Patent Grant
9981471
Technical Field
The present disclosure relates to a method for the surface treatment of a substrate of semiconductor material, in particular of a nozzle plate for ink-jet printers, and more specifically to a process for application of a chemically stable antiwetting coating confined on the surface of said nozzles.
Description of the Related Art
In numerous applications, it is necessary to apply a water-repellent and/or oil-repellent coating on surfaces exposed to liquids. In the case of ink-jet printheads, for example, it is necessary to apply an antiwetting coating (AWC) on the printing nozzle plate to prevent formation of ink residue during and after ink-jet printing. In fact, the accumulation of residue around the orifice of the nozzle from which the drops of ink are expelled may alter the direction of the drop, thus causing a degradation of the quality of the printed images.
The antiwetting treatment must further be applied only on the outside the orifice of the nozzles to prevent the printing resolution from being affected and must be chemically stable if it is arranged in contact with acidic or basic solutions, as are many water-based inks, which would otherwise destroy the AWC in a short time.
The antiwetting treatment of surfaces such as silicon, glass, or other inorganic or organic substrates, may be obtained by depositing an antiwetting polymeric layer by lamination, spin coating, or chemical vapor deposition (CVD).
These treatments may offer good surface properties and excellent chemical stability, but are frequently unstable to delamination from the substrate when they are arranged in contact with the liquids. This phenomenon is due to the weak interaction of a physical type that binds together the deposited layer and the substrate. These physical interactions are in general due to hydrogen bonds or Van der Waals forces. Further, these deposition techniques may cause the AWC to be applied inside the orifice of the nozzle, thus causing alteration of the printing process.
Alternatively, an antiwetting treatment may be obtained through a coating of a chemical type by creating chemical bonds, which are stronger than physical bonds. Typically, this coating is obtained with the use of molecules such as alkyl silanes, perfuoro alkylsilanes, chlorosilanes, or alkoxy silanes.
On the silicon surfaces, for example, alkyl silanes form a uniform monolayer (with a thickness ranging from a few Angstrom to hundreds of nanometers) chemically bound to the silicon surface through a Si—O—Si bond.
The above coatings are not subject to delamination and make it possible to obtain the desired surface properties through an appropriate choice of the alkyl tail. This type of coating is, however, known to be unstable when exposed to aqueous environments, as many water-based inks. In particular, the Si—O—Si anchorage bonds are unstable in aqueous environments, above all if at a non-neutral pH.
Certain embodiments of the present disclosure provide a method for the application of an antiwetting coating that will be free from the known disadvantages and that in particular will not undergo physical and/or chemical degradation over time and when arranged in contact with acidic or basic aqueous solutions, and that will enable application of the coating in confined areas of the nozzle plate.
In particular, the present disclosure provides a method comprising:
a) applying, on at least one surface of a semiconductor material substrate, a metal layer of a material selected from the group consisting of noble metals, coining metals, oxides thereof and alloys thereof; and
b) forming an antiwetting coating by applying on said metal layer a layer of a thiol of formula R—SH, where R is a linear alkyl chain having from 3 to 20 carbon atoms and, optionally, at least one hetero-atom.
The present disclosure will now be described in detail with reference to the annexed drawings, wherein:
In particular, one embodiment provides a method for application of an antiwetting coating to at least one surface of a substrate of semiconductor material, said method comprising the steps of:
a) applying to said at least one surface a metal layer of a material selected from the group consisting of noble metals, coining metals, oxides thereof and alloys thereof; and
b) forming an antiwetting coating by applying on said metal layer a layer of a thiol of formula R—SH, where R is a linear alkyl chain having from 3 to 20 carbon atoms and, optionally at least one hetero-atom.
In the present text, by the term “noble metals” are meant metal elements that have a poor tendency to combine or react with oxygen. In particular, examples of said class of elements are gold, silver, palladium, platinum, ruthenium, rhodium, osmium, iridium and their alloys.
In the present text, by the term “coining metals” are meant those metal elements that may be used as components in alloys used for coining. In particular, examples of these metals are copper, zinc, iron, tin, nickel, chromium, titanium, aluminum, antimony, and the metals of Group II of the Periodic Table and their alloys.
Examples of noble or coining metals, their oxides and their alloys according to the present description are silver, gold, copper, palladium, platinum, mercury, ruthenium, nickel, titanium, indium, zinc, their oxides and alloys, in particular, TiO2 and indium tin oxide (ITO).
The present method is based upon the process of reaction between a noble or coining metal, or an oxide or alloy thereof with a thiol.
In particular, with the method described it is possible to create an antiwetting monolayer formed by the hydrocarbon chains of the thiol, characterized by a strong bond formed between the thiol (—SH) and the metal layer (e.g., the noble metal) on the substrate of semiconductor material. The antiwetting monolayer thus obtained is densely packed, with the hydrocarbon chains of the thiol that have an orientation that is inclined and orderly with respect to the surface of the substrate. Said monolayer prevents oxidation of the substrate and is stable in regard to acidic and basic solvents.
The present method further provides application, in a confined way on the substrate, of the antiwetting monolayer having appropriate chemical stability. For instance, in the case of application on an ink-jet printhead, unlike the methods known in the art, the present method enables confinement of application of the antiwetting layer only around the orifices of the nozzles, without involving or contacting the openings through which the ink is expelled.
Finally, the present method enables a simple adaptability to mass-production processes.
For instance, the substrate of semiconductor material is a silicon substrate. In particular, the substrate of semiconductor material may be a nozzle plate for ink-jet printing, as described hereinafter with reference to
The thiol used is a compound of formula R—SH, where R is a linear alkyl chain containing from 3 to 20 carbon atoms, in particular from 8 to 20 carbon atoms. An example of thiols that may be used is dodecanethiol.
The hydrocarbon chain of the thiol may further contain hetero-atoms or be functionalized to bestow upon the surface on which it is applied the desired chemical properties.
Application of the metal layer may be carried out by evaporation or sputtering according to methods known in the art. In the tests conducted thermal evaporation in a vacuum has been used for depositing gold on the surface of the substrate.
By way of example, a layer of gold 20 nm thick may be deposited by thermal evaporation at 10−6 mbar and at a rate of 0.5 nm/s.
Application of the layer of thiol is carried out by dipping the substrate of semiconductor material provided with the metal layer in a solution of thiol, in particular in an ethanol solution of thiol. Alternatively, the thiol may be deposited using CVD techniques.
The present method will now be described with reference to
As illustrated in
On the surface 7 of the substrate 1, a metal layer 2 of a noble metal, for example gold, is deposited using an evaporation technique (
After application of the metal layer 2, the substrate 1 thus obtained (
In this way, as illustrated in
In another embodiment, illustrated in
As illustrated in
On the surface 17 of the substrate 11 a metal layer 12 of a noble metal, for example gold, is then deposited using an evaporation technique (
After application of the metal layer 12, through openings 8 are made in the plate 11 in an area corresponding to the outlet channel 62 for the ink for obtaining the nozzles 56 (
The substrate 11 thus obtained (
In this way, as illustrated in
This is made possible thanks to the selectivity of the reactivity of thiols in regard to gold, and not in regard to silicon.
The above method may be used for deposition of an antiwetting layer on a nozzle plate for an ink-jet printhead of any commercially available type.
According to a further embodiment, a nozzle plate of an ink-jet printhead is provided, which presents an antiwetting layer that is chemically stable and confined on a surface thereof.
With reference to
The top surface of the nozzle plate 55 has an antiwetting layer 68, obtained with the method described with reference to
Further characteristics of the present method will emerge from the ensuing description of some merely illustrative and non-limiting examples.
The first step of the process consisted metallization of a silicon substrate of dimensions of 4 cm×4 cm.
In detail, a layer of gold 20 nm thick was deposited via thermal evaporation at a pressure of 10−6 mbar and a rate of 0.5 nm/s.
The substrate thus obtained was dipped for 30 s in a 0.8 mM solution of ethanol and dodecanethiol.
The substrate was then taken out of the solution and washed in pure ethanol to remove the thiol that had not reacted.
The performance of a plate obtained according to the method illustrated in Example 1 was evaluated as regards its antiwettability.
Three identical plates (specimens 1-3) having dimensions 40×12 mm were each introduced into a vial containing a water-based ink and containing the cyan pigment having a pH comprised between 7 and 9.
Each plate was for two thirds immersed in the ink. The vials were then closed to prevent evaporation of the ink and set at a temperature of 60° C. for 7 days.
Next, the plates were removed from the vials and cleaned with demineralized water and then with 2-propanol. The plates were then dried.
The antiwettability of the plates thus obtained was evaluated by measuring the angle of contact of a drop of water deposited thereon. In particular, comparisons were made of the values of the angle of contact on the plate prior to application of the antiwetting layer according to the method described (Angle of contact prior to application of the layer of gold-thiols), of the angle of contact on the plate after application of the antiwetting layer according to the method described (Angle of contact after application of the layer of gold-thiols) and of the angle of contact on the plate after dipping in ink. A higher contact angle indicates higher antiwetting capability. The results obtained are presented in Table 1 below.
As may be noted, notwithstanding the fact that the plates were dipped in a particularly aggressive ink, the values of the angle of contact remained very high (90% of the values after application of the layer of gold-thiols), indicating the superior chemical resistance of the coating obtained with the method according to the disclosure.
Comparison with Silane-Based Coatings of the Prior Art
A plate according to Example 2 (specimen 1) was compared with plates that have a coating obtained by silanization, as is known from the prior art.
In particular, the following specimens were obtained, which present silane coatings:
Specimen 4: plate coated with PFOTS (1H,1H,2H,2H-perfluorooctyltrichlorosilane);
Specimen 5: plate coated with silane Fluorolink S10 (Solvay)
Specimen 6: plate coated with PTMS (propyltrimethoxysilane)
Also in this case, the antiwettability was evaluated by measuring the angle of contact of a drop of water deposited on the specimens. The results appear in Table 2.
It was further observed that after dipping in ink, Specimen 1 according to an embodiment of the present disclosure largely maintained the antiwetting capability (indicated by a slight reduction of the contact angle). In contrast, Specimens 4-6 exhibited much reduced contact angles after dipping ink. The results of Table 2 demonstrated that the antiwetting layer obtained with the method described, even though it presents an initial angle of contact comparable to that of the coatings of the prior art, proves much more stable after coming into contact with the ink.
Moreover, the method described enables application of the coating in an extremely confined way, unlike the dipping method.
Evaluation of the Selectivity of the Reactivity of the Thiols in Regard to Gold
To check that the thiols bonded in a selective way to a metal layer and not also to the silicon substrate, the following experiment was carried out.
Three silicon substrates (specimens 7-9) of dimensions 4×4 cm were dipped for 30 s in the 0.8 mM solution of ethanol and dodecanethiol.
The supports were then taken out of the solution and washed in pure ethanol.
Also in this case, the antiwettability was evaluated by measuring the angle of contact of a drop of water deposited on the specimens. The results appear in Table 3.
As may be noted, treatment of the silicon substrates with the thiol solution leaves their angle of contact unchanged. This demonstrates that thiol does not bind to silicon surfaces, the angle of contact of which thus remains unchanged. Consequently, in the production of a nozzle plate according to the method described, the deposition of the thiol by dipping in a thiol solution will exclusively regard the areas in which the metal layer has been previously deposited and not the free silicon surfaces, such as for example the nozzles of the nozzle plate.
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| 102015000088126 | Dec 2015 | IT | national |
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