Method and apparatus for endpoint detection of a cleaning process

Abstract

Apparatus (10) for detecting or predicting an end point of a cleaning process in a vacuum deposition system, wherein the apparatus comprises - a process chamber (1), the interior of which can be cleaned by said cleaning process, - a vacuum pump arrangement (2) connected to said process chamber via an exhaust line (3), - a flow restriction element (4), in particular a throttle valve, in said exhaust line, defining an upstream part (3') of the exhaust line between the process chamber and the flow restriction element, and defining a downstream part (3'') of the exhaust line be flow restriction element an the vacuum pump arrangement, - a vacuum gauge (5) arranged to measure a pressure in said downstream part of the exhaust line, and - a processing unit (6) arranged and configured to evaluate a time course of pressure values measured by said vacuum gauge and to detect the end point of said cleaning process. Further in the scope of the invention are a device (11) and a method.

Description

[0001] METHOD AND APPARATUS FOR ENDPOINT DETECTION OF A CLEANING

[0002] PROCESS

[0003] TECHNICAL FIELD

[0004] The invention addressed herein relates to the technical field of operating a vacuum deposition facility . In a speci fic application, the invention relates to the field of semiconductor fabrication . More speci fically, the invention relates to an apparatus or a device for detecting an end point of a cleaning process in a vacuum deposition system . Under further aspects , the invention relates to a method of detecting an end point of a cleaning process in a vacuum deposition system and to a method of operating the apparatus or device .

[0005] BACKGROUND OF THE INVENTION

[0006] As an example , wafer processing tools used in semiconductor manufacturing suf fer from detrimental accumulation of deposits (byproduct buildup ) on the chamber walls of a vacuum deposition chamber . This buildup may flake of f during processing, resulting in particle contamination and yield loss as well as impacting other process parameters ( e . g . , film deposition thickness ) . To avoid this , various chamber clean strategies are often used where the processing chamber is subj ected to an etch process which removes unwanted deposits . Reactive gases and plasmas may be used for such cleaning processes in the context of various fabrication processes , such as CVD ( chemical vapor

[0007] P220855 deposition) , Etch, ALD (atomic layer deposition) , Implant, Inspection, Diffusion, MOCVD (metal organic chemical vapor deposition) and others.

[0008] The duration of the chamber clean process is important, as either too short or too long clean time may have deleterious effect. Stopping a cleaning process too early (under-cleaning) may result in leftover deposits which can result in particle contamination. Running a clean process for too long can erode and damage chamber parts, resulting in shorter life-time and a need for expensive and timeconsuming chamber rebuilds. It may also consume more clean precursors, which may be toxic, expensive, and environmentally damaging, such that it is advantageous to use as little precursor substance as possible.

[0009] When a chamber for vacuum deposition processes undergoes a cleaning process, this cleaning process is preferably an in situ process, i.e. the process does not require physical (mechanical) cleaning or disassembling and rebuild of the chamber. There are three main techniques for in situ chamber cleans, which are briefly discussed in the following .

[0010] - The in-situ plasma clean generates reactive plasma in the process chamber which etches the byproducts. This process usually results in light emission from the excited plasma which can be used for clean endpoint detection using optical spectrometry.

[0011] - The remote plasma source clean uses a remote plasma

[0012] P220855 source , where the plasma generates an activated etch gas , which in turn flows into the main process chamber and cleans the main process chamber . This process keeps the unwanted erosion of process chamber parts at a minimum, resulting in longer chamber li fe between maj or rebuilds . It is becoming more common, but optical monitoring of a clean endpoint may be impossible as there is no excited plasma in the process chamber and therefore no light emissions from the region, where the cleaning process takes place .

[0013] - The dry cl ean process relies on flowing reactive gases like fluorine and does not use plasma activation .

[0014] Therefore , optical endpoint detection of dry cleans is also not possible since there is no light emission .

[0015] Several methods for plasma clean end point detection are known and used in the industry . The simplest is the time base end point method . The duration of the clean is estimated based on a calculation of the deposition thickness and its estimated etch rate , then refined experimentally to achieve optimal performance . The optical emission spectroscopy method is based on the analysis of the light emitted by the plasma in the process chamber . The emissions corresponding to the atomic and molecular species resulting from byproduct etch are monitored and used to ascertain the end of the clean process , i . e . the moment , when no more byproduct is left to etch . This technique can be applied only for in situ plasma cleans . Radiofrequency plasma spectrometry measures the impedance of the chamber , which is a resonant cavity, for in situ cleans . Impedance

[0016] P220855 changes are used to assess changes in the chemical composition of plasma species . Mass spectrometry monitors the chemical precursors and products during the clean process . This method can be applied to all three types of chambers cleans , but it relies on relatively expensive instrumentation which requires signi ficant maintenance due to plasma damage of the mass spectrometer components ( e . g . , filament and electron multiplier ) . Infrared spectroscopy ( either non-dispersive or Fourier-trans form) is another technique that can be used to monitor molecular composition of reactive gas and etch products to accurately detect clean endpoint . Like mass spectrometry, IR spectrometry ( and especially FTIR) suf fer from high instrument cost .

[0017] Optical sel f-emission spectrometry uses a combination of an optical spectrometer with a plasma generator as the light source . This technique can be used for remote plasma cleans and dry cleans , measuring either at the process chamber or process chamber exhaust line . Finally, a quartz crystal microbalance ( QCM) can be used for etch rate monitoring and thus clean end point detection . This technique has excellent sensitivity, but it is highly locali zed, as it only measures the state of the quartz crystal . While the QCM sensor itsel f may be clean from deposits ( indicating the endpoint of the clean) , other areas of the chamber may still have leftover byproduct .

[0018] The obj ect of the present invention is to provide an alternative apparatus or a method for end point detection of a cleaning process . More speci fically, the obj ect of the

[0019] P220855 invention is an apparatus or a method, which avoids or at least reduces problems of the state of art .

[0020] SHORT DESCRIPTION OF THE INVENTION

[0021] This obj ect is achieved by an apparatus according to claim 1 .

[0022] The inventive apparatus is an apparatus for detecting or predicting an end point of a cleaning process in a vacuum deposition system . The apparatus comprises

[0023] - a process chamber, the interior of which can be cleaned by said cleaning process ,

[0024] - a vacuum pump arrangement connected to said process chamber via an exhaust line ,

[0025] - a flow restriction element , in particular a throttle valve , in said exhaust line , defining an upstream part of the exhaust line between the process chamber and the flow restriction element , and defining a downstream part of the exhaust line be flow restriction element an the vacuum pump arrangement ,

[0026] - a vacuum gauge arranged to measure a pressure in said downstream part of the exhaust line , and

[0027] - a processing unit arranged and configured to evaluate a time course of pressure values measured by said vacuum gauge and to detect the end point of said cleaning process .

[0028] The flow restriction element may be , but is not limited to , a throttle valve . During a clean process , the chamber pressure may be kept constant by means of a pressure control valve , sometimes called throttle valve or pendulum valve . The conductance of this valve (valve "phase" ) is

[0029] P220855 continuously adj usted by a control loop in response to pressure reading coming from a chamber pressure gauge . This invention proposes to use exhaust line pressure measured at a point after (i . e . downstream) the throttle valve to monitor the chamber clean process . Since the main vacuum pump maintains a constant pumping speed (with a constant vacuum flow throughput ) , the exhaust line pressure provides an accurate means of measuring the rate of gas flow . In addition, a vacuum foreline downstream of the vacuum gauge may act as an ori fice plate , further improving the sensitivity and resolution of flow determination via pressure monitoring . When referring to the foreline here , the exhaust line downstream of the vacuum gauge , establishing a connection of the system to the vacuum pump, is meant . A more sophisticated version of this approach may use two pressure sensors , one measuring the pressure in the proximity to the downstream side of the process chamber throttle valve and another monitoring pressure immediately prior to the pump inlet . The di f ference in the pressure measured by the two sensors gives an accurate indication of the gas flow in the system, as well as the state ( a conductance of the pipe for gas ) of the vacuum foreline .

[0030] In an alternative , the flow restriction element may be an ori fice plate or a similar local reduction in the diameter of the exhaust line . Also in this alternative , a version using two pressure gauges is feasible . An additional pressure gauge may be placed in the chamber itsel f .

[0031] As etching of byproducts changes the amounts of gaseous species flowing towards the exhaust , the exhaust line

[0032] P220855 pressure serves as a convenient and accurate indicator of the chamber clean progress . A time derivative of pressure value over time ( i . e . the slope of the pressure trend) can be used to indicate the end point ( flattening of the pressure trend line ) .

[0033] The vacuum pump arrangement may comprise one or more pumps , depending on the requirements of the processes and the pressure levels needed . As an example , a turbomolecular pump connected in series with a backing vacuum pump may form the vacuum pump arrangement .

[0034] Further in the scope of the invention lies a device according to claim 2 .

[0035] The device according to the invention is a device for detecting or predicting an end point of a cleaning process in a vacuum deposition system . The device is connectable to an exhaust line of the vacuum deposition system in a vacuum-tight manner . The device comprises

[0036] - a vacuum gauge arranged to measure a pressure in said exhaust line when the device is connected to said exhaust line , and

[0037] - a processing unit arranged and configured to evaluate a time course of pressure values measured by said vacuum gauge and to detect the end point of said cleaning process .

[0038] With this device , an autonomous system is provided, which is connectable to a process chamber exhaust line for clean end point detection and for better process control for deposition and etch processes . A possible way of using the device is to provide a vacuum flange on an exhaust line

[0039] P220855 between a vacuum deposition chamber and a vacuum pump system . The device according to the invention may be attached to this flange such that a fluid dynamic connection is established between the interior of the exhaust line and the vacuum gauge of the device . Once this connection is established, an apparatus with the features described in context of claim 1 can be built .

[0040] Further in the scope of the invention lies a method according to claim 3 .

[0041] The method according to the invention is a method of detecting or predicting an end point of a cleaning process in a vacuum deposition system . The method uses the apparatus of the invention . The end point of the cleaning process is detected by identi fication of a first time span of falling pressure in the downstream part of the exhaust line followed by a second time span of essentially constant pressure in said downstream part of said exhaust line .

[0042] As an intermediate step, the method may evaluate the first time derivative or a higher time derivative of the pressure course measured . To reduce unwanted ef fects of measurement noise in the raw pressure data, the method may apply a filtering method to the measured pressure values , such as for example calculating an exponential moving average . A criterion may be applied to the pressure and / or its time derivatives , to detect the reaching of an endpoint . As an example , a time period of dropping pressure values followed by a time period of approximately constant pressure may be the " fingerprint" of reaching an endpoint . Additional

[0043] P220855 parameters , such as the minimal duration of the mentioned time periods , may enter the evaluation of the criterion . Alternatively, or in combination with the criterion, a prediction, whether and when an endpoint will be reached in the future may be derived from the measured pressure course . For such a prediction, the measured values may be fitted with an appropriate mathematical function and extrapolated pressure values for the near future may be calculated .

[0044] As an example , a criterion might be applied to the first time-derivative of the pressure signal .

[0045] Under speci fic circumstances , di f ferent to the example discussed above , a constant pressure value on a higher absolute value than immediately preceding values may be the fingerprint of reaching the endpoint , as well .

[0046] The invention is further directed to an apparatus or a device , which has the features of the inventive apparatus or the inventive device as discussed above , and is arranged and configured to perform the inventive method as discussed above .

[0047] DETAILED DESCRIPTION OF THE INVENTION

[0048] The invention shall now be further exempli fied with the help of figures . The figures show :

[0049] Fig . 1 a schematic view of an embodiment of the apparatus according to the invention .

[0050] P220855 Fig. 1 shows schematically and simplified, an embodiment of the apparatus 10. A process chamber 1 forms a part of a vacuum deposition system. The interior surfaces of this process chamber may need to undergo a cleaning process from time to time. The invention aims at detecting or predicting an end point of such a cleaning process. A vacuum pump arrangement 2 is connected to the process chamber through an exhaust line 3. A flow restriction element, here in form of a throttle valve, separates the exhaust line in an upstream part 3' and a downstream part 3' ' . A vacuum gauge 5 is connected to the downstream part 3' ' . A processing unit 6 receives pressure values measured by the vacuum gauge over time. From a time-series of measured pressure values p(t) it derives a criterion C[p(t) ] in function of the time course of the pressure in the downstream part of the exhaust line. The criterion may depend on additional parameters, such as a tolerance range for stable pressure. The criterion may be a yes / no criterion providing the information, whether an endpoint of the ongoing cleaning process has been reached in the past. Alternatively, or in combination with the criterion, a time course of the pressure may be extrapolated into the near future and a prediction about an endpoint may be provided, such as for example, "the endpoint will be reached in 10 seconds". In the example shown, a communication connection 7, which may be wireless, transmits the result derived by the processing unit to a display unit 8. There, as shown here, the reaching of the endpoint may be displayed to a user. In addition, a valve 9 for gas inlet is shown in the figure. Such a gas inlet may form an actuator in a feedback control

[0051] P220855 loop that adj usts the pressure in the process chamber .

[0052] Reactive gas or inert gas may enter the process chamber through such a gas inlet .

[0053] An embodiment of the device 11 is shown surrounded by a dash-dotted polygon line . The device may comprise the vacuum gauge 5 and the processing unit 6 and optionally additional units , as shown in Fig . 1 . The device may be connectable and separable from the rest of the vacuum deposition system, thus forming an autonomous system .

[0054] In an embodiment , the apparatus may comprise the following components :

[0055] Process chamber : The cleaning process occurs within this enclosed space . It is pumped via an exhaust line which is monitored by a vacuum gauge .

[0056] Vacuum Gauge : Positioned at the chamber exhaust line and after a throttle valve , this gauge continuously monitors the pressure levels within the chamber exhaust . It detects changes in vacuum pressure that indicate the progression of the cleaning process . At the end of the clean, the pressure in the exhaust line becoming constant as no additional byproduct is being consumed and corresponding chemical reactions no longer occur .

[0057] Data Processor : This central unit receives data from the vacuum gauge and processes the information to determine when the chamber has reached its clean end point . The data processor may use a predefined algorithm and thresholds stored in the memory unit .

[0058] P220855 Memory Unit : This component may store critical data, including baseline pressure levels , pressure thresholds for clean end detection, and furthermore may store historical cleaning process data . It is arranged and configured to provide the processor with the necessary information to accurately determine the clean end point .

[0059] Data processor and memory unit together may form a processing unit , which is arranged and configured to evaluate a time course of pressure values measured by said vacuum gauge and to detect the end point of said cleaning process .

[0060] Optionally, a Display Unit : This unit may present real-time pressure data and the status of the cleaning process to the user . It may provide visual alerts when the clean end point is reached .

[0061] Optionally, a Communication Module : This module may enable the apparatus to communicate with external systems for data logging, remote monitoring, and further analysis . It may support various communication protocols .

[0062] Power Source : Supplies the necessary electrical power to all components of the apparatus , ensuring continuous operation .

[0063] Optionally, an Interface Module : Allows users to interact with the apparatus , set parameters , start or stop the cleaning process , and monitor system performance . A user interface module may in particular be arranged to send and receive commands and information from further elements of a vacuum deposition facility .

[0064] P220855 In conclusion, the Invention provides an inexpensive , robust , and simple method to identi fy a chamber clean end point . The apparatus and the method are suitable for all three types of chambers cleans , i . e . the invention may be applied in connection with in si tu plasma clean, with remote plasma clean, as well as with dry clean . The inventive method may be used to monitor all wetted surfaces inside the vacuum deposition system, up to the pressure gauge . It is therefore able to give a complete picture of the cleaning process for all chamber parts .

[0065] This invention may be used in combination with other sensors , like mass spectrometer, optical or IR spectrometer, RF sensor, or QCM to give additional insight into the clean process . In addition, measuring the base exhaust pressure gives information on pump performance and provides a leading indicator for potential pump failures .

[0066] P220855 List of reference signs

[0067] 1 process chamber

[0068] 2 vacuum pump arrangement

[0069] 3 exhaust line

[0070] 3' upstream part (of exhaust line)

[0071] 3' ' downstream part (of exhaust line)

[0072] 4 flow restriction element

[0073] 5 vacuum gauge

[0074] 6 processing unit

[0075] 7 communication connection

[0076] 8 display unit

[0077] 9 valve (for gas inlet)

[0078] 10 apparatus (for detecting or predicting an end point of a cleaning process)

[0079] 11 device

[0080] C[p(t) ] criterion derived from the time course of pressure

[0081] P220855

Claims

Claims1. Apparatus (10) for detecting or predicting an end point of a cleaning process in a vacuum deposition system, wherein the apparatus comprises- a process chamber (1) , the interior of which can be cleaned by said cleaning process,- a vacuum pump arrangement (2) connected to said process chamber via an exhaust line (3) ,- a flow restriction element (4) , in particular a throttle valve, in said exhaust line, defining an upstream part (3' ) of the exhaust line between the process chamber and the flow restriction element, and defining a downstream part (3' ' ) of the exhaust line be flow restriction element an the vacuum pump arrangement,- a vacuum gauge (5) arranged to measure a pressure in said downstream part of the exhaust line, and- a processing unit (6) arranged and configured to evaluate a time course of pressure values measured by said vacuum gauge and to detect the end point of said cleaning process.

2. Device (11) for detecting or predicting an end point of a cleaning process in a vacuum deposition system, wherein the device is connectable to an exhaust line of the vacuum deposition system in a vacuum-tight manner, wherein the device comprises- a vacuum gauge arranged to measure a pressure in said exhaust line when the device is connected to said exhaust line, andP220855- a processing unit arranged and configured to evaluate a time course of pressure values measured by said vacuum gauge and to detect the end point of said cleaning process . 3 . Method of detecting or predicting an end point of a cleaning process in a vacuum deposition system, the method using the apparatus of claim 1 and wherein the end point of said cleaning process is detected by identi fication of a first time span of falling pressure in said downstream part of said exhaust line followed by a second time span of essentially constant pressure in said downstream part of said exhaust line .4 . Apparatus according to claim 1 or device according to claim 2 , arranged and configured to perform the method according to claim 3 .P220855

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