Selective Vapor Etching of Semiconductor Layers Using XeF2
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Solution Overview
Problem
Current methods for vapor etching semiconductor or MEMS devices face challenges in selectively removing top layers while preserving underlying dielectric layers, as etching gases like XeF2 can undesirably increase the etching of dielectric materials, reducing the effectiveness of selective etching.
Innovation Solution
A method involving two sets of process conditions for vapor etching, using different etching gases and conditions to selectively remove top and underlying layers, with the first layer being fully removed under initial conditions and the second layer being fully removed under distinct conditions, while maintaining the integrity of the dielectric layer, which can include varying temperatures, pressures, and the use of UV light or electric fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If XeF2 gas is used for etching silicon and other materials, then the etching rate is much higher than for underlying dielectric materials, but the chemical reaction between XeF2 and the etched material undesirably increases the etching of the dielectric material
Solution Approach 1:
The etching process is divided into multiple sequential steps, each targeting a specific layer with optimized conditions. The first step removes the silicon layer, the second step removes the transitional metal layer, and the third step removes the nitride layer. Each step uses specific process parameters (temperature, pressure, gas composition) tailored to maximize selectivity for that particular layer while minimizing etching of underlying dielectric layers.
Solution Approach 2:
The patent systematically varies process parameters including temperature (from -70°C to 100°C), pressure (from 0.1 to 760 Torr), and gas composition (different ratios of XeF2 to carrier gases like N2 or He) to optimize etching selectivity for each specific layer. These parameter changes enable precise control over etching rates for different materials while preserving the dielectric layer.
2Productivity
If the etching rate for top layers is increased to improve productivity, then the removal of top layers is faster, but the etching of underlying dielectric material also increases
Solution Approach 1:
A transitional metal layer (such as tungsten, molybdenum, or tantalum) is deposited as a preliminary barrier layer between the silicon layer and the underlying dielectric layer before any etching begins. This barrier layer is specifically designed to be resistant to XeF2 etching under certain conditions, preventing direct contact between the etchant and the dielectric layer, thus preventing dielectric material loss while allowing rapid removal of the silicon layer above it.
Solution Approach 2:
The transitional metal barrier layer serves as an intermediary that selectively protects the dielectric layer from etching. This intermediate layer has different chemical reactivity toward XeF2 compared to both the silicon layer above and the dielectric layer below, enabling it to act as a protective shield during the etching process.
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 approach allows for precise control of etching rates and selective removal of materials, enhancing the selectivity between top and underlying layers, thereby improving the efficiency of semiconductor and MEMS device manufacturing by minimizing dielectric material loss.
Implementation Method 1
XeF2 gas reacts with one or more solid materials, such as silicon and molybdenum, such that the material(s) is/are converted to a gas phase
Implementation Method 2
a UV light applied to the sample during etching
Data Source
AI summary
In a method of vapor etching, a sample that includes a first layer atop of and in contact with a second layer which is atop of and in contact with a third layer, wherein at least the first and second layers are comprised of different materials. The sample is etched by a vapor etchant under first process conditions that cause at least a part of the first layer to be fully removed while leaving the third layer and the second layer underlying the removed part of the first layer substantially unetched. The sample is then etched by the same or a different vapor etchant under second process conditions that cause at least the part of the second layer exposed by the removal of the at least part of the first layer to be fully removed while leaving the third layer underlying the removed part of the second layer substantially unetched.