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Specific Process Knowledge/Thin film deposition/Deposition of Silicon Oxide/Deposition of Silicon Oxide using LPCVD TEOS: Difference between revisions

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DTU Nanolab has one furnace for deposition of LPCVD TEOS oxide. The furnace was installed in the cleanroom in 1995.
DTU Nanolab has one furnace for deposition of LPCVD TEOS oxide. The furnace was installed in the cleanroom in 1995.


In the furnace LPCVD oxide can be deposited on 4" wafers. It is not possible to deposit LPCVD TEOS oxide on 6" wafers in he cleanroom.  
In the furnace LPCVD TEOS oxide can be deposited on 4" wafers. It is not possible to deposit TEOS oxide on 6" wafers in he cleanroom.  


TEOS is is Tetra-Ethyl-Ortho-Silicate, sometimes also referred to as Tetra-Ethoxy-Silane, and it has the chemical formula Si(C<sub>2</sub>H<sub>5</sub>O)<sub>4</sub>. It is a liquid that is stored in a bubbler. When a deposition is started, the bubbler is heated to 75 C, and TEOS is then vaporized and introduced into the furnace.  
TEOS is is Tetra-Ethyl-Ortho-Silicate, sometimes also referred to as Tetra-Ethoxy-Silane, and it has the chemical formula Si(C<sub>2</sub>H<sub>5</sub>O)<sub>4</sub>. It is a liquid that is stored in a bubbler. When a deposition is started, the bubbler is heated to 75 <sup>o</sup>C, and TEOS is then vaporized and introduced into the furnace.  


In the furnace, TEOS is thermally decomposed on the sample surface, so that a layer of silicon dioxide (SiO<sub>2</sub>) is deposited on the wafer surface:
In the furnace, TEOS is thermally decomposed on the sample surface, so that a layer of silicon dioxide (SiO<sub>2</sub>) is deposited on the wafer surface:
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The difference between TEOS and silane gas (used for deposition of silicon nitride) is essentially that in TEOS the silicon atom is already oxidized. Therefore the conversion of TEOS to silicon dioxide is a rearrangement rather than an oxidation. As can be seen from figure 1 what is basically required to deposit silicon dioxide is a removal of two oxygen atoms, and that to happen a relative high temperature of 725 <sup>o</sup>C is needed.     
The difference between TEOS and silane gas (used for deposition of silicon nitride) is essentially that in TEOS the silicon atom is already oxidized. Therefore the conversion of TEOS to silicon dioxide is a rearrangement rather than an oxidation. As can be seen from figure 1 what is basically required to deposit silicon dioxide is a removal of two oxygen atoms, and that to happen a relative high temperature of 725 <sup>o</sup>C is needed.     


TEOS has a very high surface mobility enabling it to fill holes that has a large aspect ratio and leaving the surface quite smooth see figure 2, hence it also covers corners and side walls very well.
TEOS has a very high surface mobility enabling it to fill holes that have a large aspect ratio and leaving the surface quite smooth see figure 2, hence it also covers corners and side walls very well.


There one standard process for deposition on the LPCVD TEOS oxide on the furnace, and this recipe is called "TEOS". On the furnace there are also two standby recipes, which are used for wafer loading and unloading. One standby recipe is called "STANDBY". The other standby recipe is called "STB-SLOW", and this is being used, if a thicker TEOS oxide layer (> 1 µm), because the furnace then has to open slowed to avoid stress and this cracks in the deposited film..
TEOS oxide has an amorphous crystal structure. If TEOS oxide is annealed, the crystal structure becomes more dense, and the thickness decreases.
 
There one standard process for deposition of LPCVD TEOS oxide on the furnace, and this recipe is called "TEOS". On the furnace there are also two standby recipes, which are used for wafer loading and unloading. One standby recipe is called "STANDBY". The other standby recipe is called "STB-SLOW", and this is being used, if a thicker TEOS oxide layer (> 1 µm) is deposited, because the furnace then has to open slower to avoid stress and thus cracks in the deposited film.


TEOS can be used as an alternative to thermally grown or PECVD oxide, but this is not at option at DTU Nanolab at the moment.


==Process parameters for the two standard deposition recipes on the TEOS furnace:==
==Process parameters for the two standard deposition recipes on the TEOS furnace:==
{| border="1" cellspacing="0" cellpadding="4"  
{| border="1" cellspacing="0" cellpadding="4"  
!Recipe name
!Recipe name
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| Process recipe
| Process recipe
|}
|}


==Deposition rate and refractive index:==
==Deposition rate and refractive index:==
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TEOS has compressive stress (around 100-300 MPa).
TEOS has compressive stress (around 100-300 MPa).


==Using LPCVD TEOS as a masking material for KOH etching==
==Using LPCVD TEOS as a masking material for KOH etching==


It is possible to use LPCVD TEOS pxide as a masking layer for KOH etching. However, it is not as suitable as LPCVD silicon nitride for deep KOH etching, as the the etch rate for TEOS oxide is higher than the etch rate for silicon nitride.
It is possible to use LPCVD TEOS pxide as a masking layer for KOH etching. However, it is not as suitable as LPCVD silicon nitride for deep KOH etching, as the the etch rate for TEOS oxide is higher than the etch rate for silicon nitride.
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