SCANDIUM-ALUMINUM ALLOY SPUTTERING TARGETS
A sputtering target comprises an alloy of scandium and aluminum, wherein the alloy has a concentration of 3-10 at % scandium and 90-97 at % aluminum. The sputtering target can be used to produce a piezoelectric layer for an apparatus such as an acoustic resonator.
1 . A method of manufacturing a sputtering target, comprising:
forming a scandium-aluminum alloy comprising 3-10 at % scandium and 90-97 at % aluminum; and
preparing the scandium-aluminum alloy for use as a sputtering target in plasma deposition equipment.
2 . The method of claim 1 , further comprising measuring a composition of the scandium-aluminum alloy, comparing the measured composition to a desired composition, and adjusting a composition of a subsequent sputtering target according to the comparison.
3 . The method of claim 2 , wherein measuring the composition comprises performing inductively coupled plasma (ICP) mass spectrometry (MS).
4 . The method of claim I, further comprising measuring a microstructure of the scandium-aluminum alloy, comparing the measured microstructure to a desired microstructure, and adjusting a microstructure of a subsequent sputtering target according to the comparison.
5 . The method of claim 4 , wherein the measured microstructure comprises a grain size of ScAl 3 within the sputtering target.
6 . The method of claim 5 , wherein adjusting the microstructure comprises modifying a process parameter to reduce the average grain size to less than 40 μm.
7 . The method of claim 1 , further comprising measuring scandium segregation of the scandium-aluminum alloy, comparing the measured segregation to a desired segregation, and adjusting a segregation of a subsequent sputtering target according to the comparison.
8 . The method of claim 1 , wherein forming the scandium-aluminum alloy comprises:
melting precursor materials comprising pure scandium and pure aluminum;
fast casting the melted precursor materials to produce a scandium aluminum alloy ingot;
forging or rolling the scandium aluminum alloy ingot;
heat treating the forged or rolled scandium aluminum alloy ingot; and
bonding and machining the heat treated scandium aluminum alloy ingot.
9 . The method of claim 8 , wherein forming the scandium-aluminum alloy further comprises:
performing inductively coupled plasma (ICP) relative intensity analysis on the scandium aluminum alloy ingot to determine its scandium content.
10 . The method of claim 9 , further comprising adjusting at least one process parameter for the manufacture of a subsequent sputtering target according to the determined scandium content.
11 . A method of manufacturing an acoustic resonator structure, comprising:
in an atmosphere containing nitrogen gas, performing a sputtering process using a sputtering target comprising a scandium aluminum alloy having 3-10 at % scandium and 90-97 at % aluminum.
12 . The method of claim 11 , wherein the sputtering target comprises ScAl 3 with a grain size less than 40 μm .
13 . The method of claim 11 , further comprising:
forming a first electrode on a substrate;
performing the sputtering process to deposit a layer of aluminum scandium nitride (ASN) on the first electrode; and
forming a second electrode on the layer of ASN.
14 . The method of claim 13 , further comprising:
measuring a uniformity of an electromechanical coupling coefficient (kt 2 ) across the layer of ASN; and
adjusting a process parameter used to produce a subsequent sputtering target according to the measurement.
15 . The method of claim 14 , wherein measuring the uniformity comprises performing inductively coupled plasma (ICP) mass spectrometry (MS).
16 . The method of claim 13 , further comprising:
measuring an electromechanical coupling coefficient (kt 2 ) of the layer of ASN;
comparison the measured kt 2 with a kt 2 of at least one other layer of ASN produced by the sputtering target; and
adjusting a process parameter used to produce a subsequent sputtering target according to the comparison.
17 . The method of claim 16 , wherein the process parameter comprises a relative proportion of scandium in precursor materials used to produce a scandium aluminum alloy.
18 . An apparatus, comprising:
a sputtering target comprising an alloy of scandium and aluminum, wherein the alloy has a concentration of 3-10 at % scandium and 90-97 at % aluminum.
19 . The apparatus of claim 18 , wherein the alloy comprises ScAl 3 with a grain size less than 40 μm.
20 . The apparatus of claim 18 , further comprising plasma deposition equipment incorporating the sputtering target.