WO1998055667A1

WO1998055667A1 - Method and apparatus for measurement of cvd exhaust deposits

Info

Publication number: WO1998055667A1
Application number: PCT/US1998/010572
Authority: WO
Inventors: Paul B. Comita; David K. Carlson; Doria W. Fan; Ann P. Waldhauer
Original assignee: Applied Materials, Inc.
Priority date: 1997-06-02
Filing date: 1998-05-21
Publication date: 1998-12-10
Also published as: TW403791B

Abstract

A method and system for quantifying the amount of byproduct buildup in the reaction chamber and support systems used to fabricate semiconductor device layers is disclosed. One embodiment of the present invention places a film thickness measuring device in an exhaust pipe (150) of a reactor (100). The film thickness measuring device is positioned such that the operating parameters, for example temperature, of that particular device are optimized. The thickness of the exhaust byproduct buildup is then measured using the film thickness measuring device. Once the amount of byproduct buildup is quantified at the location of the film thickness measuring device then the byproduct buildup at other locations in the system be determined.

Description

ETHOD AND APPARATUS FOR MEASUREMENT OF CVD EXHAUST DEPOSITS

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of semiconductor device fabrication, and more specifically, to a method and apparatus for determining byproduct buildup in the exhaust system of a semiconductor process chamber.

2. Background Information

In semiconductor device fabrication semiconductor devices are fabricated in layers by depositing (or growing) and patterning materials one on top of another on a semiconductor substrate (or wafer). These materials, for example: metals, insulating dielectrics, photoresists, etc., are deposited and /or grown on the semiconductor substrate in process /reaction chambers (reactors).

Some examples of reactors are Evaporative Reactors, Sputtering Reactors, and Chemical Vapor Deposition (CVD) Reactors. Such reactors are used to deposit and /or grow thin films of materials on the semiconductor substrate. The problem with such reactors is that the materials and byproducts of the materials deposited or grown on the substrate may also grow or deposit elsewhere in the reaction chamber itself and /or the exhaust system of the reactor. Byproduct buildup may potentially contaminate the semiconductor substrates being processed.

As semiconductor device density increases and device sizes decrease the need to control potential contamination increases. Particle and film contamination during the fabrication of a semiconductor device can cause major problems in device performance and reliability on down the line.

Therefore, it is important to be sure the reactors used to fabricate the semiconductor devices are as clean and contaminant free as possible.

Keeping the reactors clean requires that the reactor have a good exhaust and/or ventilation and/or vacuum system (support systems) to keep and remove any unwanted particles, debris, chemicals, etc. (contaminants) so that such contaminants are not deposited onto the substrate during processing. The reactors themselves and their support systems sometimes need to be taken apart and thoroughly cleaned in order to remove any buildup of potential contaminants.

A problem with cleaning the reactors and their support systems is that this requires significant downtime and can be costly to the manufacturer if done too often. Downtime decreases the number of substrates that can be processed which limits the throughput of the system. A decrease in throughput can dramatically change a manufacturer's production costs.

On the other hand, it can be just as costly if not more so, to wait too long before cleaning because the semiconductor devices being fabricated may become contaminated. If byproduct buildup begins to flake off in the reaction chamber or builds up too significantly in the exhaust system decreasing the flow of gases and /or air, then the semiconductor devices being fabricated may become contaminated. The contamination may cause the devices to either not function properly or not function at all. Thus, the manufacturer's production yield would decrease. Worse yet, is that the effects of the contamination may not show up as a problem until after the product has been shipped to a customer.

An example of the problem of buildup may be seen in Chemical Vapor Deposition (CVD) of thin films. In a CVD reactor the chemicals used react to form the desired film or layer on the substrate, however, these reactions also produce byproducts which are to be removed from the reaction chamber through the exhaust system. Often these byproducts build up in the pipes of the exhaust system and eventually constrict the amount of gas flow through the exhaust system. If the exhaust system is not cleaned the restriction of flow may become so great that it causes backstreaming of the exhaust. Backstreaming blows the byproducts of the CVD reaction and the exhaust buildup back into the reaction chamber which can potentially contaminate the substrate being processed.

Some prior art methods for cleaning the reactor and support systems are based upon the amount of time a particular reactor has been in use and /or the number of substrates that have been processed. For example, a particular semiconductor device manufacturer may decide to clean its reactors and support systems after they have run for 72 hours of actual processing time. As another example, another semiconductor device manufacturer may decide to clean its reactors and support systems after every 10,000 wafers have been processed. Still another example may combine the two, and a semiconductor device manufacturer may decide to clean its reactors and support systems after every 10,000 wafers have been processed or 72 hours whichever is lesser (or greater as the case may be).

The prior art method most often used to determine if the reactor and /or support systems actually need cleaned is visual inspection of the reaction chamber and support systems. Unfortunately, the problem with visual inspection is that the reactor must be shut down and the reactor and /or support system being inspected must be torn apart to see the amount of buildup on the inside. In the example given above for the exhaust system of the CVD reactor, the exhaust pipes (or portions thereof) would be dismantled in order to visually inspect the amount of buildup.

After visual inspection and after the amount of buildup has been determined, then the particular manufacturer must determine whether or not the support systems and reactor are to be cleaned. Here again the manufacturer must weigh and balance the cost effectiveness of taking the time to clean the reactor if the buildup is not too great versus the cost effectiveness of putting the reactor and support systems back together and then having to recheck and /or clean them later.

Determining when to clean the reactor and support systems depends largely upon the parameters of the process. What process is being run, how much contamination can a particular process tolerate, what types of chemicals are being used in that process, what are the concentrations of the chemicals being used, what are the byproducts of these chemicals, etc. The variables are so numerous that it is hard to determine when the reactor and support systems should be cleaned.

Thus, what is needed is a method and apparatus for determining when a reactor and its support systems need to be cleaned without the problems associated with visual inspection, with less risk of contamination of the substrates being processed, and improving the cost effectiveness of the cleaning process. SUMMARY OF THE INVENTION

The present invention describes a method and apparatus for detecting exhaust buildup. One embodiment of the present invention places a film thickness measuring device in an exhaust pipe of a reactor. The film thickness measuring device is positioned at a first location in the exhaust pipe. The thickness of the exhaust byproduct buildup at the first location is then measured using the film thickness measuring device.

Additional features and benefits of the present invention will become apparent from the detailed description, figures, and claims set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitation in the accompanying figures in which:

Figure 1 illustrates a cross-sectional view of one embodiment of a CVD reactor.

Figure 2 illustrates a cross-sectional view of one embodiment of a CVD reactor and exhaust system.

Figure 3 illustrates one embodiment of a QCM. DETAILED DESCRIPTION

A Quartz Crystal Microbalance for Measurement of CVD Exhaust Deposits is disclosed. In the following description, numerous specific details are set forth such as specific materials, process parameters, equipment, etc. in order to provide a thorough understanding of the present invention. It will be obvious, however, to one skilled in the art that these specific details need not be employed to practice the present invention. In other instances, well known materials or methods have not been described in detail in order to avoid unnecessarily obscuring the present invention.

The present invention describes a method and apparatus for detecting exhaust buildup in a semiconductor process chamber without the need for visual inspection and taking the exhaust system apart. In the manufacture of semiconductor devices it is important to maintain the cleanliness of the process/ reaction chambers (reactors) and their support systems in order to reduce the potential contamination of the semiconductor devices being fabricated.

In the manufacture of semiconductor devices the reactions and processes used to fabricate semiconductor films and /or layers form byproducts. These byproducts often build up on the inside walls of the reaction chamber or in the exhaust system of the reaction chamber. Such a buildup of these byproducts could potentially contaminate the semiconductor substrate (or wafer) being processed. Therefore, periodically the reactors and exhaust systems must be cleaned and the byproduct buildup removed.

As stated above, the frequency of the maintenance of the reactor and support systems will vary depending upon many factors that influence the amount of byproduct deposit formation. Such factors include, but are not limited to: the particular process that is being run, how much contamination can a particular process tolerate, what types of chemicals are being used in that process, what concentrations of chemicals are being used, what are the byproducts of these chemicals, etc.

The present invention is a method and apparatus for quantifying the amount of exhaust byproduct formation in a reactor. Although the following description describes the use of the present invention with respect to a

Chemical Vapor Deposition (CVD) reactor, it should be noted and it will be obvious to one with ordinary skill in the art that the present invention may also be used in conjunction with other reactors, for example evaporative reactors and sputtering reactors. The particular advantages of the use of the present invention with respect to a CVD reactor are discussed in further detail below. In a CVD reactor, chemicals are combined to deposit a film, for example, an epitaxial silicon layer, on a semiconductor substrate. One embodiment of a CVD reactor 100 is illustrated in Figure 1. An example of a

CVD reactor is the Epi Centura Model available from Applied Materials

Corporation in Santa Clara, California. A semiconductor substrate

(substrate) 110 is held in place by substrate holder 120 and susceptor 125 within reaction chamber (chamber) 130 of reactor 100. Substrate 110 is subjected to a combination of chemicals and high temperatures in order to grow a film (or layer) on the surface of substrate 110. The reactant chemicals

(or gases) are delivered into chamber 130 and across the surface of substrate

110 as is illustrated by laminar gas flow 140 in Figure 1.

As the gases are delivered to chamber 130 the pressure within chamber 130 is maintained at a constant pressure, for example, at approximately atmospheric pressure or reduced pressure, and the temperature of chamber 130 is raised in order to promote the chemical reaction of the gases. The combination of the gases, pressure, high temperature, and other parameters cause the desired film to be deposited or grown on substrate 110. This process continues until the desired film thickness is reached. The byproducts of the CVD reaction (byproducts) and excess gas flow are pushed through the chamber 130 and out the exhaust 150 to the exhaust system (not shown).

Figure 2 illustrates the CVD reactor of figure 1 connected to an exhaust system. The excess gas flow and byproducts are pushed out of chamber 130 into exhaust system 200. As the exhaust travels through exhaust system 200 the byproducts build up on the walls of the exhaust piping. In general, larger amounts of byproduct buildup are formed in the beginning end 210 of the exhaust pipes while smaller amounts of byproduct buildup are formed in the latter end 280 of the exhaust pipes. In any case, the buildup of byproduct deposits on the inside of the exhaust pipes will constrict the gas flow through exhaust system 200 and may cause backstreaming as is discussed above. Backstreaming would force exhaust gases and byproduct particles back into chamber 130 and may cause contamination of the semiconductor devices being fabricated.

In order to prevent backstreaming the present invention determines the amount of byproduct buildup that is deposited in the exhaust pipe without requiring visual inspection of the inside of the exhaust pipes. In other words, the present invention does not require that the reactor and support systems be shut down, dismantled, and visually inspected in order to determine the amount of byproduct buildup in the reactor and support systems. Instead, by using a film thickness measuring device the present invention allows for the determination of the amount of buildup without affecting the throughput of the reactor. The present invention also eliminates the need to account for all of the varying factors that affect deposit buildup by determining or quantifying the amount of buildup that is actually occurring regardless of the particular process that is being used in the reaction chamber.

One embodiment of the present invention uses a film thickness measuring device in the exhaust pipe of a reactor. Placing the film thickness measurement device in the exhaust pipe allows for the measurement of the byproduct buildup at that location in the process chamber. Then based upon the positioning of the film thickness measuring device and the amount of byproduct buildup at that location, the amount of byproduct buildup at other locations in the exhaust pipe and even in the reaction chamber itself may be determined. Thus, the present invention uses a film thickness measuring device in order to measure the thickness of the byproducts made during the film deposition process rather than the thickness of the film that is being deposited or grown on the substrate.

It should be noted and it will be obvious to one with ordinary skill in the art that the film thickness measuring device may be placed in other areas of the reactor support systems, for example, the film thickness measuring device may be placed in the ventilation system. It should be noted however, that the film thickness measuring device should be placed in an area that will be exposed to the reactant gases and /or byproducts of the process being performed in the reactor (i.e. in an area that is subject to byproduct deposition and buildup).

By measuring the byproduct rather than the film itself, the present invention may be performed "in-line" rather than "in-situ" which is typically required in film thickness measurement techniques. For example, in order to determine the thickness of a film that is being deposited or grown, a film thickness measurement device is placed directly in the reaction chamber (i.e. in-situ) and is subjected to the same process that the substrate is subjected to and the same film layer that is grown on the substrate is also grown on the film thickness measuring device.

There are several problems associated with the measurement of the film thickness. One problem is that the film thickness tells us very little about the byproduct buildup that is occurring. Depending upon the type of process being used the amount of byproduct buildup may be disparate from the thickness of the film actually being grown deposited on the substrate. In other words, depending upon a number of varying factors the byproduct buildup may be much greater than the thickness of the film, or vice versa.

Another problem is that some film thickness measuring devices may not be used in some reaction chambers. For example, due to the high temperatures used in a CVD reactor many film thickness measuring devices cannot be used. Film thickness measurement devices are typically very sensitive to temperature and temperature changes and since the temperatures used in

CVD reactions are typically very high thus making in-situ measurements very inaccurate.

In one embodiment of the present invention the film thickness measurement device is used for measuring the byproduct deposition and is placed "in-line" in the exhaust system. In order to avoid the problems associated with temperature and temperature fluctuation the film thickness measurement device may be placed at a location in the exhaust system where the exhaust flow has cooled and the temperature is more stable. In one embodiment of the present invention the thickness measurement device is placed at a location where the temperature is approximately ambient temperature. As illustrated in Figure 2, film thickness measurement device 290 is located far enough from reaction chamber 130 that the exhaust will have cooled to a temperature more suitable for a QCM.

In one embodiment of the present invention a Quartz Crystal Microbalance Sensor (QCM) is used as the film thickness measuring device. A QCM is a thickness measurement device that measures the mass by determining the amount of material that attaches (or is deposited) on the sensing surface of the QCM. Figure 3 illustrates one embodiment of a QCM. QCM 300 measures the thickness of layers that are deposited on sensing surface 310.

A QCM may be used in-situ to measure the thickness of the layer or film that is being deposited /grown on the wafer in the reactor. However, the present invention does not use the QCM for this purpose. Rather the present invention uses the QCM to measure (or determine) the amount of byproduct buildup that results from the process of fabricating a film on a substrate, not the thickness of the film itself. Additionally, the present invention does not use the QCM in-situ, but rather locates the QCM in one of the support systems to the reactor. By placing the QCM in one of the support systems to the reactor the amount of byproduct buildup in that support system may be determined. Once the amount of byproduct buildup is determined at the location of the QCM, the amount of byproduct buildup at other locations in the same support system, other support systems, and reactor may also be determined by looking at factors such as, distance from the QCM, location of QCM with respect to the reaction chamber, the types of gases or reactant chemicals being used, reaction time, etc.

When it is determined that the byproduct buildup has reached a certain level then the manufacturer may shut down and dismantle the reactor and support systems, as necessary, in order to clean the reaction chamber, exhaust system, and other support systems. By determining the amount of deposit buildup without having to take the exhaust system and chamber apart, the amount of downtime normally associated with cleaning the reaction chamber and support systems is reduced. Decreasing the downtime increases the throughput of the reactor. The present invention also eliminates the need to account for all of the varying factors that affect deposit buildup by determining or quantifying the amount of buildup that is actually occurring regardless of the particular process that is being used in the reaction chamber.

A QCM is sensitive to temperature and gas density. In other words, the accuracy of the QCM depends greatly upon the stability of the temperature and gas density. If the temperature or gas density tend to fluctuate, so will the measurements of the QCM. A QCM functions up to a temperature of approximately 120°C and may be used in-situ with evaporative and sputtering reactors because the temperature within the reaction chambers are fairly constant and are generally lower temperature reactions than used in CVD reactors.

However, since the QCM in the present invention is being used to measure the amount of byproduct buildup and is placed within the exhaust system the dependency of the QCM on temperature is reduced. Thus, it does not matter what temperature is required for the process in the reaction chamber, it only matters what the temperature is at the location in the exhaust system where the QCM is located. In one embodiment of the present invention the QCM is placed at a location in the exhaust system where the exhaust has cooled, for example to ambient temperature, by the time it reaches the QCM. Thus, the present invention may be used in the exhaust system of any reaction chamber including chambers that use high temperatures such as CVD reaction chambers.

It should be noted that the QCM is generally used in connection with the measurement of film thicknesses on the order of atomic-monolayers. It therefore becomes important to locate the QCM at a location in the exhaust system where the byproduct buildup is on the atomic-monolayer scale.

Locating the QCM at a position where heavier buildup occurs may cause the

QCM to fail.

It should also be noted that in a system at atmospheric pressure, for example a CVD reactor, the quantity of gas flowing through the exhaust pipe is much larger (or higher) than the quantity in the environment in which a

QCM is typically used. Therefore, it will be advantageous to place the QCM further from the reaction chamber in a CVD system. As illustrated in Figure 2, thickness measuring device 290 is located near the latter end 280 of the exhaust pipe. In general the exhaust will have had time to cool before it reaches the latter end 280 of the exhaust pipe. It should be noted, however, that the thickness measuring device 290, may be placed at any location in the exhaust system 200 if the temperature at that location is within the functional parameters of the particular thickness measuring device being used. Also, the byproduct buildup at the latter end

280 of the exhaust pipe is much less than the byproduct buildup at the beginning end 210 of the exhaust pipe. Therefore, the thickness measuring device 290 will not be subjected to heavy layers of byproduct buildup. It should be noted, however, that the thickness measuring device 290, may be placed at any location in the exhaust system 200 if the byproduct buildup at that location is within the functional parameters of the particular thickness measuring device being used.

Once the amount of byproduct buildup at the location of the thickness measuring device has been quantified, the byproduct buildup at other locations within the exhaust system, other support systems, and reactor itself may be determined. The determination of byproduct buildup at these other locations requires the use of conversion factors. For example, if thickness measuring device 290 quantifies the amount of byproduct buildup at the latter end 280 of exhaust system 200, then by using a conversion factor the amount of byproduct buildup at the beginning end 210 of exhaust system

200 may be determined. Such conversion factors may require, for example, the distance from the thickness measuring device to the location where the buildup is being determined, the length of the pipe, the diameter of the pipe, the rate of flow, the distance from the reaction chamber, etc. Although the present invention is described above with respect to a

QCM, it should be noted that other thickness measuring devices may also be used. For example, another embodiment of the present invention uses a sensor with a window and a light stream (sensor). Such a sensor may also be used to measure the thickness of byproduct buildup and /or determine when the amount of byproduct buildup is thick enough that the reactor and support systems should be cleaned.

Thus, Quartz Crystal Microbalance for Measurement of CVD Exhaust

Deposits has been described. Although specific embodiments, including specific equipment, parameters, methods, and materials have been described, various modifications to the disclosed embodiments will be apparent to one of ordinary skill in the art upon reading this disclosure. Therefore, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention and that this invention is not limited to the specific embodiments shown and described.

Claims

CLAIMSWhat is claimed is:

1. A method for detecting exhaust buildup comprising: placing a film thickness measuring device in an exhaust pipe of a reactor; positioning said film thickness measuring device at a first location in said exhaust pipe; measuring the thickness of an exhaust by-product buildup using said film thickness measuring device at said first location.

2. The method as described in claim 1 further comprising the step of: determining the thickness of said exhaust by-product buildup at a second location in said exhaust pipe.

3. The method as described in claim 1 wherein said film thickness measuring device is a QCM device.

4. The method as described in claim 1 wherein said reactor is a CVD reactor.

5. The method as described in claim 3 wherein said reactor is a CVD reactor.

6. The method as described in claim 5 wherein said first location is at a point in said exhaust pipe wherein the temperature of the exhaust traveling through said exhaust pipe is approximately ambient temperature.

7. The method as described in claim 5 wherein said first location is at a point in said exhaust pipe wherein the temperature of the exhaust traveling through said exhaust pipe is approximately less than 120┬░C.

8. The method as described in claim 3 wherein said first location is at a point in said exhaust pipe wherein said exhaust by-product buildup is in the range of atomic monolayers.

9. The method as described in claim 2 wherein said step of determining the thickness of said exhaust by-product buildup at a second location in said exhaust pipe is performed based upon the measurement of said exhaust byproduct measurement at said first location.

10. A method for detecting exhaust buildup comprising: placing a film thickness measuring device in an exhaust pipe of a reactor; positioning said film thickness measuring device at a first location in said exhaust pipe; measuring the thickness of an exhaust by-product buildup using said film thickness measuring device at said first location; determining the thickness of said exhaust by-product buildup at a second location in said exhaust pipe.

11. The method as described in claim 10 wherein said film thickness measuring device is a QCM device.

12. The method as described in claim 10 wherein said reactor is a CVD reactor.

13. The method as described in claim 11 wherein said reactor is a CVD reactor.

14. The method as described in claim 13 wherein said first location is at a point in said exhaust pipe wherein the temperature of the exhaust traveling through said exhaust pipe is approximately ambient temperature.

15. The method as described in claim 13 wherein said first location is at a point in said exhaust pipe wherein the temperature of the exhaust traveling through said exhaust pipe is approximately less than 120┬░C.

16. The method as described in claim 11 wherein said first location is at a point in said exhaust pipe wherein said exhaust by-product buildup is in the range of atomic monolayers.

17. A reactor comprising: a reaction chamber; a gas input; an exhaust output, wherein said exhaust output includes an exhaust pipe; and a film thickness measuring device, wherein said film thickness measuring device is located in said exhaust pipe.

18. The reactor as described in claim 17 wherein said reactor is a CVD reactor.

19. The reactor as described in claim 17 wherein said film thickness measuring device is a QCM device.

20. The reactor as described in claim 18 wherein said film thickness measuring device is a QCM device.

21. The reactor as described in claim 19 wherein said film thickness measuring device is located at a point in said exhaust pipe wherein the temperature of the exhaust traveling through said exhaust pipe is approximately ambient temperature.

22. The reactor as described in claim 19 wherein said film thickness measuring device is located at a point in said exhaust pipe wherein the temperature of the exhaust traveling through said exhaust pipe is approximately less than 120┬░C.

23. The reactor as described in claim 19 wherein said film thickness measuring device is located at a point in said exhaust pipe wherein said exhaust by-product buildup is in the range of atomic monolayers.