Patent Application
20090293807
The present disclosure relates to an apparatus for removing particles from a gas/vapor mixture stream while at the same time improving the uniformity of the thin film being formed on a substrate. The apparatus is particularly useful for fabricating integrated circuit devices on silicon and other semiconducting wafers. It is suitable for a variety of thin film deposition processes, including chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma enhanced CVD (PE-CVD) processes, among others. In these processes a liquid precursor is often vaporized to form vapor in a carrier gas. The resulting gas/vapor mixture is then introduced into a deposition chamber for thin film deposition on a substrate.
Vaporization of a liquid or solid precursor to form vapor is often accompanied by the formation of particles. These particles can range in size from a few nanometers (nm) in diameter to hundreds or thousands of nanometers. Particles carried by the gas/vapor mixture stream from a vaporization apparatus into the deposition chamber can deposit on the wafer surface to cause harmful effects, including the loss of product yield. Particulate contamination is a major cause of product yield loss in semiconductor device fabrication. Left uncontrolled, particle contamination can severely impact the productivity and profitability of the semiconductor device fab.
One known method of reducing particulate contamination of wafers is to place a filter in the process gas stream to remove particles and prevent them from being carried by the gas/vapor stream into the deposition chamber. Precursor vaporization systems such as those described in U.S. Pat. No. 6,409,839 includes a filter for particle removal, thus insuring that the output gas/vapor mixture will be substantially free of particulate contaminants. Since hot vapor can condense in a cold filter, the filter must be heated. The vaporization apparatus described in U.S. Pat. No. 6,409,839 has a built-in filter that is heated to substantially the same temperature as the vaporizer system itself, thus minimizing potential vapor condensation on an unheated or insufficiently heated filter.
Another aspect of the vaporization process is the need to have a gas/vapor mixture that is uniform in gas/vapor composition across the mixture stream. Non-uniform mixing of the gas and vapor can create variation in the mixing ratio of the gas and vapor that can lead to thickness variations in the deposited film. When hundreds, or even thousands, of integrated device chips are made on a single 300-mm diameter wafer, variation in film thickness across the wafer or from wafer to wafer will cause variation in the device quality, sometimes causing device failure that can lead to a product yield loss.
The present disclosure relates to an apparatus for removing particles from a gas/vapor mixture while at the same time improving the uniformity of gas/vapor mixture to create a more uniformly-mixed mixture stream for thin film deposition and semiconductor device fabrication.
In one embodiment of the apparatus, a filter is placed inside an enclosure designed to promote the uniform mixing of the gas and vapor while the mixture stream passes through the apparatus for particle removal. The enclosure is electrically heated and provided with a temperature sensor to permit the enclosure and the filter enclosed therein to be heated to a substantially uniform temperature to prevent vapor condensation in the apparatus. Mixing is created by centrifugal force by forcing the gas/vapor mixture stream to undergo a change in flow direction without using any external power or moving parts. Mixing is also created by using a turbulent jet formed within the filtration apparatus.
In the preferred embodiment, the inlet and outlet tubes are perpendicular to the cylindrically-shaped enclosure and designing the apparatus in such a manner as to cause the gas/vapor mixture to undergo two right angle turns of approximately 180 degrees in the total angular change in flow direction to create the needed centrifugal force for mixing. It also uses a turbulent jet to further enhance the mixing of the gas and vapor.
In another embodiment, the apparatus has internal passageways that cause the gas stream to undergo a total of six right-angle turns of approximately 90 degrees each, for a total cumulative directional change of 540 degrees.
Yet in another embodiment, two parallel filtration and mixing systems are incorporated into the same apparatus to provide twice the flow capacity of a single filtration and mixing system.
The thin film deposition system shown generally at 50 is comprised of a deposition chamber 55 containing a wafer 50 on which thin film is to be deposited. Commonly used deposition processes used for fabricating integrated circuit device chips on wafers include CVD, PE-CVD, ALD, among others. The deposition chamber 55 is provided with an inlet 60 through which the gas/vapor mixture can enter and an outlet 65 through which the gas/vapor mixture can exit to the vacuum pump 70 located downstream of the deposition chamber. The system is usually provided with electronic controls so that the chamber can be maintained at a proper pressure, and the wafer contained therein and the chamber itself can be maintained at their respective temperatures suitable for the optimal formation of thin films on the wafer.
For the proper functioning of the apparatus, diameter, D1, of orifice 150 must not be too small or too large compared to the diameter, D2, of the inlet passageway 130. A small D1 will provide good mixing, but can cause too high a pressure drop. A large D1 will reduce the overall pressure drop through the apparatus, but may provide inadequate mixing of the gas/vapor mixture stream. For the proper functioning of the apparatus the ratio D1/D2 is usually kept between approximately 0.5 and 2.0. Similarly, the ratio D3/D4 of the diameter, D3, of orifice 160 and the diameter, D4, of the exit flow passageway 140, is also kept within proper limits, typically between approximately 0.5 and 2.0.
The apparatus is generally provided with an electric heater 170 and a temperature sensor 180. By means of electronic controls (not shown), the entire apparatus can be heated to a suitably high and substantially uniform temperature to prevent vapor condensation inside the apparatus. The operating temperature of the apparatus is usually the same or somewhat higher than the set-point temperature of vaporizer 10 shown in
Since thin film deposition often occurs under vacuum conditions, the entire apparatus must also be vacuum tight to prevent leakage of ambient air into the system. To meet these requirements, the apparatus is usually constructed of stainless steel and all parts are welded together to permit high temperature and vacuum tight operations.
In the absence of apparatus 100 of the present disclosure placed between the vapor generation system 40 and the film deposition system 50 in
In gas flow through circular tubes, the nature of the gas flow is determined by the Reynolds number. The Reynolds number, Re, is defined as:
where V is the velocity of the gas through the tube, D is the diameter of the tube, ρ is the density of the gas, and μ is the viscosity of the gas. For example, for a gas flow of 1 standard liter per minute (slm) of nitrogen through a tube of ½″ in diameter, the Reynolds number is approximately 100. In fluid flow through tubes, the transition from laminar to turbulent flow will usually occur around a Reynolds number of 2300. A Reynolds number below 2300 will usually lead to a laminar flow in the tube. A Reynolds number above 2300 will usually cause fluid turbulence to develop leading to a turbulent flow in the tube. At the Reynolds number of 100, the flow is thus laminar.
Gas flow in thin film deposition apparatus can be higher than the 1.0 slm value cited in the above example. In some processes, gas flow can be as high as 10 slm. Even at 10 slm the Reynolds number is still around 1,000. The flow is likely to remain laminar. Only when the gas flow reaches the >20 slm range, condition of turbulent flow may develop.
In laminar flow, gas and vapor cannot mix effectively. Mixing can still occur through the process of molecular inter-diffusion. But molecular inter-diffusion is a much slower process than turbulent mixing and often would not be sufficient to provide the truly uniform mixing requirements of the semiconductor industry involved in the high volume commercial fabrication of integrated circuit devices.
In the apparatus of
In order to heat the enclosure 110 uniformly, a band heater is used for 170. The band heater is made in the form of a metal band with a gap 115 allowing it to be placed around the enclosure 110 and tightened by screws (not shown) tightly around the enclosure. This creates good thermal contact between the heater and the enclosure to improve the thermal response of the system.
This disclosure describes a basic approach to designing filtration and mixing apparatus based on an understanding of the requirements of thin film deposition and semiconductor integrated circuit device fabrication and a fundamental understanding of the fluid mechanics of filtration and fluid flow. Those skilled in the art of filter and filtration system design will recognize the improvements that have been made in this disclosure based the approach and apply it to other possible designs that do not fundamentally differ from the one described here. These addition possible designs will not be further described.
The present application is based on and claims the benefit of U.S. provisional patent application Ser. No. 61/057,271, filed May 30, 2008, the content of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61057271 | May 2008 | US |
