Patent Application
20210146716
The present invention relates to the field of marking of solid state materials, and more particularly to the marking of gemstones including diamonds.
Gemstone identification and grading has been long-established by international standards laboratories including GIA, IGI, Gem-A and NGTC. The identification and grading result is typically stored in an electronic media such as hard-disks, tapes, compact discs and the like, and a paper certificate is issued along with the corresponding gemstone.
When the certificate is lost, or when the gemstone is mixed with other gemstones, the identity of the gemstone is lost, and is required to be recertified.
The direct marking of gemstones including diamonds is a generally straight-forward method to avoid such circumstance and allows for re-identification.
Conventional techniques within the art for the marking of gemstones including diamonds include laser marking and ion beam marking.
However, when using laser marking, generates coarse patterns and leaves unrecoverable ablation marks on the gemstone, causing permanent damage and can devalue the gemstone.
When using ion beam marking, such a technique can be used to inscribe fine patterns on the surface of the gemstone which can be 1000 times smaller than those using laser marking, however the process is typically relatively slow and requires precision.
Other than item identification, gemstone marking can provide traceability of an item such that its origin, its owner, and its features and the like. Such marking techniques can also assist in the prevention of the counterfeiting of precious articles such as artworks or jewellery, and be of assistance in the incident of theft.
It is an object of the present invention to provide a process for the marking of solid state materials, including gemstones and an identification marking which overcomes or at least partly ameliorates at least some deficiencies as associated with the prior art.
In a first aspect, the present invention provides a method of forming a non-optically detectable identifiable marking invisible to the naked eye, said marking is formed from a plurality of recesses of multiple levels at an outer surface of an article formed from a solid-state material, and said method including the steps of:
The marking may be viewable by use of a 10× loupe or a 20× loupe. Alternatively, the maximum width of the etched portions of the article less than 200 nm such that the identifiable marking is non-optically detectable in the visible light spectrum.
The plurality of recesses may extend through the photoresist and so as to provide one or more apertures therethrough and providing one or more exposed portions of said outer surface of the article prior to application of the etching process, such that etched portions corresponding to the one or more apertures have depths into the article of approximately the same depth.
The recesses may extend through the photoresist at varying depths to each other prior to application of the etching process, such that the etched portions have varying depths into the article.
The grayscale lithography process may use masks with holes of different sizes and shapes.
The grayscale lithography pattern is preferably generated by laser interference lithography.
The grayscale lithography pattern may be generated by direct laser writing in the photoresist.
The recesses of said plurality of recesses maybe arrange in a periodic and uniform arrangement with respect to each other within said predetermined region of a photoresist. Alternatively, the recesses of said plurality of recesses are arranged in a non-periodic and non-uniform arrangement with respect to each other within said predetermined region of a photoresist.
The photoresist may have a uniform thickness, or may have a non-uniform thickness.
The outer surface of said article may be a flat surface, or may be a non-flat surface.
The recesses of said plurality of recesses may be of the same width, or said plurality of recesses may have non-uniform widths.
One or more recesses may be formed from a plurality of adjacent recesses.
Preferably, the etching process is a plasma etching process.
One or more recesses of the plurality of recesses may be inclined with respect to the outer surface of an article.
One or more recesses of the plurality of recesses may be curved in at least one plane with respect to the outer surface of an article.
The solid state material is preferably selected from the group of gemstones consisting of diamond, pearl, silicon, and synthetic sapphire.
In a second aspect, the present invention provides an article formed from solid state material having a non-optically detectable identifiable marking thereon which is invisible to the naked eye, wherein said non-optically detectable identifiable marking is applied to said solid state material by the method according to the first aspect.
The solid state material is preferably selected from the group of gemstones including diamond, pearl, silicon, and synthetic sapphire.
The marking may be viewable and inspected by use of a 10× loupe or a 20× loupe. Alternatively, the marking may be non-optically detectable under the visible light spectrum.
In order that a more precise understanding of the above-recited invention can be obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. The drawings presented herein may not be drawn to scale and any reference to dimensions in the drawings or the following description is specific to the embodiments disclosed.
The accompany drawings illustrate the present invention and explain its principle. In the drawings, like reference numbers refer to like parts throughout:
In order that a more precise understanding of the above-recited invention can be obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. The drawings presented herein may not be drawn to scale and any reference to dimensions in the drawings or the following description is specific to the embodiments disclosed.
The present invention is directed to a method to provide a non-optically detectable identification marking at an outer surface of an article formed from a solid-state material. Although the description and examples as follows is directed to the marking of gemstones, in particular diamonds, the present invention is applicable to the marking of the surface of any solid-state material.
The process of a marking on a surface of an article of solid state material in accordance with the present invention consists of two process steps:
The mask is comprised of a plurality of recesses formed within a predefined region of a photoresist which is applied to an outer surface of the article.
The plurality of recesses is formed by grayscale lithography, and one or more recesses extend at least partially through the photoresist from an outer surface of the photoresist and towards said outer surface of the article formed from a solid-state material upon which the mask is applied.
The etching process is plasma etching, which can be microwave plasma etching, reactive-ion etching (RIE), or inductively-coupled plasma (ICP) etching.
The etching process removes at least a portion of the outer surface of said article to form a plurality of etched portions extending into the article from the outer surface of the article and corresponding to said plurality of recesses which are formed in the photoresist.
Advantageously, the present inventors have utilized properties of grayscale lithography to provide the photoresist provided at the outer surface of the article from a solid-state material to be of uneven thickness at a predefined area. As such, the patterns to be created are in multi-level, or, two and a half-dimensional (2.5D).
The etching process then removes the material at the surface of the article at a constant rate, regardless of whether the material is photoresist or the substrate.
This results in a plurality of etched portions at the predetermined region of said photoresist, forming the non-optically detectable identification marking on the outer surface of the article.
In embodiments of the invention, the maximum width of the etched portions of the article can be less than 200 nm, so that the marking is non-optically detectable under the visible light spectrum, and does not change the appearance of the article or result in a marking which is unsightly. Such marking being non-optically detectable is termed an “invisible marking”.
Referring to
In grayscale lithography, the selection of a photoresist is critical and paramount. In conventional photolithography, an ideal photoresist is required to have a distinct response upon exposure. The photoresist is chemically changed when exposed to radiation such as UV or visible light, regardless the intensity of the illumination. This type of response is required to fabricate patterns with high dimensional accuracy and with high contrast.
Referring to
However, such high exposure may damage the substrate or article to which the marking is to be applied, and the patterns created is typically limited to two-dimensional patterns.
The photoresist used in grayscale lithography may have several features. Firstly, instead of having a sharp response curve which is favored in convention lithography, the photoresist is preferred to have a wide exposure dose window so the development rate can be controlled by the exposure dose. Such response behavior is illustrated by the response curve 102 of
Another characteristic of the photoresist used in grayscale lithography is that the photoresist may change its absorptivity or transmissivity upon exposure. In one example to illustrate this property, a photoresist AZ 9260 is semi-transparent to UV and the typical penetration depth for UV exposure is 1 to 2 microns.
Under a UV exposure dose, the absorptivity of the photoresist changes such that said photoresist becomes transparent. Another term to describe this behavior is “photo-bleached”. When the top layer of said photoresist is bleached, the UV exposure can reach deeper into the photoresist to continue the reaction.
The development of common photoresists and photoresist for grayscale development is illustrated in
By contrast, in grayscale intensity, the development rate is controlled by the exposure dose E, which can be expressed as:
E=|t,
where | is the exposure flux and t is the exposure time.
This concept is demonstrated and depicted in
Referring to
Referring to
For an excitation source that has a large illumination area, or non-adjustable intensity and timing, the pattern cannot be generated by directly exposing the photoresist to the excitation source. As such, grayscale mask is needed to control the exposure dose to the photoresist.
A method to implement this control is shown in an embodiment in which the dose is adjusted by the size of the holes across the photoresist mask which is placed in between the illumination and the substrate coated with photoresist as represented and depicted in
As shown in
Referred back to the exposure dose expression, this grayscale mask approach varies the exposure flux I to the photoresist upon being exposed by excitation 302, so that development rate is different at different portions of the photoresist 304 on the substrate 305. The final pattern is a step-wise structure as shown.
One short-coming of this mask-approach to create a 2.5D pattern is that the resolution of the final pattern is limited by the fabrication method and quality of the mask.
Even if a technology can create a mask of high resolution, the diffraction of excitation at the tiny hole has to be taken into consideration because this destroys the resolution.
Therefore, a more practical approach for grayscale lithography is to use an excitation source in which the intensity and the timing of said excitation source can be adjusted.
A light amplification by stimulated emission of radiation device, generally known as laser, is a common solution to this application.
Nowadays, the intensity of a laser radiation can be easily adjusted for any lasing devices, and the size of the laser spot can be focused down to the micron scale with appropriate set of lenses.
Then the flux I can be tuned with a correct set of parameters. For the exposure time t, ultrafast lasers can generate laser pulse in femtosecond time scale. By controlling the number of laser pulse to be fired, the exposure time t can be fine-tuned in a time scale of femtosecond. This implies an ultra-high resolution of the exposure dose to the photoresist.
In grayscale lithography, exposure of photoresist by direct laser writing is a common approach, however the exposure of the photoresist can be done by other optical techniques.
Laser interference lithography is another approach to expose photoresist for grayscale lithography, and this principle is illustrated in
These two split beams are directed to different paths for modulations. The reference beam 401 is irradiated directly to photoresist 405, while the other beam 402 is directed to a set of optical modulation components 403 and emitted as beam 404 wherein the phase and/or the intensity are changed.
The beam 401 and beam 404 recombine and interfere. The resultant beam has an uneven intensity distribution across the surface of the photoresist 405 on the substrate 406. This variation of exposure flux I induced different exposure doses to the photoresist 405 and creates 2.5D pattern on the photoresist 405 after development.
Another feature of grayscale lithography is that the pattern of the photoresist can be generated on a substrate with non-flat or uneven surface as depicted in
In conventional lithography, the thickness of the photoresist layer being coated on the substrate is typically uncontrollable for a non-flat or uneven substrate surface. As conventional lithography cannot precisely control the depth of the exposure and the development rate, an accurate pattern cannot be written precisely on the photoresist in technique of the prior art.
The use of grayscale lithography provides a solution of developing photoresist on a non-flat substrate surface. As shown in
Once a photoresist masked with desired patterns is prepared, the sample substrate is then ready for the next process step in which the sample substrate is etched to remove the photoresist and a very thin layer of material from the surface of the substrate so as to form the marking in accordance with the present invention.
Referring to
Firstly, as shown in
Referring to
The next process step is whereby plasma etching is applied to the surface of the substrate of the solid-state material 602. The unexposed photoresist 604 acts a protective layer on the surface of the designated region of the solid-state material 602. Since plasma etching can be a non-selective process, the material at the surface of the solid-state material 602 will be remove at a constant rate regardless of position. Therefore, the photoresist layer 601 will be removed first before the material of the solid-state material 602 underneath it. By controlling the exposure dose 605, desired 2.5D pattern can be formed on the surface 606 of the substrate of the solid-state material 602 as shown in
In reactive ion etching (RIE) processes, a typical plasma etching technique, large numbers of ions are produced that are accelerated towards the target to remove material by sputtering and related processes. Such a process is known to have low selectivity.
In comparison to RIE, inductively-coupled plasma (ICP) etching is a chemical process in which a plasma is used to breakdown the etching gases into a mixture of free radicals and ions. As such, whilst other etching processes may be implemented within the present invention, ICP etching is chemical etching process which has a higher selectivity, and is a preferred etching technique in preferred embodiments of the invention.
The present invention provides for the marking of a solid state material, in particular marking of a gemstone including diamonds.
To increase the security in maintaining the identification of gemstones including diamonds, the technical challenge to fabricate and inscribe the marking has to be increased.
The present invention provides for a new process to create a non-optically visible identifiable mark. The marking pattern created with this method is in multi-level which significantly increases the difficulty of counterfeit, allows more flexibility and uniqueness in pattern design, as well as enhances the amount of information to be inscribed by such a mark.
The marking can be made sufficiently small so as to be invisible to the naked eye, and so as not to alter the optical properties of the article to which it is applied, such as a gemstone, in particular a diamond.
In some embodiments of the invention, a marking may be applied which may be viewable and inspected by use of a 10× loupe or a 20× loupe.
In some embodiment of the invention, a marking may be applied which may be non-optically detectable under the visible light spectrum.
Particular advantages of the present invention include:
Such advantages provide enhanced security, and provides significant technical impediments for the reproduction of the marking and as such, provides enhanced anti-counterfeiting attributes.
The marking method and marking from such method of the present invention provides the following further advantages:
It should be noted that although the marking is of a general three-dimensional structure, the term “2.5D” or “two and a half dimensions” is used, as will be known by those skilled in the art to pertain to a structure which although can have varying heights, does not include “undercuts”. As such, the term “multi-level” is considered synonymous with 2.5D. It should also be noted that “multi-level” also includes inclined surfaces, and that the surfaces of the marking of the present invention need not be parallel with each other, and may be curved in one or more planes.
It should be noted and understood that the embodiments of the present invention illustrate the idea and principle, not limitation. In these embodiments the methodology and the implementation mechanism may be modified or substituted for an efficient presentation without departing from the scope of the invention. Thus, the appended claims are not to be limited by the embodiments.
The term “marking” is used throughout the description and claims, and such a “marking” will be understood by those skilled in the art to pertain to a “mark” provided to the surface of an article, and the terms are synonymous with each other and may be used interchangeably without alteration of meaning or interpretation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18102632.0 | Feb 2018 | HK | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2019/075953 | 2/22/2019 | WO | 00 |
