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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

Resistant Evaporation

Sputtering

PLD : Pulse Lasr Deposition

MBE: Molecular Beam Epitaxy

Chemical Deposition CVD

Chemical Deposition PECVD

Chemical Deposition MOCVD

Vacuum      About

Rotary           Pump

Turbomolecular   Pump

Cryojenic           Pump

Diffusion            Pump

The barometer History

Low vacuum range gauge


Thickness Monitoring

MOCVD deposition method
This expensive system is applied more for use in the field of optoelectronic, semiconductor lasers such as manufacturing, LED, and photodetectors. For better understanding of done process, we consider the structure of one semiconductor laser , similar to Figure 1, in which on a substrate of GaAs is used the GaAs layers and or its triplex compounds with aluminum.

Figure 1: Schematic view of a semiconductor laser

In systems MOCVD, as is clear from its name, use of metal-organic combined sources. These sources are combined generally in two forms:
a) To form the desired layer according to the following formula is used combination of two organic radicals:
Where R represents the methyl ethyl, or even heavier alkyl radical. M is a metal of group II or III, and E is an element of group V or VI. III-V Compounds (or combinations of groups II-VI) in addition to metal alkyls (with low molecular weight) form compounds such as dimethyl cadmium, three-methyl gallium. For example, according to the following equation GaSb layer obtained by using the reaction between three methyl gallium (TMGa) and antimony tri-methyl (TMSb).
B) In some reactions, instead of organic radicals, they use hydrogen. In this case, the general form of reaction between metal-organic and Hydrad is as follows:
That in this formula R, organic radical, M and metal elements form the binary compound and n is an integer. An example of this type of reaction is combination of three methyl gallium (CH3) 3Ga, with AsH3:
To build triplex compound, they use a combination of metal-organic sources and one Hydrad with specific concentration. For example, to create a layer on the wafer, according to the figure ... we have:
Figure 2 shows a schematic view of a MOCVD system. According to this figure, the vapors of organic - metal sources are combined with the sources of Hydrad laminar flow of carrier gas (hydrogen or nitrogen), insert into the reaction chamber and passes on the substrate that is is warming in the range of 700-400 ° C. By heating reactions such as that things are mentioned above, occur on the surface of the substrate and form one solid layer crystal on it.
On the other hand side products that is produced from peripheral reactions such as methane and hydrogen go out from the gas purification system after passing through the venting system. The influencing factors in this process are:
The rate of producing ingredients of layer.
The reaction rate of this material.
The temperature of the substrate.
The pressure of chamber.
The geometry structure of chamber.
Although MOCVD used to coating a wide range of materials, Group III-V and II-VI, recently used more than MBE systems to produce blue-green lasers AlGaInN and ZnSSe.

Figure 2: Schematic view of a MOCVD reactor

Table 1: common layers and substrates

The growth temperature	Substrate	Type of material
750-700	GaAs	AlGaAs
650-600	GaAs	InGaAs (strained)
750-700	GaAs	InGaAlP
650-600	InP	InGaAsP
650-600	InP	InGaAs
400-350	GaAs	HgCdTe
550-420	GaAs	ZnSSe

In Figure 3, shown is a schematic view of and real from inside a MOCVD system.

A real view of the inside a MOCVD system. (b) Schematic view from inside a MOCVD system, 1. The thermocouple 2. Heater 3. The gas inlet 4. The space above the chamber 5. The optical probes 6. The double-sided O-ring 7. The inside of wall, which is cooled with water 8. The quartz wall 9. Output.
In Table 2 compared togather the growth parameters in MBE, CVD and MOCVD methods.

Table 2: Comparison of growth parameters in several coating system.

MBE	MOCVD	CVD	Parameter
01/0	1/0	1/0	Deposition rate
550	750	750	The growth temperature
5	25	250	Thickness control

Table 3: Characteristics of different systems of chemical coating.

APCVD	LPCVD	MOCVD	PECVD	*
Simple, high deposition rate, cheap .	Excellent uniformity, high purity .	Usable for metals, semiconductors and dielectrics .	Low temperature for coating . High adhesion	Advantages
Less uniformity, less purity	Low deposition rate	Very toxic, expensive	Plasma, sometimes cause destructing layer and even sample .	Disadvantage
Thick oxide layer	The coating of dielectrics and polysilicon .	Making LED, diode lasers, semiconductors	dielectric coating	The major application

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