Refrigeration – Storage of solidified or liquified gas – Liquified gas transferred as liquid
Reexamination Certificate
2002-04-24
2003-10-28
Doerrler, William C. (Department: 3744)
Refrigeration
Storage of solidified or liquified gas
Liquified gas transferred as liquid
Reexamination Certificate
active
06637212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus and process for delivering a vapor phase product having a constant impurity level from a liquefied gas source to an end point. More specifically, this invention relates to an apparatus and process that delivers a liquefied gas having a level of soluble impurities from a storage container to a vaporization unit external from the storage container, whereupon the liquefied gas and the soluble impurities are completely converted to the vapor phase having a substantially equivalent (i.e., constant) concentration of said impurities as in the liquefied gas, thereby preventing the build-up of such impurities in the storage container or in the vaporization unit. The vapor phase product is then directed to a point of use such as a semiconductor fabrication tool.
2. Description of the State of Art
Electronic specialty gases (ESG's) play an important role in the production of integrated circuits. Examples of such specialty gases include ammonia (NH
3
), hydrogen chloride (HCl), hydrogen bromide (HBr), chlorine (Cl
2
), tungsten hexafluoride (WF
6
), hydrogen fluoride (HF), carbon dioxide (CO
2
), nitrous oxide (N
2
O), dicholorosilane (SiH
2
Cl
2
), phosphine (PH
3
), arsine (AsH
3
), silane (SiH
4
), disilane (Si
2
H
6
), chlorine trifluoride (ClF
3
), and boron trichloride (BCl
3
). Additional ESG's include, for example, the class of materials known as perfluorocarbons (PFC's). Processes for the production of integrated circuits using such gases include chemical vapor deposition (CVD), diffusion, reactive ion etching (RIE), plasma and thermal etching of silicon and gallium arsenide wafer surfaces, deposition of silicon nitride layers, metal organic chemical vapor deposition (MOCVD) and growth of gallium nitride films in light emitting diodes (LED's). Moisture or any other impurities in the electronic specialty gases can adversely affect the performance of all these processes. These impurities can be carried to the semiconductor fabrication tools used in these processes and consequently have a direct impact on the wafer yield.
Typically, these electronic specialty gases are stored in a storage container as compressed gases in the liquid phase under their own vapor pressure, and are used in a semiconductor fabrication tool in the vapor phase. Currently, conventional gas delivery systems require the gas to be vaporized directly within the storage container and then delivered throughout the gas distribution system. However, conventional gas phase delivery systems possess many problems due to the inability to maintain constant flow for long periods of time. Additionally, gasses delivered from conventional gas delivery systems have inconsistent impurity concentrations. The build-up of impurities within conventional gas delivery systems causes severe fluctuations in the impurity concentrations as a function of time, temperature, pressure and flow rate. These fluctuations may influence the process performance, and the build-up of impurities may reduce the amount of product usage. Furthermore, it is impossible to have a specification for a certain impurity on a fall storage container, since the concentrations of impurities change as the container is consumed.
Conventional gas delivery systems using cylinders also require frequent cylinder changes and multiple connections, which increase the probability of impurity build-up within the container, decrease the lifetime of gas manifolds, and increase the chance for accidents. Delivery systems which do not require frequent cylinder changes and which are capable of high flow rates greater than 5000 standard liters per minute will soon be required by the semiconductor industry because of the transition to larger fabrications along with introduction of 300 mm wafers. Furthermore, conventional gas delivery systems can cause the formation of liquid droplets that are entrained in the gas flowing through the gas delivery system. These entrained droplets contain contaminants that increase corrosion and lead to the failure of downstream components such as regulators, valves, mass flow controllers, and pressure transducers. Moisture in corrosive gases can farther lead to metallic particulate contamination within the gas distribution system, which has a direct impact on the wafer yield.
U.S. Pat. No. 5,644,921 discloses an apparatus for storing ultra-high purity non-cryogenic liquefied compressed gases and a method for delivering a vaporized gaseous product produced from the liquefied gas for semiconductor process applications. The delivery method includes withdrawing and heating a gaseous product from a storage vessel containing the liquefied compressed gas, then piping the heated gas through the liquid contained in the storage vessel in a heat exchange fashion.
U.S. Pat. No. 6,032,438 describes a method and a system for the delivery of a vapor phase product to a point of use and an on-site chemical distribution system and method. The system includes a storage vessel containing a liquid chemical under its own vapor pressure, a column connected to receive the chemical in a liquefied state from the storage vessel where the chemical is fractionated into a contaminated liquid heavy fraction and a purified light vapor fraction, and a conduit connected to the column for removing the purified light vapor fraction therefrom. This system requires that the residual contaminated liquid be periodically drained.
U.S. Pat. No. 5,894,742 describes a method and system for delivering an ultra-high purity gas to a point of use. The method involves transporting an ultra-high purity pressurized liquid from a container to a phase change device (i.e., an evaporator) where the pressurized liquid-phase gas is converted into the gas phase, and delivering the gas to a point of use. The flow of liquid into the evaporator is controlled by sensors that maintain the liquid level in the evaporator to about 70% of total capacity. In this type of evaporator, the impurities dissolved in the liquid phase build up in the evaporator, similar to conventional gas phase delivery systems. The phase change device of this system does not allow for 100% vaporization since a pool of liquefied gas constantly resides in the evaporator. This system also requires the whole system, including the bulk container, the distribution conduits, and the evaporators to be totally emptied of its liquid content periodically. The entire system must then be carefully cleaned and purged before being refilled with fresh product. The purpose of this periodical maintenance is to discard the growingly impure liquid phase chemical from the system. Thus, the build up of the soluble impurities and subsequent elimination of a portion of the liquid phase chemical ultimately causes the consumer to discard 10-30% of the original amount of the liquid chemical.
Conventional vaporizers, which are used for the vaporization of liquefied gases in the semiconductor industry, may be classified as follows: (i) a heating medium separated from the evaporating liquid by tubular heating surfaces, (ii) a heating medium confined by coils, jackets, double walls, flat plates, etc., (iii) a heating medium brought into direct contact with evaporating liquid, and (iv) heating by solar radiation (see, Perry and Green, Chemical Engineer's Handbook, 1984). Delivery systems that allow the evaporating liquid to be stored in a storage tank, where the evaporating liquid is not effectively in contact with the heating medium, work by principles very similar to a conventional gas delivery system. The liquefied gas undergoes a single plate distillation within the vaporizing device and is only partially vaporized. Therefore, this kind of vaporizer causes the concentration of impurities to change with time. Conventional vaporizers, which are used for the vaporization of liquefied gases in the semiconductor industry, are of this kind, i.e., they only partially vaporize the liquefied gas. Therefore, with conventional vaporizers, it is difficult to del
Giagnacova Joseph
Torres, Jr. Robert
Vininski Joseph V.
Yucelen Belgin
Doerrler William C.
Hogan & Hartson LLP
Matheson Tri-Gas
O'Rourke Sarah
Petersen Steven C.
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