Patent Publication Number: US-2016244871-A1

Title: Multi-source gis for particle-optical apparatus

Description:
BACKGROUND OF THE INVENTION 
     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 mm 2  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
         Mixing occurs after exiting the nozzles,   No shadowing occurs,   When tilting the sample the distance between the sample and each of the nozzles is identical (although maybe different from the distance before tilting),   The nozzles can be positioned close to the sample.       

     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 (MeCpPtMe 3 ) while directing a jet of oxygen with a much higher flux (J ox /J prec &gt;10 2 , preferably J ox /J prec &gt;10 4 ) platinum tracks with low resistivity (ρ&lt;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 O 2 , H 2 O) or a reducing fluid (for example H 2 ). 
    
    
     
       The invention is now elucidated using figures, in which identical reference numerals refer to corresponding features. To that end: 
         FIG. 1  shows a schematic drawing of an add-on dual nozzle, 
         FIG. 2  shows a micrograph of the add-on nozzle of  FIG. 1 , and 
         FIG. 3  shows a micrograph of a detail of  FIG. 2 . 
         FIG. 4  shows an arrangement used for depositing high purity metals. 
         FIG. 5  shows a schematic front view of other types of nozzles. 
     
    
    
       FIG. 1  shows a schematic drawing of an add-on dual nozzle. 
       FIG. 1  shows an existing single channel needle  102  (also referred to as a single channel nozzle) to which an “add-on” nozzle is attached. Not shown, but clear to the skilled person, is that the existing single channel needle is connected to a position unit for finely positioning the needle with respect to a sample. The “add-on” nozzle has an outer body  104  removably attached to the existing single channel needle  102 . The outer body of the add-on is connected to an outer nozzle  106 , which allows the outflow of gas  112  flowing through the single channel needle  102 . Gas inlet  110  is connected via a hose (not shown) to a gas reservoir. It is connected via a channel to nozzle  108 . The nozzle  108  protrudes through outer nozzle  106 . As a result the gas  114  flowing though nozzle  108  is surrounded by a gas envelope flowing from the nozzle  106 . At the sample these gasses will have mixed. 
     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 . 
       FIG. 2  shows a micrograph of the add-on nozzle of  FIG. 1 . This dual nozzle is made using 3D printing of titanium. 
       FIG. 3  shows a micrograph of a detail of  FIG. 2 . 
       FIG. 3  shows the inner, protruding, nozzle  108 , surrounded by the outer nozzle  106 . Between these nozzles an outflow opening  304  is visible, through which the gas supplied by the needle  102  (see  FIG. 2 ) can flow. The inner nozzle has a central opening  302  through which the gas supplied via gas inlet  110  (see  FIG. 2 ) can flow. 
     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 MeCpPtMe 3 ”, Nanotechnology 24 (2013) 145303 (7 pp), further referred to as Mehendale et al., describes a Pt layer deposited with an electron beam using MeCpPtMe 3  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 O 2  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 O 2 . 
     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. 
       FIG. 4  shows an arrangement used for depositing high purity metals. 
       FIG. 4  shows an inner nozzle with an opening  402  and an outer nozzle with an opening  403 . From these openings a gas flow is directed to a sample  401 . The outer nozzle has a low flux of precursor gas exiting the outer opening. Because of the low flux the amount of gas introduced to evacuated volume in which the process takes place is limited. It is noted that the gas directed to the sample adhere to the sample, but after a time leave the sample to be evacuated by vacuum pumps. The concentration of precursor gas adhering to the surface of the sample is schematically given by curve  406 . This shows a lopsided curve, as the nozzle is placed off-axis. The minimum near the middle of the curve is due to shadowing of the outer nozzle by the inner nozzle. However, only where the beam of energetic electrons  404  hit the sample surface, precursor molecules are dissociated. Here a high concentration of for example oxygen is realized by directing a beam of molecules from nozzle opening  402  at a high flux. The high flux, together with the small distance of the opening to the sample, results in an excess of oxygen where the beam hits the sample (concentration of oxygen schematically shown as curve  405 ). It is noted that the excess of precursor molecules at other positions is not a problem, as these molecules are only adsorbed, and desorb from the sample intact. 
     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 CO 2  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. 
       FIG. 5  shows a front view of other types of nozzles. 
       FIG. 500 a    shows a front view of the nozzle with two concentric outflow openings, an inner opening  402  and a surrounding, outer opening  403 . 
       FIG. 500 b    shows a front view where a third outflow opening  502  surround the openings  402  and  403 . 
       FIG. 500 c    shows a front view where an outflow opening  504  and an outflow opening  506  are spaced round central opening  402 . 
     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.