Semiconductor Substrate Evaluation via Segmented Depletion Layers
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Solution Overview
Problem
Conventional semiconductor substrate evaluating methods are limited in evaluating the quality of silicon wafers beyond a depth of several tens of nanometers for surface electrical characteristics and 1 μm for leakage current, failing to accurately assess deep region substrate quality, which is crucial for high-yield semiconductor devices like CCDs and CMOS sensors.
Innovation Solution
A semiconductor substrate evaluating method involving the growth of an epitaxial layer with a different conductivity type, forming a well and channel stop layer, and diffusing dopants to create a pn junction, allowing for the measurement of junction leakage currents from two depletion layers using a Test Element Group (TEG) composed of cells, which reflects the wafer quality in both deep and surface regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional GOI evaluation or leakage current measurement methods are used, then surface electrical characteristics can be evaluated, but the evaluation depth is limited to several tens of nanometers for surface characteristics and only 1 μm for leakage current, failing to assess deep region substrate quality
Solution Approach 1:
The evaluation structure is segmented into multiple depletion layers at different depths: a first depletion layer formed in the well region (evaluating surface/near-surface quality up to 1 μm depth) and a second depletion layer formed at the interface between the epitaxial layer and substrate (evaluating deep region quality). This segmentation allows simultaneous evaluation of both surface and deep substrate regions, resolving the contradiction between measurement depth and assessment accuracy.
Solution Approach 2:
The invention extends the evaluation from a single-depth measurement to multi-depth measurement by utilizing the vertical dimension of the epitaxial layer structure. The first depletion layer evaluates characteristics in the well region (shallower depth), while the second depletion layer at the epitaxial-substrate interface evaluates deeper substrate quality, effectively adding a depth dimension to the evaluation process.
2Measurement precision
If a pn junction is formed in a wafer surface with a guard ring structure, then leakage current can be measured to evaluate wafer quality, but parasitic depletion capacitance and defects affecting Gate Oxide Integrity may occur
Solution Approach 1:
An intrinsic or lightly-doped epitaxial layer is introduced as an intermediary between the substrate and the well region. This epitaxial layer acts as a mediator that prevents direct interaction between the guard ring structure and the substrate, thereby eliminating parasitic depletion capacitance and preventing defects that would otherwise affect Gate Oxide Integrity, while still allowing accurate leakage current measurement through the controlled depletion layers.
Solution Approach 2:
The epitaxial layer provides locally different doping characteristics: it is intrinsic or lightly-doped in the regions forming the depletion layers (enabling precise leakage current measurement) while being structured to prevent parasitic effects in the guard ring regions. This local quality differentiation resolves the contradiction between measurement accuracy and prevention of harmful parasitic effects.
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
This method enables highly accurate evaluation of leakage current characteristics, preventing parasitic depletion capacitance and avoiding defects that affect Gate Oxide Integrity, thereby ensuring high-quality wafer evaluation for deep and surface regions.
Implementation Method 1
an epitaxial layer having a second conductivity type different from the first conductivity type is grown
Implementation Method 2
a dopant having the first conductivity type different from the conductivity type of the well is diffused in the well to form a pn junction
Data Source
AI summary
On an EP substrate 1, an EP layer 2 having a conductivity type different from that of the EP substrate 1 is grown. With ion implantation, a well 5 having the same conductivity type as the EP layer 2 is formed, and a channel stop layer 10 is also formed. A dopant having a conductivity type different from that of the well 5 is diffused in the well 5 to form a pn junction 7 in the well 5. A plurality of cells 20 each having the diffusion layer 6 as one electrode and a rear surface 1a as the other electrode are formed as a TEG. Using the TEG, junction leakage currents from two depletion layers, a depletion layer 8 in the well and a depletion layer 4 at an interface between the EP layer 2 and the EP substrate 1, are measured.