Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018)
    Energy Harvesting & Storage Thursday Sessions
       Session EH-ThM

Paper EH-ThM3
Reactive Ion Beam Etching of Piezoelectric ScAlN and LiTaO3 for RF Filter Applications

Thursday, December 6, 2018, 8:40 am, Room Naupaka Salon 6-7

Session: Batteries
Presenter: Robinson James, Plasma Therm
Authors: R. James, Plasma Therm
Y. Pilloux, Plasma Therm
H. Hegde, Plasma Therm
Correspondent: Click to Email
Etching piezoelectric Scandium Aluminum Nitride (ScAlN) and lithium tantalate (LiTaO3) films with controllable profile angle and very smooth surface is required for next generation Bulk Acoustic Wave (BAW) and Thin Film Surface Acoustic Wave (TF SAW) RF filter applications respectively. First part of the paper reports the facile etching of ScAlN with 15% Scandium concentration by Reactive Ion Beam Etching (RIBE) with very smooth surface of less than 5 nm average roughness and controllable profile angle between 60 to 80 degrees. Recent studies indicate that incorporating high concentration Sc into AlN improves the piezoelectric response of the device by five times and the band width of RF filters also improved. However, etching highly Sc doped ScAlN using traditional RIE and ICP based methods are extremely difficult. Moreover RIE and ICP etching methods exhibit low etch rate and results in rough surfaces when Sc concentration increases more than ~ 8% in ScAlN. Reactive Gas/Ar based RIBE processes were developed with highly controllable profile angle from 60 to 80 degrees, improved etch rate (~ 36 nm/min) and selectivity to photoresist mask (0.7:1), in comparison to conventional IBE. ScAlN selectivity to photoresist was improved significantly when using Reactive Gas/Ar compared to pure Ar based etching. Second part of the paper reports the optimization of LiTaO3 etching with either RIBE or IBE. LiTaO3 etch rate and selectivity were optimized by varying the Reactive gas/ Ar ratio and wafer tilt. LiTaO3 etch rate of ~ 80 nm/min, 1.25: 1 selectivity to PR and a very smooth surface with roughness of ~ 2 nm was achieved. Further improvements in etch rate, selectivity are under investigation. Etching ScAlN and LiTaO3 were characterized using scanning electron microscope (SEM) and white light interferometer (WLI) was used for measuring surface roughness. By varying wafer tilt, Reactive Gas/Ar ratio, beam voltage and current we achieved desired profile angle, etch rate, selectivity and smooth surface. This research has significant importance in fabricating ScAlN based BAW and LiTaO3 based TF SAW RF filters for next generation mobile and wireless applications.