Silicon Nitride Etching via IR-Excited HF Modified Layers
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Solution Overview
Problem
Existing etching methods for silicon nitride films face challenges in achieving high etching rates with uniformity and selectivity to silicon dioxide, particularly due to the short lifetime of vibrationally excited HF and scavenging effects, leading to insufficient etchant supply and non-uniform etching in complex device structures.
Innovation Solution
The method involves forming modified layers on the silicon nitride surface by supplying hydrogen and fluorine-containing etchants, followed by infrared irradiation to generate and efficiently supply vibrationally excited HF, allowing for controlled etching with self-saturation and precise control over etching amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vibrationally excited HF is supplied using NF3/N2/O2/H2 plasma, then silicon nitride etching can be achieved with high selectivity to silicon dioxide, but the lifetime of vibrationally excited HF is only about a microsecond or shorter and hydrogen plasma consumes generated fluoride ions and fluoride radicals under a scavenger effect, making it difficult to supply a sufficient amount of vibrationally excited HF to the substrate region
Solution Approach 1:
The patent applies preliminary action by first forming a modified layer containing hydrogen and fluorine on the silicon nitride surface before etching. This pre-modification ensures that when infrared irradiation is applied, vibrationally excited HF is generated directly at the etching site, eliminating the need to transport HF from the plasma source and ensuring sufficient concentration is achieved despite the short lifetime of vibrationally excited HF.
Solution Approach 2:
The patent uses an intermediary approach by introducing a modified layer as an intermediate structure between the silicon nitride and the plasma environment. This modified layer acts as a localized reaction zone where HF is generated in situ through infrared irradiation, serving as an intermediary that bridges the gap between plasma chemistry and surface etching.
2Adaptability or versatility
If higher density and large number of stacked layers are used in device, then device functionality is improved, but supply rate-controlled state occurs where sufficient etchant cannot be supplied to details such as bottom portion of hole, making it difficult to implement uniform etching irrespective of location
Solution Approach 1:
The patent applies segmentation by dividing the etching process into distinct stages: first forming a modified layer with hydrogen and fluorine, then applying infrared irradiation to generate vibrationally excited HF, and finally performing the etching. This segmented approach allows precise control over where and how etching occurs, enabling uniform etching even in complex three-dimensional structures with stacked layers and deep holes.
Solution Approach 2:
The patent transitions from conventional plasma etching to a method that adds the dimension of infrared irradiation. By using infrared radiation to excite HF molecules in the modified layer, the process creates a new dimension of control over etching rate and uniformity, allowing sufficient etchant generation even in hard-to-reach areas of complex device structures.
3Productivity
If conventional dry etching or wet etching is used, then etching can be performed, but pattern collapse due to surface tension of chemical liquid occurs in wet etching, and insufficient etchant supply occurs in dry etching for complex structures
Solution Approach 1:
The patent replaces the mechanical/chemical wet etching process with a photochemical process using infrared irradiation. Instead of using liquid etchants that cause pattern collapse due to surface tension, the method uses infrared light to excite HF molecules in a gaseous modified layer, eliminating the harmful surface tension effects while maintaining high etching rates.
Solution Approach 2:
The patent changes the fundamental parameter of etching from liquid-phase chemical reaction to gas-phase vibrationally excited reaction. By changing the phase and excitation method, the process achieves high etching rates without the pattern collapse problems associated with wet etching, and overcomes the supply rate limitations of conventional dry etching.
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 enables high etching rates with atomic-layer-level controllability and uniformity, maintaining high selectivity to silicon dioxide, and efficiently supplying vibrationally excited HF to ensure effective etching of silicon nitride films.
Implementation Method 1
a first step of supplying an etchant containing hydrogen to a sample having a surface at which a silicon nitride is exposed to form a first modified layer in which the hydrogen is bonded to the silicon nitride; a second step of supplying an etchant containing fluorine to the sample to form, over the first modified layer, a second modified layer in which the hydrogen and the fluorine are bonded to the silicon nitride
Implementation Method 2
a third step of irradiating the first modified layer and the second modified layer with an infrared ray
Implementation Method 3
the vibration energy of oxygen and hydrogen is substantially equal to the vibration energy of fluorine and hydrogen, and accordingly resonance occurs and the activation energy does not decrease
Implementation Method 4
The technology in each of Nonpatent Literatures 1 and 2 applies the vibrationally excited HF to the silicon nitride to reduce activation energy for bond breaking between nitrogen and silicon and thereby etch the silicon nitride
Data Source
AI summary
Provided are an etching method and an etching apparatus that allow etching processing of a silicon nitride film to be performed at a high etching rate, while maintaining high processing dimension controllability at an atomic layer level, high uniformity in a pattern depth direction, and high selectivity to silicon dioxide. An etching method includes a first step of supplying an etchant containing hydrogen to a sample having a surface at which a silicon nitride is exposed to form a first modified layer in which the hydrogen is bonded to the silicon nitride, a second step of supplying an etchant containing fluorine to the sample to form, over the first modified layer, a second modified layer in which the hydrogen and the fluorine are bonded to the silicon nitride, and a third step of irradiating the first modified layer and the second modified layer with an infrared ray.