Patent Application
20160244871
The invention relates to a Gas Injection System (GIS) for applying at least two fluids in the vacuum chamber of a particle-optical apparatus, the gas injection system having two or more channels, each channel connected to an associated reservoir holding a fluid at a first side and having an associated exit opening at the other side.
The invention further relates to a method using said GIS.
Such a GIS is described in Nanofabrication using focused ion and electron beams, Ed. Ivo Utke, et al., ISBN 978-0-19-973421-4, more specifically in chapter 3.7.2.3: multi-nozzle (pages 173-175).
A GIS is used to process a sample, such as a silicon sample.
The processing may be Ion Beam Induced Deposition (IBID), where a focused ion beam is directed to the sample and the gas adhered to the sample is split in a part deposited on the sample surface and a, typically gaseous, by-product.
Likewise in Electron Beam Induced Deposition (EBID) a focused electron beam is directed to the sample and the gas adhered to the sample is split in a part deposited on the sample surface and a gaseous by-product.
Not only deposition, but also gas assisted etching or milling are known to be used.
The before mentioned book chapter mentions that “for sophisticated focused-beam processing, multi-GISs are preferably used, allowing mixing of multiple precursor gases locally in the vacuum chamber above the processing area. This avoids mixing of reactive gases at higher densities inside the supply tubes. Typically, such systems are intended for complex gas chemistries for beam-induced processing.”
The book chapter further mentions that a problem that may arise is “gas shadowing effects” on uneven surfaces. A solution to that is the NanoChemix™ marketed by FEI Company, Hillsboro, Oreg., USA. Here three nozzles are used for applying two gases. Two needles (nozzle) are opposing each other and are used for one gas (fluid) and the third needle is used to apply the other gas (fluid), for example a precursor for metal deposition. This not only avoids gas shadowing effects, but also “maintains more homogeneous gas coverage leading to a better floor uniformity or planarity of the processed structure”.
It is noted that the precursor is responsible for deposition, but another gas may be used for, for example, in-situ cleaning, for example to remove carbon contaminants by oxidizing, or in-situ reduction.
When using a single needle, it is common practice to position the exit opening (the nozzle) as close as possible to the target (the sample). In that way only a small area of the sample is exposed to gas and little gas is needed, resulting in a relatively low background pressure of the vacuum chamber where the processing takes place. Distances of 0.5 mm or less from nozzle to sample are commonly used.
When using two opposing nozzles it is implicit that the beam (a focused ion beam or an electron beam) is directed to the sample and hits the sample between the two opposing nozzles. The three nozzles are placed on a circle, the two opposing needles are 0° and 180°, the third needle at 90°, and the beam passing through the center of the circle.
This in turn implies that the nozzles are placed at a distance large enough to let the beam pas between them. A typical distance of at least 1 mm should be kept between the nozzles. This relatively large distance means that a spot of at least 1 mm2 is covered with gas, resulting in a corresponding higher background pressure.
Another problem occurring with the three-nozzle approach is that tilt is limited: not only is tilt physically limited by the two opposing nozzles, but even more so by the third nozzle. Another problem is that when tilting the distance between sample and the nozzles changes unevenly (unless the cluster of needles is tilted as well, resulting in a complicated system).
There is a need for a multi-GIS system where
More specifically there is a need to upgrade an existing single channel GIS to a multi-GIS system.
The invention addresses at least in part said problems.
To that end at least two exit openings are separated by less than the diameter of the channels near the exit openings.
Inventors found that when the nozzles are sufficiently close together, for example less than the diameter of one of the channel, no shadowing occurs, and also the tilt limitations are much reduced. If the channels have different diameters, then the diameter of the thickest channel is leading.
In an embodiment the GIS of claim 1 in which one of the exit openings is at least partly concentric with another exit opening.
By making the openings concentric to each other, no shadowing occurs. Although concentric nozzles may seems hard to make, by using additive manufacturing techniques (“3D printing” of titanium) making of such concentric nozzles proved to be well possible. It is noted that this embodiment also works when a part of the outer channel is blocked, and the outer nozzle thus not completely surrounds the inner nozzle.
In a preferred embodiment one of the exit openings is concentric with another exit opening and the inner exit opening protrudes through the outer exit opening.
A protruding inner nozzle minimizes mixing and back-streaming of the gas used for the inner nozzle into the outer nozzle.
In another embodiment the fluids are, in working, mixed after exiting the exit opening.
To avoid reaction of the gases in the channels the fluids (gases) should mix after exiting the nozzle. Such reaction could give rise to clogging, heating, and other unwanted effects.
In another embodiment a first channel is connected with a positioning unit for positioning the GIS, and at least one other channel is detachably mounted on the first channel.
Using additive manufacturing techniques inventors were capable to make an ‘add-on’ nozzle that can be mounted on an existing single channel system. This makes it possible to upgrade existing systems.
In yet another embodiment a particle-optical apparatus is equipped with a GIS according to the invention.
In an aspect of the invention a method of using a GIS according to the invention is characterized in that at least two fluids are delivered at a flux differing at least two orders of magnitude.
Inventors found that with a prototype of this concentric nozzle it was possible to deliver gases with highly different flux to the sample. As a result a single step process can be used to apply a platinum precursor (MeCpPtMe3) while directing a jet of oxygen with a much higher flux (Jox/Jprec>102, preferably Jox/Jprec>104) platinum tracks with low resistivity (ρ<100 μΩ·cm) were obtained, indicating a high purity and dense (void free) structure of the tracks.
In an embodiment of the method a first fluid is a precursor material and a second fluid is reactive to at least one breakdown product of the precursor material.
Preferably the second fluid is delivered with the highest flux.
The second fluid may be an oxidizing fluid (for example O2, H2O) or a reducing fluid (for example H2).
The invention is now elucidated using figures, in which identical reference numerals refer to corresponding features. To that end:
It is noted that, although in this schematic drawing the parts 104/106 and 108/110 are shown as separate parts (different shading), in a preferred embodiment all these parts are one part, formed by added manufacturing (“3D printing”).
It is further mentioned that in the above paragraphs the words channel and nozzle are used interchangeable to describe the same items.
It is noted that the inner nozzle 108 need not protrude through nozzle 106, but that slight back-streaming may then be expected, possibly resulting in the formation of reaction products inside nozzle 106.
The presence of two concentric, or at least closely spaced, nozzles, enables two gasses (or fluids) to be applied simultaneously without shadowing to occur. It also enables a first gas to be applied at a first flux and a second gas to be applied with a much higher flux, for example with a flux two orders of magnitude (thus: 100×) higher than the first flux.
As known to the skilled person a deposition of a material, for example a metal, often contains a large fraction of contaminants, such as carbon, due to the fact that not all residual material are turned in volatile by-products. By a post-treatment of a sample with for example oxygen exposure while directing a beam of electrons to the sample, part of these contaminants are removed. As an example: Mehendale S. et al., “A new sequential EBID process for the creation of pure Pt structures from MeCpPtMe3”, Nanotechnology 24 (2013) 145303 (7 pp), further referred to as Mehendale et al., describes a Pt layer deposited with an electron beam using MeCpPtMe3 as a (platinum) precursor. The resistance of a track was measured to be 107 μΩ·cm. EDX analysis showed a large amount of carbon in the deposit. Post-treatment with oxygen while irradiating with electrons resulted in a drop of resistance to 88+/−10 μΩ·cm. However, inspection showed that the deposited metal was not void free.
This two-step method, although giving good results, is time consuming.
By applying the same precursor and under comparable conditions, the precursor flowing from the outer nozzle and O2 at a much higher flux from the inner nozzle resulted in a track with a specific resistivity of 60+/−5 μΩ·cm.
This compares qualitatively favorably to the results of the two-step method as described by Mehendale et al. and it is also a much quicker method, as it eliminated the positioning of the second GIS providing the oxygen and the following processing step with O2.
The invention thus enables a quicker processing (purification) of deposited materials in which, for example, carbon contamination is present.
Likewise one-step processing can be performed with a reducing gas instead of an oxidizing gas. Simultaneous with two needles: also good, difficult to position, not completely void free, slightly higher resistance.
The result of this is that all carbon reacts with the oxygen (which is dissociated at the beams interaction position as well) and form volatile CO and CO2 molecules, which desorb from the sample surface. The resultant deposit proved to be homogeneous (void free) and showed a low specific resistance.
It is noted that, although the example given in the above, explains the invention using a platinum precursor and oxygen to form volatile by-products, the skilled person will recognize that other precursors and other oxidizing or reactive materials can be used. Also, the example worked at room temperature, but the invention works equally well with other gasses at other temperatures.
The invention has been elucidated for one inner nozzle and a concentric outer nozzle. The skilled person recognizes that similar results can be obtained by multi-nozzle design in which three or even more nozzles are concentric to each other, or where two nozzles surround the inner nozzle. In the latter case slight shadowing can be expected.
Many more options will be clear to the skilled artisan.
It is mentioned that the invention is explained using an add-on nozzle, enabling to upgrade an existing GIS to a GIS with, for example, concentric nozzles. It will be clear how to implement a non-add-on version.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15156537.1 | Feb 2015 | EP | regional |
