WO2009068784A1

WO2009068784A1 - Method and device for producing a homogeneous discharge on non-insulating substrates

Info

Publication number: WO2009068784A1
Application number: PCT/FR2008/051997
Authority: WO
Inventors: Françoise MASSINES; Nicolas Naude; Denis Jahan
Original assignee: L'air Liquide Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude; Centre National De La Recherche Scientifique
Priority date: 2007-11-21
Filing date: 2008-11-05
Publication date: 2009-06-04
Also published as: EP2212900A1; FR2923945A1

Abstract

Method of forming a discharge in a controlled atmosphere, at a pressure below 2 ´ 105 Pa and preferably at atmospheric pressure, in which: a system comprising a first applicator and a second applicator is provided, at least one applicator being an electrode (1) covered with a dielectric (2), the useful spacing between the applicators being between 0.02 and 1 cm, an AC high-voltage generator, 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 placed between the two applicators; the high-voltage system is supplied so as to form a homogeneous discharge on the non-insulating substrate (3) by limiting the current flowing through the discharge to a level which prevents the appearance of preferential current flow sites, and thus obtaining a homogenous discharged, and application of such a method to the deposition of thin films on non-insulating substrates.

Description

Method and apparatus for producing a homogeneous discharge on non-insulating substrates

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" designates a discharge which begins 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.

It may be pointed out that EP-1 548 795 (Fuji) proposes the implementation of an inductance in the circuit. But it should be noted that inductance limits the variation of the current but does not limit the actual current. In practice, this solution proves very difficult to implement, and in any case, the discharge proposed by this document is visibly very limited in terms of power since the authors indicate that it is preferable to limit the voltage to some % of the plasma holding voltage. The field of operation is therefore necessarily very limited.

Until now, never a deposit assisted by a dielectric barrier controlled discharge (DBD) had been used to make deposits of homogeneous layers of materials such as oxides or nitrides, on non-insulating substrates, especially not under pressure atmospheric.

US2003 / 104141 (Amato-Wierda) gives some elements for the implementation of a DBD discharge for depositing a silicon nitride layer on a silicon substrate but without explaining how to achieve a homogeneous discharge while the homogeneity of the discharge is a critical element to achieve a deposit fulfilling the expected functions.

In this context, the subject of the present application is a method for forming a homogeneous discharge on a substrate at a pressure less than

2.10 ⁵ Pa and preferably at atmospheric pressure, avoiding the appearance of preferential places of passage of the current, characterized in that the substrate is a non-insulating substrate.

Under preferred conditions of implementation of the invention, the current passing through the discharge is limited to a level avoiding the appearance of preferential passage places of the current.

In this application and in what follows, the term

"Applicator" means an electrode, possibly covered with a dielectric, used to perform 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, an installation is provided 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 included. 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 high voltage system is supplied to form a homogeneous discharge on the non-insulating substrate 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.

Depending on the intended application, the controlled atmosphere is composed of one or more gaseous species whatever they are. Preferentially, this controlled atmosphere will be composed of at least one carrier gas, for example chosen from N 2 or H 2, and in particular Ar or He, to which chemical vapors may be added, for example vapors of organometallic compounds, halogenated compounds such as NF ₃ , SF ₆ , C 2 F ₆ , CF ₄ , BBr ₃ , CCI ₄ , CIF ₃ or hydrides such as SiH ₄ or NH ₃ . 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.

Furthermore, 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 even 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 deposit wished etc.); - in other cases we will work somehow in

"Batch" or "batch", by the fact that the atmosphere will be put in place but not renewed: a given and desired atmosphere will be put in place in the inter-applicator space, this tightly closed space, the applied discharge and the targeted process, 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 I kHz and 100 kHz, again it will depend 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 the IN-V groups such as Al, Ga, In, N, P, As and / or Sb, materials such as, for example, CdTe, ZnO, ZnSe, CdS, ZnS that may contain elements of the N-IV groups, chalcopyrites, for example of the Cu _x ln _y Ga _z SetS _{u family} . The limitation of the current flowing through the discharge can for example be achieved by adding a resistor 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 process, 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 from 2 × 10 ⁵ Pa to 0.7 × 10 ⁵ Pa, preferably from 1.5 × 10 ⁵ Pa to 0.8 × 10 ⁵ Pa, preferably from 1.2 × 10 ⁵ Pa to 0.9 ⁵ Pa, especially 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 below in the experimental part.

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 even thinning of substrates, the same types of precursors are then used, allowing such removal of material.

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 sufficient volume to use the latter to initiate chemical reactions complementary or alternative to the use of radicals which is the majority in the case of DBD not homogeneous.

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,

an installation is provided for depositing 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 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 voltage to form a homogeneous discharge and a plasma producing a deposit of the material to be deposited on the non-insulating substrate, by 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 the following, the term "thin layer" refers to a layer with a thickness generally less than 10 microns.

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 method is implemented 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 implementing the above deposition method, comprising a first applicator having a first electrode plate covered with a dielectric plate, a second applicator having 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 for producing in the inter-applicator space the controlled atmosphere containing the gas required for the deposition, 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 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 appended drawings in which FIG. 1 represents a schematic diagram of an assembly making it possible to produce a DBD, FIG. principle 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-electrode assembly dielectric 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.

Experimental Editing

Figure 3 and the table below describe the experimental conditions.

Example 1: Discharge comparison on an alumina substrate and on a silicon substrate without current limiting means.

Two discharges were carried out under the same conditions indicated in the table below without current limiting means (series resistance of OΩ), 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:

Example 2: Comparison of Discharge on an Alumina Substrate and on a Silicon Substrate with a Resistor Inserted in Series to Limit Current A resistor of 50 kΩ 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.

Claims

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) 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 high voltage installation is supplied to form a homogeneous discharge on the non-insulating substrate (3) by limiting the current flowing through the discharge to a level that avoids the appearance of preferential passage places for the current, and thus obtaining 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.

6. A method according to one of claims 1 to 5, characterized in that the limitation of the current flowing through the discharge is achieved by adding in a conventional high voltage power supply circuit a resistor, or by using a limited or controlled power supply. current.

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 is provided for depositing a thin layer on a substrate comprising a first applicator, and a second applicator, at the 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 containing a precursor of the material to be deposited is produced between the two applicators and the installation is supplied with high voltage to form a homogeneous discharge and a plasma producing a deposit of the material to be deposited on the non-insulating substrate (3); 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 implementing 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.