EDGE TERMINATION DESIGNS FOR SUPER JUNCTION DEVICE

Abstract

This invention discloses a semiconductor power device formed on an upper epitaxial layer of a first conductivity type supported on a semiconductor substrate comprises an active cell area and a termination area disposed near edges of the semiconductor substrate. The semiconductor power device having a super junction structure with the epitaxial layer formed with a plurality of doped columns of a second conductivity type. The termination area further comprises a plurality of surface guard ring regions of the second conductivity type dispose near a top surface of the epitaxial layer close to the doped columns of the second conductivity type. In one of the embodiments, one of the surface guard ring regions extending laterally over several of the doped columns in the termination area.

Claims

1. A semiconductor power device formed on an upper epitaxial layer of a first conductivity type supported on a semiconductor substrate comprises an active cell area and a termination area disposed near edges of the semiconductor substrate wherein: the semiconductor device having a super junction structure with a plurality of doped columns of a second conductivity type disposed in the epitaxial layer; and a plurality of surface guard ring regions of the second conductivity type dispose in the termination area extending laterally underneath a top surface of the epitaxial layer contacting the doped columns of the second conductivity type wherein at least one of the guard ring regions is disposed inside and having a width narrower than one of the doped columns of the second conductivity type.

2. The semiconductor power device of claim 1 wherein: at least one of the surface guard ring regions of the second conductivity type extending laterally over at least two of the doped columns of the second conductivity type underneath the top surface of the epitaxial layer.

3. The semiconductor power device of claim 1 wherein: the surface guard ring regions of the second conductivity type having gradually decreasing lateral lengths underneath the top surface of the epitaxial layer as each of the guard ring regions disposing further away from the active cell area.

4. The semiconductor power device of claim 1 wherein: at least one of the surface guard ring regions of the second conductivity type disposed inside and having substantially a same width as one of the doped columns of the second conductivity type underneath the top surface of the epitaxial layer.

5. A semiconductor power device formed on an upper epitaxial layer of a first conductivity type supported on a semiconductor substrate comprises an active cell area and a termination area disposed near edges of the semiconductor substrate wherein: the semiconductor device having a super junction structure with a plurality of doped columns of a second conductivity type disposed in the epitaxial layer; and a plurality of surface guard ring regions of the second conductivity type dispose in the termination area extending laterally underneath a top surface of the epitaxial layer contacting the doped columns of the second conductivity type wherein at least one of the surface guard ring regions of the second conductivity type is disposed immediately adjacent and contacting one of the doped columns of the second conductivity type and having a width narrower than a width between the doped column of the second conductivity adjacent to each other.

6. The semiconductor power device of claim 5 wherein: at least one of the surface guard ring regions of the second conductivity type extending laterally over at least two of the doped columns of the second conductivity type underneath the top surface of the epitaxial layer.

7. The semiconductor power device of claim 5 wherein: the surface guard ring region of the second conductivity type that is disposed immediately adjacent and contacting one of the doped columns of the second conductivity type is disposed on a side of the doped columns of the second conductivity type that is closer to the active cell area.

8. The semiconductor power device of claim 5 wherein: the surface guard ring region of the second conductivity type that is disposed immediately adjacent and contacting one of the doped columns of the second conductivity type is disposed on a side of the doped columns of the second conductivity type that is opposite from the active cell area.

9. The semiconductor power device of claim 1 further comprising: a field plate disposed on the top surface of the epitaxial layer at an outer edge of the semiconductor substrate; and an outmost ring of the first conductivity type is formed as an channel stop ring disposed at the outer edge of the semiconductor substrate wherein the outmost channel stop ring is disposed under and electrically connected to the field plate.

10. The semiconductor power device of claim 1 wherein: the active cell area further comprises a MOSFET device.

11. A method for manufacturing a semiconductor power device in an upper epitaxial layer of a first conductivity type supported on a semiconductor substrate, the method comprising: forming a hardmask on top of the upper epitaxial layer and applying a photolithography to pattern the hardmask into a plurality of super-junction openings in an active cell area and a termination area followed by etching a plurality of trenches through the super-junction openings; removing the hardmask followed by filling the trenches with a doped epitaxial layer of a second conductivity type to form a plurality of doped columns of the second conductivity type in the upper epitaxial layer; and applying a planarization process to planarize a top surface on top of the upper epitaxial layer followed by applying a surface guard-ring mask to implant a plurality of surface guard ring regions of the second conductivity type in the termination area under the top surface of the upper epitaxial layer wherein each of the surface guard ring regions contacting the doped columns of the second conductivity type.

12. The method of claim 11 wherein: the step of implanting the surface guard ring regions of the second conductivity type further comprising a step of implanting the surface guard rings to extend laterally over different lateral lengths underneath the top surface of the epitaxial layer.

13. The method of claim 11 wherein: the step of implanting the surface guard ring regions of the second conductivity type further comprising a step of implanting the surface guard rings to extend laterally over gradually decreasing lateral lengths underneath the top surface of the epitaxial layer for each of the guard rings disposing further away from the active cell area.

14. The method of claim 11 wherein: the step of implanting the surface guard ring regions of the second conductivity type further comprising a step of implanting at least one of the surface guard ring regions to extend laterally across several doped columns of the second conductivity type.

15. The method of claim 1 wherein: the step of implanting the surface guard ring regions of the second conductivity type further comprising a step of implanting at least one of the surface guard ring regions that is disposed closest to the active area of the power device extending laterally across several doped columns of the second conductivity type underneath the top surface of the epitaxial layer.

16. The method of claim 1 wherein: the step of implanting the surface guard ring regions of the second conductivity type further comprising a step of implanting the surface guard rings to extend laterally over different lateral lengths underneath the top surface of the epitaxial layer and several of the surface guard ring regions disposed with a spacing corresponding to a spacing between the doped columns of the second conductivity type.

17. The method of claim 1 wherein: the step of implanting the surface guard ring regions of the second conductivity type further comprising a step of implanting the surface guard rings to extend laterally over different lateral lengths underneath the top surface of the epitaxial layer and several of the surface guard ring regions are disposed on a side of the doped columns of the second conductivity type that is closer to the active cell area.

18. The method of claim 1 wherein: the step of implanting the surface guard ring regions of the second conductivity type further comprising a step of implanting the surface guard rings to extend laterally over different lateral lengths underneath the top surface of the epitaxial layer and several of the surface guard ring regions are disposed on a side of the doped columns of the second conductivity type that is opposite from the active cell area.

19. The method of claim 1 further comprising: forming a field plate on the top surface of the epitaxial layer at an outer edge of the semiconductor substrate; and electrically connecting the field plate to an outmost ring of the first conductivity disposed underneath the field plate formed as an outmost channel stop ring disposed at the outer edge of the semiconductor substrate.

20. The method of claim 1 further comprising: forming a MOSFET device in the active cell area.

21. The semiconductor power device of claim 1 wherein: at least one of the doped columns of the second conductivity type in the termination area does not encompass or in contact with one of the surface guard ring regions.

22. The semiconductor power device of claim 5 wherein: at least one of the doped columns of the second conductivity type in the termination area does not encompass or in contact with one of the surface guard ring regions.

23. The semiconductor power device of claim 1 wherein: the surface guard ring regions having a higher dopant concentration than the doped columns of the second conductivity type.

24. The semiconductor power device of claim 5 wherein: the surface guard ring regions having a higher dopant concentration than the doped columns of the second conductivity type.

25. The semiconductor power device of claim 5 wherein: the surface guard ring regions of the second conductivity type having gradually decreasing lateral lengths underneath the top surface of the epitaxial layer as each of the guard ring regions disposing further away from the active cell area.

26. The semiconductor power device of claim 5 further comprising: a field plate disposed on the top surface of the epitaxial layer at an outer edge of the semiconductor substrate; and an outmost ring of the first conductivity type is formed as an channel stop ring disposed at the outer edge of the semiconductor substrate wherein the outmost channel stop ring is disposed under and electrically connected to the field plate.

27. The semiconductor power device of claim 5 wherein: the active cell area further comprises a MOSFET device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIGS. 1A to 1D are cross sectional views showing four different termination configurations of the conventional super junction semiconductor power devices.

[0013] FIG. 2 is a cross sectional view of a super junction MOSFET device implemented with the surface guard rings in the termination area of this invention.

[0014] FIGS. 3 and 4 are cross sectional views of alternate super junction MOSFET devices implemented with the surface guard rings in the termination area of this invention.

[0015] FIGS. 5A to 5K are a series of cross sectional views for illustrating the manufacturing processes of devices shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] FIG. 2 is a cross section view of a semiconductor power device 100 as a preferred embodiment of this invention. The semiconductor power device 100 includes an active cell area 101 and a termination area 102 and is formed on an N-type semiconductor substrate 105 supporting an N-type epitaxial layer 110 on top of the bottom substrate layer 105. The epitaxial layer 110 is formed with a super junction structure with the epitaxial layer 110 comprises a plurality of P-columns 115 separated by the 110-N regions between two adjacent P-columns 115. In order to improve the device reliability and the UIS capability, this invention implements a new and improved termination configuration by implanting a plurality of guard rings 120 near the top surface of the epitaxial layer. With the guard rings immediately below the top surface, the surface electric-field can be controlled to distributed over the termination area 102. The device reliability and the UIS capability is improved. As shown in FIG. 2, the guard ring 120-1 that is formed immediately next to the active cell area 101 has a longest lateral length that extends over three P-columns 115 while the guard rings 120-2 to 120-8 have gradually reduced lateral lengths.

[0017] As shown in FIG. 2, in an exemplary embodiment, the active cell area 101 comprises a plurality of MOSFET transistor cells disposed on top of the super junction structure wherein the distance between two P-columns 115 in the active cell area 101 is equal to the distance between two P-columns in the termination area 102. Each transistor cell in the active cell area includes a planar polysilicon gate 130 padded by a gate oxide 135 underneath the gate 130 on top surface of the epitaxial layer 110. The planar gate 130 extended laterally over two p-columns 115 with a P-type body region 140 encompassing an N-type source region 145 formed on top of the P-column 115. The termination area 102 is covered by a field oxide layer as a first insulation layer 150 in the termination area and a top insulation layer 165 is formed to cover the top surface of the active cell area and the termination area. Through the top insulation layer are contact trenches opened therethrough to provide a source contact 155 to electrically connect the body and source regions to the source metal 160 on top of the insulation layer 165. The source metal 160 is further electrically connected to a first floating polysilicon segment 130-1 disposed on top of field oxide 150. A field plate 170 is formed at the outer edge of the device on top of the top insulation layer 165. The channel stop is formed by the outmost N-type doped region 140′, which is implanted simultaneously with the source implant. The field plate 170 is electrically connected to an outmost N-type doped region 140′ and also to a second floating polysilicon segment 130-2 disposed on top of the oxide filed layer 150.

[0018] FIG. 3 is a cross section view of an alternate embodiment of this invention. The semiconductor power device 100′ is formed on a super junction structure with the P-columns 115 similar to the device of FIG. 2. The major differences between the device 100′ and the device 100 as that shown in FIG. 2 are the configuration of the surface guard rings 120′. The guard rings 120′ of device 100′ are formed with width and spacing that independent from the P-columns 115. Furthermore, in device 100′, the outer surface guard rings 120′ are formed on the side of the P-columns 115 thus the outer surface guard rings 120′ are closer to the active cell area 101.

[0019] FIG. 4 is a cross section view of another alternate embodiment of this invention. The semiconductor power device 100″ is formed on a super junction structure with the P-columns 115 similar to the device of FIGS. 2 and 3. The major differences between the device 100′ and the device 100 as that shown in FIG. 2 are the configuration of the surface guard rings 120′. The guard rings 120″ of device 100′ are formed with width and spacing that independent from the P-columns 115. Furthermore, in device 100″, the surface guard rings 120″ are formed on the side of the P-columns 115 thus the outer surface guard rings 120″ are formed opposite and farther from the active cell area 101.

[0020] FIGS. 5A-5K are a series of cross sectional views to show the fabrication processes of a semiconductor power device shown in FIGS. 2 to 4. In FIG. 5A, a hard mask 108 is deposited at first on top of the epitaxial layer 110 supported on the silicon substrate 105. In FIG. 5B, a trench mask (not shown) is applied on top of the hard mask 108 to carry out a trench etch process to open a plurality of trenches in the epitaxial layer 110. In FIG. 5C, the hard mask 108 is removed followed by necessary steps to smooth the trench sidewalls including a sacrificial oxidation and an oxide-etch to remove the damaged surface on the trench wall. Then the trenches are filled with a P-type epitaxial layer to form P-columns 115 in the N-type epitaxial layer 110 followed by a planarization process. The P-columns can also be alternately formed by multiple epitaxial growth process with masked P-type implantation after each epitaxial growth. In FIG. 5D, a top guard ring implant is carried out by applying a guard ring implant mask (not shown) to form the top surface guard ring regions 120. The P-type body implant in the core cell in the active area can also be formed at the same time. Depending on the different process conditions and requirements on threshold voltage (Vth). The P-type body implant can be formed separately in the later process.

[0021] In FIG. 5E, a filed oxide layer 150 is deposited on top of the epitaxial layer 110 and in FIG. 5F, a mask (not shown) is applied to etch the field oxide layer 150 to open up the active area for further device manufactures. In FIG. 5G, a gate oxide layer 135 is deposited followed by depositing and patterning of polysilicon layer to form gate 130 (shown in FIG. 2) and polysilicon segments 130-1 and 130-2. In FIG. 5H, the P-type body implant is skipped because it shares the same implant when the P-type surface guard rings is formed. Alternately, another body implant can be carried out to adjust the threshold voltage (Vth) of the device (not shown in FIG. 2). A source implant is carried out to form the source regions 145 encompassed in the body regions and the outmost channel stop region 140′ (shown in FIG. 2).

[0022] In FIG. 5I, a local thermal oxide (LTO) and BPSG deposition processes are performed to form an insulation layer 165 covering over the field oxide 150 and the top surface of the semiconductor power device. In FIG. 5J, a contact trench etch is performed to open contact trench through the passivation/insulation layer 165 followed by filling the contact trench with a barrier layer metal and a contact metal layer to form trench contacts 155. Then the processes are completed with the deposition and patterning of the top metal layer to form the source metal 160 and the terminal field plate 170. In the termination area, the field plate 170 is electrically connected to the outer edge N-type doped regions 140′ and the second polysilicon segment 130-2 through the trench contacts 155 that penetrate through the insulation layer 165 to form the channel stop of the device. In FIG. 5K, a super junction MOSFET device is shown as a final product that is also shown in FIG. 2.

[0023] Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. For example, though the conductivity types in the examples above often show an n-channel device, the invention can also be applied to p-channel devices by reversing the polarities of the conductivity types. Various alterations 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 alterations and modifications as fall within the true spirit and scope of the invention.