Examples of Ion Beam Etching (IBE) of Semiconductors

By AZoNano

Table of Contents

Introduction
Examples of Applications of Ionfab300Plus IBE Tool
Conclusion
About Oxford Instruments Plasma Technology


Introduction

OIPT’s ion beam processing tools are suited for a wide range of markets and applications, and this previous year has seen significant demand from customers for our ion beam tools. These include Ion-beam etch (IBE),Reactive ion-beam etch (RIBE) and Chemically-assisted ion beam Etch (CAIBE), as well as Ion beam deposition (IBD) applications.

Examples of Applications of Ionfab300Plus IBE Tool

Below are some examples of applications for which the Ionfab300Plus IBE tool has recently been purchased. The first two examples are Ion Beam Milling (IBM using Argon gas alone) of high-temperature superconductors for the Department of Microtechnology and Nanoscience, Chalmers University of Technology, Sweden. Secondary Ion Mass Spectrometry (SIMS) probe monitoring is used for process control in these examples.

Example 1

This sample is a 5 x 5 mm square located in the centre of a 150 mm Si carrier wafer. The sample material was Strontium Titanate (SrTiO3) coated with a layer stack: Au(32nm)/YBa2Cu3O7 (40nm).

The ion milling parameters for this technique are listed below:

  • Substrate angle to beam: 90º
  • Beam voltage (energy): 250V
  • Beam current density (intensity): 0.51 mA/cm2

Inspite of the small relative area covered by the sample, Figure 1 shows that signals from all the elements present in the various layers can be clearly differentiated, except for Cu which is lost in the noise. Even the isotopes Y and Sr with an adjacent mass number (89 and 88, respectively) are differentiated well. The gold layer can be seen to be etched through first followed by the YBa2Cu3O7 layer. As this layer is removed, the Sr and Ti signals of the substrate material rise.

Figure 1. SIMS traces for Sample 1

Example 2

This sample took the form of a 10 x 10mm square located in the centre of a 150 mm Si carrier wafer. The sample comprised a multilayer: GaAs (40nm) / AlGaAs(61nm). The ion milling parameters for this process are listed below:

  • Substrate angle to beam: 90º
  • Beam voltage (energy): 500V
  • Beam current density (intensity): 0.64 mA/cm2

In Figure 2, the transition between the GaAs and AlGaAs layers can clearly be seen, in particular from the Ga signal. The As signal also varies in the same manner between the two layers showing the reduced amounts of these two elements in the AlGaAs alloy. The Al signal shows a high background level due the presence of aluminium in chamber components, but the variation from one layer to the next can still clearly be observed. Comparing the times for each of the layers, correlates well with the known difference in thickness (21nm) of the two alternating alloys.

Figure 2. SIMS traces for Sample 2

Example 3 - IBE of MRAM multilayers with SIMS probe

The next example is the SIMS – controlled milling by IBE of tunnelling magneto-resistive (TMR) magnetic multilayers for MRAM applications at the University of Twente, NL, on OIPT’s Ionfab300Plus tool. This tool was also supplied with a cryo-cooled chuck that can reach - 170 º C in 14 mins from room temperature.

The ion milling parameters for this technique are listed below:

  • Substrate angle to beam: 90º
  • Beam voltage (energy): 250V
  • Beam current density (intensity): 0.51 mA/cm2

Figure 3. SIMS traces for MTJ magnetic multilayer: Ta(5nm)/Co(15nm)/ Al2Ox(2.3nm)/ Co (3.5nm)/ FeMn(10nm)/Co(5nm)/ Ta(5nm)/SiO2(2mm)/ (Si substrate)

The highly uniform and slow, controlled milling process through the multilayer allows the SIMS to be used to precisely stop at a specific point in the multilayer. Of particular note in Figure 3 is the very significant and clean Al signal from the MTJ barrier layer in the MRAM stack. The other metal layers are clearly differentiated; the Fe and Mn peaks were not acquired in this run.

Example 4- Blazed grating fabrication

Figure 4 shows another example of the application of OIPT’s Ionfab etch tool in the photonics area in order to fabricate a blazed grating. The ‘blaze angle’ can be precisely determined by the substrate positioning flexibility of the tool.

Figure 4. 300nm blazed grating etch in quartz

Conclusion

OIPT’s ion beam processing tools are ideal for a wide range of markets and applications, and this past year has seen unprecedented demand from customers for their ion beam tools.

About Oxford Instruments Plasma Technology

Oxford Instruments Plasma Technology provides a range of high performance, flexible tools to semiconductor processing customers involved in research and development, and production. They specialise in three main areas:

  • Etch
    • RIE, ICP, DRIE, RIE/PE, Ion Beam
  • Deposition
    • PECVD, ICP CVD, Nanofab, ALD, PVD, IBD
  • Growth
    • HVPE, Nanofab

This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Plasma Technology.

For more information on this source, please visit Oxford Instruments Plasma Technology.

Date Added: Nov 18, 2011 | Updated: Sep 24, 2013
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