FR2890167A1 - Mass measurement device for e.g. ion implanter, has microprocessor receiving gaseous flow delivered by flow-meter and storing flux value of gaseous flow present at time in working memory if gaseous flow exceeds preset threshold - Google Patents

Abstract

The device has a microprocessor (20) receiving a gaseous flow (FI) delivered by a flow-meter (11) and storing a flux value (gi) of the flow present at a time (ti) in a working memory (21) if the flow exceeds a preset threshold. The microprocessor, at a time (t1), reads a value (g1) in the memory, calculates a consumed gas mass (m1) and stores the result in a permanent memory (22), when the device is put in service. The microprocessor, at a time (t2), reads a value (g2), calculates a consumed gas mass (m2) and adds the result to the content of the memory (22).

Description

n m = Em1 i = 1

  The present invention relates to a mass measurement device by summation.

  The field of the invention is that of the management of gas cylinders connected to an industrial equipment. More particularly, it is necessary to know the quality of residual gas in a bottle in use in order to anticipate its replacement.

  When a gas is stored in a bottle under high pressure, it is thus common to have a pressure gauge at the outlet of the bottle, upstream of a pressure reducer that supplies the gas to the operating pressure. The indication of the manometer gives an idea of the amount of gas remaining in the bottle. This indication is not precise and it requires the addition of a pressure gauge and its connections in the gas distribution line.

  In addition, some industries, particularly the semiconductor industry, use extremely toxic gases such as boron trifluoride (BF3), arsenic trihydride (AsH3) or phosphorus trihydride (PH3). Are directly concerned ion implantation equipment. For safety reasons, suppliers of toxic gases have developed cylinders that deliver gas streams at subatmospheric pressures. It is therefore very difficult or impossible to determine how much gas has been consumed or, what is equivalent, the quantity of gas remaining in the bottle.

  The present invention thus relates to a device for measuring the amount of gas consumed does not require the addition of an additional component in the distribution line.

  According to the invention, the mass measuring device performs the sum of a succession of n elementary masses m; to deliver a consumed mass m: n m = Eml i = 1 Furthermore, this device accesses a respective succession of n mass flow values qm each associated with a duration D; and it comprises means for producing the ith elementary mass m; by making the product of the corresponding mass flow value g; and the duration D; associated with it.

  Indeed, the equipment concerned commonly include a flow meter on each gas distribution line. Flow meters generally measure the flow of gas through them.

  Thus, preferably, the device accesses a respective succession of n flux values g; and comprises means for converting a flux value to a mass flow value by multiplication with a conversion coefficient K. This conversion coefficient is equal to the ratio of a molar mass M to the product of a constant R and the temperature:

K_ M R.T

  On the other hand, the device comprises means for acquiring the molar mass M. Moreover, the device comprises means for acquiring the temperature T. Advantageously, the durations D; are all equal to a predetermined value.

  Preferably, the device receiving a gas flow FI, it comprises means for producing a flux value g; worth this gas flow only if it exceeds a predetermined threshold.

  In addition, the device is integrated in microelectronic manufacturing equipment.

  In particular, the equipment is an ion implanter.

  The present invention will now appear in more detail in the context of the following description of exemplary embodiments given by way of illustration with reference to the single appended figure which represents a front view of a block diagram of the mass measuring device. by summation.

  For the record, we recall the perfect gas equation: PÉV = nÉRÉT m n =

M

  equation in which the different symbols whose units are expressed in the International System are the following: - n: number of moles (moles), - m: mass of the quantity of gas (g), - M: molar mass (g / mole), - R: perfect gas constant = 83.14 mbar. I. K "mole -1, - P: pressure (mbar), - V: volume (I), - T: temperature (" K).

  It follows that: m = MÉPÉV RT By definition, the mass flow rate qm is the variation of the mass of gas per unit of time t: m M PÉV qm t RT t By noting, q9 the gaseous flow measured per unit of time The mass flow is then written: M which RT qe The gas quality is obtained by integrating the gaseous flow with respect to time: t Qg = ffggdt We deduce the gaseous mass consumed m (t) at the time (t ): m (t) = E fqg dt (1)

R

  With reference to the figure, the device of the invention is coupled to a gas distribution line 10 provided with a flow meter 11 which delivers a gas flow FI.

  This device comprises a microprocessor 20 which receives the gas flow FL Due to the electronic drifts, the flowmeter 11 seldom delivers a zero output signal when the gaseous flow therethrough is zero. Thus, preferably, the microprocessor records in a working memory 21 as a flux value g; the gas flow FI present at time t; only if it exceeds a predetermined threshold.

  The flowmeters are generally intended to deliver a signal whose value is expressed in the unit system of the United States of America, the gas flow unit being the sccm (<Standard Cubic Centimeter per Minute in qg = English). This value is related to the normal conditions of pressure and temperature, namely a pressure of 1 atmosphere and a temperature of 0 Celsius.

  The conversion in the International System takes into account the fact that: 1 sccm =. 10.2 mbar.ls "1 60.103 Thus, taking up equation (1), the mass of gas consumed mi for a duration Di from the time ti is: mi = 1013 M iti + DI q dt 60.103 83.14 T For a duration Di sufficiently short for the flow rate to be considered constant and equal to gi, this new equation can be written as follows: 1013 M mi = Equal 60.103 83.14 T Time t and duration Di can be set freely.

  By way of example, we adopt here whatever the value of i: ti = Di = 0.1 second It follows that: mi = 2.03.10-5. M. gi By sampling the flowmeter at the period Di: ti + 1 = ti + Di During the commissioning of the device, at time ti, the microprocessor 20 reads the value gi in the working memory 21, calculates half and records the result in a permanent memory 22 which is saved in case of power failure.

  At time t2, the microprocessor 20 reads the value g2 in the working memory 21, calculates m2 and adds it to the contents of the permanent memory 22 to store the result of the addition in this permanent memory.

  The same operation is thus performed every 0.1 second so that, at time t i, the microprocessor stores in the permanent memory: n m = m; 2890167 5 Note that it is sufficient to initialize the permanent memory 22 to zero to obtain a calculation procedure common to different times t.

  The device also carries a display 23 and an input keyboard 24 having a reduced number of keys.

  The keypad is used to perform the following operations: - entering the constant of the perfect gases: 83.14 mbar. I. - "mole", - recording of the nature of the gas, - recording of the molar mass of the gas, recording of the temperature of the gas, - resetting of the permanent memory 22 during the change of the bottle.

  It is noted that the temperature T of the gas could be directly acquired by the microprocessor 20 by means of a sensor.

  The display 23 makes it possible to obtain the following information: - initial mass of the gas in the bottle - mass of gas consumed - mass of gas remaining - instantaneous value of the flow meter - scale of the flow meter (0, 1, 3, 5, 10. ..sccm) - nature of the gas used.

  The embodiments of the invention presented above have been chosen in view of their concrete nature. It would not be possible, however, to exhaustively list all the embodiments covered by this invention. In particular, any means described may be replaced by equivalent means without departing from the scope of the present invention.

Claims (9)

  1) mass measuring device performing the sum of a succession of n elementary masses m; to deliver a consumed mass m: n m = E i = 1 characterized in that, accessing a respective succession of n mass flow rate values each associated with a duration Di, it comprises means for producing the ith elementary mass m; by making the product of the corresponding mass flow value and the duration D; associated with it.   2) Device according to claim 1, characterized in that, accessing a respective succession of n flux values gi, it comprises means for converting a flow value into mass flow rate value by multiplication with a conversion coefficient K. 3) Device according to claim 2, characterized in that said conversion coefficient is equal to the ratio of a molar mass M to the product of a constant R and the temperature: K_ M R.T 4) Device according to claim 3, characterized in that it comprises means for acquiring said molar mass M. 5) Device according to any one of claims 3 or 4, characterized in that it comprises means for acquiring said temperature T. 6) Device according to any one of the preceding claims, characterized in that said durations D; are all equal to a predetermined value.   7) Device according to any one of claims 2 to 6, characterized in that, receiving a gas flow FI, it comprises means for producing a flux value g; worth this gas flow only if it exceeds a predetermined threshold).   8) Device according to any one of the preceding claims, characterized in that it is integrated in a microelectronic manufacturing equipment.   9) Device according to claim 8, characterized in that said equipment is an ionic implanter.