Abstract
This invention discloses a semiconductor power device. The trenched semiconductor power device includes a trenched gate, opened from a top surface of a semiconductor substrate, surrounded by a source region encompassed in a body region near the top surface above a drain region disposed on a bottom surface of a substrate. The semiconductor power device further includes an implanting-ion block disposed above the top surface on a mesa area next to the body region having a thickness substantially larger than 0.3 micron for blocking body implanting ions and source ions from entering into the substrate under the mesa area whereby masks for manufacturing the semiconductor power device can be reduced.
Claims
1. A method for manufacturing a trenched semiconductor power device comprising: opening a plurality of trenches from a top surface of a semiconductor substrate and forming a gate insulation layer on sidewalls and bottom surface of said trenches; forming an implanting-ion block above said top surface in a mesa area at a distance away from said trenches for blocking body implanting ions and source ions from entering into said substrate under said mesa area whereby masks for manufacturing said semiconductor power device can be reduced; and implanting body ions into said semiconductor substrate with said implanting-ion block blocking said mesa area and diffusing said body ions into a body region with said body region separated as two separated body regions disposed on two opposite sides of said trenches.
2. The method of claim 1 further comprising: forming trenched gate in each of said trenches as a split gate including a lower gate segment covered by an insulation layer and an upper gate segment above said insulation layer.
3. The method of claim 1 further comprising: applying a HDP deposition process to form a thick oxide layer on bottom surface of said trenches simultaneously with and implanting ion blocks as HDP oxide layer and forming split gate in each of said trenches.
4. A trenched semiconductor power device comprising a trenched gate, opened from a top surface of a semiconductor substrate, surrounded by a source region encompassed in a body region near said top surface above a drain region disposed on a bottom surface of a substrate, wherein said semiconductor power device further comprising: an implanting-ion block disposed above said top surface on a mesa area next to said body region having a thickness substantially for blocking body implanting ions from entering into said substrate under said mesa area whereby masks for manufacturing said semiconductor power device can be reduced; and
5. The trenched power semiconductor power device of claim 4 further comprising: a termination area wherein said implanting-ion block having a greater width than said implanting-ion block on said mesa area for separating said body regions and forming floating body regions in said termination area to form at least a guard ring in a trenched gate surrounded by said floating body region in said termination area.
6. The trenched power semiconductor power device of claim 4 further comprising: an integrated Schottky field effect transistor (FET) including a body dopant region, with a higher dopant concentration than said body region, disposed adjacent to said source region, and said body dopant region having a region boundary substantially aligned with said ion-implanting block.
7. The trenched power semiconductor power device of claim 4 wherein: said trenched gate further comprising a split gate including a lower gate segment covered by an insulation layer and an upper gate segment above said insulation layer.
8. The trenched power semiconductor power device of claim 4 wherein: said trenched gate further comprising a split gate including a lower gate segment covered by an insulation layer and an upper gate segment above said insulation layer.; and said trenched gate further including a thick oxide layer disposed on a bottom surface of said trenched gate having a thickness greater than a gate oxide layer padding sidewalls of said trenched gate.
9. The trenched power semiconductor power device of claim 4 wherein: said thick oxide layer disposed on said bottom of said trenched gate is a high-density plasma (HDP) deposited thick oxide layer and said implanting-ion block further comprising a HDP deposited oxide layer formed simultaneously with said thick oxide layer disposed on said bottom of said trenched gate.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIGS. 1A to 1G are cross sectional views for describing the manufacturing processes in applying a new HDP process to form the trenched MOSFET devices of this invention with reduced number of masks.
[0037] FIG. 2 is a cross sectional view of a MOSFET device for illustrating the configuration of the guard rings in the termination area for a MOSFET device of shown in FIG. 1.
[0038] FIGS. 3A to 3C are cross sectional views for describing the manufacturing processes by applying a new HDP process to form a trenched MOSFET device of this invention with thick oxide with embedded Schottky FET with reduced number masks.
[0039] FIGS. 4A to 4E are a series of cross sectional views for describing the manufacturing processes by applying a new HDP process to form a trenched MOSFET device of this invention with split gate and thick oxide layer on the trench bottom by using reduced number masks.
[0040] FIGS. 5A to 5E are a series of cross sectional views for describing the manufacturing processes by applying a new HDP process to form a trenched MOSFET device of this invention with split gate by using reduced number masks.
[0041] FIGS. 6A to 6C are a series of cross sectional views for describing the manufacturing processes by applying a new process to form a trenched MOSFET device of this invention with reduced number of masks by using an implanting-ion blocks on the mesa areas in the MOSFET device.
DETAILED DESCRIPTION OF THE METHOD
[0042] Referring to FIGS. 1A to 1G for a series of cross sectional views for describing the manufacturing processes of a new and improved trench MOSFET device of this invention. In FIG. 1A, a first mask (not shown) is first applied to open a plurality of trenches 108 into an epitaxial layer 110 supported on a semiconductor substrate 105. Then a high-density plasma (HDP) oxide layer is applied to form a thick oxide layer 115 at the trench bottom and thinner oxide layer 119 on trench sidewalls and thicker oxide layer 120 on the top surface of the substrate. In FIG. 1B, an oxide wet etch is carried out to etch out the thinner oxide layer 119 surrounding the sidewalls of the trench 108 and also a part of the thick oxide layer 120 near the trenches 108 and leaving only the thick oxide layer 120 in the mesa area and the thicker oxide layer 115 on the trench bottom. In FIG. 1C, a gate oxide layer 125 is then formed by thermal oxidation followed with filling the trenches 108 with polysilicon and etch back to form the polysilicon gate 130 in the trenches. Alternatively gate oxide 125 may be formed by depostition, preferably using HTO (high temperature oxide) techniques by mixing dicholorosilane with oxygen, at reduced pressure, in the range of 700-900 C, resulting a conformal oxide deposition layer over the trench sidewall, as well as the remaining HDP oxide. Gate oxide thickness can be in the 100 A to 1500 A range, or more, depending on the desired gate-source voltage rating for the transistor.
[0043] In FIG. 1D, a body implant is performed followed by a diffusion operation to drive the body region 135 into the epitaxial layer 110. Alternatively, the body implant may be carried out with angled and rotated implant before gate oxide layer 125 is formed, using oxide region 120 on top of the mesa and oxide region 115 on the trench bottom as a mask. One advantage of this later approach is the body does not need to drive as far as the previous approach, therefore the lateral diffusion is less and the body region can be narrower, thus the cells can be packed tighter. Then a source implant is performed followed by a source region drive operation to form the source regions 140. As shown in FIG. 1D, with the thicker oxide layer 120 disposed in the mesa areas, the body and source implant operations are carried out without requiring implant masks thus achieve manufacturing process simplification and cost savings.
[0044] In one embodiment, the thick oxide 120 blocks the body implant that the two body regions under each side of oxide 120 are completely separated after diffusion (not shown); in another embodiment, the two body regions merge together after diffusion forming an inverted V shape profile in the merging area in the middle of the two trenches, as shown in FIG. 1D. The vertical position of the inverted V pinnacle point can be carefully controlled by adjusting the mesa width, the implant energy and diffusion depth.
[0045] In FIG. 1E, insulation layer 145, e.g., LTO oxide layer and BPSG layer, is deposited on the top surface. In FIG. 1F, a third mask (not shown) is applied to open a plurality of source and gate contact openings 150-S and 150-G respectively. A P+ contact region 155 is implanted then activated at elevated temperature to form source/body metal ohmic contact and gate metal ohmic contact through the layer 145. In FIG. 1G, the manufacturing processes are then completed with metal layer deposition and patterning on the top surface to form the source metal 160-S and gate pad 160-G and backside metal contact formation for drain connection 170 to the MOSFET 100 device.
[0046] A new and improved manufacturing process is disclosed with the MOSFET 100 shown above that has thicker oxide layer at the bottom of the trench gate and is manufactured with only three masks. The MOSFET device further has a new structure wherein the thick oxide layer 115 at the bottom of the trench gate is formed by HDP oxide as the HDP oxide layer 120 in the mesa area. By controlling the mesa width, the body depth and the P+ contact implant regions 155, a high electric filed may be created between the bottom of P+ contact implant 155 and the inverted V pinnacle point so that the breakdown at this region will occur before other area reach breakdown voltage.
[0047] Referring to FIG. 2 for a cross sectional view of a MOSFET device for illustrating the configuration of the guard rings in the termination area for a MOSFET device 100 shown in FIG. 1. For the purpose of forming the guard rings to sustain higher voltages, the spacing between the trenches 130 in the termination area is increased to have a wider space between the trench gates 130 and consequently the body regions 135 are formed as separated floating regions as shown to provide the guarding ring protection functions. If necessary, a separate mask may be applied to block the n+ implant into the guard ring areas and that would increase the number of masks to four as required for manufacturing the MOSFET device with guard rings that are different from FIG. 2 without the n+ regions 140.
[0048] Referring to FIGS. 3A to 3C for a series of cross sectional views for describing the manufacturing processes by applying a new HDP process to form a trenched MOSFET device of this invention with thick oxide at bottom of trench gate and with embedded Schottky diode. The new method enables the manufacture of such device with reduced number masks. Referring to FIGS. 1A to 1D for the processing steps by applying a first mask to complete the manufacturing processes for a partially completed device as shown in FIG. 3A. The only exception is that the body regions 135 in FIG. 3A are formed as separated body regions instead of merging together as that shown in FIG. 1D. In FIG. 3B, a second mask 123 is applied as a contact block mask to pull back the HDP surface oxide layer 120 followed by a P+ contact implant to form the contact implant regions 148.
[0049] The manufacturing processes proceed by first removing the contact block mask 123 and the deposition of insulation layers of LTO/BPSG then applying a third mask as a contact mask to open the metal contact openings through the insulation layers. After BPSG reflow a Schottky barrier 170 followed by a metal layer 160 is deposited and patterned as source pad and gate pad as that shown and described in FIGS. 1E to 1G above. The final structure as shown in FIG. 3C is therefore completed with four masks that has a MPS (Merged PIN/Schottky) or JBS (junction barrier shcottky) rectifier within each cell. Specifically, the Schottky barrier layer 170, the P body regions 135 and the N-epi region between the separated P body regions configuring a MPS/JBS that greatly reduces the voltage drop over the MOSFET body diode in reverse conducting mode.
[0050] Referring to FIGS. 4A to 4E for a series of cross sectional views for describing the manufacturing processes by applying a new HDP process to form a trenched MOSFET device of this invention with split gate and thick oxide layer on the trench bottom by using reduced number masks. In FIG. 4A, a first mask (not shown) is first applied to open a plurality of trenches 208 into an epitaxial layer 210 supported on a semiconductor substrate 205. Then a high-density plasma deposition (HDP) of oxide layer is applied to form a thick oxide layer 215 at the trench bottom and thinner oxide layer 219 and thicker oxide layer 220 on the top surface of the substrate. In FIG. 4B, a deposition of first polysilicon gate and etch back of the polysilicon is carried out to form the bottom segment of the gate 225 at the bottom portion of the trenches 208. In FIG. 4C, a second high-density plasma deposition (HDP) oxide layer is carried out to deposit a second oxide layer 230 on top of the first HDP oxide layer 215 and the first gate segment 225. In FIG. 4D, an oxide etch is carried out to etch out part of the oxide layers 230 and the upper portion of thinner oxide 219 surrounding the sidewalls of the trench 208. The oxide etch also removes the second HDP layer 230 and a part of the thick oxide layer 220 near the trenches 208 and leaving only thick oxide layer 220 in the mesa area and the thick second HDP oxide layer 230 on top of the bottom gate segment. In FIG. 4E, the split gate is formed by a depositing a second polysilicon layer 240 followed by a polysilicon etch back to form the upper gate segment 240 on top of the inter-poly insulation layer 230 formed by the second HDP oxide deposition process. After the formation of the split gate, the MOSFET manufacturing processes proceed according to the steps as that described in FIGS. 1D to 1G.
[0051] Referring to FIGS. 5A to 5E for a series of cross sectional views for describing the manufacturing processes by applying a new HDP process to form a trenched MOSFET device of this invention with split gate by using reduced number masks. The manufacturing processes are similar to that described for FIGS. 4A to 4E. The only differences are shown in FIGS. 5A and 5B where normal thermal oxide layer 215 with uniform thickness is formed on the trench bottom without applying a HDP oxide deposition to form the thick trench bottom oxide 215 as shown in FIGS. 4A and 4B. The remainder of the processing steps as shown in FIGS. 5C to 5E are basically identical to that shown in FIGS. 4C to 4E with the exception that the thick oxide layer 230 in the mesa area is formed by the only HDP oxide deposition since unlike the processes shown in FIGS. 4A to 4E, there is only one HDP oxide deposition process. Therefore, the MOSFET device with split gates can be manufactured with reduced number of masks by taking advantage of the HDP oxide deposition process that is provide to form oxide layer with different thickness in different targeted areas.
[0052] The goal to reduce the mask count in MOSFET manufacturing process can also be achieved using regular thermal oxidation process or CVD deposition. FIGS. 6A-6C describe such a process. In FIG. 6A a thick oxide layer 620 is grown through thermal oxidation or CVD deposition and is used as a hard mask by applying trench mask to etch trench 608 into the epi layer 610 overlaying substrate 605. In FIG. 6B, an oxide pull back etch is carried out to remove the oxide near the trench forming a source/body implant block. A gate is then formed within the trench following the standard process to form a split gate or a normal gate before the body and source are implanted. Alternatively, the body and source implant may be carried out before the gate formation using a resist 630 to fill the trench to block source body implanting into the bottom of trench as shown in FIG. 6C. The device is then completed with the normal manufacturing process.
[0053] 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. 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.
