Wet abatement system for waste SiH4

A new method of silane abatement is achieved. The novel silane abatement system comprises a water-filled chamber within an outer chamber. An air intake is located in one upper portion of said outer chamber and an exhaust output is located in another upper portion of the outer chamber. A silane gas intake pipe runs into the outer chamber and has its output under water in the water-filled chamber. A drain is connected through a valve at a bottom portion of the water-filled chamber. Many safety features are built into the wet abatement system, including temperature and water level sensors, water sprinklers, and means for shutting off air supply, exhaust, and silane intake. Waste silane gas is bubbled into a water-filled chamber. The waste silane gas is reacted with oxygen in water in the water-filled chamber whereby SiO2 precipitates are formed and wherein the SiO2 precipitates settle to a bottom surface of the water-filled chamber. The SiO2 precipitates are drained out of the water-filled chamber to complete the abatement process.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to a method of and device for abatement of waste SiH4in the fabrication of integrated circuits, and more particularly, to a method of and device for safe wet abatement of waste SiH4in the manufacture of integrated circuits.

(2) Description of the Prior Art

Chemical vapor deposition (CVD) processes are widely used in integrated circuit manufacturing. For example, polysilicon or silicon dioxide layers can be deposited by CVD using silane (SiH4) gas or other similar gases. After the CVD process has been completed, excess silane gas remains in the CVD system. Typically, excess reactant gases are removed by an exhaust system. The exhaust system may vent the reactant gas to the atmosphere. However, silane gas is pyrophoric and cannot be released into the atmosphere. Silanes and similar gases must be filtered from the exhaust gas stream or converted to compounds that can be disposed of safely. A common method of converting waste silane to a disposable compound is through combustion in a so-called “burn box”. In the burn box, the SiH4is converted to SiO2by the reaction: 2SiH4+2O2→2SiO2+4H2. However, the risk is that the burn box may be a source of fire if system failure occurs suddenly. For example, if the exhaust system fails, residue SiH4will collect in the burn box making it likely that an uncontrolled fire will start.

U.S. Pat. No. 6,174,349 to DeSantis, U.S. Pat. No. 6,126,906 to Imamura, and U.S. Pat. No. 5,183,646 to Anderson et al describe processes and devices including burn boxes. Wet scrubbers and other abatement methods are also used. U.S. Pat. No. 6,174,349 to DeSantis teaches a wet scrubber in combination with the burn box. U.S. Pat. No. 5,955,037 to Holst et al shows an oxidation treatment. U.S. Pat. No. 5,320,817 to Hardwick et al uses an amine-forming metal salt to scrub silane.

SUMMARY OF THE INVENTION

Accordingly, a principal object of the present invention is to provide an effective and very manufacturable method of silane abatement in the fabrication of integrated circuit devices.

Another object of the present invention is to provide an effective and very manufacturable method of silane abatement wherein the abatement system does not present the danger of being a source of fire.

Another object of the invention is to provide a silane abatement system that does not present the danger of being the source of fire.

In accordance with the objects of this invention a new method of silane abatement is achieved. Waste silane gas is bubbled into a water-filled chamber. The waste silane gas is reacted with oxygen in water in the water-filled chamber whereby SiO2precipitates are formed and wherein the SiO2precipitates settle to a bottom surface of the water-filled chamber. The SiO2precipitates are drained out of the water-filled chamber to complete the abatement process.

Also in accordance with the objects of this invention a new silane abatement system is achieved. The silane abatement system comprises a water-filled chamber within an outer chamber. An air intake is located in one upper portion of the outer chamber and an exhaust output is located in another upper portion of the outer chamber. A silane gas intake pipe runs into the outer chamber and has its output under water in the water-filled chamber. A drain is connected through a valve at a bottom portion of the water-filled chamber. Many safety features are built into the wet abatement system, including temperature and water level sensors, water sprinklers, and means for shutting off air supply, exhaust, and silane intake.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a method and a device for waste silane abatement. The waste silane abatement system of the present invention successfully deals with the waste silane without danger of being a fire source. No burn box is used in the method and device of the invention. Rather, waste SiH4gas is reacted with dissolved oxygen to form solid SiO2which can be disposed of safely. Safety features of the device of the present invention include sprinklers that will be automatically triggered in the event of fire.

FIGS. 1 and 2illustrate the waste SiH4abatement system of the present invention. Referring now toFIG. 1, waste abatement device10is shown. A portion of the device is filled with water22. Oxygen gas is dissolved in the water22. Waste SiH4gas enters the chamber10from through a pressurized pipe18. High pressure N2gas flow19pushes the SiH4gas through the pipe18, into the chamber10and out through the pipe24under the water. N2gas here is used to prevent back fire to the process tool. If backfire occurs, N2is activated to push the fire into the water chamber. The N2gas flow is at a high pressure of about 100 psi.

The SiH4gas is bubbled into the water22.FIG. 2is a close-up of the pipe24. The waste SiH4gas is pumped through pipe18into a C-shaped stainless steel square pipe24. Flippers14are pushed upward by pressure to release SiH4gas for reaction with dissolved O2for abatement. In water at 25° C., there is about 8.4 ppm of dissolved O2. The gas reacts with dissolved oxygen in the water to form a heavy precipitate of SiO2. The SiO2precipitate sinks slowly to the base of the chamber. The drain valve26is opened, subject to the SiO2level, to clear the solid SiO2out through the drain28. Most likely, the drain valve may be opened once a day.

Chamber20provides for water overflow. Continuous fresh air intake30into the chamber10insures the process of oxygen dissolving into the water from the air is not interrupted. An open-ended drain36in the chamber20will capture water over-flow from the water-filled section22of the chamber. An exhaust pipe38is separated from the chamber10by an exhaust flipper32. The exothermic abatement process may release smoke into the chamber. This smoke is exhausted into the pipe38. The exhaust pipe also provides forced air ventilation from the chamber outside into chamber10for the air dissolving process.

A controller34controls the water supply42and fusible link44. The controller also monitors a water temperature sensor46, a water level sensor48, and an exhaust temperature sensor50. Water sprinklers52located in the chamber ceiling and in the exhaust pipe are triggered by the controller by a high water temperature, high exhaust pipe temperature, or when the fusible link is broken. The fusible link is a burnable material such as nylon. If this link is exposed to heat high enough to break it, the controller will turn on the water sprinklers. The water level sensor avoids “dry-run” operations if the water level is not high enough.

If a minor explosion occurs within the chamber10, the air intake30and the exhaust flipper32will shut. The flippers are normally open, but will be pushed closed by the pressure of an explosion. The oxygen source will also be cut off to stop any fire. That is, the air intake flipper30, normally open, will be pushed closed by pressure due to fire. If the fusible link49within one or both of the N2high pressure pipes is broken, indicating high heat, high pressure N2flow19will be triggered to push the fire back into the water chamber22and to form N2blanketing to stop a fire.

The wet abatement system of the present invention consists of a water-filled chamber within an outer chamber. An air intake flipper and an exhaust flipper control input and output of air. A drain is connected through a valve to the water-filled chamber. An overflow drain is at the bottom of the outer chamber. A controller controls the water supply and monitors the water level, water temperature, exhaust temperature, and a fusible link within the exhaust pipe. A pipe brings waste SiH4gas into the water-filled chamber. A high pressure pump pushes the waste gas through the pipe.

In the wet abatement process of the present invention, waste silane gas is bubbled into the water-filled chamber of the wet abatement system of the present invention. N2gas at high pressure pushes the silane gas through a pipe into the water-filled chamber. The silane gas reacts with oxygen dissolved in the water to form a precipitate of SiO2. The SiO2settles to the bottom of the chamber and is removed from the chamber through a drain.

The process of the present invention abates waste SiH4in the water state. The abatement system will not be a source of fire because of the safety features of the wet abatement system of the present invention. These safety features include: water sprinklers located on the ceiling of the outer chamber above the water-filled chamber and in the exhaust pipe, air intake and exhaust flippers that close in the event of an explosion, a process pump trip, fusible links located within the exhaust pipe and within the N2pipes that will break if exposed to high heat, water temperature and exhaust temperature sensors, and a water level sensor. The controller monitors the sensors and the fusible links. If either of the temperature sensors show a high temperature or if any of the fusible links are broken, the water sprinklers are triggered, the air intake and exhaust flippers are closed, the oxygen supply into the chamber is cut off, and the N2gas pump is shut down after pushing residue waste gas into the water-filled chamber. If the water level sensor shows the water level is too low, the system is also shut down.

The process and device of the present invention provide wet silane abatement without danger of fire from the abatement system. The wet abatement system of the present invention has a variety of safety features that work together to provide safe and effective silane abatement.