Level sensor

Abstract

Apparatus (10) for detecting the position of a top surface (11) of a material (12) contained in a container, wherein the apparatus comprises - said container (1) having an aperture (2) for withdrawal of said material from an interior of said container; - an optical emitter (3) for emitting pulsed electro-magnetic radiation in the optical wavelength range towards said top surface, in particular, wherein said optical emitter is adapted to produce pulses with rise and fall times in the sub-nanosecond range; - an optical receiver (4) for detecting said pulsed electro-magnetic radiation after being reflected or scattered from said top surface and for producing a time-dependent signal indicating the incoming intensity of said pulsed electromagnetic radiation, in particular, wherein said optical receiver has a time resolution in the sub-nanosecond range; - a control unit (5) operationally connected to said optical emitter and said optical receiver, said control unit being arranged and configured to measure a time of flight of said pulsed electromagnetic radiation from the optical emitter to the optical receiver. Furthermore, the invention is directed to a method.

Description

[0001] Level sensor

[0002] The invention addressed herein relates to the technical field of measuring or indicating a level of fluid or solid material in a container . More speci fically, the invention relates to an apparatus for determining the amount of a chemical substance remaining in a container . Under further aspects , the invention relates to a method of determining a level of fluid or solid material in a container and to a method of operating the apparatus . In a speci fic application, the invention relates to the technical field of semiconductor fabrication .

[0003] In various contexts , a fill level of a container needs to be determined, for example , to indicate the approaching necessity of refilling the container or exchanging the container with a filled one . In the following, a speci fic example of measuring the fill level of a precursor substance in a semiconductor fabrication process is discussed . Similar problems and disadvantages occur in other fields , such that the inventive solution may be applied in other fields as well .

[0004] As the speci fic example of semiconductor fabrication, chemical delivery is sometimes facilitated using bottles or ampoules . These chemicals may come in liquid, slurry or solid form . The containers , which may be precursor bottles containing a precursor substance , may have ports for fill level sensors and temperature sensors . Both parameters have a big impact on the processes in process chambers . Known fill level sensors extend into the precursor bottles . They

[0005] P220900 usually work either by using ultrasonic excitation or by measuring the capacitance between an insert rod and the bottle wall .

[0006] The chemicals in these bottles are then fed to a gas delivery line . Sometimes a carrier gas is used which is either also introduced through the top of the bottle or fed through the chemical to reach a higher concentration .

[0007] The current fill level sensors suf fer from several drawbacks . An uneven distribution of precursor in the bottle is hard / impossible to detect since the probe is very local . This can lead to wafer scrap or early exchange of the bottles resulting in waste and lost time . The accuracy of the ultrasonic sondes is poor, the process engineer doesn ' t get real information about the consumption of the precursor .

[0008] Measurement inaccuracies in the bottom region of the container can lead to an early exchange of the bottles resulting in waste of expensive precursors and lost time . This type of inaccuracy may be particularly pronounced with ultrasonic probes , as the ultrasonic sondes don ' t reach the bottom of the bottle .

[0009] A typical level sensor device is not able to measure the temperature of the precursor . Therefore , an additional port is needed .

[0010] It is di f ficult to handle l iquid and solid precursors with the same sensor , i f high accuracy for liquid state and solid-state material is required .

[0011] P220900 The obj ect of the present invention is to provide an alternative apparatus or a method for measuring the fill level of a container . In particular, it is an obj ect to at least reduce some of the problems of the state of the art .

[0012] This obj ect is achieved by an apparatus according to claim 1 . The inventive apparatus is an apparatus for detecting the position of a top surface of a material contained in a container . This material may be a liquid material , a slurry material or a solid material , for example in form of a powder, in form of grains , or in form of chunks .

[0013] The apparatus comprises

[0014] - said container having an aperture for withdrawal of said material from an interior of said container ;

[0015] - an optical emitter for emitting pulsed electro-magnetic radiation in the optical wavelength range towards said top surface , in particular, wherein said optical emitter is adapted to produce pulses with rise and fall times in the sub-nanosecond range ;

[0016] - an optical receiver for detecting said pulsed electromagnetic radiation after being reflected or scattered from said top surface and for producing a time-dependent signal indicating the incoming intensity of said pulsed electromagnetic radiation, in particular, wherein said optical receiver has a time resolution in the subnanosecond range ;

[0017] - a control unit operationally connected to said optical emitter and said optical receiver, said control unit being

[0018] P220900 arranged and configured to measure a time of flight of said pulsed electromagnetic radiation from the optical emitter to the optical receiver .

[0019] The optical wavelength range in particularly comprises the wavelengths of infrared light , visible light and ultraviolet light . The combination of the optical emitter, the optical receiver and the control unit together may form a time-of- f light ( abbreviated TOP) detector .

[0020] A reaction time in the sub-nanosecond range has the ef fect , that distances in the centimeter range or even in the millimeter range can be measured with appropriate precision for detecting the level of the material in the container . An appropriate precision may e . g . be in the order of about 1% of the maximum filling height of the container .

[0021] In one embodiment , which may be combined with any of the embodiments still to be addressed unless in contradiction, said optical receiver is constructed as a photonic mixing device .

[0022] A photonic mixing device , abbreviated PMD, has the advantage , that outgoing and incoming electromagnetic waves directly interact in the PMD, such that very short time delays can be detected .

[0023] In one embodiment , which may be combined with any of the embodiments still to be addressed unless in contradiction, the optical receiver comprises multiple sensing pixels , each sensing pixel being arranged to detect incoming

[0024] P220900 electromagnetic radiation from an individual direction . In particular, the sensing pixels may be arranged in an array .

[0025] In one embodiment , which may be combined with any of the embodiments still to be addressed unless in contradiction, the apparatus further comprises a receiver configured to detect thermal infrared radiation .

[0026] In one embodiment , which may be combined with any of the embodiments still to be addressed unless in contradiction, the apparatus further comprises a pressure sensor arranged to measure a pressure in said interior of said container, wherein the pressure sensor is operationally connected to said control unit .

[0027] Further in the scope of the invention lies a method according to claim 6 .

[0028] This method is a method for detecting the position of the top surface of a material contained in a container . The method comprises :

[0029] - Providing the apparatus according to the invention,

[0030] - sending, by means of said optical emitter, a pulse of electromagnetic radiation towards said top surface ,

[0031] - receiving, by means of said optical receiver, said electromagnetic radiation after being reflected or scattered from said top surface and producing a timedependent signal indicating the incoming intensity of said pulsed electromagnetic radiation,

[0032] - sampling and digiti zing said time-dependent signal ,

[0033] P220900 determining, by means of said control unit , a distance travelled by the electromagnetic radiation from said optical emitter to said optical receiver .

[0034] In a further development , a method comprises a preparation sequence compris ing the steps of the above-mentioned method being conducted with an empty or essentially empty container and it comprises a main sequence comprising again the steps of the above-mentioned method, this time being conducted with an at least partially filled container . The container in the preparation sequence and the container in the main sequence have the same form and dimension . The method further comprises a comparison of the distance determined in the preparation sequence and of the distance determined in the main sequence to determine a measure for the fill level of the partially filled container .

[0035] This way, high precision in the prediction of the approaching point in time , at which point the container will be empty, can be achieved also in cases where a geometrical form of the bottom of the container renders it di f ficult to determine the remaining volume of material in the container . An example may be a container in the form of a bottle with a hemispherical bottom .

[0036] Alternatively, other ways for calibrating the container form and dimensions may be used for achieving the goal of determining the end point of the emptying process . Such alternatives include access to a database containing geometry and dimensions of the container in use , a user interface allowing to enter geometry and / or dimensions of the container in use , as well as combinations of these

[0037] P220900 options . For example , a certain type of container may undergo in its empty state a measurement using a TOF detector, as described above , before it is in use for the first time . The measurement data then may be stored in a database , and at the moment , when a newly filled container is attached to the system, a user selects on a user interface the type of bottle from a selection of containers in the database .

[0038] In the case , when an at least partially transparent material is used, the time delay of a reflection on the top surface of the material , as well as the time delay of a reflection from a bottom surface of the container may be evaluated and compared to each other . When the di f ference of these two time delays tends to zero , this indicates that the container will be empty soon .

[0039] In an even further development , which may be applied to the previously discussed methods , the optical receiver used comprises multiple sensing pixels . The distance travelled by the electromagnetic radiation from the optical emitter to the optical receiver is evaluated for each sensing pixel separately . An estimation of a gas interacting surface of the material is derived from the set of distances evaluated .

[0040] The invention shall now be further exempli fied with the help of figures . The figures show :

[0041] P220900 Fig . 1 shows schematically and simpli fied, a container with a level sensor according to the state of the art ;

[0042] Fig . 2 shows a cross-sectional and schematic view of an embodiment of the apparatus according to the invention ;

[0043] Fig . 3 shows a cross-sectional and schematic view of an embodiment of the apparatus according to the invention .

[0044] Fig . 1 illustrates the problem occurring in the state of the art , that the volume ( 17 ) , which interacts with the sensor rod ( 16 ) is small compared to the volume of the complete interior ( 6 ) of the container . A local fill level , in particular in the case , when the material has the form of chunks , as in the situation shown in this figure , may not be representative of the fill level of the container .

[0045] Fig . 2 shows the situation with the solution according to the present invention . A TOF sensor, including at least the elements optical emitter and optical receiver, may shine light onto practically the complete top surface of the material remaining in the container and receive light from practically the complete top surface of the material remaining in the container, as illustrated with the field of view marked as dotted area .

[0046] Fig . 3 shows an embodiment of the apparatus according to the invention, including possible pathways of the pulsed electromagnetic radiation from the optical emitter via the surface of the material to the optical receiver .

[0047] P220900 The present invention provides a solution to many of the problems in the state of the art . It may come in the form of a time-of- f light ( TOF) sensor that can be mounted on pre-existing precursor bottle ports , for example the filling port . Such a TOF sensors may send out infrared light and record the time it takes for a reflection to come back . From the time-of- f light of the light a distance from the sensor is calculated . Having multiple sensing pixels within one TOF sensor allows to get a height map of the precursor below and to calculate how much of the chemical is exposed to the gas flowing through the bottle . This method can give a more precise indication of the fill level of a bottle than previously known methods .

[0048] Knowing the level and the distribution of chemicals in the bottle exactly allows for a more precise time schedule for exchanging the chemicals , resulting in less chemical waste , less wafer scrap and more productive tool time . Furthermore , knowing the precise distribution allows for an estimation of the gas interacting surface . Knowing these parameters inside the bottle allows to optimi ze process flows resulting in more precise chemical dosing in the process chambers .

[0049] The apparatus according to the present invention may be a part of a speci fic tool to which a chemical from the container of the apparatus is supplied . It may deliver measuring results back into a software managing the operation of a speci fic tool or even to a software managing a complete semiconductor fabrication system . Based on the

[0050] P220900 increased precision with regard to the fill level of containers , process optimi zation and improved scheduling of maintenance processes become possible .

[0051] TOF sensors that have small dimensions compared to typical openings of containers are available . Thus , in an apparatus according to the invention, additional space becomes available , such that additional sensors may be attached to the same port that houses the TOF sensor, as e . g . an infrared temperature sensor . With this additional infrared temperature sensor on the same port , one can measure the temperature of the chemical in the interior of the container directly, in particular , one can measure the temperature on the top surface of the chemical . This is an improvement compared to getting a proxy for the temperature by measuring the bottle temperature .

[0052] Optionally one can also extend the sensor arrangement used for monitoring the container by adding a pressure sensor and use the combined data of filling level and pressure , optionally further combined with temperature , to get a better idea of the concentration of precursor that is gaseous . This may be of particular importance , where a precursor substance is provided in solid form, but wherein only the fraction of precursor substance that has changed to gaseous form is available to be carried away by a process gas .

[0053] Furthermore , one can derive a complementary measure for the depletion of the precursor bottle via a temperature measurement , since the chemical composition changes lead to changes in emi ssivity and thermal conductivity .

[0054] P220900 List of reference signs

[0055] 1 container (e.g. precursor bottle)

[0056] 2 aperture

[0057] 3 optical emitter

[0058] 4 optical receiver

[0059] 5 control unit

[0060] 6 interior (of the container)

[0061] 7 gas delivery

[0062] 8 T-sense port

[0063] 10 apparatus

[0064] 11 top surface (of material)

[0065] 12 material (e.g. precursor material)

[0066] 13 time-of-f light sensor (TOF sensor)

[0067] 14 field of view of the TOF sensor

[0068] 15 connectors of sensor of state of the art

[0069] 16 sensor rod (inserted into container)

[0070] 17 volume interacting with the sensor rod

[0071] P220900

Claims

Claims1 . Apparatus ( 10 ) for detecting the position of a top surface ( 11 ) of a material ( 12 ) contained in a container, wherein the apparatus comprises- said container ( 1 ) having an aperture ( 2 ) for withdrawal of said material from an interior of said container ;- an optical emitter ( 3 ) for emitting pulsed electromagnetic radiation in the optical wavelength range towards said top surface , in particular, wherein said optical emitter is adapted to produce pulses with rise and fall times in the sub-nanosecond range ;- an optical receiver ( 4 ) for detecting said pulsed electro-magnetic radiation after being reflected or scattered from said top surface and for producing a timedependent signal indicating the incoming intensity of said pulsed electromagnetic radiation, in particular, wherein said optical receiver has a time resolution in the subnanosecond range ;- a control unit ( 5 ) operationally connected to said optical emitter and said optical receiver, said control unit being arranged and configured to measure a time of flight of said pulsed electromagnetic radiation from the optical emitter to the optical receiver .2 . Apparatus according to claim 1 , wherein said optical receiver is constructed as a photonic mixing device .P2209003 . Apparatus according to claim 1 or claim 2 , wherein the optical receiver comprises multiple sensing pixels , each sensing pixel being arranged to detect incoming electromagnetic radiation from an individual direction, in particular, wherein the sensing pixels are arranged in an array .4 . Apparatus according to any one of claims 1 to 3 , wherein the apparatus further comprises a receiver configured to detect thermal infrared radiation .5 . Apparatus according to any one of claims 1 to 4 , wherein the apparatus further comprises a pressure sensor arranged to measure a pressure in said interior of said container, wherein the pressure sensor is operationally connected to said control unit .6 . Method for detecting the position of a top surface of a material contained in a container , wherein the method comprises- providing an apparatus according to any one of claims 1 to 5 ,- sending, by means of said optical emitter, a pulse of electromagnetic radiation towards said top surface ,- receiving, by means of said optical receiver, said electromagnetic radiation after being reflected or scattered from said top surface and producing a timedependent signal indicating the incoming intensity of saidP220900pulsed electromagnetic radiation,- sampling and digiti zing said time-dependent signal ,- determining, by means of said control unit , a distance travelled by the electromagnetic radiation from said optical emitter to said optical receiver .7 . Method according to claim 6 , comprising a preparation sequence comprising the steps of claim 6 being conducted with an empty or essentially empty container , comprising a main sequence comprising the steps of claim 6 being conducted with an at least partially filled container, wherein the container in the preparation sequence and the main sequence have the same form and dimension, wherein the method further comprises a comparison of the distance determined in the preparation sequence and of the distance determined in the main sequence to determine a measure for the fill level of the partially filled container .8 . Method according to claim 6 or 7 , wherein the optical receiver used comprises multiple sensing pixels , wherein a distance travelled by the electromagnetic radiation from said optical emitter to said optical receiver is evaluated for each sensing pixel separately, and wherein an estimation of a gas interacting surface of the material is derived from the set of distances evaluated .P220900

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