Copper Gapfill Grain Engineering for Low-Temperature Bonding
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Solution Overview
Problem
Traditional hybrid bonding processes for substrates with copper bonding surfaces require high temperatures (300-400°C) that exceed the thermal budgets of certain devices, limiting their use.
Innovation Solution
A method involving the use of a grain control layer on vertical surfaces of structures to control grain orientation and growth, using non-conducting materials like SiN, SiO2, and fluoropolymer, to enable low-temperature copper bonding by controlling grain parameters and orientation, allowing bonding at temperatures below 250°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional hybrid bonding processes are used with copper bonding surfaces, then copper-to-copper bonds can be formed, but bonding temperatures of 300-400°C are required which exceed the thermal budgets of certain devices
Solution Approach 1:
The patent changes the grain orientation parameter of the copper metal from random/grainy structure to a controlled <111> crystallographic orientation. This parameter change enables copper bonding at temperatures below 250°C, resolving the contradiction between achieving reliable copper bonds and maintaining compatibility with devices that have limited thermal budgets.
Solution Approach 2:
The patent applies a grain control layer selectively on the bonding surface of the copper metal to induce <111> grain orientation. This local modification of the copper surface properties enables low-temperature bonding without affecting the bulk copper material, allowing devices with thermal budget constraints to undergo hybrid bonding processes.
2Manufacturing precision
If grain control layer is deposited conformally onto structures, then grain orientation can be controlled on vertical surfaces, but the grain control layer must be removed from horizontal surfaces to enable proper grain growth
Solution Approach 1:
The patent segments the grain control layer removal process by selectively removing the layer only from horizontal surfaces while preserving it on vertical surfaces. This is achieved through targeted etching or removal processes that exploit the geometric differences between horizontal and vertical surfaces, enabling precise grain orientation control without overly complicating the overall manufacturing process.
Solution Approach 2:
The patent uses the dimensional difference between horizontal and vertical surfaces to achieve selective grain control layer removal. By orienting the removal process to act differently on surfaces with different orientations, the patent achieves precise spatial control over where the grain control layer remains or is removed, simplifying the overall process compared to attempting uniform control.
3Reliability
If polymer layer is deposited in etch chamber to cover exposed corners during etching, then corner protection is achieved, but the polymer layer must be removed after etching
Solution Approach 1:
The patent applies the polymer layer as a preliminary protective measure before the etching process to prevent damage to exposed corners. This preliminary action ensures structure integrity during the etching step. The polymer is then removed in a subsequent step, completing the temporary protection function.
Solution Approach 2:
The polymer layer serves as a cushioning protective layer deposited beforehand to shield vulnerable corner regions during the etching process. This beforehand cushioning prevents potential damage or over-etching at corners, maintaining structure integrity. The polymer is subsequently removed after it has served its protective purpose.
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
Enables low-temperature copper bonding while preserving device performance by maintaining grain orientation and strength, facilitating fine-pitch bonding and scalability for high-density wafer-level packaging.
Implementation Method 1
depositing a grain control layer conformally onto the substrate and into the at least one structure where the grain control layer is a non-conducting material... depositing a metal gapfill material onto the at least one structure such that at least one grain parameter of the metal gapfill material is controlled, at least in part, by a remaining portion of the grain control layer
Implementation Method 2
etching the grain control layer using an etch process to remove portions of the grain control layer on horizontal surfaces within the at least one structure... an etch process that is a direct deep reactive ion etch (DRIE) process
Implementation Method 3
depositing a metal gapfill material onto the at least one structure... a metal gapfill material that is deposited using electrochemical plating... depositing a copper gapfill material onto the at least one structure
Data Source
AI summary
A method for depositing copper onto a substrate includes grain engineering to control the internal structure of the copper. In some embodiments, the method comprises depositing a grain control layer conformally onto a copper seed layer in a structure on the substrate where the grain control layer is a non-conducting material, etching the grain control layer using a direct deep reactive ion etch (DRIE) process to remove portions of the grain control layer on horizontal surfaces within the structure, and depositing a copper material onto the structure such that at least one grain parameter of the copper material is controlled, at least in part, by a remaining portion of the grain control layer on vertical surfaces of the structure. In some embodiments, the deposited copper material in the structure has a <111> grain orientation normal to a horizontal surface of the structure.