WO2002000962A1

WO2002000962A1 - System and method for in-situ cleaning of process monitor of semi-conductor wafer fabricator

Info

Publication number: WO2002000962A1
Application number: PCT/US2001/013333
Authority: WO
Inventors: Joseph Ashurst Maher, Jr.
Original assignee: Mks Instruments, Inc.
Priority date: 2000-06-28
Filing date: 2001-04-25
Publication date: 2002-01-03

Abstract

An in-situ cleaning system for cleaning deposits created by process gases in a sampling chamber (16) of a semi-conductor wafer manufacturing process monitor (18). The system includes a cleaning valve (36) for connecting a source of cleaning gas to the sampling chamber (16). The cleaning gas is known to react with the process deposits in the sampling chamber to create a gaseous cleaning by-product upon generation of a plasma within the sampling chamber. The system also includes a controller for opening the cleaning valve and allowing cleaning gas to be drawn into the sample chamber, activating a plasma generator of the process monitor within the chamber, detecting the amount of gaseous cleaning by-product within the sampling chamber using an analyzer of the process monitor, and evacuating gaseous cleaning by-product from the chamber using a pump of the process monitor. The in-situ cleaning is repeated until the detected amount of gaseous cleaning by-products falls to a predetermined level. Preferably, the in-situ cleaning system is incorporated in the semi-conductor wafer manufacturing process monitor, and programmed to clean between normal process sampling intervals of the monitor.

Description

SYSTEM AND METHOD FOR IN-SITU CLEANING OF PROCESS MONITOR OF SEMI-CONDUCTOR WAFER FABRICATOR

Field of Disclosure

The present disclosure relates to a process monitor of a semi-conductor wafer fabricator and, more particularly, to a system and method for in-situ cleaning of a process monitor of a semi-conductor wafer fabricator.

Background of Disclosure

The progress of semi-conductor wafer manufacturing, e.g., by physical deposition, chemical vapor deposition, or reactive ion etching, within a process chamber of a wafer fabricator can be monitored and controlled by analyzing the chemical by-products of the manufacturing. For example, if a reactive ion etching process involves removing a pattern of a layer of silicon oxide with a reactant such as CF or CHF₃, a carbon-oxygen component, CO, is created from the reaction of CF or CHF₃, and silicon oxide. Accordingly, the level of CO in the process chamber can be monitored to determine the progress of the etching procedure. A decrease or absence of CO in the process chamber, therefore suggesting an absence of silicon oxide, signifies that the etching procedure is completed.

The chemical by-products of a wafer manufacturing process can be analyzed directly using a residual gas analyzer (RGA) having a probe extending into the process chamber. The assignee of the present disclosure, for example, provides an RGA under the trademark Orion^® CompactRGA^™ that comprises a quadrupole mass spectrometer having. a probe for insertion into a process chamber (or sampling chamber) for gas analysis.

The by-products can also be analyzed indirectly using an endpoint detection system focusing on the by-products through a window of the process chamber. For example, laser endpoint detection systems can be used to indirectly monitor the chemistry of the by-products through the end-point detection window. However, it has been found that deposits, such as polymers comprised of carbon, hydrogen, oxygen and fluorine, are created during semi-conductor wafer manufacturing and can coat a probe of an RGA or an inside surface of an end point detection window. After numerous manufacturing cycles, a buildup of deposits on the RGA probe and the window degrades process monitoring. The built-up deposits on the RGA probe and the window, therefore, limit the number of semi-conductor wafers that can be successively processed, without degradation of process monitoring.

In addition, process deposits can also accumulate, for example, on a support stand within the process chamber upon which the semiconductor wafer rests during the manufacturing cycle. Such deposits must be removed periodically since they tend to change the dimensions of the chamber. In addition, the deposits may flake off the support surfaces and contaminate the wafer being processed, or chemically change the process chamber environment for subsequent manufacturing cycles. In general, therefore, built-up deposits within a wafer fabricator limit the number of semi- conductor wafers that can be successively manufactured.

To remove such deposits, wafer fabricators are usually provided with scheduled maintenance, wherein the wafer fabricator is shut down and the deposits are physically removed from fabricator. Physical removal is accomplished by using a wet clean, such as a chemical solution containing isopropyl alcohol, to remove the deposits. The amount of time needed to remove the deposits and ready the system for subsequent use, however, can be considerable, e.g., eight hours, thereby significantly reducing wafer production.

In an attempt to reduce system down time, in-situ cleaning methods have been developed. For example, U.S. Patent No. 5,207,836 shows an in-situ cleaning process for removing deposits such as tungsten from a susceptor in a vacuum deposition chamber without leaving flourine residue. The process includes a first step of pumping flourine into the chamber and igniting a plasma, such that tungsten deposits react with the flourine plasma. The flourine plasma is maintained for between 30 seconds and 2 minutes per micron thickness of tungsten deposits. Then, hydrogen is pumped into the chamber and a second plasma is ignited, such that any flourine deposits react with the ignited hydrogen. The hydrogen plasma is maintained for between 20 seconds and 5 minutes. Finally, all gaseous reactants are pumped from the chamber.

U.S. Patent No. 5,417,826 shows an in-situ cleaning process for removing carbon-based polymer residues from an etching chamber. A cleaning gas is pumped into the chamber and a plasma is ignited such that the cleaning gas reacts with the residues to create a gaseous reactant. The process uses ozone as the cleaning gas to increase the amount of elemental oxygen present during the cleaning process. The plasma is maintained in the chamber for between 15 and 30 minutes, and the gaseous reactant is then pumped from the chamber.

U.S. Patent No. 5,679,214 shows an in-situ cleaning process for removing polymer deposits from a transparent end-point detection window of an etching chamber. The method consists of injecting oxygen into the etching chamber and then creating plasma to produce elemental oxygen, which reacts with the polymer deposits to create a gaseous reactant. The plasma is maintained in the chamber for between 0.1 and 1.0 minutes, and the gaseous reactant is then pumped from the chamber.

U.S. Patent No. 5,746,835 shows an in-situ cleaning process for an electrostatic probe contained in a housing connected to a process chamber. During cleaning, the probe is first retracted into the housing and isolated from the process chamber. Then a cleaning gas is pumped into the probe housing and a plasma is ignited such that the cleaning gas reacts with residues on the probe to create a gaseous reactant, which is pumped from the housing.

U.S. Patent No. 5,911,833 shows a method of in-situ cleaning of a chuck within a plasma chamber. A cleaning gas is pumped into the chamber and plasma is ignited such that the cleaning gas reacts with residues on the chuck to create a gaseous reactant. The plasma is maintained in the chamber for between 100 and 300 seconds until it is determined by visual inspection that the chuck is cleaned. The gaseous reactant is then pumped from the chamber. All these above described in-situ dry cleaning procedures of the prior art reduce wafer fabricating down time in comparison to the traditional wet cleanup of deposits from wafer fabricators. However, there is still desired an improved method of in-situ dry cleaning of wafer fabricating systems.

Preferably, an improved in-situ dry cleaning process will be process transparent, i.e., will be operated between normal wafer manufacturing intervals such that wafer production is not interrupted. In addition, an improved in-situ dry cleaning process preferably will be self-monitoring, so that visual inspection of the sampling chamber is not required, and so that cleaning is only conducted when needed.

Summary of Disclosure

The present disclosure, accordingly, provides an in-situ cleamng system for cleaning deposits created by process gases in a sampling chamber of a semi-conductor wafer manufacturing process monitor. The system includes a cleaning valve for connecting a source of cleaning gas to the sampling chamber. The cleaning gas is known to react with the process deposits in the sampling chamber to create a gaseous cleaning by-product upon generation of a plasma within the sampling chamber.

The system also includes a controller for opening the cleaning valve and allowing cleaning gas to be drawn into the sampling chamber, activating a plasma generator of the process monitor within the chamber, detecting the amount of gaseous cleaning by-product within the sampling chamber using an analyzer of the process monitor, and evacuating gaseous cleaning by-product from the chamber using a pump of the process monitor. The in-situ cleaning is repeated until the detected amount of gaseous cleaning by-products falls to a predetermined level.

Preferably, the in-situ cleaning system is incorporated in the semi-conductor wafer manufacturing process monitor, and programmed to clean between normal process sampling intervals of the monitor, such that wafer manufacturing cycles are not interrupted by the cleaning process. Brief Description of the Drawings

Fig. 1 is a schematic illustration of a process monitor according to the present disclosure shown connected to a process chamber of a semi-conductor wafer fabricator;

Fig. 2 is a flow chart illustrating a method of in-situ cleaning according to the present disclosure for the process monitor of Fig. 1 ;

Fig. 3 is a flow chart illustrating operation of the process monitor of Fig. 1; and

Fig. 4 is a flow chart illustrating another method of in-situ cleaning according to the present disclosure for the process monitor of Fig. 1.

Detailed Description of Disclosure

Referring to Fig. 1 , the present disclosure generally provides an in-situ cleaning system 10 for cleaning deposits created by process gases in a process chamber 12 of a semi-conductor wafer fabricator 14 or a sampling chamber 16 of a process monitor 18. As is known, such deposits are by-products of the wafer fabrication process, which may comprise physical deposition, chemical vapor deposition, or reactive ion etching, for example. The deposits are unwanted since they can adversely affect the quality and quantity of wafer production. In particular, such deposits can coat a probe 32 of a residual gas analyzer (RGA) 30 or an inside surface of an end point detection window (not included in the particular embodiment shown) or other process monitoring devices, and degrade process monitoring.

The presently disclosed in-situ cleaning system 10 removes such deposits and provides the benefit of being self-monitoring, so that visual inspection is not required and cleaning is only conducted when needed. In addition, the in-situ cleaning system 10 is process transparent, i.e., is operated between normal wafer manufacturing intervals such that wafer production is not interrupted.

Referring to Fig. 1, a simplified version of the wafer fabricator 14 is shown, wherein the fabricator includes the process chamber 12, a wafer stand 20 within the process chamber, and a tool pump 22 for creating a vacuum within the process chamber and controlling the pressure therein. While the fabricator 14 is described as a "wafer" fabricator, the disclosure is not to be limited to a system for fabricating semi-conductor wafers, and can be used with any fabricator incorporating vapor deposition, such as a vapor deposition fabricator for coatings products.

As shown in Fig. 1, the in-situ cleaning system 10 is preferably incorporated as part of the process monitor 18. In addition to the in-situ cleaning system 10 and the sampling chamber 16, the process monitor 18 includes a sampling valve 24 connecting the sampling chamber to the process chamber 12 of the wafer fabricator 14, a purge valve 26 for connecting a source of inert purging gas to the sampling chamber, a pump 28 for controlling the pressure within the sampling chamber, and the RGA 30 having the probe 32 extending into the sampling chamber. The RGA 30 comprises both a plasma generator for generating a plasma within the sampling chamber 16, and an analyzer for chemically analyzing gases within in the sampling chamber.

The process monitor 18 also includes a computer controller 34. During a wafer fabricating process carried out by the fabricator 14 within the process chamber 16, the controller 34 of the monitor 18 causes the sampling valve 24 to open and the pump 28 to draw a sample of process gases from the process chamber, through the open sampling valve, and into the sampling chamber 16. The controller 34 then instructs the RGA 30 to generate a plasma within the sampling chamber 16 (or at least around a distal tip of the probe 32 of the RGA) such that the sample of process gases is ionized, and to analyze the composition of the ionized gases. The RGA 30 then transmits its analysis of the process gases to the controller 34.

Examples of such process monitors include the Orion^® CompactPVD^™ and the Orion^® CompactCVD^™ process monitors, which are both available from the assignee of the present disclosure. Each process monitor includes an Orion^® CompactRGA ^M that comprises a quadrupole mass spectrometer having a probe for extending into a process chamber or sampling chamber for direct gas analysis. Other types of process monitors are also known, including other types of spectrometers, such as "ion trap" mass spectrometers. Still referring to Fig. 1, the in-situ cleaning system 10 of the present disclosure includes a cleaning valve 36 for connecting a source of cleaning gas to the sampling chamber 16 and for allowing cleaning gas from the source to be drawn into the sampling chamber upon the cleaning valve being opened. The particular cleaning gas used is dependent upon the type of deposits to be cleaned. The cleaning gas must be known to react with the process deposits in the sampling chamber to create a gaseous cleaning by-product upon generation of a plasma within the sampling chamber. The gaseous cleaning by-product can then be evacuated from the sampling chamber 16 by the pump 28 of the process monitor 18.

For example, if a reactive ion etching process involves removing a pattern of a layer of silicon oxide with a reactant such as CF₄ or CHF₃, polymer deposits comprised of carbon and fluorine, are created and can coat the probe of the RGA. In such a case, a suitable cleaning gas comprises a source of oxygen O₂, which, when ionized by the plasma generator, provides chemically active oxygen O⁺. The chemically active oxygen reacts with the polymer deposits to create a gaseous cleaning by-product comprising carbon monoxide CO and fluorine F.

As shown in Fig. 1, the controller 34 of the process monitor 18 is preferably programmed to act as the controller for the in-situ cleaning system 10. Accordingly, the controller 34 is programmed to conduct a method of in-situ cleaning according to the present disclosure, as shown in Fig. 2. The in-situ cleaning method is conducted when the process monitor 18 is inactive, i.e., not analyzing samples of process gases, and includes opening the cleaning valve 36 and allowing cleaning gas to be drawn into the sampling chamber 16. Then the controller 34 instructs the RGA 30 to generate a plasma at the tip of the RGA probe 32, such that the cleaning gas is ionized and reacts with any deposits on the probe to create the gaseous cleaning by-product(s). While the gaseous cleaning by-product is created, the controller 34 instructs the pump 28 of the process monitor 18 to evacuate the gaseous cleaning by-product from the sampling chamber 16. The controller 34 also instructs the RGA 30 to continually detect the amount of the gaseous cleaning by-product within the sampling chamber 16. When the detected amount of gaseous cleaning by-products falls to a predetermined minimum level, the controller 34 closes the cleaning valve 36 and terminates the plasma to end the in-situ cleaning. As shown in Fig. 2, the predetermined minimum level of the gaseous cleaning by-product is preferably equal to about zero, thereby indicating that no process deposits remain in the sampling chamber 16.

Referring to Fig. 3, the controller 34 of the process monitor 18 controls the in- situ monitoring of process gases within the process chamber 12 of the wafer fabricator 14, the in-situ cleaning of the sampling chamber 16, and also an in-situ purge of the sampling chamber. The in-situ monitoring and the in-situ purging are not described here in detail since they are methods conducted by existing process monitors.

In general, however, the in-situ monitoring is conducted while a wafer is chemically fabricated within the process chamber 12 of the wafer fabricator 14. The sampling valve 24 is opened, and the pump 28 is operated such that a sample of process gases is continually drawn into the sampling chamber 16, where the RGA 30 analyses the composition of the process gases. When the chemical fabrication of the wafer is completed, the sampling valve 24 is closed, sampling gases are evacuated from the sampling chamber 16 by the pump 28, and the in-situ monitoring is completed.

The in-situ purge generally includes opening the purge valve 26 and drawing inert gas through the sampling chamber 16 and the RGA probe 32 to ensure that process gases from previous samples are removed from the chamber and the probe, such that the previous samples do not affect subsequent samples.

As shown in Fig. 3, a method of process monitoring according to the present disclosure includes, in sequence, the in-situ monitoring or sampling, the in-situ cleaning and the in-situ purging. In addition, the method of process monitoring is preferably time limited. For example, if the wafer fabricator 14 fabricates a wafer or batch of wafers for thirty (30) seconds of every minute, then the controller 34 of the process monitor 18 is programmed to conduct the in-situ monitoring for a period "Tl " equal to 30 seconds, and to repeat the entire method of process monitoring at intervals "T2" equal to one minute. As shown in Fig. 3, the in-situ cleaning and the in-situ purging are conducted after "Tl" but before "T2", i.e., between the sampling periods "Tl". Accordingly, the in-situ cleaning is preferably conducted after each in-situ sampling. Alternatively, however, the controller 34 could be programmed to conduct the in-situ cleaning only after a predetermined number of samples have been taken.

Referring now to Fig. 4, another method of in-situ cleaning according to the present disclosure is shown. The method of Fig. 4 is similar to the method of Fig. 2, but is limited to a predetermined cleaning time, e.g., ten (10) seconds. If the in-situ cleaning is preferably conducted between in-situ sampling intervals of 30 seconds every minute, then the in-situ cleaning will have to be at least less than 30 seconds to fit between the sampling intervals (since Tl - T2 = 30 seconds). Accordingly, as shown in Fig. 4, if the detected amount of gaseous cleaning by-products within the sampling chamber does not fall to the predetermined minimum level prior to the expiration of the predetermined cleaning time, then in-situ cleaning is automatically terminated.

Alternatively, the controller 34 can be programmed to delay the wafer fabricator 14 such that the processing of a next wafer is not started until the in-situ cleaning removes all deposits from the monitor 18.

Because certain changes may be made in the above described in-situ cleaning system and method without departing from the scope of the present disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted in an illustrative and not a limiting sense.

Claims

What is Claimed is:

1. An in-situ cleaning system for cleaning deposits created by process gases in a sampling chamber of a process monitor also having a sampling valve for connecting the sampling chamber to a process chamber of a wafer fabricator and for allowing a sample of process gas to be drawn from the process chamber into the sampling chamber, a plasma generator for generating a plasma within the sampling chamber, and an analyzer for analyzing process gas in the sampling chamber, the in- situ cleaning system comprising: a cleaning valve for connecting a source of cleaning gas to the sampling chamber and for allowing cleaning gas from the source to be drawn into the sampling chamber upon the cleaning valve being opened, the cleaning gas known to react with the process deposits in the sampling chamber to create a gaseous cleaning by-product upon generation of a plasma within the sampling chamber; and a controller controlling the in-situ cleaning system by, opening the cleaning valve and allowing cleaning gas to be drawn into the sampling chamber, activating the plasma generator of the process monitor, detecting the amount of the gaseous cleaning by-product within the sampling chamber using the analyzer, evacuating the gaseous cleaning by-product from the sampling chamber using a pump of the process monitor, and closing the cleaning valve and terminating the plasma when the detected amount of gaseous cleaning by-products falls to a predetermined level.

2. An in-situ cleaning system according to claim 1 , wherein the predetermined level is equal to about zero.

3. A process monitor including an in-situ cleaning system according to claim 1, and further comprising: a sampling chamber connected to the cleaning valve; a sampling valve for connecting the sampling chamber to a process chamber of a wafer fabricator; a pump connected to the sampling chamber; a plasma generator for creating a plasma within the sampling chamber; an analyzer for analyzing contents of the sampling chamber; and a controller for analyzing samples of process gases at predetermined sampling intervals by, opening the sampling valve and allowing the pump to draw a sample of the process gases from the process chamber into the sampling chamber, analyzing the sample of process gases using the analyzer, closing the sampling valve, and allowing the pump to evacuate the sampling chamber; and wherein the in-situ cleaning system cleans process deposits in the sampling chamber between sampling intervals.

4. A process monitor according to claim 3, wherein a quadruple mass spectrometer residual gas analyzer comprises the analyzer and the plasma generator.

5. A process monitor according to claim 3, wherein the predetermined level is equal to about zero.

6. A method of in-situ cleaning of deposits from a wafer fabricator, comprising: transferring a cleaning gas into the wafer fabricator, the cleaning gas reactive with process deposits upon generation of a plasma to create a known gaseous cleaning by-product; generating a plasma in the wafer fabricator such that the cleaning gas reacts with the deposits to create the gaseous cleaning by-product; detecting the amount of gaseous cleaning by-product within the wafer fabricator; evacuating the gaseous cleaning by-product from the wafer fabricator; and stopping the plasma generation and the transfer of cleaning gas when the detected amount of gaseous cleaning by-products falls to a predetermined level.

7. A method of in-situ cleaning according to claim 6, wherein a quadruple mass spectrometer residual gas analyzer is used to generate the plasma and detect the amount of gaseous cleaning by-product.

8. A method of monitoring a process conducted within a wafer fabricator including a method of in-situ cleaning according to claim 6, and further comprising: analyzing process gases from the wafer fabricator at predetermined sampling intervals; and conducting the method of in-situ cleaning between sampling intervals.

9. A method of monitoring a process according to claim 8, wherein each in-situ cleaning between sampling intervals is limited to a pre-determined maximum cleaning interval.

10. A method of monitoring a process according to claim 8, further comprising purging the wafer fabricator after each in-situ cleaning.

11. A method of in-situ cleaning of deposits in a wafer fabricating process monitor, comprising: transferring a cleaning gas into a sampling chamber of the process monitor, the cleaning gas reactive with process deposits upon generation of a plasma to create a known gaseous cleaning by-product; generating a plasma in the sampling chamber such that the cleaning gas reacts with the deposits to create the gaseous cleaning by-product; detecting the amount of gaseous cleaning by-product within the sampling chamber; evacuating the gaseous cleaning by-product from the sampling chamber; and stopping the plasma generation and the transfer of cleaning gas when the detected amount of gaseous cleaning by-products falls to a predetermined level.

12. A method of in-situ cleamng according to claim 11 , wherein a quadruple mass spectrometer residual gas analyzer is used to generate the plasma and detect the amount of gaseous cleaning by-product.

13. A method of in-situ cleaning according to claim 11 , wherein the in-situ cleaning is conducted between predetermined sampling intervals.

14. A method of in-situ cleaning according to claim 13, wherein each in-situ cleaning between sampling intervals is limited to a pre-determined maximum cleaning interval.

15. A method of monitoring a process conducted within a wafer fabricator including a method of in-situ cleaning according to claim 11, and further comprising: analyzing process gases from the wafer fabricator at predetermined sampling intervals; conducting the method of in-situ cleaning between sampling intervals; and purging the sampling after each in-situ cleaning.

16. A method of in-situ cleaning of deposits from a vapor deposition product fabricator of the type including a process monitoring system for monitoring the constituents of vapors introduced into the fabricator during a fabrication process, the method of in-situ cleaning comprising: introducing a cleaning gas into the fabricator following a fabrication process under conditions so that the cleaning gas reacts with process deposits so as to create a known gaseous cleaning by-product; detecting the amount of gaseous cleaning by-product within the fabricator; evacuating the gaseous cleaning by-product from the fabricator; and stopping the introduction of cleaning gas when the detected amount of gaseous cleaning by-products falls to a predetermined level.

17. A method of in-situ cleaning according to claim 16, wherein the process monitoring system includes a mass spectrometer.

18. A method of in-situ cleaning according to claim 16, wherein a mass spectrometer residual gas analyzer is used to generate a plasma within the fabricator so as to create a condition to allow reaction of the cleaning gas and the process deposits and to detect the amount of gaseous cleaning by-product.

19. A method of monitoring a process conducted within a fabricator including a method of in-situ cleaning according to claim 16, and further comprising: analyzing process gases from the fabricator at predetermined sampling intervals; and conducting the method of in-situ cleaning between sampling intervals.

20. A method of monitoring a process according to claim 19, wherein each in-situ cleaning between sampling intervals is limited to a pre-determined maximum cleaning interval.