MBE Components, In-situ Processing System ISES

ISES

In-situ Etching System

ISES control panel
  • AsBr3 atomic precise etching

  • No carrier gas required

  • Full UHV and MBE compatibility

  • No significant affectation on MBE growth properties

  • Free standing system

  • Integrated safety management

  • Computer controlled operation

  • Second material optional

Valve and flux control panel of the ISES

The In-situ Etching System ISES - is a fully UHV and MBE compatible gas source for high vapour pressure materials like AsBr3 which is used for in-situ etching applications.
AsBr3 in-situ etching provides atomic layer precise manipulation of thin films and nanostructures. The use of AsBr3 as the etchant species without any carrier gas guaranties full compatibility to all standard III-V-MBE systems. Due to the very small amount of AsBr3 which is injected into the MBE system, no extra installations (extra pumps etc) are needed and no significant interaction, corrosion, etc of the MBE system is observed even after several years of operation.

etching mechanism

AsBr3 etching mechanism

The in-situ etching system is a stand-alone system which requires external supply of compressed air, clean N2, cooling water and waste air as well as electrical power. Only a free DN40 CF (O.D. 2.75") flange for the gas injector unit is needed to connect to the MBE system.

The solid state (or liquid) etchant material is stored and evaporated in a gas cabinet. The gas cabinet also includes a mass flow controller (MFC) for vapour flow control and an own UHV system to provide a continuous flow and for evacuating the gas system to achieve high purity operation conditions. An exhaust filter and an integrated gas alert system guarantees a safe and non-polluting operation.
All equipment needed for operation is mounted into the gas cabinet and therefore it represents a compact and easy handing tool. Most electronic controllers have integrated standard computer interfaces which enables fully automated operation.
Optionally the in-situ etching system can be extended to a second material source as well as to a second gas injector unit.

ISES gas cabinet

Gas cabinet of the AsBr3 in-situ etching system ISES


Application

AsBr3 in-situ etching allows atomic precise layer by layer etching inverse to the layer by layer MBE growth. The figure above shows RHEED oscillations of a typical growth - etching sequence indicating the precise removal of 6 monolayers of GaAs which have been deposited earlier. Due to the lower etching rate of AlAs the oscillations slow down after the removal of the GaAs and when the AlAs layers are reached.

RHEED oscillations of a typical growth - etching sequence

Material selectivity is a typical property of AsBr3 etching of the group III-metal atoms. Indium shows the highest etching rate while Aluminium shows the lowest rate of the group III atoms In, Ga and Al. An application is for example the growth of etch-stop layers for precise etching depth control or the modification of self assembled InAs or InGaAs quantum dots.

Another feature is the crystallographic selectivity which allows the preparation of atomically planar facets. The forming of a very sharp V-groove after in-situ etching of a masked GaAs sample is shown in the SEM picture on the right. Using suitable processing conditions AsBr3 underetches the SiO2 mask and forms smooth crystallographic facets and a narrow, linear ridge which allows the preparation of wire structures in an in-situ regrowth process as shown in SEM images below. Forming of V-grove

V-grove formed by in-situ etching of a patterned GaAs sample

Forming of smooth surface facets

Forming of smooth surface facets by in-situ etching

Forming of stripe structures

Forming of stripe structures by in-situ etching of masked GaAs sample


References

Several publications based on samples prepared with ISES are listed in section References / List of Publications

Technical Data

Etching Material AsBr3, optional: SbBr3, PBr3 etc.
Bakeout temperature gas injector: max. 250°C; gas supply tubing: max 100°C
Dimensions (h x w x d) gas cabinet: 198 x 124 x 55 cm
Requirements high purity N2, compressed air, cooling water, waste air, electrical power