Pd-Co Barrier Stack for GaAs Adhesion and Diffusion Control
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Solution Overview
Problem
The existing barrier layers between GaAs semiconductor substrates and metal layers, such as Cu, Ag, or Au, face issues with insufficient adhesion and material diffusion due to low reactivity, leading to ineffective barrier function and adhesion problems when using materials like TiW, W, Ta, TaN, Ti, TiN, Co, Pd, or Ru.
Innovation Solution
A semiconductor device is fabricated with a Pd adhesion layer on the GaAs substrate, a Co barrier layer, and a Cu, Ag, or Au metal layer, where a heat treatment forms a Pd-Ga-As adhesion layer and a Co-Pd alloy layer, enhancing adhesion and preventing metal diffusion through the use of Co as the barrier material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Pd is used for the barrier layer, then the adhesion between the barrier layer and the semiconductor substrate is improved, but the barrier layer forms an alloy with the semiconductor substrate and fails to prevent material diffusion
Solution Approach 1:
The invention divides the barrier structure into two separate layers: a Pd adhesion layer in contact with the GaAs substrate and a Co diffusion barrier layer above it. This segmentation allows each layer to perform its specific function - Pd provides strong adhesion to GaAs while Co provides effective diffusion barrier properties, resolving the contradiction between adhesion and barrier function.
Solution Approach 2:
The Co layer acts as an intermediary between the Pd adhesion layer and the Cu/Ag/Au metal layer. It mediates the interaction by providing a diffusion barrier while allowing the Pd layer to maintain its adhesion function to the substrate, thus preventing direct contact between Pd and the metal layer that would cause alloying.
2Reliability
If materials such as TiW, W, Ta, TaN, Ti, TiN, Co, or Ru are used for the barrier layer, then the barrier function is maintained, but the adhesion between the barrier layer and the semiconductor substrate is insufficient
Solution Approach 1:
The barrier structure is segmented into two functional layers: a Pd adhesion layer that provides strong bonding to the GaAs substrate and a Co diffusion barrier layer that prevents metal atom migration. This segmentation allows each material to be optimized for its specific function rather than requiring a single material to fulfill both roles.
Solution Approach 2:
The invention uses a composite structure combining Pd and Co layers, where Pd serves as the adhesion-promoting component and Co serves as the diffusion-blocking component. This composite approach leverages the complementary properties of both materials to achieve both strong adhesion and effective barrier function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration improves adhesion between the semiconductor substrate and the metal layer, effectively preventing metal diffusion into the substrate while maintaining the barrier function, even at elevated temperatures.
Implementation Method 1
a heat treatment step of increasing the temperature of the semiconductor substrate, the adhesion layer and the barrier layer to 25°C to 250°C to form Pd-Ga-As on the adhesion layer and to form an alloy layer containing Co and Pd between the adhesion layer and the barrier layer
Implementation Method 2
to form Pd-Ga-As on the adhesion layer and to form an alloy layer containing Co and Pd between the adhesion layer and the barrier layer
Implementation Method 3
a step of performing electroless plating on the semiconductor substrate to form a barrier layer of Co-P or Co-W-P on the adhesion layer
Data Source
Figure 1~2
Figure 3A~4
Figure 5A~5B
AI summary
According to present invention, a semiconductor device includes a semiconductor substrate formed of GaAs, an adhesion layer formed of Pd or an alloy containing Pd on the semiconductor substrate, a barrier layer formed of Co or an alloy containing Co on the adhesion layer, and a metal layer formed of Cu, Ag or Au on the barrier layer.