And the films are continuous. (Exept MBE).
What about sputtering methods?
Semiconductor thin films have been prepared by many techniques such as thermal evaporation in vacuum, sputtering, pulsed laser ablation, spray pyrolysis, chemical bath deposition, successive ionic layer adsorption and reaction (SILAR) method etc. If you are looking for a simple, low cost technique then you can try the last two (chemical bath and SILAR). However, the films deposited by all these techniques are usually amorphous or polycrystalline. Hence their resistivity is usually high. If you are looking for low resistivity, crystalline films MBE is the only way.
As you already ask for sputtering methods, I assume that you may have access to that method. However, there are several sputtering variants, one of the most common ones being magnetron sputtering. With that method you can practically evaporate everything. By variation of sputter parameters you can also adjust the film properties (not only thickness, but also morphology and crystallinity). If you want to obtain highly crystalline thin films, you can achieve that by installation of a substrate heating.
You can also try by wet methods
- See Electrografting: a powerful method for surface modification
Daniel Be´langer, and Jean Pinson Chem. Soc. Rev., 2011,40, 3995–4048
Electrochemical Formation of Close-Packed Phenyl Layers on Si(111)
C. Henry de Villeneuve, J. Pinson, M. C. Bernard, and P. Allongue
J. Phys. Chem. B1997,101,2415-2420
Depending on how thin you want the thin films to be (~100nm) to (~500nm) sol-gel dip coating or spin coating could be an option coupled with annealing. Whilst not achieving quite the crystalline uniformity of films deposited by MBE the method still achieves highly crystalline films. The sol gel synthesis is routine and film formation of relatively easy going. It is also dependent upon what semiconductor you wish to deposit. This method is especially good for metal oxides.
As Kothari said, thin films can be prepared by both PVD and CVD methods. With the variation of deposition parameters, the films thickness can be easy controlled above 100 nm or even 50 nm. But I have found that it's difficult to grow films with a thickness smaller than 10 nm.
For the sputtering method you can use DC sputtering and the RF sputtering. If you are depositing the metal then DC sputtering will be more useful than the RF. But if you have to deposit Insulator or Semiconducting material then RF sputtering will give better control and quality of the films.
Apart from that if you have access to the Pulsed Laser Deposition (PLD) system then it will be ideal for you to control the film thickness under 10 nm. For that you have to optimize the no. of shots. I think that will be ideal for you.
RF Magnetron Sputtering is good technique to fabricate several nanometer thin film. You can vary several deposition parameter like substrate temperature, substrate to target distance and deposition angle to achieve desired quality thin film.
Though, the MBE technique is very good but it is not available to everyone.
Since it is possible to deposite several nanometer films by PLD and DC/RF sputtering methods, how to obtain a continuous and uniform semiconductor film?
How to characterize a super thin films (thickness < 10 nm ) would be a hot potato.
films with thickness less than 10 nm can be characterized by ellipsometry, by AFM scratching. the paper below descibes the method, but it also works on Si....any hard surface.
Mono- and Multilayer Formation by Diazonium
Reduction on Carbon Surfaces Monitored with
Atomic Force Microscopy “Scratching”
Franklin Anariba, Stacy H. DuVall, and Richard L. McCreery Anal. Chem.2003,75,3837-3844
The best way to achieve so low thickness fill is ALD (Atomic Layer deposition) process. But I'm not sure about semiconductor films formation by this method. Basically epitaxial techniques are used - MBE or CVD epitaxy. For example if you want to receive 5-10 nm SiGe films you can use CVD process with the next X-Ray methods of characterization.
Our publications lay down the power of EDXRF technique in conjunction with use of microbalance and ellipsiometry to provide precise measurement on ultra thin film thickness.The paper is downloaded on this website under our names ( D.K. Kaushik, S.K. Chattopadhyaya and N.Nath )
Sputtering will just do fine for even sub 10 nm thin films. Just optimize the deposition parameters, mainly - power, working pressure and deposition rate. You may as well increase the target-to-substrate distance for better controls over uniformity and deposition rate.
X-ray reflectivity can be used to characterize the thickness. TEM can also be used.
Dear Singh, during the sputtering process, is it possible to damage the surface of substrate even with low power (< 50 W)?
Dear Zhu,
What is the variant of sputtering you are using? RF, RF magnetron, DC, pulsed DC ?
and what is the substrate? Damage as in development of surface roughness in the substrate? or the chemical environment at the film/substrate interface?
The best one technique to fabricate the thin-film in nanomater range is Langmuir Blodgett. Via this technique you can fabricate the well aligned atomic layers. But to use this technique, first you have to make your material hydrophobic. Because in this technique thin film is fabricated on the surface of water.
The standard ways to grow semiconductor films from one monolayer to even hundreds of nm with atomically precise composition and structure are Molecular Beam Epitaxy (MBE), Metal Organic Chemical Vapour Deposition or Epitaxy (MOVCD or MOVPE) and (though not so accurate) Pulsed Laser Deposition (PLD). Are you interested in any one of these to know more?
Whatever technique you may use to prepare muli-layer thin film system, it is essential to have in-situ measurement of thickness as well as have control on deposition rate. This is greatly facilitated using our Patented system of ' Doubly-oscillating Quartz crystal Micro balance, that eliminates temperature and pressure changes encountered during such a deposition in a chamber.
Basically there are two simple ways depending on your material properties and the equipment you have in hand. One way is chemical deposition in a high vacuum chamber. The source material evaporate with certain electric current applied. The deposition rate can be facilely controlled by adjusting the current. In-situ measurement of thickness could be achieved by Quartz crystal Micro balance. All you need is an instrument, like "Edwards Auto 306" which equipped with the thickness monitor and easy to access. Another way is solution-process generally. Langmuir Blodgett or dip-coating method, by dragging your substrate from the solution of your materials with a constant speed, you can get the thin film you need. In order for this method to be valid, your material should have good solubility in common solvents, so that you can optimize the conditions, including solvent choice, concentration, dragging speed, etc. Generally a faster speed in a diluted solution tends to generate thinner film. But the thickness can only be determined afterwards, by AFM or ellipsometry.
depends on materials to be used in reactant, most of techniques in electronic used; Sputtering techniques, Electron beam deposition (EBD) and Plasma enhanced chemical vapor deposition (PECVD)
Depends on the specific semiconductor that shall be deposited. Here's a review paper:
http://www.sciencedirect.com/science/article/pii/S0040609005000532
Several nanometers... First of all, if you could write correctly your question, maybe we can answer properly. Being so broad on the subject doesn't aid at all. Please, try to focus on your particular interest.
One needs an in-situ measurement of thin film thickness and we demonstrarted doubly -oscillating quartz xtal microbalance to just satisfy such condition in a evaporation or sputtering chamber!
Dear Singh,
I have utilized DC and RF sputtering methods to grow Si and Ge thin films on SiO2/Si sbustrate.
During the grow process, the SiO2 film maybe destroyed. Because after the supttering, the gate leakage current was as large as micro ampere. I'm not sure whether our sputtering equipment is suitable for growth semiconductor thin films on SiO2 to fabricate TFT transistors.
Dear Moseke,
I have a wonder if the electrodeposition of semiconductors films can be thinner than 10 nm.
It is an art to grow very thin layers. It can only be done if one controls the rate of growth to low levels and the state of vacuum is of high order. The Use of device called Doubly-oscillating Quartz Xtal Microbalance will help ascertain both the rate of growth as well as measure the thickness in-situ.
sol gel spin and dip coating process are also suitable for your request
you can use Atomic layer deposition technique to prepare these thichnesses
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