compatible with in-line diffusion processes. The oxide materials deposited by. APCVD include amorphous and polycrystalline titanium oxide (a-TiOx and pc- TiOx. deposition by APCVD employs the same reaction chemistry as has been .. CdTe PV device fabrication process compatibility in that APCVD is. Deposition Process for the Development of V2O5 as (APCVD)—makes such a process compatible with on-line glass manufacturing.
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Epitaxy means “on top” or “assigned to”, and represents a process in which a layer is created on top of another layer and inherits its crystal structure. If the deposited layer is of the apcv material as the substrate one speaks of homoepitaxy, if it’s another material it’s so-called heteroepitaxy.
The most significant process in the homoepitaxy is the deposition of silicon on silicon, in heteroepitaxy usually a silicon layer is deposited on an insulator such as oxide Silicon On Insulator: Depending on the process, the wafers can be delivered from the wafer manufacturer with an epitaxial layer e.
As a gas for generating the epitactical layer, pure hydrogen is used in conjunction with silane SiH 4dichlorosilane SiH 2 Cl 2 or silicon alcvd SiCl 4. The silicon inherits the structure of the substrate and is growing, for energy reasons, layer by layer successively on.
To not grow up a polycrystalline silicon, one must always prevail a shortage of silicon atoms, e. When silicon tetrachloride is used, the reaction proceeds in two steps:.
Chemical vapor deposition – Wikipedia
In order to inherit the substrate’s orientation the surface must be absolutely clear. Prkcess one can utilize the equilibrium reaction. Both reactions can occur in the other direction, depending on the ratio of the gases. If there prkcess only few hydrogen in the atmosphere, as in the trichlorosilane process for the purification of raw silicon, material is removed from the silicon wafer surface due to the high chlorine concentration.
Only with increasing concentration of hydrogen growth is achieved.
With SiCl 4 the deposition rate is approximately 1 to 2 microns per minute. Since the monocrystalline silicon grows only on the bare surface, certain areas can be masked with oxide where the silicon grows as polycrystalline silicon. This polysilicon, however, is etched very easily compared to single-crystalline silicon through the backward-running reaction.
Diborane B 2 H 6 or phosphine PH 3 are added to the process gases, to create doped layers, since the doping gases decompose at high temperatures and the dopants are incorporated in the crystal lattice. The process to create home-epitactical layers is realized under vacuum atmosphere. As mentioned above, due to a low hydrogen concentration there occurs a back etch on the silicon surface. This can be used to clean the surface before the actual process starts.
If the gas concentration is varied post this cleaning the deposition begins. Due to the high process temperatures there’s a diffusion of dopants in the substrate or impurities, which have been used in earlier processes, can move to the substrate. If SiH 2 Cl 2 or SiH 4 are used there’s no need for such high temperatures, so these gases are used primarily.
To achieve the etch back process to clean the surface, HCl has to be added separately. The disadvantage of this silanes is that they form germs in the atmosphere right before deposition, and thus the quality of the layer is not as good as with SiCl 4. There is often a need of layers which can’t be created right from the substrate. To deposit layers of silicon nitride or silicon oxynitride one has to use gases which contain all necessary components.
The gases are decomposed via thermal energy. That’s the principle of the chemical vapor phase deposition: The wafer surface doesn’t react with the gases but serves as bottom layer. Depending on the process parameters – pressure, temperature – the CVD method can be devided in different methods whose layers differ in density and coverage. If the growth on horizontal surfaces is as high as on vertical surfaces the deposition is conform.
A high conformity can only be achieved by high process temperatures. The deposited oxide has a low density and the coverage is moderate due to a relatively low temperature. The high wafer throughput is a big advantage of this process. As process gases silane SiH 4 highly deluted with nitrogen N 2 and oxygen O 2 are used. Added ozone O 3 can cause a better conformity because it improves the movability of the accumulated particles.
The oxide is porous and electrical instable and can be densified by a high temperature process. To avoid edges which can result in difficulties at the deposition of additional layers, phosphorus silicate glass PSG is used for interlayers.
A high amount of phosphorus leads to a high increase of the flow properties, however, phosphoric acid can be proess which corrodes aluminum conductor paths.
Because annealing affects earlier processes e. LPCVD processes enable a high conformity of almost 1. The particles dispread due to collisions and cover vertical surfaces as well as horizontal ones. A tungsten film can only be fabricated on bare silicon.
Chemical vapor deposition
Therefore silane has to apccd added if there is no silicon substrate. Due to low temperatures the process gases can not be decomposited thermal. With a high frequency voltage, the gas is transformed into a plasma state. The plasma is energetic and disposes on the surface. Instead of SiH 2 Cl 2 silane is used because it decomposes at lower temperature. The process uses several gases which are led into the process chamber alternating.
Each gas reacts in such a way that the current surface is saturated, and therefore the reaction comes to a standstill. The alternative gas is able to react with this surface in the same way. Between the reactions of these gases the chamber is purged with an inert gas, like nitrogen or argon.
A simple ALD process could look like this:.
First step is the elimination of hydrogen atoms which are bound to oxygen at the wafer surface. The remaining molecules bond with the unsaturated oxygen. The chamber is purged and subsequent water steam is led into the chamber. Ever one hydrogen atom of the H 2 O molecules now can react with the former deposited surface atoms to form methane, while the hydroxyl anion is bond to the aluminum atoms.
Chemical vapor deposition – Deposition – Semiconductor Technology from A to Z –
Pfocess, there are new hydrogen atoms at the surface which can react in a afterwards step with TMA like in the beginning.
The atomic layer deposition provides significant advantages over other deposition techniques, and therefore it’s a very important process to manufacture thin films. With ALD even 3-dimensional structures can be deposited very uniform.
Insulating films are possible as well as conductive ones, which can be created on differet substrates semiconductors, polymers, The film thickness can be controlled very precise by the number of cycles.
Since the reactive gases are not led into the chamber simultaneously, they can not form germs right before the actual deposition. Thus the quality of the films is very high. Atomic Layer deposition Epitaxy means “on top” or “assigned to”, and represents a process in which a layer is created on top of another layer and inherits its crystal structure.
Homoepitaxy Depending on the process, the wafers can be delivered from the wafer manufacturer with an epitaxial layer e.
When silicon tetrachloride is pprocess, the reaction proceeds in two steps: Inhalt Plasma, the fourth aggregation state of a material Chemical vapor deposition Physical deposition methods.