Semiconductor manufacturing system with getter safety device

Details Semiconductor manufacturing system with getter safety device Semiconductor manufacturing system with getter safety device

1999-02-16

2001-05-15

Booth, Richard (Department: 2812)

Semiconductor device manufacturing: process

Gettering of substrate

C438S477000, C438S909000, C096S112000

Reexamination Certificate

active

06232204

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to the production of semiconductor devices and, more particularly, to semiconductor manufacturing systems including a getter-based gas purifier with a safety device.
Modern semiconductor manufacturing systems use ultrapure gases to produce high density semiconductor devices. One way of providing such ultrapure gases is through the use of a getter-based gas purifier. This type of gas purifier typically includes a getter column which has a vessel containing a bed of getter material. The getter material purifies gas flowing therethrough by adsorbing impurities from the gas.
Getter columns are hazardous because the getter material contained therein is highly reactive with high concentrations of impurities. For example, in the event a high concentration, e.g., a few percent depending on the gas flow rate, of an impurity, e.g., oxygen, is introduced into a getter column containing a known zirconium-based getter material, an exothermic reaction occurs the heat from which may cause melting of the containment wall of the vessel. The containment wall, which is typically formed of stainless steel, may melt at temperatures as low as about 1,000 C. because the getter material contacting the containment wall reacts therewith and forms a eutectic composition. If melting of the containment wall results in the formation of a hole therein, then breach of containment of the getter material occurs, which is potentially catastrophic.
One known getter-based gas purifier for purifying argon includes an alarm device for protecting the getter column from breach of containment of the getter material. This alarm device includes a thermocouple element located three inches below the top of the bed of getter material. Existing getter columns do not have a thermocouple at the bottom of the bed. When a control unit coupled to the thermocouple element measures a temperature of 450 C., which is 50 C. above the normal operating temperature of this getter column, the control unit actuates isolation valves which isolate the getter column, i.e., shut off the flow of gas into and out of the getter column. Unfortunately, the alarm device typically does not stop the flow of high impurity gas into the getter column in time to prevent the getter column from sustaining substantial damage caused by overheated getter material contacting the stainless steel walls of the vessel. Thus, the alarm device does not reliably protect the getter column from breach of containment of the getter material.
In view of the foregoing, there is a need for a safety device for getter-based gas purifiers which reliably protects against breach of containment of the getter material in the event high concentrations of impurities are introduced into a getter column. There is also a need for a semiconductor manufacturing system which includes a getter-based gas purifier having such a safety device so that the fabrication facility in which such system is installed is protected from damage which may result from catastrophic failure of a getter column.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing a getter-based gas purifier with a safety device which reliably protects against breach of containment of the getter material in the event high concentrations of impurities are introduced into a getter column. The safety device rapidly detects the onset of an exothermic reaction which occurs when excess impurities come into contact with getter material, protects a vessel in which the getter material is disposed by inhibiting the formation of a eutectic composition between the getter material and a containment wall of the vessel, and safely shuts down the getter column before breach of the vessel.
In one aspect of the present invention, a semiconductor manufacturing system is provided. The semiconductor manufacturing system includes a getter-based gas purifier coupled in flow communication with a gas distribution network for a semiconductor fabrication facility. The gas distribution network supplies purified gas to at least one wafer processing chamber in the semiconductor fabrication facility. The gas purifier includes a getter column having a metallic vessel with an inlet, an outlet, and a containment wall extending between the inlet and the outlet. Getter material which purifies gas flowing therethrough by sorbing impurities therefrom is disposed in the vessel. A first temperature sensor is disposed in a top portion of the getter material. The first temperature sensor is located in a predicted “melt zone” to detect rapidly the onset of an exothermic reaction which indicates the presence of excess impurities in the incoming gas to be purified. A second temperature sensor is disposed in a bottom portion of the getter material. The second temperature sensor is located in the predicted melt zone to detect rapidly the onset of an exothermic reaction which indicates that excess impurities are being backfed into the getter column.
In a preferred embodiment, the getter column further includes a first high melting point, nonmetallic liner disposed in the vessel such that at least some of the top portion of the getter material is separated from the containment wall of the vessel and a second high melting point, nonmetallic liner disposed in the vessel such that at least some of the bottom portion of the getter material is separated from the containment wall of the vessel. The first and second high melting point, nonmetallic liners are preferably comprised of a ceramic material, e.g., quartz, zirconia (Zr
2
O
5
), SiC, SiN, and Al
2
O
3
.
In another aspect of the present invention, a getter-based gas purifier is provided. The getter-based gas purifier includes a getter column having a metallic vessel with an inlet, an outlet, and a containment wall extending between the inlet and the outlet. The vessel has getter material disposed therein. A first isolation valve and a vent valve are in flow communication with the inlet of the vessel. A second isolation valve is in flow communication with the outlet of the vessel. First and second temperature sensors are disposed in the top and bottom portions, respectively, of the getter material. A control unit is coupled to the first and second temperature sensors, the first and second isolation valves, and the vent valve. The control unit measures temperatures sensed by the first and second temperature sensors. When a temperature above a first alarm temperature is measured, the control unit actuates the first and second isolation valves to isolate the getter column. When a temperature above a second alarm temperature is measured, the control unit actuates the vent valve to vent gas from the getter column. The vent valve permits the removal of pressurized gaseous impurities causing the exothermic reaction from above the melt zone. This process is facilitated by the pressurized purified gas (e.g. Argon) contained by the previously operating getter column which helps purge the gaseous impurities through the vent valve.
In a preferred embodiment, the first isolation valve is in flow communication with a source of feed gas to be purified, the second isolation valve is in flow communication with an outlet for purified gas, and the gas purifier further includes a bypass valve in flow communication with the source of feed gas and the outlet for purified gas. The control unit opens the bypass valve when a temperature above the first alarm temperature is measured. When a temperature above a third alarm temperature is measured, the control unit closes the bypass valve.
The first alarm temperature is preferably about 10 C. to about 100 C., more preferably about 40 C. to about 60 C., and most preferably about 50 C., above a normal operating temperature of the getter column. The second alarm temperature is preferably at least about 100 C. above the normal operating temperature of the getter column. The third alarm temperature is preferably at least about 200 C., and more preferably at least about 300 C., above the normal oper

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