Soft Cap Layer for Probeable Oxidation-Resistant Bond Pads
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Solution Overview
Problem
During wafer acceptance testing (WAT) of integrated circuit (IC) dies, the exposure of WAT pads to oxidation leads to poor electrical coupling and non-uniform bond structures due to the formation of pad openings, which results in reduced manufacturing yields and increased costs from photolithography/etching processes.
Innovation Solution
A soft cap layer, such as silicon carbon nitride or silicon carbide, is deposited over the interconnect pads to prevent oxidation, allowing probes to penetrate without forming pad openings, thereby maintaining the integrity of the pads and ensuring uniform bond structure formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pad openings are formed to expose WAT pads for testing, then electrical coupling can be achieved, but oxidation occurs leading to poor electrical coupling and non-uniform bond structures
Solution Approach 1:
A cap layer is deposited over the WAT pads before testing to prevent oxidation. This preliminary protective action allows the pads to remain covered during subsequent processing steps, eliminating the need to form pad openings for oxidation prevention while still enabling electrical coupling through the cap layer.
Solution Approach 2:
The cap layer acts as an intermediary between the WAT pads and the oxidizing environment. It provides a protective barrier that prevents direct contact between oxygen and the pad metal, while still allowing electrical coupling to occur through the cap layer material.
2Ease of operation
If photolithography/etching processes are used to form pad openings, then WAT testing can be performed, but manufacturing costs increase and yields decrease
Solution Approach 1:
The cap layer is deposited in advance before any testing or bonding operations. This preliminary action eliminates the need for subsequent photolithography and etching steps to create pad openings, thereby reducing manufacturing complexity and improving yields while maintaining full testing capability.
3Object-affected harmful factors
If a hard cap layer is used to prevent oxidation, then pad protection is improved, but probe penetration becomes difficult and bond structure uniformity is compromised
Solution Approach 1:
The cap layer material properties are specifically selected to have low hardness (less than silicon nitride) while maintaining oxidation resistance. This parameter change allows the cap layer to protect against oxidation without interfering with probe penetration and bond structure formation, ensuring manufacturing precision is maintained.
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 soft cap layer prevents oxidation and etch damage, leading to improved electrical coupling and uniform bond structure formation, enhancing manufacturing yields and reducing costs.
Implementation Method 1
the cap layer is configured to block oxygen from reaching the interconnect pad
Implementation Method 2
A soft cap layer, such as silicon carbon nitride or silicon carbide, is deposited over the interconnect pads
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a semiconductor structure (e.g., an integrated circuit (IC) die) comprising an enhanced cap layer for pad oxidation prevention, as well as a method for forming the IC die. An interconnect pad overlies a substrate at a top of an interconnect structure, and a bond structure overlies and extends from a surface of the interconnect pad. A cap layer and an etch stop layer overlie the surface around the bond structure. Further, the cap layer separates the etch stop layer from the interconnect pad and is soft. Soft may, for example, refer to a hardness less than silicon nitride and/or less than the etch stop layer. Because the cap layer is soft, a probe may be pushed through the cap layer to the interconnect pad for testing without first forming a pad opening exposing the interconnect pad.