Copper Wiring Void Prevention via Low Vacancy Metal Mediator
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Solution Overview
Problem
The use of copper (Cu) in semiconductor wiring leads to issues with void formation due to high vacancy density and impurities, causing stress-induced voiding and reliability concerns, especially when heat treatment is applied, as the Cu film shrinks and vacancies agglomerate, forming voids in critical areas like via plugs.
Innovation Solution
A method involving the formation of a low vacancy density metal film and a compression stress applying film on a semiconductor substrate, where the low vacancy density film is used to diffuse vacancies and apply compression stress to the Cu film during heat treatment, reducing initial voids and improving wiring reliability by CMP removal of excess films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrolytic plating method is used to form Cu film, then wiring resistance is decreased and EM/SM resistance is improved, but vacancies and impurities are generated causing void formation during heat treatment
Solution Approach 1:
A second metal film with lower vacancy density is introduced as an intermediary layer between the first Cu film and the compression stress applying film. This intermediary film acts as a buffer that reduces the overall vacancy density in the wiring structure while maintaining the beneficial electrical properties of Cu wiring.
Solution Approach 2:
The wiring structure is transformed from a single-material Cu film to a composite structure consisting of multiple metal films with different vacancy densities. This composite structure combines the low resistance of Cu with the low vacancy density of other metal materials, resolving the contradiction between electrical performance and void formation resistance.
2Stability of the object's composition
If heat treatment is performed on Cu film after electrolytic plating, then crystal growth occurs, but vacancies agglomerate at crystal grain boundary forming voids
Solution Approach 1:
The second metal film serves as a mediator during heat treatment, protecting the first Cu film from excessive crystal growth and vacancy agglomeration. This intermediary layer absorbs some of the thermal stress and prevents direct vacancy migration to grain boundaries in the Cu film.
Solution Approach 2:
The compression stress applying film is formed beforehand to apply compressive stress during heat treatment, which counteracts the tensile stress that would otherwise cause vacancy agglomeration and void formation. This prior cushioning prevents the harmful effect before it occurs.
3Object-generated harmful factors
If compression stress is applied to Cu film during heat treatment, then void formation is suppressed, but additional process steps are required
Solution Approach 1:
The compression stress applying function is merged with the structural film layers already present in the wiring structure. By integrating the stress-applying function into the existing multi-layer film structure, the solution suppresses void formation without adding excessive complexity, as the additional layers serve dual purposes of structural support and stress management.
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 reduces initial voids in Cu wiring by diffusing vacancies and applying compression stress, enhancing the reliability of the semiconductor device by minimizing void formation and stress-induced issues.
Implementation Method 1
forming on the first metal film a second metal film having lower vacancy density than that of the first metal film
Implementation Method 2
forming on the second metal film a compression stress applying film which applies compression stress to the first metal film through the second metal film when heat treatment is applied
Implementation Method 3
performing heat treatment on the first metal film, the second metal film and the compression stress applying film
Data Source
AI summary
According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, the method including forming on a semiconductor substrate an insulating film having a recessed portion in a surface thereof, forming on the insulating film a first metal film so as to fill up the recessed portion, forming on the first metal film a second metal film having lower vacancy density than that of the first metal film, forming on the second metal film a compression stress applying film which applies compression stress to the first metal film through the second metal film when heat treatment is applied, performing heat treatment on the first metal film, the second metal film and the compression stress applying film, and removing the second metal film and the first metal film except a portion thereof filling up the recessed portion to thereby form a wiring in the recessed portion.