Patent Application
20210348266
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.
In the semiconductor industry, for more than 25 years, companies in the sector have been using Focused Ion Beam (FIB) and Focused Ion Beam Induced Deposition (FIBID) roughing out techniques.
In the case of the FIB technique, a focused ion beam (typically accelerated to 30 kV) has sufficient linear energy and momentum for causing a local roughing out of a material, being therefore a subtractive lithography technique.
In the case of the FIBID technique, and by means of an injector, a precursor gas is applied that is adsorbed to the work surface, generally at room temperature, and ion beam scanning dissociates the precursor gas, causing the growth of a material locally in the scanned area, referred to as deposit, constituting an additive lithographic technique.
The technique enables electrical contacts in integrated circuits to be repaired or reconfigured [D. Xia et al., Journal of Vacuum Science and Technology B 33 (2015) 06F501], as seen in
It is common for both FIB and FIBID techniques to be integrated in combination with a scanning electron microscope, into a microscope called FIB-SEM (Scanning Electron Microscope, or SEM). We are talking about advanced microscopes that cost around a million euros per unit and that companies that manufacture microelectronic components sometimes need by the dozens in the case of mass production in microelectronic foundries. Therefore, a significant advance in the efficiency of the FIB and FIBID processes can have a high economic impact in editing microelectronic circuits and in repairing lithography masks.
For the applications described, the FIBID technique exhibits two notable limitations: on the one hand, the growth rate of the deposits at room temperature is very slow and on the other hand, many defects are introduced into the work surface/substrate and/or into the deposited material/deposit, associated with the use of ions (implantation, amortisation, extrinsic doping, etc.).
Therefore, it is necessary to develop fast methods for depositing elements by means of a focused ion beam that also minimise the appearance of defects.
The present 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 said substrate of interest.
In the present invention “the elements” can be physically linked, such as, for example, the metal contacts of an electronic device, or they may be isolated as with the various parts of a lithography mask.
In the present invention the deposited “element” may have any composition, for example, it can be composed of a metal or an alloy in the event that metal elements of an electronic device are to be deposited.
In the present invention, the “element” can also have any geometry: it can be a sheet, a microwire, a nanowire, a circle, etc.
The term “defective element” is understood in the present invention as that defective or deteriorated element that makes the electronic device, the integrated circuit or lithography mask stop working or malfunction.
In addition, the present invention relates to a device that comprises all the means necessary for carrying out the method of the present invention, 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 present invention can be used to remove and repair electrical contacts of an integrated circuit or to repair defective portions of an optical lithography mask, so the present invention is of interest in the sector of manufacturing and repairing devices of the electronic industry, and in the field of nanotechnology for manufacturing, for example, sensors and devices based on quantum technologies.
In the present invention, the term “substrate of interest” refers to a support of an electronic device, of an integrated circuit, or an optical lithography mask.
The advantages of the method and the device of the present invention are:
In a first aspect, the present invention relates to a method for depositing new elements (8) on a substrate of interest (3) (hereinafter “the method of the present invention”), by means of a device that comprises
wherein the microscope (1) and the focused ion beam system (2) are integrated into a device that contains them,
wherein there is a distance between the precursor gas injector (6) and the support platform of the substrate (4), and
wherein said method is characterised in that it comprises the following steps
The method of the present invention can be repeated as many times as necessary or desired, without the substrate of interest (3) being damaged by the continuous condensations of the precursor gas.
Step (a) of the method of the present invention is related to identifying the position of the surface of the substrate of interest (3) on which new elements (8) are to be deposited with the help of a microscope (1), such as a scanning electron microscope or the ion microscope itself.
Step (b) of the method of the present invention relates to depositing the new elements (8) on the position of the surface identified in step (a) by means of a variation of the focused ion beam induced deposition (FIBID) technique.
The method of the present invention, specifically in step (b), further relates to the formation of a condensed precursor layer on the substrate of interest (3) with a thickness of up to 1 μm at a temperature lower than the condensation temperature of the substrate with the help of a support platform of the substrate (4) connected to a cooling element (5) configured for condensing the precursor gas coming from the precursor gas injector (6) on the substrate of interest (3). In the present invention, the condensed precursor layer is homogeneous.
In the present invention the term “precursor or precursor gas” refers to that precursor gas of the new elements (8).
The thickness of the condensed precursor layer is established by controlling the time during which the precursor gas injection valve is open and the distance between the precursor injector and the substrate. The condensed layer has a thickness of between 10 nm and 30 nm in the case of using a gallium source FIB system which works at 30 kV, as shown in the exemplary embodiment of the invention.
In a preferred embodiment of the method of the present invention, the focused ion beam (2) is selected from gallium, helium, neon, hydrogen, lithium, oxygen, xenon, argon, silicon, cobalt, germanium, gold, bismuth and metal alloys. More preferably, the focused ion beam (2) is selected from gallium, hydrogen, helium, neon, xenon, argon, lithium, oxygen, silicon, cobalt, germanium, gold, bismuth and metal alloys.
Examples of metal alloys are AuSi, AuGe, AuGeSi, CoNd, CoGe, ErNi, ErFeNiCr, NiB, GaIn.
In a preferred embodiment of the method of the present invention, the condensed precursor layer is formed on the substrate of interest (3) by cooling the substrate to cryogenic temperatures below −80° C., for example using liquid nitrogen as a cooling element.
In a preferred embodiment of the present invention, the method relates to depositing elements for electrical or electronic circuits and the precursor preferably gives rise to metal deposits/elements.
In another preferred embodiment of the method of the present invention, the precursor is selected from W(CO)6, Co2(CO)8, Fe2(CO)9, HCo3Fe(CO)12, (CH3)3PtCp(CH3), CuC16O6H26 or gold precursors such as dimethylgold(III)-acetyl-acetonate, dimethylgold(III)-trifluoroacetyl-acetonate, dimethylgold(III)-hexafluoroacetyl-acetonate, PF3AuCI, Au(CO)CI, [CIAuIIIMe2]2, CIAuI(SMe2), CIAuI(PMe3) and MeAuI(PMe3).
Next, the position of the surface of the substrate of interest (3) on which new elements (8) are to be deposited, which had been previously identified in step (a), is irradiated with a focused ion beam (2).
The localised irradiation of the condensed precursor layer is carried out by scanning the surface of the substrate of interest (3) with a focused ion beam for a certain time; said time depends on the scanned area and the working conditions. The irradiation carried out by the ion beam causes physicochemical changes in the condensed layer.
In a preferred embodiment of the method of the present invention, the voltage applied for generating the ion beam in step (d) is comprised between 5 kV and 50 kV.
In another preferred embodiment of the method of the present invention, irradiation with a focused ion beam (2) of step (d) is carried out in a range that is comprised between 3×10−4 nC/μm2 and 9×10−4 nC/μm2.
Lastly, the non-irradiated condensed precursor layer is allowed to evaporate at a temperature higher than the condensation temperature of the precursor on the substrate of interest (3), turning off the flow of cooling element that reaches the support platform of the substrate (4), for example leaving the substrate of interest at room temperature.
In another preferred embodiment of the method of the present invention, the method comprises an additional step (a′) prior to step (a), of identifying the defective elements (7) of the substrate of interest (3) with the help of a microscope and roughing them out with the help of a focused ion beam (2).
Therefore, the method of this preferred embodiment relates to a method for depositing new elements (8) on a substrate of interest (3) (hereinafter “the method of the present invention”), by means of a device that comprises
wherein the microscope (1) and the focused ion beam system (2) are integrated into a device that contains them,
wherein there is a distance between the precursor gas injector (6) and the support platform of the substrate (4), and
wherein said method is characterised in that it comprises the following steps
Another aspect of the present invention relates to the device to rough out defective elements (7) that are located on a substrate of interest (3) and depositing new elements (8) on said substrate of interest (3) (hereinafter the device of the present invention) within a high vacuum growth chamber (9) characterised in that it comprises the following means:
wherein the microscope (1) and the focused ion beam system (2) are integrated into a device that contains them, and
wherein there is a distance between the precursor gas injector (6) and the support platform of the substrate (4).
The distance between the precursor gas injector (6) and the platform of the substrate of interest (4) influences the local pressure caused by the precursor gas on the surface of the substrate of interest (3) and, therefore, the temperature at which the condensation of said precursor gases is caused on the surface of the substrate of interest. The distance will vary as a function of the inner diameter of the precursor gas injector (6) and the distance between the end of the precursor gas injector (6) and the support platform of the substrate (4).
Throughout the description and the claims, the word “comprises” and its variants do not intend to exclude other technical features, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention may be partially deduced from both the description and the embodiment of the invention. The following examples and figures are provided by way of illustration, and are not intended to limit the present invention.
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)6, which enables tungsten W to be deposited and thus repair conductive elements.
For this, the device that is outlined in
wherein the microscope (1) and the focused ion beam system (2) are integrated into a device that contains them.
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.
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).
The substrate is cooled to cryogenic temperatures of around −100° C., causing the condensation of the precursor gas W(CO)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)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 5.5×10−4 nC/μm2. 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.
The condensation temperature of the precursor gas W(CO)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.
The following table 1 illustrates the phenomenon:
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.
We also studied the influence of the irradiation dose on the degree of porosity of the deposit: below,
Finally, we studied the influence of the irradiation dose on the electrical resistance of the deposit: in the experiment shown in
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)6.
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.
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.).
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].
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.
To verify that the “cryo-deposits” based on the precursor W(CO)6 are metal, electrical measurements were carried out, as shown in
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 (5.5×10−4 nC/μm2). We can conclude from these experiments that the process described is of high lateral resolution, reaching lateral dimensions as small as 38 nm.
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.
With an irradiation dose of 8×10−4 nC/μm2, 54 nm nanowires can be grown, with an aspect (length/diameter) ratio of 63, as can be observed in
| Number | Date | Country | Kind |
|---|---|---|---|
| P 201830757 | Jul 2018 | ES | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/ES2019/070526 | 7/25/2019 | WO | 00 |
