Alignment Pad Hardness for Wafer Probing
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Solution Overview
Problem
In semiconductor device manufacturing, the hard metallization of die pads makes it difficult to visually determine the position of probing needles during wafer probing, as the imprints are not or only barely visible, leading to unreliable alignment.
Innovation Solution
Incorporating alignment pads with a hardness lower than the die pads, which are designed to create visible imprints upon contact with probing needles, allowing for optical inspection and precise alignment during semiconductor wafer probing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pad metallization is made hard to ensure durability and electrical connection, then the reliability of electrical connection is improved, but the visibility of needle imprints deteriorates making alignment measurement impossible or insufficient
Solution Approach 1:
The pad structure is segmented into two distinct parts: die pads with hard metallization for electrical connection and alignment pads with soft metallization for optical measurement. This segmentation allows each part to fulfill its specific function without compromise - the die pads maintain durability while the alignment pads enable visible imprint detection for precise alignment measurement
Solution Approach 2:
Different metallization hardness properties are applied to different locations on the wafer surface. The die pads use hard metallization (e.g., tungsten, titanium) for reliable electrical connection, while the alignment pads use soft metallization (e.g., aluminum, copper) that deforms visibly under probe needle contact. This local differentiation of material properties resolves the contradiction between connection reliability and measurement precision
2Measurement precision
If the alignment pad hardness is reduced to improve optical detection visibility, then the measurement precision of needle position is improved, but the strength of the pad structure deteriorates
Solution Approach 1:
The pad system is divided into functionally distinct die pads and alignment pads. The alignment pads specifically use softer metallization layers that deform visibly under probe needle contact, enabling high-precision optical measurement of needle position. The softer material is strategically placed only where measurement is needed, not where structural strength is critical
Solution Approach 2:
The alignment pads are designed with locally optimized soft metallization properties at specific locations on the wafer. This localized softness enables visible deformation for optical detection while the overall pad structure maintains adequate strength through the underlying substrate and surrounding hard metallization structures. The soft metallization is confined to the alignment pad regions rather than the entire wafer surface
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 use of softer alignment pads enables reliable optical detection of needle imprints, improving the accuracy of wafer alignment and positioning relative to the probe card, overcoming the visibility issues with hard die pads.
Implementation Method 1
The alignment pad has a hardness smaller than a hardness of the plurality of die pads... determining the position of a needle imprint on the at least one alignment pad by optical inspection
Data Source
AI summary
A semiconductor device includes a semiconductor substrate having a main surface over which a plurality of die pads and at least one alignment pad for optical process control for semiconductor wafer probing are arranged. The alignment pad has a hardness smaller than a hardness of the plurality of die pads.