METHOD FOR DEPOSITING ELEMENTS ON A SUBSTRATE OF INTEREST AND DEVICE

Abstract

The invention relates to a method for depositing new elements on a substrate of interest by means of a beam of focused ions and a platform for cooling the substrate of interest to cryogenic temperatures that can also rough out defective elements that are located on same. In addition, the invention relates to a device that comprises all the means necessary for carrying out the method, in particular the means necessary for condensing precursor gases on the surface of the substrate of interest at cryogenic temperatures. The method and the device of the invention can be used to remove and repair, for example, metal contacts of an electronic device or of an integrated circuit, or to repair, for example, portions of an optical lithography mask. Therefore, the present invention is applicable in the electronics industry and in the field of nanotechnology.

Claims

1. A method for depositing new elements on a substrate of interest, by means of a device that comprises a microscope configured for visualising and identifying the position of the surface of the substrate of interest and of the defective and new elements (7 and 8) that are on said substrate of interest a focused ion beam system configured for emitting a focused ion beam on the position of the surface of the substrate of interest and of the defective and new elements (7 and 8) identified by the microscope and for depositing new elements on said substrate of interest a precursor gas injector directed towards said substrate of interest and configured for depositing the new elements on the substrate of interest and a support platform of the substrate connected to a cooling element on which the substrate of interest is located, and configured for condensing the precursor gas coming from the precursor gas injector on the substrate of interest, wherein the microscope and the focused ion beam system are integrated into a device that contains them wherein there is a distance between the precursor gas injector and the support platform of the substrate, and wherein said method comprises the following steps: a) identifying the position of the surface of the substrate of interest on which new elements are to be deposited with the help of a microscope, and b) depositing the new elements on the position of the surface identified in step (a), forming a condensed precursor layer on the substrate of interest with a thickness of up to 1 μm at a substrate temperature lower than a condensation temperature of the substrate, precursor, irradiating the position of the surface identified in step (a) on which new elements are to be deposited with a focused ion beam and evaporating the non-irradiated condensed precursor layer.

2. The method according to claim 1, wherein the focused ion beam is selected from gallium, hydrogen, helium, neon, xenon, argon, lithium, oxygen, silicon, cobalt, germanium, gold, bismuth and metal alloys.

3. The method according to claim 1, wherein the condensed precursor layer is formed on the substrate of interest by cooling the substrate to cryogenic temperatures below −80° C.

4. The method according to claim 1, wherein the precursor is a precursor that gives rise to metal elements.

5. The method according to claim 1, wherein the precursor is selected from W(CO).sub.6, Co.sub.2(CO).sub.8, Fe.sub.2(CO).sub.9, HCo.sub.3Fe(CO).sub.12 (CH.sub.3).sub.3PtCp(CH.sub.3), CuC.sub.16O.sub.6H.sub.26 or gold precursors such as dimethylgold(III)-acetyl-acetonate, dimethylgold(III)-trifluoroacetyl-acetonate, dimethylgold(III)-hexafluoroacetyl-acetonate, PF.sub.3AuCI, Au(CO)CI, [CIAu.sup.lllMe.sub.2].sub.2, CIAu.sup.I(SMe.sub.2), CIAu.sup.I(PMe.sub.3) and MeAu.sup.I(PMe.sub.3).

6. The method according to claim 1, wherein a voltage applied for generating the ion beam is between 5 kV and 50 kV.

7. The method according to claim 1, wherein the irradiation with a focused ion beam is carried out in a range that is comprised between 3×10.sup.−4 nC/μm.sup.2 and 9×10.sup.−4 nC/μm.sup.2.

8. The method according to claim 1, which further comprises an additional step a′), prior to step (a), of identifying the defective elements of the substrate of interest with a microscope and roughing them out with a focused ion beam.

9. The method according to claim 8, wherein voltage applied for generating the ion beam in step (a′) is comprised between 5 kV and 50 kV.

10. A device to rough out defective elements that are located on a substrate of interest and/or depositing new elements on said substrate of interest, characterised in that the device comprises the following elements within a high-vacuum growth chamber a microscope configured for visualising and identifying the position of the surface of the substrate and of the defective and new elements that are on said substrate of interest a focused ion beam system configured for irradiating the position of the surface of the substrate and of the defective and new elements identified by the microscope with a focused ion beam and to rough out defective elements that are located on the substrate of interest and depositing new elements on said substrate of interest a precursor gas injector directed towards said substrate of interest configured for depositing the new elements on the substrate of interest and a support platform of the substrate connected to a cooling element on which the substrate of interest is located, configured for condensing the precursor gas coming from the precursor gas injector on the substrate of interest, wherein the microscope and the focused ion beam system are integrated into a device that contains the microscope and the focused ion beam and wherein there is a distance between the precursor gas injector and the support platform of the substrate that enables the thickness of the condensed precursor layer to be controlled.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0072] FIG. 1 Image of an integrated circuit wherein cuts have been made using the FIB technique and W metal contacts using the FIBID technique to reconfigure the behaviour thereof. This image is part of the state of the art.

[0073] FIG. 2. Images of a mask used for optical lithography taken with an SEM microscope. (a) The mask exhibits defective material in a certain area. (b) Using the FIB technique the material from the defective area can be roughed out. (c) Using FIBID, deposits can be created to restore the defective area. This image is part of the state of the art.

[0074] FIG. 3. Diagram of the device of the present invention [0075] (1) Microscope [0076] (2) Focused ion beam system [0077] (3) Surface of the substrate [0078] (4) Support platform of the substrate of interest [0079] (5) Cooling element [0080] (6) Precursor gas injector [0081] (7) Defective or damaged elements [0082] (8) New elements [0083] (9) Growth chamber

[0084] FIG. 4. The images show SEM images that enable the degree of homogeneity of the condensed W(CO).sub.6 precursor layer on the substrate to be assessed as a function of the substrate temperature at a distance of 5 mm between the injector-substrate.

[0085] FIG. 5. Porousness of the condensed layer as a function of the irradiation dose. (a) dose=4.21×10.sup.−5 nC/μm.sup.2, (b) dose=3.57×10.sup.−4 nC/μm.sup.2.

[0086] FIG. 6. Electrical resistance as a function of the irradiation dose of the condensed layer.

[0087] FIG. 7. Time necessary for growing W(CO).sub.6 deposits of the same thickness and same area as a function of the substrate temperature. It is observed that when the precursor is in the condensed phase (−80° C.), the time required is reduced by a factor close to 1000.

[0088] FIG. 8. (a) Scanning electron microscopy image of the structure grown by means of the method of the present invention using the precursor W(CO).sub.6 in order to assess the electrical properties thereof. (b) Measurements of voltage (V) versus current (I) of 3 samples as that shown in (a), from where the metallic behaviour (linear dependence V vs I) is inferred and from where an average resistivity value close to that obtained in a method carried out at a substrate temperature around room temperature (standard FIBID) is obtained.

[0089] FIG. 9. Scanning electron microscopy images of nanowires grown using the device and method of the present invention using two different irradiation doses. (a) 8×10.sup.−4 nC/μm.sup.2 irradiation dose. (b) 6×10.sup.−4 nC/μm.sup.2 irradiation dose. In both cases, the high lateral resolution of the method and the minimum proximity effect are observed, which enables two close threads that are independent to be obtained.

[0090] FIG. 10. Transmission electron microscopy image of one of the condensed layers, wherein it is observed that it exhibits a total thickness of less than 30 nm.

EXAMPLES

Example 1

[0091] To demonstrate that the method of the present invention is viable and useful for editing/repairing, for example, integrated electronic circuits and lithography masks used in the manufacture of microelectronic devices in the semiconductor industry, our experiments have focused on the use of the precursor W(CO).sub.6, which enables tungsten W to be deposited and thus repair conductive elements.

[0092] For this, the device that is outlined in FIG. 3 has been used and which comprises the following elements: [0093] a microscope (1) configured for visualising and identifying the position of the surface of the substrate (3) and of the defective and new metal elements (7 and 8) that are on said substrate of interest (3) [0094] a focused ion beam system (2) configured for emitting a focused ion beam on the position of the surface of the substrate of interest (3) and of the defective and new metal contacts (7 and 8) identified by the microscope (1) and for roughing out defective contacts (7) that are located on the substrate of interest (3) and/or depositing new metal contacts (8) on said substrate of interest (3) [0095] a precursor gas injector (6) directed towards said substrate of interest (3) configured for depositing the new metal contacts (8) on the substrate of interest (3) and [0096] a support platform of the substrate of interest (4) connected to a cooling element (5) on which the substrate of interest (3) is located, configured for condensing the precursor gas coming from the precursor gas injector (6) on the substrate of interest (3),

[0097] wherein the microscope (1) and the focused ion beam system (2) are integrated into a device that contains them.

[0098] First, the general method to rough out defective metal contacts (7) of the substrate of interest (3) involves imaging with an optical, electronic (SEM) or ion (FIB) microscope to detect the defective area. Next, scanning with the ion beam (FIB) is carried out to remove defective material from said area. Finally, an inspection of the place is carried out again to observe that the defective metal contact has disappeared from said area.

[0099] The general method for depositing new metal contacts (8) on the substrate of interest (3) can be described as follows: The substrate of interest (3) on which new metal contacts (8) are to be deposited is introduced into the growth chamber (9). The inlet valve of the cooling element (5) which is extracted from a bottle of liquid nitrogen opens. This cooling element circulates to the support platform of the substrate of interest (4) wherein the substrate of interest (3) rests, which can be cooled from room temperature to the temperature of the liquid nitrogen (−196° C.). The precursor injector valve (6) opens, and the precursor comes out in the form of gas and condenses on the substrate of interest (3) forming a layer of condensed precursor on the substrate of interest (3). The thickness of this condensed layer is controlled through the time the valve remains open. Next, the condensed layer is irradiated by scanning the ion beam (2) over same and subsequently the substrate of interest (3) is allowed to heat to room temperature so that the condensed layer evaporates except in the areas irradiated with the ion beam (2) wherein a metal material remains on the substrate of interest (3) that corresponds to the shape of the scanning of the ion beam (2).

[0100] The substrate is cooled to cryogenic temperatures of around −100° C., causing the condensation of the precursor gas W(CO).sub.6 on the surface of the substrate when it makes contact with it. The thickness of the condensed layer is established by controlling the time during which the precursor gas injection valve is open and the distance between the precursor gas injector (6) and the substrate of interest (3). In our working conditions, the optimum thickness of the condensed layer is 10-30 nm, since this is the average depth reached by the beam of gallium ions accelerated at 30 kV. Localised irradiation of the condensed layer of W(CO).sub.6 is carried out by scanning a focused ion beam for a certain time. In our experiments we optimised this time that depends on the scanned area, obtaining the corresponding optimal irradiation doses. The optimal irradiation dose depends on the working conditions and in our case it has been found to be 5.5×10.sup.−4 nC/μm.sup.2. The irradiation carried out by the ion beam causes physicochemical changes in the condensed layer. These changes remain latent until the condensed layer evaporates as the substrate is heated to room temperature. As a result, the deposit only remains in the area irradiated by the beam of gallium ions and the rest of the layer evaporates. In this way we manage to grow a deposit on the area of interest and with the specified shape.

[0101] The condensation temperature of the precursor gas W(CO).sub.6 depends on the distance between the precursor gas injector (6) and the support platform (4) where the substrate of interest (3) rests, surely due to the fact that the local pressure of the precursor on the condensation surface changes with distance and therefore, if the local pressure changes, the condensation temperature will change.

[0102] The following table 1 illustrates the phenomenon:

TABLE-US-00001 Distance between injector-support of the 1 mm 5 mm 10 mm substrate Temperature at which condensation is first −20° C. −30° C. −60° C. observed Temperature at which a homogeneous layer of −30° C. −80° C. −80° C. condensation is obtained Condensed layer thickness for the same 6000 nm 400 nm 10-30 nm injector valve opening time (10 s)

[0103] FIG. 4 shows the condensed layer at different substrate temperatures: the formation of a homogeneous condensed layer only occurs when the substrate temperature is −80° C.

[0104] We were able to deduce from these results that the optimum working conditions occur at substrate temperatures equal to or lower than −80° C. and for a distance between injector-substrate of 10 mm since a higher temperature implies inhomogeneity of the condensed layer and a distance of less than 10 mm between injector-substrate implies an excessively thick condensed layer for subsequent irradiation.

[0105] We also studied the influence of the irradiation dose on the degree of porosity of the deposit: below, FIG. 5 shows two images of deposits created under the same conditions except that the one on the right has been subjected to an irradiation dose 10 times higher than that on the left. The one on the left shows a high degree of porosity that is not suitable for obtaining low electrical resistance.

[0106] Finally, we studied the influence of the irradiation dose on the electrical resistance of the deposit: in the experiment shown in FIG. 6 it can be observed that a variation of a factor 3 in the irradiation dose implies a variation of a factor 4 in the electrical resistance thereof.

[0107] Below is a comparative test which demonstrates that the method of the present invention requires a much lower amount of ion irradiation, and therefore of irradiation time, compared to a method carried out at a substrate temperature around room temperature. In Table 2, the data are compared for the same structure of about 20 nm thick grown by means of the precursor W(CO).sub.6.

TABLE-US-00002 Table 2. Comparative data using the precursor W(C0)6 and a structure about 20 nm thick. Volume of material Ion dose per unit per dose unit Temperature (° C.) area (nC/μm.sup.2) (μm.sup.3/nC) Resistivity (μΩcm) −100 5.5 × 10.sup.−4 16.35 423 23 0.399 2.25 × 10.sup.−2 332

[0108] Under the working conditions of the present invention, the ion dose per area necessary is approximately a thousand factor less than in the method carried out at a substrate temperature around room temperature; the results obtained indicate that with the method of the present invention the growth rate of the material is greater by a thousand factor.

[0109] In addition, the method of the present invention does not generate defects on the substrate. In fact, measuring the composition of the “cryo-deposits” using the X-ray microanalysis technique, no presence of gallium is detected due to the low irradiation dose used. We can assume that if the gallium dose is a thousand times less, the gallium concentration will be too. In this case, the gallium concentration will be of the order of 0.01%, virtually undetectable with standard characterisation techniques (EDX, EELS, etc.).

[0110] As a comparative data, it is worth mentioning that the compositional analysis detects that the gallium content in the deposits is approximately 10% in a method carried out at a substrate temperature around room temperature (standard FIBID) [Z. Cui et al., Journal of Vacuum Science and Technology B 14 (1996) 3942].

[0111] If we translate these results into time, taking as reference the example shown in table 1, with the doses per unit area necessary, to grow a deposit of one square micron in area and 20 nm thick with an ion beam current of 10 pA, at room temperature it takes 40 seconds while at −100° C. it takes only 55 milliseconds.

[0112] FIG. 7 shows the time it takes to grow a layer of 1 m.sup.2 in area and 20 nm thick as a function of the substrate temperature, we clearly see the reduction of three orders of magnitude when the precursor is in the condensed phase.

[0113] To verify that the “cryo-deposits” based on the precursor W(CO).sub.6 are metal, electrical measurements were carried out, as shown in FIG. 8. Measurements carried out on 3 samples with similar features indicate a linear dependence between current and voltage, as expected in the case of metal behaviour. The average resistivity value obtained in these samples is 439 μΩcm, a value that is similar to that obtained in samples prepared by means of a method carried out at a substrate temperature around room temperature (standard FIBID) [7, 8]. These data confirm the metal functionality of the deposits and therefore the interest thereof in microelectronic circuit editing.

[0114] In order to find out the potential of the device of the present invention in terms of lateral resolution and packing of metal contacts in circuit editing, several nanowires were grown using doses very close to the optimum irradiation (5.5×10.sup.−4 nC/μm.sup.2). We can conclude from these experiments that the process described is of high lateral resolution, reaching lateral dimensions as small as 38 nm.

[0115] When a line the width of which is determined by the diameter of the beam of ions is scanned using 1 pA of current, the beam diameter is obtained which is about 10 nm.

[0116] With an irradiation dose of 8×10.sup.−4 nC/μm.sup.2, 54 nm nanowires can be grown, with an aspect (length/diameter) ratio of 63, as can be observed in FIG. 9(a). While if we reduce the irradiation dose to 6×10.sup.−4 nC/μm.sup.2 we obtain highly packed 38 nm nanowires with a distance of 7 nm between two of them, and with an aspect ratio of 42 (see FIG. 9 (b)).

[0117] FIG. 10 shows a transmission electron microscopy image of the W-C deposit obtained following the optimised method described herein, wherein the formation of a granular material with a thickness of less than 30 nm and which is conductive can be observed as the electrical measurements in FIG. 8 show.