Patent EP-4177945-A2 (EP)
Title: Die-substrate assembly having a sinter-bonded backside via structure and associated fabrication method
Inventor: VISWANATHAN LAKSHMINARAYAN
IPC: H01L21/603
Filed: 2022-10-10
Abstract: Die-substrate assemblies (20) having sinter-bonded backside via structures, and methods for fabricating such die-substrate assemblies (20), are disclosed. The method includes obtaining an integrated circuit (IC) die (24) (e.g., a power radio frequency (RF) die) having a backside (28) over which a backmetal layer (34) is formed and into which a plated backside via (38) extends, the plated backside via (38) having a backside via lining (40) electrically coupled to the backmetal layer (34). The IC die (24) is attached to an electrically-conductive substrate (30) by producing a sinter-bonded backside via structure, the producing comprising: (i) applying sinter precursor material (32(a)', 32(b)') over the backmetal layer (34) and into the plated backside via (38); (ii) after or in conjunction with application of the sinter precursor material (32(a)', 32(b)'), positioning the IC die (24) adjacent a die support surface (frontside) (36) of the electrically-conductive substrate (30) (e.g., a metallic base flange, an electrically-conductive (e.g., metallic) coin or block embedded in a printed circuit board (PCB), a coreless substrate or another dielectric (e.g., ceramic) body); and (iii) sintering the sinter precursor material (32(a)', 32(b)') to yield a sintered bond layer (32) metallurgically bonded to the backside via lining (40), the backmetal layer (34) and the die support surface (36) of the electrically-conductive substrate (30). The sintered bond layer (32) consists of a die attach (DA) sintered region (32(b)) and a via fill (VF) sintered region (32(a)). The sintered bond layer (32) may fill at least a majority of the plated backside via (38) by volume and may extend over a substantial entirety of the backmetal layer (34) by surface area. The IC die (24) may comprise a gallium nitride portion (56) and a silicon carbide portion (58); and the method may comprise forming the sintered bond layer (32) to extend from a mouth region (42) of the plated backside via (38), through the silicon carbide portion (58), and into the gallium nitride portion (56) of the IC die (24). Applying the sinter precursor material (32(a)', 32(b)') may comprise depositing the sinter precursor material (32(a)', 32(b)') into the plated backside via (38) under vacuum to promote inflow of the sinter precursor material (32(a)', 32(b)') into the plated backside via (38). Applying the sinter precursor material (32(a)', 32(b)') may comprise depositing a first body of sinter precursor material (VF sinter precursor material (32(a)')) into the backside via (38) while the IC die (24) remains interconnected with a plurality of other IC dies contained in a device wafer structure (100) and further depositing a second body of sinter precursor material (DA sinter precursor material (32(b)')) over the backmetal layer (34) and the plated backside via (38) after singulation of the device wafer structure (100). The VF sinter precursor material (32(a)') may be sintered prior to or following the singulation of the device wafer structure (100). The VF sinter precursor material (32(a)') may have a lower viscosity than does the second body of sinter precursor material (32(b)'). The VF sinter precursor material (32(a)') may have a lower Ag content and/or a higher Cu content by weight (e.g., to be predominately composed of Cu by weight) than does the DA sinter precursor material (32(b)'), such as to be essentially free of Ag. Additionally or alternatively, the DA sinter precursor material (32(b)') may have a higher Au and/or Ag content by weight than does the VF sinter precursor material (32(a)') (e.g., predominately composed of Ag by weight). The sintered DA region (32(b)) may contain organic materials that increase pliability, such as an epoxy, to reduce the likelihood of crack formation and propagation across thermal cycles, while the sintered VF region (32(a)) may contain a lesser amount, or may be free of, such organic materials. The respective compositions of precursor VF and DA materials (32(a)', 32(b)'), and the resulting compositions of the sintered VF region (32(a)) and the sintered (DA) region (32(b)) of the sintered bond layer (32) may differ in other respects or may be substantially identical. Alternatively, the sinter precursor material utilized to form sintered bond layer (32) may be deposited, prior to or following singulation of the device wafer structure (100), as a single mass or layer over the backmetal layer (34) of IC die (24) to concurrently form the via fill (VF) sinter precursor material region (32(a)') and the die attach (DA) sinter precursor material region (32(b)'), preferably under vacuum (e.g., in a vacuum chamber) to promote the inflow of the sinter precursor material into the interior of the backside via (38).