# Patent

## Title
Power semiconductor devices integrated with clamp diodes having separated gate metal pads to avoid breakdown voltage degradation

## Abstract

A structure of power semiconductor device integrated with clamp diodes having separated gate metal pad is disclosed. The separated gate metal pads are wire bonded together on the gate lead frame. This improved structure can prevent the degradation of breakdown voltage due to electric field in termination region blocked by polysilicon or gate metal.

## Background
This application is a divisional of and claims the benefit of the earlier filing date of co-pending U.S. patent application Ser. No. 12/453,630 filed on May 18, 2009, the entire disclosure of co-pending application Ser. No. 12/453,630 is herein incorporated by reference.


FIELD OF THE INVENTION
This invention relates generally to the cell structure and device configuration of semiconductor devices. More particularly, this invention relates to an improved device configuration of power semiconductor devices integrated with clamp diodes having separated gate metal pad.
BACKGROUND OF THE INVENTION
In order to enhance avalanche capability, clamp diodes are formed between Gate and Drain for MOSFET and between Gate and Collector for IGBT, respectively. However, breakdown voltage degradation in main devices may be introduced while forming this integrated configuration in prior art if the clamp diodes are made on a polysilicon layer placed across the edge termination. The interaction between the electric fields in the polysilicon clamp diodes and edge termination may significantly degrade breakdown voltage of the main devices.
FIG. 1 is a circuit diagram of a MOSFET with gate-drain clamp diodes and FIG. 2 is the cross section view of a MOSFET of prior art (U.S. Pat. No. 5,631,187) where the cell is formed on N substrate 200. On the top surface of the substrate 200, there is an N+ source region 210 surrounded by a P body region 211. A metal layer 220 makes electrical contact to both said N+ source region 210 and P body region 211 acting as a source electrode. Meanwhile, metal layer 222 and 221 are deposited to function as a gate electrode and a drain electrode of the cell structure, respectively. Between the gate electrode and drain electrode, a serial of back-to-back polysilicon diodes 230 are formed across over the termination to enhance the avalanche capability of the semiconductor power device.
The prior art discussed above is encountering a technical difficulty which is that, as the gate-drain (or gate-collector for IGBT) clamp diode crosses over termination, a problem of breakdown voltage degradation will be arisen due to electric field in termination region is blocked by polysilicon.
Accordingly, it would be desirable to provide a new and improved device configuration to prevent the degradation of breakdown voltage from happening.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a new and improve device configuration to solve the problem discussed above.
One advantage of the present invention is that, separated gate metal pads are used to integrate MOSFET with gate-drain clamp diodes and gate-source clamp diodes (or to integrate IGBT with gate-collector clamp diodes and gate-emitter clamp diodes), as shown in FIG. 3A (or FIG. 3B for IGBT) of circuit Diagrams and FIG. 4 of top view. The first gate metal pad 550 in FIG. 4 located inside of the metal field plate ring area 552 is connected directly to trench gate of MOSFET (IGBT) or through a resistor (not shown). The first gate metal pad 550 is also connected to source metal 553 (or emitter metal for IGBT) through a gate-source clamp diode 554 of MOSFET (or gate-emitter clamp diode for IGBT) and the metal field plate 552 as gate metal runner as well. The second gate metal pad 551 located outside of edge termination including the metal field plate ring area 552 is connected to drain of MOSFET (or collector of IGBT) through a gate-drain clamp diode 555 (or gate-collector clamp diode for IGBT). Said first and second gate metal pads are wire bonded together on the gate lead frame with separated bond wires. Because the gate-drain clamp diode 555 (or gate-collector clamp diode for IGBT) is located outside of the edge termination, there will be no degradation in breakdown voltage due to no polysilicon clamp diodes crossing over the edge termination. Alternatively, as shown in FIG. 5, the same above result can be achieved with a single gate bond wire which is bonded from the gate lead frame to the first gate metal pad 550, and then bonded to the second gate metal pad 551.
Briefly in a preferred embodiment according to the present invention, as shown in FIG. 6, which is also the A-B cross section view of FIG. 4. The present invention discloses a trench MOSFET device formed on a substrate heavily doped with a first semiconductor doping type, e.g., N+ doping type. Onto said substrate, grown an N epitaxial layer and a plurality of trenches were etched wherein. Doped poly was filled within a plurality of trenches over a gate oxide layer along the inner surface of said trenches to serve as trench gates. Especially, the trench gates underneath contact trenches of gate-drain clamp diodes and gate-source clamp diodes are employed to prevent shortage may caused by over etching of contact trenches. Near the top surface of P-body regions, N+ source regions are formed between two adjacent trench gates. A thick oxide interlayer is deposited over epitaxial layer, as well as over the top surface and sidewalls of a doped polysilicon layer comprising multiple back to back Zener diodes which composed of alternated doping areas of a first semiconductor doping type next to doping areas of a second semiconductor doping type. Through the thick oxide interlayer, source-body contact trenches, gate contact trenches and drain contact trenches are etched into epitaxial layer for source-body connection, gate connection and drain connection, respectively. Around the bottom of these contact trenches, a p+ contact area is formed. Especially, N+ contact regions are implanted near the bottom of the drain contacts trenches to further reduce the contact resistance. Meanwhile, other contact trenches are etched into cathodes of the Zener diodes for the formation of gate-drain clamp diodes and gate-source clamp diodes. To fill these contact trenches, a barrier layer and tungsten material are deposited and then etched back to act as metal plug. The first gate metal pad 550 and the second gate metal pad 551 is deposited to contact one electrode of gate-source clamp diodes and gate-drain clamp diodes via trench contacts etched into Zener diodes, respectively. At the same time, source metal is deposited to contact another electrode of gate-source clamp diodes with source region and body regions; drain metal is deposited to contact the other electrode of gate-drain clamp diodes with drain region. Said two separated gate metal pads are wire bonded together on the gate lead frame. In termination area, gate metal runner which also serving as metal field plate is formed overlying P-body and top surface of epitaxial layer. The gate-drain clamp diode as shown in FIG. 6 is located outside of termination and has no gate metal or polysilicon cross over the edge termination, therefore resulting in no degradation in breakdown voltage which occurred in the prior art. Nevertheless, the second metal pad 551 in the gate-drain clamp diode is still able to be connected to the gate of main device through bond wire instead of metal or polysilicon cross over the edge termination.
Briefly in another preferred embodiment according to the present invention, as shown in FIG. 7, which also shows the A-B cross section view of FIG. 4, the trench MOSFET structure disclosed is similar to the structure in FIG. 6 except that there is a deep guard ring under said metal field plate in termination area.
Briefly in another preferred embodiment according to the present invention, as shown in FIG. 8, which also shows the A-B cross section view of FIG. 4, the trench MOSFET structure disclosed is similar to the structure in FIG. 6 except that there are n* regions in top surface of said epitaxial layer next to P-body region as termination and there are n* regions having higher doping concentration than the epitaxial layer underneath trench bottom for Rds reduction.
Briefly in another preferred embodiment according to the present invention, as shown in FIG. 9, which also shows the A-B cross section view of FIG. 4, the trench MOSFET structure disclosed is similar to the structure in FIG. 8 except that there is a deep guard ring under said metal field plate in termination area.
Briefly in a preferred embodiment according to the present invention, as shown in FIG. 10, which is also the A-B cross section view of FIG. 4. The present invention discloses a trench IGBT device formed on a substrate heavily doped with a second semiconductor doping type, e.g., P+ doping type. Onto said substrate, grown a heavily doped epitaxial layer with a first semiconductor doping type, e.g., N+ doping type, onto which a second epitaxial layer lightly doped with the same first doping type is formed, and a plurality of trenches were etched wherein. Doped poly was filled within a plurality of trenches over a gate oxide layer along the inner surface of said trenches to serve as trench gates. Especially, the trench gates underneath contact trenches of gate-collector clamp diodes and gate-emitter clamp diodes are employed to prevent shortage may caused by over etching of contact trenches. Near the top surface of P-body regions, N+ emitter regions are formed between two adjacent trench gates. A thick oxide interlayer is deposited over front surface of epitaxial layer, as well as over the top surface and sidewalls of doped polysilicon layer comprising multiple back to back Zener diodes which composed of alternated doping areas of a first semiconductor doping type next to doping areas of a second semiconductor doping type. Through the thick oxide interlayer, emitter-base contact trenches, gate contact trenches and collector contact trenches are etched into the second epitaxial layer for emitter-base connection, gate connection and collector connection, respectively. Around the bottom of these contact trenches, a p+ contact area is formed. Especially, N+ contact regions are implanted near the bottom of the collector contacts trenches to further reduce the contact resistance. Meanwhile, other contact trenches are etched into cathodes of the Zener diodes for the formation of gate-collector clamp diodes and gate-emitter clamp diodes. To fill these contact trenches, a barrier layer and tungsten material are deposited and then etched back to act as metal plug. The first gate metal pad and the second gate metal pad is deposited to contact one electrode of gate-collector clamp diodes and gate-emitter clamp diodes via trench contacts etched into Zener diodes, respectively. At the same time, emitter metal is deposited to contact another electrode of gate-emitter clamp diodes with emitter region and base regions; collector metal is deposited to contact the other electrode of gate-collector clamp diodes with collector region. Said two separated gate metal pads are wire bonded together on the gate lead frame. In termination area, gate metal runner which also serving as metal field plate is formed overlying P-base and top surface of epitaxial layer and there is a deep guard ring and a floating ring under said metal field plate under said metal field plate as termination.
Briefly in another preferred embodiment according to the present invention, as shown in FIG. 11, which also shows the A-B cross section view of FIG. 4, the trench NPT IGBT device disclosed is similar to the structure in FIG. 10 except that the device is built on a lightly doped N substrate and P+ is formed on rear side of the N substrate after backside grinding.
Briefly in another preferred embodiment according to the present invention, as shown in FIG. 12B, which also shows the A-B cross section view of FIG. 4, the present invention discloses a trench NPT IGBT device with gate-collector diode, gate-emitter diode and collector shorting diode having separated gate metal pad. FIG. 12A shows a circuit diagram that illustrates the implementation of gate-emitter clamp diode, gate-collector clamp diode and collector shorting diode with IGBT device. The trench NPT IGBT device disclosed is similar to the structure in FIG. 11 except the collector comprising alternated P+ and N+ regions.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various drawing figures.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein:
FIG. 1 is a circuit diagram illustrates the implementation of a MOSFET cell with gate-drain clamp diodes of prior art.
FIG. 2 is a side cross-sectional view of prior art shown in FIG. 1.
FIG. 3A is a circuit diagram that illustrates the implementation of a MOSFET cell with gate-drain clamp diodes and gate-source clamp diodes of this invention.
FIG. 3B is a circuit diagram that illustrates the implementation of an IGBT cell with gate-emitter clamp diodes and gate-collector clamp diodes of this invention.
FIG. 4 is top view of this invention with two bonding wires connected to separate gate metal pads.
FIG. 5 is a top view of this invention with a single bonding wire connected to separate gate metal pads.
FIG. 6 is a side cross-sectional view of a trench MOSFET along A-B axis marked in FIG. 4 of a preferred embodiment according to the present invention.
FIG. 7 is a side cross-sectional view of a trench MOSFET along A-B axis marked in FIG. 4 of another preferred embodiment according to the present invention.
FIG. 8 is a side cross-sectional view of a trench MOSFET along A-B axis marked in FIG. 4 of another preferred embodiment according to the present invention.
FIG. 9 is a side cross-sectional view of a trench MOSFET along A-B axis marked in FIG. 4 of another preferred embodiment according to the present invention.
FIG. 10 is a side cross-sectional view of a trench PT IGBT along A-B axis marked in FIG. 4 of another preferred embodiment according to the present invention.
FIG. 11 is a side cross-sectional view of a trench NPT IGBT along A-B axis marked in FIG. 4 of another preferred embodiment according to the present invention.
FIG. 12A shows a circuit diagram that illustrates the implementation of an IGBT cell with gate-emitter clamp diode, gate-collector clamp diode and collector shorting diode of this invention.
FIG. 12B is a side cross-sectional view of a trench NPT IGBT along A-B axis marked in FIG. 4 of another preferred embodiment according to the present invention shown in FIG. 12A.



DETAILED DESCRIPTION OF THE EMBODIMENTS
Please refer to FIG. 6 for a preferred embodiment of this invention showing the A-B cross section of FIG. 4 where a trench MOSFET device cell integrated with gate-drain and gate-source clamp diodes is formed on a heavily N+ doped substrate 600 coated with back metal 690 on rear side as drain electrode. Onto the substrate 200, a lighter N doped epitaxial layer 601 is grown, and a plurality of trenches is etched wherein. Doped poly is filled into the trenches padded with a gate insulation layer 620 formed over the inner surface of said trenches. Within these gate trenches filled with doped poly, gate trenches 611 with a wider trench width than contact trenches 612 right below the center of the contact trenches 612 are formed as buffer trenched gates to prevent shortage of the contact trenches 612 to the epitaxial layer 601 may caused by over etching of the contact trenches 612. P-body regions 602 are extending between every adjacent trench gates 610 with N+ source region 603 near the top surface only within active area 640. Trench source-body contacts 613 filled with tungsten plug are formed penetrating through a thick oxide interlayer 604 and source region 603, and extending into P-body region 602, and surrounded with p+ contact area 622 underneath each source-body contact bottom to contact source region 603 and P-body region 602 with source metal 605. Trench gate contacts 614 filled with the tungsten plugs are formed penetrating through the thick oxide interlayer 604 and extending into the trench gates 610 to connect the trench gates 610 with gate metal. Trench drain contacts 615 filled with tungsten plug are formed penetrating through said oxide interlayer and source region 603, and extending into the epitaxial layer 601 to connect drain region with drain metal 607. There are gate-drain clamp diodes 630 above an oxide layer 624 between the second gate metal pad 608 and drain metal 607, and gate-source clamp diodes 631 above said oxide layer 624 between the first gate metal pad 606 and source metal 605. Said two gate metal pads are wire bonded together on the gate lead frame as shown in FIG. 4. In termination area 650, gate metal overlying P-body region 602 and top surface of epitaxial layer 601 also serves as metal field plate.
Please refer to FIG. 7 for another preferred embodiment of this invention showing the A-B cross section of FIG. 4 where the trench MOSFET structure disclosed is similar to the structure in FIG. 6 except that there is a deep guard ring 760 under the said metal field plate in termination area 750.
Please refer to FIG. 8 for another preferred embodiment of this invention showing the A-B cross section of FIG. 4 where the trench MOSFET structure disclosed is similar to the structure in FIG. 6 except that there are n* regions 861 in top surface of said epitaxial layer next to P-body region 802 as termination and there are n* regions 862 having higher doping concentration than the epitaxial layer underneath trench bottom for Rds reduction.
Please refer to FIG. 9 for another preferred embodiment of this invention showing the A-B cross section of FIG. 4 where the trench MOSFET structure disclosed is similar to the structure in FIG. 8 except that there is a deep guard ring 960 under said metal field plate in termination area 950.
Please refer to FIG. 10 for a preferred embodiment of this invention showing the A-B cross section of FIG. 4 where a trench PT (Punch-through) Type IGBT device cell integrated with gate-collector and gate-emitter clamp diodes is formed on a heavily P+ doped substrate 100 coated with back metal 190 on rear side as collector electrode. Onto said substrate 100, a heavily N+ doped epitaxial layer 101′ and a lightly N doped epitaxial layer 101 are successively grown, and a plurality of trenches are etched wherein. Doped poly is filled into the said trenches padded with a gate insulation layer 120 formed over the inner surface of said trenches. Within these gate trenches filled with doped poly, gate trenches 111 with a wider trench width than contact trenches 612 right below the center of the contact trenches 112 are formed as buffer trenched gates to prevent shortage of the contact trenches 112 to the epitaxial layer 101 may caused by over etching of contact trenches 112. P-base regions 102 are extending between every adjacent trench gates 110 with N+ emitter region 103 near the top surface only within active area 140. Trench emitter-base contacts filled with tungsten plug 113 are formed penetrating through a thick oxide interlayer 104 and emitter region 103, and extending into P base region 102, and surrounded with p+ contact area 122 underneath each emitter-base contact bottom to contact the emitter region 103 and the P-base region 102 with emitter metal 105. Trench gate contacts 114 filled with the tungsten plug are formed penetrating through said oxide interlayer 104 and extending into trench gates 110 to connect the trench gates 110 to gate metal. Collector contacts 115 filled with tungsten plug are formed penetrating through said oxide interlayer and emitter region 103, and extending into the epitaxial layer 101 to connect collector region with collector metal 107. There are gate-collector clamp diodes 130 above an oxide layer 124 between the second gate metal pad 108 and collector metal 107, and gate-emitter clamp diodes 131 above said oxide layer 124 between the first gate metal pad 106 and emitter metal 105. Said two gate metal pads are wire bonded together on the gate lead frame as shown in FIG. 5 In termination area 150, gate metal overlying P-base region 102 and top surface of epitaxial layer 101 also serves as metal field plate and there is a deep guard ring 164 and a floating ring 165 under said metal field plate under said metal field plate as termination.
Please refer to FIG. 11 for another preferred embodiment of this invention showing the A-B cross section of FIG. 4 where trench NPT (Non-punch-through) type IGBT structure disclosed is similar to the structure in FIG. 10 except that the device is built on a lightly doped N substrate and P+ region 300 is formed on rear side of the N substrate after backside grinding.
FIG. 12A shows a circuit diagram that illustrates the implementation of an IGBT cell with gate-emitter clamp diode, gate-collector clamp diode and collector shorting diode. Please refer to FIG. 12B for another preferred embodiment of this invention showing the A-B cross section of FIG. 4 where the trench NPT IGBT device disclosed is similar to the structure in FIG. 11 except the collector comprising alternated P+ and N+ regions on the rear side of the lightly doped N substrate.
Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alternations and modifications as fall within the true spirit and scope of the invention.

## Claims

1. A vertical semiconductor power IGBT device comprising a plurality of semiconductor power cells with each cell comprising a trenched gate surrounded by an emitter region with first type conductivity in active area encompassed in a base region with second type conductivity, wherein said IGBT cell further comprising:
a heavily doped substrate with said second type conductivity;
a first epitaxial layer grown on the substrate and heavily doped with the first type conductivity;
a second epitaxial layer grown on the first epitaxial layer and lightly doped with the first type conductivity;
an emitter metal layer connected to said emitter regions and said base regions via trench emitter-base contacts;
a gate-emitter clamp diode connected between a first gate metal and an emitter metal, composed of multiple back-to-back Zener diodes disposed inside of edge termination area;
a gate-collector clamp diode connected between a second gate metal and a first collector metal, composed of multiple back-to-back polysilicon Zener diodes disposed outside of edge termination area without having said polysilicon zener diode or said second gate metal cross over said edge termination;
said first collector metal connected to a first collector region formed in said second epitaxial layer via trench collector contacts;
a second collector metal layer connected to a second collector region formed on a bottom surface of the substrate; and
said first and second gate metals connected together at a gate lead frame through at least a bonding wire.

2. The IGBT of claim 1, wherein said first gate metal and second gate metal connect together to said gate lead frame through two separated bond wires.

3. The IGBT of claim 1, wherein said second gate metal connects to said first gate metal and then said gate lead frame through a single bond wire.

4. The IGBT of claim 1, wherein said IGBT is PT IGBT having said first and second epitaxial layers.

5. The IGBT of claim 1, wherein said IGBT is NPT IGBT having a lightly doped substrate with said first type conductivity type instead of said first and second epitaxial layers on said heavily doped substrate; and said second collector region with said second type conductivity is disposed on the rear side of said lightly doped substrate.

6. The IGBT of claim 1, wherein said IGBT is NPT IGBT having a lightly doped substrate with said first type conductivity type instead of said first and second epitaxial layers on said heavily doped substrate; and said second collector region comprising alternately heavily doped regions with said first and second type conductivity formed on the rear side of said lightly doped substrate.

7. The IGBT of claim 1, further comprises a buffer trenched gate right below the center of each contact trench in said gate-emitter and said gate-collect clamp diodes, having a wider trench width than said trenched gates.