Junction barrier Schottky diode with enforced upper contact structure and method for robust packaging

• US 8,362,585 B1
• Filed: 07/15/2011
• Issued: 01/29/2013
• Est. Priority Date: 07/15/2011
• Status: Active Grant

• Current Assignee: Alpha & Omega Semiconductor, Ltd.
• Original Assignee: Alpha & Omega Semiconductor, Inc. (Alpha & Omega Semiconductor, Ltd.)
• Inventors: Bhalla, Anup, Pan, Ji, Ng, Daniel
• Primary Examiner(s): Ngo, Ngan
• Application Number:
  US13/184,488
• Publication Number:
  US 20130015550A1
• Time in Patent Office: 564 Days
• Field of Search: 257/476, 257/483, 257/484, 257/486, 257/495, 257/E29.013, 257/E29.338, 438/534, 438/571
• US Class Current: 257/476
• CPC Class Codes: H01L 24/05 of an individual bonding area
• CPC Class Codes: H01L 29/0619 with a supplementary region doped oppositely to or in rectifying contact with the semiconductor containing or contacting region, e.g. guard rings with PN or Schottky junction
• CPC Class Codes: H01L 29/417 carrying the current to be rectified, amplified or switched
• CPC Class Codes: H01L 29/872 Schottky diodes
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/01029 Copper [Cu]
• CPC Class Codes: H01L 2924/12032 Schottky diode

Abstract

A semiconductor junction barrier Schottky (JBS-SKY) diode with enforced upper contact structure (EUCS) is disclosed. Referencing an X-Y-Z coordinate, the JBS-SKY diode has semiconductor substrate (SCST) parallel to X-Y plane. Active device zone (ACDZ) atop SCST and having a JBS-SKY diode with Z-direction current flow. Peripheral guarding zone (PRGZ) atop SCST and surrounding the ACDZ. The ACDZ has active lower semiconductor structure (ALSS) and enforced active upper contact structure (EUCS) atop ALSS. The EUC has top contact metal (TPCM) extending downwards and in electrical conduction with bottom of EUCS; and embedded bottom supporting structure (EBSS) inside TPCM and made of a hard material, the EBSS extending downwards till bottom of the EUCS. Upon encountering bonding force onto TPCM during packaging of the JBS-SKY diode, the EBSS enforces the EUCS against an otherwise potential micro cracking of the TPCM degrading the leakage current of the JBS-SKY diode.

Claims

1. A semiconductor junction barrier Schottky (JBS-SKY) diode with enforced upper contact structure (EUCS), the JBS-SKY diode comprising, referencing an X-Y-Z Cartesian coordinate system:

a semiconductor substrate (SCST) with its major plane lying parallel to the X-Y plane;

an active device zone (ACDZ) atop the SCST and having a built-in JBS-SKY diode with its major device current flowing parallel to the Z-axis;

a peripheral guarding zone (PRGZ) atop the SCST and being located in an adjacent and surrounding relationship to the ACDZ, said PRGZ being structured for an increased breakdown voltage of the built-in JBS-SKY diode;

said ACDZ comprising an active lower semiconductor structure (ALSS) and an enforced active upper contact structure (EUCS) atop the ALSS with the juncture between ALSS and EUCS forming said JBS-SKY diode;

said EUCS comprising;

a top contact metal (TPCM) extending downwards and in electrical conduction with bottom of the EUCS; and

an embedded bottom supporting structure (EBSS), being embedded inside the TPCM and being made of a hard material, said EBSS further extending downwards till the bottom of the EUCS

such that, upon encountering a downward mechanical bonding force onto the TPCM during later packaging of the JBS-SKY diode, the EBSS acts to enforce the EUCS against an otherwise potential micro cracking of the TPCM degrading the leakage current of the built-in JBS-SKY diode.

2. The JBS-SKY diode with EUCS of claim 1 wherein the bottom of EUCS further comprising an intervening barrier metal layer (BRML) between the bottom of TPCM and the top surface of ALSS, said BRML:

a) forms, together with a top surface portion of the ALSS, the Schottky diode portion of the built-in JBS-SKY diode; and

b) also functions as a barrier preventing the TPCM from diffusing into thus poisoning the top surface portion of ALSS.

3. The JBS-SKY diode with EUCS of claim 2 wherein the hard EBSS material is an insulator hence:

c) the embedded EBSS comprising, throughout an X-Y area bounded by the ACDZ, a two dimensional grid of separated upward pointing EBSS bumps; and

d) the lower portion of TPCM comprising a grid of downward pointing TPCM fingers complementary to and embedding the separated EBSS bumps

whereby forming a two dimensional grid contact between the TPCM and a top surface portion of the ALSS throughout the ACDZ.

4. The JBS-SKY diode with EUCS of claim 3 wherein the BRML is a double layer comprising:

e) a lower barrier metal layer (LBML) extended along an X-Y plane throughout the ACDZ; and

f) an upper barrier metal layer (UBML) atop the LBML only extended throughout the X-Y footprints of the TPCM fingers

such that double barrier metal layers are only placed beneath the TPCM fingers where they are most needed.

5. The JBS-SKY diode with EUCS of claim 4 wherein:

The SCST is made of silicon;

The TPCM is made of aluminum-copper (Al—

Cu);

The LBML is made of titanium silicide; and

the UBML is made of titanium silicide.

6. The JBS-SKY diode with EUCS of claim 3 wherein the hard insulating EBSS material is low temperature thermal oxide-phosphosilicate (LTO-BPSG) reflow glass or Tetraethyl orthosilicate (TEOS);

and correspondingly, the PRGZ comprising a peripheral upper supporting substructure (PUSST) that, except for being extended inside the PRGZ and accordingly patterned, is made of the same material and cross sectioned at the same elevations as the EBSS bumps.

7. The JBS-SKY diode with EUCS of claim 3 wherein the grid of EBSS bumps is geometrically characterized by:

a bump cross sectional dimension (X-Y plane) of from about 0.3 micron to 50 microns;

a bump height (Z-axis) of from about 0.3 micron to about 15 microns; and

a minimum bump-bump spacing (X-Y plane) of about 1.4 microns.

8. The JBS-SKY diode with EUCS of claim 3 further comprising a top device passivation layer (TDPL), covering the ACDZ and the PRGZ, patterned with one or more top pad openings (TPO) at pre-determined locations along the X-Y plane, for receiving downward mechanical bonding forces during later packaging of the JBS-SKY diode.

9. The JBS-SKY diode with EUCS of claim 8 wherein, to better enforce the EUCS against potential TPCM micro cracking, the two dimensional grid of separated upward pointing EBSS bumps is geometrically configured such that only a solid EBSS bump top lies below each TPO.

10. The JBS-SKY diode with EUCS of claim 8 wherein, to maximize electrical conductance of the EUCS, the grid of EBSS bumps is geometrically configured such that below those areas of the TDPL absent a TPO there is an absence of EBSS bumps as well hence the corresponding volume of EUCS is filled with solid TPCM material.

11. The JBS-SKY diode with EUCS of claim 8 wherein the TDPL is made of silicon oxide, silicon nitride or polyimide.

12. The JBS-SKY diode with EUCS of claim 4 wherein:

The SCST is of N++ type conductivity with heavy dopant concentration; and

the ALSS comprising a semiconductor drift layer (SDFL), of N type conductivity, extended into and through the PRGZ with the top surface portion of ALSS further comprising, along an X-Y plane, a plurality of surface junction barrier pockets (SJBP) of P+ type conductivity into the SDFL and forming the junction barrier portion of the built-in JBS-SKY diode therewith; and

correspondingly, the PRGZ comprising a plurality of peripheral guard rings (PPGR) that, except for being extended into the PRGZ and accordingly patterned, are made of the same material and cross sectioned at the same elevations as the SJBP.

13. The JBS-SKY diode with EUCS of claim 12 wherein the lateral dimensions and locations (X-Y plane) of said plurality of SJBP do not have to match those of said grid of upward pointing EBSS bumps.

14. The JBS-SKY diode with EUCS of claim 12 wherein, between the plurality of PPGR and the PUSST, the PRGZ further comprising an intervening stack of:

a plurality of hard mask rings (HMRG) atop yet placed in a spatially interdigitated relationship to the PPGR along an X-Y plane; and

an LTO layer atop the plurality of HMRG yet beneath the PUSST.

15. The JBS-SKY diode with EUCS of claim 12 wherein:

the depth (Z-direction) of SJBP is from about 0.1 micron to 50 microns; and

the separation (along an X-Y plane) between adjacent SJBPs is from about 0.3 micron to 50 microns.

16. A method of making a semiconductor junction barrier Schottky (JBS-SKY) diode with enforced upper contact structure (EUCS), the JBS-SKY diode comprising, referencing an X-Y-Z Cartesian coordinate system:

a semiconductor substrate (SCST) parallel to the X-Y plane;

an active device zone (ACDZ) atop the SCST and having a built-in JBS-SKY diode;

a peripheral guarding zone (PRGZ) atop the SCST and in adjacent and surrounding relationship to the ACDZ;

the ACDZ comprising an active lower semiconductor structure (ALSS) and an enforced active upper contact structure (EUCS) atop the ALSS jointly forming the JBS-SKY diode, the EUCS comprising;

an embedded bottom supporting structure (EBSS) comprising a two dimensional grid of separated upward pointing EBSS bumps made of a hard insulating material; and

a top contact metal (TPCM) extending downwards with the lower portion of TPCM comprising a grid of downward pointing TPCM fingers complementary to and embedding the separated EBSS bumps such that they act to enforce the EUCS against micro cracking of the TPCM during later packaging of the JBS-SKY diode;

the method comprising;

providing an SCST, partitioning it into an ACDZ and a PRGZ and making a partial JBS-SKY diode atop with;

a semiconductor drift layer (SDFL), of N type conductivity atop the SCST, having numerous surface junction barrier pockets (SJBP) of P+ type conductivity built into the SDFL thus forming the ALSS therewith; and

a completed PRGZ with numerous peripheral guard rings PPGR built into the SDFL;

forming a lower barrier metal layer (LBML) atop the ACDZ;

forming the grid of EBSS bumps atop the LMBL;

forming an upper barrier metal layer (UBML) atop the LBML; and

depositing and patterning the TPCM.

17. The method of making a JBS-SKY diode of claim 16 wherein the LBML is made of titanium silicide and forming the LBML atop the ACDZ is a two-step self-aligned silicide formation (Salicide) process comprising:

depositing titanium (Ti) then titanium nitride (TiN) atop the device in progress; and

subjecting the device in progress to a rapid thermal process (RTP) whereby forming, only in the ACDZ, the LBML.

18. The method of making a JBS-SKY diode of claim 16 wherein forming the grid of EBSS bumps comprising:

Depositing LTO then BPSG glass atop the device in progress then subjecting it to a thermal reflow process whereby forming an LTO-BPSG reflow glass;

masking, with an LTO-BPSG glass mask corresponding to X-Y cross section of the grid of EBSS bumps, then anisotropically etching away portions of the LTO-BPSG reflow glass with self termination at the LBML; and

removing the LTO-BPSG glass mask whereby forming the grid of EBSS bumps.

19. The method of making a JBS-SKY diode of claim 16 wherein forming the grid of EBSS bumps comprising:

depositing a layer of Tetraethyl orthosilicate (TEOS) atop the device in progress;

masking, with a TEOS mask corresponding to the X-Y cross sectional geometry of the grid of EBSS bumps, then anisotropically etching away portions of the TEOS layer with self termination at the LBML; and

removing the TEOS mask whereby forming the grid of EBSS bumps.

20. The method of making a JBS-SKY diode of claim 16 wherein the UBML is made of titanium silicide and forming the UBML atop the LBML is a two-step self-aligned silicide formation (Salicide) process comprising:

depositing titanium (Ti) then titanium nitride (TiN) atop the device in progress; and

subjecting the device in progress to an RTP whereby forming, only in the ACDZ, the UBML.

21. The method of making a JBS-SKY diode of claim 20 wherein depositing and patterning the TPCM comprising:

depositing a TPCM layer atop, then subjecting the device in progress to a heating step for an improved contact between the TPCM layer and the UBML;

with a TPCM mask, masking then patterning the TPCM by etching away portions of unwanted TPCM layer; and

removing the TPCM mask.

22. The method of making a JBS-SKY diode of claim 16 wherein making the partial JBS-SKY diode comprising:

making said ALSS and said PPGR plus a plurality of hard mask elements located atop but offset into an interdigitated relationship to the SJBP along the X-Y plane;

depositing a low temperature thermal oxide (LTO) layer onto the device in progress;

with an LTO mask corresponding to the PRGZ, masking then patterning the LTO by etching away portions of unwanted LTO layer; and

removing the LTO mask whereby completing the PRGZ and the ALSS.

23. The method of making a JBS-SKY diode of claim 16 further comprising:

depositing and patterning a top device passivation layer (TDPL), covering the ACDZ and the PRGZ, patterned with one or more top pad openings (TPO) at pre-determined locations along the X-Y plane, for receiving downward mechanical bonding forces during later packaging of the JBS-SKY diode.