US20050284572A1

US20050284572A1 - Heating system for load-lock chamber

Info

Publication number: US20050284572A1
Application number: US10/881,417
Authority: US
Inventors: Wen-Ming Chen; Wen-Chi Wang; Kou-Ien Chang
Original assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Current assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Priority date: 2004-06-29
Filing date: 2004-06-29
Publication date: 2005-12-29

Abstract

A system for heating a load-lock chamber, particularly that of a plasma etching system for etching semiconductor wafer substrates. The load-lock chamber heating system includes a heater that is provided in fluid communication with a gas supply which contains an inert gas such as nitrogen. A gas pump pumps the gas from the gas supply through the heater, and from the heater into the load-lock chamber. The gas heats the load-lock chamber to prevent or minimize condensation of corrosive etching gases onto the interior surfaces of the load-lock chamber as well as the surfaces of substrates contained therein.

Description

FIELD OF THE INVENTION

The present invention relates to etching chambers used in the etching of material layers on a semiconductor wafer substrate to fabricate semiconductor integrated circuits on the substrate. More particularly, the present invention relates to a heating system for heating a loadlock chamber in a semiconductor substrate etching system to reduce or eliminate condensation of etchant gases in the chamber.

BACKGROUND OF THE INVENTION

In the semiconductor production industry, various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal interconnection pattern, using standard lithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby etching the conducting layer in the form of the masked pattern on the substrate; removing or stripping the mask layer from the substrate typically using reactive plasma and chlorine gas, thereby exposing the top surface of the conductive interconnect layer; and cooling and drying the wafer substrate by applying water and nitrogen gas to the wafer substrate.
Etching processes used to fabricate integrated circuits on substrates include “wet” etching, in which one or more chemical reagents are brought into direct contact with the substrate, and “dry” etching, such as plasma etching. In wet etching, liquid chemicals such as acids, bases and solvents are used to chemically remove wafer surface material. Wet etching is generally applicable only for geometries having a size larger than 3 m. Dry etching, on the other hand, is useful for smaller geometries and includes plasma etching, one of the most widely-used forms of etching.
In plasma etching processes, a gas such as HBr or Cl₂is first introduced into a reaction chamber and then plasma is generated from the gas. This is accomplished by dissociation of the gas into ions, free radicals and electrons by using an RF (radio frequency) generator, which includes one or more electrodes. The electrodes are accelerated in an electric field generated by the electrodes, and the energized electrons strike gas molecules to form additional ions, free radicals and electrons, which strike additional gas molecules, and the plasma eventually becomes self-sustaining. The ions, free radicals and electrons in the plasma react chemically with the layer material on the semiconductor wafer to form residual products which leave the wafer surface and thus, etch the material from the wafer.
FIG. 1 illustrates a typical conventional wafer processing station 10 such as a plasma etcher used in etching material layers on semiconductor wafers 14. The processing station 10 typically includes a loading port 13 which receives a cassette holder 12 from an automatic guided vehicle (AGV), overhead transport (OHT) vehicle or other pod transfer vehicle (not illustrated) in the cleanroom. A robot or other wafer transfer device 20 unloads the wafers 14 from a wafer cassette 15 inside the cassette holder 12 and transfers the wafers 14 through a wafer transfer chamber 18 to a load-lock chamber 22. A wafer transfer robot 26 in a wafer transfer chamber 24 transfers the wafers 14 from the load-lock chamber 22 to a process chamber 28.
The wafer transfer robot 26 positions each wafer 14 on a corresponding set of multiple wafer lift pins (not shown) which are upwardly extended from a heater block 30 contained inside the process chamber 28. The lift pins are vertically slidably disposed in respective lift pin openings (not illustrated) in the heater block 30 and contact the bottom surface or backside of the wafer 14 in order to lower the wafer 14 to rest on the heater block 30 prior to the etching process and also lift the wafer 14 from the heater block 30 after the etching process. In the process chamber 28, the heater block 30 heats the wafer 14 to temperatures typically in the range of about 200 degrees C.-250 degrees C. during the etching process as reactive plasma or reactive gases such as chlorine and/or hydrogen bromide are used to etch the unmasked conductive layer or layers from each wafer.
After completion of the etching process, the wafer transfer robot 26 transfers the wafers 14 from each process chamber 28 back to the load-lock chamber 22. Finally, the cooled wafers 14 are loaded on the wafer transfer robot or devices 20 in the wafer transfer chamber 18 and transferred to a cassette holder 16 at an unloading port 17, where the wafers 14 are removed from the wafer processing station 10 for subsequent transfer of the wafers 14 to another processing station or tool (not illustrated) in the clean room.
One of the problems frequently associated with etching wafers 14 in the process chambers 28 is that some of the residual HBr and Cl₂gases used in the etching process drift from the process chambers 28 into the loadlock chamber 22, where the gases condense onto the surfaces of the loadlock chamber 22. This can cause contamination of wafers 14 therein, as well as contribute to poor KLA performance and corrosion of the loadlock chamber 22, and may cause release of excessive concentrations of the gases into the environment of the station 10 when wafers 14 are loaded into and unloaded from the wafer cassettes 15 in the cassette holders 12. Accordingly, a system is needed for introducing a heated gas such as nitrogen into a load-lock chamber for the purpose of preventing or minimizing condensation of hydrogen bromide, chlorine and/or other corrosive gases in the load-lock chamber.
An object of the present invention is to provide a system for heating a chamber of a processing system.
Another object of the present invention is to provide a system for preventing or minimizing condensation of corrosive gases in a chamber.
Still another object of the present invention is to provide a system which is suitable for preventing or minimizing the condensation of corrosive gases such as hydrogen bromide and chlorine in a load-lock chamber of an etching system for semiconductors.
Yet another object of the present invention is to provide a chamber heating system which is capable of reducing the frequency of wet chamber cleanings.
A still further object of the present invention is to provide a chamber heating system which is capable of reducing the time required to carry out a wet chamber cleaning.
Still another object of the present invention is to provide a system for heating a load-lock chamber, which system substantially reduces the concentrations of corrosive etching gases in an environment surrounding the chamber.
Another object of the present invention is to provide a load-lock heating chamber system which enhances wafer throughput through an etching system.
A still further object of the present invention is to provide a load-lock heating chamber system which is capable of reducing a temperature gradient between a load-lock chamber, a buffer chamber and a process chamber.
Yet another object of the present invention is to provide a novel method of reducing or preventing condensation of corrosive gases in a load-lock chamber of a semiconductor processing tool or system.

SUMMARY OF THE INVENTION

In accordance with these and other objects and advantages, the present invention is generally directed to a novel system for heating a load-lock chamber, particularly that of a plasma etching system for etching semiconductor wafer substrates. The load-lock chamber heating system includes a heater that is provided in fluid communication with a gas supply which contains an inert gas such as nitrogen. A gas pump pumps the gas from the gas supply through the heater, and from the heater into the load-lock chamber. The gas heats the load-lock chamber to prevent or minimize condensation of corrosive etching gases onto the interior surfaces of the load-lock chamber as well as the surfaces of substrates contained therein.
The present invention further includes a method of preventing condensation of corrosive gases on surfaces in a load-lock chamber. The operational speed of the pump may be controlled to facilitate a desired flow rate of the gas from the heater into the load-lock chamber. In a preferred embodiment, the flow rate of the gas is from about 20 sccm to about 100 sccm. The temperature of the heating gas is typically from about 70 degrees C. to about 100 degrees C., and preferably, about 80 degrees C.
Reduction or elimination of corrosive gas condensation in a load-lock chamber prolongs the time available for operation of the etching or other processing system by reducing the frequency of wet-cleanings required for the load-lock chamber. Furthermore, the time required for carrying out each wet cleaning is reduced because particle contamination caused by gas condensation is correspondingly reduced or eliminated. The lifetime of system elements such as SMIF (standardized mechanical interface) systems used to load wafers into and unload wafers from the processing system is also increased, due to the reduction or elimination of the corrosive gases.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic view of a typical conventional wafer processing station for the etching of semiconductor wafer substrates;
FIG. 2 is a schematic view of a wafer processing system in conjunction with a load-lock chamber heating system of the present invention; and
FIG. 3 is a flow diagram illustrating sequential process steps in typical implementation of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention has particularly beneficial utility in preventing the condensation of hydrogen bromide, chlorine or other corrosive gases used to etch material layers on semiconductor wafer substrates on the interior surfaces of a load-lock chamber in an etching system. However, the invention is not so limited in application and while references may be made to such etching chambers and load-lock chambers, the invention is more generally applicable to preventing or minimizing condensation of gases on interior chamber surfaces in a variety of industrial and mechanical applications.
In a preferred embodiment, the present invention includes a heating system for a load-lock chamber and includes a heater the inlet end of which is provided in fluid communication with a supply of an inert gas such as nitrogen. The outlet end of the heater is provided in fluid communication with the load-lock chamber. A fan, blower or pump is provided for flowing the gas at a selected gas flow rate from the gas supply through the heater, which heats the gas to a selected temperature, and from the heater into the load-lock chamber.
The heated gas flowing into the load-lock chamber raises the temperature of internal surfaces in the chamber and thereby prevents the condensation of hydrogen bromide, chlorine or other corrosive gases used in the etching process onto the chamber surfaces. This reduces the frequency of wet chamber cleanings necessary to maintain the interior of the load-lock chamber in optimum condition for the processing of substrates, and eliminates or substantially reduces the deposition of particles onto interior chamber surfaces, including the surfaces of WIP substrates. Furthermore, leakage of the corrosive gases from the load-lock chamber through the entry and exit ports of the etching system is substantially reduced or eliminated, thus enhancing the working environment around the etching system and minimizing or reducing corrosion of mechanical systems which are associated with the etching system, such as SMIF (standardized mechanical interface) arms used to load and unload wafer cassettes in the system.
The present invention further includes a method of preventing condensation of corrosive gases on surfaces in a load-lock chamber. The operational speed of the pump may be controlled to facilitate a desired flow rate of the gas from the heater into the load-lock chamber, and the temperature of the gas may be controlled to impart a desired temperature to the interior surfaces of the load-lock chamber. In a preferred embodiment, the flow rate of the gas is from about 20 sccm to about 100 sccm. The temperature of the heating gas is typically from about 70 degrees C. to about 100 degrees C., and preferably, about 80 degrees C. The gas may be introduced into the load-lock chamber for a period of typically from about 30 seconds to about 2 minutes to thoroughly warm the interior surfaces of the chamber after an etching process and prevent the condensation of corrosive gases that have a tendency to drift from a process chamber onto the interior surfaces of the load-lock chamber.
Referring to FIG. 2, a wafer processing station 40 such as an etching system for the etching of semiconductor wafer substrates 44 is shown schematically in implementation of the present invention. It is understood that the wafer processing station 40 shown in FIG. 2 and hereinafter described is just one example of a wafer processing station or tool which is suitable for implementation of the present invention, and the invention may be suitable for use with wafer processing tools having designs which depart from that of the wafer processing station 40. The wafer processing station 40 includes a wafer transfer chamber 48 to which is attached a cassette holder 42 with a loading port 43 and an adjacent cassette holder 46 with an unloading port 47. A load-lock chamber 52 is provided adjacent to the wafer transfer chamber 48. Wafer transfer devices 50 are provided in the wafer transfer chamber 48 for transferring semiconductor wafers 44 from the cassette holder 42 into the load-lock chamber 52, and from the load-lock chamber 52 into the cassette holder 46. A wafer transfer chamber 54 is provided adjacent to the load-lock chamber 52, and contains a wafer transfer robot 56 which transfers the wafers 44 between the load-lock chamber 52 and a process chamber 58. Each process chamber 58 may contain a heater block 60 for controlling the temperature of a wafer 44 placed thereon by the wafer transfer robot 56 during etching of material layers on the wafer 44.
According to the present invention, a heating system 36 for the load-lock chamber 52 includes a heater 62 the outlet end of which is provided in fluid communication with the load-lock chamber 52 through a heater outlet conduit 66. Multiple heating coils or elements 63 are provided in the heater 62 and may be operably connected through heater control wiring 67 to a controller 65 which controls the heat of the heating elements 63, according to the knowledge of those skilled in the art. Through a gas distribution conduit 76, the inlet end of the heater 62 is provided in fluid communication with a gas supply reservoir 72 which contains an inert gas 70 such as nitrogen. A gas blower, fan or pump 74 is typically provided in the heater outlet conduit 66 for pumping the gas 70 from the gas supply 72, through the heater 62 and into the load-lock chamber 52 at a selected flow rate. The controller 65 may be operably connected, according to the knowledge of those skilled in the art, to the gas pump 74 through pump control wiring 75 to control the operational speed of the gas pump 74, and thus, the flow rate of the gas into the load-lock chamber 52.
In typical application of the present invention, the loading port 43 of the wafer processing station 40 receives a cassette holder 42, which contains a wafer cassette 45 holding multiple semiconductor wafers 44, from an automatic guided vehicle (AGV), overhead transport (OHT) vehicle or other pod or container transfer vehicle (not illustrated) in the cleanroom. The wafer transfer device 50 unloads individual wafers 44 from the wafer cassette 45 inside the cassette holder 42 and transfers the wafers 44 through the wafer transfer chamber 48 into the load-lock chamber 52. The wafer transfer robot 56 in the wafer transfer chamber 54 transfers the wafer 44 from the load-lock chamber 52 to the process chamber 58.
The wafer transfer robot 56 typically positions each wafer 44 on a corresponding set of multiple wafer lift pins (not shown) which are upwardly extended from the heater block 60 contained inside the process chamber 58. The lift pins are vertically slidably disposed in respective lift pin openings (not illustrated) in the heater block 60 and contact the bottom surface or backside of the wafer 44 in order to lower the wafer 44 to rest on the heater block 60 prior to the etching process and also lift the wafer 44 from the heater block 60 after the etching process. In the process chamber 58, the heater block 60 heats the wafer 44 to temperatures typically in the range of about 200 degrees C.-250 degrees C. during the etching process as reactive plasma or reactive gases such as chlorine and/or hydrogen bromide are used to etch the unmasked conductive layer or layers from each wafer 44 or to perform STI (shallow trench isolation) procedures, for example.
After completion of the etching process carried out in the process chamber 58, most of the corrosive etchant gases are removed from the process chamber 58 using an exhaust pump evacuating system (not shown), as is known by those skilled in the art. However, some residual gases typically remain in the process chamber 58 after the evacuation process. Therefore, as the wafer transfer robot 56 subsequently transfers each wafer 44 from the process chamber 58 back to the load-lock chamber 52, these residual gases have a tendency to drift from the process chamber 58 into the load-lock chamber 52. Accordingly, in implementation of the present invention, the heating system 36 is operated to heat the interior surfaces of the load-lock chamber 52 to prevent the residual etchant gases from cooling and condensing on those surfaces. First, the desired temperature, the desired gas flow rate and the desired gas flow time for the heating gas 70 is programmed into the controller 65. As the wafer transfer robot 56 next transfers each wafer 44 from the process chamber 58 into the load-lock chamber 52, the heating gas 70, typically nitrogen, is drawn from the gas supply 72, through the gas distribution conduit 76 and into the heater 62, where the heating gas 70 is heated to the preset temperature as programmed into the controller 65. In a preferred embodiment, the heating gas 70 is heated to a temperature of from about 70 degrees C. to about 100 degrees C., and preferably, about 80 degrees C. The controller 65 operates the gas pump 74 at the preset operational speed to pump the heated gas 70 from the heater 62, through the heater outlet conduit 66 and into the load-lock chamber 52, at the desired gas flow rate, typically about 20 sccm to about 100 sccm, for a time period of typically from about 30 seconds to about 2 minutes. Accordingly, the heated nitrogen 70 contacts and heats the interior surfaces of the load-lock chamber 52 to a temperature which is roughly equal to the temperature of the heated gas 70, thereby preventing residual corrosive etchant gases from cooling and condensing on the interior surfaces of the load-lock chamber 52, including on the surfaces of the wafer or wafers 44 held therein. Continued operation of the gas evacuation system (not shown) of the wafer processing station 40 evacuates both the heating gas 70 and the uncondensed residual etchant gases, which remain in the gaseous state, from the load-lock chamber 52. Finally, the wafer 44 is loaded onto the wafer transfer device 50 in the wafer transfer chamber 48 and transferred to the cassette holder 46 at an unloading port 47, where the wafers 44 are removed from the wafer processing station 40 for subsequent transfer of the wafers 44 to another processing station or tool (not illustrated) in the clean room.
Referring next to the flow diagram of FIG. 3, a typical process sequence in implementation of the present invention is summarized. In process step 1, a wafer substrate is subjected to an etching process, such as an STI (shallow trench isolation) process, in an etching chamber. In process step 2, a selected gas temperature and flow rate, as well as gas flow time, are programmed into the temperature and flow rate controller. In process step 3, the heating gas is pumped from the gas source into the heater. In process step 4, the heater heats the gas to the preset temperature programmed into the controller. In process step 5, the heated gas is pumped into the load-lock chamber at the preset gas flow rate programmed into the controller for the gas flow time period programmed into the controller. In process step 6, the heated gas, as well as the uncondensed etchant gases, are evacuated from the load-lock chamber.
While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.

Claims

1. A system for preventing condensation of a gas in a chamber, comprising:

a gas source for containing an inert gas;

a heater provided in fluid communication with said gas source for fluid communication with the chamber and receiving the inert gas from said gas source and heating the inert gas; and

a pump provided in fluid communication with said heater for pumping the gas from said heater to the chamber.

2. The system of claim 1 further comprising a controller connected to said heater for operating said heater.

3. The system of claim 1 further comprising a controller connected to said pump for operating said pump.

4. The system of claim 3 wherein said controller is further connected to said heater for operating said heater.

5. A method of preventing condensation of a gas in a chamber, comprising the steps of:

providing a heater in fluid communication with the chamber;

heating a heating gas by distributing said heating gas through said heater; and

distributing said heating gas from said heater into the chamber.

6. The method of claim 5 wherein said heating gas comprises nitrogen.

7. The method of claim 5 wherein said heating said heating gas comprises heating said heating gas to a temperature of from about 70 degrees C. to about 100 degrees C.

8. The method of claim 7 wherein said heating gas comprises nitrogen.

9. The method of claim 5 wherein said distributing said heating gas from said heater into the chamber comprises distributing said heating gas from said heater into the chamber at a flow rate of from about 20 sccm to about 100 sccm.

10. The method of claim 9 wherein said heating gas comprises nitrogen.

11. The method of claim 9 wherein said heating said heating gas comprises heating said heating gas to a temperature of from about 70 degrees C. to about 100 degrees C.

12. The method of claim 11 wherein said heating gas comprises nitrogen.

13. A method of preventing condensation of a gas in a load-lock chamber, comprising the steps of:

providing a heater in fluid communication with the load-lock chamber;

heating a heating gas to a gas temperature by distributing said heating gas through said heater; and

distributing said heating gas from said heater into the chamber at a gas flow rate.

14. The method of claim 13 wherein said heating gas comprises nitrogen.

15. The method of claim 13 wherein said gas temperature is from about 70 degrees C. to about 100 degrees C.

16. The method of claim 15 wherein said heating gas comprises nitrogen.

17. The method of claim 13 wherein said gas flow rate is about 20 sccm to about 100 sccm.

18. The method of claim 17 wherein said gas temperature is from about 70 degrees C. to about 100 degrees C.

19. The method of claim 17 wherein said heating gas comprises nitrogen.

20. The method of claim 19 wherein said gas temperature is from about 70 degrees C. to about 100 degrees C.