JPH05304103A - Method and apparatus for treating substrate with low-voltage plasma - Google Patents

Abstract

PURPOSE: To uniformly treat a substrate over its entire surface, so as to spread equal r-f voltages between the entire substrate surface and plasma region facing it and between a conductive framing surface of the substrate and plasma facing it. CONSTITUTION: This method for treating a surface 17a of a substrate 17b which is mounted so as to enclose the side face with a conductive material zone 21 and covered with a plasma is intended to uniformly treat substrate surface 17a with a plasma 26 facing this surface, so that equal r-f voltages spread between the substrate surface and the plasma 26 and between the framing surface 21 of the substrate and the plasma. Thus the entire exposed surface of the substrate is treated uniformly.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention finds particular use in the area of electronic devices, and in particular to methods and apparatus for plasma treating a surface of a flat object such as a substrate which is particularly used in electronic optical devices. It is about.

[0002]

2. Description of the Related Art In the surface treatment by plasma, especially the surface treatment by low-pressure plasma, its application field is rapidly expanded.

Various results can be obtained by exposing the surface of an object to a luminescent discharge.
In particular, such as the etching and surface modification of the substrate, the cleaning of the substrate, or the deposition (deposition) of the electronic components required, for example, in the production of solar cells or field effect transistors as thin films. Even getting results.

It goes without saying that semiconductors, insulators and even metals can be deposited by plasma. Currently, there are several ways to excite a plasma, especially to excite a low pressure plasma. However, in very many cases electrical energy can be used at any practical frequency from DC to the microwave. Although practically all frequencies can be used, the majority of systems use radio frequencies, particularly the industrially accepted frequency of 13.56 MHz. This radio frequency power source can be combined with a discharge region, in particular, where plasma is generated. The plasma is either a coil (which is commonly referred to as an "inductive discharge") or an electric field (which is called a "capacitive""Is what is referred to as a discharge"). What is generally predominant in this latter form is that it appears to be best suited for the processing of flat plate substrates, especially for plate type substrates. The present invention is preferably applied to this latter form in the field of usable frequencies covering all radio frequencies, that is, typically about 0.5 MHz.
To the frequency range of up to about 200 MHz.

What is depicted in the accompanying FIG. 1 is a typical configuration for a capacitive radio frequency discharge. What constitutes the plasma generating means of the example illustrated here is a substantially flat plate type electrode 1, which has a short concentric airtight inlet 3 and a plasma impedance of radio frequency. The electrode 1 is excited with a radio-frequency voltage via a tuning box 5 intended to match that of the power generator 7 of FIG. The tuning box here is a variable capacitor 6, an inductor 8 and a decoupling capacitor 9 that blocks direct current to the electrodes. The electrodes are arranged inside an enclosure 11 which is provided with electrically conductive walls (in particular metal walls) which define the boundaries of the reaction space, which are generally labeled with 13. The body of the reactor 11 facing the plasma will be defined here as earth.

To that end, in the case of FIG. 1, the screen is formed by this ground behind the electrode, and the insulating space 15 is in this example sufficiently narrow (typically to prevent internal discharge). Is 0.3 mm-3
mm width). However, for example,
Two symmetrical plasmas can be formed on either side of the substantially central electrode, the electrodes can be perforated, or transformed into a simple grid. The substrate 17 to be treated is arranged facing the electrode 1. This substrate is arranged in an opening 19 formed in one of the longitudinal walls 21 of the enclosure 11, and on the opposite side of the surface 17a facing the reaction space 13, a "substrate holder" is provided. Or a conductive back plate 23 forming a "rear electrode".

Therefore, according to such a structure, the luminescent type discharge for generating plasma spreads between the electrode 1 and the opposing earth in the space 13 having a thickness of about several cm. That is why, generally speaking, the substrate 17 is arranged at this ground location and, in this example, is set back to the position of the back plate 23. However, the substrate may be placed on the electrode, or the plasma and the earth and the electrodes may be arranged symmetrically with respect to each other with respect to the substrate. Therefore, since the concept of earth is generally relative, for a given substrate, the earth is constituted by the enclosure surrounding it and the voltage on the conductive wall 21 of the corresponding backplate 23. It is thought to be done. From the difference between the opposing plasma voltage and that of the substrate bearing or framing assembly, the plasma voltage will be inferred.

Further attention should be paid to improving the adhesion condition by placing the enclosure 11 in an airtight chamber 25 capable of maintaining a pressure of the order of 10 ^-4 to 10 ^-5 Pa. That is. To achieve the desired luminescent discharge in the enclosure, a pressure of about 10 ¹ Pa (such as hydrides, organometallics, volatile fluorides, metal carbonyls) is applied through the channel 20 on one side.
The reaction gas is introduced and discharged from the channel 22 on the opposite side. In this chamber 25, it is possible, for example by means of a suction pipe 24, which is connected to a vacuum pump, to maintain the pressure difference between the enclosure / chamber and to suck up any remaining material slag. Thus,
Internal space 3 separating the airtight chamber from the reaction enclosure
The pressure inside 0 is kept lower than that inside the enclosure.

"Dual chamber" under controlled vacuum
For a device of the same type with
A-0 221 812 and EP-A-0 312 4
47, or their corresponding US patents USA 4,7
98,739 and USA 4,989,543, the contents of which are incorporated by reference. Although the construction of such a device provides a number of advantages, particularly related to the purity of the electronic deposits on the substrate, in many applications the conditions for processing the substrate are nevertheless high. It was not necessarily homogeneous.

In addition to the non-uniform processing thickness,
Alterations were observed in the properties of certain deposited materials, especially internal tension, texture, photoconductivity, mobility, etc. Initially, these problems were not necessarily thought to be associated with the dual chamber device configurations outlined above.

On the other hand, it was noted that the total elongation is, in the best case, from the edge of the substrate several times the thickness of the sheath of an essentially non-conductive, weakly ionized plasma. Up to some distance, processing inhomogeneities were observed on the substrate of present day conventional equipment. The plasma sheath here is a region that constantly separates the electroluminescent plasma region (on average from 1 cm to 5 cm wide) from the opposing surfaces of the substrate and from the substantial environment of the substrate. Is. Given that the surface of the substrate was very slightly conductive, its electrostatic effects and the induced surface currents spread this disturbance over decimeter scales. Furthermore, if the surface of the substrate becomes very conductive (eg, through the deposition of a thin conductive layer on the solar cell), radio frequency propagation also induces disturbances if the edges of the substrate were not insulated. Will be done.

[0012]

Therefore, after all, crowns of the order of a few centimeters must be regularly removed from the periphery of the substrate. This loss should be avoided. Therefore, it is unavoidable to treat the exposed surface of the substrate as homogeneously as possible.

[0013]

In order to do this, what is proposed in the method of the invention is on the one hand between the entire surface of this substrate and said opposing plasma region, and on the other hand the substrate. To spread a substantially equal radio frequency voltage between the straight conductive framing surface and the opposing plasma. Plasma is generated by AC voltage with capacitive discharge, and
By electrically connecting another conductive zone to the conductive framing zone of the substrate,
The radio frequency voltages are made substantially equal.
Here, the conductive zone is independent of the framing zone, but is linked to the substrate away from the surface exposed to the plasma, and the radio frequency voltage through the thickness of the substrate. The value is adapted via at least one impedance in order to compensate for fluctuations in

For some applications, it is preferred to use an electrically insulated substrate, or at least a portion of its thickness (in the latter case). The substrate will then be coated with at least one conductive layer). However, the present invention is equally applicable when the substrate is made of a semiconductor material. As a result, a more uniform deposition or processing thickness and speed can be achieved and the properties of the deposited material are homogeneous. Therefore, the reliability of the finished product is improved.

The device according to the invention which is able to solve the problems mentioned above with regard to homogeneity is characterized in that it comprises the following means: That is, the radio frequency voltage described above between the substrate and the plasma, and between this same plasma and the framing zone of the substrate can contribute to the generation of the above described equivalence. It has a means, which means can consist of at least one capacitance or one compensation lead. As regards the device of the invention, it is advantageous as a whole by means of a dual chamber of the type described above and by means of a controlled decompression, which, of course, also comprises means capable of equalizing said radio frequency voltage Will be done.

Apart from this, the invention also relates to a system in which the value of the compensation lead can be defined, the compensation lead here being described above for compensation for variations in the voltage on the substrate. It can be used for devices or equipment. Thus, the operation in processing this substrate is more uniform. According to the present invention, this system comprises the following means. That is, the “second electrode” arranged on the surface of the substrate facing the plasma generating electrode.
Electrode, a radio frequency power source, and means for recording the signal generated by the second surface electrode of the substrate excited by this power source, and the equation (L≈C / ω ² ) is satisfied. Until it is made up of means for varying the value of the inductor. However, in the above formula, L is the value of the inductor; C is the sum of the capacitance of the substrate and the capacitance that couples the back plate to the ground; and ω is the angular frequency of the radio frequency.

[0017]

For a proper understanding of the invention, some practical examples are presented in connection with the accompanying drawings, given by way of non-limiting example. The substrate 17 found again in FIG. 2 is, in this example,
It consists of an insulating or substantially insulating block, for example of glass or of plastic or of ceramics, surrounded by a conductive boundary zone 21 at its periphery. This zone 21 is below the substrate, away from the plasma region 26 and on the back plate or substrate holder 3 on which the substrate rests.
1 to the part forming 1.

In order to promote processing homogeneity of this substrate, a kind of "guard ring" 33 of dielectric material is provided on the substrate and the conductive zone 21.
Is laterally insulated from both sides and is interposed between the substrate and its framing zone 21. The width l of the strip 33 of this material, the volume of which per unit surface area is selected to be virtually equal to that of the substrate, is preferably the average of the electrical transition area or sheath 28. The thickness is larger than about 2 to 3 times. The sheath 28 here comprises the opposing surfaces 17a of the substrate and its framing zone,
The plasma region 26 for electroluminescence is separated from 21a.

It should be noted that in order to limit variations in plasma thickness or level, the surfaces 17a and 21a of the substrate and its framing zone (in addition to this, here surface 33a of ring 33). ) Are arranged to be substantially coplanar with the flat surface 35 and are substantially parallel to the surface 1 a facing the electrode 1.

In FIG. 3, the guard strip 33 is coated with a pure metal surface 37, where the surface 37 projects internally to the edge of the substrate to ensure its retention. It is desirable to limit the thickness of the metal thin film 37 as much as possible in order to limit the variation in thickness in the electrical transition zone 28 whose nominal boundaries are drawn with dotted lines. However, applying it, despite the solution of FIGS. 2 and 3, it is necessary to use complementary dielectric components.

Therefore, in another proposed solution, the conductive framing zone 2 of the substrate is used.
At least one compensation which is structurally separated from the back plate 23 (or 31) of 1 and its substrate, and which is intended to compensate for variations in radio frequency voltage through the thickness of the substrate. It is electrically connected by impedance. This makes it possible to achieve this equivalence of voltage between the surface of the substrate and its framing zone with respect to the opposing plasma region. Thus, in the alternative embodiment shown in FIG. 4, the substrate 17 is framed and structurally separated by an electrically insulating metal crown 39. This crown 39 is a conductive part 3 forming a back plate.
1 are linked by several electrical connections 41. Then, the value of the capacitor 43 interposed on it is substantially equalized,
The thickness es of the substrate is used to compensate the radio frequency voltage drop.

An electrical connection 41 consisting of mechanically resistant and relatively elastic components is provided to retain the crown 39 and, via a metal lug 45,
The substrate can be pressed against the back plate 31 at the rear portion. It should be noted that it is preferable for the surface of the substrate exposed to the plasma to extend substantially in the same plane as that of the framing crown 39, but the thickness of this crown should be the same as that of the substrate. Can be less than. On the other hand, as in the guard ring 33, the width l'of the framing crown 39 is
It is desirable to be about 2-3 times larger than the average thickness e of the opposing plasma sheath 28.

Shown schematically in FIG. 5 is the application of the solution of FIG. 4 to a reaction enclosure contained in an apparatus with a dual chamber of that type of FIG. Is. Therefore, the plasma generating electrode 1 found again in this FIG.
And via a connection box 5 to a radio frequency power supply 7. In the internal reaction space bounded by the enclosure 11, its electrodes face the peripherally enclosed substrate 17 at a short distance due to its electrically conductive framing strip 39.
Since it is incorporated here with the enclosure 11 (metal priori), the back plate 31 is grounded so that radio frequency currents are returned to the generator. The frame 39 is insulated and is connected to the back plate by a capacitive compensation connection 43.

The modification of FIG. 6 differs from the previous one as follows. That is, as in FIG. 1, the direct framing zone of the substrate is
Formed by the longitudinal walls 21 of the
It differs from the previous one in that it is linked to earth. The back plate of the substrate consisting of independent metal components 23 is insulated and the
Framing part 2 via an electrical connection with 7
It is connected to 1. Compensating induction 47 of the, as the capacitor of Figure 5, in which are intended to compensate for the voltage drop of the radio frequency through the thickness e _s of the substrate. The substrate in this example then includes a thin conductive layer 44 on its surface and is held in place by a peripheral metal film 45 which forms a "bridge" between the substrate and zone 21. ing. It should be clear here that, depending on its application, one or more impedances may be used, either capacitor 43 or inductor 47, as appropriate.

Shown in FIGS. 7 and 8 are two other embodiments of the basic inductor. When the substrate to be treated is of relatively small size, one end 49a is provided at the rear of the metal wall 21.
Is fixed and self-induction in the form of a wound electrical wire 49 is created so as to push the back plate 23 against the substrate from the rear with the other end 49b. The peripheral portion of the substrate here is held by a fixing tab 21b which is integrated with the wall portion 21. It should be noted here that the blank electrically insulating space 50 allows the back plate 23 to be enclosed in the enclosure wall 2.
It means that it can be separated from 1. For considerably higher frequencies, it is also possible to reduce the self-induction of the bridge 51, which consists of a fine conductive strip connecting the back plate 23 and the enclosure wall 21 at the rear. To ensure the relative elastic pressure, these bridges 51 can be of arched type with a convex surface towards the outside of the enclosure (see Figure 8).

An application of the solution of the invention using at least one compensation lead to that described in US Pat. No. 4,989,543 (FIG. 1) is shown in FIG. In order to improve the sealing of the walls of the reaction enclosure 11, the enclosure is enclosed within the volume 30 in an external, airtight chamber (schematically indicated by the dotted line 25). In addition, the elastic and conductive pressure means is
In this example, it is composed of a metal pressing device 53,
The back plate 23 is held on the rear surface of the back plate 23, and the substrate 17 is pushed between the back plate, which is the rear portion, and the metal fixing portion 21b, which is the front portion. As can be observed here, at the pressing position of the pressing device 53, the back plate 23 is abutted on the periphery against the pad 55 so as to be electrically insulated from the enclosure wall portion 21, and The mechanical conditions for holding the substrate are improved.

It should also be noted here that the compensating means with the inductive part consists in this example of an electrical wire wound to be a self-inducing 57. The self-induction 57 here is connected to the pusher 53 on one side, and is curved and wound like a spring on the rear part of the surrounding enclosure wall part 21 on the other side. To be held elastically.

Finally, FIG. 10 shows schematically the principle of one solution. In order to substantially equalize the voltage between the surface to be treated of the substrate and the plasma on the one hand, and the corresponding surface of the conductive frame zone of this substrate and the plasma on the other hand, the compensation impedance The value of can be adjusted.

The relations linking these various quantities in order to fix the concept are as follows. | Vp-Vs | = | Vp -Vm | · [e g / (e g + e s / ε)] Note, Vp-Vs: Potential between the plasma and the substrate of the processed surface to be facing thereto Corresponding to the potential difference between Vp-Vm: the plasma and the opposing surface of the conductive framing zone of the substrate, e _g : average thickness of the sheath or transition zone 28 represents a, e _s: what corresponds to the thickness of the substrate, and, epsilon: which corresponds to the dielectric acceptability of the substrate.

In the following, only the case where the compensation impedance is entirely inductive will be dealt with. It would, of course, be expensive to devise a tunable self-induction that could change under vacuum. The principle devised there is to allow regulation in air when no plasma is present.

With this goal, and as illustrated in FIG. 10, a coaxial cable 59 is inserted into the reactor. The core 61 is connected to the ground. The electrically active cable strand 63 is connected to a thin conductive layer 65 which covers most of the surface 17a of the substrate to be treated. This "secondary electrode"
Reference numeral 65 is a thin member fixed to the substrate and is electrically insulated from the ground formed by the framing wall portion 21. In the case of a very large substrate, it is preferable that the maximum dimension L does not exceed 10 cm to 20 cm.

Compensation guide 47 (eg, adjustment stud 47)
To proceed with the tuning (of the type with a), the electrode 1 will first be excited by a radio frequency generator 7. The tuning is then optimized to obtain a very high voltage on the electrodes to maximize the capacitively detected signal on the secondary electrode layer 65. The signal circulating in the active strand 63 of the coaxial cable can then be recorded by recording means, such as an oscilloscope 67, which also accepts the signal from the radio frequency generator 7. ..

The induction coil 47 can be tuned, for example, from the display screen of an oscilloscope by varying its value until the following relationship is satisfied: L ≈ C / ω ² (1) where L is the self-induction 47 to be tuned, C is the sum of the capacitance of the substrate and the capacitance for coupling the back plate to ground, and ω is the radio frequency. Is the angular frequency of. When "equation" (1) is virtually satisfied, the curve corresponding to the signal from electrode 65 passes through "zero" and appears in a substantially straight line form. It should be noted here via the information that in order to make the treatment of the substrate more homogeneous, even when the surface opposite the surface exposed to the plasma is covered by a conductive (eg metal) layer. The solution proposed in this invention is no different. What is clear, as already mentioned, is that the invention is also applicable to semiconductor substrates, for example silicon or any other material with the electrical properties of a semiconductor.

[Brief description of drawings]

FIG. 1 is an illustration of a representative configuration for capacitive radio frequency discharge.

FIG. 2 is a schematic cross-sectional view of an embodiment of a device of the present invention to allow for homogenization of substrate processing.

FIG. 3 is a schematic cross-sectional view of an embodiment of a device of the present invention to allow for homogenization of substrate processing.

FIG. 4 is a schematic cross-sectional view of an embodiment of the device of the present invention for enabling homogenization of substrate processing.

5 is an illustration of the principle of the device of FIG. 4 placed in a reaction enclosure of the type that can be used in the present invention.

FIG. 6 shows an alternative embodiment for the installation of FIG. 5, where an inductive connection is used as the voltage compensation impedance.

FIG. 7 is a diagram schematically showing an example of such guidance.

FIG. 8 is a diagram schematically showing an example of guidance as described above.

FIG. 9 is a diagram schematically showing an example of such guidance.

FIG. 10 is an illustration of the principle that allows the induction to be adjusted to achieve the desired voltage compensation at the substrate level.

[Explanation of symbols]

1-electrode; 3--coaxial leak-proof inlet; 5--
Tuning box; 6-Variable capacitor; 7-Radio frequency power generator; 8--Inductor; 9-Decoupling capacitor; 11-Enclosure; 13-Reaction space; 15-Insulation space; 17- -Substrate; 25 --- Airtight chamber;

Claims (4)

[Claims] 1. A zone (21, 39) of electrically conductive material is mounted so that it is surrounded on its sides by at least 1.
In a method for treating a plasma-facing surface (17a) of a substrate (17) covered with a conductive layer of a layer, said surface (17a) of the substrate
Between the surface of the substrate (17) and the opposing plasma (26) on the one hand, and the framing surface (21, 39) of this same substrate on the other hand. With the plasma,
A method of processing a substrate, characterized in that the radio frequency voltages are substantially equal. 2. Material zone (21, 3) directed towards the plasma.
3,39) side is framed by at least the thickness (e _s) partially over substantially electrically insulating and the surface of the substrate (17) of (17a)
An apparatus for treating a plasma with a radio frequency power source (7) and a generating means (1) for generating a plasma opposite the surface of the substrate (17) and its framing zones (21, 39). ), And, further, on the one hand said surface (17a) of the substrate (17)
And the opposing plasma (26) and, on the other hand, the framing zone (21, 39) of the substrate
An apparatus for treating a substrate, characterized in that it comprises means (23, 31; 43, 47) for producing a substantially equal radio frequency voltage between said plasma and said plasma. 3. A device for plasma treating a surface (17a) of a substrate (17) having a surface facing the plasma and flanked by zones of conductive material (21, 39). A frequency power source (7) and generating means (1) for generating a plasma facing said surface of the substrate (17) and its framing zones (21, 39), forming a back plate A conductive structure or part of the structure (23, 31) is arranged in contact with the second surface of the substrate facing towards the plasma (26) and said framing of this back plate and substrate. The zones (21, 39) are structurally separated and at least one impedance (4
A device for treating a substrate, characterized in that it is electrically connected via 3, 47) and is substantially compensated for variations in the radio frequency voltage through the thickness of the substrate (17). 4. A device for treating with plasma a surface (17a) of a substrate (17), at least a part of the thickness (e _s ) of which is substantially electrically insulating, facing the reaction space. Having a surface and a zone of conductive material (21, 3
9) an enclosure (11) defining the reaction space (13) facing the surface (17a) of the substrate laterally framed by 9) and for setting a plasma region (26) in the space. Generating means (1, 20), a radio frequency power source (7), an airtight outer chamber (25) accommodating the reaction enclosure (11), and an enclosure inside the outer chamber (25) Pressure reducing means (22, 24) for setting a pressure lower than that in (11), and further, on the one hand, the surface (17a) of the substrate (17).
And the opposite plasma region (26) and on the other hand the framing zone (2) of the substrate.
1, 39) and said plasma region, comprising adjusting means (43, 47) for producing substantially equal radio frequency voltages.