A method of producing high aspect ratio domes by vapor deposition

Method for producing high aspect ratio dome by vapor deposition

<p>10. . . furnace</p><p>12. . . Water-cooled stainless steel vacuum chamber shell</p><p>14. . . Graphite distiller</p><p>15. . . Molten reactant</p><p>16. . . Rectangular isolation fixture</p><p>17. . . bolt</p><p>18. . . Second heating device</p><p>20. . . Gas injector</p><p>twenty two. . . Gas vent</p><p>twenty four. . . Thermocouple</p><p>26. . . Thermocouple</p><p>28. . . Thermocouple</p><p>30. . . Isolation device</p><p>32. . . Concave mandrel</p><p>34. . . Reactant</p><p>36. . . Gas injector</p><p>38. . . exhaust vent</p><p>40. . . convection</p><p>42. . . Convex mandrel</p><p>44. . . Deposition chamber</p><p>46. . . Isolation fixture</p><p>48. . . Gas flow</p><p>50. . . Gas flow</p><p>52. . . Deposition chamber</p><p>54. . . Convex mandrel</p><p>56. . . Chemical reactant</p><p>58. . . Inside the deposition chamber</p><p>60. . . exhaust vent</p><p>62. . . Convective airflow</p><p>64. . . Deposition chamber</p><p>66. . . Arched element</p><p>68. . . Isolation fixture</p><p>70. . . Mandrel</p><p>71. . . bolt</p><p>72. . . Reactant</p><p>73. . . bolt</p><p>74. . . Convection path</p><p>76. . . Arc angle</p><p>78. . . Mandrel</p><p>82. . . Mandrel holder</p><p>84. . . bolt</p><p>85. . . Mandrel bottom</p><p>86. . . Back panel</p><p>88. . . bolt</p><p>90. . . plate</p><p>91. . . Flange</p><p>92. . . Flange</p><p>93. . . Flange</p><p>94. . . Axis</p><p>96. . . Mandrel</p><p>98. . . bolt</p><p>100. . . Back panel</p><p>101. . . Mandrel bottom</p><p>102. . . bolt</p><p>103. . . Flange</p><p>104. . . plate</p><p>106. . . Mandrel holder</p><p>108. . . Flange</p><p>109. . . Flange</p><p>110. . . Axis</p><p>112. . . Edge ring</p><p>116. . . Knife edge</p><p>122. . . Deposited material</p><p>124. . . seam</p><p>126. . . top</p><p>127. . . end</p><p>128. . . wall</p><p>138. . . Titanium mandrel</p><p>140. . . Mandrel</p><p>142. . . Hollow space</p><p>144. . . Threaded hole</p><p>148. . . Support column</p><p>150. . . Mandrel vertex</p><p>152. . . Small flange</p>

Figure 1 is a partial cross-sectional schematic diagram of a chemical vapor deposition furnace.

Figure 2 shows a schematic diagram of the multiple concave mandrels in the isolating fixture.

Figure 3 shows a schematic diagram of a two-stage impulse flow configuration for manufacturing a dome on a convex mandrel.

Figure 4 shows a schematic diagram of the multiple convex mandrels installed on the wall of the deposition chamber so that the airflow does not directly impinge on the mandrel.

Figure 5 shows a schematic view of the multiple convex mandrels installed on the wall of the deposition chamber, with arcuate elongated elements to prevent airflow from impinging on the mandrels.

Figure 6 is a side view of the convex mandrel of the isolating fixture.

Figure 7 is an explanatory view of the side view of the dome after the convex mandrel of the isolation fixture and the edge ring is set to assist the mandrel to remove the vapor deposition.

Figure 7a shows an enlarged illustration of the edge ring firmly fixed to the mandrel holder and resting on the mandrel flange.

Figure 8 shows a close-up view of the edge ring of the vapor-deposited material on the mandrel and the seam formed by the ring.

Figure 9 shows a cross-sectional view of the edge ring used to assist the removal of the deposition dome from the mandrel.

Figure 10 shows a photograph of three zinc sulfide domes manufactured according to the method of the present invention.

Figure 11 shows the titanium mandrel used in the preparation of high aspect ratio domes by the method of the present invention.

Figure 12 shows a photograph of three zinc sulfide domes prepared on a titanium mandrel, one of which is split to show the thickness of the dome.

[Background of the invention]

The present invention is directed to a device and method for preparing high aspect ratio objects by vapor deposition. More specifically, the present invention is directed to an apparatus and method for preparing high aspect ratio objects by vapor deposition on a convex mandrel.

Chemical vapor deposition (CVD) is used to provide a variety of materials in the form of a self-standing body or a layered coating on a substrate. The CVD method for providing zinc sulfide layers and objects is described in commonly assigned US Patent Nos. 4,978,577 and 5,686,195, and references cited therein. Generally, the previous method of manufacturing the bulk material by the CVD process has provided a solid shape, and then machined the surface into its final object shape. Proposal to reduce the cut to a minimum for the production of "near-net-shape parts" replication technology and some of its results are described in Goela et al., "CVD replication for optical applications", SPIE Proceedings, 1047, pp. 198-210 (1989 year). The replication method for manufacturing silicon carbide objects is described in US Patent No. 4,997,678. The replication method provides in-situ application of a carbon coating to the polished pre-formed substrate before chemical vapor deposition of silicon carbide is started to form a replicable substrate Objects on the surface.

Although the techniques described in the aforementioned reference documents produce near-net-shape objects, there continues to be a need for precise replication technology that will produce precisely-shaped objects, such as optical components, without the need for final mechanical cutting of the optical surface. The technology described in U.S. Patent No. 4,997,678 provides relatively good replication, but the carbon-rich film used here is applied in situ at the beginning of the respective production of deposits. This does not provide an opportunity to measure or otherwise verify the dimensions of the film before starting the manufacturing operation, and results in non-uniform growth of the carbon-rich film, resulting in uncontrollable deviations of the copied objects. In addition, when the carbon-rich film is separated from the substrate, it tends to stick to the surface of the replicated object. This characteristic limits the use of this technology to replicate the finish of the substrate.

In particular, it is necessary to provide a technology that accurately replicates and is easily released from the substrate. For example, infrared sensors used for navigation, guidance, and locking on airplanes and missiles need to use transmissive windows or domes to avoid such components. Preferably, the window or dome provides a shape that minimizes aerodynamic drag while avoiding irregularities in transmission. For missiles, the preferred location is the nose. The spherical dome at this position generates a relatively large traction force by using a dome that expands into a roughly conical shape, and the relatively large traction force can be significantly reduced due to two or more factors. However, it becomes difficult or even impossible to manufacture such a dome when it is necessary to cut the inner surface of the dome. The reason is that the required device function decreases as the diameter of the cone decreases and the length increases. Accurately replicating the inner surface of this dome on a reusable mandrel without mechanical cutting or grinding on the surface will provide significant manufacturing advantages. Certain CVD can produce bulk materials, such as zinc sulfide and zinc selenide, but due to their thermal expansion characteristics and preferred mandrel materials, they have not been made on the outer surface of a curved convex mandrel in the past. Instead, when this material has been used to make curved products, it has been produced by deposits formed on the inner surface of the curved concave mandrel. The inner surface of this curved object requires considerable mechanical cutting to provide a final Value and finish.

The manufacture of zinc sulfide and zinc selenide shaped parts, such as domes, is described in US Patent No. 5,453,233 to Teverosky et al. In this method, as shown in Figure 2, the material is deposited on the concave mandrel. FIG. 2 shows a schematic diagram of the isolating device 30 with a plurality of concave mandrels 32. The reactant 34 passes through the gas injector 36 toward the exhaust port 38. Each mandrel 32 is manufactured to have a negative shape of the actual object to be manufactured. In this configuration, the outer surface of the dome is made into a near net shape by the CVD method. In order to make this arrangement successful, the thermal expansion coefficient of the mandrel is preferably lower than the thermal expansion coefficient of the material to be deposited. Since the flow of the mandrel between the reactant 34 and the convection 40 is not ejected and affects the flow pattern of the deposition area, the concave configuration is better than the convex configuration. This method can be extremely effective in manufacturing domes with an aspect ratio (AR)&lt;0.5. The aspect ratio is also called the fineness ratio, which is defined as the ratio of the length of the dome to the diameter. Similarly, refer to "Replicating conformal surfaces by chemical vapor deposition", author Goela et al., page 315, lines 2 to 3, proposed by the U.S. Air Force Association on April 24 to 27, 2000.

If an aspect ratio equal to or greater than 0.5 is required, the aforementioned method is also used to manufacture a zinc sulfide dome by a CVD process, but the aforementioned method does not produce a dome of satisfactory quality. The reasons are as follows: (1) The thickness of the material deposited on the bottom of the dome is greater than the thickness of the top to reduce the effective diameter of the concave mandrel opening; (2) The bottom sediment is thick and it is difficult to remove the sediment by the isolation device; (3) With As the deposition thickness becomes thicker, the quality of the material deposited on the bottom of the dome will deteriorate. As such, there is a need for better methods that can deposit high-quality shaped parts with high aspect ratios.

US Patent No. 6,042,758, assigned to GOela of CVD Corporation, discloses a method for preparing objects with precise dimensions by chemical deposition. The '758 patent discloses that the concave mandrel is a better mandrel for preparing objects with a high aspect ratio (column 4, lines 1-2). The ratio defined in the '758 patent is the ratio of the diameter of the object to the height (or length) (column 4, lines 3-4). When an object with an aspect ratio of less than 2 is required, a convex mandrel is better (column 4, rows 4-5). When the aspect ratio is determined by the ratio of length to diameter, the aspect ratio is less than 0.5. However, the '758 patent did not address the issue discussed in the previous section regarding the manufacture of domes with an aspect ratio greater than 0.5. The '758 patent also fails to disclose the orientation of the mandrel in the vapor deposition chamber to obtain a high aspect ratio dome.

The report of Goela et al., titled "Making Conformal Zinc Sulfide Domes by Chemical Vapor Deposition", was presented at the SPIE Conference in Orlando, Florida on April 5-9, 1999 and May 11-13, 1999. The report reveals the use of convex mandrels to make domes made of zinc sulfide with a high aspect ratio. Although the report revealed the process conditions and the materials that make up the mandrel, the report did not mention the directionality of the mandrel in the deposition chamber. An earlier report by Goela et al. entitled "Precise Reproduction of Conformal Zinc Sulfide Optical Devices" was revealed at the 7th DOD Electromagnetic Window Seminar at APL, Raleigh, Maryland on May 5-7, 1998. Yes, the report reveals objects manufactured on convex mandrels. Reveal the process conditions of vapor deposition of zinc sulfide on the mandrel, but without the orientation of the mandrel in the deposition chamber.

Figure 3 shows a schematic diagram of chemical deposition by impinging flow. In the impulse flow diagram, convex and concave mandrels can be used, and the gas flow direction is parallel to the dome axis. The parallel orientation of the domes reduces the available deposition area, in other words, there are fewer mandrels that can be placed in the deposition chamber. Placing various mandrels on the platform can increase the deposition area. However, in this way, the deposition thickness is significantly reduced from one platform to the next due to the effect of reactant consumption. A dome with a very large thickness variation is produced. At the same time, the manufacturing time is prolonged and the yield rate of the spindle is reduced. As such, this method is not cost-effective. FIG. 3 shows the convex mandrel 42 on the isolation fixture 46 of the deposition chamber 44 in a two-stage impulse flow arrangement. The gas flow 48 must coordinate several bends to move from one platform to another. This bending depletes the reactants at a faster rate and increases the unevenness of the dome thickness between the platforms. Thus, there is a need for a method and device with improved mandrel orientation to prepare domes with high aspect ratios.

Another problem with vapor deposition on the mandrel is the cracking of the object when it is removed from the mandrel. During chemical vapor deposition, cracks or flaws can be formed on the weak points of the object's structure. Such defects are common along the flange formed at the bottom of the mandrel. Such defects may cause the dome to crack when the dome is removed from the mandrel. For the industry, the cost of the loss of sedimentary objects is quite high. There is also a need for a method to prevent undesired cracking of the deposited objects.

The main purpose of the present invention is to provide a device and method capable of forming a high aspect ratio dome.

Another object of the present invention is to provide a device and method that can use a convex mandrel to prepare a high aspect ratio dome.

Another object of the present invention is to provide a method for preparing a high aspect ratio dome, where the deposit on the top of the dome is thicker than the bottom.

Another object of the present invention is to provide a method of manufacturing a dome with a high aspect ratio so that the dome does not split when it is removed from the mandrel.

Other purposes and advantages of the present invention will be obvious to those skilled in the art who are familiar with this technique after studying the descriptions below and the scope of the accompanying patent application.

[Summary of the invention]

The present invention relates to a device and method for preparing high aspect ratio domes by chemical vapor deposition on convex mandrels. The configuration of the convex mandrel is negative relative to the surface of the dome to be manufactured. The mandrel is placed in any deposition chamber suitable for chemical vapor deposition furnace, so the reactant gas flow will not directly impinge on the mandrel. The directionality of the mandrel is that the axis of each mandrel is perpendicular to the gas flow of the vapor deposition chamber.

The mandrel can be firmly fixed in the vapor deposition chamber by any appropriate means, so that the airflow will not impact on the mandrel. One way to securely fix the mandrel in the chamber is by isolating clamps. The isolation fixture also isolates the mandrel from the rest of the vapor deposition furnace. In an embodiment of the present invention, the arched element of the vapor deposition chamber maintains the mandrel at the distal end of the reactant gas flow path and the convective flow path. Advantageously, the dome produced by the device and method results in a thicker deposit on the top of the dome than at the bottom of the dome. When the steam flow is allowed to directly impact the mandrel, the observed dome thickness changes significantly. The present invention also prevents deterioration of the quality of the material on the mandrel.

In addition, the device and method of the present invention allow the dome to be easily separated from the mandrel and reduce the chance of the dome being split. Further, a smaller number of gas injectors can produce a larger number of domes than in the impingement flow configuration. The directivity of the mandrel of the present invention can avoid air flow obstacles, thereby reducing the requirements of reactants and gas injectors. The method of the device of the invention also produces a high aspect ratio. The high aspect ratio dome system is highly desirable. The high aspect ratio domes used in missiles and airplanes can substantially reduce traction. Similarly, when the high aspect ratio dome adopts the infrared sensor window as the navigation, locking and guiding system, the dome obtains a good coverage rate of the expected locked area. The dome manufactured by the present invention does not need to be further cut into its final shape, and may or may not require a minimum amount of buffing to provide the required surface smoothness or finish.

Another object of the present invention is to provide an edge device that can assist the vapor deposition dome to be removed from the mandrel. The edge device is firmly fixed to the mandrel holder so that during the vapor deposition, the part of the edge device contacts the bottom part of the mandrel. The edge device advantageously allows a seam to be formed in the bottom part of the deposited material. The seams allow the deposited dome to move away from the mandrel without cracking. Preferably, the edge device has a ring shape, which can be easily and firmly fixed to the spindle holder of the device.

Schematic description

Figure 1 is a partial cross-sectional schematic diagram of a chemical vapor deposition furnace.

Figure 2 shows a schematic diagram of the multiple concave mandrels in the isolating fixture.

Figure 3 shows a schematic diagram of a two-stage impulse flow configuration for manufacturing a dome on a convex mandrel.

Figure 4 shows a schematic diagram of the multiple convex mandrels installed on the wall of the deposition chamber so that the airflow does not directly impinge on the mandrel.

Figure 5 shows a schematic view of the multiple convex mandrels installed on the wall of the deposition chamber, with arcuate elongated elements to prevent airflow from impinging on the mandrels.

Figure 6 is a side view of the convex mandrel of the isolating fixture.

Figure 7 is an explanatory view of the side view of the dome after the convex mandrel of the isolation fixture and the edge ring is set to assist the mandrel to remove the vapor deposition.

Figure 7a shows an enlarged illustration of the edge ring firmly fixed to the mandrel holder and resting on the mandrel flange.

Figure 8 shows a close-up view of the edge ring of the vapor-deposited material on the mandrel and the seam formed by the ring.

Figure 9 shows a cross-sectional view of the edge ring used to assist the removal of the deposition dome from the mandrel.

Figure 10 shows a photograph of three zinc sulfide domes manufactured according to the method of the present invention.

Figure 11 shows the titanium mandrel used in the preparation of high aspect ratio domes by the method of the present invention.

Figure 12 shows a photograph of three zinc sulfide domes prepared on a titanium mandrel, one of which is split to show the thickness of the dome.

[Detailed Description of the Invention]

The solid chemical vapor deposition system is prepared by the reaction of chemical precursor materials in the presence of a suitable substrate. The reaction of the precursor materials causes the predetermined material to form a deposit on the substrate. The reaction continues for a sufficient time to form a deposit having a predetermined thickness. Once the predetermined thickness is deposited, the reaction is discontinuous and the deposit is separated from the substrate. The present invention uses a convex mandrel to deposit appropriate materials on the mandrel by chemical vapor deposition to form a high aspect ratio dome. The convex mandrel has a negative structure with a predetermined shape of a dome. The bottom of the mandrel is joined to the entire periphery of the bottom by a flange. The mandrel system is firmly fixed to the isolating fixture, so that when the mandrel is placed in the chemical vapor deposition chamber of the vapor deposition furnace, the chemical reactant stream does not impact on the mandrel. Preferably, the mandrels are arranged such that the axis of each mandrel is perpendicular to the flow direction of the reactants in the deposition chamber. In one embodiment, the spacer clip has a backside support device that contacts and supports the bottom of the mandrel. The backside support device engages the spindle holder through the spindle holder coupling device. The mandrel holder contacts the flange of the mandrel to firmly fix the mandrel to the back support device. The mandrel holder is a fixing device connected to the vapor deposition chamber for fixing the mandrel holder and the backside support device to the vapor deposition chamber. The device connecting the isolation fixture to the deposition chamber may be an integral part of the deposition chamber or a separate structure that may be connected to the chamber. The isolation fixture is placed in the deposition chamber so that the axis of each mandrel is at least 1 mm away from the reactant stream. Preferably, the axis of the mandrel is about 1 mm to about 20 mm from the reactant stream. The deposition chamber can be firmly fixed in the furnace by any suitable device. The chamber can be bolted to the furnace, or the chamber can be freely placed in the furnace.

In addition to fixing the mandrel to a position where the reactant stream does not impact on the mandrel, the isolation fixture also ensures that the material deposited on the mandrel is truly isolated from the deposition chamber. During the deposition, most of the inside of the deposition chamber and the deposition furnace are covered by the deposition material. The cracks in the deposition material formed in the furnace and the deposition chamber can continue to be connected to the deposition material on the mandrel. The isolation fixture isolates the deposited material on the shaft from the cracks formed in the chamber and the furnace. In this way, the isolation fixture improves the dome yield.

Figure 4 is a schematic diagram showing a device within the scope of the present invention. FIG. 4 shows multiple convex mandrels 54 firmly fixed along both sides of the deposition chamber 52. The chemical reactant 56 in gaseous form flows from a source (not shown in the figure) through the interior 58 of the deposition chamber to the exhaust port 60 without impacting the mandrel 54. The convective gas stream 62 containing the reactants also passes over the mandrel without impacting the mandrel. The chemical reactants of the vapor deposition chamber diffuse on the surface of the mandrel to form a dome, the top of which is thicker than the bottom.

Figure 5 shows another embodiment of the present invention. The deposition chamber 64 has an arched element 66 coupled to the isolation jig 68 to maintain the mandrel 70 away from the flow path of the reactant 72 and away from the convection path 74. The mandrel 70 is firmly fixed to the isolation clamp 68 by bolts 73. The arched element can be coupled to the deposition chamber in any suitable manner. The arched element can be integrated with the chamber. The arched element 66 in FIG. 5 is connected to the deposition chamber 64 by bolts 71. The arc angle 76 of the arched element can keep the mandrel away from the reactant flow in the deposition chamber and the convective flow. The arc angle 76 ranges from about 30 degrees to about 100 degrees, preferably from about 45 degrees to about 90 degrees.

Figures 6 and 7 show a more complicated convex mandrel fixed to the isolating fixture than that shown in Figure 5. The spindle holders 82 and 106 contain bolts 84 and 98 to firmly fix the spindle holder back plates 86 and 100 to the spindle holders 82 and 106. The mandrel holder back plates 86 and 100 support the mandrel bottoms 85 and 101 in the isolation fixture. The bolts 88 and 102 securely fix the spindle holders 82 and 106 to the plates 90 and 104. The bolts 88 and 102 pass through the spindle holder flanges 91 and 103, respectively. The sides of the plates 90 and 104 are connected to the deposition chamber (not shown in the figure). The plates 90 and 104 securely fix the isolation fixture and the mandrel to the deposition chamber. The flanges 92 and 108 of the mandrel holders 82 and 106 contact the flanges 93 and 109 of the mandrels 78 and 96 to further securely fix the mandrel to the isolation clamp. The axis 94 of the mandrel 78 and the axis 110 of the mandrel 96 are tied to their respective deposition chambers, and are arranged perpendicular to the flow direction of the reactants. Figure 7 shows another structure not included in the isolation clamp of Figure 6. Figure 7 shows the edge ring 112 firmly fixed to the mandrel clamp flange 108 and the contact flange 109. The edge ring helps to remove the deposition dome from the mandrel. The structure and function of the edge ring are described in detail later. The device for firmly fixing the mandrel in the deposition chamber is not limited to the devices shown in Figs. 5, 6 and 7. The mandrel can be set in the chemical vapor deposition chamber of the vapor deposition furnace by any suitable device, as long as the reactant gas does not impact on the mandrel.

The vacuum deposition chamber furnace of the present invention contains a vacuum shell. The vacuum housing can be composed of polygons, or the housing can be cylindrical. The distiller with the first heating device is placed at the bottom of the furnace. The still contains molten reactants. The furnace bottom also has a gas source for generating gas reactants and inert gas carriers into the deposition chamber. The cover on the top of the shell is equipped with an exhaust port. The deposition chamber is placed in the furnace so that the entrance of the deposition chamber is in fluid contact with the distiller and the gas source. The opposite side of the entrance is the exhaust port of the deposition chamber that contacts the exhaust port of the furnace. The unreacted material is sent out from the inside of the chamber through the exhaust port.

The furnace system for manufacturing the dome within the scope of the present invention is illustrated in Fig. 1. The furnace 10 is sealed in a vertically oriented water-cooled stainless steel vacuum chamber shell 12. The graphite distiller 14 is arranged near the bottom of the chamber 12, the distiller contains molten reactant, such as zinc, 15 and is provided with a first heating device, such as a resistance and/or a radiant heating element. The rectangular isolation fixture 16 is arranged above the distiller 14, and its interior is in fluid communication with the distiller. The isolation fixture 16 contains multiple convex mandrels, each mandrel axis is vertical and deviates from the path of the reactant (not shown in the figure). Each mandrel is bolted to the isolation clamp 16 by a bolt 17. The isolation fixture 16 of the embodiment in FIG. 1 also serves as a deposition chamber. The second heating device 18 capable of heating the mandrel is arranged on the mandrel. The gas injector 20 provides gaseous reactants, such as hydrogen sulfide, and an inert carrier gas to the bottom of the inside of the deposition chamber. The gas exhaust port 22 on the top of the housing 12 is operatively connected to a filter system (not shown in the figure) to remove particles, and then connected to a vacuum source, such as a vacuum pump (not shown in the figure), and finally connected to the cleaning system. The gas generator (not shown in the picture) is used to remove unreacted hydrogen sulfide and any other toxic products. The temperature of the deposition chamber is measured by a thermocouple 24, and the outer surface of the thermocouple contacts the chamber. The temperature of the molten material inside the still is measured by two thermocouples. One thermocouple 26 touches the upper part of the still wall (higher than/close to the height of the molten material), and the other thermocouple 28 extends to the lower part of the still wall (lower At the height of the molten material).

During operation, the deposition chamber is adjusted to increase the temperature and the pressure in the furnace decreases. The molten material vaporized at the first temperature inside the distiller 14 is mixed with the injected gas reactant and carrier gas when it enters the isolation fixture 16. The mixed gas flows through the inside of the deposition chamber, and inside the chamber, the mixed gas contacts the inner surface of the chamber and the mandrel. The chamber and mandrel are heated to a second temperature, or substrate temperature, causing the reactants to react and deposit on the surface of the mandrel. The carrier gas and any gaseous or entrained reaction products are removed from the chamber by the gas exhaust port 22, and processed through the filtering system and the scrubbing system. Once the treatment is started, the process is continued until a product of a predetermined thickness is deposited on the mandrel. This process takes more than 15 hours and may take up to 1100 hours, and more commonly it takes between 100 and 600 hours. When the predetermined thickness is reached, the gas flow through the gas injector 20 is interrupted. The first heating device turns low, and the second heating device 18 is turned off. The pressure in the furnace returns to the surrounding pressure, the chamber shell 12 is opened, and the mandrel is removed. The dome deposited on the mandrel is removed from the mandrel, and if necessary, the dome is cut and ground on the inner side to produce a dome with predetermined dimensions. Preferably, the thickness of the inner side surface is reduced to about 10 to about 200 angstroms.

The manufacture of the substrate or mandrel is of critical importance to the manufacturing process of the present invention. The mandrel is preferably made of a material that can withstand the high temperature and corrosive environment of a chemical vapor deposition (CVD) process. The mandrel material is preferably non-reactive to the deposited material, has an appropriate coefficient of thermal expansion (CTE), is durable, and can be manufactured in the required size, shape, and degree of smoothness or interest. When the thermal expansion coefficient of the mandrel material is the same as that of the deposit, there is no need to modify the thermal expansion coefficient of the mandrel shape. The separation of the mandrel from the copy can be assisted by providing the convex mandrel with a thermal expansion coefficient slightly larger than that of the deposited material. The mandrel will shrink away from the sediment.

The mandrel material used for most purposes is the same material as the deposit to be replicated. Such deposits on the mandrel of the same material are difficult or impossible to separate by the mandrel. The release coating is applied to the mandrel, and the mandrel can easily separate deposits from the mandrel. The release coating is better (a) endure the high temperature and corrosive environment of the CVD process, (b) have the lowest stress that can change the shape and smoothness of the mandrel, (c) completely cover the surface of the mandrel to be copied without pinholes, (d) The outer shape and smoothness of the lower mandrel surface can be substantially maintained, and (e) the binding force to the mandrel is stronger than the binding force to the copied object. The best combination of these properties appears in the coating material, and compared to the mandrel/deposit material, the coating material is formed by at least one element selected from different groups of the periodic table. For example, if the mandrel and the replica are made of zinc sulfide, which is a compound derived from the second and sixth groups of the periodic table, a better combination of coating properties, especially release properties, will be found in at least one A material made from elements other than the second and sixth groups of the periodic table. Metals and oxides are believed to be particularly suitable for difficult coating materials.

The release coating is applied as a thin coating covering the surface to be replicated. The thickness of the coating is up to about 20 microns, preferably about 1500 to about 3500 angstroms. Care must be taken to avoid pinholes extending through the coating. Applying the coating in two layers reduces the possibility of pinholes penetrating the coating. The function of some coatings, especially metal coatings, can be improved by annealing the coated mandrel.

Excessive materials for the mandrel of the present invention include, but are not limited to, zinc sulfide, tantalum, titanium, platinum, aluminum oxide (including aluminum oxide and sapphire), zinc selenide, graphite, and the like coated with aluminum oxide. Preferred mandrel materials are aluminum oxide and zinc sulfide alloy, titanium and tantalum alloy, and aluminum oxide and titanium alloy. Tantalum is also a release coating material for zinc sulfide deposits. A variety of mandrels and coating materials for zinc sulfide are also useful for accurate replication of zinc selenide and silicon carbide deposits. The mandrel used in this method can be ground to a high degree of finish, and can be used again to make precise replicas, which significantly reduces the mechanical cutting required to provide objects with the required shape and finish. Although graphite is a suitable substrate material for manufacturing near-net-shaped objects, it is quite porous and cannot be ground to a high profile and smooth finish. This property, along with its tendency to easily leave contaminants on the surface of the copy, limits the use of graphite to make near-net-shaped objects or larger objects. Depending on the material used, the surface smoothness of the mandrel ranges from about 4 to about 100 Angstroms effective value (RMS). For example, the surface smoothness of a tantalum mandrel is in the range of about 5 to 6 angstroms effective value, zinc sulfide is about 24 to 41 angstroms effective value, and titanium is about 33 to 90 angstroms effective value.

Another aspect of the present invention is an edge device for assisting the removal of the deposited dome from the mandrel. The edge device is attached to the flange of the mandrel before vapor deposition. When the material is deposited on the mandrel, the edge device contacting the flange of the mandrel is coated with the material. The deposited material forms a seam along the edge of the edge device. The seam forms a crack line along the flange of the dome, so the dome can be easily removed from the mandrel without breaking. The edge device can be any suitable shape as long as a seam is formed on the dome flange. Preferably, the edge device is a ring with a base resting on the flange of the mandrel. The connecting side of the base ends at the top end with a knife-shaped edge.

Figure 7 shows the mandrel on the isolation fixture similar to Figure 6, but with the addition of edge devices. The edge device 112 is annularly arranged on the flange 109 of the spindle 96 and is firmly fixed in the lateral direction by contacting the flange 108 of the spindle holder. Figure 7a shows an enlarged explanatory view of the edge ring 112 firmly fixed to the flange 109 of the mandrel 96. The knife edge 116 of the ring faces upward and opposite to the flange 109. As shown in FIG. 8, when the deposition material 122 coats the surface of the mandrel 96, the seam 124 is formed at the knife edge 116 of the deposition material. Advantageously, the seam 124 formed in the deposit 122 by the knife edge 116 prevents the dome from cracking when the dome is removed from the mandrel 96.

Figure 9 shows a cross-sectional view of a ring 112 with a knife-shaped edge 116 and a wall 128, a top 126, and a bottom 127. The knife edge 116 surrounds the entire top 126 of the ring 112. The size and size of the edge device can be changed with the size of the used mandrel and mandrel holder. The ring diameter ranges from about 50 to about 100 cm. The ring thickness ranges from about 0.1 to about 5 mm. The angle of the knife-shaped edge relative to the annular surface is about 30 degrees to about 90 degrees. The edge device can be made of any suitable material that is compatible with the conditions of chemical vapor deposition. Such materials are, for example, tantalum, titanium, platinum, aluminum, stainless steel, and the like. Preferably, the edge device is made of tantalum or titanium.

The method of the present invention produces domes with an aspect ratio of about 0.1 or more. Preferably, the aspect ratio is greater than 0.5. The aspect ratio (AR) is defined as the ratio of the length of the dome to the diameter of the dome. As discussed above, the gaseous reactant stream in the deposition chamber flows perpendicular to the axis of the convex mandrel and the dome formed on the mandrel. In order to obtain a dome within the scope of the present invention, the gaseous reactant stream must not impact the mandrel. The gaseous reactant diffuses onto the surface of the mandrel, so that the thickness of the dome toward the apex is gradually greater than the thickness of the bottom. The thickness of the dome at the apex of the dome ranges from about 0.75 cm to about 2.5 cm thick. The thickness of the thinnest point at the bottom of the dome ranges from about 0.5 cm to about 1.25 cm. This dome structure is less likely to break when removed from the mandrel. In this way, a more durable dome is manufactured and the output of the dome is increased. Preferred chemical vapor deposition materials, such as zinc sulfide, zinc selenide, and silicon carbide are deposited on the convex mandrel, and a release coating is applied to the convex mandrel. Other suitable deposition materials include, but are not limited to, aluminum nitride, boron nitride, diamond, and silicon.

The reaction conditions of the process of the present invention adopt a furnace temperature ranging from about 500°C to about 1500°C. The temperature range of the molten metal-containing distiller is from about 500°C to about 1000°C. The furnace pressure is about 10 to about 80 Torr. The flow rate of the gas reactant ranges from about 5 slpm (5 liters per minute) to about 80 slpm (80 liters per minute). Depending on the reactants used, the specific conditions are changed within the aforementioned range. The reactant used in the present invention is gaseous, and the conditions of the furnace and the deposition chamber can produce gas. Furthermore, the gaseous reactants react together and are transported through the deposition chamber in an inert gas medium. Any suitable inert gas can be used to practice the present invention. Suitable gases include, but are not limited to, argon, helium, krypton, xenon and the like. For example, the special conditions for preparing zinc sulfide domes are furnace temperatures ranging from about 670°C to about 740°C. The furnace pressure ranges from about 10 Torr to about 60 Torr, and the temperature of the distiller that produces zinc vapor is from about 600°C to about 650°C. The sulfur source is preferably hydrogen sulfide gas, and the inert gas preferably used is argon. After the deposition is completed, the sediment is released from the mandrel to obtain a self-erecting dome. The inner surface of the dome is machine ground to produce a finished dome with predetermined dimensions.

Example 1

A near-net shape zinc sulfide dome with an aspect ratio of about 0.8 has been manufactured using the device and method of the present invention. Zinc sulfide is deposited on the mandrel using the CVD process described below.

The vacuum furnace used to manufacture high aspect ratio zinc sulfide domes is shown in Figure 1. The vacuum furnace is composed of a water-cooled cylindrical stainless steel chamber, which is electrically resistively heated by a graphite heating element. A graphite distiller containing zinc is placed at the bottom of the furnace. The distiller is heated to a temperature of about 600 to 650°C to generate zinc vapor with a pressure of about 10 Torr. The zinc vapor is carried to the deposition area where argon is used as the carrier gas. Zinc sulfide is introduced into the deposition zone via a central injector. Zinc sulfide is deposited on the six convex mandrels by diffusion. The mandrel system is oriented so that its apex is perpendicular to the reactant stream. The reactant stream does not impact on the mandrel. Three of the mandrels are made of titanium and three are made of graphite. The mandrel system used to form the high aspect ratio dome is mounted on the inner wall of the chamber, as shown in Figures 6 and 7. The three graphite mandrels are installed as shown in Figure 6 without the titanium ring. One of the titanium mandrels is installed with a titanium ring, as shown in Figure 7, and the other two are installed as shown in Figure 6. Because the rectangular chamber obtains the maximum deposition area in the vacuum chamber furnace, this kind of chamber is adopted. Since the diameter of the dome product is smaller than the width of the narrow side of the chamber, the mandrel is installed on the narrow side of the rectangular chamber. Otherwise the mandrel will be installed on the wider side of the chamber.

The furnace temperature during the deposition process was approximately 690°C. The ratio of hydrogen sulfide/zinc sufficient particles is about 0.775. The flow rate of hydrogen sulfide is about 9.3 slPm. The argon flow rate is about 60 slPm for 25% of the operating time, slowed down to about 20 slPm for the next 25% of the time, and then maintained constant for the rest of the operating time. The deposition of zinc sulfide ended after about 189 hours.

After the vapor deposition is over, check the quality of the dome. The three domes deposited on the titanium mandrel were removed from their respective mandrels without any cracks. The dome vapor deposited on the mandrel with the titanium ring can be removed by the clamp without difficulty. Conversely, the dome vapor deposited on a jig without a ring is difficult to remove. In this way, the use of a ring structure on the fixture is an improvement.

Figure 10 is a black and white reproduction of the dome made on three titanium mandrels. The surface of the deposited zinc sulfide can be seen. The inner sides of these domes have a near-net shape. The dome is machine-ground on the inner side to produce a finished dome with the desired dimensions. The three domes on the graphite mandrel are split. The cracks are caused by the stress associated with the mismatch of the coefficient of thermal expansion between graphite and zinc sulfide.

Example 2

The chemical vapor deposition method of the present invention is used to prepare zinc sulfide domes ranging from about 5.4 cm in diameter × about 4.4 cm in length to about 17.30 cm in diameter × about 14.06 cm in length.

Titanium mandrels are used to prepare zinc sulfide domes. Figure 11 shows a schematic view of the titanium mandrel 138 used. Since the inner side of the dome is made to be a nearly clean surface, the outer surface of the mandrel 140 is made to be close to but slightly smaller than the inner side of the dome. This structure allows mechanical cutting and grinding of the dome surface. The inner dimension of the dome is approximately 16.26 cm diameter x approximately 13.92 cm length. The titanium mandrel has a hollow space 142 to reduce weight. The threaded hole 144 is provided in the center of the supporting column 148 for installation on the graphite isolation jig in the deposition area. The support post 148 contacts the apex 150 of the mandrel. The small flange 152 is arranged at the bottom of the mandrel so that the shape of the dome can be smoothly changed from bending to a flat shape.

Figure 5 shows a schematic diagram of the CVD deposition area for manufacturing a large zinc sulfide dome. The deposition chamber 64 is elongated on one side using an arch-shaped elongate member 66. The graphite isolation jig 68 is fixed to the arch-shaped elongated element 66 using bolts 71. Each spindle 70 is attached to a graphite isolation jig 68 using bolts 73. The edge forming ring used in Example 1 above was not used. The arcuate elongated element 66 maintains the direct flow of the mandrel away from the deposition gas 72 and the flow of the convective gas flow 74. This device prevents airflow from impacting on the surface of the mandrel. The deposition material deposited on the mandrel diffuses to form a zinc sulfide dome. The part of the dome facing the apex is thicker than the bottom of the dome.

The process conditions were the same as those described in Example 1 above, except that the zinc sulfide deposition was carried out for 190 hours. Since no titanium ring was used to assist the removal of the dome from the mandrel, the dome cracked. Other domes are prepared with titanium rings on the bottom. Figure 12 shows three completed dome photographs, including photographs of the dome that split when the mandrel was removed.

The completely taken out two domes are mechanically cut and ground to produce domes with required dimensions. The aspect ratio of the zinc sulfide dome is about 0.8, and the diameter of the dome is about 17.30 cm × about 14.06 cm. Although the third dome is split in the middle, the dome shows that the upper dome area manufactured by the method of the present invention is thicker than the bottom.

The foregoing examples are intended to further illustrate the present invention but are not intended to limit the scope of the present invention.

Symbol description of main components

10. . . furnace

12. . . Water-cooled stainless steel vacuum chamber shell

14. . . Graphite distiller

15. . . Molten reactant

16. . . Rectangular isolation fixture

17. . . bolt

18. . . Second heating device

20. . . Gas injector

twenty two. . . Gas vent

twenty four. . . Thermocouple

26. . . Thermocouple

28. . . Thermocouple

30. . . Isolation device

32. . . Concave mandrel

34. . . Reactant

36. . . Gas injector

38. . . exhaust vent

40. . . convection

42. . . Convex mandrel

44. . . Deposition chamber

46. . . Isolation fixture

48. . . Gas flow

50. . . Gas flow

52. . . Deposition chamber

54. . . Convex mandrel

56. . . Chemical reactant

58. . . Inside the deposition chamber

60. . . exhaust vent

62. . . Convective airflow

64. . . Deposition chamber

66. . . Arched element

68. . . Isolation fixture

70. . . Mandrel

71. . . bolt

72. . . Reactant

73. . . bolt

74. . . Convection path

76. . . Arc angle

78. . . Mandrel

82. . . Mandrel holder

84. . . bolt

85. . . Mandrel bottom

86. . . Back panel

88. . . bolt

90. . . plate

91. . . Flange

92. . . Flange

93. . . Flange

94. . . Axis

96. . . Mandrel

98. . . bolt

100. . . Back panel

101. . . Mandrel bottom

102. . . bolt

103. . . Flange

104. . . plate

106. . . Mandrel holder

108. . . Flange

109. . . Flange

110. . . Axis

112. . . Edge ring

116. . . Knife edge

122. . . Deposited material

124. . . seam

126. . . top

127. . . end

128. . . wall

138. . . Titanium mandrel

140. . . Mandrel

142. . . Hollow space

144. . . Threaded hole

148. . . Support column

150. . . Mandrel vertex

152. . . Small flange