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EP-4739079-A1 - METHOD FOR IMPROVING ADHESION OF A WETTABLE METALLIZATION MULTILAYER IN AN INTEGRATED ELECTRONIC DEVICE

EP4739079A1EP 4739079 A1EP4739079 A1EP 4739079A1EP-4739079-A1

Abstract

A process for forming silver-containing wettable material structures, wherein, on a metal layer (26) containing aluminum, a zinc layer (28) is deposited, the zinc layer reacting with the metal layer and creating a surface microroughness (30); the zinc layer (28) is removed; and a wettable layer (36) containing silver is deposited by vapor deposition. The wettable layer (36) is formed by an adhesion layer (33), containing titanium or chromium; a barrier layer (34), containing nickel, on the adhesion layer (33); and a bonding layer (35), containing silver, on the barrier layer (22).

Inventors

  • CAFRA, Brunella
  • LANDI, ANTONIO
  • RENNA, CROCIFISSO MARCO ANTONIO

Assignees

  • STMicroelectronics International N.V.

Dates

Publication Date
20260506
Application Date
20251014

Claims (14)

  1. A process for forming silver-containing wettable material structures, comprising: forming a metal layer (26) containing aluminum; depositing a zinc layer (28) on the metal layer (26), the zinc layer reacting with the metal layer and creating a surface micro-roughness (30); removing the zinc layer (28); and depositing a wettable layer (36) containing silver by vapor deposition.
  2. The process according to claim 1, wherein depositing a wettable layer (36) comprises: forming an adhesion layer (33), containing titanium or chromium, on a front side (26A) of the metal layer (26); forming a barrier layer (34), containing nickel, on the adhesion layer (33); and forming a bonding layer (35), containing silver, on the barrier layer (22).
  3. The process according to claim 1 or 2, wherein the metal layer (26) is of pure aluminum or an alloy of aluminum and copper or an alloy of aluminum, silicon, copper.
  4. The process according to any of the preceding claims, wherein the barrier layer (34) is of nickel or a nickel-vanadium alloy.
  5. The process according to any of the preceding claims, wherein depositing a zinc layer (28) and removing the zinc layer (28) are repeated.
  6. The process according to any of the preceding claims, wherein removing the zinc layer (28) is performed by stripping.
  7. The process according to any of the preceding claims, further comprising, after forming a metal layer (26), etching a surface (26A) of the metal layer using strongly acidic or strongly basic compounds.
  8. The process according to any of the preceding claims, further comprising defining the wettable layer (36) to form a contact structure on a top side (61A) of a wafer (61) of semiconductor material.
  9. The process according to any of the preceding claims, wherein depositing a wettable layer (36) is performed by sputtering.
  10. An electronic device (60) comprising: a die (61) of semiconductor material having a front surface (61A) and a back surface (61B); a wettable contact structure (63) extending on the front surface (61A) and including: a metal layer (26) containing aluminum, the metal layer having a surface micro-roughness (30), with irregularities having dimensions comprised between 20 and 30 nm; and a wettable layer (36) containing silver, deposited by PVD; and a back contact metallization (64), extending on the back surface (61B) of the die (61).
  11. The device according to the preceding claim, wherein the wettable layer (36) comprises: an adhesion layer (33), containing titanium or chromium, on a front side (26A) of the metal layer (26); a barrier layer (34), containing nickel, on the adhesion layer (33); and a bonding layer (35), containing silver, on the barrier layer (34).
  12. The device according to claim 10 or 11, wherein the metal layer (26) is of pure aluminum or an alloy of aluminum and copper or an alloy of aluminum, silicon, copper.
  13. The device according to any of claims 10-12, wherein the barrier layer (34) is of nickel or a nickel-vanadium alloy.
  14. The device according to any of claims 10-13, wherein the surface micro-roughness (30) has a Ra comprised between 20 and 30 nm.

Description

Technical Field The present invention relates to a method for improving adhesion of a wettable metallization multilayer in an integrated electronic device. Background As is known, integrated electronic devices are connected to the outside through connection regions, for example pads, of highly conductive material, typically metal. Connection regions allow sintering of electrical connectors, such as wires, ribbons or clips, which electrically couple active and passive regions of the integrated electronic device to the outside, e.g. with conductive tracks formed on or in a printed circuit board or other support. For example, Figure 1 shows an integrated electronic device 1 having a top metallization including a wettable layer. In particular, the integrated electronic device 1 of Figure 1 is a MOSFET transistor formed in a substrate 2, of semiconductor material (e.g. silicon) and of a first conductivity type, for example of N-type, having a front surface 2A and a back surface 2B. The substrate 2 accommodates body regions 3. In turn, the body regions 3, of a second conductivity type opposite to the first conductivity type, in the example of P-type, accommodate source regions 4, of the first conductivity type, and body contact regions 5, of the second conductivity type and dopant concentration greater than the body regions 3. Insulated gate regions 6 extend above the front surface 2A of the substrate 2, astride two adjacent body regions 3. A source metalization layer 10 covers the front surface 2A of the substrate 2, where exposed, and the insulated gate regions 6. A wettable layer 11 covers the source metalization layer 10. The source metalization layer 10 is formed by a plurality of layers, such as titanium Ti and a copper-based alloy (for example AlSiCu), and the wettable layer 11 comprises silver Ag, as discussed below. The back surface 2B of the substrate 2 is covered by a drain metalization 12, for example formed by a plurality of layers including titanium Ti, nickel-vanadium NiV or nickel Ni and silver Ag. The MOSFET transistor shown in Figure 1 is only one example of integrated electronic device to which the present disclosure relates. For example, the integrated electronic device 1 might be a High Electron Mobility Transistor (HEMT) or other device formed on a silicon (Si), silicon carbide (SiC), or gallium nitride (GaN) substrate. Currently, for forming the contact regions arranged on the front side of electronic devices and comprising a wettable layer similar to the wettable layer 11 of Figure 1, stacks of different metals are used, which ensure good adhesion both to the surface of the integrated device and to the wires, ribbons and connection clips (electrical connectors; hereinafter, for the sake of simplicity, reference will be made to wires, meaning by this term also flatter structures, such as ribbons, clips and the like). For example, a stack of metal layers, currently widely used for forming the wettable layer 11, comprises three-four layers, as shown in Figure 2. Figure 2 shows a device 14, including for example an integrated transistor, as schematically represented, formed by the substrate 2, regions and layers integrated into the substrate 2 and/or extending above the substrate 2. The device 14 is overlaid by a metallization layer 15, for example the source metallization layer 10 of Figure 1. The metallization layer 15 is typically formed of pure aluminum or an alloy of aluminum and copper or an alloy of aluminum, silicon, copper (wherein aluminum is the main component). The metallization layer 15 is overlaid by a wettable layer 16 (corresponding to the wettable layer 11 of Figure 1) formed by a stack of layers deposited by PVD (Physical Vapor Deposition). For example, Figure 2 shows a wettable layer 16 including a first layer 17, for example of titanium Ti or chromium Cr; a second layer 18, for example of a nickel-vanadium alloy NiV or of nickel Ni alone, and a third layer 19, of silver Ag. In some cases, an additional layer of nickel Ni may be provided between the second layer 18 and the third layer 19 and/or a chromium layer may be arranged between the metallization layer 15 and the first layer 17, when made of nickel. Furthermore, according to Italian patent application 102023000021621 filed on 17 October 2023, the third layer 19 (and possibly the second layer 18) may contain aluminum or tin atoms, and/or an intermetal layer containing aluminum or tin atoms may extend between the second layer 18 and the third layer 19. The first layer 17 has the function of ensuring good adhesion of the wettable layer 16 with the metallization layer 15 and is also referred to as "adhesion layer"; the third layer 19 has the function of allowing a good bonding process between the third layer 19, of silver, and a wire or other external electrical connector and is also referred to as "bonding layer"; and the second layer 18 has a diffusive barrier function between the first layer 17 and the third layer 19 an