Resonator Electrode Sputtering for Low-Resistivity Mo Layers
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Solution Overview
Problem
Existing methods for sputter depositing metallic layers in resonator devices, such as BAW and SAW devices, face challenges in achieving low resistivity, stress control, and thickness uniformity, particularly for electrode layers like Mo, which are crucial for reducing device losses and improving quality factors in next-generation RF filters.
Innovation Solution
A method involving DC magnetron sputtering with a chamber pressure of at least 6 mTorr and a target power density of at least 6 W/cm², combined with controlled substrate temperature and bias power, to deposit metallic layers with resistivity less than 10 μΩ·cm and stress range of less than 250 MPa, ensuring excellent thickness and stress uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If known methods of sputter depositing Mo electrode layers are used, then the deposition process is simple and straightforward, but the resulting Mo layer has high resistivity (not less than about 11 μΩ·cm) which increases device losses
Solution Approach 1:
The patent applies parameter changes by modifying multiple sputtering process parameters simultaneously: increasing chamber pressure to 3-30 mTorr, increasing target power density to 5-20 W/cm², controlling substrate temperature to 25-450°C, and adjusting bias power to -50 to -500 V. These parameter changes transform the deposition conditions to produce Mo layers with resistivity below 10 μΩ·cm, directly reducing device energy losses while maintaining manufacturing feasibility
Solution Approach 2:
The patent employs dynamic control of deposition parameters during the sputtering process. The method dynamically adjusts the balance between ion bombardment energy (through target power density and substrate bias) and deposition rate (through chamber pressure and target power) to optimize film density and electrical properties. This dynamic parameter control enables achievement of low resistivity values that were not attainable with static, conventional parameters
2Productivity
If the piezoelectric layer thickness is reduced to develop devices for 5G and future RF filters, then device performance for next-generation applications is improved, but within wafer stress variation across electrode layers becomes more prominent and makes a larger contribution to coupling properties
Solution Approach 1:
The patent uses parameter changes to control stress in electrode layers by adjusting substrate temperature (25-450°C), chamber pressure (3-30 mTorr), and bias power (-50 to -500 V) during sputtering. These parameter adjustments enable precise stress management in thin electrode layers, ensuring coupling uniformity across the wafer even when piezoelectric layers are thinned for 5G and future RF filter applications
Solution Approach 2:
The method incorporates feedback control through monitoring and adjustment of deposition parameters to maintain stress within acceptable ranges. By controlling target power density and substrate bias power, the process compensates for stress variations that occur during deposition, ensuring uniform coupling properties across the entire wafer surface despite reduced layer thickness
3Loss of energy
If electrode layers are made thinner to reduce device losses, then quality factor of resonator devices is improved, but resistivity of the electrode layers increases and offsets the benefits
Solution Approach 1:
The patent applies comprehensive parameter changes to the sputtering process: chamber pressure (3-30 mTorr), target power density (5-20 W/cm²), substrate temperature (25-450°C), and bias power (-50 to -500 V). These parameter changes enable deposition of thinner electrode layers with maintained or reduced resistivity (below 10 μΩ·cm), allowing thickness reduction for lower device losses without the penalty of increased resistivity
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 results in metallic layers with reduced resistivity and stress variation, enabling the production of higher quality resonator devices with improved quality factors and reduced losses, suitable for advanced RF filter applications.
Implementation Method 1
performing a DC magnetron sputtering step that comprises sputtering the metallic material from the target onto the substrate so as to form a metallic layer on the substrate
Implementation Method 2
a plasma generating device, wherein the substrate support and the target are separated by a distance of 10 cm or less
Data Source
AI summary
Sputter depositing a metallic layer on a substrate in the fabrication of a resonator device includes providing a magnetron sputtering apparatus comprising a chamber, a substrate support disposed within the chamber, a target made from a metallic material, and a plasma generating device, wherein the substrate support and the target are separated by a distance of 10 cm or less; supporting the substrate on the substrate support; performing a DC magnetron sputtering step that comprises sputtering the metallic material from the target onto the substrate so as to form a metallic layer on the substrate, wherein during the DC magnetron sputtering step the chamber has a pressure of at least 6 mTorr of a noble gas, the target is supplied with a power having a power density of at least 6 W/cm2, and the substrate has a temperature in the range of 200-600° C.