May 13, 2022

Semiconductor industry: mass production of the SoIC-WoW process

The author is an analyst at NH Investment & Securities. He can be reached at [email protected] — Ed.

Graphcore has collaborated with TSMC to unveil the first AI processor that uses the SoIC-WoW process, which applies hybrid bonding and rear TSV technology. Associated players include BESI, Fujimi and Hanmi Semiconductor

SoIC-WoW based processor unveiled

Graphcore, one of the leading AI computer processor companies, recently unveiled its third-generation product named Bow, which is produced in cooperation with TSMC. The product uses the SoIC-WoW (wafer on wafer) process for the first time. WoW is a technology that makes a chip by connecting two wafers, a CPU wafer and a power wafer.

The power board contains a deep trench capacitor with a structure similar to that of a DRAM capacitor. It is responsible for storing charge and connecting it to the arithmetic transistor on the processor chip. This allows for high energy efficiency and faster operation than conventional transistors. In the WoW process, hybrid bonding and back TSV technologies are applied.

Mass production using hybrid bonding process

Hybrid bonding is a technology that can form a much thinner 10μm level electrode than the previous technology. The pads are made by etching via patterns on the wafer and depositing copper. When the wafer surface is polished with CMP, the copper pad is scraped, creating a fine groove. After measuring the shape of the pad with AFM, the wafer is glued through the exposed pad to form a 3D casing.

Companies linked to the hybrid bonding process include BESI (BESI.NL), Fujimi (5384.JP) and Hanmi Semiconductor (042700.KS). According to Graphcore, the system mounted on four Bow CPUs can run 1.4 PetaFLOPS. It offers comparable performance for half the price of Nvidia’s competing systems.