METHOD TO INCREASE THE PRODUCTION IN PROCESSES OF DEPOSITION OF THIN LAYERS ON A SUBSTRATE
The present invention relates to a method for increasing the production in the deposition processes of thin layers on a substrate. The processes for the deposition of thin layers on a substrate are widely applied in various industrial branches. For example, in these processes the production of integrated electronic circuits (also known in this field as ICs) is based; of the supports for storing information, such as CDs (where a thin layer of aluminum is deposited on a substrate of transparent plastics) or hard disks for computers (where a magnetic material is deposited on a support, usually aluminum ); of flat displays; finally, the processes to deposit thin layers are adopted in the development field of micromechanical devices, elaborated with techniques quite similar to those used in the elaboration of ICs. The main industrial processes of deposition of thin layers are found in the chemical deposition of the vapor phase and the physical deposition of the vapor phase, better known in the field as
"chemical vapor deposition" and "physical vapor deposition", respectively, or by their acronyms "CVD" and "PVD". In CVD processes, two or more gaseous species are caused to react in an evacuated chamber in which a substrate exists; in the reaction a solid product is formed which is placed on the substrate in the form of a thin layer. The pressure at which the chamber must be evacuated may be noticeably different in several CVD processes; some of them (defined as the low pressure or ultra high vacuum type) may require initial evacuations of the chamber to pressure values of 10 ~ 8 - 10"9 mbar, in the subsequent, the indication of the CVD processes provided The latter are referred to by the abbreviated name of PVD, but all of these techniques show the following common characteristics: to obtain the thin layer, a target of the material proposed is used. deposit, generally having the shape of a cylinder of short height, which is placed in the chamber in front of the substrate and parallel to it, the chamber is evacuated first and after that is filled with an atmosphere of a noble gas, usually argon , at a pressure of 10"2 - 10 ~ 5 mbar; by applying a potential difference of a few thousand volts between the substrate and target supports (so that the latter has a cathodic potential), a plasma of electrons and Ar + ions are generated in the space between the substrate and the objective; these ions are accelerated by the electric field towards the target, thus originating their erosion by impact; the resulting species (usually atoms or "groups" of atoms) of the target erosion will be deposited on the substrate (as well as the other available surfaces) thus forming the thin layer. Each process can comprise several stages of deposition of thin layers and there are also hybrid processes, comprising both stages of CVD and PVD. It is known that the properties of thin-film devices, particularly in the case of ICs, strongly depend on the presence of defects within the deposited layers. These defects are mainly due to the presence of atoms of chemical species different from those that form the layer. Consequently, it is necessary to reduce to a minimum the possible sources of pollution in all stages of the process, through the use of reagents of the highest possible purity (reactive gases in the case of CVD and the objective in the case of PVD) and ensuring maximum cleaning of all surfaces in the process chamber and the process atmosphere. further, even if it is possible to carry out the deposition at the same time in several substrates (in both cases of CVD and PVD), the industrial trend is in the direction of processes with a single substrate that allows a better control of deposition characteristics . To comply with the above-mentioned requirements, the deposition processes of the thin layers are carried out in systems comprising at least one chamber, but generally a plurality of chambers, each of which is designated for a specific operation; for example, there are current process chambers where deposition steps are carried out, or conditioning chambers that are used, for example, to clean or heat substrates before deposition. In the following, process and conditioning chambers will be generally indicated as treatment chambers. In the case of several treatment chambers, these can be placed online, connect directly to others; alternatively, these cameras can be placed around a central transfer chamber. Each chamber is connected to the adjacent ones by means of valves that are closed and opened only to allow the transfer of the substrates from one chamber to the other during the various stages of the process. In order to ensure maximum possible cleaning, in general, all the chambers are kept under vacuum, with the best vacuum values in the deposition chambers. The substrates are handled from a chamber to the subsequent ones through automated means, in general, mechanical arms. In a simple operational example of a process system (of the type comprising cameras placed around a transfer chamber), the substrates are introduced into a first chamber inside properly configured boxes, the inner walls of which are provided with tabs whose purpose is to keep the substrates separated from each other in order to simplify the automated handling operations. A vacuum of approximately 10 ~ 5 - 10"6 mbar is made in this first chamber and a first valve is opened to communicate this chamber with a transfer chamber, a mechanical arm takes a substrate from the box and transports it to the chamber. transfer, where the pressure is at lower levels than in the first chamber, generally about 10"7 mbar and the first valve closes; a second valve is then opened to communicate the transfer chamber with a process chamber, the substrate is led to the position at which the deposition will take place and the process chamber is closed upon closing the second valve. After finishing the deposition of the thin layer, the substrate can then be transferred, again by means of mechanical arms and through transfer chambers, to the outside of the system or to another chamber thereof. Ideally, thin layer deposition systems should always be kept isolated from the atmosphere. However, the treatment chambers must be periodically opened for operations concerning the maintenance of the automated equipment, the cleaning of the internal surfaces or, in the case of PVD, for the replacement of the target when it is evacuated or a different material has been deposited. . In each opening, the chamber is led to an ambient pressure and its internal walls, the surfaces of the equipment and the target absorb atmospheric gases, in particular, water vapor. The gases are then released into the chamber during the processing steps. During processing, continuous pumping is maintained in the chambers in order to remove impurities therefrom and, particularly, atmospheric gases released by the surfaces, as described above. The balance between the flow of degassing from the surfaces and the speed of removal of the gas from the pumps during the manufacturing process is determinant for the basic pressure of the system; the lower the basic pressure, the lower the amount of possible contaminants for the layers under the deposition. Typically, in order to improve the basic pressure, after each opening, the chambers are caused to undergo pumping under heating at temperatures of about 100-300 ° C (this step is known in the field as "cooking"). This treatment is intended to increase the degassing of all surfaces in the chamber and the removal, as much as possible, of the gases initially adsorbed on these surfaces; The higher the pumping speed during the cooking stage, the more efficient the removal is. In this way, the residual amount of adsorbed gases is reduced and, consequently, the degassing flow during the processing steps; the pump speed being the same during processing, a lower basic pressure of the chamber is obtained and, consequently, a lower amount of impurities in the process atmosphere. After cooking, the evacuation begins; the cleaning of the chamber is considered acceptable for the start of a new cycle of depositions when the pressure reaches a preset value, generally comprised between 10"7 and 10" 9 mbar. The target surface used in PVD processes is cleaned by the treatment in which the same deposition stage is carried out as in the manufacturing process on a test substrate that is then discharged; this stage of conditioning the target is known in the field with the definition of "reinforcement". With the present technology, the pumping step to return the chamber pressure from about 1 000 to about 1 0"8 mbar, requires a time ranging from about 4 to 12 hours, for the reinforcement stage a time is required It varies between half an hour and 4 hours, these two preparatory stages are necessary to obtain high quality devices, but they involve downtimes in terms of productivity Another possible source of contamination of the deposition chambers in the repeated opening of these for the Substrate transfer As previously stated, the transfer chambers are normally maintained at higher pressures than the treatment chambers and, in turn, the chambers with the substrates containing boxes are maintained at higher pressures than the transfer chambers. Whenever the valves that communicate the cameras open, there is a transfer of gases from the highest pressure chamber towards the lower pressure, resulting in a continuous transfer of contaminating gases from the chambers of substrate boxes to the treatment chambers. In addition, the surface of the substrates itself is generally "dirty", having atmospheric gases adsorbed therein; these gases are released in the low pressure environment of the treatment chambers. According to the above, there are a number of possible sources of contamination of thin layers under formation that can lead to waste production. The production of devices produced by the use of thin layer deposition techniques can be increased either by reducing the periods of inactivity of pumping of the chambers or by reducing the total pollution of the working atmosphere or, even better, acting on both characteristics of the process. An object of the present invention is to provide a method for increasing the production in the deposition processes of thin layers on a substrate. These objects are achieved in accordance with the present invention, which in a first aspect thereof deals with a method for increasing the production of processes for the deposition of thin layers, comprising the contact of a degassing device in activated form with the working atmosphere inside a process chamber when the sum of the partial pressures of the reactive gases in the chamber is less than approximately 10"3 mbar and, when no real production substrate is in processing, by the use of equipment of automated substrate handling and procedures used in the elaboration stages The reactive gases indicated above are those gases, well known in the matter of degassing, towards which the degassing materials are highly reactive, these gases mainly include oxygen, water, dioxide carbon, carbon monoxide, hydrogen and in some cases nitrogen. As it is known, the degassing materials require for their operation a heating treatment for activation at temperatures between approximately 250 and 900 ° C and for a time comprised between a few minutes and approximately one hour, according to the chemical composition of the material specific. In the event that an activated degassing device is exposed to an atmosphere where the sum of the partial pressures of the reactive gases is greater than approximately 10"3 mbar, violent reactions may take place, potentially dangerous for the equipment present in the chamber. On the other hand, the degassing materials are totally inert to noble gases, which are normally used as the working atmosphere in the deposition processes of thin layers.Therefore, as will be described in the following, the method of the invention provides for the possibility that a degassing device is present in activated form in the treatment chamber when the total pressure in it is well above 1 0"3 mbar, taking into account that it is the maximum pressure obtained by adding the partial pressure of the reactive gases defined above. The invention will be described below in some of its modalities with reference to the drawings in which: - Figures 1-4 show, as flow diagrams, some possible alternative embodiments of the method according to the invention; Figures 5-7 show some possible modalities of degassing devices according to the invention;
Figure 8 shows curves representing the pressure in a PVD chamber during its evacuation, registered respectively according to known procedures and according to the method of the invention. The use of degassing materials and devices inside thin layer deposition chambers has already been disclosed in patent application EP-A-693626, international patent application publications WO 96/13620 and WO 97/17542 and in the U.S. Patent No. 5,778,682. However, all these documents describe degassing systems that remain in the chamber also during the manufacturing process. The method of the invention is different from the use of degassing systems according to these documents, since the latter require substantial modifications of the configuration of the process chambers, in particular, to provide adequate heating means for the activation and operation The European patent application EP-A-926258, in the name of the applicant, discloses an additional use of the degassing systems in PVD processes, however, also in this case, the degassing system is maintained in the chamber during the process The presence of a degassing device activated in a treatment chamber according to the invention can help both to increase the speed of evacuation thereof and the reduction of total contamination, thus contributing in different ways to the production yield These results can be obtained through the use of degassing in a number of ways. In a first possible embodiment of the method of the invention, a non-activated degassing device is introduced into an open chamber, on the substrate support; the camera closes then and begins its evacuation. As soon as the pressure reaches a value of approximately 10 ~ 3 mbar, the degassing device previously introduced into the chamber is thermally activated, for example, by the use of the heating means in the substrate support. At the same time, cleaning by discharge of water from the chamber with a noble gas such as argon and, possibly the cooking process, are initiated; The pumps connected to the cameras are always running during these operations. Cleaning by discharging water with argon continues until the level of the contaminant is below a given value, as can be verified with sensors or analyzers, such as a mass spectrometer, connected to the chamber. In an alternative and after calibration of the parameters of the evacuation chamber, the cleaning by discharging water with argon can be continued for a given time. When the level of contamination is adequate for production, the degassing device is removed from the chamber and a new production cycle is started. At this point, the camera is already filled with argon, the middle of the process. According to > this procedure, the pressure in the chamber never goes below 10 ~ 7 mbar or less, and the removal of pollutants from the atmosphere of the chamber is carried out by the action of rinsing the noble gas by cleaning water discharge in cooperation with the degassing device activated. As an alternative, the same previous process can be carried out by closing the chamber and beginning its evacuation without present degassing device. In this case, a pre-activated degassing device is introduced in the chamber (not necessarily in the substrate support) coming from a transfer chamber by means of mechanical arms. The degassing devices of the invention can also be re-introduced and perform their function at fixed times during the operations of the process, for example to help reduce the contamination introduced by the repeated openings of the valves of the chamber or by degassing. of the surface of the substrates. In accordance with this possible application of the method of the invention, a degassing device is introduced into the chamber at fixed times. In this case, a step of cleaning the atmosphere of the process chamber can be provided after a given number of substrates have been processed.; for example, this can be done after all the substrates have been processed in a box and before the use of the substrates of a new box. For this purpose, it is sufficient to transfer in the treatment chamber a degassing device of the invention (pre-activated or activated) in place of a production substrate and between the processing of two such substrates. As previously mentioned, a new production cycle could be started after the opening of a camera without 7 previously reaching pressures in the chamber of 10"mbar or less, however, reaching very low pressures in the chamber before a new one. Production cycle is the most commonly adopted procedure in the industry.In this case, the method of the invention is particularly useful in reducing the time required to lead the chamber back to its operational condition after any opening, contributing the degassing devices to the elimination of atmospheric gases In the following description, by "pressure necessary to start production" means a pressure of 10"7 mbar or less. According to this preferred way of implementation, the method of the invention comprises the steps of: introducing a degassing device into the treatment chamber after its opening, before or during its evacuation, operating so that the degassing device is present in the chamber in an activated form only when the pressure in it has reached values of 1 0 3 mbar or less; - continuing the evacuation of the chamber while the activated degassing device is kept there until the necessary pressure is reached to begin the elaboration process; and removing the degassing device from the chamber by using the same automated substrate handling equipment and procedures used in the processing stages. In a variation of the process outlined above, it is possible to maintain the degassing device in the chamber even after reaching the pressure necessary to begin production, when some operations are carried out which are preliminary to the actual processing stages. Figures 1-4 represent, in the form of flowcharts, some alternative possible modes of the preferred way to implement the method of the invention. With reference to Figure 1, after each opening of the process chamber, it closes again and begins its evacuation (stage 1); For evacuation, low vacuum mechanical pumps (for example, rotary pumps) are usually used at the beginning and, subsequently, when the pressure in the chamber is approximately 1 -1 0"2 mbar, medium vacuum pumps are used. and elevated, such as turbomolecular and cryogenic pumps.When the pressure has reached values of 10 ~ 3 mbar or less and is still under pumping, the degassing device is taken from the box and conducted to the process chamber (stage 2) by means of the same automated substrate management equipment and the procedures used in the elaboration stages, the degassing device is thus placed in the same zone, in the subsequent defined as deposit zone, normally occupied by the substrates during the elaboration of Thin layers This is usually formed of a substrate support supported by a possibly movable pedestal that locates the substrate in approximately the center of the camera. The possibility of heating the reservoir area is generally provided in the thin-bed reservoir chamber: in fact, the heating of the substrate during the processing steps allows obtaining more homogeneous thin layers; In addition, during the initial stages of evacuation, it is necessary that the pedestal be heated to allow degassing. For this purpose, heating means are provided on the pedestal, such as electrical resistors or infra-red lamps that heat the deposit area either from the inside or from the outside of the chamber, through quartz windows. The degassing device, placed in the reservoir area, is subjected to a thermal activation treatment (step 3) at temperatures comprised between approximately 300 and 700 ° C for a time comprised between approximately ten minutes and one hour according to the degassing material employee, by means provided by the heating of the substrate. The degassing device thus activated increases the speed of the subsequent pumping of the chamber to the pressure required for the start of the manufacturing process, generally about 10"8 mbar, and improves the base pressure of the system due to the residual degassing of the walls. The degassing device is then removed from the chamber (step 4), by means of the use of handling means and the procedures adopted in the processing for the transportation of the substrates and it is originated that the elaboration process begins by the introduction of the substrates of Figure 2 shows a possible alternative way of carrying out the method of the invention, after starting the evacuation (step 5), after reaching the pressure of 1 0"3 mbar, a degassing device has been used. activated is introduced into the process chamber (stage 6); the device can be activated, for example, in another treatment chamber, such as a chamber provided for the pre-heating of the processing substrates. Subsequently, after reaching the desired pressure to start the processing steps, the degassing device is removed from the chamber (step 7). Figure 3 shows another possible alternative embodiment of the method of the invention. In this case, the degassing device is introduced into the process chamber (step 8) before the start of the evacuation step (step 9); in this case, the degassing device can be introduced into the chamber immediately after its closure, making use of the automated system management means or even manually before such closure. When the pressure in the process chamber has reached values of 1 0"3 mbar or less, the device is activated by heating to temperatures between approximately 300 and 700 ° C, making use of the means and procedures adopted in the preparation for the heating of the substrates (stage 10) After this, the evacuation continues with the degassing device activated in the chamber until the desired pressure is reached for the start of the elaboration processes, at whose pressure the The degassing device is removed from the chamber (step 1 1) and the manufacturing process is started Finally, when the process provides the preliminary stages to the actual processing stages, it is also possible during the first stages to keep the degassing device inside the The possibility is represented in Figure 4: according to this embodiment of the method of the invention, the steps are repeated initials of any of the methods described in relation to figures 1-3, but after reaching the desired vacuum level, a preliminary step (12) is carried out before processing, before removal of the chamber degassing device. (stage 13). An example of the processes of this type is given by the processes of PVD where, after the evacuation of the chamber at pressures of less than approximately 10"7-10 ~ 8 mbar, the reinforcement stage described above is carried out by introducing argon in the chamber at a pressure of 1 0"3 mbar and simulating a manufacturing process. Under these conditions, the degassing device is covered with the target material and quickly loses its gas sorption efficiency; On the other hand, the action of gas sorption is still present in the first stage of the treatment, thus helping to keep the atmosphere of the process clean and, in any case, the presence of the degassing device saves a stage of transfer of a test substrate from the box to the camera. According to a second aspect thereof, the invention relates to degassing devices for carrying out the previously described method.
As mentioned above, the degassing devices of the invention are loaded in the same boxes of the substrates used in the processing and are handled by the same automated equipment that handle said substrates. For this purpose, the degassing devices must have essentially the same size of the processing substrates; in fact, the larger degassing devices could not be placed in the containers nor could they pass through the valves that close the transfer chambers, while the degassing devices of smaller size than the substrates could not be captured by the handling equipment automated Another reason for using degassing devices of the same size as the substrates is that the surface available for the degassing material and, therefore, also the gas sorption properties of the device, are thus led to a maximum. The degassing devices of the invention can consequently have a thickness of between about 0.5 and 5 mm, and the lateral dimensions vary between about 10 and 100 cm; To give some examples, in the case of les, devices will be used essentially round, with a thickness between approximately 0.5 and 1 mm and a diameter from approximately 1 50 to 300 mm, while in the case of the development of deployments flat, the devices are generally rectangular with a thickness between approximately 1 and 5 mm and a lateral size that varies between 10 cm and one meter. The degassing devices of the invention can be made only of degassing material, for example, of sintered powders. However, considering their particular geometry, with lateral dimensions much greater than the thickness, the sintered bodies exclusively elaborated of powders could result in a low mechanical resistance, resulting, as a consequence of a possible rupture, that the portions already do not adapt to be handled by automated equipment and fragments or dust are presented in the process chambers. Accordingly, it is preferable to use degassing devices formed of a layer of degassing material deposited on a support, which ensures the necessary mechanical strength. Since it is possible to use the support with any material on which the degassing meterials have a good adhesion and that shows good characteristics of mechanical resistance and resistance to the conditions that the devices must undergo in the cameras, in particular, the activation treatment of the degassing material. It is also preferable that the support material does not release a large amount of gas under vacuum at the temperatures reached during activation in order not to contribute appreciably to the amount of gases in the chamber. The best materials in compliance with these conditions are metals and metal alloys, for example, steel, titanium, nickel-chromium or silicon alloys, ceramics or glass. The devices formed of degassing materials on a support can have the deposit on both sides or on only one of them. In some thin layer deposition processes, the substrates are handled in a vertical position within the system, being only in contact with a guide by which they are supported through a projecting portion and having both faces essentially free: an example is the elaboration of hard disks for computers, which are covered with magnetic material for the storage of information on both sides. In this case, it is preferable to use devices with degassing material deposited on both sides, which allows the maximum use of the active material surface. In different cases the use is proposed in chambers where the substrate is treated in a horizontal position, with one face resting on a sample holder, preferably having the tanks to be used the deposit of degassing material only on one side only; in fact, in this configuration, a possible deposit of degassing material on the face in contact with the sample holder would involve the possibility of particle losses therein without, however, contributing to the removal of gas. The examples of processes that adopt this substrate configuration are the elaboration of ICs and CD. In both cases, it would also be preferable that the support surface is not completely covered with the degassing material, but at least a portion of the support protrusion is left free from the reservoir. These avoid the possibility that the degassing device may lose particles by gumming, either when it is in the substrate box, where it is held in a vertical portion by suitable tabs, or when handled by the automated means provided in the chamber. process, which may comprise fasteners that hold the substrates by their projection. Figures 5-7 report some examples of possible degassing devices of the invention. Figure 5 shows in an exploded representation, a degassing device 50 suitable for use in systems for the production of computer hard drives. The device consists of a support 51 of circular shape, covered on both sides with tanks 52, 52 'of degassing material; the tanks 52, 52 'do not completely cover the faces of the support, but leave two free areas, 53 and 53', corresponding to the support projection on both sides. A device of this type is operated in vertical position in a process system by means of automated systems that end with fasteners that hold the device in the projection. Figure 6 represents a degassing device (60) suitable for use in systems for the production of integrated circuits. The case is exemplified in which, as support 61, a processing substrate is used, being formed as a "slice" of monocrystalline silicon; these substrates have an essentially circular shape except for a portion subtended by an arc, which allows to recognize and maintain constant the orientation of the substrate in the process system. The reservoir 63 of degassing material is presented only on one face 62 of the support 61; the reservoir makes clear a projection 64 of the face 62 for the purposes described above.
Finally, figure 7 shows a degassing device
70 to be used in the system for the elaboration of flat displays. The device consists of a support 71 covered only on one side
72, with a reservoir 73 of degassing material that leaves a projection 74 of the support uncovered. The degassing materials that can be used for the production of the devices according to the invention are diverse and comprise, for example, metals such as Zr, Ti, Nb, Ta, V; the alloys between these metals or of them with one or more different elements selected from Cr, Mn, Fe, Co, Ni, Al, Y, La and rare earth, such as binary alloys Ti-V, Zr-V, Zr -Fe and Zr-Ni or ternary alloys Zr-Mn-Fe or Zr-V-Fe; and mixtures of metals with the alloys previously indicated. The degassing materials suitable for the purposes are the alloys made and sold by the applicant under the name St 787 and having the weight percentage composition of Zr 80.8% - Co 14.2% - A 5%, where with A means any item selected from trio, lanthanum, rare earth or mixtures thereof; the alloy of percentage composition by weight of Zr 84% - Al 16% made and sold by the applicant under the name St 101 ®; the alloy with a percentage composition by weight Zr 70% - V 24.6% -Fe 5.4% made and sold by the applicant under the name St 707; or mechanical mixtures of the last two mentioned alloys with Zr or Ti metals; these mixtures are preferable thanks to their good mechanical characteristics, particularly with respect to particle loss. Particularly suitable for the purposes of the invention are the devices obtained through the mixture elaborated and sold by the applicant under the name St 121, formed by 70% by weight of titanium powders and by 30% by weight of St alloy powders. 1 01 ®. The degassing devices formed as a layer of degassing material on a support can be obtained by following various different techniques. A first possibility is the deposition of the layer on the support with the PVD technique. The preparation of degassing devices with the PVD technique is described for example in the publication of International Patent Application WO 97/49109. This technique provides the advantage of allowing the deposition of degassing material on many kinds of supports, glass and ceramic included; In addition, the deposits obtained through the PVD technique do not present the possible disadvantage of possible loss of particles. Other techniques consist of deposition on a support of degassing material in the form of powders. The deposition of powders can be carried out by cold rolling; This technique is widely known in the field of powder technology, but can only be adopted with metallic supports. Another possibility is the spraying of a suspension of degassing particles in a suitable solvent onto the hot maintained support, as described in
Patent application WO 95/23425 to which reference is made for the details of this technique. In addition, the support can be covered with particles of degassing material by the electrophoretic technique. In this case, it is required that the support be electrically driven: for the details of this technique reference is made to the U.S. Patent.
No. 5,242,559. Finally, the deposition of degassing material powders on the support can be carried out by the screen printing technique, as described in International Patent Application Publication WO 98/03987. The serigraphic technique is particularly convenient, since it allows to deposit degassing material on supports of different nature (metals, silicon, glass, ...) and to obtain shaped deposits, thus making it easier, for example, to produce the degassing devices exemplified in Figures 4-6, where a portion of the support surface is free of deposit. The invention will be further illustrated by means of the following examples. These non-limiting examples show some modalities designed to teach those skilled in the art how to practice the invention and represent the best considered mode for putting the invention into practice. EXAMPLE 1 (COMPARATIVE) This example is representative of a known evacuation procedure of a process chamber. An evacuation cycle is carried out in a standard PVD chamber, monitoring the pressure variations throughout the cycle. The chamber comprises a pedestal supporting a sample holder which, in turn, comprises heating means in the form of an internal electrical resistance. The chamber comprises, as an additional internal heating means, two quartz lamps located in two opposite side walls. For evacuation, the chamber is carried to a group below the pump comprising a rotary pump and a cryogenic pump. At pressures below 10"5 mbar, the pressure in the chamber is measured by a Bayard-Alpert pressure gauge.At the beginning of the test, the chamber is closed and the pumping starts.When the pressure in the chamber reaches a value of approximately 10"8 mbar, the cooking process is started, heating the inside of the chamber when lighting the quartz lamps and providing the heater inside the sample holder, which is conducted up to 500 ° C; as discussed above, this procedure has the function of causing the release of gases, mainly H2O, adsorbed on all surfaces inside the chamber, in order to remove these to a maximum extent possible during the pumping stop stage and to prevent them from subsequently being released into the atmosphere of the chamber during processing. The cooking lasts 2 hours. At the end of the cooking process, the heating is turned off and the chamber is allowed to cool, always under pumping. The pressure values measured in the chamber during the test are reported in Figure 8 as curve 1. EXAMPLE 2 This example is representative of a preferred way of implementing the method of the invention. In particular, this example is an embodiment of the method described with reference to Figure 3. A non-activated degassing device of a silicon chip of approximately 200 mm in diameter is provided on a surface from which it is deposited by printing with a lattice a layer (thickness 150 μm) of the degassing material St 121 described above. The degassing device is placed on the sample holder of the chamber. The evacuation procedure illustrated in example 1 is then repeated. During the cooking process, the sample holder conducts the temperature of the degassing device to approximately 500 ° C, thus activating the degassing material. The pressure values measured in the chamber during the test are reported in Figure 8, as curve 2. As can be easily observed by comparing curves 1 and 2 in Figure 8, the use of a degassing device according to the method of the invention helps to free the amount of gases released by all the surfaces present inside the chamber (walls and surfaces of the chamber of any part and devices present in the chamber). In particular, the curves in Figure 8 show an increase in pressure in test 1, due to the equilibrium of the rate of release of gases from the surface and the rate of removal of gases from the pumping group; no similar increase in pressure was observed in the test according to the invention, since in this case, the degassing device contributes to the total gas sorption. At the end of cooking, the pressure in the chamber is lower in the test of the invention than in the test according to the prior art; similarly, the method of the invention makes it possible to achieve lower final pressure values than with the execution of the tests according to the prior techniques. Looking at things from another point of view, possibly even more interesting for the semi-conductor industry, the invention offers the relevant advantage of allowing a given base pressure to be reached (for example, a pre-set pressure value at which a new pressure can be initiated). production cycle) in a shorter time. This is shown by the dotted line (indicated as Preset P) in Figure 8: a pressure value of approximately 2 x 10"8 mbar is reached in just over 4 hours with the method of the invention and in more than 5 hours with normal procedures The method of the invention can be easily implemented in all known deposition processes, since it uses to transfer the degassing devices the same management means used to move the processing substrates in and out of the treatment chambers , while to activate the degassing devices it uses the same substrate heating medium already normally present in the chamber, therefore, the method does not require that suitable additional equipment be available. normal preparatory processes, without requiring substantial modifications nor of particular prolongations of these stages.