Polysilicon Capacitor Dielectric Segmentation for Field Dependence
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Solution Overview
Problem
Existing semiconductor capacitive elements face issues with increased applied electric field dependence of capacitance value and initial defects due to impurity-related defects in dielectric films, particularly in two-layered polysilicon capacitive elements.
Innovation Solution
A semiconductor device and manufacturing method involving a lower polysilicon electrode with implanted impurities, a thermal oxide film formed by partial oxidation, and a deposited oxide film using low-pressure CVD, where the outer layer of the thermal oxide film is etched to reduce impurity concentration and defect density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the concentration of impurities is reduced in the polysilicon film, then the breakdown voltage is improved, but the applied electric field dependence of the capacitance value increases
Solution Approach 1:
The dielectric film is segmented into two distinct layers: a first dielectric layer formed by thermal oxidation containing impurities for low electric field dependence, and a second dielectric layer deposited by CVD providing high breakdown voltage. This segmentation allows each layer to fulfill its specific function independently, resolving the contradiction between reliability and productivity.
Solution Approach 2:
The invention changes the impurity concentration parameter across different dielectric layers. The first dielectric layer has high impurity concentration (10^19 to 10^21 atoms/cm³) to suppress electric field dependence, while the second dielectric layer has low impurity concentration (10^16 to 10^18 atoms/cm³) to ensure high breakdown voltage. This parameter gradient resolves the technical contradiction.
2Productivity
If a thermal silicon oxide film is used as dielectric, then the applied electric field dependence is suppressed, but initial defects increase due to impurity incorporation
Solution Approach 1:
The dielectric structure is segmented into two layers where the first layer (thermal oxide) handles the electric field dependence function and the second layer (CVD oxide) handles the breakdown voltage function with fewer defects. This segmentation allows the system to benefit from the thermal oxide's electrical properties while mitigating its defect issues through the protective second layer.
Solution Approach 2:
The invention uses a composite dielectric structure combining thermal silicon oxide and CVD silicon oxide. The thermal oxide layer provides good interface properties and electric field control, while the CVD oxide layer provides high quality and low defect density, creating a composite structure that leverages the advantages of both materials.
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 method effectively suppresses both the increase in applied electric field dependence of capacitance value and initial defects, improving the breakdown voltage and reliability of the semiconductor device.
Implementation Method 1
a thermal oxide film formed by partially oxidizing the lower electrode to partially remove a surface of the lower electrode in a depth direction
Implementation Method 2
a deposited oxide film formed on the thermal oxide film
Data Source
AI summary
A two-layered polysilicon capacitive element is manufactured to enable suppression of both of an increase in the applied electric field dependence of the capacitance value and the initial defect of the dielectric film. Included are a lower electrode into which phosphorous ions are implanted, a dielectric film formed on the lower electrode, and an upper electrode formed on the dielectric film. The dielectric film includes a thermal oxide film formed by partially oxidizing a polysilicon film constituting the lower electrode and etching out its outer layer part, and a deposited oxide film formed on the thermal oxide film.