KR20110022734A - A method and apparatus for monitoring liquid levels within a vessel - Google Patents

Abstract

A method and apparatus for monitoring the level of an organometallic compound in a liquid level, in particular in a bubbler, inside a vessel. The metal probe 10 is sealed to the mounting portion sealed in the opening of the container 2. The portion of the probe that is sealed inside the mount is made of nickel alloy and surrounded by a glass material by a metal-glass bond seal.

Description

METHOD AND APPARATUS FOR MONITORING LIQUID LEVELS WITHIN A VESSEL}

FIELD OF THE INVENTION The present invention relates to metrology probes and, more particularly, to probes for monitoring levels of reactive liquids, such as metalorganic compounds in a container.

Metal thin films are deposited on solid substrates for use in the electronics or optoelectronics industries by a process known as organometallic chemical vapor deposition (MOCVD). The metal precursor is usually delivered to the substrate by a bubbler. The bubbler comprising the metal precursor material has an inlet tube, a dip tube, and an outlet tube. Carrier gas, such as hydrogen, helium or nitrogen, is introduced into the vessel through the inlet tube and delivered to the bottom of the vessel through the dip tube. The gas may pick up a portion of the vapor of the metal precursor before leaving the bubbler through the discharge tube. The gas transports the precursor vapor to the side of the reactor where the precursor decomposes to deposit metal on the solid substrate.

The amount of precursor material in the bubbler varies constantly with the use of the device. Conventional probes cannot be used because organometallic compounds erode the probes. This also causes contamination of the precursors. The volume of precursor in the bubbler can be measured by single point measurements for high and low charge levels based on optical systems. However, because the glass tube is used for this measurement, the contents of the bubbler become contaminated when broken. Alternatively, the bubbler may be provided without an accurate level indicator, in which the level is lowered or changed by calculation over time of use under certain conditions. This results in early replacement of the bubbler even when 10% of the material remains in the bubbler.

Therefore, there was a need to provide an accurate probe for monitoring the level of organometallic precursor contained within the bubbler. However, in providing an appropriate probe, its strength and compatibility with the organometallic compound in contact with it have emerged as a problem. In this regard, the probe should not react with the chemicals contained within the vessel so that high purity metal deposits can be obtained. Also, the contents of the bubbler must not be damaged because the contents are sensitive to air and the pressure inside the container must be maintained.

It is an object of the present invention to provide a method for continuously monitoring the level of a reactive liquid in a container, specifically the level of an organometallic compound, to solve the above problems.

Another object of the present invention is to provide an apparatus for continuously monitoring the level of the reactive liquid in the container, specifically the level of the organometallic compound, to solve the above-mentioned problem.

Accordingly, a first aspect of the invention provides a method of monitoring the level of organometallic compound in a container, the method comprising at least one end surrounded by a glass material inside the container to serve as a first electrode. Inserting one metal probe, sealing one end of the probe enclosed with glass material within the vessel, spaced apart from the first electrode to form a capacitor, providing an additional electrode, a current in the capacitor Applying a; and monitoring the capacitance of the capacitor.

A second aspect of the present invention provides an apparatus for monitoring the level of liquid in a vessel, the apparatus being at least one metal probe, a capacitor sealed inside the vessel and acting as a first electrode, one end of which is surrounded by glass material. A second electrode spaced apart from the first electrode, a means for applying a current to the capacitor, and a means for monitoring the capacitance of the capacitor to form a.

The two spaced apart electrodes are provided to set the required dielectric constant therebetween. The capacitance of the capacitor thus formed will vary with the amount of liquid between the probes and thus the liquid level inside the vessel can be monitored.

The container itself is preferably a metal container, for example stainless steel, and serves as the second electrode. Alternatively, two parallel probes may be sealed inside the device to act as first and second electrodes, respectively.

The metal probe inserted into the vessel may be in the form of a rod, a flat and elongated plate, or a tube. The probe can be hollow or solid. The probe is preferably made of stainless steel.

The probes according to the invention are particularly suitable for use in monitoring the levels of organometallic compounds.

The probe is attached to an opening at the top of the vessel, and the vessel is preferably in the form of a bubbler comprising an inlet tube and an outlet tube. One end of the probe is preferably surrounded by a glass material and sealed inside the opening. The probe is preferably sealed inside a mount or cap that is inserted into the opening of the container. The mounting preferably has an electrical connection for the probe, for example a bayonet type connector such as a BNC connector.

At least a portion of the probe extending from the seal is coated with an elastic material, such as Teflon ^™ .

At least a portion of the probe surrounded by the glass material to form a metal-glass seal preferably comprises a nickel alloy, more specifically 70% nickel. The alloy is preferably capable of precipitation hardening by addition of aluminum and / or titanium. Suitable alloys include those sold under the trade names Inconel X-750, Inconel 600 or Kovar, preferably using Inconel X-750 alloy. The glass sealed around this portion of the probe is preferably borosilicate glass. The probe to be sealed in the glass is preferably by such a corresponding seal.

The glass material can then be sealed inside the mount. The mounting portion preferably comprises a nickel alloy such as Inconel X-750. The mounting portion preferably integrates the inner face with a gasket face seal fitting, such as a VCR profile at the connection face, to suit the electrical connector and the glass-metal seal. The gasket is preferably deformed and tightened to provide a reliable metal-metal seal. The electrical connector is preferably surrounded by a layer of insulation, such as polyether ether ketone (PEEK).

Along with monitoring means, such as a capacitance meter for measuring capacitance change, conventional means for applying alternating or direct current power to the probe can be provided. It is also desirable to provide a recorder for recording the change in capacitance. The recorder may comprise display means such as a liquid crystal display. It is desirable for the capacitance to be monitored continuously so that the liquid level in the vessel is read continuously.

The apparatus of the present invention preferably comprises means for calibration of the system so that a specific capacitance corresponds to a specific volume of liquid inside the container. For example, the recording means may be set such that the depleted container is set such that the value of the capacitance is recorded as "0" and the filled container is set such that the value of the capacitance is recorded as "100". The device preferably calibrate the device to respond to the properties of the liquid contained within the container. The apparatus may also be adapted to provide a rate of decrease or increase of liquid to the container.

A preferred embodiment of the present invention provides a bubbler comprising an organometallic compound, the bubbler comprising a sealed metal container having an inlet tube, an outlet tube and a dip tube, sealed inside the container and having one end of the glass material. It further includes a metal probe surrounded by a vessel, a vessel and a probe forming a capacitor, means for applying a current to the capacitor and monitoring means for measuring capacitance.

Preferably, the metal probe can be sealed inside the bubbler as described above.

1 is a schematic diagram of a device fitted with a probe according to an embodiment of the present invention.
2 is a cross-sectional view of a probe included in the device of FIG. 1.
3 is a graph showing the level change of TMG in a bubbler measured over time using the apparatus shown in FIGS. 1 and 2.
4 is a graph showing the level change of TMA in a bubbler measured over time using the apparatus shown in FIGS. 1 and 2.
5 is a longitudinal sectional view of a probe according to another embodiment of the present invention.
6 is a cross-sectional view of the probe shown in FIG. 5.
FIG. 7 is a graph showing the level change of TMA in a bubbler measured over time using the apparatus shown in FIGS. 5 and 6.
FIG. 8 is a graph showing the level change of TMG in the bubbler measured over time using the apparatus shown in FIGS. 5 and 6.

DETAILED DESCRIPTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings in order to better understand the contents of the present invention and to clarify the effect thereof. Example 1 contemplates using a device according to one embodiment of the invention in measuring the level change of trimethylgallium (TMG) in the bubbler, and Example 2 shows the level change of trimethylaluminum (TMA) in the bubbler. Considering the use of the same device in the measurement, Example 3 considers using the device according to another embodiment of the invention in measuring the level change of the TMA in the bubbler, and Example 4 in the bubbler. It is considered to use the same apparatus to measure the level change of the TMG.

1 and 2 show an apparatus for continuously monitoring the levels of organometallic compounds in a container, such as a bubbler, according to a first embodiment of the invention. The bubbler 2 has an injection tube 4, an immersion tube 6 connected to the injection tube 4, and an discharge tube 8. In the center of the bubbler container is provided a metal probe 10 extending in the longitudinal direction. The top of the probe is surrounded by a glass layer 12 and sealed to the top of the bubbler to ensure that the pressure inside the bubbler is maintained and that the contents of the bubbler are isolated from air. The lower end of the probe immersed in a precursor contained in the container is coated with an inert heat-resistant material such as polytetrafluoroethylene (PTFE) or other elastic material. The upper portion of the probe is connected to an electronic controller, which communicates with a monitoring device that includes a power supply and reads and displays the liquid level in the bubbler.

Example 1

This study was conducted to demonstrate the performance of the device according to the first embodiment of the present invention for continuously monitoring the level of trimethylgallium (TMG) in the bubbler. The probe was sealed inside the bubbler and the scale was zero with the bubbler depleted. The bubbler was filled with TMG (approximately 180 g = 157 ml) and the scale was set to maximum. The charge was then discharged from the bubbler to the receiver via a dip leg. The teletrend ^TM scale was recorded continuously. This record showed that the scale changed from 100% to 0% as the filling was depleted, as shown in FIG. 3. The degree of tilt of the graph depends on the rate of depletion of the charge. Once all of the filling was exhausted, the system was confirmed by recharging the filling into the bubbler to return the scale from 0% to 100%.

Example 2

This study was conducted to demonstrate the performance of the device according to the first embodiment of the present invention for continuously monitoring the level of trimethylaluminum (TMA) in the bubbler. As described in Example 1, the monitor connected to the probe showed zero when the bubbler was depleted. The bubbler was filled with TMA (approx. 120 g = 160 ml) and the scale was set to maximum. The charge was then discharged from the bubbler through the immersion leg to the receiver. The scale of the trend Tele (Teletrend ^TM) were recorded. This recording showed that the scale changed from 100% to 0% as the charge was depleted, as shown in FIG. 4. The degree of tilt of the graph depends on the rate of depletion of the charge.

5 and 6 show a probe according to a second embodiment of the present invention. This probe represents the one before being inserted into a container such as a bubbler. The probe includes a hollow elongated stainless steel tube 20 sealed inside the mount 30. The end section 22 of the tube to be sealed inside the mount is made of a nickel alloy sold under the trade name Inconel X-750 ^™ , which is generally 70% nickel (Ni ^a ). Inconel X-750 alloy are similar to the properties of Inconel 600 ^TM, but made available to the precipitation hardening by the addition of aluminum and titanium. The end section 22 is sealed to a glass material 34.

Inconel 600 ^™ is a nichrome steel with high heat and corrosion resistance. The high nickel content makes it resistant to corrosion by many organic and inorganic compounds and prevents cracking due to chloride-ion stress corrosion. Chromium makes them resistant to sulfur compounds and to oxidizing conditions in hot or corrosive solutions. It also has excellent resistance to corrosion by high purity water. Inconel X-750 alloy has good oxidation resistance and high tensile strength and creep rupture characteristics up to approximately 1300 ° F (700 ° C).

Inconel X-750 section 22 of the probe consists of a glass-metal seal and depends on an oxygen layer to form a metal seal for the glass. Glass and metals choose similar thermal expansion coefficients so that minimal stress is applied to the glass during fusion. Inconel or Kovar ^TM steels are optimally fused with borosilicate glass to provide good sealing.

The body 32 of the mounting portion 30, which receives the section of the probe body that makes up the glass-metal seal, is also made of a nickel alloy such as Inconel X-750 alloy. The mount incorporates a ½ inch VCR profile and inner profile on the interface to ensure a good fit between the BNC connector and the glass-metal seal. The VCR is a gasket face seal fitting of a fully integrity high purity metal. The gasket will be deformed in cross section during the tightening of the fitting to provide a reliable metal-to-metal seal. BNC insulation 36, such as a polyether ether ketone (PEEK) material, is located on top of section 22 with electrode connecting member 38.

Example 3

This study was conducted to demonstrate the performance of the device according to the second embodiment of the present invention for continuously monitoring the level of trimethylaluminum (TMA) in the bubbler. The results shown in FIG. 7 show a calibration step of filling the bubbler with TMA, reading to 100% and returning to 0%. The liquid was filled by the pump and discharged from the bubbler using pressure, allowing for a quick level change.

Example 4

Another study was conducted to demonstrate the performance of the device according to the second embodiment of the present invention for continuously monitoring the level of trimethylgallium (TMG) in the bubbler. The process is the same as described in Example 3 but the calibration step is read from 100% unlike Example 3. The results are shown in FIG.

The results obtained in Examples 3 and 4 show that continuous level monitoring in the bubbler is possible by providing a bubbler with a probe according to a second embodiment of the present invention. It can also be seen that the graph slope of charging and depletion yields a fast response time.

The present invention provides a metrology probe suitable for monitoring the level of filler in the bubbler that is robust and compatible with organometallic compounds contained within the vessel. This allows the level of organometallic compound in the individual bubbler to be continuously monitored and allows the user to know when to order additional charge as the level of charge in the bubbler indicates exhaustion. It also enables complete exhaustion of the raw material inside the bubbler. The glass seal connecting the probe to the opening of the bubbler maintains pressure inside the vessel and isolates the air from the highly sensitive contents contained in the vessel.

In addition, the seal is resistant to high temperatures and does not interfere with the level measurement or the contents of the container. The elastomer that coats the probe helps to provide overall inertness to maintain precursor purity. In addition, the probes are less brittle than previously provided glass probes. This is important for transportation. Probes should not break due to the material properties inside the bubbler, which can cause leakage and fire.

Sealing the probe to the mount provides a leak-tight seal bond to the container, particularly the bubbler body, to form an ultra-pure, flawless, high-strength container suitable for containing organometallic precursors, which is conventionally found. I can't. Sealed units have been found to withstand high temperatures and withstand impact when dropped and do not contaminate the product even at impurity levels in ppm. It is essential for the probe to continuously display the level of organometallic precursor in a completely intact supply vessel (bubble) of stainless steel. To date, no such probe meets the requirements of inertness, strength, simplicity, reliability and accuracy. Furthermore, the provision of a capacitor formed as an integral part of a cap or mounting unit and having electrical connections for the probe is not known in the art.

Claims (17)

A method of monitoring the level of organometallic compound in the vessel (2),
Inserting at least one metal probe 1 into the container at one end surrounded by a glass material so that the metal probe 1 acts as a first electrode,
Hermetically sealing one end of the probe inside the vessel via a metal-glass-metal seal,
Providing a second electrode capable of forming a capacitor with the first electrode,
Applying a current to the capacitor, and
Monitoring the change in capacitance at the capacitor
Including,
Wherein the glass material surrounding the sealed end of the metal probe constitutes the glass in the metal-glass-metal seal. The method of claim 1,
And the probe is made of stainless steel. The method of claim 1,
And the probe is hermetically sealed in an opening provided in an upper portion of the container. The method of claim 3,
And the probe is sealed in a mount or cap (30) inserted into the opening of the container. The method of claim 4, wherein
And the mounting portion has an electrical connection to the probe. The method according to any one of claims 1 to 5,
And at least a portion of the probe extending from the sealed portion is coated with an elastic material. The method according to any one of claims 1 to 5,
And the portion (22) of the probe surrounded by the glass material comprises a nickel alloy. The method of claim 7, wherein
The alloy is an Inconel® or Kovar® alloy. The method of claim 8,
And wherein said alloy contains at least one component of aluminum and titanium. 10. The method of claim 9,
And wherein said alloy is Inconel® X-750. The method according to claim 4 or 5,
Monitoring method characterized in that the mounting portion 32 is made of nickel alloy. The method of claim 11,
And wherein said alloy is Inconel® X-750. The method according to any one of claims 1 to 5,
And a recorder for recording the change in capacitance. The method of claim 13,
And monitoring means for displaying the liquid level in the container. The method according to any one of claims 1 to 5,
And calibration means for calibrating the device such that a specific capacitance corresponds to a particular volume of liquid in the vessel. The method according to any one of claims 1 to 5,
The glass material is a monitoring method, characterized in that the borosilicate glass material. The method according to any one of claims 1 to 5,
The vessel is a bubbler.

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