Patent Application
20080044572
In the annexed drawings:
The present invention provides a method and system for purifying precursor materials prior introduction into a high purity fluid processing application such as, for example, chemical vapor deposition. In general, the method includes providing a precursor material having one or more impurities and distilling the precursor material to produce, as a distillate, a purified precursor material.
An exemplary method and system for purifying a precursor material may be understood with reference to
The purified precursor material may then be transported to a high purity fluid processing application such as, for example, a chemical vapor deposition system. As shown in
Distilling the precursor liquid may be accomplished by any suitable distillation technique. The distillation step may include simply heating the precursor material to a desired temperature and collecting, as a distillate, a purified precursor material. The distillation step may also include heating the precursor material to a first temperature below the boiling point of the precursor material (at a selected pressure), and then subsequently heating at a second temperature at about the boiling point of the precursor material (at a selected pressure). The distillate produced at the first, lower temperature may be collected along with the distillate from the distillation at the second temperature as purified precursor material. Alternatively, the distillate at the lower temperature, which may include lower boiling components, may be discarded (such as by evacuation or sent to the waste receptacle). It is not necessary to form an azeotropic mixture in the precursor material and then distill the precursor via azeotropic distillation to obtain a purified precursor material in accordance with the present invention.
The distillation may be carried out at any suitable temperature depending on the boiling point of the precursor material being used. The pressure inside the distillation vessel may be adjusted to lower the boiling point of the precursor material to prevent degradation of the precursor. The distillation vessel may be evacuated to provide a pressure below atmospheric pressure (760 torr) such as, for example, below about 200 torr, below about 150 torr, below about 100 torr, below about 50 torr, or even lower.
Additionally, the distillation vessel may be purged to remove oxygen from the system and apply a blanket of inert gas over the precursor liquid to prevent oxidation of the precursor. Suitable inert gases include, but are not limited to, nitrogen, helium, and the like.
Referring back to
Precursor material is then distilled, and purified precursor vapor is condensed in the condenser 120 and passes through the line 124 to receivers 128 and 134. The valve 126 may be used to control the flow of purified precursor material to receivers 128 and 134 through lines 130 and 136, respectively. Receivers 128 and 134 may include a level sensor (e.g., level sensors 132 and 138, respectively, and upon reaching a desired level in a receiver, the valve 126 may be closed to stop the flow of purified precursor liquid to one of the receivers. Generally, the receivers are filled one at a time.
The system may contain a gas inlet or delivery line 170 in fluid communication with a gas source 168 and receivers 128 and 134 through delivery lines 176 and 178, respectively. The system may also include valves 172 and 174 to control the flow of gas into the receivers 128 and 134, respectively. After receivers the 128 and 134 are filled to a desired level with purified precursor material, the receivers may be pressurized by applying a gas blanket from the gas source 168 over the liquid in the receiver. The gas and pressure in the receiver may facilitate the flow of purified precursor from the receivers to the chemical vapor deposition apparatus. The gas applied to the receiver may be any suitable gas including, for example, helium, argon, hydrogen, and the like. A CVD apparatus typically employs a push pressure gas, such as helium, to facilitate the flow of precursor material whereby the carrier gas is mixed with the liquid precursor prior to entering a vaporizer or whereby the carrier gas is mixed with precursor vapor after the liquid precursor has been vaporized in a vaporizer. The apparatus shown in
Purified precursor may be delivered to the chemical vapor deposition apparatus 148 by opening a delivery valve 144 to allow the purified precursor to flow through lines 140 or 142 through an outlet or delivery line 146 to the chemical vapor deposition apparatus. The purified precursor material is pushed from the pressurized receivers 128 or 134. To provide a continuous flow of purified precursor to the chemical vapor deposition apparatus, the purified precursor material is generally delivered from one receiver at a time. When the purified precursor is depleted to a selected volume, the system is transitioned to deliver precursor from the other receiver. For example, after supplying purified precursor material from receiver 128 and reaching a selected low level of purified precursor, the valve 144 is opened to line 142 to allow purified precursor from receiver 134 to flow into the outlet/line 146. For a selected period of time, the valve 144 also may remain open to the line 140 such that purified precursor is delivered from both receiver 128 and receiver 134. After the transition period, the delivery valve 144 is closed to line 140 and purified precursor is delivered solely from receiver 134.
A substantially continuous flow of purified precursor material may be provided by refilling the receiver having a depleted volume of purified precursor material while another full receiver delivers material to a CVD apparatus. For example, while purified material is being delivered from receiver 134, receiver 128 may be conditioned (such as by applying a vacuum to the receiver to provide a desired low pressure) and refilled by distilling precursor material and directing the flow into receiver 128. If necessary, the distillation vessel may be conditioned (e.g., by emptying any waste and evacuating the distillation vessel to provide a desired pressure level) and refilled with bulk precursor material prior to refilling an empty receiver. When the receiver 134 reaches a desired low level of precursor material, the system may be transitioned to deliver purified material from refilled receiver 128, and receiver 134 may then be refilled. To provide a substantially continuous flow, it may be desirable that the flow rate of the distillation process be about equal to the flow rate of purified precursor material to the high purity fluid processing system.
After distilling the precursor material, the distillation vessel may contain some undistilled material and waste residue. With reference to
The distillation system may be automated and include any sensors (e.g., level sensors 112, 132, and 138 for monitoring the level of liquid in the distillation vessel and the receivers, spill sensors, leak sensors, or the like), temperature probes (e.g., probes 114 and 118), pneumatic banks (e.g., pneumatic control bank 180), and management of clean dry air for pneumatically actuated valves, interlocks, tubing, hardware (e.g., touch screen 182 and programmable logic controller 184), software, and/or circuitry necessary to operate the system and provide high purity liquid to meet the desired requirements of the high purity fluid processing system (e.g., chemical vapor deposition tool). The distillation system could be programmed as desired to control the operation of the system such as, for example, automatically supplying precursor material to the distillation vessel. As another example, the distillation of a precursor material could be stopped upon reaching a selected low level of material in the distillation vessel and not restarted until a signal is received that a receiver is at a selected low volume of purified precursor material and needs to be refilled.
As shown in
As shown in
It will be appreciated that the distillation system does not have to be connected to a chemical vapor deposition apparatus. Rather, the distillation system may serve as a “filling station” to collect purified precursor material in a receiver. A receiver could be disconnected from the distillation system and moved to a desired location where it may be hooked up for local delivery of purified precursor material.
The precursor material may be any material as desired for a particular purpose or intended use. A particularly suitable class of precursor materials includes silicone based precursors. Suitable silicone based precursors include, but are not limited to, alkyl silanes alkoxy silanes, siloxanes silsesquioxanes, and the like. An example of a suitable alkoxy silane is tetraethoxysilane (TEOS). Suitable silsesquioxanes include, for example, polyhedral oligomeric silsesquioxanes. Suitable siloxanes include, but are not limited to, cyclosiloxanes such as, for example, octamethylcyclotetrasiloxane, hexamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, and the like. The method in accordance with the present invention may remove non-volatile impurities from such materials, which may prevent clogging of components in a CVD apparatus.
Prior to purification the precursor material by a method in accordance with the present invention, the bulk precursor material may have a purity, on a metals basis, of about 98% or higher, about 99% or higher, about 99.5% or higher, or even about 99.99% or higher. The method in accordance with the present invention allows a processor to purchase bulk precursor material of a relatively low purity (e.g., 98%) and purify the material as needed to supply to the processing system. Higher purity materials are generally more expensive, thus by purifying “on site” the cost of starting materials may be reduced.
TEOS having a purity of 98% is purified via vacuum distillation as follows: TEOS is charged to a flask (distillation vessel) equipped with a condenser, which is connected to a receiver. The flask is evacuated and a nitrogen blanket is applied over the TEOS in the flask to provide a reduced pressure of about 0 to about 50 torr. The flask is heated to distill the TEOS and the boiling point of the TEOS is 45-47° C. After distillation, a residue is obtained in the distillation vessel and the distillate collected in the receiver is a purified TEOS.
Samples of TEOS are flowed through a D2000i series liquid mass flow controller available from Porter Instruments (Hatfield, Pa.). Pre-distilled, 98% pure TEOS is utilized as a control and is flowed through the controller. After flowing the control TEOS through the controller, the controller contains some crystals or oily residue, which could clog the controller. After the purified (distilled) TEOS precursor material is flowed through the controller, the controller does not contain any significant amount of crystal material or oil residue.
It is anticipated that certain changes may be made in the present invention without departing from the precepts involved herein. It is intended that all matter contained in the foregoing description shall be interpreted as illustrative and not in a limiting sense.
The present application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/822,401, filed Aug. 15, 2006, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60822401 | Aug 2006 | US |
