Conductive Cap Layer Protection During Via Soft Ashing
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Solution Overview
Problem
The oxidation of metal cap layers during semiconductor device manufacturing, particularly due to oxygen-containing etchant gases and subsequent soft ashing processes, leads to the formation of fragile metal oxide layers that are prone to significant loss during wet cleaning, affecting the integrity and conductivity of the semiconductor device.
Innovation Solution
A soft ashing process using a gas mixture of nitrogen and hydrogen is employed to convert the metal oxide layers into more stable metal oxynitride layers, which provide enhanced bonding and protection against further oxidation and damage during wet cleaning, thereby reducing metal loss and maintaining the conductive cap layer's integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxygen-containing etchant gas is used in the etching process, then via opening can be formed effectively, but metal oxide layer is formed on the conductive cap layer which is fragile and easily stripped
Solution Approach 1:
A protective carbon-rich layer is formed on the conductive cap layer surface before the etching process through exposure to hydrocarbon-containing atmosphere. This preliminary protective layer prevents direct oxidation of the metal surface during subsequent oxygen-containing etching, eliminating the formation of fragile metal oxide layers while maintaining effective via opening formation.
Solution Approach 2:
A carbon-rich intermediate layer is introduced between the oxygen-containing etchant and the metal surface. This intermediary layer acts as a barrier that allows the etching process to proceed effectively while preventing direct contact between oxygen and the metal, thus avoiding metal oxide formation. The carbon layer is subsequently removed without damaging the underlying metal.
2Ease of manufacture
If soft ashing process is conducted using oxygen gas, then organic residue can be removed, but metal oxide layer is formed and stripped during wet cleaning causing metal loss
Solution Approach 1:
The soft ashing process parameters are changed from using pure oxygen gas to using a reduced oxygen atmosphere or alternative atmospheres such as air or inert gases. This parameter change allows sufficient organic residue removal while limiting the oxygen availability that would cause excessive metal oxide formation, thereby reducing metal loss during subsequent wet cleaning.
Solution Approach 2:
A composite protective structure is formed consisting of a carbon-rich layer and a controlled oxide layer. The carbon-rich layer provides primary protection during wet cleaning, while the controlled oxide layer serves as a sacrificial protective layer that can be removed without significant metal loss. This composite structure enables effective organic residue removal while minimizing metal loss.
3Productivity
If conventional etching and soft ashing processes are used, then via opening is formed, but significant metal loss occurs due to metal oxide layer stripping during wet cleaning
Solution Approach 1:
A protective carbon-rich layer is deposited on the conductive cap layer before etching. This preliminary protective layer remains intact during the etching and wet cleaning processes, preventing metal oxide formation and subsequent metal loss. The protective layer is removed after via opening formation is complete, ensuring the conductive cap layer integrity is maintained throughout the manufacturing process.
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
The conversion of metal oxide layers to metal oxynitride layers using a nitrogen-hydrogen gas mixture significantly reduces metal loss and enhances the protective properties, ensuring better preservation of the conductive cap layer and improving the semiconductor device's manufacturing process efficiency.
Implementation Method 1
converting the metal oxide layer into a metal oxynitride layer by a soft ashing process using a processing gas containing nitrogen gas
Implementation Method 2
soft ashing process using a gas mixture of nitrogen and hydrogen is employed to convert the metal oxide layers
Data Source
AI summary
A method for making a semiconductor device includes patterning at least one dielectric layer disposed over a conductive cap layer to form a via opening penetrating through the at least one dielectric layer to expose the conductive cap layer and to form a top portion of the conductive cap layer into a metal oxide layer; converting the metal oxide layer to a metal oxynitride layer by a soft ashing process using a processing gas containing nitrogen gas; removing the metal oxynitride layer from a remaining portion of the conductive cap layer; and forming a via contact in the via opening to electrically connect the remaining portion of the conductive cap layer.