US 12,154,967 B2
Method for manufacturing an ohmic contact for a HEMT device
Ferdinando Iucolano, Gravina di Catania (IT); and Cristina Tringali, Augusta (IT)
Assigned to STMICROELECTRONICS S.r.l., Agrate Brianza (IT)
Filed by STMICROELECTRONICS S.R.L., Agrate Brianza (IT)
Filed on Nov. 26, 2019, as Appl. No. 16/697,051.
Claims priority of application No. 102018000010656 (IT), filed on Nov. 28, 2018.
Prior Publication US 2020/0168718 A1, May 28, 2020
Int. Cl. H01L 29/66 (2006.01); H01L 29/20 (2006.01); H01L 29/778 (2006.01)
CPC H01L 29/66462 (2013.01) [H01L 29/2003 (2013.01); H01L 29/7786 (2013.01); H01L 29/7787 (2013.01)] 18 Claims
OG exemplary drawing
 
1. A method for manufacturing an ohmic contact for a high electron mobility transistor (HEMT) device, comprising:
forming a heterostructure that includes a substrate, a first gallium nitride layer on the substrate, and a barrier layer on the first gallium nitride layer;
forming a second gallium nitride layer on the barrier layer of the heterostructure, the barrier layer being between the first gallium nitride layer and the second gallium nitride layer, the barrier layer having a first surface vertically separated from a second surface, the second surface being in contact with the first gallium nitride layer;
forming a photoresist layer on the second gallium nitride layer;
forming an opening through the photoresist layer and through the second gallium nitride layer, the opening extending into the barrier layer, the forming the opening including:
forming vertical sidewalls of the second gallium nitride layer by forming the opening;
forming inclined sidewalls of the photoresist layer, the inclined sidewalls inclined from vertical inward toward a center of the opening; and
forming a recessed region in the barrier layer using the photoresist layer as an etching mask, the opening terminating inside the barrier layer between the first and second surface of the barrier layer;
forming a stack of metal layers in the recessed region in the barrier layer, the stack of metal layers includes an interface layer having a first thickness and a filling layer having a second thickness that is greater than the first thickness, the filling layer being directly on the interface layer, at least a portion of the interface layer and the filling layer being vertically between the first and second surfaces of the barrier layer, including:
forming sidewalls of the stack of metal layers vertically and forming the sidewalls of the stack of metal layers spaced from the sidewalls of the second gallium nitride layer and spaced from the inclined sidewalls of the photoresist layer; and
removing the second gallium nitride layer and removing the photoresist layer.