WO2017046349A1

WO2017046349A1 - Device for evaluating a per-unit-area particulate concentration in an environment with a controlled atmosphere, such as a cleanroom, and associated method

Info

Publication number: WO2017046349A1
Application number: PCT/EP2016/072009
Authority: WO
Inventors: Nina MENANT; Delphine FAYE; Frédéric Bourcier
Original assignee: Centre National D'etudes Spatiales
Priority date: 2015-09-16
Filing date: 2016-09-16
Publication date: 2017-03-23
Also published as: FR3041098A1; FR3041098B1

Abstract

The invention relates to a device for evaluating a per-unit-area particulate concentration in an environment with a controlled atmosphere, such as a cleanroom, the device comprising: a transparent area (1) for deposition of the particles; an optical system (2) placed above the area for deposition of the particles, the optical system comprising a focusing system configured to emit from an optical source (21) an optical beam focused on the area for deposition of the particles, which area is transparent at the wavelength of the optical beam; a detecting system (3) placed above the area for deposition of the particles, the detecting system (3) being configured to detect an intensity of an optical beam transmitted by the area for deposition of the particles; and a scanning system (4) to which the optical system (2), the optical source (21) and the detecting system (3) are connected, the scanning system being configured to scan the area for deposition of the particles in two dimensions allowing a continuous measurement.

Description

Device for evaluating a surface particle concentration in a controlled atmosphere environment such as a clean room and associated method

DOMAI NE TECHNI GENERAL

The invention relates to a system and a method for measuring the surface concentration of particles in a clean room, that is to say counting the number of particles on a surface.

STATE OF THE ART

A clean room is a room with a controlled environment (temperature, humidity, particle concentration, etc.) used in industrial or research fields, areas where particulate contamination control is important.

So we use a clean room for example in the field of microelectronics, space industry, optics.

These clean rooms are usually classified according to the amount of particles in a volume of air according to the standard I SO 1 4644-1. This standard specifies for each particle size considered the maximum permissible concentration in a clean room and consequently makes it possible to characterize the performances of the clean room according to the intended application.

In recent years, a need to be able to characterize the performance of a clean room according to the cleanliness of the surfaces has appeared so that such a classification is proposed by the standard I SO 1 4644-9.

In order to classify clean rooms according to this standard a number of devices have been developed.

These devices are, however, of large dimensions and / or do not make it possible to measure particles smaller than 5 milli and in any case do not make it possible to provide a measurement in a restricted environment because of their dimensions and / or in real time .

PRESENTATION OF I NVENTI ON

The invention proposes to overcome at least one of these disadvantages.

For this purpose, the invention proposes a device for evaluating a surface particle concentration in a controlled atmosphere environment such as a clean room, the device comprising: a transparent surface for depositing the particles;

an optical system disposed above the deposition surface of the particles, the optical system being configured to emit a focused optical beam from an optical source onto the deposition surface of the transparent particles for the wavelength of the optical beam;

a detection system disposed beneath the deposition surface of the particles, the detection system being configured to detect an intensity of an optical beam transmitted by the particle deposition surface;

a scanning system to which the optical system and the detection system are attached, the scanning system being configured to scan the deposition surface of the particles in two dimensions for continuous measurement.

The invention is advantageously completed by the following characteristics, taken alone or in any of their technically possible combination.

The optical system includes a focusing system disposed between the optical source and the deposition surface of the particles.

The focusing system consists of at least two aspherical lenses. The optical source is a laser source typically constituted by a laser diode. The Laser Diode is single-mode and monochromatic.

The optical system is configured to emit an optical beam having a diameter on the particle deposition surface of 1 μm.

The optical system is configured to emit a power beam of between 1 and 4 mW, typically between 2.5 mW and 3.5 mW.

The scanning system comprises two pivotally integral arms disposed on either side of the particle deposition surface and are configured to simultaneously move the optical system and the detection system.

The device includes an autonomous power supply unit such as a rechargeable battery.

The device comprises a processing unit configured to control the optical system and the scanning system, the detection system being configured to detect the transmitted optical beam by the particle deposition surface, the processing unit detecting a particle. when the optical intensity is below a threshold and then associating with this detected particle, a particle size at a scanning speed, the processing unit being further configured to determine after the entire particles was scanned, a surface particle concentration. The device comprises a wireless com m unication unit configured to transmit data relating to a surface concentration of particles: number of particles, particle size, particle shape.

The invention also relates to a method for evaluating a surface particle concentration in a controlled atmosphere environment such as a clean room by means of a device according to the invention, the method comprising the steps of:

positioning the device according to one of the preceding claims on a plane in a controlled atmosphere environment to be monitored;

sweeping the deposition surface of the particles to determine a reference surface particulate concentration;

regularly sweep the deposition surface of the particles in order to regularly determine a surface particle concentration;

compare the reference surface particulate concentration with the regularly obtained surface particulate concentration (s).

The advantages of the invention are manifold.

The device of the invention is compact and can be placed closer to the area to be monitored by providing a local measurement to measure closer critical surfaces so in a well defined area without hindering the performance of operations.

The invention makes it possible to measure particles with a diameter greater than 1 μm.

The invention makes it possible to measure in real time the surface particulate contamination and thus to rapidly alert in the event of a contamination event. PRESENTATION OF THE FI GURES

Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings in which:

FIG. 1 illustrates a device for evaluating a surface particle concentration according to a first embodiment,

FIG. 2 illustrates a device for evaluating a surface particle concentration according to a second embodiment,

FIG. 3 illustrates a method for evaluating a surface particle concentration.

In all the figures the sim ilaires elements bear identical references. DESCRI PTI ON PETAI LLEE OF I NVENTI ON

In connection with FIG. 1, a device for evaluating a surface particle concentration in a controlled atmosphere environment such as a clean room, the device comprises:

a transparent surface 1 for depositing the particles;

an optical system placed above the deposition surface of the particles;

a detection system 3 placed beneath the deposition surface of the particles;

a scanning system 4 to which the optical system and the detection system are attached, the scanning system being configured to scan the deposition surface of the particles in two dimensions referenced x and y in FIG.

Deposit area

The particle deposition surface 1 is preferably constituted by a disc of transparent material such as glass or plastic. Other forms may be envisaged for the deposition surface of the particles.

By "transparent material" is meant a material that passes a portion of the optical beam. The notion of transparency depends on the wavelength of the optical beam used.

The particle deposition surface 1 is preferably greater than 1 cm ^{2 in} order to obtain significant data. In the case of a disc, the latter typically has a diameter greater than 1.2 cm.

Optical system

The optical system 2 comprises a focusing system 22 arranged between the optical source 21 and the particle deposition surface 1. The optical system is configured to emit an optical beam focused on the particle deposition surface 1.

The optical beam 24 must be directed perpendicular to the deposition surface of the particles.

The optical source 21 is typically constituted by a laser diode, monochromatic and preferably monomode.

To precisely guide the optical beam from the laser diode, the latter is advantageously connected to a monomode and monochromatic optical fiber by means of a PC FC type connector for example. Indeed, single-mode optical fiber and monochromatic allows to have a single spot of circular shape that sweeps the deposition surface of the particles.

This focusing system 22 is preferably constituted by at least two aspherical lenses 23.

The diameter of the optical beam must be of the same order of magnitude as the smallest particle to be measured, here by 1 μm.

Other montages are possible, since the opening of the optical system makes it possible to obtain a diffraction spot (spot) of diameter equal to 1 μm.

The optical system is preferably configured to emit an optical beam with a wavelength of between 500 nm and 700 nm, typically 635 nm and a power of between 1 and 4 mW, typically between 2.5 mW and 3.5 mW.

Other wavelengths are possible especially in the ultraviolet range.

Advantageously, the total length of the optical system is less than or equal to 15 m and the focusing system 22 is of a molded part to promote the compactness of the device.

Thus, the optical system is such as to generate a spot on the deposition surface of particles having a diameter which corresponds to the smallest particle diameter. This diameter corresponds to the resolution of the measurement.

Detection system

The detection system 3 is configured to detect an intensity of an optical beam transmitted through the deposition surface of the particles.

This is for example a photodiode.

The detection system is capable of detecting particles having a diameter of between 1 μηη and 20 μηι.

This is made possible because the optical beam is directed perpendicular to the deposition surface of the particles. Scanning system

The device comprises a scanning system 4 to which the optical system 2, the optical source 21 and the detection system 3 are linked.

Thus, during the scanning, the optical system 2, the optical source 21 and the detection system 3 move simultaneously and in solidarity. In addition, the scanning system 4 is configured to scan the deposition surface of the particles in two dimensions.

In FIG. 2, the scanning system consists of two pivoting arms 41 arranged on either side of the particle deposition surface 1 and are configured to move at the same time the optical system 2, the optical source 21 and the detection system 3 in two dimensions (along the x and y axes in FIGS. 1 and 2).

A motor 42 controls both arms 41.

The scanning system makes it possible to scan a circular surface in two dimensions by coupling a rotation and a translation performed by the two integral arms. The deposition surface remains im movable so that the particles do not move during the scan which could distort the measurement.

Processing unit

In a complementary manner, the device comprises a processing unit 5 configured to control the optical source 21 and the scanning system 4. This processing unit 5 is advantageously constituted by a processor programmed to operate via the detection system 3 the data detected by the detection system 3.

In particular, the detection system 3 is configured to detect the transmissive optical beam through the particle deposition surface 1, the processing unit 5 then detecting a particle as soon as the optical intensity is below a defined threshold. . Then is associated with the particle size, a scanning speed.

In addition, the processing unit is configured to determine after all the particle deposition surface 1 has been scanned, a surface concentration of particles.

The surface concentration depends on the level of cleanliness of the clean room and the particle sizes considered (large particles are rarer than small particles).

The acceptable surface concentrations according to the particle sizes are described in the standard I SO 1 4644-9.

Communication unit, power supply and alarm system

The device also includes a wireless communication unit 6 comprising an antenna 61 configured to transmit data from the processing unit to a remote unit (not shown). The transmitted data are in particular the different concentrations obtained. In order to have an autonomous device, the latter comprises a power system (not shown) comprising for example one or more rechargeable battery (s). The power system is used to power all the elements of the device.

Finally, to prevent a possible surface particle concentration, the device may include an alarm system (not shown). This alarm can be either visual or auditory.

Process

The device described above is advantageously used as part of a method for evaluating a surface particle concentration in a controlled atmosphere environment such as a clean room.

In connection with FIG. 3, such a method comprises the following steps.

Positioning E1 the device on a plane in the room to monitor. Given the small size of the device, it can be positioned closer to where the monitoring is necessary (on a satellite assembly plan for example).

Then, the device is calibrated in that the particle deposition surface 1 is scanned E2 in order to determine a reference surface particulate concentration. Indeed, when the device is positioned, it is considered that the part to be monitored is clean. Thus, it is by comparison with this reference value that we can determine if the particulate surface concentration characterizes the surfaces have seen their level of cleanliness evolve.

Then, regularly, the particle deposition surface 1 is scanned E3 in order to determine, regularly, a surface particle concentration.

Then E4 is compared to the reference surface particle concentration, the surface particle concentrations regularly obtained to determine a surface cleanliness of the monitored part.

In a complementary manner, it can be expected to indicate E5 that a particulate concentration is different from the reference particle surface concentration.

Different particle concentration means the maximum permissible concentration on the surfaces according to the classification of the clean room by the standard I SO 1 4644-9 which provides threshold values to be respected.

Claims

REVENDI CATI ONS

1. A device for evaluating a surface particle concentration in a controlled atmosphere environment such as a clean room, the device comprising:

a transparent surface (1) for depositing the particles;

an optical system (2) disposed above the particle deposition surface, the optical system comprising a focusing system configured to emit a focused optical beam from an optical source (21) onto the transparent particle deposition surface for the wavelength of the optical beam;

a detection system (3) disposed below the particle deposition surface, the detection system (3) being configured to detect an intensity of an optical beam transmitted by the particle deposition surface;

a scanning system (4) to which the optical system (2), the optical source (21) and the detection system (3) are linked, the scanning system being configured to scan the deposition surface of the particles according to two dimensions allowing continuous measurement.

2. Device according to claim 1, wherein the optical system (2) comprises a focusing system disposed between the optical source and the surface (1) of deposition of the particles.

3. Device according to claim 2, wherein the focusing system is constituted by at least two aspherical lenses.

4. Device according to one of claims 1 to 3, wherein the optical source (21) comprises a laser source typically constituted by a laser diode.

5. Device according to claim 4, wherein the laser diode is monomode and monochromatic.

6. Device according to one of claims 1 to 5, wherein the optical system is configured to emit an optical beam having a diameter on the particle deposition surface of 1 rm.

7. Device according to one of claims 1 to 6, wherein the optical system is configured to emit a power beam of between 1 and 4 mW, typically between 2.5 mW and 3.5 mW.

8. Device according to one of claims 1 to 7, wherein the scanning system (4) comprises two arms (4) pivoting disposed on either side of the surface (1) of deposition of the particles and are configured for at the same time move the optical system (2), the optical source (21) and the detection system.

9. Device according to claim 8, comprising an autonomous power supply unit such as a rechargeable battery.

Device according to one of Claims 1 to 9, comprising a processing unit (5) configured to control the optical system (2) and the scanning system (4), the detection system (3) being configured to detect the transmissive optical beam by the particle deposition surface (1), the processing unit (5) detecting a particle as soon as the optical intensity is below a threshold and then associating with this detected particle, a particle size at a scanning rate, the processing unit being further configured to determine after all the particle deposition surface (1) has been scanned, a surface particle concentration.

1 1. Device according to one of claims 1 to 10, comprising a wireless com m unication unit (6) configured to transmit data relating to a surface concentration of particles: number of particles, particle size, particle shape.

A method for evaluating a surface particle concentration in a controlled atmosphere environment such as a clean room by means of a device according to one of claims 1 to 11, the method comprising the steps of:

positioning (E1) the device according to one of the preceding claims on a plane in a controlled atmosphere environment to be monitored;

sweeping (E2) the particle deposition surface (1) to determine a reference particle surface concentration;

sweeping (E3) regularly the particle deposition surface (1) in order to regularly determine a surface particle concentration; comparing (E4) the reference surface particulate concentration with the regularly obtained surface particulate concentration (s).