Cyclic Deposit Etch Silicon Germanium Strain Preservation
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Solution Overview
Problem
Conventional selective deposition methods for silicon germanium alloys fail to achieve fully-strained films with germanium concentrations greater than 45 atomic percent due to lattice mismatch and relaxation issues, particularly at lower temperatures where hydrogen chloride provides negligible etch rates, limiting further device scaling in CMOS technology.
Innovation Solution
A cyclic deposit and etch (CDE) process using a combination of high order silane gases and hydrogen chloride with a germanium-containing gas at temperatures between 400°C and 550°C, enhancing etch rates and maintaining strain without relaxation, allowing for meta-stable pseudomorphic silicon germanium alloys with high germanium concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional selective deposition is performed at temperatures higher than 625°C to achieve sufficient etch rates with hydrogen chloride, then etch selectivity is improved, but the deposited silicon germanium alloy cannot maintain full strain for germanium concentrations greater than 45 atomic percent
Solution Approach 1:
The patent changes the temperature parameter to below 625°C and modifies the chemistry parameters by introducing a germanium-containing gas to enhance etch rates, allowing simultaneous achievement of strain preservation and adequate etch selectivity
Solution Approach 2:
The germanium-containing gas acts as an intermediary that enhances the etch rate of hydrogen chloride at lower temperatures, enabling selective etching without compromising the strain state of the silicon germanium alloy
2Stability of the object's composition
If temperature is lowered below 625°C to preserve strain in silicon germanium alloy, then strain preservation is improved, but hydrogen chloride provides only negligible etch rates making selectivity unattainable
Solution Approach 1:
The patent introduces a germanium-containing gas to change the chemical reactivity parameters, enabling enhanced etch rates at the lower temperature regime where strain preservation is maintained
Solution Approach 2:
The etch chemistry becomes a composite system combining hydrogen chloride with germanium-containing gas, where the germanium component specifically enhances etching of silicon germanium while allowing strain preservation at lower temperatures
3Reliability
If germanium concentration is increased to greater than 35 atomic percent to provide sufficient compressive stress for 22 nm CMOS scaling, then device performance is improved, but lattice mismatch causes misfit dislocations and stacking faults exceeding metastable thickness
Solution Approach 1:
The patent employs cyclic deposit and etch to segment the deposition process into repeated cycles, where each cycle deposits a thin layer that remains within metastable thickness limits, preventing dislocation formation while achieving high overall germanium concentration
Solution Approach 2:
The cyclic nature of the process applies periodic deposition and etching actions, allowing the film to remain in a metastable state throughout growth and achieve high germanium content without exceeding critical thickness in any single layer
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 high strain epitaxial silicon germanium alloys with germanium concentrations above 35 atomic percent, preserving strain and achieving high deposition rates and thickness uniformity, thus supporting further device scaling in CMOS technology beyond 22 nm nodes.
Implementation Method 1
performing at least one deposition step that deposits a silicon germanium alloy material on a substrate by flowing a high order silane gas having a chemical formula of SinH2n+2 and a germanium precursor gas as reactant gases into a process chamber
Implementation Method 2
performing at least one etch step that etches at least a portion of the deposited silicon germanium alloy material by flowing a combination of a hydrogen chloride gas and a germanium-containing gas into the process chamber
Implementation Method 3
The low temperature growth method of the present disclosure provides meta-stable pseudomorphic silicon germanium alloys with high germanium concentrations that preserve strain without relaxation
Data Source
AI summary
Cyclic deposit and etch (CDE) selective epitaxial growth employs an etch chemistry employing a combination of hydrogen chloride and a germanium-containing gas to provide selective deposition of a silicon germanium alloy at temperatures lower than 625° C. High strain epitaxial silicon germanium alloys having a germanium concentration greater than 35 atomic percent in a temperature range between 400° C. and 550° C. A high order silane having a formula of SinH2n+2, in which n is an integer greater than 3, in combination with a germanium-containing precursor gas is employed to deposit the silicon germanium alloy with thickness uniformity and at a high deposition rate during each deposition step in this temperature range. Presence of the germanium-containing gas in the etch chemistry enhances the etch rate of the deposited silicon germanium alloy material during the etch step.