• پارسی (Persian)

Titles

Surface and Thin Film Analysis
The interaction  particles& thin layer

The interaction  X Ray with thin layer

The interaction   Light with thin layer

SEM:  Scanning Electron Microscopy

TEM:Transmission Electron Microscopy
SPM :  Scanning   probe   Microscopy

AFM :  Atomic   Force      Microscopy

STM :  Scanning  Tunneling Microscopy

Sims: Secondary  ion  mass  Spectroscopy

RBS: Rutherford Backscattering Spectroscopy

 XRD:      X_Ray Diffraction

XPS:   X_Ray Photoelectron
 
Spectrophotometer

Ellipsometry

Thin film Structure

  Electron_Beam  Gun
Vacuum          About

Rotary               Pump

Turbomolecular   Pump

  Cryojenic           Pump

  Diffusion            Pump

The barometer History

  Low vacuum range gauge

  
Thickness Monitoring




MBE:Molecular Beam Epitaxy

 

MBE:Molecular Beam Epitaxy

MBE

MBE is one of specialized methods, which layer is placed on the substrate, almost in crystalline form, and is used in many advanced industries including the manufacture of electronic components such as transistors and integrated circuits. The most researches of this system is done on the elements of Group III and Group V (such as Al, Ga, In, As, P and Sb) also germanium on silicon.
In recent decades, this method has had a experimentally considerable growth and the number of published books and articles in this period is a good criterion of its progress. However, the main process of MBE has been done since long ago, but the main work in this field was formed in the field of combined semiconductor growth that Cho & Arthur were its founder. They investigated the growth process of gallium arsenide in atomic size using mass spectrograph and surface analysis techniques.
After them, Chang and others developed this process, so that it is now called the system MBE. The most important change was the improved vacuum chamber, which was increasing to 11-10 tour, but a correct understanding of MBE has rooted in the superficial analysis, as well as, the growth of epitaxial layers at the atomic scale. Chamber is made of stainless steel 304 or 316, which the inner surfaces is polished completely, to be minimized the absorption of gases and humidity by walls.
Usually, all parts are made in such a way that the wafers are easily portable, under the ultra-high vacuum. This system is included various processes such as the layer analysis, substrate preparation and the growth process. The system can also have a separate chamber for metal coating (sputtering or thermal evaporation).
The vacuum is about 10-11 torr, and in this condition gases-free path is several times greater than the distance between the sample and the substrate (20 cm).
Reactions occur in particular on the surface of the substrate, where the rays of various sources are combined together. Because it is necessary a long time, sometimes a few days, to be ready ultra-high vacuum conditions. Usually the system is placed under a constant vacuum and only limited space of the system is in contact with air. In most of these systems can be found the chemical and structural analysis of production, inside the vacuum chamber.
Depending on the type of growth techniques and the
  •  number of analysis is used of various chambers, which are attached often separately to their respective vacuum pumps, and create desired vacuum. Often they use a small chambers, called Load lock as a separate chamber from the growth chambers to move the sample.
In Figure 1, it can be seen schematic view of the MBE system. There are various sources with power to create the flux, with different rates, which can be used in these systems. These sources everyone are concentrated to the substrate, which is heated by a heater, to give greater mobility to the surface of the substrate, and thus, form a single crystal layer.
In Figure 1 (left) can be seen, more detail including molecular beam sources, sample transfer and its rotating system, one gauge BAYARD ALPERT to measure the pressure of chamber and molecular beam flux, fluorescent plate to control the structure layer, quadrupole mass analysis, heater, sample, and the holder of Nudsen cells.


  

Schematic view of the MBE system at different angles.

  As mentioned, one of the advantages of MBE systems is the analysis of samples in the system. This analysis may be done in the main chamber or in its side chambers.
The most commonly used analysis can be noted the Auger electron spectrometer, secondary ion mass spectrometry (SIMS), photoelectron spectroscopy and X-ray (XPS).
In these systems, is used commonly from one ion gun for cleaning the substrate. Thus, the standard MBE systems, as shown in Figure 2 and Figure 3, is made usually from several different vacuum chamber.
- Load-lock, for entrance and exit of substrate.
- Vacuum chamber for film growth.
- Vacuum chamber for analysis. (- Been Multi chamber in this system, gives more possibility of maneuver to the operator for various analyses and diversity of growth).
One Load-lock chamber is discharged to about 10-8 torr. While other vacuum chambers reach to the vacuum above 5 × 10-10 - 5 × 10-11 torr. 

 



Figure 2: Schematic view of the system MBE.



Common methods in the growth chamber are resistive thermal evaporation method, electron gun, ion source and Implantation method.
  


The actual sample of MBE systems that is manufactured by Veeco.



In the growth process of MBE systems, the control of temperature, shutters, molecular or atomic beams, and deposition rate of each sources, which are directed toward the sample (under proper temperature), is very important in the growth of epitaxial layer taxi .
Now we research about the generally growth process in one MBE system:
1. Preparation of wafers, which include cleaning, and sometimes removing stain from their surface.
2. Lie the wafers within the system and vacuum chamber evacuation. The used substrates are single-crystalline wafers and are cleaning up before the deposition through the سونش, and usually an oxide layer is used to protect against air gases and the wafer materials on the substrate.
3. Creating heat below the wafers, so that the surface become completely clean and pure. For example, 550-500 ° C is considered for Ga V900-700 for silicon.
4. Under high vacuum and by several sources, with rate higher than a micron per hour, layer                     begins to grow.
5. The various analyses is doing on the growing layer or produced layers.
Since, the electrical properties of these materials are related directly to crystalline structure of layer, MBE is the best choice for them. Due to the precise process of them and applying a high vacuum of them in systems MBE, there are many applications for it, which the most important of them can be noted to manufacture of solar cells of them, superconductors of them, semiconductor lasers and LED manufacturing.

movie about MBE

       
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