Chip comprising an integrated circuit, fabrication method and method for locally rendering a carbonic layer conductive

A chip includes an integrated circuit and a carbonic layer. The carbonic layer includes a graphite-like carbon, wherein a lateral conducting path through the graphite-like carbon electrically connects two circuit elements of the integrated circuit.

TECHNICAL FIELD

This invention relates to a chip comprising an integrated circuit, to a fabrication method and to a method for locally rendering a carbonic layer conductive.

BACKGROUND

A chip usually comprises different layers formed on a substrate. The different layers may form a part of an integrated circuit such as interconnecting lines for circuit elements of the integrated circuit. In particular, the circuit elements are usually electrically connected to each other by conducting layers or conducting paths separated from each other by isolating layers. Such conducting paths are typically made of metal or polysilicon or other conducting materials. Methods for providing conducting paths, such as lift-off processes, result in embedding the paths in trenches of isolating layers. These methods comprise several processing steps for the embedding such as lithographic steps, structuring and chemical etching. One possibility is, for example, to fill trenches previously formed with conducting material, e.g., by a deposition process with a further step of chemical-mechanical polishing (CMP) in order to archive a planar surface of the isolation layer across the trenches after same have been filled with conducting material. Due to the several manufacturing steps the shown method for providing conducting paths is very labor intensive.

SUMMARY OF THE INVENTION

An embodiment of the invention provides a chip comprising an integrated circuit and a carbonic layer, wherein the carbonic layer comprises a graphite-like carbon, and wherein a lateral conducting path through the graphite-like carbon electrically connects to circuit elements of the integrated circuit.

A further embodiment of the invention provides a chip comprising a substrate, an integrated circuit and a carbonic layer on the substrate, wherein the carbonic layer comprises an isolated portion comprising amorphous carbon and a conducting portion comprising graphite-like carbon, and wherein a lateral conducting path through the graphite-like carbon electrically connects two circuit elements of the integrated circuit.

Some embodiments of the invention provide a method for locally rendering a carbonic isolating layer conductive, wherein the method comprises the following steps: directing a laser beam onto the carbonic isolating layer so as to convert amorphous carbon of the carbonic isolating layer into graphite-like carbon.

Some embodiments of the invention provide a method for fabricating a chip comprising an integrated circuit and a carbonic layer, wherein the method comprises the following steps: heating the carbonic layer so as to form a conducting portion of the layer, wherein a lateral path through the conducting portion connects two circuit elements of the integrated circuit.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1shows a chip10comprising an integrated circuit and a carbonic layer12formed on a further layer14. The carbonic layer12may, for example, comprise CoSi or CoSi2. The integrated circuit is substantially formed within layer14, but for illustration purpose, merely two circuit elements16aand16bthereof are shown inFIG. 1. Layer14may, for example, comprise a semiconductor substrate or a semiconductor stack of a substrate and further layers between the substrate and layer12. The two circuit elements16aand16bare formed in the further layer14at laterally distinct portions, and may be, for example, a transistor, a capacitor and a diode, respectively. The circuit elements16aand16bare exemplarily shown as abutting an interface between layer14and layer12. However, this is not necessary and alternatives will be shown hereinafter. Generally, the circuit elements16aand16bare connectable via lateral distinct portions of layer12. At laterally surrounding portions, layer14has isolating material which electrically isolates the elements16aand16b, for example. The layer12has a thickness, e.g., 100 nm, and comprises a graphite-like carbon portion18which, in turn, may be surrounded by an isolating amorphous carbon portion of the layer12. The isolating amorphous carbon portion of the layer12may, for example, comprise diamond-like carbon or be diamond-like carbon. The graphite-like carbon portion18in the layer12is illustratively shown to have the form of a line having a width w18which may, for example, be between 5 and 50 nm and a depth d18which may, for example, be between 3 and 300 nm. The graphite-like carbon portion18is arranged such that a lateral conducting path18through the graphite-like carbon electrically connects the two circuit elements16aand16bof the layer14. In the embodiment ofFIG. 1, the conducting path18continuously extends down to the surface of layer12interfacing to the lower layer14so that the conducting path18inherently interconnects all circuit elements16aand16bbeing connectable at portions of this surface overlapping the conducting path18. However, alternative embodiments will be described below.

Thus, via the conducting path18an electrical current may be conducted, or control signals may be transmitted, from the circuit element16ato the circuit element16bof the integrated circuit, e.g., a logical circuit. The conducting path18through graphite-like carbon has an electrical conductivity, e.g., 0.5×1010U/cm2, which depends on the width w18and depth d18of the conducting graphite-like carbon portion18. The conductivity may be chosen to be sufficient for transmitting control signals and low currents, for example.

In the following, a method for providing the lateral conducting path18is described. The layer14comprising the two circuit elements16aand16bis provided. The first step of the method is then to provide the carbonic isolating layer12onto the layer14. The carbonic isolating layer12thus provided may, for example, comprise amorphous carbon and diamond-like carbon, respectively. Vapor depositing may be used. The next step is to locally heat the carbonic isolating layer12in a lateral area where the lateral conducting path18should be provided. A grid structure of the amorphous carbon and the diamond-like carbon, respectively, is destroyed by the local heating so as to covert the amorphous carbon to graphite-like carbon in said area. A grid structure of the graphite-like carbon enables electrical conductivity of same. Thus, the carbonic isolating layer12is (locally) rendered conductive in the areas so as to generate the conducting path18via the graphite-like carbon portion18. The local heating may be performed by using a diffusively radiating heat source or by directing a laser beam onto the portion18of the carbonic isolating layer12. Generally, an area where the conversion should take place, may be scanned by the heat source by moving a local heat spot over this area, such as a laser spot, or by covering surrounding areas besides the area of interest against the heating, e.g., by use of a mask and irradiating layer12at the non-masked portion.

Dependent on the duration of directing the laser beam onto the carbonic isolating layer onto a certain location and dependent on a power of the laser beam the depth d18of the graphite-like carbon18may be adjusted. In other words, due to absorbance, the heat intensively decreased from the side of layer12facing the heat source and the heating may be stopped at a location of layer12prior to the layer12completely converted along depth direction. This is, the depth d18of the conduction path18may be equal to the thickness of the layer12, as shown inFIG. 1.

The thickness of the carbonic layer12and thus the depth d18of the portion18and the depth of the portion of amorphous carbon are constant. The described method does not change the topology of the layer12and thus main surfaces of the layer12are plane or approximately plane. The graphite-like carbon18may have the width w18which is smaller compared to the width of the connecting areas of the circuit elements16aand16bat the interface between the layer12and14. The width w18of the graphite-like carbon portion18may be adjusted by varying the frequency of the laser or by varying a diameter of the laser beam. Alternatively, the width w18may be increased by providing two adjacent graphite-like carbon portions such that a broad graphite-like carbon portion is formed.

It is beneficial that the conducting path18may be provided by a simple and cost efficient method. A further advantage is that this method enables providing structured conductive paths embedded in the isolating layer12directly, without the need for a further step of planarization the surface of the layer12, e.g., before providing further layers. Therefore, the mechanical stress for the chip10caused by filling trenches and by the planarization process is reduced.

InFIG. 2, a graphite-like carbon portion having a reduced depth when compared to the embodiment ofFIG. 1is discussed.FIG. 2shows a further embodiment of a chip having three layers. A carbonic isolating layer13is arranged between the layer14and a layer22. The first layer14at the first side of the layer13is equal to the layer14of the first embodiment. The second layer22at a second side of the layer13comprises two circuit elements16cand16d. The circuit elements16cand16dare formed on, or have connectable areas at, a surface of the upper layer22facing the layer13. The layer13comprises amorphous carbon and graphite-like carbon which occupy laterally distinct areas of the carbonic layer13. In this embodiment, the lateral conducting path24through the graphite-like carbon electrically connects the two circuit elements16cand16d. A first part24bof the graphite-like carbon portion24extends in a first lateral direction (in parallel with the layer stack) so as to extend between the position of the circuit element16cand a point24a. A second part24cextends in a second lateral direction through the layer13, i.e. between the position of the circuit element16dand the point24a. That is, the conducting path24is shown inFIG. 2illustratively to have a non-straight form. Differing from the embodiment ofFIG. 1, the graphite-like carbon of the lateral conducting path24merely extends down to a depth d24which is smaller than the thickness of the carbonic layer13so that the circuit elements16cand16dare not electrically connected to each other by the conducting path24. That is, the conducting path24is embedded in the isolating amorphous carbon of the layer13merely at one side of layer13, and as the connecting areas of the circuit element16cand16dare located at opposite sides of the layer13. Some are not electrically connected via the path24, although path24overlaps both connecting areas. To be precise, circuit element16cis separated from the conducting path24via the isolating amorphous carbon portion along the thickness direction.

The graphite-like carbon of the conducting path24may be provided by local heating of the carbonic layer13, for example, by directing a laser beam onto the carbonic isolating layer13, as described above. In contrast to the embodiment ofFIG. 1, the local heating of the carbonic layer13is performed by using a lower energy density of the laser compared to the embodiment ofFIG. 1, for example. Alternatively, instead of reducing the power of the laser, the duration of directing the laser beam onto the layer13may be varied. The reduced power density of the laser or the shorter duration of directing the laser beam results in the reduced depth d24of the graphite-like carbon portion24when compared to the depth d18(seeFIG. 1). In other words, the method enables forming the lateral conducting path24in the carbonic isolating layer13by using the laser, wherein the depth d24of the conducting path24is adjustable.

The layer22comprising the two circuit elements16cand16dmay be provided before or after converting the amorphous carbon of the carbonic isolating layer into graphite-like carbon24. In the latter case, in this embodiment, the step of directing the laser beam onto the carbonic isolating layer13may be performed so that the laser beam travels through the layer22before impinging onto the carbonic isolating layer13in the area of the portion24. Here, parameters of the laser, e.g., frequency and power density, may be set such that the amorphous carbon of the layer13in the area of the portion24is converted into a graphite-like carbon while the characteristic of the layer22is not changed.

FIG. 3illustrates a graphite-like carbon portion providing a lateral and vertical conducting path.FIG. 3shows an embodiment of a chip having four layers. A layer25comprises the first circuit element16awhile a layer26comprises the second circuit element16e. Between the layers25and26two isolating layers28and30are arranged. The isolating layer28comprises a via32. The layer30is a carbonic layer comprising an amorphous carbon portion and a conductive graphite-like carbon portion34. The lateral conducting path34electrically connects the circuit element16earranged at a surface of the layer26facing layer28to the via32of the layer28. The via32is electrically connected to the circuit element16aarranged at a surface of the layer25facing layer30. Thus, the via32and the conducting path34laterally and vertically connect the two circuit elements16aand16e, i.e., through the two layers28and30and through the layer stack, respectively, and in parallel with the layers25,26,28,30.

The layer30may be provided and locally rendered conductive, as described above. The width w34of the graphite-like carbon portion34is shown exemplarily as being increased when compared to the width w18of the graphite-like carbon portion18according to the embodiment ofFIG. 1. As a consequence of this, the electrical conductivity of the conduction path34is increased when compared to the conduction path18according toFIG. 1. The depth of the graphite-like carbon portion34extends over the whole thickness of the layer30in order to provide an electrical connection in a vertical direction from the via32in the lower layer28to the circuit element16ein the upper layer26.

FIG. 4illustrates a graphite-like carbon portion having a bifurcation and different depths at different locations of the graphite-like carbon portion.FIG. 4shows a further embodiment having two layers35and36. The layer35comprises two circuit elements16aand16fwhich are arranged at a surface of the layer35facing the layer36. The carbonic layer36comprises a first portion of amorphous carbon and a second portion of graphite-like carbon38embedded in the amorphous carbon portion. The circuit element16ais electrically connected via a conducting path38in a first lateral direction through the graphite-like carbon38to a contact pad38awhich is formed as a locally laterally enlarged portion of the graphite-like carbon. Via this contact pad38athe chip may be electrically connected by a further via of a further (upper) layer arranged at a surface of layer36. The enlarged shape of the contact pad38aenables, for example, accommodating positioning imprecision of the further layer or the further via, such as by lithographic processes used for defining the via. The contact pad38ahas a geometry that is exemplarily square-shape and a part38cof the graphite-like carbon between the via38band a position of the circuit element16aat an area38bextends down to a depth which is smaller than the thickness of the layer36. The depth of the graphite-like carbon portion38extends over the whole thickness of the carbonic layer36in the area38bat the circuit element16ain order to electrically connect the circuit element16avia the surface of the layer36.

The graphite-like carbon38comprises further a second part38din a second lateral direction. A lateral conducting path through the second part38dof the graphite-like carbon electrically connects the circuit element16fto the circuit element16aand thus to the contact pad38a. Therefore, the graphite-like carbon38in an area38eat the circuit element16fextends over the whole thickness of the layer36while the depth of the part38dof the graphite-like carbon38is smaller than the thickness of the layer36.

The carbonic layer36may be locally rendered conductive in the portion38, as described with respect to the embodiment ofFIG. 1. The depth differences between the areas38a,38cand38bas well as the depth differences between the areas38dand38emay, for example, be the result of using a different power density of the laser at different locations. The square shaped geometry of the contact pad38aor, in other words, the extensive surface of the contact pad38amay be generated by providing a plurality of adjacent graphite-like carbon portions.

According to another embodiment, instead of local heating laterally global heating may be performed so that a whole surface area of the carbonic isolating layer or an extensive area of the layer is converted into graphite-like carbon. This step may, for example, be performed by using an oven. Alternatively, the local heating may be performed by another heating source or by an ion source. It is beneficial that the extensive heating of the layer does not cause deformations of the layer or of a substrate.

Although some aspects have been described in the context of a method, these aspects also correspond to the chip10(seeFIG. 1) comprising the carbonic layer12which comprises the conductive graphite-like carbon portion18, wherein the lateral conducting path18through the graphite-like carbon18electrically connects to circuit elements16aand16bof the integrated circuit. As illustrated with respect toFIG. 1, the chip10may comprise an isolating portion which comprises amorphous carbon in which the graphite-like carbon18is embedded. The chip10may further comprise a substrate.

Although in some embodiments the circuit elements (e.g.,16a,16b) and the conducting paths (e.g.,18) have been shown in a different layer (e.g.,12,14), the invention also relates to embodiments in which at least one of the circuit elements and the graphite-like carbon of the conducting path are arranged in the same layer.