Modeling of Chemical Vapor Deposition of Tungsten Films

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Reaction efficiency is high, what results in high deposition rate and low gas consumption. Also the gas cost is low.

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There are less toxic gases and the overall quality of the tungsten film may be improved with respect to the prior art two step methods. During the tungsten deposition, hydrogen is preferably supplied with a flow rate of to sccm.

The invention will now be described by way of example and with reference to the accompanying drawings in which:. The deposition according to the invention of a tungsten W film on a substrate, more particularly a wafer 1 of semiconductor material, such as silicon, already covered with an insulating silicon oxide layer and an intermediate layer of TiN, is carried out in a commercially available chemical vapor deposition chamber 2 which is mounted in a deposition system.

In this system, the deposition chamber 2 has a vacuum port 3 coupled to a vacuum pump 4 through a pressure control device 5. The system comprises a number of supply lines 6 - 10 coupled to specific sources not shown for supplying respectively tungsten hexafluoride WF 6 , reducing gas hydrogen H 2 , reducing gas silane SiH 4 , inert carrier gas argon Ar , and carrier gas nitrogen N 2. The flow rate of gas through these supply lines 6 - 10 is controlled by flow controllers In order to avoid reduction of the WF 6 outside the chamber 2 , the supply lines 6 and 7 for WF 6 and the carrier gas N 2 , respectively are coupled to a manifold 12 , while the supply lines 8 , 9 and 10 for SiH 4 , H 2 and Ar, respectively are coupled to a second manifold Both manifolds 12 and 13 supply a distribution head 14 inside the chamber 2 through a common gas line Inside the deposition chamber 2 , a support 16 having a bottom and upstanding edges is installed.

Between the edges and the bottom, channels 17 may traverse the support 16 , which channels 17 are connected to supply lines 18 for so-called edge gases, more particularly a mixture of controlled flow rates of H 2 and Ar, ensuring the same thickness of the tungsten film at the edges of the wafer 1 as in the center. A heating means 19 , for instance a heating resistance, is incorporated in the support 16 for heating the wafer 1.

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In step 21 , the chamber 2 is pumped down through the vacuum port 3 until a predetermined base pressure, which is for instance less than 0. After this, in step 23 , the chamber 2 is pressurized with inert gases Ar and N 2 , provided through the lines 10 and 7 , to a pressure from 0. As soon as the wafer I is placed on the support 16 , it is heated to a temperature of to 20 C. The heating has been indicated in FIG. In fact, the heating means 19 are activated from the start of the method and as long as wafers 1 are subsequently covered by a film of tungsten. In a single step 25 , a layer of W is deposited by opening the mass flow controllers 11 in the supply lines 6 and 7 so that WF 6 is mixed with a flow of N 2 in the manifold 12 , while the flow controllers 11 in the supply lines 8 , 9 and 10 are opened and SiH 4 and H 2 gases are mixed in the manifold 13 with a flow of Ar.

Consequently, a mixture of hydrogen Ar, N 2 , H 2 , WF 6 and SiH 4 is supplied through the common supply line 15 and the distribution head 14 to the chamber 2. The mass flow controllers 11 determine the flow rate of the different gases. Flow rates of Ar and N 2 are not critical and Ar may for example be dispensed at flow rates from to sccm and N 2 at flow rates from 10 to sccm. These flow rates may be higher during the pressurization step 23 than during the deposition step. These limits are important as a flow rate of WF 6 lower than 30 sccm results in a decreased step coverage, as well as a flow rate higher than 60 sccm causes a loss of reaction efficiency.

Too much SiH 4 will result in a WF 6 gradient in the hole or trench, decreasing the step coverage.

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H 2 is supplied with a flow rate from to sccm. This flow rate is not critical. If, as shown, the support 16 is provided with channels 17 , during step 25 , an edge flow from 0 to sccm H 2 added to a flow of Ar is supplied through these channels These flow rates are continuous and are maintained until the film of W has the required thickness. The gases which do not react on the wafer 1 are pumped away through port 3.

The pressure control device 5 ensures that the above mentioned pressure from 0. These limits are critical since at a pressure lower than 0. After the required thickness is obtained, the chamber 2 is purged in step 26 with Ar and N 2 gases, the flow rates of which may be higher than during the deposition step 25 , after which the chamber 2 is pumped down in step The chamber 2 may again be purged with Ar and N 2 and is then ready to be pumped down for another depositing a W film on another wafer 1 and the above mentioned steps may be repeated.

The complete deposition of W takes places in one step.

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There is only one pressure during deposition and consequently no pressurizing step between depositions. Only one set of gas settings is required. The flow rates of WF 6 and SiH 4 are critical and adjusted by relatively expensive mass flow controllers 11 which are difficult to calibrate. As the flow rate does not have to be changed during the tungsten deposition, one flow controller for each of these gases is sufficient.

In the known two-step methods, two controllers are needed for the WF 6 as there is a low flow and a high flow, which is more expensive. In a first step 21 the chamber 2 is pumped down to a pressure of 0. In a following step 23 , the chamber 2 is pressurized at a pressure of approximately 4. A H 2 edge flow of approximately 50 sccm is supplied through channels 17 in order to obtain a more uniform tungsten film.

The chamber 2 is purged with sccm Ar and scam N 2 and pumped down to a pressure of 0, kPa, and the wafer 1 is removed. The deposition time was Stress and reflectivity were good. Although no additional advantages could be found if a SiH 4 soak step is used, such step may be used between the step 23 and the depositing step This pre-nucleation step is much shorter, for example 1 to 7 seconds compared to the nucleation step in the known methods which take about 20 seconds. It is also important to remark that the pressure during the pre-nucleation and the deposition step remains the same.

Thereby an extra step is avoided resulting in a simple deposition system.

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Step coverage and growth rate were investigated. During these experiments WF 6 flow was varied between 20 and 60 sccm, and SiH 4 flow varied between 10 and 30 sccm. Pressure was kept at 4 kPa 30 Torr , deposition temperature was degrees C.

  1. Modeling of Chemical Vapor Deposition of Tungsten Films.
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  5. Results are shown in FIGS. In FIG.

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    These results are indicated with an asterisk. Step coverage becomes excellent from ratios above 3. The layer thickness D, shown in FIG. Highest deposition rates are thus obtained with the highest flow rates. While the principle of the invention has been described above in connection with the described examples, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention. Effective date : Year of fee payment : 4. Fingerprint Tungsten. Chemical vapor deposition.

    Aspect ratio. Computer simulation. Keywords Chemical vapour deposition Tungsten Modelling Voids solid Surface topography Integrated circuit technology Metallic thin films. Journal of the Electrochemical Society , 7 , Schmitz, J. In: Journal of the Electrochemical Society. In: Journal of the Electrochemical Society , Vol. AU - Hasper, A. PY - Y1 - N2 - In this study, computer modeling of the contact fill process with chemical vapor deposition, CVD of tungsten is usedto show the importance of several details on the quality of the fill process.

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