Abstract:
The present invention relates to a pump of resin deposition on a semiconductive wafer including a pump body divided by a membrane of definition of a resin dispensation chamber and of a control chamber and an element of filtration of the resin before its dispensation to an outlet access of the pump body. The pump includes a control system for injecting the resin under constant pressure into the control chamber and aspiring the resin from the control chamber, and a capacitive presence sensor for detecting a first position of the membrane.

Description:
TECHNICAL FIELD 
     The present invention relates to a filtering pump for dispensing a given amount of a fluid, and in particular to equipment used for depositing resin on semiconductive wafers. The present invention more specifically relates to pumps used to filter and deposit a certain amount of photosensitive resin from a tank on a semiconductive wafer during a spin-on resin deposition and will be described hereafter in the context of this application. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 schematically shows a conventional resin deposition pump. The pump is essentially formed of a body 1 provided with an access 2 of admission of resin r from a tank (not shown) and with an access 3 for dispensing a given amount of resin r on a wafer (not shown) rotated for a spin-on deposition. A filtering element 4 masks access 3 inside body 1 to filter the resin r when dispensed. The inlet and dispensing of resin r are controlled by means of an impervious membrane 5 delimiting, within pump body 1, a chamber 6 of resin dispensation and a chamber 7 of control by means of an adapted control fluid, for example, air a. Membrane 5, which is deformable under the action of the control fluid, is generally made of Teflon. 
     Chamber 7 communicates with a control system (not shown) via a duct 8 on the path of which are inserted valves 9, 10 of air aspiration or injection into chamber 7. A three-way valve can, if desired, replace valves 9 and 10. Accesses 2 and 3 meant for the passing of the resin r can be obtruded through means of respective flaps 11 and 12. Flap 11 associated with admission access 2 is a check valve preventing any sending back of resin r into the tank. Flaps 11 and 12 can be controlled individually by the pump control system, for example, electrically by means not shown, or can be provided with means of elastic return to their respective neutral positions to be controlled by the pressure differences between the inside and the outside of dispensation chamber 6 at the level of accesses 2 and 3. 
     A cycle of deposition of a determined amount of resin on a wafer comprises at least two steps. It is assumed that chamber 6 is initially filled with resin, that is, a pump initialization cycle consisting of filling chamber 6 from the tank has previously been performed, and that chamber 7 is empty, membrane 5 being against bottom 13 of body 1. 
     In a first resin dispensation step, air a is injected into chamber 7 via valve 10, valve 9 being closed. The volume of chamber 7 increases and the resulting pressure increase in chamber 6 causes the opening of flap 12 and a dispensation of resin r through access 3, flap 11 being closed during this last step. Air is injected at constant pressure for a given time. The volume of resin r deposited on the wafer thus depends on the time and on the air pressure, set by the control system. 
     In a second step, the positions (open/closed) of valves 9 and 10 are inverted and air a is aspired from chamber 7. This aspiration causes a volume increase of chamber 6 and the resulting pressure decrease causes the opening of flap 11 and a filling of (chamber 6 from the resin tank, flap 12 being closed. The aspiration goes on until membrane 5 is again against bottom 13. 
     If desired, the second step is preceded by a step of partial aspiration during which the amount of unused resin r --  remaining in the pipe connecting access 3 to the area of deposition on a semiconductive wafer is aspired back into chamber 6. The opening delay of flap 11 to enable, during this intermediary step, the return of the undispensed resin r can be obtained by the respective sizing of accesses 2 and 3 and by the opening resistance of flap 11. 
     A disadvantage of conventional pumps is that filter 4 progressively clogs up during the dispensation cycles. This causes a decrease of the volume deposited on the wafer for a given air injection time. 
     Now, the volume deposited on each wafer has to be regular from one wafer to another in a same manufacturing series. The user must thus, with a conventional pump, periodically control the deposited volume to adapt the time of the dispensation cycle in the control system, to compensate the pressure increase necessary to maintain a same displacement of membrane 5 to obtain a constant volume deposition. 
     SUMMARY OF THE INVENTION 
     The principles of the present invention aim at overcoming the disadvantages of conventional pumps by providing a device of volume control of the mount of resin deposited for each dispensation cycle. 
     The principles of the present invention provide, in particular, a device which enables to control the duration of the dispensation cycle with the resin volume effectively dispensed. 
     The principles of the present invention provide, in particular, a device which can easily adapt to an existing pump, without requiring any modification of the inside of the pump. 
     The principles of the present invention further provide for enabling to automatically detect a malfunction of the pump. 
     According to an embodiment of the present invention a device is provided to control of the volume issued by a pump providing a liquid product. The device includes a membrane, of separation between a dispensation chamber and a control chamber, deformable by a pressurized fluid, and a capacitive presence sensor for detecting a first determined position of the membrane with respect to the bottom of the control chamber. The device also includes a control system for measuring, for each cycle of dispensation of the liquid product, the duration taken by the membrane to reach the first determined position, and determining from this duration an additional duration for the membrane to reach a second predetermined position corresponding to the supply of a desired volume of the liquid product. 
     According to another embodiment of the present invention, the additional duration is calculated by applying, to the first duration, a multiplying coefficient, determined during a calibration phase. 
     According to another embodiment of the present invention, the capacitive sensor is chosen for the distance between the first position that it detects and the bottom to be much lower than a displacement range of the membrane for which the pump is designed. 
     Another embodiment of the present invention provides a pump of resin deposition on a semiconductive wafer of the type including a pump body divided by a membrane of definition of a resin dispensation chamber and of a control chamber by means of a pressurized fluid. The pump includes an element of filtration of the resin before its dispensation to an outlet access of the pump body and a control system for, alternately, injecting the fluid under constant pressure into the control chamber and aspiring the fluid from the control chamber. The pump also includes a capacitive presence sensor for detecting a first position of the membrane corresponding to a first distance from a bottom of the control chamber. 
     According to another embodiment of the present invention, the control system includes a circuit for measuring, at each dispensation cycle, the time taken by the membrane to cover the first distance, and for calculating the fluid injection time required for the membrane to cover a second predetermined distance, the sum of the two distances corresponding to a desired volume of resin dispensation. 
     According to another embodiment of the present invention, the control system includes a circuit for indicating a malfunction of the pump. 
     According to another embodiment of the present invention, the control system includes a circuit for comparing the time measured and/or the time calculated with a predetermined threshold value indicative of a need for replacement of the filter. 
     According to another embodiment of the present invention, the control system further includes a circuit for memorizing the times measured and/or calculated, and for comparing the evolution of these times with respect to a calculated curve. 
     A feature of the embodiments of the present invention is the use of a pump membrane displacement sensor to control the duration of a resin dispensation cycle. 
     Among known displacement sensors, the embodiments of the present invention provide to use a capacitive sensor. Indeed, optic sensors are not adapted due to the non-reflectiveness of the Teflon membrane. If the membrane were reflective then an optical sensor could be used to determine its position. Inductive sensors do not operate, since neither the Teflon membrane, nor the resin r are conductive. Again, an inductive sensor could be used if the membrane or the resin were conductive. The required precision does not enable to use a mechanical sensor, unless a linear sensor which is then particularly expensive and complex is used. 
     Among capacitive filters, a capacitive presence detection sensor is preferred rather than a linear capacitive filter which is much more expensive. Further, a linear capacitive filter is much more bulky. This bulk must be taken down to the size of a conventional pump which is generally on the order of some ten centimeters high and from 5 to 10 cm of diameter. 
     The foregoing, features and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1, previously described, is a schematic representation of a resin deposition pump according to the prior art. 
     FIG. 2 shows a schematic view of a portion of a resin deposition pump equipped with a sensor according to an embodiment of the present invention. 
     FIG. 3 shows a schematic view of a portion of a portion of a resin deposition pump equipped with a sensor according to another embodiment of the present invention. 
     FIG. 4 is a flow chart illustrating a method for controlling the resin deposition pump of FIG. 3. 
     FIG. 5 is a flow chart illustrating a method of calibrating the pump of FIG. 3. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention is shown schematically in FIG. 2. Similar elements in FIGS. 1 and 2 have been referred to by the same references in the different drawings. For clarity, only those elements necessary to the understanding of the embodiment of the present invention have been shown in the drawings and will be described hereafter. 
     The embodiment of the present invention is adapted to a conventional pump such as schematically shown in FIG. 1, for example, a pump sold by MILLIPORE Company under trade name WCDS. 
     In FIG. 2 illustrating the embodiment of the present invention, only a portion of pump body 1 including control chamber 7 and membrane 5 delimiting dispensation chamber 6 has been shown. This portion generally includes bottom 13 of pump body 1 from which pipe 8 of communication between chamber 7 and a system of aspiration and injection of air a (not shown) opens. 
     According to the embodiment of the present invention, a capacitive presence sensor 14 is placed in the vicinity of pipe 8 to detect a given position of membrane 5. This sensor 14 is connected, for example by a link 15, to a pump control system 20. The control system 20 may, for example, include a microprocessor 22 and a memory 24 and may be programmed to carry out the functions described below. 
     As previously, a pump operating cycle includes a step of dispensation of resin r and a step of filling of the chamber 6 with, if desired, a step of aspiration of the residual amount of undispensed resin r. The aspiration and filling steps are not modified by the implementation of the embodiment of the present invention. 
     As previously, membrane 5 is against bottom 13 after the filling step so that the volume of chamber 7 is almost null and the volume of chamber 6 is maximum. 
     It is assumed that sensor 14 detects the presence of membrane 5 to as far as a distance d1 from bottom 13. 
     At each dispensation cycle, air under constant pressure is injected through pipe 8 and the time required by the membrane 5 to cover distance d1 from bottom 13 of the pump body is measured by detecting, by means of the control system 20, the loss of detection by presence sensor 14. 
     Since the air injection pressure is constant, the duration during which the air injection must be pursued for membrane 5 to move by a given additional distance d2, setting the desired resin volume, can be induced from the previous duration. 
     As a first approximation, it can be considered that the relation between the dispensed volume and the displacement of the membrane 5 is linear, so that the time required to cover distance d2 can be induced from the time required to cover distance d1 with a simple rule of three. Indeed, the resin r is incompressible and the membrane 5 diameter (on the order of 5 to 10 cm) is very large with respect to the displacement (on the order of 1 to 3 mm) imposed thereto. 
     However, to refine this approximation, it will be preferred to calibrate the system when the filter 4 is new. 
     Thus, with a new filter 4, the duration required to dispense the desired volume of resin r is determined. During this initial dispensation, the time taken by the membrane 5 to cover distances d1 and d2 is also measured. The control system 20 then calculates a coefficient α of proportionality between the additional time required to cover distance d2 and the time of loss of detection by the presence sensor, and stores this coefficient. After this, the control system 20 assigns, for each dispensation cycle, this, coefficient to the duration measured to cover distance d1, to obtain the duration required to cover distance d2, and thus the desired volume. 
     The more the filter 4 is clogged, the more the time measured, required to cover distance d1, increases, and the more the calculated time, necessary to cover distance d2, accordingly increases. Thus, the more the filter 4 is clogged, the more the control system 20 automatically increases the air injection time to keep distance d1+d2 constant, and thus a constant dispensed volume. 
     Preferably, the control system 20 stores the different durations that it calculates and/or that it measures in the memory 24, to detect aberrations in the evolution of these durations, and thus a malfunction of the pump, for example, a breaking of filter 4 or of membrane 5. Such a detection is performed, for example, by comparing the evolution of the air injection durations (measured and/or calculated) with a calculated evolution curve in the microprocessor 22. 
     The air injection duration (measured and/or calculated) can also be compared with a threshold value stored to indicate a too high clogging of the filter 4 and a need to change the filter 4. 
     An advantage of the embodiment of the present invention is that by controlling the air injection duration with the effective displacement of the membrane 5, any need of control of the volume dispensed during the filter 4 clogging is avoided, while respecting the precise desired volume. 
     Another advantage of the embodiment of the present invention is that it enables to generate alarm signals to the operator in case of a too high clogging of the filter 4 or of pump malfunction, these conditions being automatically detected by the control system 20. 
     Another advantage of the embodiment of the present invention is that it easily adapts to an existing pump. It is enough to drill a hole into bottom 13 of the pump to place the capacitive filter, and use a control system 20 adapted to the above-described functionalities. As a specific example, a capacitive filter manufactured by German company SENSORIC can be used. The diameter of such a sensor is approximately 5 mm. 
     Sensor 14 is, preferably, chosen and positioned so that distance d1 is much lower than the minimum distance (d1+d2) of displacement of membrane 5 for which the pump is provided. 
     Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. In particular, the practical implementation of the control system 20 for implementing the present invention is within the abilities of those skilled in the art based on the functional indications described hereabove. Further, although the present invention has been described in the context of a specific application, it generally applies to any pump meant for supplying a determined amount of a filtered fluid, especially of a viscous fluid. 
     Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.