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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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In the furnace LPCVD TEOS oxide can be deposited on up to 15 4" wafers. It is not possible to deposit TEOS oxide on 6" wafers in he cleanroom.  
In the furnace LPCVD TEOS oxide can be deposited on up to 15 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 <sup>o</sup>C, and TEOS is then vaporized and introduced into the furnace. The TEOS flow is controlled by an MFC (mass flow controller).  
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>. The molecular structure can be seen figure 1. 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. The TEOS flow is controlled by an MFC (mass flow controller).  


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 there:


Si(C<sub>2</sub>H<sub>5</sub>O)<sub>4</sub> ''(l)'' → SiO<sub>2</sub> ''(s)'' + 4 CH<sub>2</sub>H<sub>4</sub> ''(g)'' + 2 H<sub>2</sub>O ''(g)''
Si(C<sub>2</sub>H<sub>5</sub>O)<sub>4</sub> ''(l)'' → SiO<sub>2</sub> ''(s)'' + 4 CH<sub>2</sub>H<sub>4</sub> ''(g)'' + 2 H<sub>2</sub>O ''(g)''
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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 for that to happen a relative high temperature of 720 <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 for that to happen a relative high temperature of 720 <sup>o</sup>C is needed.     


The TEOS molecules have 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. However very small nanometer trenched and/or very deep trenches will be challenging to fill.
TEOS molecules have a very high surface mobility enabling the TEOS oxide 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. However very small nanometer trenched and/or very deep trenches will be challenging to fill.


TEOS oxide has an amorphous crystal structure. If TEOS oxide is annealed at a high temperature, ~720 <sup>o</sup>C, the crystal structure becomes more dense, and thus the thickness decreases. The quality of an annealed TEOS oxide film is actually almost similar to the quality of a thermal oxide film.
TEOS oxide has an amorphous crystal structure. If TEOS oxide is annealed at a high temperature, ~720 <sup>o</sup>C, the crystal structure becomes more dense, and thus the thickness decreases. The quality of an annealed TEOS oxide film is actually almost similar to the quality of a thermal oxide film.
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