, in a preferred embodiment is about 2.5 m (10%). Ntype field stop 138 is constructed of Ntype material that has doping of between about 10.sup.15 and about 10.sup.17 atoms/cm.sup.3 (10%).

(32) P+collector 140 is formed as a layer beneath Ntype field stop 138. P+collector 140 extends into wafer 102 to depth 152. Depth 152 is typically on the order of 1 m-5 m, and is typically obtained using a series of chained mid-energy or high-energy implants or both. Doping of the P+collector is Ptype material and can vary from about 10.sup.17 atoms/cm.sup.3 (10%) to about 10.sup.19 atoms/cm.sup.3 (10%).

(33) N+drain gap 144 is formed in P+collector 140. N+drain gap 144 forms an SJMOS Ntype drain and allows unipolar conduction at low current density levels and enables bipolar conduction through the P+collector 140 at high current density levels. N+drain gap 144 permits direct connection to the SJMOS Ndrift region 154, which allows for low-R.sub.ds(on) MOSFET operation during device switch on and switch off. N+drain gap 144 extends into wafer 102 to a depth 152, which is generally about the same depth as P+collector 140. N+drain gap 144 has gap width 150. Gap width 150 is typically on the order of about 0.5 m to about 8 m (10%). N+drain gap 144 has an n-type doping level between about 10.sup.14 and about 10.sup.16 atoms/cm.sup.3 (10%). The portion of the N+drain gap 144 within about 1-2 m of the Ntype field stop 138 has a doping level between about 10.sup.14 and about 10.sup.17 atoms/cm.sup.3 (10%) because of outdiffusion from the Ntype field stop region 138. N+drain gap 144 transitions to drain contact 148. The portion of the N+drain gap 144 within about 1-2 m of drain contact 148 has a doping level between about 10.sup.15 and about 10.sup.17 atoms/cm.sup.3 (10%) because of outdiffusion from drain contact 148.

(34) Drain contact 148 is in contact with N+drain gap 144 and P+collector 140. Drain contact 148 has an n-type doping level between about 10.sup.18 and about 10.sup.20 atoms/cm.sup.3 (10%). In a preferred embodiment, the connection between N+drain gap 144 and P+collector 140 is provided by metal layer 156.

(35) PN junctions 141 and 142 are formed between P+collector 140 and each side of N+drain gap 144. In operation, the combination of gap width 150, depth 152 and the net doping of the gap, the P+collector and the Ntype field stop results in a voltage drop sufficient to cause PN junctions 145 and 146 to forward-bias at a desired SJMOS drain current level as a direct result of this drain current passing through the gap. This current level also forward-biases the PN junction between Ntype field stop 138 and P+collector 140 and as a result causes bipolar operation of the device as the dominant current-carrying mode. Prior to reaching this current level, unipolar operation of vertical semiconductor device 100 is the dominant current-carrying mode.

(36) Referring then to FIG. 1C, topside 104 of vertical semiconductor device 100 is shown. Topside 104 includes source terminal 132 and gate terminal 134. Source terminal 132 is connected to source portions 118, 123, 125 and 130, and also to body contact portions 126 and 127. Gate terminal 134 is connected to gate portions 116, 120 and 128. Gate portion 116 is directly above and adjacent oxide portion 117, which is above source portion 118 at one end. Source portion 118 is adjacent source portion 123. Source portion 118, source portion 123, and body contact portion 126 are each located at the top of P+column 110. Gate portion 120 is above and directly adjacent oxide portion 121, which is above source portion 123 at first end 122 and above source portion 125 at second end 124. Source portion 125 is adjacent source portion 130. Source portion 125, source portion 130, and body contact portion 127 are located at the top of P+column 111. Gate portion 128 is above and directly adjacent oxide portion 129, which is above source portion 130 at one end. Gate portions 116, 120, and 128 are typically n-type polysilicon. The gate portions are typically about 3 m-5 m wide (10%) and less than about 1 m deep (10%). Source portions 118, 123, 125, and 130 are n-doped silicon, typically arsenic and/or phosphorus. The source portions are typically less than about 1 m wide and less than about 1 m deep (10%). In another preferred embodiment, each of the source portions for each of the oxide portions are discrete, do not overlap, and are formed with separate electrically isolated doping wells.

(37) Referring to FIG. 1D, another preferred embodiment is shown. In this embodiment, vertical semiconductor device 100 has one N+drain gap 144 for every Ncolumn 112. This device transitions from SJMOS behavior (unipolar conduction and increasing R.sub.ds(on) with increasing drain current) to IGBT behavior (bipolar conduction and decreasing R.sub.ds(on) with increasing collector current) at a very high level of drain current, since the large number of drain current openings (i.e., N+drain gaps 144 in P+collector 140) is close to the number of Ncolumns and so reduces the current flowing through any single opening, thus requiring a higher total drain current to achieve the forward-biasing of the P+collector to Nfield stop diode.

(38) Referring to FIG. 1E, another preferred embodiment is shown. In this embodiment, vertical semiconductor device 100 has one N+drain gap 144 for every two Ncolumn 112. This device transitions from SJMOS behavior to IGBT behavior at a lower level of drain current compared to the device in FIG. 1D, since the fewer number of drain current openings, in relation to the number of Ncolumns, increases the current flowing through any single opening, thus requiring a lower total drain current to achieve the forward-biasing of the P+collector to Nfield stop diode required.

(39) Referring to FIG. 1F, another preferred embodiment is shown. In this embodiment, vertical semiconductor device 100 has one N+drain gap 144 for every ten Ncolumn 112. This device transitions from SJMOS behavior to IGBT behavior at a lower level of drain current compared to the device in FIG. 1E, since the fewer number of drain current openings, in relation to the number of Ncolumns increases the current flowing through any single opening, thus requiring a lower total drain current to achieve the forward-biasing of the P+collector to Nfield stop diode.

(40) Referring then to FIG. 2, plot 200 of R.sub.ds(on) versus current density between IGBT, SJMOS, and SJMOSBT devices is shown. Curve 202 is for a traditional IGBT device and starts with a large on-resistance at zero current density and exponentially decays to less than 110.sup.2 ohms at 600 Amperes per centimeters squared (A/cm.sup.2). Curve 204 is for a traditional SJMOS device that starts with an on-resistance that increases generally exponentially at current densities greater than 400 A/cm.sup.2. Curve 206 is for a mixed device, such as vertical semiconductor device 100. As can be seen at low current densities, the on-resistance is about 910.sup.2 ohms and well below the on-resistance of the IGBT. As current density increases, the on-resistance of the SJMOSBT decreases, in a generally exponential fashion, approaching a steady 1.210.sup.2 ohms at 600 A/cm.sup.2.

(41) Referring then to FIG. 3, plot 300 of R.sub.ds(on) versus current density comparison by showing five different designs for SJMOSBT structures (SJMOSBT 1, SJMOSBT 2, SJMOSBT 3, SJMOSBT 4, and SJMOSBT 5), one IGBT, and one SJMOS is shown. Table 1 below describes the parameters of the devices of FIG. 3.

(42) TABLE-US-00001 TABLE 1 Final drain gap Drain gap n-type Collector p-type width in doping in Collector depth doping in micrometers atoms/cm.sup.3 in micrometers atoms/cm.sup.3 (10%) (10%) (10%) (10%) Range of values 1 to 6 10.sup.14 to 10.sup.16 1 to 5 10.sup.17 to 10.sup.19 for SJMOSBT IGBT 0 N/A 1 2.00 10.sup.19 SJMOSBT 1 6.0 7.30 10.sup.14 4.1 2.40 10.sup.17 SJMOSBT 2 5.0 6.80 10.sup.14 4.4 2.00 10.sup.19 SJMOSBT 3 2.5 6.90 10.sup.14 4.1 2.40 10.sup.17 SJMOSBT 4 2.0 6.90 10.sup.14 4.4 2.00 10.sup.19 SJMOSBT 5 1.0 7.20 10.sup.14 4.4 2.00 10.sup.19 SJMOS N/A 1.00 10.sup.15 0 N/A

(43) Table 2 below enumerates additional parameters for SJMOSBT 1, SJMOSBT 2, SJMOSBT 3, SJMOSBT 4, and SJMOSBT 5.

(44) TABLE-US-00002 TABLE 2 Drawn Drain P+Collector Total width (Drawn Drawn Gap Implant Dose Pitch of Four P+Collector Gap in % of width of @ each Cells (m) Width (m) P+Collector), every 4 Cells Energy (10%) (10%) (m) (10%) (10%) (10%) SJMOSBT 1 24 18.0 6.0 25% 10.sup.13 SJMOSBT 2 24 18.0 6.0 25% 10.sup.15 SJMOSBT 3 24 21.0 3.0 12.5% 10.sup.13 SJMOSBT 4 24 21.0 3.0 12.5% 10.sup.15 SJMOSBT 5 24 21.6 2.4 10% 10.sup.15
The collectors of the five different SJMOSBT designs are created by implanting P+dopant impurities into the backside of the wafer six times at different energy levels. Different embodiments may use different numbers of implants at different energy levels to achieve a desired collector depth and dopant level. Table 2 above identifies the implant dosage level used for each of six implants of dopant impurities for SJMOSBT 1, SJMOSBT 2, SJMOSBT 3, SJMOSBT 4, and SJMOSBT 5.

(45) Table 3 below enumerates the energy levels that are used for the six implants of dopant impurities for SJMOSBT 1, SJMOSBT 2, SJMOSBT 3, SJMOSBT 4, and SJMOSBT 5. For example, each P+collector implant for SJMOSBT 1 implants 10.sup.13 atoms/cm.sup.2 of dopant impurities into the masked backside of the vertical semiconductor. The first implant is performed at about 450 thousand electron-volts (KeV), the second implant at about 925 KeV, the third implant at about 1400 KeV, the fourth implant at about 1850 KeV, the fifth implant at about 2325 KeV, and the sixth implant at about 2800 KeV. The energy level increases for each successive implant to place the doping impurities further into the wafer.

(46) TABLE-US-00003 TABLE 3 P+collector: Six Implants at the following energies (KeV) (10%) Ener- Ener- Ener- Ener- Ener- Ener- gy 1 gy 2 gy 3 gy 4 gy 5 gy 6 SJMOSBT 1 450 925 1400 1850 2325 2800 SJMOSBT 2 450 925 1400 1850 2325 2800 SJMOSBT 3 450 925 1400 1850 2325 2800 SJMOSBT 4 450 925 1400 1850 2325 2800 SJMOSBT 5 450 925 1400 1850 2325 2800
Preferred embodiments can vary in the number of implants and dosage for each energy level, including those identified in Table 4 below.

(47) TABLE-US-00004 TABLE 4 Minimum (10%) Maximum (10%) Number of Implant Steps 1 10 Implant Dose (atoms/cm.sup.2) 10.sup.12 10.sup.17 First Energy Level (Kev) 300 700 Second Energy Level (Kev) 600 1200 Third Energy Level (Kev) 1100 1600 Fourth Energy Level (Kev) 1500 2100 Fifth Energy Level (Kev) 2000 2600 Sixth Energy Level (Kev) 2500 3100 Seventh Energy Level (Kev) 3000 3600 Eighth Energy Level (Kev) 3500 4200 Ninth Energy Level (Kev) 4100 4700 Tenth Energy Level (Kev) 4600 5200

(48) SJMOSBT 1, shown by curve 304, has the most SJMOS-like on-resistance curve due to having the largest gap width, highest gap doping, lowest collector depth, and lowest collector doping of the SJMOSBTs.

(49) SJMOSBT 2, shown by curve 306, has the second most SJMOS-like on-resistance curve. SJMOSBT 2 had the same mask-drawn drain gap as SJMOSBT 1 but then used a P+collector implant that was two orders of magnitude higher than SJMOSBT1, resulting in a smaller gap width and gap doping, and a larger collector depth than SJMOSBT 1. For both SJMOSBT 1 and SJMOSBT 2, FIG. 3 clearly shows the distinctive transition from SJMOS-mode (R.sub.ds(on) increase with increasing current density) to IGBT-mode (R.sub.ds(on) decrease with increasing current density).

(50) SJMOSBT 3, shown by curve 308, has the third most IGBT-like on-resistance curve. SJMOSBT 3 had a mask-drawn drain gap that was half the width of SJMOSBT 1 and SJMOSBT 2, and the same P+collector implant as SJMOSBT 1, resulting in a much smaller final gap width than SJMOSBT 1 and SJMOSBT 2, and hence much more IGBT-like R.sub.ds(on) versus current density, although the transition from SJMOS-like to IGBT-like can still be observed around 20 A/cm.sup.2.

(51) SJMOSBT 4, shown by curve 310, has the second most IGBT-like on-resistance curve. SJMOSBT 4 had the same mask-drawn drain gap as SJMOSBT 3 but then used a P+collector implant that was two orders of magnitude higher than SJMOSBT3, resulting in a smaller gap width, similar gap doping, and a larger collector depth than SJMOSBT 3.

(52) SJMOSBT 5, shown by curve 312, has the most IGBT-like on-resistance curve. SJMOSBT 5 had a smaller mask-drawn drain gap than SJMOSBT 3 and 4, and the same P+collector implant as SJMOSBT 4, resulting in the smallest gap width of the SJMOSBTs.

(53) An IGBT device is shown by curve 302 and an SJMOS device is shown by curve 314. SJMOSBT 1 (curve 304) and SJMOSBT 2 (curve 306) are the most SJMOS-like of the SJMOSBT devices with lower on-resistance at very low current densities compared to the IGBT of curve 302. SJMOSBT 4 (curve 310) and SJMOSBT 5 (curve 312) are the most IGBT-like of the SJMOSBT devices with high on-resistance at very low current densities and lower on-resistance at higher current densities. These variations show that it is possible to control the SJMOSBT characteristics, depending on the chosen gap width, gap doping level, collector depth, and collector doping level. This design flexibility allows for optimizing the device for best performance in a variety of end-use circuit applications.

(54) Referring to FIGS. 4A through 4F, curve 402 shows the current switching waveform for the IGBT described in FIG. 3 and curves 404, 406, 408, 410, and 412 of FIGS. 4B through 4F show the current switching respectively for SJMOSBT 1, SJMOSBT 2, SJMOSBT 3, SJMOSBT 4, and SJMOSBT 5 described in FIG. 3.

(55) Referring then to FIG. 4A, curve 402 shows that the current for the IGBT begins to turn off at about 8.39 microseconds from about 65 amps and settles at about 9.25 microseconds to about 0.18 amps for a current switching time of about 0.86 microseconds with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device.

(56) Referring then to FIG. 4B, curve 404 shows that the current for the first SJMOSBT begins to turn off at about 8.39 microseconds from about 64 amps and switches off at about 8.42 microseconds at about 0.06 amps for a current switching time of about 0.03 microseconds with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device.

(57) Referring then to FIG. 4C, curve 406 shows that the current for the second SJMOSBT begins to turn off at about 8.39 microseconds from about 64 amps and switches off at about 8.42 microseconds at about 0.16 amps for a current switching time of about 0.03 microseconds with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device.

(58) Referring then to FIG. 4D, curve 408 shows that the current for the third SJMOSBT begins to turn off at about 8.39 microseconds from about 64 amps and switches off at about 8.42 microseconds at about 0.07 amps for a current switching time of about 0.03 microseconds with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device.

(59) Referring then to FIG. 4E, curve 410 shows that the current for the fourth SJMOSBT begins to turn off at about 8.39 microseconds from about 64 amps and switches off at about 8.43 microseconds at about 0.21 amps for a current switching time of about 0.04 microseconds with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device.

(60) Referring then to FIG. 4F, curve 412 shows that the current for the fifth SJMOSBT begins to turn off at about 8.39 microseconds from about 64 amps and switches off at about 8.45 microseconds at about 0.63 amps for a current switching time of about 0.06 microseconds with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device.

(61) Referring to FIGS. 5A through 5F, curve 502 shows the voltage switching waveform for the IGBT described in FIG. 3 and curves 504, 506, 508, 510, and 512 of FIGS. 5B through 5F show the voltage switching respectively for SJMOSBT 1, SJMOSBT 2, SJMOSBT 3, SJMOSBT 4, and SJMOSBT 5 described in FIG. 3.

(62) Referring then to FIG. 5A, curve 502 shows a voltage switching waveform for an IGBT. The device begins to turn on at about 8.18 microseconds at about 2.22 volts, begins to ramp vertically at about 8.37 microseconds at about 44.78 volts, overshoots at about 8.41 microseconds to about 438.88 volts, begins to ramp horizontally at about 8.45 microseconds at about 414.14 volts, and settles at about 8.60 microseconds at about 403.87 volts with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device.

(63) Referring then to FIG. 5B, curve 504 shows a voltage switching waveform for a first SJMOSBT. The device begins to turn on at about 8.18 microseconds at about 6.35 volts, begins to ramp vertically at about 8.22 microseconds at about 18.35 volts, overshoots at about 8.24 microseconds to about 506.05 volts, begins to ramp horizontally at about 8.27 microseconds at about 415.87 volts, and settles at about 8.39 microseconds at about 403.92 volts with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device and which is a clear improvement over the switching time of the IGBT of curve 502 of FIG. 5A.

(64) Referring then to FIG. 5C, curve 506 shows a voltage switching waveform for a second SJMOSBT. The device begins to turn on at about 8.18 microseconds at about 5.95 volts, begins to ramp vertically at about 8.22 microseconds at about 14.40 volts, overshoots at about 8.24 microseconds to about 511.59 volts, begins to ramp horizontally at about 8.27 microseconds at about 418.10 volts, and settles at about 8.39 microseconds at about 403.93 volts with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device and which is a clear improvement over the switching time of the IGBT of curve 502 of FIG. 5A.

(65) Referring then to FIG. 5D, curve 508 shows a voltage switching waveform for a third SJMOSBT. The device begins to turn on at about 8.18 microseconds at about 4.83 volts, begins to ramp vertically at about 8.22 microseconds at about 12.74 volts, overshoots at about 8.24 microseconds to about 510.48 volts, begins to ramp horizontally at about 8.27 microseconds at about 417.55 volts, and settles at about 8.39 microseconds at about 404.02 volts with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device and which is a clear improvement over the switching time of the IGBT of curve 502 of FIG. 5A.

(66) Referring then to FIG. 5E, curve 510 shows a voltage switching waveform for a fourth SJMOSBT. The device begins to turn on at about 8.18 microseconds at about 3.15 volts, begins to ramp vertically at about 8.23 microseconds at about 11.77 volts, overshoots at about 8.25 microseconds to about 497.28 volts, begins to ramp horizontally at about 8.28 microseconds at about 418.41 volts, and settles at about 8.39 microseconds at about 404.23 volts with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device and which is a clear improvement over the switching time of the IGBT of curve 502 of FIG. 5A.

(67) Referring then to FIG. 5F, curve 512 shows a voltage switching waveform for a fifth SJMOSBT. The device begins to turn on at about 8.18 microseconds at about 2.41 volts, begins to ramp vertically at about 8.23 microseconds at about 12.91 volts, overshoots at about 8.27 microseconds to about 481.39 volts, begins to ramp horizontally at about 8.30 microseconds at about 422.21 volts, and settles at about 8.39 microseconds at about 404.86 volts with each value being selected from a range of plus or minus 10 percent that is based on the geometry of the device and which is a clear improvement over the switching time of the IGBT of curve 502 of FIG. 5A.

(68) Referring to FIG. 6, chart 600 shows the power loss for the IGBT described in FIG. 3 and for SJMOSBT 1, SJMOSBT 2, SJMOSBT 3, SJMOSBT 4, and SJMOSBT 5 described in FIG. 3. Table 5 below shows the percent reduction in energy loss of the SJMOSBTs compared to that of the IGBT.

(69) TABLE-US-00005 TABLE 5 Switching energy loss in millijoules (mJ) Percent reduction IGBT 3.301 0.000% SJMOSBT1 0.299 90.937% SJMOSBT2 0.295 91.050% SJMOSBT3 0.292 91.140% SJMOSBT4 0.341 89.671% SJMOSBT5 0.532 83.874%
Chart 600 describes the switch energy loss calculated from the switching waveforms in FIGS. 4A-4F and 5A-5F. The SJMOSBTs reduce lost energy from the IGBT by about 80 to 90 percent.

(70) Referring to FIG. 7A, process 700 creates vertical semiconductor device 100 from wafer 102.

(71) At optional step 701, characteristics for vertical semiconductor device 100 are selected. In a preferred embodiment, the collector doping level, depth 152 into backside 106, gap width 150, collector doping, and doping level within the N+drain gap are chosen in order to minimize the switching loss energy of the composite device. In a preferred embodiment, the current density level for transition between unipolar conduction to bipolar conduction, the wafer doping level, the collector doping level, depth 152 into the backside, gap width 150 and doping level within the N+drain gap are chosen to simultaneously provide a low switching loss energy, high switching speed, and a low R.sub.ds(on) at low current density in unipolar conduction mode as compared to a similarly sized device which is capable of only bipolar conduction at both low and high current densities, such as an IGBT that does not include the N+drain gap.

(72) At step 702, wafer 102 is processed to form P+column 110 and Ncolumn 112. In one preferred embodiment, alternating columns of p-type and n-type doping are created using multiple epi depositions with intervening masked implants. In another preferred embodiment, alternating columns of p-type and n-type doping are created using a deep trench etch and selectively-deposited epi trench refill, or refill with an insulator, or cover the trench opening with an insulating layer before refilling the remainder with polysilicon.

(73) At step 703, topside 104 is processed. In one preferred embodiment, the MOSFET of vertical semiconductor device 100 is constructed using a planar gate on topside 104. In another preferred embodiment, the MOSFET of vertical semiconductor device 100 is constructed using a trench gate.

(74) At optional step 704, if the device characteristics were not previously selected in step 701, then the device characteristics are selected. It is possible with this device and process to defer selection of the device characteristics (i.e., the degree of SJMOS vs. IGBT behavior, which is controlled by gap width, number of gaps, total gap width, collector depth, and doping levels for the gaps and collector) until after the topside processing is completed. The SJMOS on the topside is not modified by adding the drain gaps to the backside collector so that only the backside of the wafer need be processed to control the SJMOS vs. IGBT behavior of a device.

(75) At step 705, backside 106 is processed. In a preferred embodiment, Ntype field stop 138 is created using a hydrogen implant or phosphorus implant or other n-type doping methods. In a preferred embodiment, the collectors are created in backside 106 using one or more of photolithographic masking, high-energy implants, and laser annealing.

(76) Referring to FIG. 7B, a preferred embodiment of wafer processing step 702 is further described. Processing step 702 creates Ncolumn 112 and P+column 110 in vertical semiconductor device 100. Ncolumn 112 has near the high 10.sup.15-level atoms/cm.sup.3 doping near its center, then doping falls of laterally due to outdiffusion from the P+column 110 p-type doping.

(77) At step 721, an initial epitaxial (Epi) layer is created. In a preferred embodiment, the initial epitaxial layer includes what will become Ndrift region 154 and has a homogeneous doping level of mid 10.sup.14 atoms/cm.sup.3 n-type.

(78) At step 722, an additional Epi layer is created. The additional Epi layer is a higher doped n-type Epi layer with relatively homogeneous high 10.sup.15-level atoms/cm.sup.3 doping as compared to the initial Epi layer.

(79) At step 723, the topside of the additional Epi layer is patterned with an implant mask. The implant mask includes one or more holes that allow for implantation of doping impurities into the additional Epi layer.

(80) At step 724, doping is implanted through the implant mask. In a preferred embodiment, the implanted doping is p-type impurities with relatively homogeneous high 10.sup.15-level atoms/cm.sup.3. At step 726 process 702 ends.

(81) Referring to FIG. 7C, a preferred embodiment of topside processing step 703 is further described. Processing step 703 creates source portions 118, 123, 125 and 130, oxide portions 117, 121, and 129, and gate portions 116, 120 and 128 in vertical semiconductor device 100.

(82) At step 731, material that forms oxide portions 117, 121 and 129 is grown on topside 104.

(83) At step 732, material that forms gate portions 116, 120 and 128 are deposited on top of oxide portions 117, 121, and 129. In a preferred embodiment, a continuous gate layer is applied to a previously grown or deposited oxide layer and the extraneous gate and oxide material that are not required are removed by etching. In another preferred embodiment, the gate is created as a trench gate.

(84) At step 733, the body, body contact, and source dopings for vertical semiconductor device 100 are implanted into topside 104 of wafer 102. In a preferred embodiment, doping is performed with n-type impurities that are implanted into P+column 110 at topside 104 utilizing photolithographic processes.

(85) Referring to FIG. 7D, a preferred embodiment of backside processing step 705 is further described.

(86) At step 741, the Ntype field stop is blanket implanted into the backside.

(87) At step 742, the backside is patterned with a mask for the P+collector.

(88) At step 743, the backside is implanted with a chain of KeV or MeV (or both) p-type implants to form the deeply extended P+collector.

(89) At step 744, a contact implant for the N+drain gap is blanket implanted into the backside. The dose for the contact implant is selected to be less than the P+collector contact implant so that the it does not invert the P+collector contact.

(90) At step 745, the backside implants are annealed using either low-temperature furnace or, preferably, using laser annealing.

(91) At step 746, the blanket backside metallization is deposited for making simultaneous contact to the N+drain gap and P+collector regions.

(92) It will be appreciated by those skilled in the art that modifications can be made to the embodiments disclosed and remain within the inventive concept. Therefore, this invention is not limited to the specific embodiments disclosed but is intended to cover changes within the scope and spirit of the claims.