Polyimide Buffer Bump Structure for Low-k Delamination Control
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Solution Overview
Problem
Delamination of extreme low-k dielectric layers in semiconductor devices leads to device failure or malfunction, particularly in smaller devices with three-dimensional integrated circuits, due to the processing and reliability issues of bumps used for interconnecting stacked chips.
Innovation Solution
The use of polyimide layers with higher Young's modulus, formed from polyamic acid compositions, to enhance the adhesion and protect the device from damage during flip chip bonding, combined with under bump metallization and solder layers to create robust bump structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If extreme low-k dielectric layers are used in smaller semiconductor devices, then device performance is improved, but delamination occurs leading to device failure
Solution Approach 1:
A polyimide layer is introduced as an intermediary between the extreme low-k dielectric layer and the bump structure. This polyimide layer serves as a buffer that absorbs thermal stress and mechanical pressure, preventing direct contact and potential delamination between the dielectric layer and the bump structure during flip chip bonding and operation.
Solution Approach 2:
The polyimide layer is applied beforehand to the extreme low-k dielectric layer before forming the bump structure. This layer provides pre-cushioning against the high pressure and thermal stress that will be applied during subsequent bump formation and operation, preventing delamination before it can occur.
2Adaptability or versatility
If bump structures are formed for interconnecting stacked chips, then device functionality is improved, but processing and reliability issues arise
Solution Approach 1:
The bump structure is formed as a composite system consisting of multiple layers: the extreme low-k dielectric layer, the polyimide buffer layer, the bump itself, and the overlying structure. This composite structure combines materials with different mechanical and thermal properties to achieve both interconnect functionality and reliability under stress.
Solution Approach 2:
The polyimide layer changes the mechanical parameters of the structure by providing a compliant interface that can deform under pressure without causing delamination. This parameter change allows the structure to accommodate thermal expansion and mechanical stress during bump formation and operation.
3Strength
If pressure is applied during flip chip bonding, then chip interconnection is achieved, but delamination of dielectric layers occurs
Solution Approach 1:
The polyimide layer acts as a mediator between the applied pressure and the extreme low-k dielectric layer. It distributes the pressure uniformly across the surface and prevents concentration of stress at interfaces, thereby preventing delamination while still allowing effective bonding to occur.
Solution Approach 2:
The polyimide layer functions as a flexible thin film that can deform under applied pressure during flip chip bonding. This flexibility allows the layer to accommodate the bonding process while protecting the underlying dielectric structure from delamination caused by excessive or localized stress.
Data Source
AI summary
A method of manufacturing a bump structure includes forming a passivation layer over a substrate. A metal pad structure is formed over the substrate, wherein the passivation layer surrounds the metal pad structure. A polyimide layer including a polyimide is formed over the passivation layer and the metal pad structure. A metal bump is formed over the metal pad structure and the polyimide layer. The polyimide is a reaction product of a dianhydride and a diamine, wherein at least one of the dianhydride and the diamine comprises one selected from the group consisting of a cycloalkane, a fused ring, a bicycloalkane, a tricycloalkane, a bicycloalkene, a tricycloalkene, a spiroalkane, and a heterocyclic ring.