Specific Process Knowledge/Thin film deposition/Deposition of Silicon Oxide/Deposition of Silicon Oxide using LPCVD TEOS: Difference between revisions
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<i> Unless otherwise stated, this page is written by <b>DTU Nanolab internal</b></i> | <i> Unless otherwise stated, this page is written by <b>DTU Nanolab internal</b></i> | ||
==LPCVD TEOS | ==LPCVD TEOS oxide deposition== | ||
[[Image:teos1.jpg|300x300px|thumb|Figure 1: TEOS molecule structure]] | [[Image:teos1.jpg|300x300px|thumb|Figure 1: TEOS molecule structure]] | ||
[[Image:TEOS.jpg|300x300px|thumb|Figure 2: LPCVD TEOS oxide deposited on Si trenches]] | [[Image:TEOS.jpg|300x300px|thumb|Figure 2: LPCVD TEOS oxide deposited on Si trenches]] | ||
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 is a Tempress horizontal furnace, and it was installed in the cleanroom in 1995. | ||
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. | 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. | 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). | ||
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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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)'' | ||
Carbon can be incorporated in the | Carbon can be incorporated in the TEOS oxide layer, but this can be reduced by an annealing - see below. | ||
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 | 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. | ||
TEOS | 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 oxide has an amorphous crystal structure. If TEOS oxide is annealed, the crystal structure becomes more dense, and the thickness decreases. | 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. | ||
There one standard process for deposition of LPCVD TEOS oxide on the furnace, and this recipe is called "TEOS". | There is one standard process for deposition of LPCVD TEOS oxide on the furnace, and this recipe is called "TEOS". The Thin Film group will have to be involved, if the depositions have to done with other process parameters. The exact TEOS flow is unfortunately not know, but it is expected to be much higher than the setpoint, because the MFC is not calibrated for TEOS (it has not been possible to buy a correctly calibrated MFC). | ||
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. | |||
==Process parameters for the two standard deposition recipes on the TEOS furnace:== | ==Process parameters for the two standard deposition recipes on the TEOS furnace:== | ||