FR2923945A1 - METHOD AND DEVICE FOR PRODUCING HOMOGENEOUS DISCHARGE ON NON-INSULATING SUBSTRATES - Google Patents

Abstract

Process for forming a controlled atmosphere discharge in which, at a pressure of less than 2 × 10 5 Pa and preferably at atmospheric pressure: an installation is provided comprising a first applicator and a second applicator, at least one applicator being an electrode (1) covered with a dielectric (2), a high voltage alternating generator, the useful gap between the applicators being between 0.02 and 1 cm, a device (5) for producing a controlled atmosphere between the applicators, and optionally a heating or cooling device (4) - a non-insulating substrate (3) is installed between the two applicators, - the installation is supplied with high voltage to form a homogeneous discharge on the substrate (3) non-insulating by limiting the current flowing through the discharge to a level avoiding the appearance of preferential passage places of the current, and thus obtaining a homogeneous discharge, and applica Such a process can be applied by depositing thin layers on non-insulating substrates.

Description

The present invention relates to a method of forming a homogeneous discharge on a substrate and the applications of said method, in particular for the deposition of thin layers on a non-insulating substrate. Currently, many applications require thin layer deposition at low cost. One of the possibilities is to make these deposits continuously. In particular, the deposition on moving substrate is more and more sought after. Atmospheric deposition technologies can partially meet this need. Among them, the deposition assisted by a homogeneous dielectric barrier discharge (DBD) has already been used to deposit various oxides. However, by its principle, homogeneous DBD applies to insulating substrates. The deposition of homogeneous layers on non-insulating substrates has hitherto never been carried out at atmospheric pressure. In the present application and in what follows, the term homogeneous discharge means a discharge which starts and develops following a breakdown of Townsend without development of preferential passage places of the current between the electrodes. Recall that the preferential passage places of the current consist of an ionized region, slightly conductive composed of positive ions and electrons and an "active" region composed of positive ions which promotes the development of secondary electronic avalanches. The regime with preferential flows of currents corresponds to the filamentary regime of DBD which prevails in the most general case if special precautions are not taken. Obtaining homogeneous discharges is possible at atmospheric pressure for millimeter inter-electrode distances when the emission of secondary electrons to the cathode is exacerbated and the rate of ionization in the gas limited. This is the case in the noble gases in the case of a Penning mixture or in the nitrogen when a dielectric covers each of the electrodes and the excitation frequency is greater than a few kHz (it will be possible to refer in particular to all work of Okazaki et al., well known to those skilled in the art). An assembly making it possible to produce a homogeneous DBD thus conventionally comprises two parallel conductive plates serving as electrodes, connected to a high-voltage alternating generator. Dielectric (insulating) plates are installed on each of the electrodes on the inside of the assembly. The presence of dielectrics makes it possible to locally store charges opposing the creation of preferential passage places of the current by increasing the secondary emission coefficient of the material. In addition, the accumulation of charges increases the potential drop at the dielectric (Vds), which decreases the voltage applied to the gas (Vg) and thus avoids the avalanche of electrons. At atmospheric pressure, to achieve uniform thin film deposition, the discharge itself must be uniform. Homogeneous DBD technology is well suited for deposition on insulating substrate such as glass or plastic film. Unfortunately, if one wants to deposit on a semiconductor substrate, the substrate is no longer a perfect insulator, especially when heated. The introduction of a partially conductive substrate in the space between the electrodes greatly destabilizes the discharge and leads to the appearance of preferential passage places of the current. Indeed, the conductive nature of the substrate allows the charges to be distributed on the surface. This implies the reduction of the surface charge density and leads to an increase in the dielectric capacity of the assembly. It is then necessary to have a larger amount of stored charges to obtain an equivalent local potential drop (Vds). This leads to an increase in the current flowing through the gas present in the space between the electrodes and therefore to a stronger ionization and to the appearance of an avalanche effect forming preferential passage places of the current. The system thus returns to the conventional non-homogeneous filamentary regime.

But after long research the Applicant has discovered that if we limit the maximum current flowing through the gas, we get a homogeneous discharge and no longer observed the appearance of preferential passage places of the current. In particular, up to now, never a deposit assisted by a dielectric barrier controlled discharge (DBD) had been used to carry out deposits of homogeneous layers of materials such as oxides or nitrides, on non-insulating substrates, in particular not at the atmospheric pressure. This is why the subject of the present application is a process for forming a homogeneous discharge on a substrate, at a pressure of less than 2 × 10 5 Pa and preferably at atmospheric pressure, avoiding the appearance of preferential passage places for the current, characterized in that the substrate is a non-insulating substrate. Under preferred conditions of implementation of the invention, the current flowing through the discharge is limited to a level which avoids the appearance of preferential passage places for the current. In the present application and in what follows, the term "applicator" designates an electrode, possibly covered with a dielectric, used to carry out a discharge. More specifically, the subject of the invention is a method of forming a controlled atmosphere discharge in which, at a pressure of less than 2 × 10 5 Pa and preferably at atmospheric pressure, provision is made for an installation comprising a first applicator, and a second applicator, at least one applicator and preferably each of the applicators being an electrode covered with a dielectric, a high-voltage alternating generator, the useful spacing between the applicators being preferably between 0.02 and 1 cm , and more preferably between 0.05 and 0.4 cm, optionally a device for producing a controlled atmosphere between the applicators and a heating or cooling device, a non-insulating substrate is installed between the two applicators, the installation is supplied with high voltage to form a homogeneous discharge on the non-insulating substrate by limiting the current tra pouring the discharge at a level avoiding the appearance of preferential passage places of the current, and thus obtaining a homogeneous discharge. Depending on the intended application, the controlled atmosphere is composed of one or more gaseous species whatever they are. Preferably, this controlled atmosphere will be composed of at least one carrier gas, for example chosen from N 2 or H 2, and especially Ar or He, to which may be added chemical vapors, for example vapors of organometallic compounds, halogenated compounds such as NF3, SF6, C2F6, CF4, BBr3, CCl4, CIF3 or hydrides such as SiH4 or NH3. The composition of the atmosphere will depend on the intended application.

It will be understood that according to the targeted applications the presence of heating means is necessary or not. Moreover, what must be understood by the device for producing a controlled atmosphere between the applicators can be explained as follows: in many cases, this device will comprise means of injection or control and regulation of all the gases required by the targeted process, in the inter-applicator space (for example a carrier gas, a gaseous precursor of a desired deposit, etc.); - In other cases we will work somehow in batch or batch mode, in that the atmosphere will be set up but not renewed: a given and desired atmosphere will be set up in the inter-applicator space, this sealingly closed space, the applied discharge and the targeted method, for example a layer deposition, performed. It is therefore understood that the device for producing a controlled atmosphere between the applicators makes it possible, as required, to set up the atmosphere before the process (for example the deposition) or during the process (for example the deposition) by injecting and continuously controlling the necessary gas mixture. The electrodes can have any type of shape and structure since they do not alter the homogeneity of the electric field in the inter-applicator space. They may for example be formed of powders, blocks or points, preferably plates or braided fabrics, and in particular conductive coatings. At least one of the two electrodes is covered by a dielectric. The dielectric (s) used may be, for example, oxides, in particular silica or alumina, or nitrides, in particular silicon or boron nitride, or ceramics or even minerals such as mica. The high voltage is for example between 500 and 15000 V, preferably between 500 V and 7000V, in particular between 700 V and 1000V. The voltage to be applied will depend on the intended application and therefore these figures will be readily understood are given for illustrative purposes only. Similarly, the frequency may commonly be between 10 Hz and 20 MHz, preferably between 100 Hz and 13.56 MHz, in particular between 1 kHz and 100 kHz, again depending on the intended application. The optional gas injection device can for example allow the introduction, circulation and extraction of gas, in particular, it can provide control of the atmosphere by renewal thereof. The heating or cooling device and, more generally, the optional temperature control device, may make it possible, according to the intended applications, to regulate the temperature of the system, in particular elements introduced into the discharge and in particular substrates to which a process using the discharge such as a surface treatment or the deposition of a material. This temperature control device can in particular make it possible to heat a substrate in order to obtain a more efficient method. This type of device is conventionally known to those skilled in the art.

The heating may for example be obtained by using a heating resistor or irradiating lamps. For example, a substrate will be heated at a temperature of 100 ° C. to 600 ° C. depending on the intended application. The non-insulating substrate may be, for example, a conductive material such as a metal or alloy such as copper of aluminum or steel, or a metal nitride. The non-insulating substrate is preferably a doped or non-doped semiconductor material such as silicon, germanium, crystalline carbon, materials that may contain elements of groups III-V such as Al, Ga, In, N, P, As and / or Sb, materials such as for example CdTe, ZnO, ZnSe, CdS, ZnS which may contain elements of groups II-IV, chalcopyrites, for example of the CuXlnyGa family, SetSu. The limitation of the current flowing through the discharge can for example be achieved by adding an inductance or a resistance in a conventional high-voltage supply circuit, or by using a limited power supply, or even a current-controlled power supply.

Under preferred conditions of implementation of the invention, one proceeds by adding a series resistance in the circuit. By correctly choosing the value of this resistance, the current remains low enough to avoid the appearance of preferential passage places of the current and ensure the stability of a homogeneous discharge in the presence of a non-insulating substrate, for example conductive. For each implementation of the method, it is possible by some routine experiments to determine the current not to be exceeded. In other preferred conditions of implementation of the invention, each of the electrodes is covered with a dielectric plate. The useful gap between the applicators is defined as the distance between their nearest points. Generally, the applicators will have trays or plates installed face to face with their closest parallel points and the useful spacing will be the spacing between the two trays or plates. For example, it is possible to operate at a pressure of 2 × 10 5 Pa at 0.7 × 10 5 Pa, preferably at least 1.5 × 10 5 Pa at 0.8 × 10 5 Pa, preferably at least 1.2 × 10 5 Pa at 0.9 × 10 5 Pa. at atmospheric pressure. The method of forming a discharge on a non-insulating substrate object of the present invention has very interesting properties and qualities. The invention makes it possible to avoid the appearance of preferential passage places for the current and thus to remain in a homogeneous regime during a discharge. These properties are illustrated hereinafter in the experimental section. They justify the use of the methods and devices described above, in the deposition of a thin layer on a non-insulating substrate. They also make it possible to envisage applications of the invention (method and device) for performing etching, stripping or thinning of substrates, the same types of precursors are then used, allowing such removals. of matter. They also make it possible to envisage applications of the invention (process and device) for carrying out gas treatment, for example for chemical synthesis, the destruction of molecules or reforming. The advantage here is to have a zone having a homogeneous electron density in a volume sufficient to use these in order to initiate chemical reactions in a complementary or alternative manner to the use of radicals which is the majority in the case non-homogeneous DBDs.

The present application also relates to a method for depositing a thin layer on a non-insulating substrate under a controlled atmosphere, in which, at a pressure of less than 2 × 10 5 Pa and preferably at atmospheric pressure, a deposit installation is provided. a thin layer on a substrate comprising a first applicator, and a second applicator, at least one applicator being an electrode covered with a dielectric, a high voltage alternating generator, a device for producing a controlled atmosphere between the applicators, and optionally a heating or cooling device, the non-insulating substrate is installed between the two electrodes, a controlled atmosphere containing the precursor of material to be deposited is produced in the inter-applicator space, and the installation is supplied with high power. voltage to form a homogeneous discharge and a plasma producing a deposit of the material to be deposited on the subs non-insulating process, limiting the current flowing through the discharge to a level avoiding the appearance of preferential passage places of the current. Non-exhaustively, there may be mentioned, for example, as the material to be deposited organic or inorganic materials, preferably metals and their various alloys, in particular their oxides, their carbides, their nitrides and / or their fluorides, and particularly their compounds. silicon, oxides, carbides and nitrides or semiconductor materials. In the present application and in what follows, the term "thin film" refers to a layer with a thickness generally less than 10 μm.

The carrier gas containing the material to be deposited may be for example one of those mentioned above for the controlled atmosphere. The above method of depositing a thin layer on a non-insulating substrate has very interesting properties. The invention makes it possible to avoid, during the deposition of a thin layer on a substrate, the appearance of preferential passage places for the current, and thus to remain in a homogeneous regime. Remarkably uniform thin film deposits are obtained. In addition, the method of the invention is compatible with a continuous implementation. Thus, in other preferred conditions of implementation of the invention, the above deposition process is carried out continuously. For this purpose, a relative displacement of the substrate relative to the electrodes in the device in operation is carried out in order to deposit on the moving substrate. Preferably, the substrate is moved. The present application also relates to a device for carrying out the above deposition method, comprising a first applicator comprising a first electrode plate covered with a dielectric plate, a second applicator comprising a second electrode plate. preferably also covered with a dielectric plate, the applicators being installed face to face, the useful gap between the applicators being between 0.02 and 1 cm, preferably between 0.05 and 0.4 cm, a device allowing performing in the inter-applicator space the controlled atmosphere containing the gas required for deposition, optionally a heating device, and comprising a high voltage generator comprising a device for regulating or limiting the current flowing through the discharge to a level avoiding the appearance of preferential passage places of the current in the conditions of deposition of thin layers on a substrate. Under preferred conditions of implementation, the device described above comprises means for producing a relative displacement of the substrate relative to the electrodes, thus making it possible to perform a continuous deposition. The preferred conditions of implementation of the methods described above also apply to the other objects of the invention referred to above, in particular to the devices for their implementation.

The following examples illustrate the present application and the invention will be better understood with reference to the accompanying drawings, in which FIG. 1 represents a schematic diagram of an assembly making it possible to produce a DBD, FIG. a schematic diagram of the invention; a resistor R has been inserted in the traditional assembly; - FIG. 3 represents a diagram of the assembly used as an example. In FIG. 1, two electrodes 1 can be observed, one placed at the top and one placed at the bottom, in the form of plates. The electrodes 1 are covered on one side with a dielectric plate 2. Each electrode-dielectric assembly constitutes an applicator. The dielectric plates 2 are installed face to face, that is to say interposed between the electrodes 1. A high voltage power supply circuit (HT) is shown. In FIG. 2, the same elements can be observed as in FIG. 1. For the implementation of the invention, a silicon wafer 3 (substrate to be treated) was installed on the bottom electrode. A resistor R has been added in series in the circuit. In Figure 3, one can observe the same elements as in Figure 2. It can also be observed the heating systems 4 and gas injection 5. The bottom arrow symbolizes the possible movement of the lower part of the device.

Montaqe Experimental

Figure 3 and the table below describe the experimental conditions.

Example 1: Comparison of discharge on an alumina substrate and on a silicon substrate without current limiting means. Two discharges were performed under the same conditions indicated in the table below without current limiting means (series resistance of On), one on an alumina substrate (insulator) and the other on a substrate of silicon (non-insulating at the test temperature). In the case of alumina, a homogeneous discharge is observed, whereas preferential localized paths of currents are formed in the case of the silicon substrate.

Experimental conditions: PARAMETERS Without wafer With wafer GEOMETRIC Dimensions of the electrode 35 x 50 mm (I x L) lower Dimensions of the electrode 10 x 50 mm higher Nature of the electrodes Silver Thickness of the dielectric 2 mm lower Thickness of the dielectric 2,5 mm higher Nature of dielectric AI2O3 (99.8% for the higher dielectric and 96% for the lower dielectric) Distance between the dielectrics 1 mm 1.5 mm Substrate dimensions 0.5 x 70 x 70 mm THERMAL PARAMETERS Experimental temperature 320 ° C at the surface of the substrate GAS PARAMETERS Flow Ar 3 I / min Flux NH3 0.45 cm3 / min ELECTRICAL PARAMETERS Frequency 50 kHz Rated voltage 640 V Power density P = 1.32 W.cm-3 P = 1.52 W .cm-3 Resistance in series 50 kn Example 2: Comparison of discharge on an alumina substrate and on a silicon substrate with a resistance inserted in series to limit current.

A resistor of 50 kn in series was inserted, as shown in FIG. 3, and carried out the same experiments again as in example 1. In the configuration used, the addition of the resistor allowed to limit the maximum current. at a value less than 6 mA. This allowed to observe a homogeneous discharge with the two types of substrate, alumina (insulator) and silicon (non-insulating at the temperature of the test). The limitation of the current makes it possible to obtain a homogeneous discharge despite the semiconducting and then conductive nature of the substrate. 10

Claims (9)

1. A method of forming a discharge on a non-insulating substrate, under a controlled atmosphere, in which, at a pressure of less than 2 × 10 5 Pa and preferably at atmospheric pressure: an installation is provided comprising a first applicator and a second applicator, at least one applicator being an electrode (1) covered with a dielectric (2), a high voltage alternating generator, the useful gap between the applicators being between 0.02 and 1 cm, a device (5) embodiment 10 of a controlled atmosphere between the applicators, and optionally a heating or cooling device (4), - a non-insulating substrate (3) is installed between the two applicators, - the installation is supplied with high voltage to form a homogeneous discharge on the non-insulating substrate (3) by limiting the current flowing through the discharge to a level avoiding the appearance of preferential passage places of the current, and insi getting a homogeneous discharge. 2. A method according to claim 1, characterized in that each of the two applicators is an electrode covered with a dielectric. 3. A method according to claim 1 or 2, characterized in that the high voltage is between 500 and 15000 V. 4. A method according to one of claims 1 to 3, characterized in that the installation comprises a temperature control device (4). 5. A method according to one of claims 1 to 4, characterized in that the non-insulating substrate (3) is a semiconductor material. 25 6. A method according to one of claims 1 to 5, characterized in that the limitation of the current through the discharge is achieved by adding in a conventional high-voltage power supply circuit an inductance, a resistance, or using a limited power supply. or controlled by running. 7. A method of depositing a thin layer on a non-insulating substrate (3) under a controlled atmosphere, in which, at a pressure of less than 2 × 10 5 Pa and preferably at atmospheric pressure, an installation for depositing a thin layer on a substrate comprising a first applicator, and a second applicator, at least one applicator being an electrode (1) covered with a dielectric (2), a high-voltage alternating generator, a device (5) for producing a controlled atmosphere between the applicators, and optionally a heating or cooling device (4), - the non-insulating substrate is installed between the two electrodes, - a controlled atmosphere is produced between the two applicators containing a precursor of the material to be depositing and feeding the installation in high voltage to form a homogeneous discharge and a plasma producing a deposit of the material to be deposited on the substrate no n insulation (3) by limiting the current flowing through the discharge to a level avoiding the appearance of preferential passage places of the current. 8. A method according to claim 7, characterized in that the material to be deposited is selected from metals and their various alloys, their oxides, their carbides, their nitrides and their fluorides and semiconductor materials. 9. A device for carrying out the deposition method as defined in one of claims 7 or 8, comprising a first applicator comprising a first electrode plate covered with a dielectric plate, a second applicator comprising a second electrode plate preferably covered with a dielectric plate, the applicators being installed face to face, the useful gap between the applicators being between 0.02 and 1 cm, a device for producing a controlled atmosphere between the applicators optionally a heating device and comprising a high-voltage generator comprising a device for regulating or limiting the current flowing through the discharge at a level avoiding the appearance of preferential passage places for the current in the conditions of deposition of thin layers on a substrate , and optionally including means for producing a relative displacement of the substrate relative to the app cators, thus allowing a continuous deposit.