Copper Plug Contact Resistance Reduction via CVD Titanium Glue Layer
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Solution Overview
Problem
The existing methods for forming copper plugs in semiconductor devices face challenges such as void formation and increased contact resistance due to difficulties in burying barrier layers in deep contact holes, leading to potential copper diffusion into silicon substrates and junction leakage, especially when contact hole diameters are less than 80 nm and aspect ratios exceed 3.
Innovation Solution
A method involving the formation of a titanium layer by chemical vapor deposition (CVD) as a glue layer on the inner surfaces of contact holes, followed by a copper diffusion preventing barrier layer and a copper layer, which ensures good coverage and prevents voids, thereby maintaining effective contact with silicide layers and reducing contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is used as plug material to reduce contact resistance, then electrical conductivity is improved, but copper diffusion into silicon substrate occurs causing junction leakage
Solution Approach 1:
A barrier layer comprising a first layer and a second layer is introduced as an intermediary between the copper plug and the silicon substrate. The first layer is in contact with the copper plug and the second layer is in contact with the silicon substrate, preventing copper diffusion while maintaining electrical conductivity. This multi-layer barrier structure effectively blocks copper atoms from migrating into the silicon substrate.
Solution Approach 2:
The barrier layer is constructed as a composite structure with two distinct layers having different material compositions and properties. The first layer is optimized for interface with copper, while the second layer is optimized for interface with silicon substrate, creating a composite barrier that addresses both electrical conductivity and diffusion prevention requirements.
2Object-generated harmful factors
If barrier layer is formed in deep contact holes to prevent copper diffusion, then copper diffusion is prevented, but void formation occurs due to difficulty in burying the barrier layer
Solution Approach 1:
The barrier layer is segmented into two separate layers (first layer and second layer) with different thicknesses and compositions. This segmentation allows each layer to be optimized for its specific function and makes the barrier structure easier to form without voids in deep contact holes.
Solution Approach 2:
Different regions of the barrier layer have different properties: the first layer near the copper plug has specific material characteristics optimized for copper interface, while the second layer near the silicon substrate has different characteristics optimized for silicon interface. This local quality variation prevents void formation while maintaining diffusion prevention.
3Productivity
If contact hole diameter is reduced to increase device density, then device integration is improved, but barrier layer burial becomes difficult leading to voids and increased contact resistance
Solution Approach 1:
The barrier layer is divided into two thinner layers instead of one thick layer, making it easier to bury the barrier material completely in small contact holes without forming voids. This segmentation enables effective barrier formation even when contact hole diameters are reduced for higher device density.
4Object-generated harmful factors
If tungsten is used as plug material, then diffusion prevention is achieved, but contact resistance is high compared to copper
Solution Approach 1:
The barrier layer acts as an intermediary that allows copper to be used in contact with silicon substrate without direct contact. This mediator structure enables the use of low-resistance copper while preventing copper diffusion into the silicon, achieving both low contact resistance and effective diffusion prevention.
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 approach effectively prevents copper diffusion and defective connections, reduces contact resistance, and maintains thermal stability, even at smaller contact hole diameters, by ensuring a satisfactory connection between copper plugs and silicide layers, as demonstrated by the reduction in contact resistance to about one-third compared to prior art.
Implementation Method 1
forming a titanium layer by chemical vapor deposition (CVD) as a glue layer on the inner surfaces of contact holes
Implementation Method 2
forming a copper diffusion preventing barrier layer over the titanium layer
Data Source
AI summary
A method of manufacturing a semiconductor device, includes the steps of forming an insulating film on a semiconductor substrate having a silicide layer, forming a hole in the insulating film on the silicide layer, cleaning an inside of the hole and a surface of the silicide layer, forming a titanium layer on a bottom surface and an inner peripheral surface of the hole by a CVD method, forming a copper diffusion preventing barrier metal layer on the titanium layer in the hole, and burying a copper layer in the hole.