EA015000B1 - Method for applying polyethylene on silicon and silicon optical element with polyethylene antireflecting coating applied by said method - Google Patents

Abstract

A thermo-mechanical method is disclosed for applying polyethylene coating on silicon characterized in that silicon and polyethylene surfaces are joined and the joined surfaces are slowly heated to a temperature above 150°C. For providing sufficient adhesion an air gap between silicon and polyethylene is mechanically removed after which the joined silicon/polyethylene structure is placed into a capacity with a temperature below 100°C. After cooling down slowly to an ambient temperature an optical element is removed therefrom as a target article. There also described a silicon optical element with an antireflecting coating applied by the above method.

Description

FIELD OF THE INVENTION

The invention relates to the field of optical and optoelectronic technology, in particular to optical coatings, and can be used to create transmission optical elements (OE) of silicon with antireflection coatings for the terahertz (THz) radiation region (ν = 0.1 - 10 THz or λ = 30 - 3000 microns), which can be used in terahertz optoelectronics.

State of the art

Silicon is widely used in optical instrumentation, including devices and devices of the THz range as the basis for OE. When radiation is transmitted through such OEs due to the high refractive index of silicon in this range (n = 3.42), the reflection loss is very high, on average, about 46% for two surfaces. For individual sections of the infrared (IR) range, antireflection coatings are made by applying to the silicon surface coatings made, for example, of zinc selenide Ζηδο (n = 2.4) or zinc sulfide Ζηδ (n = 2.2), see patent KI 2097801. In addition to these coatings from the prior art, other coatings are known for the THz range, for example, from parylene, however, the disadvantage of these coatings is that their application technologies are quite complex and expensive, while in most cases a simpler and faster production is required antireflective coatings.

In connection with the foregoing, an urgent task is the application of antireflection coatings on silicon products that provide a high level of transmission of THz radiation (for example, over 85%), using relatively simple technologies, and at the same time, the task of ensuring satisfactory adhesion of the coating to silicon surface. The material used for the manufacture of coatings should be transparent in the THz region, have a refractive index in the range η = 1.1 - 1.85, and good adhesion to silicon. To find a material that would meet the specified requirements and at the same time the technology of manufacturing coatings from it on silicon would be simple and inexpensive, it is quite difficult. Japanese Patent 1P 6132551 discloses a method for attaching a metal conductor to a silicon wafer with glue, the conductor and part of the silicon wafer being coated with polyethylene film. The document does not disclose a method of fixing polyethylene to silicon, which provides satisfactory adhesion of polyethylene to silicon, which, apparently, in this case does not have much significance, since the conductor is attached to silicon and polyethylene with glue, thereby ensuring reliable retention of polyethylene. In addition, the optical properties of such a compound are unknown, i.e., the transmission level of optical radiation in the THz range. Nevertheless, polyethylene is one of the most promising materials for use as an antireflective coating, since it has a refractive index of n = 1.54, transmits THz radiation well (see Fig. 1), and is a widely used material with a low cost price.

SUMMARY OF THE INVENTION

The objective of the present invention is to develop a simple technology for applying polyethylene to silicon, providing satisfactory adhesion and a high level of transmission of optical radiation, as well as providing an optical element made of silicon, which is coated with an antireflection coating of polyethylene with satisfactory adhesion and a high level of transmission of optical radiation.

The objective of the invention is solved using the thermomechanical method of applying a polyethylene coating to silicon, which is as follows: connect the surface of silicon and polyethylene and then the combined silicon and polyethylene are slowly heated to a temperature above 150 ° C, after which the combined silicon and polyethylene are transferred to a volume with a temperature below 100 ° C. After slowly cooling the combined silicon and polyethylene to room temperature, they are recovered as a finished product. Polyethylene in one embodiment is heated to a temperature in the range from 170 to 200 ° C. In a preferred embodiment, it is from 180 to 190 ° C. The movement of polyethylene in one embodiment can occur in a volume with a temperature in the range from 70 to 90 ° C, in the preferred embodiment, it is 80 ° C. Heating and cooling are preferably carried out in furnaces, the furnace used for heating is preferably a muffle. The heating rate is preferably 3-5 ° C / min.

Before applying polyethylene to silicon, it is desirable to purify silicon, for example, by chemical means.

In an advantageous embodiment, when a silicon wafer with a film polyethylene reaches a temperature of 100 ° C. during heating, the polyethylene is pressed against the silicon surface, preferably by rolling with a roller. The roller can be made of Teflon or glass. In the event that air bubbles have formed, they can be eliminated by rolling at a temperature of 110-130 ° C during heating. In one embodiment, at a temperature of 150 ° C. during heating, a plate with film polyethylene is mounted in a holder.

This problem is also solved using an optical element made of silicon, which is coated with a polyethylene coating in accordance with any of the above modifications of the method of applying polyethylene to a silicon surface. Polyethylene is preferably a film.

- 1 015000 nm. Silicon in one embodiment is made in the form of a plate, which can be plane-parallel, and in the preferred embodiment, the plate is connected with a film of polyethylene.

To press the film polyethylene to the side surface of the silicon wafer, it can be installed inside the washer, the hole of which in shape and size essentially coincides with those for the silicon wafer with an allowance of the thickness of the film polyethylene. The silicon wafer can be made in a cylindrical form, then the hole in the washer should be round. In all variants using silicon in the form of a plate, polyethylene film can be applied on both sides. For this case, two washers can be used to press the film polyethylene to the side surface of the silicon wafer.

In another embodiment, silicon may have a convex surface, preferably hemispherical. In this case, the film polyethylene is pulled onto a convex surface, for example, using a washer holder.

The technical result achieved by the presented method consists in improving the adhesion of polyethylene to silicon compared with the prior art while maintaining a high level of transmission of optical radiation due to the fact that the polyethylene is in direct contact with and adheres tightly to silicon. Thanks to heating, polyethylene fills micropores in the surface of silicon and provides retention of polyethylene on silicon. The optical element resulting from the present invention provides excellent optical characteristics, that is, a high level of transmission of optical radiation, while ensuring satisfactory adhesion of polyethylene to silicon.

List of drawings

In FIG. 1 shows the transmission spectrum of polyethylene in the THz range;

in FIG. 2 - the process of rolling a silicon wafer with plastic films by a roller;

in FIG. 3 - stage of sealing the silicon wafer in polyethylene;

in FIG. 4 - transmittance of silicon OE with a double-sided antireflection coating of polyethylene with a thickness of 20 μm depending on the wavelength.

Information confirming the possibility of carrying out the invention

The following describes an embodiment of the present invention. Before applying polyethylene to silicon, it is preferred that silicon is purified, for example by chemical means. The polyethylene applied to silicon can have any configuration in which the present method can be implemented, in particular, it must be possible to press the polyethylene to silicon. In the most convenient way, this can be realized using film polyethylene, since in addition to applying direct compressive strength to the polyethylene and silicon, the pressing can be carried out by rolling a roller. Therefore, the method will be further described with respect to the case of applying a film of polyethylene to silicon, although the method itself can be applied to any form of polyethylene.

The silicon element on which the polyethylene is applied can also have a different shape, and the shape of the surface to which the polyethylene is connected is also not regulated in advance and can be varied. However, to simplify the description, the method will be described with respect to a silicon wafer, which can be plane parallel and, for example, have a cylindrical shape, as well as to a silicon element whose surface has a hemispherical shape. At the same time, it should be understood that the present method in a slightly modified form can be applied to silicon elements of different shapes, as well as polyethylene is not necessarily film.

To apply a layer of polyethylene to silicon, polyethylene made, for example, in the form of a film, is superimposed on a silicon product made, for example, in the form of a plane-parallel plate of cylindrical shape. In the preferred embodiment shown in FIG. 2, a silicon wafer 1 is placed between two layers of polyethylene 2, since a two-sided coating of a plane-parallel wafer 1 with polyethylene 2 provides an increase in the antireflection effect due to interference amplification between the two coatings.

After connecting silicon 1 with polyethylene 2, such an assembly is mounted on a stand 3 with a flat surface made, for example, of Teflon, and then, together with the stand, it is placed in an environment where heating will be performed. Heating is usually carried out in a furnace, in this case the furnace is a muffle.

In the furnace, the silicon 1 and polyethylene 2 are slowly (preferably 3-5 ° C / min) heated to a temperature of about 100 ° C, at which the polyethylene 2 is pressed against the surface of silicon 1, which can be done by rolling with a roller 4 made, for example, made of teflon or glass. In FIG. 2 shows the process of rolling a roller 4 assembly of a plane-parallel silicon plate 1 and a film of polyethylene 2 located on both sides of the plate. In this case, rolling is carried out from two sides.

After the polyethylene is pressed to the silicon surface, heating continues, and at a temperature of 110-130 ° C, additional air bubbles can be eliminated by additional rolling.

- 2015 case of their formation.

Further, heating continues at a temperature of 150 ° С, silicon with polyethylene can be installed in a holder, which allows holding products without touching surfaces in the future. To remove the remains of the polyethylene film and to provide polyethylene coating on the silicon side surface, the silicon plate can be installed inside the washer, the hole of which in shape and size essentially coincides with those for the silicon plate with an allowance for the thickness of the film polyethylene. In the case where the film polyethylene is applied on both sides of the silicon wafer, two washers can be used to press the film polyethylene to the side surface of the silicon wafer, as shown in FIG. 3. There you can see that if the silicon plate has a cylindrical shape, then the inner holes of the washers are round.

After all the manipulations have been performed with the assembly of silicon and polyethylene at a temperature of 150 ° C, the heating continues and is preferably carried out to a temperature in the range of 170-200 ° C, and the greatest effect is achieved by heating to a temperature in the range from 180 to 190 ° FROM. Next, the heated assembly of silicon and polyethylene is transferred to a furnace or other volume heated to a temperature of less than 100 ° C, preferably in the range from 70 to 90 ° C, and the optimum temperature is 80 ° C. Here, the product is slowly cooled to room temperature, by gradually lowering the temperature in the furnace volume after the temperature of the product drops to the appropriate value. After cooling, the product can be used.

In FIG. 4 shows the transmission spectrum of a plane-parallel silicon wafer 1 mm thick with a polyethylene coating thickness of 20 μm on each side. On the graph you can see that in a given range of 90-200 microns, the transmittance exceeds 85%, and at the maximum the transmittance is 96%.

In the event that the polyethylene coating is performed on a convex, for example, hemispherical surface, then polyethylene in the form of a film can be applied to the surface using a washer and a table.

The assembly is also placed in a furnace, where silicon and polyethylene are heated to a temperature of preferably about 180 ° C, and then placed in a furnace with a temperature of 80 ° C, where they cool to room temperature.

Thanks to the present method of applying a polyethylene coating to silicon, it is possible to obtain good adhesion due to the penetration of molten polyethylene into micropores in a silicon element, which is best carried out under open temperature conditions. The resulting products have good optical properties, which allows the use of optical elements made of silicon with a polyethylene coating in accordance with the present method for optical devices operating in the THz range.

Claims (15)

CLAIM 1. The method of applying a polyethylene coating on silicon, containing the following steps: connect the surface of silicon and polyethylene; The combined silicon and polyethylene are heated to a temperature above 150 ° C, after which the combined silicon and polyethylene are transferred to a volume with a temperature below 100 ° C and the combined silicon and polyethylene are cooled to room temperature. 2. The method according to claim 1, characterized in that the polyethylene is heated to a temperature in the range from 170 to 200 ° C, preferably in the range from 180 to 190 ° C. 3. The method according to claim 1, characterized in that the polyethylene is transferred to a volume with a temperature in the range from 70 to 90 ° C, preferably 80 ° C. 4. The method according to claim 1, characterized in that the heating rate is 3-5 ° C / min. 5. The method according to claim 1, characterized in that the heating and / or cooling is carried out in furnaces. 6. The method according to claim 1, characterized in that before connecting the surfaces of silicon and polyethylene, silicon is purified, and the purification of silicon is produced by chemical means. 7. The method according to claim 2, characterized in that when silicon and polyethylene reach a temperature of 100 ° C during heating, the polyethylene is pressed to the silicon surface. 8. The method according to claim 7, characterized in that, if air bubbles have formed, at a temperature of 110-130 ° C during heating is carried out the rolling of polyethylene. 9. The method according to p. 2, characterized in that at a temperature of 150 ° C during heating silicon with polyethylene is installed in the holder. 10. Optical element made of silicon, which is coated with a polyethylene coating in accordance with the method according to any one of claims 1 to 9. 11. The element of claim 10, characterized in that the polyethylene is a film, and silicon has a convex surface, and the surface is preferably hemispherical. 12. The element of claim 10, characterized in that the polyethylene is film, and silicon is made in the form of a plate, and the plate is preferably plane-parallel. 13. The element indicated in paragraph 12, characterized in that the silicon wafer is installed inside the washer, from - 3 015000 version of which in shape and size essentially coincides with those for a silicon plate with an allowance for the thickness of the film of polyethylene, preferably the silicon plate is made in a cylindrical form, and the hole in the washer is made round. 14. The element according to claim 12, wherein the polyethylene film is installed on both sides of the silicon wafer. 15. An element according to claim 12, characterized in that the silicon wafer is installed inside two washers, the holes of which in shape and size essentially coincide with those for a silicon wafer with an allowance for the thickness of the polyethylene film, and the washers are installed on those sides of the film polyethylene, which are not connected to the silicon plate.