Oxford Instruments Plasma Technology (OIPT) has been working on nanoscale etching for several years featuring sizes below 100 nm and they are continually adding to their ‘portfolio’ of materials etched. The flexibility of the new Cobra ICP source will enable acceleration of their capacity in nanoscale etching. OIPT is established well to exploit the growing nanotechnology revolution, not only with their etching tools but also with their growth and deposition tools. They are a leading supplier of such tools to many of the major nanotechnology research facilities and universities in the world. This application note focuses on the etching aspect of nanotechnology, where there are several applications in memories, displays, novel semiconductor, optoelectronic and quantum computing devices.
Challenges Faced in Nanoscale Etching
Nanoscale etching is fundamentally difficult for two basic reasons:
- Difficult transport of neutral species in and out of the smaller features and
- Increased effects of charging by ions and electrons as sidewalls get close together. The situation is compounded by the fact that in the design of tinier devices, the lateral shrink is usually more than the vertical shrink so the aspect ratio increases.
OIPT ICP tools have the ability to operate at low pressure yet with high plasma density and low (controllable) DC bias that can be compared to simple RIE. Low pressure enhances anisotropy by reducing scattering of species by gas phase collisions.
The latest Cobra source provides increased flexibility through the following options:
- Active spacer enables independent control of ion distribution and offers optimized process uniformity across the electrode.
- Pulsing: ICP Source. Pulsing reduces wafer charging for enhanced aspect ratio etching. It may also be used for adjustment of ion radical ratios. Bias power pulsing, which is done normally with low frequency power reduces notching at interfaces with insulators and minimises aspect ratio dependent etching (ARDE).
The white paper referred to below gives several examples of nanoscale etching in the specific areas of nano-imprint lithography and photonic crystal holes as well as silicon and other miscellaneous etches. The two examples given here in Figure 1 and Figure 2 are by courtesy of Anders Holmberg, Biomedical and X-Ray Physics, Royal Institute of Technology, Stockholm, Sweden.
Figure 1. O2 process chemistry at -100°C uses the low temperature capability of the System 100 ICP65 for HAR anisotropic nanoscale polyimide etching. 50-nm half-pitch polyimide-gratings, 500 nm high (AR 10:1).10nm evaporated titanium hard mask. Polyimide etch rate 100nm/min.
Figure 2. Cl2 process chemistry used in the System 100 ICP65 for high aspect ratio anisotropic nanoscale Ge etching 10nm evaporated titanium hard mask. Ge etch rate 100nm/min. 25-nm half-pitch Ge-grating, 310nm deep (AR 12:1).
Read the full review article Nanoscale Etching in Oxford Instruments ICP Systems in a White Paper authored by Colin Welch downloadable from the Oxford Instruments Plasma Technology site.
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.