WO1995015570A1

WO1995015570A1 - Method for the manufacture of a capacitor and capacitor obtained

Info

Publication number: WO1995015570A1
Application number: PCT/FR1994/001404
Authority: WO
Inventors: Ronan Stephan
Original assignee: Compagnie Europeenne De Composants Electroniques Lcc
Priority date: 1993-12-03
Filing date: 1994-12-01
Publication date: 1995-06-08
Also published as: KR960706683A; CA2177987A1; FI962293A; FR2713388A1; FI962293A0; EP0731974A1; FR2713388B1; JPH09505943A

Abstract

Method for the manufacture of a stacked-type capacitor consisting of alternating dielectric layers and conducting layers. The dielctric and conducting layers are deposited in succession. The dielectric layers are deposited by polymerization of elements derived from the dissociation, by remote nitrogen plasma, of an organo-siliceous or organo-germanium gas. The conducting layers are formed by deposition of conducting elements derived from the dissociation, by remote nitrogen plasma, of a precursor gas of the conducting elements.

Description

METHOD FOR MANUFACTURING CAPACITOR AND CAPACITOR DERIVED FROM SUCH A METHOD

The present invention relates to a method for manufacturing a stacked type capacitor as well as the capacitor resulting from such a method.

The manufacture of stacked type capacitors can be carried out in different ways. One of them is to use metallized flexible plastic films.

Generally the flexible plastic films then have a metallized zone and a non-metallized lateral margin and result from the cutting of a width of metallized flexible plastic film of large width.

One of the stages of the manufacturing process consists in winding at least one pair of metallized flexible plastic films on a large diameter wheel. The winding is carried out so that the non-metallized margins of two overlapping films are found on opposite sides.

A capacitive strip of desired thickness is then obtained according to the number of turns performed. Each side of the capacitive strip is then covered with a metal or a metal alloy.

This is the shooping operation intended to create the output armatures of future capacitors. The capacitive strip thus obtained is called the mother capacitor. We then proceed to cut the mother capacitor into unit blocks called semi-finished capacitors.

Another way of making stacked type capacitors is to assemble metallized ceramic sheets. The metallized sheets are assembled by sintering after stacking the sheets flat on top of each other. It is then necessary to cut the assemblies thus formed and to produce the armatures of the elementary capacitors.

It is also known to produce capacitors on a glass substrate consisting of two metal electrodes framing a dielectric layer formed in a discharge plasma. The disadvantage of such methods consists, on the one hand, in their large number of steps and, on the other hand, that the components obtained have relatively limited volume capacities due to the nature and thickness of the dielectrics used.

For example, the dielectrics used to make the plastic films used in the composition of metallized flexible plastic film capacitors are polyester, polycarbonate, polyphenylene sulfide or even polypropylene. The volume capacity obtained then does not exceed 10 nF per mrrr-- ^* .

The invention does not have these drawbacks. The present invention relates to a method for manufacturing a stacked type capacitor consisting of an alternation of dielectric layers and conductive layers characterized in that the dielectric layers are deposited by polymerization of elements resulting from the dissociation by nitrogen plasma d an organo-siliceous or organo-germanized gas and in that the conductive layers are produced by depositing conductive elements resulting from the dissociation by nitrogen plasma of a precursor gas of the conductive elements.

Advantageously, the deposition of the conductive layers and the deposition of the dielectric layers are carried out within the same reactor.

According to the preferred embodiment of the invention, the deposition of a conductive layer follows the deposition of a dielectric layer and vice versa. The invention however relates to other embodiments for which the deposition of several dielectric layers takes place simultaneously with the deposition of several conductive layers. The substrate on which the dielectric layers and the conductive layers are deposited is then unwound in several deposition cavities distributed alternately so that the deposition of a conductive layer follows the deposition of a dielectric layer on the same portion of the substrate.

An advantage of the invention is to simplify the method of manufacturing stacked type capacitors. Other characteristics and advantages of the invention will appear on reading a preferred embodiment made with reference to the appended figures in which:

- Figure 1 is a principle representation of a discharge plasma in flow as used according to the invention.

- Figure 2 is a block diagram of the device according to the invention; Figure 3 is a detailed view of the block diagram of Figure 2

- Figure 4 is a sectional view of a wire such as those used to make a mask according to the invention; - Figure 5 is a sectional view of a capacitive structure obtained according to the invention.

In all the figures, the same references designate the same elements.

Figure 1 is a principle representation of a flow discharge plasma as used according to the invention.

A nitrogen supply source 2 is sent via a tube 3 into a microwave cavity 4. The nitrogen pressure inside the tube 3 is between 1 and 20 hPa. Under the effect of the wave generated by the microwave generator 5, a discharge is maintained in the cavity 4. The frequency of the wave coming from the microwave generator 5 is, for example, equal to 2450 MHz, at 433 MHz, or 915 MHz. The flow made by a vacuum pump (not shown in Figure 1) is established along the axis of z. The hatched areas symbolically represent the distribution of ions and electrons present in the discharge plasma discharge zones located between the outlet of the discharge cavity and the vacuum pump.

Zone Z1 is a first post-discharge zone in which the concentration of ions and electrons decreases continuously between the exit from the discharge cavity and an extinction zone of very small extension, represented by the point P.

Zone Z2, which succeeds zone Z1, is a second ion post-discharge zone in which the concentration of ions and electrons is not negligible. It has a larger extension than zone Z1.

Zone Z3, which succeeds zone Z2, is an intermediate zone between zone Z2 and zone Z4, which is almost devoid of electrons and ions. The concentration of ions and electrons decreases continuously between the second half of zone Z2 and zone Z4.

The Z4 zone is a post-discharge zone likely to expand widely in space. In the zone Z4, the effective lifetime of the energy carriers, in particular of the vibrationally excited nitrogen, is advantageously long. Lifespans of the order of 10 seconds have been measured. Advantageously, it is therefore the deferred flow plasma situated in this extended post-discharge zone which is used according to the invention. By way of example, it has been measured that the distance separating the outlet from the cavity 4 from the start of the zone Z4 can be greater than or equal to 1 meter.

Figure 2 is a block diagram of the device for the deposition of dielectric and conductive elements according to the invention. When the dielectric deposition operation is selected, the switching valve 9 is positioned so as to allow access of the organo-siliceous or organo-germanized gas originating from the source 10 into the reactor 6 where the process is carried out .

According to the preferred embodiment of the invention and as will be specified later, a source of oxygen 11 and a doping element 12 are also introduced into the reactor 6.

According to the invention, the dielectric layers are deposited by polymerization of elements resulting from the dissociation by delayed nitrogen plasma of a precursor gas of the deposit such as an organosilicate or organo-germanium gas.

The deferred plasma used is a cold plasma deferred in flow. The cold plasma delayed in flow is obtained under a pressure of a few hPa, by extraction and expansion in the reactor 6, outside the electric field, of the active species formed in a plasma in discharge such as that described in FIG. 1.

As described above, the cold plasma deferred in flow according to the invention contains practically no electrons or ions. Reactive species are essentially atoms, free radicals and electronically and vibrationally excited molecular species. Such a delayed cold plasma can only be obtained in regions relatively distant from the cavity 4. It follows that the distance which separates the outlet from the cavity 4 from the surface 1 where the deposits take place must be chosen accordingly. . For example, this distance can be greater than or equal to 1 meter. The flow is carried out using the vacuum pump 14. As described in FIG. 1, a source 2 of nitrogen supply is sent into a microwave cavity 4, via a tube 3. The pressure of the nitrogen inside the tube 3 is between 1 and 20 hPa. Under the effect of the wave generated by the microwave generator 5, a discharge is maintained in the cavity 4. The frequency of the wave coming from the microwave generator 5 is, for example, equal to 2450 Mhz, at 433 Mhz, or at 915 MHz. The nitrogen is excited at the outlet of the cavity. For example, the percentage of dissociated nitrogen can be between 0.5 and 3 percent.

The organo-siliceous or organo-germanized gas is introduced into the reactor 6 by means of a device 8, the diagram of which will be detailed in FIG. 3. The flared end 7 of the device 8 allows the gas coming from the source 10 to spread over the surface 1 on which the deposition of dielectric is to be carried out.

The excited nitrogen is therefore mixed with the precursor gas of the deposit in the zone located between the flared end 7 of the device 8 and the surface 1 where the polymerization takes place. This flared end is located in the extended non-ionic post-discharge region of the flowing nitrogen plasma. The use of an extended delayed plasma is an advantage of the invention. The absence of an electric field which results therefrom promotes the deposition of heavy elements on the conductive layers and improves the deposition rate.

As mentioned previously, the precursor gas of the deposit can be an organo-German compound. It can also be an organosilicate compound chosen from alkoxysilanes, siloxanes or silazanes. According to the preferred embodiment of the invention, it is tetramethyldisiloxane.

According to the preferred embodiment of the invention, the device 8 for injecting the gaseous organo-siliceous compound is connected to a source of oxygen 11. The introduction of oxygen into the reactor 6 at the same time as the organo compound -silicate advantageously accelerates the speed of formation of the dielectric layer on the conductive layer. Oxygen also promotes the formation of polar groups, such as OH groups, in the deposited layers, thereby improving the dielectric constant of these layers. The oxygen content is of the order of a few percent of the gas mixture present in reactor 6. It can reach values of 10 to 15% in the case of large reactors.

Another doping agent 12 can be introduced into the reactor by the device 8 for injecting the organosilicate compound. It may, for example, be a gas from the family of tetrakysdialkylamidotitanium IV. This second doping agent then makes it possible to increase the action of the first doping agent with regard to the formation of polar groups. The polar groups deposited are then groups based on titanium oxide. An advantage of the invention is the deposition of a dielectric layer having excellent adhesion and homogeneity qualities and the thickness of which obtained can vary, as required, from 0.05 micron to a few microns.

The organosilicate compounds introduced into the reactor can be

an alkoxysilane of formula

R1

O

RI - O - [Si - O] _n - R ₃ with n less than or equal to 5

H

a siloxane of formula

R2

Rl - [Si - O] _n - R ₃ with n less than or equal to 4

H

a silazane of formula

R2 R2

R-! - [Si - NH] _n - Si - R- | with n less than 4

H H

The relative dielectric constant of the deposits obtained can then reach values greater than 30. According to the invention, the oxygen source 11 or the doping element 12 can contain titanium oxide, for example titanium isopropylate (IV), in order to further increase the value of the relative dielectric constant of the deposit. A priori, it is known to those skilled in the art that dielectrics having high relative dielectric constants often exhibit high losses, as well as poor temperature resistance. In the present case, it has been observed that the dielectric deposition according to the invention does not have these drawbacks.

The temperature resistance is improved, the maximum use temperature reaching up to around 300 ° C.

The breakdown voltages of the dielectrics are also greatly improved, reaching, for example, 2,000 volts per micrometer.

In general, the method according to the invention relates to various precursor gases of the deposit (organo-germanized compound, alkoxysilane, siloxane, silazane). Thus, the method according to the invention advantageously allows the polymerization of different dielectrics on the layers of conductive elements.

By way of example, when a silazane is introduced into reactor 6, a dielectric layer formed from the following compounds is obtained:

- Si - NH - Si - Si - O - Si - Si - C - Si

When a siloxane is introduced, a dielectric layer is obtained formed from the following compounds:

crosslinked polymer (Si - O - Si) - Si - (CH ₃ ) 1

- Si - OH - Si - NH - Si

for a very low oxygen content. or else: crosslinked polymer (Si - O - Si)

- If - (CH ₃ ) ₂

- Si - (CH ₃ ) ₂ - Si - OH

- SI - NH -Si for a higher oxygen content.

According to the preferred embodiment of the invention, the doping gas is oxygen. According to other embodiments, it may more generally be a gaseous compound containing oxygen.

According to the preferred embodiment of the invention, the deposition of dielectric layer alternates with the deposition of conductive layer. Thus when a dielectric layer has been deposited, the switching valve 9 is positioned so as to allow access of the precursor gas of the conductive elements originating from the source 13 into the reactor 6.

Preferably, the precursor gas of the conductive elements is a metallic complex. This metal complex can be a carbonyl metal such as, for example, iron carbonyl or nickel carbonyl, or alternatively an acetyl acetonate or a fluoro-acetyl acetonate. According to other embodiments, the precursor gas of the conductive elements can be hydrogen sulphide or alternatively sulfur dichloride. By radical recombination of the radical SN, the conductive polymers deposited are then sulfur polynitrides of chemical formula S N4 or (SN) _X , x being an integer greater than 4. Advantageously, the method according to the invention makes it possible to produce layers conductive with low thicknesses. These can indeed be of the order of 0.05 μm.

According to the invention, each deposit of dielectric or conductor is carried out with the presence of a mask consisting of a set of strips or wires arranged parallel to each other and, preferably, equidistant from each other. The presence of these masks serves to constitute a capacitive structure such as that shown in FIG. 5. The bands or threads constituting each mask are unwound by any device known to those skilled in the art so as to position themselves in contact with the surface where the deposition is to be carried out.

FIG. 3 is a detailed view of the block diagram of FIG. 2.

This view represents the injection device 8. A set of injection tubes 16 is contained in a sheath 15, which comprises, for example, a flared part 7 at its end. Each injection tube 16 opens onto an orifice 17 in the flared part of the sheath. During the dielectric deposition step, each injection tube

16 carries the precursor gas from the deposit from the source 10, preferably accompanied by oxygen from the source 11 and the doping element of the precursor gas from the source 12.

During the conductor deposition step, each injection tube 16 conveys the precursor gas of the conductive elements. In all cases, as mentioned previously, the flaring 7 allows the elements conveyed by the injection tubes 16 to be distributed uniformly above the surface where the deposition takes place.

The distance between the orifices 17 and the surface where the deposits are made is preferably of the order of a few centimeters. It can be, for example, between 5 and 10 cm.

FIG. 3 represents the injection device 8 according to the preferred embodiment. In general, the injection device 8 can be any system known to those skilled in the art and making it possible to distribute the precursor gases of the deposit uniformly above the surface where the deposition takes place.

Figure 4 is the sectional view of a wire such as those used to make the masks according to the preferred embodiment of the invention.

In general, the cross section of the elements - bands or wires - constituting the mask is of any geometry. It suffices that each element has for example a useful masking width of the order of 100 to 200 μm.

Preferably, however, the cross section of the wire is in the shape of a three-pointed star, said branches being equidistant from each other. ..--.,. „-”. „

PCT FR94 / 01404

11

each other. This geometry is advantageously chosen in order to avoid twisting of the wire during its unwinding.

In order to provide a masking area of the order of magnitude mentioned above, the length I of a branch varies from approximately 50 to 100 μm. FIG. 5 is a sectional view of a capacitive structure obtained according to the preferred embodiment of the method described in FIG. 2.

In FIG. 5 are also represented symbolically the masks used during the four successive stages (E1, E2, E3, E4) whose repetition leads to said structure.

During the first step E1, a first level of dielectric D1 is deposited on the surface 1 of a non-conductive substrate 18 whose function is to provide support for the capacitive structure. This non-conductive support is thin, for example 100 μm. It can be made of any material whose electrical characteristics do not disturb the electrical characteristics of the capacitors resulting from the method according to the invention. It may for example be a flexible plastic film or a rigid dielectric. The surface 1 presented by the substrate 18 can be, for example, of the order of 200 cm ² . According to the prior art, deposits assisted by discharge plasma are carried out on heated substrates. Another advantage of cold flow plasma deposition is that it does not have to heat the substrate on which the dielectric and conductor deposits are made. The mechanical characteristics of the substrate are therefore not degraded and the reliability of the components resulting from the process of the invention is improved compared to that of the components resulting from the processes of the prior art.

During the first step E1, a first mask MA1 is used so as to allow the first deposit of dielectric D1 only on the authorized zones. As previously mentioned, this mask preferably consists of different wires F1 arranged parallel to each other and preferably equidistant. Their distance can be, for example of the order of 1 to 2 mm.

During the second step E2, a second mask MA2 consisting of wires F2 is used so as to allow the first deposit of conductor M1 only on the authorized zones. F2 wires are wider than F1 wires. Preferably, the width of the wires F2 is of the order of 20 to 30% greater than the width of the wires F1.

Each wire F2 defines an axis. The same is true for F1 wires.

Thus, the wires F2 are arranged so that each axis defined by a wire F2 is juxtaposed with an axis defined by a wire F1, the distance separating the axes defined by two neighboring F2 wires being twice that separating the axes defined by two neighboring F1 sons.

During the third step E3, a third mask MA3 is used so as to allow the deposition of the second dielectric level D2. This third mask MA3 is identical to the first mask MAL. The dielectric is then deposited on the conductive and non-masked dielectric zones.

During the fourth step E4, a fourth mask MA4 is used so as to allow the deposition of the second conductive level M2. Each wire F4 of the mask MA4 is of identical size to the dimension of the wires F2 defined above. Two neighboring F4 wires are separated by the same distance as two neighboring F2 wires. However, the axis defined by a wire F4 does not overlap with the axis defined by a son F2, but is equidistant between the axes defined by two neighboring wires F2. It therefore constitutes a capacitive structure which results from the repetition of the four successive stages described above. In FIG. 4, the capacitive structure comprises, for reasons of convenience of representation, only six dielectric layers and six conductive layers. Thus the four stages E1, E2, E3, E4 were repeated three times. More generally, the number of repetitions of these four stages may be much greater and the number of layers may reach several thousand.

The capacitive structure according to the invention is in the form of a set of N elementary capacitive structures Si (i = 1, 2, ..., N) in parallel. Each elementary capacitive structure is a rectangular structure having two of its opposite lateral faces covered with conductive material. Each elementary capacitive structure consists of a capacitive stack of successive electrodes of alternately odd and even rank. The conductive material which covers a first of the two opposite lateral faces connects the electrodes to one another. of odd rank and the conductive material which covers the second lateral face connects the electrodes of even rank together. Advantageously, these structures are separated from each other by wells Pi (i = 1.2 N-

1). These wells are as many zones making it possible to facilitate the cutting of the capacitive structure into elementary capacitive structures.

According to the preferred embodiment, this cutting is carried out by a set of wires, of adjusted dimensions, such as those used to make the masks MA1 or MA3.

According to the invention, the side walls of each elementary capacitive structure are covered with conductive material. It then suffices either to pass each elementary capacitive structure through a wave of molten alloy, or to deposit a brazing alloy or brazing cream on the side walls of each elementary capacitive structure in order to produce the armatures of future capacitors. The shooping operation which was necessary, according to the prior art, for the manufacture of metallized plastic film sheet capacitors is no longer necessary according to the method of the invention.

More generally, the method of the invention advantageously reduces the number of successive steps making it possible to produce stacked type capacitors.

Once the armatures have been produced, the method according to the invention comprises a step of cutting the elementary capacitive structures in order to produce elementary capacitors.

Advantageously, the capacitors thus produced are components of very low volumes whose volume capacity can reach, for example, 20,000 nF per mm ³ -

Claims

1. A method of manufacturing a stacked type capacitor, said capacitor consisting of an alternation of dielectric layers and conductive layers characterized in that the dielectric layers are deposited by polymerization of elements resulting from the dissociation by nitrogen deferred plasma of an organo-siliceous or organo-germanized gas and in that the conductive layers are produced by deposition of conductive elements resulting from the dissociation by nitrogen-delayed plasma of a precursor gas of said conductive elements.

2. Method according to claim 1, characterized in that said deferred nitrogen plasma is a cold plasma deferred in flow located in the extended post-discharge zone containing practically no electrons or ions.

3. Method according to claim 1 or 2, characterized in that the deposition of a dielectric layer alternates with the deposition of a conductive layer.

4. Method according to any one of the preceding claims, characterized in that the organo-siliceous compound is chosen from the alkoxysilanes of formula:

R1

O

I R- _j - O - [Si - O] _n - R ₃ with n less than or equal to 5

IH the siloxanes of formula

R2

Rl - [Si - O] _n - R ₃ with n less than or equal to 4

H

or the silazanes of formula

R2 R2

Rl - [Si - NH] _n - Si - Ri with n less than 4

H H

5. Method according to claim 4, characterized in that the organosilicate compound is tetramethyldisiloxane.

6. Method according to any one of the preceding claims, characterized in that the precursor gas of the conductive elements is a metal complex.

7. Method according to claim 6, characterized in that the metal complex is a carbonyl metal.

8. Method according to claim 6, characterized in that the metal complex is an acetyl acetonate or a fluoro-acetyl acetonate.

9. Method according to any one of claims 1 to 5, characterized in that the precursor gas of the conductive elements is sulfurous hydrogen.

10. Method according to any one of claims 1 to 5, characterized in that the precursor gas of the conductive elements is sulfur dichloride.

11. Method according to any one of the preceding claims, characterized in that the nitrogen pressure is between 1 hPa and 20 hPa.

12. Method according to any one of the preceding claims, characterized in that it comprises the presence of oxygen during the deposition of the dielectric layers.

13. Method according to any one of claims 3 to 12, characterized in that it comprises at least once the succession of the following four steps (E1, E2, E3, E4):

- deposition of a dielectric layer in the presence of a first mask MA1 consisting of strips or wires (F1).

- deposition of a conductive layer in the presence of a second MA2 mask consisting of bands or wires (F2), the axis defined by a band or a wire (F2) of the MA2 mask superimposed on an axis defined by a band or a wire (F1) of the mask MA1, the distance separating the axes defined by two neighboring bands or wires from the mask MA2 being twice that separating the axes defined by two neighboring bands or wires (F1) from the mask MAL - deposit of a dielectric layer in the presence of a third mask MA3 identical to the mask MAL

- Deposition of a conductive layer in the presence of a fourth mask MA4 consisting of bands or wires (F4), two bands or wires (F4) neighbors of the mask MA4 being separated by the same distance as two neighboring bands or wires (F2 ) of the mask MA2, the axis defined by a band or wire (F4) of the mask MA4 being located equidistant from the axes defined by two neighboring bands or wires (F2).

14. Method according to claim 13, characterized in that during the first succession of said four steps (E1, E2, E3, E4), the deposition of the first dielectric layer is carried out on a non-conductive substrate whose function is to serve as a support for the capacitive structure resulting from the repetition of said four successive stages (E1, E2, E3, E4).

15. Method according to claim 14, characterized in that the widths of the bands or wires (F1, F3) of the masks MA1 and MA3 are equal to each other and in that the widths of the bands or wires (F2, F4) of the masks MA2 and MA4 are equal to each other, the common width of the bands or wires (F1, F3) of the masks MA1 and MA3 being substantially less than the common width of the bands or wires (F2, F4) of the masks MA2 and MA4.

16. The method of claim 15, characterized in that it comprises a step of cutting said capacitive structure into elementary capacitive structures using wires whose axes are superimposed on the axes defined by the bands or wires of the MAL mask.

17. The method of claim 16, characterized in that it comprises the passage of each elementary capacitive structure resulting from said cutting in a wave of molten alloy in order to constitute the armatures of future capacitors.

18. The method of claim 16, characterized in that it comprises depositing an alloy to be brazed on the side walls of each elementary structure resulting from said cutting in order to constitute the armatures of future capacitors.

19. The method of claim 17 or 18, characterized in that it comprises cutting each elementary capacitive structure into elementary capacitors.

20. Method according to any one of claims 13 to 19, characterized in that the wires (F1, F2, F3, F4) constituting the different masks MA1, MA2, MA3, MA4 have a cross section in the shape of a star at 3 branches.