EP2030222A1

EP2030222A1 - Method and device for removing pollution from a confined environment

Info

Publication number: EP2030222A1
Application number: EP07766098A
Authority: EP
Inventors: Arnaud Favre; Bertrand Bellet; Roland Bernard; Xavier Metais
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2006-05-24
Filing date: 2007-05-24
Publication date: 2009-03-04
Also published as: CN101501817B; CN101501817A; FR2901546A1; KR20090017633A; US20090263216A1; SG172620A1; WO2007135347A1; FR2901546B1; US8151816B2; JP5274450B2; JP2009538000A; KR101202551B1

Abstract

The subject of the present invention is a method for removing pollution from a confined environment containing an interior space bounded by a wall, involving the following steps: the confined environment which has a leak is placed in a sealed chamber comprising means of introducing a gas and means of pumping a gas; the gas contained in the chamber and the gas contained inside the space are simultaneously pumped through the leak so that the pressure difference across the wall is always below a wall-damaging threshold. Another subject of the invention is a device for removing pollution from a confined environment comprising: a pollution removal chamber able to contain the confined environment; means of introducing a purging gas; means of pumping a gas with variable pumping capacity; means for controlling the pumping rate; means for monitoring the pressure difference between the inside and the outside of the environment.

Description

Method and device for decontamination of a confined environment

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the cleaning and the depollution of leaky confined environments such as in particular transport boxes and storage of semiconductor substrates, food products, medical or automotive products, or even such as photomasks provided with of their protective film.

Atmospheric pressure transport and storage boxes for one or more substrates, in particular for semiconductor wafers, determine a confined space, separated from the environment of use and transport of the substrates by a peripheral wall provided with a door opening opening closed by a door, This type of transport box is usually made of plastic and is generally not waterproof. The plastic peripheral wall is not designed to withstand, without damage, differential pressures greater than a few tenths of an atmosphere. The transport boxes are therefore designed with at least one leak, so that. when a pressure difference exists between the inside and the outside of the box, a flow of gas occurs to minimize the pressure difference and thereby reduce the mechanical stresses on the peripheral wall. In the case of FOUP transport boxes, a particulate filter is interposed in the leak to reduce pollution. Usually the atmosphere inside the box is not controlled, and it is considered to be the most often similar to that of the equipment from which the substrates come out or to the ambient air close to the box transport.

The transport boxes are generally effective to prevent polluting particles from entering the confined space. Their use is made necessary by the growing need to reduce particulate pollution, especially in the manufacture of semiconductors and other naπotechnofogie products. On the other hand, the plastic peripheral wall of the transport boxes is capable of degassing, preserving or providing compounds that can react with substrates and pollute them. These compounds can in particular come from an inadequate environment (presence of moisture, for example) during certain phases of manufacture of the substrates. This environment is then preserved by the internal atmosphere of the transport boxes. Thus the transport boxes are not sufficient to prevent any risk of pollution, but also participate in some cases in additional pollution (wall degassing, moisture retention, cross contamination, opening / closing mechanisms that generate particles , lack of watertightness of the walls, etc.).

EP 1 557 878 discloses purging a slice of substrate slices.

10 placed inside a waterproof mini-environment enclosure. provided with an access passage closed by a lower door, and filled with air for example. The enclosure is connected on its underside to a purge station comprising a purge compartment provided with a closable transfer upper passage opposite the lower face of the enclosure by opening the lower door, a stack of slices of

Substrate carried by the lower door is introduced into the purge chamber previously filled with nitrogen. Simultaneously with the purge of the interstices between the substrate slices, the inside of the mini-environment chamber is purged by penetration and gas outlet by the obturable access passage which is then in the open state. An analysis of the atmosphere inside the enclosure is carried out to control its

20 quality.

The method described relates to the cleaning of the substrate slices, for which it is necessary to extract them from the enclosure: the purge of the pregnant is not the main objective. This process does not guarantee a thorough cleaning of the enclosure. In particular it does not envisage the cleaning of the external walls of the enclosure. This method of

Cleaning is applicable only to a sealed enclosure and is not usable in the case of a non-sealed confined environment. In addition, it involves the operation of mechanisms for opening and closing the access and transport passages.

EP 0 626 724 discloses a method of dry cleaning the outer walls of a transport box, containing semiconductor substrates in a clean atmosphere (vacuum or inert gas), prior to introduction into an installation. The sealed box containing the substrates is placed in a tunne !. Several methods of cleaning the outer walls by gaseous means can be used, such as alternating introduction of a gas flow (N ₂ ) and evacuation. When the cleaning is finished, the tunnel is put under a vacuum equivalent to that prevailing in the installation into which the transport box will be introduced.

The cleanliness of the internal atmosphere of the box is implicitly admitted

5 in this document. This method does not suggest how to clean the interior volume, the walls of the box and the substrates that contain it. In addition, this cleaning method is applied to a sealed box intended to keep substrate slices under vacuum. Its walls therefore have a high mechanical strength, which is not the case of leaky transport boxes for transporting atmospheric pressure substrate slices.

JP 2004 128428 A discloses a device and method for replacing the gas of a confined environment such as a transport box with an inert gas by reducing the necessary amount of inert gas to ensure this replacement. For this, the document teaches to place the transport box in a

15 vacuum chamber, to open the transport box through the removal of a plug by means of an opening and closing mechanism provided in the vacuum chamber, and then to pump the gases present in (' vacuum chamber and in the transport box, and finally to introduce the inert gas in the vacuum chamber and in the transport box.The opening of the transport box inside the vacuum chamber allows to pump the gases in

The vacuum chamber without inducing a pressure difference between the outside and the inside of the transport box.

EP 1 059 660 A2 describes the replacement of the oxygenated atmosphere of an environment confined by nitrogen to prevent oxidation. This replacement is done by injecting nitrogen directly into the confined environment,

The nitrogen gradually replacing the oxygenated initial gas. He is no pumping operations of the atmosphere ^inside the confined environment.

In all the above documents, the operation involves the opening of the transport box, by the maneuvering of opening and closing mechanisms, and this maneuver is likely to generate paricular pollution. The particles thus produced can be deposited on substrate slices contained in the transport box, which is incompatible with the increasing requirements for reducing particulate pollution in the manufacture of semiconductors and other nanotechnology products. In addition, none of these documents describes or solves the problem of gaseous pollution resulting from the degassing of the plastic material walls of the transport boxes at atmospheric pressure.

A photomask is equivalent to a negative in photography: its active surface contains information to be printed on a substrate, it is used in transmission for insolations and printing on semiconductor substrates. Incident radiation is focused on the active surface of the photomask, and the patterns contained in the active surface are first reproduced on the substrate. Apart from its active surface, the details are not printed on the substrate but may have an impact on the transmission of the photomasque. Pollution in the active zone has a direct effect on the image printed on the substrate because the defects are printed. But these pollutions have only an indirect effect on this image if they intervene outside this zone, as for example the reduction of the contrast or the reduction of the transmission of the photomask.

On the other hand, the semiconductor industry seeks to reduce the size of the inscribed image to obtain ever smaller and less expensive electronic components. The size of the basic patterns of photomasks is reduced, the requirements for pollution become more and more strict. The photomask is therefore a key element, expensive and complex that one seeks to keep clean and operational.

At the end of the manufacturing process, the photomask is cleaned and inspected. If it is clean and without defects. The photomask is filmed and sent to the customer. The film is intended to protect the photomask during his life at the user. The coating consists of a deposit of an optical membrane (parallel multilayer surfaces) having a good transmission and a reduced impact on the optical rays that pass through it. This peel is deposited on the side of the active face of the photomask, and separated from it. ie ~ ci by a space. The pollutants, instead of being deposited on the active face of the photomask, will thus be deposited on the film, that is to say outside the focusing zone (physical removal of the active surface). Thus, these pollutants will not be printed in 30 If transfer lithography: the pellicuie does not directly protect the rnaîs pollutants can reduce their impact on ^the image.

The film is most often glued around the periphery of the active part of the mask. The atmosphere under the film is then isolated from the atmosphere of the photomask transport box. To prevent the film from deforming, Low conductance filters are provided on the sides of the film. These orifices provide pressure equalization between the atmosphere confined under the film and the atmosphere of the interior of the transport box.

It was recently noted that pollutants could still be present

5 under the film. Crystalline growth phenomena, which develop at the active side of the photomask, in the focusing zone, can be observed under the film. These phenomena, amplified with the decrease in the size of the technologies, have a direct effect on the stages of lithography (printing defects). Their situation under the film makes cleaning difficult. Cleaning a

The photomask already equipped with its film is long, complex and expensive because it is necessary until now to remove the film for cleaning, and then to re-deposit it. This delicate operation must be carried out by the photomask manufacturers and not by the users, which causes a loss of time and significant additional costs of inventory management related to the shortened life of the photomasks.

WO 85/1126 proposes to avoid pollution of the inner surface of the film during manufacture until it is attached to the photomask. He proposes to have a peelable protection on the side of the inner surface of the film. This document does not propose a solution for cleaning a photomask already provided with its film.

20 JP 10-308337 document proposes a method of liquid medium in the cleaning of the outer surface ^of a photomask provided with its film, and does not provide for removal of the peicule This document does not provide solution to clean the space confined between the surface of the photomask and the film.

There is no known method of cleaning the volume separating the substrate from the inner surface of the skin without the necessity of removing the peel.

The invention results from the observation that the known methods and devices, especially those mentioned above, do not sufficiently prevent the appearance of pollution on its active surfaces of photomasks film, or on ies active surfaces of the semiconductor wafers

30 conductors contained in transport boxes at atmospheric pressure.

According to the invention, it is considered that these pollutions which, in known devices and processes, still appear on its active surfaces photomasks or semiconductor wafers, result both from a parietal pollution generated by the opening and closing of non-airborne confined environments consisting of atmospheric transport boxes or film masks, and gaseous pollution by the gases present in the confined environment and which can be combined with the material of the active surfaces; make deposits on them. In particular, in the case of atmospheric transport boxes, made of plastic, gas pollution resulting in particular degassing of the plastic material.

These pollutions develop progressively over time, and in particular prevent easy storage and sufficient duration of the semiconductor wafers between various manufacturing steps of the microelectronic components or microelectronic systems, or reduce the duration of use of the photomasks with film.

SUMMARY OF THE INVENTION

The invention thus aims to substantially reduce the risk of pollution of active surfaces present in leaky confined environments, such as active surfaces of film photomasks, or the active surfaces of semiconductor wafers contained in the atmospheric transport boxes.

The invention also aims to ensure an effective dépoflütion confined environments leaky, in order to increase the time at the end of which a possible pollution is likely to appear again on the active surfaces of the products.

The invention also aims to further extend the period of non-pollution by passivatton non-active surfaces of leaky confined environments, preventing these non-active surfaces such as the walls of the transport boxes generate, during the duration of their practical use, gaseous pollution likely to affect the active surfaces of the products.

The idea underlying the invention is to ensure the detachment of a sealed non-sealed environment, by an effective pumping of the indoor atmosphere of the sealed non-sealed environment and the restoration of atmospheric pressure, but without opening the confined environment unsealed, to avoid any maneuver opening and closing mechanism likely to generate a particular pollution. The invention provides for this to pass the gases inwardly and outwardly of the unsealed environment by the only natural leak of the unsealed environment. But it is necessary to provide other means to avoid possible deterioration of the walls of the confined environment not waterproof. Indeed, these walls are not likely to withstand, without degradation, significant differential pressures: in the case of a photomask, the film can not withstand a differential pressure greater than about Pascal; in the case of atmospheric transport boxes currently used, the plastic walls can not withstand, without degradation, a differential pressure greater than a few tenths of an atmosphere.

For this purpose, the invention proposes a method of depoilution of a non-enclosed confined environment having an interior space limited by a wall having a natural leakage, comprising the following steps:

the sealed, leak-proof environment, having its natural leakage, is placed in a sealed de-oiling chamber comprising gas introduction means and gas pumping means; the gas contained in the pollution control chamber is pumped by adjusting the pressure drop in the pollution control chamber so that the pressure difference between the inside and the outside of the confined non-sealed environment is at any time less than the pressure difference causing a damaging mechanical deformation the wall of the confined environment not leakproof.

In such a method, the unsealed environment remains confined, that is to say closed, without maneuvering its opening means, and the passage of gases inwards and outwards of the confined environment is done through his only natural leak. In the case of a photomask, the passage of gases takes place through the low-conductance filter ports provided on the sides of the film. In the case of an atmospheric transport box, the passage of gases takes place through the natural leaks of the box, that is to say the existing orifices provided with filters, the door seals.

This natural leakage necessarily has a low conductance, to ensure the protection of the indoor atmosphere of the sealed non-sealed environment. It is therefore understandable that a too rapid pumping of the sealed etching chamber can reduce too quickly the gas pressure present around the unsealed sealed environment in the watertight deposition chamber, while your gases have not had time to cross the natural leakage of the uncontained confined environment, so that the inner atmosphere of the confined unsheltered environment is a higher pressure, inducing on the walls of the confined environment leakproof differential pressure in the direction from the inside to the outside. By adjusting the descent pressure in the depollution chamber, according to the invention, it is ensured that the pressure difference between the inside and the outside of the unsealed confined environment is bearable by the walls of the confined environment not watertight.

An advantage of this method is that it simultaneously performs the depollution of the inside and outside of the sealed non-sealed environment.

The risks of occurrence of too high differential pressures also exist during the stages of pressure rise in the sealed non-sealed environment. In fact, if gases are introduced into the sealed deoiling chamber, the gas pressure in the sealed dewatering chamber can rise rapidly, while the gases can penetrate more slowly through the natural low-conductance leakage of the environment. confined unsealed. there then appears a differential pressure in the direction of the outside towards the interior of the confined environment not sealed, differential pressure likely to apply a mechanical stress that can degrade the walls of the sealed non-sealed environment.

For this, the method according to the invention preferably comprises a pressure rise step during which the rise in pressure in the deposition chamber is adjusted so that the pressure difference between the inside and the the outside of the confined environment is not at any time less than the pressure difference causing a mechanical deformation damaging the wall of the confined environment not sslanche.

According to a first embodiment, during a process of the invention, it is possible to control the pressure variation in the deoiling chamber by following a theoretical curve of variation of pressure as a function of time. The theoretical curve of variation of pressure as a function of time can be previously optimized on a test bench comprising instrumented non-sealed confined environments. For example, the sealed non-leak test environment may include an inside pressure sensor and deformation sensors on its peripheral walls. Experimental pressure descent curves are produced by taking up the corresponding deformations of the peripheral walls, and a theoretical pressure descent curve is selected from them, which avoids any degradation of the peripheral walls of the non-sealed confined environment. According to a second embodiment, alternatively or in addition, it is advantageously possible to control the pressure variation in the pollution control chamber by following the signal given by at least one deformation sensor of the wall of the non-sealed confined environment. It is ensured that the deformation of the wall of the non-leakproof confined environment, measured by the deformation sensor, is less than the deformation threshold likely to cause permanent degradation of the wall.

This embodiment has the important additional advantage of more surely avoiding any risk of degradation of the wall of the non-sealed confined environment, even in the event that the natural leakage of the unsealed confined environment is partially or completely blocked accidentally and unpredictably, for example if a filter was clogged.

It is understood that the possibility of avoiding such a risk of degradation is particularly useful in the case of a semiconductor wafer transport box, because the contents of the transport box, consisting of a stack of semiconductor wafers driver, has a very high economic value in the current applications of nanotechnology: several tens of thousands of euros. However, the degradation of the transport box wall is likely to affect the subsequent capacity of its transport box to ensure the effective protection of the contents of the box against its external pollution, so that there is a risk of rendering it unusable. the totality of the contents of the transport box.

In practice, according to the invention, to adjust the pressure variation in the dewatering chamber, it is possible to vary the pumping capacity of the pumping means, by controlling their rotational speed, and / or by controlling the a variable conductance of the pumping means, and / or by the control of the gas introduction means for varying a gas flow entering the pollution control chamber.

Preferably, the method according to the invention further comprises a purge step, the purge step comprising at least one filling operation in purge çjaz during which a purge gas is introduced into the pollution control chamber.

The purge gas can be synthetic air, avoiding the introduction of moisture into the unsealed confined environment.

More preferably, the purge gas may be nitrogen, which simultaneously avoids the introduction of oxygen into the sealed non-sealed environment. Alternatively, another neutral gas, such as argon, may be used depending on the effects that this neutral gas may have either on the active surfaces of the products contained in the sealed non-sealed environment, or on the walls themselves of the confined environment not waterproof. In particular, the invention demonstrates that the walls of the sealed non-sealed environment can be given properties of neutrality or passivity which are more durable over time, by a passivation effect which avoids a significant and harmful degassing of the during the periods of practical use of a transport box, that is to say while it contains semiconductor wafers. It has been found, according to the invention, that an effective passivation of the walls of an atmospheric transport box can be obtained by the combination of a sufficient pumping step, for example down to a pressure of about 10 ^{~ 2} to 10 ^"3 Torr and maintaining this pressure for a sufficient duration of the order of twenty minutes, and a purge step with a neutral gas.It is believed that this combination can sufficiently extract gaseous molecules previously trapped in the plastic walls of the atmospheric transport box and then replaced by neutral gas molecules In the event of subsequent degassing of the walls of the transport box, this degassing essentially produces only gas neutral, which has no polluting action on the active surfaces of the semiconductor wafers contained in the transport box, and it has been found that the transport box wall thus passivated at least s tendency to recharge in polluting gas molecules.

Alternatively or additionally, the purge step of the process according to the invention may additionally contain at least one purge gas pumping operation, during which the gas mixture present is removed from the deposition chamber.

In this case, the filling and pumping of the purge gas can be carried out simultaneously, with a pumping rate preferably lower than the injection rate,

Alternatively, several filling operations and pumping purge gas can be performed simultaneously.

To further increase the passivation effect, it is possible to provide several purge steps comprising operations for filling and pumping purge gas, carried out alternately with pumping steps. At the end of the process, it is advantageous to provide a purge gas filling operation comprising a period of overpressure during which a pressure above atmospheric pressure is maintained in the depollution chamber before the return to atmospheric pressure. Effective passivation of a transport box, by a method according to the invention, then makes it possible to use the transport box not only for transporting semiconductor wafers between processing operations of these wafers, but also for the longer storage semiconductor wafers, the latter being maintained in the transport box which is itself the storage means.

According to the invention, the method can be applied to the treatment of photomasks provided with their peilicuie. In this case, the gases are introduced and extracted by the low conductance filters separating the particle from the active part of the mask, without removing the cell. Alternatively, the invention can be applied to the treatment of transport boxes at atmospheric pressure, the transport box being kept closed. The transport box may be empty, but may advantageously contain slices of semiconductor substrate.

Preferably, the pumping step is maintained for a time greater than a satisfactory duration ensuring sufficient degassing of the walls of the sealed non-sealed environment.

Satisfactory duration can be determined by prior testing of a series of leaky confined environments.

Alternatively, or in addition, means may be provided for controlling the state of depollution of the walls of the sealed non-sealed environment and any products contained in the sealed non-sealed environment, and the depollution operation is ceased when a state satisfactory deposition has been achieved.

According to a first possibility, the state of decontamination is evaluated by examining the pressure drop curve in the chamber chamber: if one reaches a predefined stable pressure level, one can then estimate that its depoilution is sufficient.

Alternatively, the pumped gases can be analyzed, and the presence of polluting gases can be investigated; the pumping step is stopped when the level of pollution in the sealed chamber becomes lower than a previously fixed value. An acceleration of the decontamination step can be achieved by heating the wall of the non-sealed confined environment, for example to a temperature of about 60 ° C.

In another aspect, the invention provides a device for de-lining a non-sealed confined environment, comprising;

- a depulution chamber adapted to contain the confined environment not waterproof,

gas introduction means capable of producing a gas injection flow rate in the de-oiling chamber,

pumping means capable of pumping the gases out of the depollution chamber, in which:

the pumping means have a variable pumping capacity,

- Control means are provided to adapt the pumping capacity and to adapt the gas injection rate,

means are provided for controlling the pressure difference between the inside and the outside of the non-sealed confined environment,

the control means adapt the pumping capacity and / or the gas injection rate so that the pressure difference between the inside and the outside of the sealed non-sealed environment determined by the control means the pressure difference, at any time less than the pressure difference causing a mechanical deformation damaging the wall of the confined environment not leakproof.

The gas introduction means may advantageously comprise a source of purge gas. The control means may act on the pumping speed of the gas pumping means, and / or on a variable coπductance connected in series with the gas pumping means, and / or on the gas introduction means.

In a simplified embodiment, the means for controlling the pressure difference may comprise a theoretical curve of variation of pressure as a function of time, recorded in a memory of the control means, and that the control means follow to vary. time ia pumping capacity and / or Ie flow ^of gas injection.

Preferably, the means for controlling the pressure difference comprise, alternatively or in addition, at least one deformation sensor, adapted to measuring the deformation of the wall of the confined environment not waterproof, and providing a signal to control its pressure variation in the pollution control chamber.

The depollution device may advantageously comprise means for analyzing the pumped gases, in particular means for analyzing the nature and the concentration of the gaseous species present. The gas analyzer may be constituted by a gas analyzer having means for ionizing gases at atmospheric pressure or under vacuum, and means for identifying the ionized gases by measuring an ion parameter. Such an analyzer is described for example in the document FR 2,883,412 incorporated herein by reference. It can include means for performing an operation on the measured parameters (e.g., an average, a sum, a combination).

The device according to the invention may also comprise means for performing an operation on the lines of the various gases present, and / or a means of measuring the humidity, for example a low pressure humidity sensor such as a source of plasma for generating a plasma in the gaseous mixture to be studied associated with means for collecting and transmitting to an optical spectrometer the radiation emitted by the plasma, as described for example in the document EP 1 568 987 incorporated herein by reference. The analysis of the composition of the gaseous mixture in the confined environment can in particular make it possible to know the origin of a contamination, and therefore the process step responsible for this (place of manufacture of the photomask or the wafer). semiconductor, transport, storage area, etc ...}.

This analysis can also monitor the quality of confined environments, provide real-time diagnostics and clean up these confined environments as needed.

In addition the depoilution device may comprise microwave-type heating means, infrared, injection of a heated purge gas, or a combination of these means for heating the sealed non-sealed environment. According to one possibiiité, the depoilution device is such that the pumping and purging steps are automated and triggered by the reading of signals from means for analyzing the pumped gases and / or a deformation sensor.

Advantageously, the pollution control chamber is of dimensions only slightly greater than those of the sealed non-sealed environment that is placed therein. The desired effects are to minimize the time of evacuation of the sealed non-sealed environment, and to be able to perform a gas analysis with as little dilution as possible. The inner volume of the deionization chamber may ideally be about twice as large as the outer volume of the transport box, and twenty times larger (for example, 2 liters) than the volume between its film and the active layer. a pneumomaniac. For this, the depollution chamber may be flexible or deformable.

The depollution device may furthermore comprise means for measuring the pressure revolution in the deionization chamber, for example a pressure sensor. The measurement of the evolution of the pressure makes it possible in particular to control whether a vacuuming of the box is abnormally difficult. This type of behavior, which can be induced by the presence of liquid, would translate a bad drying.

The gas pumping means comprise at least one primary pumping unit. Advantageously, the pumping means furthermore comprise a secondary pumping group which may be of turbomolecular, molecular or hybrid type, so as to significantly reduce the moisture content in the molecular phase by rapidly reaching low pressures of the order of 10 ^{~ 2} to 10 ^'3 Torr.

SUMMARY DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent on reading the following examples of embodiments, given of course by way of illustration and not limitation, and in the accompanying drawings, in which:

FIG. 1 schematically illustrates a depollution device according to an embodiment of the present invention,

FIG. 2 is a sectional view of a device according to an embodiment of the invention used to depict a transport box,

FIG. 3 is a sectional view of a device according to one embodiment of the invention used for etching photomasks of film;

FIG. 4 illustrates a possible shape of theoretical curve of variation of pressure as a function of time, making it possible to control the variation of pressure in the pollution chamber;

FIGS. 5 and 6 are detail views of the pressure variation curve of FIG. 4, in areas close to the equilibrium low pressure; FIGS. 7 to 10 illustrate the gas exchanges coming out of the various depollution steps of a FOUP type transport box;

- Figure 11 illustrates an embodiment of the deposition device, and in particular the adaptation of a deformation sensor; FIG. 12 illustrates measurement results of depilution;

FIG. 13 illustrates the effect of the depollution, by observing the development of the crystals on the active surface of a product in the non-ethane confined environment;

Figure 14 illustrates, in time graph form, the effect of depilution and passivation on the development of crystals on the active surface of the products; and Figure 15 illustrates the steps of a method of measuring passivation by observing the contamination.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a non-leaked confined environment 1 in the form of a volume 2 limited by a wall 3 and including a leak 4. During a first step of the method, the non-étanehe confined environment 1 is placed in a 5 etanehe decontamination chamber whose interior volume 5a is just a little higher than the volume of the non-étanehe 1 confined environment to contain it. The depollution chamber 5, which may be flexible or deformable, comprises a door 5b for the passage of the non-étanehe confined environment 1, an inlet 6 for a gas flow, and an outlet 7 connected to gas pumping means 8 . The wall 9 of the deposition chamber 5 is mechanically able to withstand the vacuum.

The pumping means 8 comprise at least one primary pumping group Sa ₁ and advantageously also a secondary pumping group 8b, for example, of turbomulecular, molecular or hybrid type. The method according to the invention comprises at least one step of simultaneous pumping of the outside and inside of the non-étanehe confined environment 1, taking advantage of the leakage 4 existing in the wall 3 of the non-étanehe confined environment. 1 so that the gases pass from the inside to the outside of the non-étanehe confined environment 1, and by ensuring that the pressure difference between the internal atmosphere and the external atmosphere of the non-étanehe confined environment 1 or at any time less than that likely to cause the mechanical deformation damaging the wall 3 of the confined environment not waterproof 1. The method also comprises at least one step of restoring the atmospheric pressure in the unsealed confined environment 1, by injecting a gas flow into the pollution control chamber 5 through the inlet 8, taking advantage of the leakage 4 so that the gases pass from the outside to the bottom of the sealed non-leaked environment 1, and further ensuring that the pressure difference between the internal atmosphere and the external atmosphere of the sealed non-leaked environment 1 is at all less time than this, which is likely to cause the mechanical deformation damaging the paras 3 of the confined environment not sealed 1.

For this purpose, the depollution device according to the invention comprises means for controlling the pressure of the atmosphere present in the deposition chamber 5. The evaporation of this pressure is monitored and controlled in order to preserve the mechanical characteristics of the wall 3 .

In the illustrated embodiment, the dewatering device comprises a pressure sensor 10, a variable conductance valve 12 connected in the pumping line in series with the pump means 8, a source of purge gas 13 connected to the input 8, control means 14, and possibly a deformation sensor 15,

In the first embodiment of the invention illustrated in FIG. 2, a depoilution device of a non-sealed confined environment 1 of transport and / or storage box type of substrates at atmospheric pressure is shown in section. , having an interior volume 2 limited by a peripheral wall 3 provided with an access passage 3a obiurabie by a door 3b and allowing the introduction and removal of a stack of slices of substrates 100. We distinguish the depollution chamber 5, for example twice larger than ^the unsealed enclosed environment 1 placed therein, connected to means ^of purge gas injection 6, 13, gas pumping means 7, 8, means for measuring pressure device 10 for measuring the gas pressure in the deionization chamber 5, means for controlling the pressure difference between the inside and the outside of the transport box 1. The method according to the invention is particularly suitable for t suitable for transport boxes 1 at atmospheric pressure, whose structure plastic material does not support too rapid or too large pressure differences that may damage the wall 3, for example in. causing a crack in the wall 3 of the transport box 1, an atmospheric transport box 1 is leaking, and the method according to the invention proposes to take advantage of the natural boxes 4 of the box during the process steps, so that the transport box 1 remains closed (door 3b closed) throughout the process.

We consider again Figure 1.

In the device shown, the pumping means, comprising the primary pump 8a, the secondary pump 8b and optionally a variable conductaπce valve 12, have a variable pumping capacity. The variation of the pumping capacity can be obtained by controlling the closing of the variable conductance valve 12, and / or by varying the driving speed of the motors of the primary pump 8a and / or the secondary pump. 8b, the gas introduction means 6, 13 are able to produce a variable flow rate of gas injection into the deposition chamber 5.

According to the invention, it is desired to control the variation of pressure in the depollution chamber 5 so that the pressure difference between the inside and the outside of the unaffected confined environment 1 is at any time less than the pressure difference causing a mechanical deformation damaging the wall 3 of the sealed non-leaked environment 1.

For this purpose, means for controlling the pressure difference between the inside and the outside of the non-sealed confined environment 1 are provided, and control means 14 are provided for adapting the pumping capacity and for adapting the pressure. gas injection rate as a function of the information received from the means for controlling the pressure difference,

The control means 14 may comprise a processor 14a associated with a memory 14b in which control programs are recorded. The processor 14a can receive information from various sensors such as the pressure sensor 10, the deformation sensor 15, a pumped gas analyzer 11.

At the output, the processor 14a is connected in a manner known per se to various actuators making it possible to act on the variable conductance valve 12, on the drive motors of the primary pump 8a and the secondary pump 8b, on a valve of flow control of gas flow of the gas introducing means 6, 13,

In a first embodiment, the control means 14 control the pressure variation in its pollution control chamber 5 by following a theoretical curve of variation of pressure as a function of time. This theoretical curve is recorded in the memory 14b, tors tors of a prior acquisition step. The Figures 4, 5 and 6 illustrate a possible form of theoretical curve of pressure variation as a function of time. There is a first step A for pumping, a second step B for maintaining the low equilibrium limit pressure, and a third stage C for increasing the pressure by injecting gas into the deposition chamber 5. The processor 14a receives the information of the pressure sensor 10, and adapts, by following a program stored in the memory 14b, the pumping capacity of the pumping means 8 and the flow rate of the gas injection means 6, 13 so that this measured pressure is constantly monitored the theoretical curve of variation of pressure as a function of time recorded in memory 14b. During an acquisition step, the theoretical pressure variation curve is determined by ensuring that, in a given type of non-sealed confined environment i, the pressure difference between the inside and the outside of the the unconfined environment 1 remains permanently less than the pressure difference causing a mechanical deformation damaging the wall 3 of the non-leakproof confined environment 1. It is then considered that the same theoretical curve of pressure variation as a function of time can be applied to all leaky confined environments 1 of the same type.

According to a preferred embodiment, the pressure variation in the depollution chamber 5 is controlled by following the signa! given by a deformation sensor 15 capable of detecting the actual deformation of the wall 3 of the non-leaked confined environment 1 during the pumping and / or upcooling steps in the deposition chamber 5. In this case, the processor 14a receives the signals emitted by the deformation sensor 15 and, as a function of a program stored in the memory 14b, drives the initiators of the gas introduction means 8, 13 and the pump means 8 so as to vary The pressure in the pollution control chamber 5 is slow enough so that the flow rate of the leakage 4 allows the interior atmosphere 2 of the enclosed environment 1 to follow closely the pressure variation in the centrifuge chamber. 5.

As deformation sensor 15, it is advantageous to use a sensor shown in FIG. 11 in connection with a non-sealed confined environment 1 of FOUP transport box type. Such a FOUP transport box comprises, on its upper face, a mushroom-shaped grip structure 1a called MUSHROOM, which is generally opaque while the rest of the transport box is made of transparent plastic. The wall 9 of the deposition chamber 5 comprises a transparent window 9a, to the right of the gripping structure 1a. The deformation sensor 15 comprises a laser transceiver which detects, through the porthole 9a, the distance which separates it from the gripping structure 1a. Such a laser transceiver capable of measuring distances between 30 mm and 130 mm can be chosen with an accuracy of about 0.5 mm.

Such a sensor can serve both as a presence sensor (if the distance is greater than 130 nm, this means that there is no unsealed confined environment 1 in the pollution control chamber 5), verification of good positioning (if the distance is not in a given range, it means that the impermeable confined environment 1 may be positioned), and of deformation measurement which ensures the integrity of the confined non-leaked environment 1 during the process (if the deformation exceeds a threshold, it is necessary to slow down / stop pumping or injection).

The advantage of using the deformation sensor 15 is to know with certainty the deformation of the wall 3 of the sealed non-sealed environment 1, that! that is the state of the leak 4, that is to say even when it is completely or partially closed.

Let us consider FIGS. 5 and 8, which illustrate a deliberate slowing down of the speed of variation of its pressure when one is close to the low limit pressure. This voluntary slowdown has the effect of reducing particulate pollution on the active surfaces of masks or semiconductor wafers. It is believed that this particulate pollution occurs under too rapid pressure changes at low pressure, and that it results from the increase in the average free path of the particles when the pressure is very low.

The depoilution device may comprise heated walls to prevent the. gases that must be expelled from being adsorbed. the wall 9 of the dépoiiution chamber 5 may advantageously be made of stainless steel polished mirror-like, allowing to ^obtain a very good surface TEAEs, or quartz. These materials make it possible to limit the degassing of the wall 9. The shape of the de-oiling chamber 5 may be cylindrical to reduce the dead volumes. The depollution chamber 5 may also include a window made of glass, quartz or any other transparent material compatible with the vacuum, the pressure variations and / or the plasma, so that the operator can verify that the stack of substrates 100 in transport box 1 did not reverse.

According to a variant not shown, the method of the invention proposes to pump simultaneously inside and outside the transport box. This pumping Differential allows faster evacuation and a better ability to interpret data. For this, the pumping means of the device comprise first pumping means for evacuation of the sealed compartment and second pumping means connected to at least one orifice, closed by a filter, the sealed peripheral wall of the box. transport for pumping the inside of the transport box. These second pumping means comprise a second pumping line.

FIGS. 7 to 10, which illustrate the mechanism of decontamination and passivation of the wall 3 of the sealed non-sealed environment 1 of the transport box type, are now considered.

The figures illustrate a wall portion,

In FIG. 7, during the work pressure descent step (curve A in FIG. 4), the gas molecules trapped in the wall 3 escape towards the interior space 2 of the sealed non-leaked environment 1. illustrated by the arrows 50.

In FIG. 8, during the step of decontamination at lower equilibrium pressure (step B in FIG. 4), the outgassing flow (arrow 51) continues and then gradually decreases as the pore is emptied. 3. After a period of about 20 minutes from step 8, the degassing fos becomes small.

In FIG. 9, corresponding to step G of FIG. 4, during which a purge gas is introduced, the purge gas molecules progressively penetrate into the wall 3, as illustrated by the arrows 52.

In FIG. 10, at the end of the rise to atmospheric pressure stage, the purge gas molecules replaced the initial gas! and form in the wall 3 a boundary layer 3a containing purge gas. The constitution of this boundary layer 3a ensures the passivation of the wall 3, by correctly selecting the purge gas. l_ _'θ _e ff t resulting from the decontamination and passivation process according to the invention was measured using the test method 108-0301 E SEMI defined and published by the Semiconductor body Equipmeni and Materials International (HE!) . This method analyzes its contamination which appears on silicon wafers placed in the non-sealed confined environment 1. it has been found that the process of the invention considerably reduces the effect of degassing the walls of a FOUP type transport box.

This reduction is illustrated in Figure 12 for various ions.

In practice, when semiconductor wafers are placed in a transport box, a gradual development of crystals on the active surface can generally be seen, as shown in the upper part of FIG. semiconductor wafers are placed in a transport box having undergone a decontamination and passivation step according to the method of the invention, the development of crystals is strongly retarded, and becomes indefinable during the useful period, as illustrated in the part bottom of Figure 13.

Figure 14 illustrates the same phenomenon: curve D illustrates a gradual increase of crystals, in a transport box which has not undergone decontamination and passivation, while curve E illustrates the almost undetectable development of crystals when the semiconductor wafers are placed in a transport box having undergone a decontamination and passivation step.

Very advantageously, the device of FIG. 1 can be used for the storage of semiconductor wafers in transport boxes. Several deposition chambers 5 may be connected in parallel to the same pumping system 8 and to the same gas injection means 6, 13, which ensure the deposition of the internal atmosphere and the substrates 100 contained in the transport boxes. 5 without damaging the walls 3,

The device according to the invention has the advantage of making it possible to increase the storage time of the substrate transport boxes. Once passed through the depollution chamber 5, the transport boxes can be stored long-term without the risk of contaminating the substrates they contain. The method implemented in the device in particular prevents ia contamination from ^the external atmosphere, e.g., oxygen which may oxidize the surface of substrates, including semiconductor wafers, and more particularly those covered with germanium deposits or copper. FIG. 3, which illustrates a second embodiment according to the present invention, will now be considered. The method of the invention is here applied to the case where the non-sealed confined environment 1 is a photomasque with its film. The confined environment comprises the volume 2 between its wall 3 constituted by the film and the active surface 32 of photomask that it covers. Low conductance filter apertures 35 are located at the periphery of the unsealed confined environment 1.

A depollution chamber 5 may contain one or more photomasks 1. The

5 depollution chamber 5 may be a transport chamber itself, or the transport chamber attached to a small additional volume 5c which allows the opening of the transport housing, or even the depollution chamber may be a separate enclosure. If there are several, the photomasks 1 are stacked in a support 33 which is placed in the watertight and low volume clearance chamber. Ii

It is preferred that the depollution chamber 5 have a small volume (eg 20 times larger than the volume 2 under the wall 3), to ensure a better dewatering effect. The deposition chamber 5 tightly encloses the support 33 on which I or the photomasks rest, so that in the closed position the deposition chamber is not much larger than the support 33.

The device comprises an inlet 6 for the injection of purge gas and an outlet connected to pumping means 8. The pumping means 8 can advantageously be adapted to perform a slow pumping which makes it possible to avoid having a gap. too much pressure on either side of the wall 3 of the toilet. It is extremely fragile and it is essential not to exceed its limit of

20 deformation (maximum internal / external pressure difference of 1 Pa).

Figure 15 illustrates the effect obtained by decontaminating masks according to the method of the invention. During a step 1, the initial degassing of a mask transport box is measured before decontamination.

From step 1 to step 3, a 20-minute decontamination cycle is conducted with nitrogen or dry air.

At the end of decontamination, the final degassing of the mask transport box is measured. It can be seen that the final degassing level is much lower than the initial degassing level.

In step 4, leave the mask transport box waiting for six days in the air

Ambient.

In step 5, the degassing of the mask transport box is measured again. It is noted that this degassing after six days of waiting has almost the same level as the final degassing before the six days of waiting. In the absence of a decontamination process, the level of degassing would have been that of initial degassing.

35 of step 1. A second decontamination cycle can be carried out for 20 minutes with nitrogen or with dry air, during a step 6, and the degassing is measured again. Then we see the effect of the second decontamination, which further reduces the degassing.

The essential finding of this Figure 15 is that the mask transport box has retained its reduced degassing property after six days of waiting time.

Sampling means associated with a gas analyzer 11 are connected to the deposition chamber 5. The pumping means 8 are separate from the sampling means, and thus allow pumping at a higher rate, of the order of 10 sîm.

Actuator means 39, such as cylinders, make it possible to raise / lower the support 33 in the depollution chamber 5.

The gas analyzer 11 may be a tonic mobility spectrometer (MS, Ion Mobility Spectrometer), for example as described in the document FR 2,883,412 incorporated herein by reference, which has the advantage of measuring in real time residual amounts of gas of a few ppb. Sampling means, such ^that a small pump having a flow rate of about 0.21 / min, allow ^to sample ^the atmosphere in the environment. Towards the end of the pumping step, a sample of the gas contained in the deposition chamber 5 is sent to the gas analyzer 11 to determine whether the set deposition level is reached, and whether the pumping can be stopped. The small volume of the dewatering chamber 5 makes it possible to improve the detection sensitivity of the measurement by limiting the dilution of the gaseous mixture contained in the internal volume 2 of the non-sealed confined environment 1.

When the desired decontamination level is obtained, the pumping is stopped and the non-sealed confined environment 1 is returned to its initial pressure by introduction of a clean gas.

During the purge step, the purge gas used may be of higher density than that of the gas present in the confined atmosphere, that is to say higher void volume and / or more cold since the conductancs to be done is proportional to the square root of the quotient of the temperature by its mass of the gas. Mass properties

And / or the temperature of the purge gas will allow it to hardly pass through the low conductance filters present on the periphery of the photomask where the film wall 3 is attached. So. The purge gas will progressively replace substantially the gaseous atmosphere in the dewatering chamber 5, and will leave the atmosphere in the sealed, non-leaked environment 1 unaffected for analysis.

Indeed, the quantities of gas to be detected are very small and it is a question of not diiuer them. In addition, this purge gas may preferentially be a gas that is not already present in most of the pollution control chamber 5, which will make it possible to differentiate the mixture originating from the atmosphere of the confined environment and to reduce the problem of dilution. . In such an application, argon is particularly suitable as a purge gas because if it has a high density, it is inert and usually available near treatment equipment.

Alternatively, the purge gas may consist of synthetic air at 80% nitrogen and 20% oxygen. Synthetic air can advantageously be used in combination with the IMS type gas analyzers which have their reference on this mixture.

More commonly, it can advantageously use azar. As indicated above, the invention finds applications in the decontamination and passivation of photomasks or transport boxes for semiconductor wafers. It can also be applied in particular in molecular control and decontamination in the medical field (prostheses, ","), the agri-food field or even the automotive field (surface oxidation of precision parts for example).

The present invention is not limited to the embodiments that have been explicitly described, but it includes the various variants and generalizations that are within the abilities of those skilled in the art.

Claims

1 - Method of defrosting a non-sealed confined environment (1) comprising an interior space (2) limited by a wall (3) having a natural leakage (4), comprising the following steps: - placing the non-sealed confined environment ( 1), having its natural leakage (4), in a sealed dewatering chamber (5) comprising gas introducing means (6) and gas pumping means (7, 8),

the gas contained in the pollution control chamber (5) is pumped by adjusting the pressure drop in the depollution chamber (5) so that the pressure difference between the inside and the outside of the environment confined unsealed (1) is at any time less than the pressure difference causing a mechanical deformation damaging the wall (3) of the confined environment unsealed (1).

2 - Process according to claim 1, characterized in that it comprises a pressure rise step during which the pressure rise is adjusted in its depollution chamber (5) so that the pressure difference between the interior and exterior of the leak-proof confined environment (1) is at any time less than the pressure difference causing a mechanical deformation damaging the wall (3) of the unsealed confined environment (1).

3 - Process according to one of claims 1 or 2, wherein one controls the pressure variation in its deposition chamber (5) by following a theoretical curve of pressure variation as a function of time.

4 - Method according to one of claims 1 or 2. wherein controlling the pressure variation in the pollution control chamber (5) following the signa! given by at least one wall deformation sensor (3) of the unsealed confined environment (1),

5 - Process according to any one of claims 1 to 4, characterized in that, to adjust the pressure variation in the deoilution chamber (5), the pumping capacity of the pumping means (7, 8) is varied. by controlling their rotational speed, and / or by controlling a variable conductance (12), and / or varying a gas flow entering the dewatering chamber (5), by controlling the flow means introduction of gas (6). 6 - Process according to any one of claims 1 to 5, further comprising a purge step, the purge step comprising at least one purge gas filling operation during which a purge gas is introduced into the chamber of depollution (5),

7 - Process according to claim 6, characterized in that the purge step further comprises at least one purge gas pumping operation during which the gas mixture present is extracted from the dewatering chamber (5).

8 - Process according to claim 7, wherein the operations of filling and pumping the purge gas are performed simultaneously, with a pumping rate lower than the injection rate,

9 - Process according to claim 7, wherein several operations of filling and purge gas pumping are performed successively.

10 - Process according to claim 6, wherein several purge steps, comprising filling operations and pumping purge gas, are performed alternately with pumping steps.

11 - Process according to any one of claims 6 to 10, in which! the purge gas filling operation comprises a period of overpressure, during which a pressure higher than atmospheric pressure is maintained in the deposition chamber (5) before the return to atmospheric pressure.

12 - Process according to any one of claims 6 to 11, wherein the purge gas is nitrogen.

13 - Process according to any one of claims 6 to 11, wherein the purge gas is of synthetic air.

14 - Process according to any one of claims 6 to 13, wherein the purge gas is introduced and extracted from the non-sealed confined environment (1) by filters {35} that it comprises,

15 - Process according to any one of claims 1 to 14, wherein, the sealed non-sealed environment (1) being a photomask provided with its film (3), the gases are introduced and extracted by low-capacitance filters (35) separating the film (3) from the active part (32) of the mask.

16 - Process seiαn any one of claims 1 to 14, characterized in that the confined environment leakproof {1) is a box of

Transport at atmospheric pressure closed.

17 - Process according to claim 16, characterized in that the transport box (1) contains slices of semiconductor substrate (100).

18 - Process according to any one of claims 1 to 17, wherein is reached in the chamber of depoilution (5) sealed low pressures,

10 of the order of 10 ^-2 to 10 ^-3 Torr,

19 - Process according to any one of claims 1 to 18, wherein the pumped gases are analyzed and the pumping step is stopped when the level of pollution in the sealed pollution control chamber (5) becomes less than a previously fixed value.

20 - Device for the depollution of a non-sealed confined environment (1), comprising:

a depollution chamber (5) able to contain the sealed non-sealed environment {1},

gas introduction means (8, 13) capable of producing a gas injection flow rate in the pollution control chamber (5),

pumping means capable of pumping the gases (7, 8) out of the deposition chamber (5), characterized in that;

the pumping means (7, 8) have a variable pumping capacity,

There is provided control means (14) for adapting the pumping capacity and for adjusting the gas injection flow rate,

means are provided for controlling the pressure difference between the inside and the outside of the non-étanehβ (1) confined environment,

the control means (14) adjusts the pumping capacity and / or the gas injection rate so that the pressure difference between the inside and the outside of the unaffected confined environment (1) determined by the means for controlling the pressure difference, at any time less than the pressure difference causing a mechanical deformation damaging the wall (3) of the unsealed confined environment (1),

21 - Device according to claim 20, wherein the means for controlling the pressure difference comprise a theoretical pressure variation curve as a function of time, stored in a memory (14b) of the control means (14), and that the control means (14) follow to vary in time the pumping capacity and / or the gas injection rate.

22 - Device according to one of claims 20 or 21, characterized in that the means for controlling the pressure difference comprise at least one deformation sensor (15), adapted to measure the deformation of the wall (3) of confined environment (1), and providing a signal to control the variation of pressure in the pollution control chamber (5).

23 - Device according to any one of claims 20 to 22, further comprising heating means of ^the unsealed enclosed environment (1).

24 - Device according to any one of claims 20 to 23, in esque! the gas introduction means (6, 13) comprise a source of purge gas (13) such as nitrogen or synthetic air.

25 - Device according to any one of claims 20 to 24, further comprising means for analyzing (11) pumped gases.

26 - Device according to claim 25, wherein the analysis means (11) comprise means for ionizing the pumped gas, means for identifying its ionized gases by measuring a parameter of the ions, and means for performing a operation on the measured parameters.

27 - Device according to one of claims 25 or 26, characterized in that its pumping and purging steps are automated and triggered by reading signals from pump analysis means (11) and / or a deformation sensor (1 5).

28 - Device according to any one of claims 20 to 27, wherein fa decontamination chamber (5) is of dimensions slightly greater than those of the non-sealed confined environment (1), 29 - Device according to any one of claims 20 to 28, further comprising means for measuring (10) the evolution of the pressure in the depollution chamber (5).

30 - Device according to any one of claims 20 to 29, wherein the pumping means (7, 8) comprise a primary pump (8a) and a secondary pump (8b) of molecular, turbomolecular or hybrid type, defining a pumping line capable of establishing in the clearance chamber (5) a vacuum of about 10 ^{-2 to} 10 ^-3 Torr.