National Nanotechnology Infrastructure Network

National Nanotechnology Infrastructure Network

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High aspect ratio etching of sub 100 nm structures in dielectrics

Significant Upgrade to the Oxford PlasmaLab 100 at Cornell for Nanoscale Dielectric Etching Enables Improved Etching of High Aspect Ratio Dielectric Structures

Vincent Genova, CNF Process Engineer
Posted October 2012

Earlier this year, a substantial upgrade to the Oxford 100 ICP etch system at Cornell was completed.  This upgrade includes the installation of a large 12 gas pod, a gas ring manifold, and the latest version of the PLC.  The installation of a larger gas pod allows us to expand our gas chemistry to include more advanced fluorocarbon based gases.  The installation of the gas ring manifold will supplement the existing gas showerhead with a gas ring for alternative gas delivery.  The gas ring is placed in close proximity to the electrode on which substrates are placed.  The gas ring will alter the dissociation and ionization percentages in the plasma and allow us to more effectively tune the plasma gas chemistry.  The new PLC will allow us to direct the flow of gases to either the showerhead or the gas ring, depending on the device etch requirements by a simple programming of the etch recipe.

This upgrade was part of CNF’s ongoing cooperative development agreement with Oxford Instruments.  The role of the CNF’s Oxford 100 system is high aspect ratio etching of dielectrics, primarily silicon oxide, fused silica, and silicon nitride.  Dielectrics, such as these, rely on the use of fluorocarbon based chemistry with a fluorine to carbon ratio of 3 or less due to its intrinsic polymer forming nature.  Polymer forming precursor gases especially those with large monomer structure such as C4F8 and C2F6 are increasing used for dielectric etching in the microelectronics industry.  Our upgrade allows us to investigate 3 new advanced fluorocarbon chemistries, specifically C4F6, CH2F2, and C5F8.  The lower F/C ratio will enhance polymerization allowing us to achieve greater etch selectivity to silicon and to advanced lithographic resists such as those used in deep UV (DUV), electron beam, and nanoimprint lithography.  As the need for nanoscale lithographic resolution at increasingly small dimensions continues to drive down the resist thickness, selectivity of the etch becomes paramount.  The use of additive gases such as O2, H2, CO, CO2, etc. can further modify the plasma gas chemistry to either increase or decrease the degree of polymerization thereby influencing selectivity.  The additional selectivity attained with respect to these advanced resist systems will enable users to achieve high aspect ratio etching of nanoscale features in excess of 15:1.  Further process development with these new advanced chemistries will expand upon our recent work of nanoscale etching of fused silica, silicon nitride,  and silicon oxide as illustrated in the following SEM images, depicting pattern transfer of nanoscale features defined by electron beam and DUV lithography.  

These enhanced capabilities of the Oxford 100 will benefit users who are fabricating a wide variety of devices including those in nanophotonics, advanced CMOS, and NEMS where precise high aspect ratio structures need to be defined by pattern transfer.  For further information on these processes, please contact CNF research staff member Vince Genova, 


Figure 1: ASML DUV defined silicon nitride etched with CHF3/O2 in Oxford 100 ICP. 90 nm lines etched 750 nm deep  (link to full resolution picture) Figure 2: ASML DUV defined silicon dioxide etched with CHF3/CO2 in Oxford 100 ICP (link to full resolution picture)
Figure 3: Electron beam lithography defined chrome masked fused silica etched with C4F8/CO2 in Oxford 100 ICP. 70 nm lines etched 930nm deep  (link to full resolution picture)





High Aspect Ratio

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