EP1054417A1 - Microcomponents of microinductance or microtransformer type and manufacturing process - Google Patents

Abstract

The microcomponent manufacture technique has a substrate etched with a number of channels. Copper is deposited by electrolys in the channels and planed flat. A central section (12) is deposited above the segments (7). The central section is then etched for arch sections, each arc connected to an adjacent segment and forming a spiral winding.

Description

Technical area

The invention relates to the field of microelectronics, and more specifically for the micro-component manufacturing sector, especially for to be used in radio frequency applications. It concerns more particularly micro-components such as micro-inductors or micro transformers. It also relates to a process for manufacturing such micro-components providing components with high value inductive, and minimal resistive and magnetic losses.

Previous techniques

As we know, the electronic circuits used in applications radio frequencies include oscillating circuits formed by the association of a capacity and inductance.

The trend towards miniaturization of devices such as in particular mobile phones, requires carrying out such components in a increasingly reduced dimensions.

Furthermore, these inductive components are asked to present optimal electrical characteristics at increasingly higher frequencies, and on increasingly wide frequency ranges.

Thus, with regard to the quality factor characterizing the inductors, a problem which arises is that of the parasitic capacities existing between the turns forming an inductive coil.

In addition, for considerations of autonomy and power consumption it is also important to limit the electrical resistance of these inductors, which has also influence the value of the quality factor.

Thus, the invention proposes to solve several problems, namely the influence of resistance on the value of the quality factor of an inductance, as well as the limitation of the self-inductance coefficient imposed by the geometries existing.

Furthermore, in radiofrequency applications, use is also made of signal or current micro-transformers, which must respond to the same space constraints than those identified for the inductors.

In addition, the problem arises of obtaining such a perfect magnetic coupling. as possible between the two windings of a transformer.

It has already been proposed to produce micro-components including windings inductive made by micro-machining techniques. Such micro-components, surface mounted, are made by winding a copper wire around a core of ferrite or ferromagnetic material, then an assembly with outdoor contact pads.

Micro-transformers have also been produced by the same techniques with additional problems inherent in the packaging plastic. Such components are very difficult to miniaturize, which results in limiting the possibility of reducing their electrical consumption, and footprint which remains high, which limits their use in devices portable.

Furthermore, it has also been proposed, as illustrated in the document US 5,279,988, to manufacture micro-inductors or micro-transformers using microelectronic technologies.

However, these techniques implement methods having a large number of steps, which makes them complex, and even expensive. In addition, the sequence of this multitude of steps does not allow to obtain a coupling optimal between the turns of the winding and the magnetic core.

In addition, solutions implementing micro-mechanical processes prove to be ineffective because the tolerances required in these technologies limit strongly the precision of such micro-components.

The invention therefore proposes to solve the congestion problems of micro-inductance or micro-transformer, while retaining very good electrical characteristics, either in inductance value and quality factor, or in magnetic coupling.

Another problem which the invention proposes to solve is that of the complexity of the manufacturing processes for such micro-components.

Statement of the invention

The invention therefore relates in particular to a method of manufacturing a micro-component electric, such as micro-inductance or micro-transformer, including at least one coil, and comprising a substrate layer.

• à graver sur le substrat une pluralité de canaux disposés de façon ordonnée selon une bande, et orientés sensiblement perpendiculairement à ladite bande ;
• à déposer par électrolyse, du cuivre dans lesdits canaux de façon à former une pluralité de segments ;
• à planariser la face supérieure du substrat et de la pluralité de segments ;
• à déposer au-dessus dudit substrat et desdits segments, au moins une couche destinée à former un noyau ;
• à graver le noyau pour ne le conserver qu'au-dessus de ladite bande ;
• à déposer par une seule étape d'électrolyse au-dessus du noyau, une pluralité d'arches, chaque arche reliant une extrémité d'un segment avec une extrémité d'un segment adjacent, en passant au-dessus dudit noyau.

This process is characterized in that it comprises the following stages consisting:

• etching on the substrate a plurality of channels arranged in an orderly fashion along a strip, and oriented substantially perpendicular to said strip;
• depositing copper by electrolysis in said channels so as to form a plurality of segments;
• planarizing the upper face of the substrate and the plurality of segments;
• depositing above said substrate and said segments, at least one layer intended to form a core;
• etching the core so as to keep it only above said strip;
• to deposit by a single electrolysis step above the core, a plurality of arches, each arch connecting one end of a segment with one end of an adjacent segment, passing over said core.

Thus, the substrate serves as a mechanical support, stiffening the base of the component. In addition, when the substrate used has good dielectric properties, the parasitic capacitance between the different segments forming the base of the micro-component is relatively small.

Thus, in accordance with the invention, these micro-components include three-dimensional turns, substantially helical in shape closest to of the ideal shape, namely for the inductors, of the circular section, which by completed tour has the slightest perimeter.

For the realization of micro-transformers, the upper part of the turns is carried out in the manner of a bridge which spans the core which will serve as a circuit magnetic.

In order to produce inductors, furthermore said elimination is carried out. core after the step of depositing the arches, the sacrificial core then being made in resin or a soluble organic polymeric material.

In this way, a micro inductance of solenoid shape is obtained which does not have no material interposed between the turns, except for the part of the substrate in which is anchored the bottom of the turns. We thus obtain a micro-inductance of high self-inductance value, and whose parasitic capacity between turns is extremely small.

Such inductors therefore operate in wide frequency ranges with a significant quality coefficient.

The use of copper, preferably in the thickness of a few tens micrometers also makes it possible to greatly reduce the resistance of the winding, and greatly increase the quality factor, from low frequencies.

In an alternative embodiment, the core is made of a material ferromagnetic. In this way, magnetic coupling is ensured between the different turns of the winding. So, if we realize a micro inductance, the use of a magnetic core further increases the value of self-inductance.

Furthermore, if the magnetic core has a loop geometry, we can thus realize micro-transformers by making a second winding analogous to the first, by selecting the ratio of the number of turns between these two windings depending on the desired application.

In practice, to make the components including a magnetic core, after the planarization step, an insulating layer is deposited, before deposition of the layer intended to form the magnetic core. After engraving of core, we proceed to the deposition of an insulating layer over the core. In this way, the segments forming the bottom of the turns and the arches forming the top part of the turns are not in contact with the magnetic material.

However, the small thickness of these insulating layers makes it possible to obtain a optimal coupling, because the segments and arches of each turn are as close as possible of the magnetic core.

In addition, when the component is intended to be used in an atmosphere wet, even chemically aggressive, a layer of passivation above the arches. In this way, we are freed from the risks of corrosion of copper, which would degrade the electrical characteristics, and in particular the electrical resistance of such a component.

As already said, the invention relates not only to the method of manufacturing, but also electrical micro-components of the micro-inductance type or micro-transformer including at least one inductive winding, and comprising a substrate layer.

• d'un segment de cuivre formé à l'intérieur de canaux gravés dans le substrat ;
• d'une arche reliant une extrémité dudit segment à une extrémité du segment de la spire adjacente, en passant au-dessus de ladite bande ;

These micro-components are characterized in that said winding is formed of a plurality of adjacent turns in series arranged in a strip, each of the turns being made up:

• a copper segment formed inside channels etched in the substrate;
• an arch connecting one end of said segment to one end of the segment of the adjacent turn, passing over said strip;

In this way, the winding of such a micro component has a shape solenoid of high rigidity, since firmly anchored in a layer of substrate, and on the other hand having optimal electrical properties, by the monolithic bridge or arch shape of the upper part of the turns.

Thus, according to different variants, the micro component can include a core made of ferromagnetic material, crossing the turns and disposed between the segments and the arches.

In the case where the nucleus forms a closed loop, the micro-component can have a second winding wound on said core, so as to form the micro transformer.

In the case of an inductor, the magnetic core has a shape of bar.

According to a characteristic of the invention, the space between the arches of the adjacent coils is filled with air, which greatly limits the value of the capacity parasite existing between turns and allows the use of such a micro inductance to high frequencies.

In a preferred form, at least the arches are covered with a layer passivation made of a material chosen from the group containing gold and gold-based alloys.

Brief description of the figures

The manner of carrying out the invention, as well as the advantages which flow therefrom will emerge clearly from the description of the embodiments which follow, in support appended figures, in which:

Figures 1 to 3, 5 and 6 are median longitudinal sectional views of a inductance carried out in accordance with the invention, as and when the sequence of steps in its manufacturing process.

Figure 4 is a top view of the same inductor after the step of core engraving.

Figure 7 is a top view of an inductor according to the invention.

FIG. 8 is a sectional view along the plane marked VIII-VIII in FIG. 7.

FIG. 9 is a sectional view along the plane marked IX-IX in FIG. 7.

FIG. 10 is a view in median longitudinal section of a transformer or an inductor illustrated at the time of the deposition of the magnetic layer.

Figure 11 is a top view of a winding of an inductor or a transformer fitted with a magnetic core.

Figure 12 is a sectional view along the plane marked XII-XII in the figure 11.

Figure 13 is a sectional view along the plane marked XIII-XIII in the figure 11.

Figure 14 is a schematic top view of a transformer made according to the invention.

Way of realizing the invention

As already said, the invention relates to a method of producing a microphone electrical component such as micro-inductance or micro-transformer which can in particular include a magnetic core.

Many steps of the process are common to the realization of micro-inductors and micro-transformers, so that in the following of the description, the common steps will only be described once.

The process for producing an inductor is illustrated in Figures 1 to 6.

As illustrated in Figure 1, one of the first steps in the process is to producing, in a substrate layer (1) preferably made of quartz, a plurality of channels (2).

By way of non-limiting example, these different channels (2) have a depth between 1 and 30 microns, width between 1 and 30 microns, and a length of the order of 5 to several tens of microns. In particular nonlimiting form, each of these channels (2) is distant from each other others by a distance of the order of half a channel width.

These different channels (2) are arranged in an orderly fashion along a strip (3) as shown in dotted lines in Figure 7, and which corresponds to the general direction of the axis (4) of the winding of the micro-inductance or the micro-transformer.

In the illustrated form, these channels (2) are perpendicular to the direction of the strip (3), but other geometries can be adopted in which by example each channel has a fixed orientation relative to the axis of the strip.

Thereafter, as illustrated in FIG. 2, a metal deposition is carried out, advantageously copper, inside the channels (2), by electrolysis.

The use of copper, combined with the depth of the channels allows to obtain segments (7) having a relatively low electrical resistance, which is advantageous in terms of electricity consumption as well as for the quality factor of an inductor.

After the electrolysis deposition step, proceed as shown in the figure 3, planarization ensuring a surface condition as flat as possible to the face top of the substrate.

By this operation, the copper segments (7) present inside the channels (2) are also planarized, and their upper face (8) is at the same level than the upper face (10) of the substrate (1).

In other words, the copper segments (7) are flush but do not protrude not from the upper face (10) of the substrate (1).

Subsequently, the process differs depending on whether an inductance is carried out in the air or a micro transformer or an inductor having a magnetic core.

Thus, in the case where an inductance is produced in the air, it is deposited above substrate (1) and copper segments (7), a layer of polymer resin (12) intended to be eliminated at the end of the process. This polymer resin (12) is a resin of the photosensitive type commonly used in this kind of application microelectronics. In this way, it is easy to define its geometry in the form of bars, then by creep to achieve a semicircular type without resorting to other process, as shown in Figure 4.

Then, a metal growth underlay (13) is deposited over the entire surface (10) of the substrate (1) and of the nucleus (s) thus formed. A resin photosensitive (14) is then deposited on this growth sublayer metallic (13).

Thereafter, the photosensitive resin (14) is exposed using a mask allowing to open patterns (16) connecting two segments (7) anchored in the substrate.

Subsequently, as illustrated in FIG. 5, the pattern (16) thus opened is filled of metal deposited by electrolysis, so as to form a bridge (17) between two ends of adjacent segments (7). These bridges (17) are obtained in a single electrolysis step. The sides of the patterns (16), made in resin, allow to obtain arches (17) whose walls are relatively flat.

Thereafter, an etching step is carried out which makes it possible to remove the resin (14) and the metal underlay (13) used for growth to obtain a plurality of arches forming the upper part of the turns, resting on the core.

To obtain, as illustrated in figure 6, an inductance in the air, one proceed to the elimination by dissolution or plasma etching of the resin core (15) on which the metal arches (17) are formed.

There is thus obtained, as illustrated in FIG. 7, an inductor comprising rectilinear segments (7) forming the lower part of each turn and arches (18) monolithic connecting adjacent segments (7).

As seen in Figure 8, such turns have a shape substantially elliptical, approaching the ideal circular shape, which has per turn made the smallest perimeter.

Thereafter, a passivation layer is typically deposited made of gold or a gold-based alloy to protect copper from oxidation. This layer has a thickness of the order of a few hundred angstroms.

In this way, the inductance thus obtained has turns which are, in their for the most part, separated from the following turns by a layer of air, which limits very strongly the parasitic capacity between turns. The only parts of the turns not being separated by air are the straight segments (7), which are separated by an area quartz substrate, whose dielectric properties are also favorable in parasitic capacity terms.

As already said, the invention also makes it possible to produce inductors incorporating a magnetic core, or micro-transformers.

Thus, to produce such micro-components, the process according to the invention follows the steps of etching the substrate, depositing copper for form the segments, and planarization as illustrated in Figures 1 to 3.

Thereafter, as shown in FIG. 10, a layer is deposited insulator (21) made flat over the entire surface of the plate, that is to say above substrate (1) and segments (7).

The thickness of this insulating layer (21) is minimized, typically by the order of a few tenths of a micron, so as to limit the distance separating the magnetic core and the copper coils to improve the magnetic coupling.

Thereafter, above the insulating layer (21), a layer of magnetic material (22), deposited either by electrolysis or by deposition in reactive sputtering.

Typically, the materials used to make this magnetic layer are alloys of iron and nickel generally called permalloy, or others laminated compounds.

Thereafter, the magnetic material layer is etched (22) to keep it only in the area corresponding to the location of the magnetic core itself. The magnetic material is for example engraved by a photolithography process known elsewhere.

Subsequently, when the magnetic material has the configuration of the core, a thin film of material is deposited above it insulator (24), with a typical thickness of the order of a few tenths of a micron.

The upper insulating film (24) extends over the magnetic core (22) and over the first insulating film (21) deposited on the substrate (2).

These two films (21, 24) are engraved directly above the ends of the segment (7) anchored in the substrate (2), so as to form a contact opening allowing the electrical connection between the segment (7) and the future arches that will be formed above the nucleus.

Thereafter, as already described for the realization of inductances in the air, we deposits a metallic growth undercoat over the core magnetic, then the one-step formation of copper arches intended for form the turns. The geometry of the ends of the arches maximizes the contact surface with the lower segment (7).

The gold-based passivation layer is subsequently deposited or gold alloy.

This gives the product partially illustrated in Figure 12, in which the turns (28) comprise rectilinear segments (7) anchored in the substrate and arches (29) connecting the ends of two adjacent segments (7) arranged on one side and on the other of the core (22).

As seen in Figures 12 and 13, the thinness of the insulating films (21, 24) allows optimal magnetic coupling.

In this way, it is possible to produce inductors having a magnetic core intended to increase the self-inductance coefficient.

Thus, by this technique, we were able to obtain inductances in a range ranging from nanoHenry to a few dozen microHenry. Such inductances, in the version without magnetic core, may have a quality factor of several tens at frequencies of a few gigaHertz.

As already said, the process according to the invention makes it possible, by combination of two windings (30, 31) and a closed loop core (32), a micro transformer as illustrated in figure 14. Such transformers are used for galvanic isolation between input and output of circuits, or even for signal transformation applications.

Industrial applications

Micro-components produced according to the process of the invention can be used in many applications, including those related to mobile telephony, signal processing and miniaturization.

Such components can in particular be mounted by the known technique under the name of "flip-chip" directly on integrated circuits.

Claims (11)

Method for manufacturing an electric micro-component such as micro-inductance or micro-transformer, including at least one coil, and comprising a layer of substrate,
characterized in that it comprises the following stages consisting: etching on the substrate (1) a plurality of channels (2) arranged in an ordered fashion along a strip (3), and oriented substantially perpendicular to said strip (3); depositing copper by electrolysis in said channels so as to form a plurality of segments (7); planarizing the upper face (10) of the substrate and the plurality of segments (7); depositing above said substrate (1) and said segments (7), at least one layer (12) intended to form a core (15); etching the core so as to keep it only above said strip; to deposit by electrolysis above the core (15), a plurality of arches (17), each arch (17) connecting one end of a segment (7) with one end of an adjacent segment, passing through above said core (15). Method according to claim 1, characterized in that the core is made of a resin (12), and in that it further comprises a step of removing said core after the step of depositing the arches (17). Method according to claim 1, characterized in that the core (22) is made of a ferromagnetic material. Method according to claim 3, characterized in that after the planarization step, an insulating layer (21) is deposited, before depositing the layer intended to form the core (22), and in that after the core has been etched, an insulating layer (24) is deposited over the core (22). A method according to claim 1, characterized in that it further comprises a step of depositing a passivation layer over the arches. Electrical micro-component of the micro inductance or micro transformer type, including at least one inductive coil, and comprising a substrate layer (2), characterized in that said coil is formed by a plurality of adjacent turns (19) in series arranged along a strip, each of the turns (19) being made up: a segment (7) of copper formed inside channels (2) etched in the substrate (2); an arch (18) connecting one end of said segment (7) to one end of the segment of the adjacent turn, passing over said strip (3); Micro-component according to claim 6, characterized in that it comprises a core (22) of ferro-magnetic material, passing through the turns, and disposed between the segments (7) and the arches (29). Micro-component according to claim 7, characterized in that the core (32) forms a loop, and in that it comprises a second coil (31) wound on said core, so as to form a micro-transformer. Micro-component according to claim 7, characterized in that the core forms a bar. Micro-component according to claim 6, characterized in that the space between the arches of the adjacent turns is filled with air. Micro-component according to claim 6, characterized in that at least the arches are covered with a passivation layer made of a material chosen from the group comprising gold and gold-based alloys.

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