Method for improving surface cracks of lanthanum fluoride film layer

Abstract

A method for improving the surface cracks of a lanthanum fluoride film layer includes the steps of: S1, incorporating lanthanum fluoride material into yttrium oxide material to form a mixed material, with the yttrium oxide material accounting for 0.2% - 1.0%; S2, placing the mixed material in an evaporation boat, covering it with a lid, and the lid has a through-hole; S3, heating the workpiece disk to 150 - 300 °C and maintaining it constant; S4, evacuating the coating chamber and maintaining it below 3.0×10<supgt;−3< / supgt> Pa; S5, preheating the mixed material in the evaporation boat by resistance heating, with the preheating using step-by-step interval heating and insulating after each step of heating, and the final temperature of the preheating being set to 80 ± 5% of the evaporation temperature of lanthanum fluoride under the maintained vacuum; S6, after the preheating in step S5 is completed, introducing argon into the coating chamber and maintaining the vacuum degree of the coating chamber at 1.0×10<supgt;−2 Pa, continuing resistance heating for evaporation coating, using segmented interval coating, pausing after each coating of 200 - 300 nm thickness, and accumulating the coating thickness until it reaches more than 1000 nm; S7, performing stepwise cooling 20 - 40 min after step S6 is completed; S8, taking out the workpiece disk together with the coating on the workpiece disk.

Description

Technical Field

[0001] The present disclosure relates to the field of optical coatings, and more particularly to a method for improving surface cracks of lanthanum fluoride film layers. Background Art

[0002] Lanthanum fluoride material has good transmittance in the ultraviolet, visible, and infrared light ranges. Its refractive index is about 1.45 in the infrared long-wave band of 8 to 12 micrometers, making it an ideal low-refractive-index material. Also, due to its certain strength to withstand harsh environments, it is often used as a protective film layer. However, when the lanthanum fluoride film layer reaches a certain thickness during the coating process, usually greater than 1000 nm, such a relatively thick film of more than 1000 nm will have many defects due to various stresses, such as internal voids, surface cracks, etc. This causes great damage to the film layer or makes the lanthanum fluoride film layer lose its protective effect. Summary of the Invention

[0003] In view of the problems in the background art, the purpose of the present disclosure is to provide a method for improving surface cracks of lanthanum fluoride film layers, which can avoid the appearance of cracks on the surface of lanthanum fluoride film layers with a coating thickness of more than 1000 nm.

[0004] Thus, a method for improving surface cracks of lanthanum fluoride film layers includes the steps of: S1, incorporating lanthanum fluoride material into yttrium oxide material to form a mixed material. Calculated based on the total mass of the lanthanum fluoride material and the yttrium oxide material, the yttrium oxide material accounts for 0.2% - 1.0%; S2, placing the mixed material into an evaporation boat in the coating chamber of a vacuum evaporation coating machine, covering the lid, and the lid has through holes communicating the inside and outside of the evaporation boat; S3, heating the workpiece tray in the coating chamber to 150 - 300 °C and maintaining it constant; S4, evacuating the coating chamber and maintaining it at 3.0×10 -3 Pa or less; S5, preheating the mixed material in the evaporation boat by resistance heating. The preheating adopts step-by-step interval heating, and each step of heating is followed by heat preservation. The final temperature of the preheating is set to 80 ± 5% of the evaporation temperature of lanthanum fluoride under the maintained vacuum; S6, after the preheating in step S5 ends, introducing argon into the coating chamber and maintaining the vacuum degree of the coating chamber at 1.0×10 -2 Pa, continuing to resistively heat the mixed material in the evaporation boat until the mixed material evaporates and evaporatively coats the workpiece tray through the through holes on the lid. The evaporation coating adopts segmented interval coating, pausing after each coating of 200 - 300 nm thickness, and accumulating the coating thickness until it reaches more than 1000 nm. Then, stop the resistance heating of the evaporation boat. The vacuum degree of the coating chamber is maintained at 1.0×10 -2 Pa from the end of the preheating in step S5 until the resistance heating of the evaporation boat stops; S7, after step S6 is completed, stop introducing argon into the coating chamber and maintain the coating chamber at 3.0×10 -3Below Pa, 20 - 40 minutes after step S6 is completed, control the workpiece disk to cool down in a stepped manner from the maintained constant temperature; S8, after the stepped cooling, take out the workpiece disk together with the coating on the workpiece disk from the coating chamber.

[0005] The beneficial effects of the present disclosure are as follows: In the method for improving the surface cracks of the lanthanum fluoride film layer of the present disclosure, through the lanthanum fluoride material doped with yttrium oxide in step 1, the lid with through holes in step S2, the heating of the workpiece disk in step S3, the step-by-step interval preheating of the mixed materials in step S5, the segmented interval coating by resistance evaporation in step S6 to reach more than 1000 nm, the maintenance of the vacuum in the coating chamber and the temperature of the workpiece disk first and then the stepped cooling in step S7, and the taking out of the workpiece disk together with the coating on the workpiece disk after the stepped cooling in step S8, it is possible to avoid the surface cracks of the coating (i.e., the lanthanum fluoride film layer) with a coating thickness reaching more than 1000 nm after step eight is completed, thereby achieving the purpose of improving the surface cracks of the lanthanum fluoride film layer with a coating thickness reaching more than 1000 nm. Description of the Drawings

[0006] Figure 1 is a schematic diagram of an exemplary vacuum evaporation coating machine used in the method for improving the surface cracks of the lanthanum fluoride film layer according to the present disclosure.

[0007] Figure 2 is a photo after the coating is completed in Example 1.

[0008] Figure 3 is a photo after the coating is completed in Comparative Example 1.

[0009] Among them, the description of the reference numerals is as follows:

[0010] 100 Vacuum evaporation coating machine

[0011] 1 Coating chamber

[0012] 11 Inlet

[0013] 12 Outlet

[0014] 2 Evaporation boat

[0015] 3 Lid

[0016] 31 Through hole

[0017] 4 Workpiece disk

[0018] 5 Heating lamp

[0019] 6 Temperature sensor

[0020] 7 Crystal thickness monitor

[0021] 8 Electrical connection conductor

[0022] 9 Bracket Detailed Implementation Modes

[0023] The accompanying drawings illustrate embodiments of the present disclosure, and it will be understood that the disclosed embodiments are merely examples of the present disclosure, and the present disclosure can be implemented in various forms. Therefore, the specific details disclosed herein should not be construed as limiting, but only as a basis for the claims and as a representative basis for teaching those of ordinary skill in the art to implement the present disclosure in various ways.

[0024] [Method for Improving Surface Cracks of Lanthanum Fluoride Film Layer]

[0025] Referring to Figure 1 , the method for improving the surface cracks of the lanthanum fluoride film layer according to the present disclosure includes the steps of:

[0026] S1. Incorporate lanthanum fluoride material into yttrium oxide material to form a mixed material. Based on the total mass of the lanthanum fluoride material and the yttrium oxide material, the yttrium oxide material accounts for 0.2%-1.0%.

[0027] S2. Place the mixed material in the evaporation boat 2 in the coating chamber 1 of the vacuum evaporation coating machine 100, cover the lid 3, and the lid 3 has a through hole 31 for communicating the inside and outside of the evaporation boat 2.

[0028] S3. Heat the workpiece disk 4 in the coating chamber 1 to 150-300°C and maintain it constant.

[0029] S4. Evacuate the coating chamber 1 and maintain it below 3.0×10 -3 Pa.

[0030] S5. Preheat the mixed material in the evaporation boat 2 by resistance heating. The preheating adopts step-by-step interval heating, and after each step of heating, heat preservation is carried out. The final preheating temperature is set to 80±5% of the evaporation temperature of lanthanum fluoride under the maintained vacuum.

[0031] S6. After the preheating in step S5 is completed, introduce argon into the coating chamber 1 and maintain the vacuum degree of the coating chamber 1 at 1.0×10 - 2 Pa, continue to resistively heat the mixed material in the evaporation boat 2 until the mixed material evaporates and evaporates and coats the workpiece disk 4 through the through hole 31 on the lid 3. The evaporation coating adopts segmented interval coating. After coating 200-300 nm in thickness for each segment, pause until the cumulative coating thickness reaches more than 1000 nm. Stop the resistance heating of the evaporation boat 2, and maintain the vacuum degree of the coating chamber 1 at 1.0×10 -2 Pa from the end of the preheating in step S5 until the resistance heating of the evaporation boat 2 stops.

[0032] S7. After step S6 is completed, stop introducing argon into the coating chamber 1 and maintain the coating chamber 1 at 3.0×10 -3Below Pa, 20 - 40 minutes after step S6 is completed, control the workpiece disk 4 to cool down in a stepped manner from the maintained constant temperature.

[0033] S8. After the stepped cooling, take out the workpiece disk 4 together with the coating on the workpiece disk 4 from the coating chamber 1.

[0034] In the method for improving the surface cracks of the lanthanum fluoride film layer in the present disclosure, through the lanthanum fluoride material doped with yttrium oxide material in step 1, the lid 3 with through holes 1 in step S2, the heating of the workpiece disk 4 in step S3, the step-by-step interval preheating of the mixed material in step S5, the resistance evaporation segmented interval coating in step S6 to reach more than 1000 nm, maintaining the vacuum of the coating chamber 1 and the temperature of the workpiece disk 4 first and then performing stepped cooling in step S7, and taking out the workpiece disk 4 together with the coating on the workpiece disk 4 after the stepped cooling in step S8, it is possible to avoid surface cracks of the coating (i.e., the lanthanum fluoride film layer) with a coating thickness reaching more than 1000 nm after step eight is completed, as shown in the Figure 1 photo reflecting the results of Example 1 described later, so as to achieve the purpose of improving the surface cracks of the lanthanum fluoride film layer with a coating thickness reaching more than 1000 nm.

[0035] In step S1, doping an appropriate proportion of yttrium oxide material helps to obtain a lanthanum fluoride film layer with a coating thickness reaching more than 1000 nm and no surface cracks. In one example, in step S1, the yttrium oxide material accounts for 0.5%. Both the lanthanum fluoride material and the yttrium oxide material are in powder form. The purity of both the lanthanum fluoride material and the yttrium oxide material is above 3.5N.

[0036] In step S2, by using a lid 3 with through holes 31 connecting the inside and outside of the evaporation boat 2, it is possible to avoid the influence of splashing materials generated when the mixed material evaporates in the evaporation boat 2 without using the lid 3 (i.e., the top of the evaporation boat 2 is directly open) on the film layer quality. For example, the splashing materials form prominent large particles on the surface of the final film layer, which has a huge impact on the imaging of the optical film. If it is a laser film, it also has a huge impact on the threshold. In one example, in step S2, the evaporation boat 2 is a tungsten evaporation boat and the lid 3 is a tungsten lid. The through holes 31 can be arranged in an array, that is, a two-dimensional array arrangement. Using tungsten material is beneficial to the resistance heating evaporation coating of yttrium oxide and lanthanum fluoride materials. Of course, molybdenum or tantalum materials can also be used. In addition, as Figure 1 shown, because resistance evaporation coating is used, the two electrical connection conductors 8 connected to an external power source (not shown) can be connected to the lid 3.

[0037] Maintain the temperature of the workpiece disk 4 constant until before the stepped cooling in steps S3 to S7. In one example, in step S3, the workpiece disk 4 is maintained constant at 160 °C. In one example, as Figure 1As shown, in step S3, the workpiece tray 4 in the coating chamber 1 is heated by irradiation with a heating lamp 5, and the temperature of the workpiece tray 4 is sensed by a temperature sensor 6. The sensor 6 communicates with the heating lamp 5 to ensure that the temperature of the workpiece tray 4 is maintained constant before the step-by-step cooling from step S3 to step S7. Of course, those skilled in the art can also use any suitable heating method other than the heating lamp 5 to heat the workpiece tray 4. The workpiece tray 4 needs to be detachably arranged in the coating chamber 1, such as Figure 1 As shown, the workpiece pan 4 is detachably mounted on the support 9 .

[0038] like Figure 1 As shown, in steps S4 to S7 , the gas in the coating chamber 1 flows through a flow path formed by the inlet 11 and the outlet 12 of the coating chamber 1 to form a maintained vacuum.

[0039] In step S5, step-by-step heating is used so that the temperature of the mixed material is gradually increased and kept warm in the evaporation boat 2 before step S6 is performed (i.e., resistance heating is used to maintain a constant temperature), so that the heat in each step is fully and evenly distributed in the mixed material, thereby making the temperature of the mixed material uniform everywhere. In one example, in step S5, step-by-step heating is performed in three steps. Under the maintained vacuum (i.e., maintained at 3.0×10 -3 Pa or less), the evaporation temperature of lanthanum fluoride is calculated as 900°C as 100%, and is heated in three steps of 30% (i.e. 270°C), 60% (i.e. 540°C), and 80% (i.e. 720°C), the heating time of each step is 40-60 seconds, and the temperature is kept for 60-100 seconds after each heating step, and the final preheating temperature is set to 720°C. Furthermore, the heating time of each step is 50 seconds, and the temperature is kept for 60 seconds after each heating step.

[0040] In step S6, segmented interval coating is adopted, and coating is paused after each segment of coating (i.e., resistance heating is stopped) to ensure that the stress inside the film layer of each segment of coating is eliminated, to avoid the formation of internal defects in the film layer of each segment of coating, and to ensure that the final cumulative coating thickness reaches more than 1000nm. The quality of the final lanthanum fluoride film layer. In one example, in step S6, the segmented interval coating adopts the number of segments that meet the cumulative coating thickness of more than 1000nm, each segment of coating is 200-300nm, and each segment of coating is paused for 10-20min. Furthermore, the number of segments is four, each segment of coating is 300nm, and each segment of coating is paused for 10min.

[0041] In one example, refer to Figure 1 In step S6, the thickness of each section of the coating is monitored by a crystal-controlled film thickness meter 7 installed in the coating chamber 1, and the crystal-controlled film thickness meter 7 communicates with the control mechanism of the resistance heating to control the coating and pause of each section (that is, the resistance heating stops, in Figure 1 In the process, the circuit electrically connected between the two electrical connection conductors 8, the cover 3 and the external power supply is disconnected).

[0042] In step S7, after step S6 is completed, the introduction of argon into the coating chamber 1 is stopped and the coating chamber 1 is maintained at 3.0×10 -3 Pa or less. After 20 - 40 minutes after step S6 is completed, the workpiece disk 4 is controlled to cool down in a stepped manner from the maintained constant temperature, so that the stress of the film layer after coating is slowly released. In one example, in step S7, the stepped cooling is such that the temperature of the workpiece disk 4 is cooled down once every 20 °C, and each cooling is natural cooling. After each cooling, it is kept at a constant temperature for 5 - 10 minutes until the temperature drops to 60 °C. Further, the stepped cooling is carried out 30 minutes after step S6 is completed, and in the stepped cooling, it is kept at a constant temperature for 5 minutes after each cooling.

[0043] The method for improving the surface cracks of the lanthanum fluoride film layer of the present disclosure may further include the step: S9, after the workpiece disk together with the coating on the workpiece disk is placed at room temperature for 24 hours, visually observe whether there are cracks on the surface of the coating.

[0044] [Test]

[0045] Example 1

[0046] Example 1 adopts the following steps:

[0047] S1, the lanthanum fluoride material is incorporated into the yttrium oxide material to form a mixed material. Based on the total mass of the lanthanum fluoride material and the yttrium oxide material, the yttrium oxide material accounts for 0.5%. Both the lanthanum fluoride material and the yttrium oxide material are in powder form, and the purities of both the lanthanum fluoride material and the yttrium oxide material are 3.5N;

[0048] S2, the mixed material is placed into the evaporation boat 2 in the coating chamber 1 of the vacuum evaporation coating machine 100, and the lid 3 is covered. The lid 3 has a through hole 31 communicating the inside and outside of the evaporation boat 2. The evaporation boat 2 is a tungsten evaporation boat, the lid 3 is a tungsten lid, and the through holes 31 are arranged in a two-dimensional array;

[0049] S3, the workpiece disk 4 in the coating chamber 1 is heated by irradiating with the heating lamp 5. The workpiece disk 4 is detachably mounted on the bracket 9. The workpiece disk 4 in the coating chamber 1 is heated to 160 °C and maintained constant. The temperature of the workpiece disk 4 is sensed by the temperature sensor 6, and the sensor 6 communicates with the heating lamp 5;

[0050] S4, the coating chamber 1 is evacuated and maintained at 3.0×10 -3 Pa or less;

[0051] S5, the mixed material in the evaporation boat 2 is preheated by resistance heating. The preheating adopts step-by-step interval heating, which is carried out in three steps. After each step of step-by-step interval heating, heat preservation is carried out under the maintained vacuum (that is, maintained at 3.0×10 -3Below Pa, taking the evaporation temperature of lanthanum fluoride as 100% at 900 °C, heating is carried out in three steps of 30% (i.e., 270 °C), 60% (i.e., 540 °C), and 80% (i.e., 720 °C), with the heating time of each step being 50 seconds, and heat preservation for 60 seconds after each step of heating. The set final temperature of preheating is 720 °C (i.e., the final temperature of preheating is set to the evaporation temperature of lanthanum fluoride under the maintained vacuum (i.e., 80% of 900 °C;

[0052] S6. After the preheating in step S5 ends, argon is introduced into the coating chamber 1 and the vacuum degree of the coating chamber 1 is maintained at 1.0×10 - 2 Pa, and continue to resistively heat the mixture in the evaporation boat 2 until the mixture evaporates and evaporatively coat the workpiece disk 4 through the through hole 31 on the lid 3. The evaporative coating is carried out by segmented intermittent coating. The number of segments is four. After coating 300 nm in thickness for each segment, pause for 10 min until the cumulative coating thickness reaches 1200 nm, then stop the resistive heating evaporation boat 2. From the end of the preheating in step S5 until the stop of the resistive heating evaporation boat 2, the vacuum degree of the coating chamber 1 is maintained at 1.0×10 -2 Pa. Among them, the thickness of each segment of coating is monitored by the crystal-controlled film thickness gauge 7 installed in the coating chamber 1, and the crystal-controlled film thickness gauge 7 communicates with the control mechanism of resistive heating;

[0053] S7. After step S6 is completed, stop introducing argon into the coating chamber 1 and maintain the coating chamber 1 at 3.0×10 -3 Pa or below. 30 min after step S6 is completed, control the workpiece disk 4 to stepwise cool down from the maintained constant temperature (i.e., 160 °C). The stepwise cooling is that the temperature of the workpiece disk 4 is cooled down by 20 °C each time, and each cooling is natural cooling. After each cooling, keep the temperature constant for 5 min until the temperature drops to 60 °C;

[0054] S8. After the stepwise cooling, take out the workpiece disk 4 together with the coating on the workpiece disk 4 from the coating chamber 1;

[0055] S9. After the workpiece disk together with the coating on the workpiece disk is placed at room temperature for 24 h, visually observe whether there are cracks on the surface of the coating.

[0056] Comparative Example 1

[0057] Except that no yttrium oxide material is incorporated in step S1 (i.e., the yttrium oxide material accounts for 0%) and step S6 uses one-time (i.e., single-segment) coating to reach 1200 nm, the rest is the same as Example 1.

[0058] Figure 2 is a photo after the coating in Example 1 is completed. Figure 3 is a photo after the coating in Comparative Example 1 is completed. As can be seen from Figure 3 there are cracks on the surface of the lanthanum fluoride film layer in Comparative Example 1. As can be seen from Figure 2It can be seen that there are no cracks on the surface of the lanthanum fluoride film layer in Example 1.

[0059] Multiple exemplary embodiments are described with the above detailed description, but the present disclosure is not intended to be limited to the explicitly disclosed combinations. Thus, unless otherwise stated, the various features disclosed herein can be combined together to form multiple additional combinations not shown for the purpose of brevity.

Claims

1. A method for improving the surface cracks of a lanthanum fluoride film layer, characterized in that Including the steps: S1, Incorporate lanthanum fluoride material into yttrium oxide material to form a mixed material. Based on the total mass of the lanthanum fluoride material and the yttrium oxide material, the yttrium oxide material accounts for 0.2% - 1.0%. S2, Place the mixed material into the evaporation boat (2) in the coating chamber (1) of the vacuum evaporation coating machine (100), cover the lid (3), and the lid (3) has a through hole (31) communicating the inside and outside of the evaporation boat (2). S3, Heat the workpiece disk (4) in the coating chamber (1) to 150 - 300 °C and maintain it constant. S4, evacuate the coating chamber (1) and maintain it at a pressure below 3.0×10 -3 Pa; S5, Preheat the mixed material in the evaporation boat (2) by resistance heating. The preheating adopts step-by-step interval heating, and after each step of heating, it is kept warm. The final temperature of the preheating is set to 80 ± 5% of the evaporation temperature of lanthanum fluoride under the maintained vacuum. S6. After the preheating in step S5 is completed, argon is introduced into the coating chamber (1), and the vacuum degree of the coating chamber (1) is maintained at 1.0×10 - 2 Pa. The mixture in the resistance heating evaporation boat (2) continues to be heated until the mixture evaporates and is evaporated and coated on the workpiece disk (4) through the through hole (31) on the lid (3). The evaporation coating is carried out in a segmented and intermittent manner. After each coating with a thickness of 200 - 300 nm, it pauses until the cumulative coating thickness reaches more than 1000 nm. Then the resistance heating evaporation boat (2) stops. The vacuum degree of the coating chamber (1) is maintained at 1.0×10 -2 Pa from the end of the preheating in step S5 until the resistance heating evaporation boat (2) stops; S7. After step S6 is completed, stop introducing argon into the coating chamber (1) and maintain the coating chamber (1) at a pressure below 3.0×10 -3 Pa. After 20 - 40 minutes after step S6 is completed, control the workpiece table (4) to cool down from the maintained constant temperature in a stepped manner; S8, After stepwise cooling, take out the workpiece disk (4) together with the coating on the workpiece disk (4) from the coating chamber (1).

2. The method for improving the surface cracks of the lanthanum fluoride film according to claim 1, characterized in that in step S1, the yttrium oxide material accounts for 0.5%.

3. The method for improving the surface cracks of the lanthanum fluoride film according to claim 1, characterized in that in step S3, the workpiece disk (4) is maintained constant at 160 °C.

4. The method for improving the surface cracks of the lanthanum fluoride film according to claim 1, characterized in that in step S5, the step-by-step interval heating adopts three steps. Under the maintained vacuum, taking the evaporation temperature of lanthanum fluoride as 100% at 900 °C, it is heated in three steps of 30%, 60%, and 80%. The heating time for each step is 40 - 60 seconds, and after each step of heating, it is kept warm for 60 - 100 seconds. The set final temperature of the preheating is 720 °C.

5. The method for improving the surface cracks of the lanthanum fluoride film according to claim 4, characterized in that the heating time for each step is 50 seconds, and after each step of heating, it is kept warm for 60 seconds.

6. The method for improving the surface cracks of the lanthanum fluoride film according to claim 1, characterized in that in step S6, the segmented interval coating adopts the number of segments that satisfies the cumulative coating thickness reaching more than 1000 nm. Each segment is coated with 200 - 300 nm, and after each segment of coating, there is a pause of 10 - 20 min.

7. The method for improving the surface cracks of the lanthanum fluoride film according to claim 6, characterized in that the number of segments is four, each segment is coated with 300 nm, and after each segment of coating, there is a pause of 10 min.

8. The method for improving the surface cracks of the lanthanum fluoride film according to claim 1, characterized in that in step S7, the stepwise cooling is that the temperature of the workpiece disk (4) is cooled by 20 °C each time, and each cooling is natural cooling. After each cooling, it is kept at a constant temperature for 5 - 10 min until it is cooled to 60 °C.

9. The method for improving the surface cracks of the lanthanum fluoride film according to claim 8, characterized in that the stepwise cooling is carried out 30 min after step S6 is completed, and in the stepwise cooling, after each cooling, it is kept at a constant temperature for 5 min.

10. The method for improving the surface cracks of the lanthanum fluoride film layer according to claim 1, characterized in that, The method for improving the surface cracks of the lanthanum fluoride film further includes the step: S9, After the workpiece disk together with the coating on the workpiece disk is placed at room temperature for 24 h, visually observe whether there are cracks on the surface of the coating.

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