Wafer Test Pad Structure for Mark-Free Flat Probe Contact
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Solution Overview
Problem
Current wafer testing methods using needle probe tips are inefficient due to high precision requirements, short usable life, and the tendency to leave marks on test pads, which complicates downstream processing.
Innovation Solution
The use of flat probe tips in conjunction with a seed layer and a sacrificial test pad made of a soft metallic material like tin, allowing for secure electrical contact without leaving marks on the test pads, and subsequent removal of the sacrificial test pad after testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If needle probe tips are used for wafer testing, then secure electrical contact is achieved, but manufacturing cost increases and maintenance difficulty increases
Solution Approach 1:
The patent employs disposable flat probe tips that are inexpensive to manufacture and replace. These flat tips are designed to be used once or limited times and then discarded, eliminating the need for expensive, maintainable needle tips. The flat probe tips achieve sufficient electrical contact for testing while being economically feasible as single-use components.
2Reliability
If needle probe tips are used for wafer testing, then electrical contact is established, but probe marks are left on test pads complicating downstream processing
Solution Approach 1:
The patent introduces a removable sacrificial test pad layer that is placed over the actual test pads during testing. The needle probes contact this sacrificial layer instead of the permanent test pads, extracting the harmful contact function from the test pad structure itself. After testing, the sacrificial pad is removed, leaving no marks on the underlying test pads.
Solution Approach 2:
The sacrificial test pad acts as an intermediary layer between the needle probes and the actual test pads. This mediator absorbs the mechanical contact and potential damage, allowing electrical testing to proceed without directly contacting the permanent test pad structures that would otherwise be marked or damaged.
3Ease of manufacture
If flat probe tips are used for wafer testing, then manufacturing cost decreases and maintenance ease increases, but they can only contact soft materials limiting applicability
Solution Approach 1:
The sacrificial test pad serves as an intermediary with soft material properties that enables flat probe tips to effectively test hard semiconductor structures. The flat tips contact the soft sacrificial pad material, which deforms to accommodate the flat tip geometry and ensures good electrical contact, while the underlying hard test pad structures remain unaffected.
Solution Approach 2:
The patent changes the material parameter of the test pad interface by introducing a sacrificial layer with different mechanical properties (softer material) over the hard semiconductor test pads. This parameter change allows flat probe tips to make effective contact by interacting with the softer sacrificial material rather than directly with the hard semiconductor substrate.
4Measurement precision
If wafer testing is performed with traditional methods, then device performance is evaluated, but test time is long and throughput is low
Solution Approach 1:
The sacrificial test pad is pre-positioned on the wafer before the testing process begins. This preliminary preparation eliminates the need for complex probe tip positioning and adjustment during testing, allowing flat probe tips to make immediate contact and significantly reducing test setup time while maintaining measurement precision.
Data Source
AI summary
A semiconductor device includes a semiconductor die. The semiconductor die includes a device layer, an interconnect layer over the device layer, a conductive pad over the interconnect layer, a conductive seed layer directly on the conductive pad, and a passivation layer encapsulating the conductive pad and the conductive seed layer. The conductive pad is between the interconnect layer and the conductive seed layer.