Vapor deposition process for coating articles of manufacture

Abstract: A method is disclosed for providing an essentially uniform coating over the outer surface of an article of manufacture. In particular, a chemical vapor deposition process is disclosed for coating relatively small articles, such as spheres which may be used as lenses in optical systems. The coating may comprise an anti-reflective or alternatively, reflective, material.

Description: Background of the Invention Technical Field The present invention relates to a method of applying a coating to articles of manufacture and, more particularly, to a vapor deposition process for the application of such a coating. Description of the Prior Art In the past, spherical lenses have been coated with an anti-reflective (AR) material such as MgF₂, SiO₂, or other physical vapor deposited films. In particular, the spherical lenses would be loaded into a fixture and inserted in a barrel coating machine. The fixture would then be physically rotated to coat the spheres with the AR material. In order to coat both sides of the spheres, the process must be shut down and the fixture turned over. As a result, this coating process leaves a ring of uncoated surface around the middle of the device. Thus, when later utilizing the lens, orientation must be carefully controlled such that the uncoated ring portion is displaced out of the optical signal path. Another problem with the physical vapor deposition approach is the lack of uniformity of the AR coating, where this lack of uniformity affects the coupling efficiency of the lens. Further, the relatively small diameter of an individual sphere (for example,≤300µm) and the fragility of such a lens when fabricated out of certain materials (such as glass), results in a significant number of lenses being irreparably damaged during the coating process. In Patent Abstracts of Japan, vol. 12, no. 242 (C-510) (3089), 08.07.1988; & JP-A-63 033 571 it is disclosed to form a film nearly uniformly on the whole surface of each spherical body in simple stages by supporting the spherical body at plural points and carrying out chemical vapor deposition. Each steel sphere such as a bearing is supported on a fixing table by support rods at three or more points. Each of the support rods is a wire made of a heat resistant material and has an acute tip. The table is set on a shelf in a reactor (not shown) and a film is formed on the surface of the steel sphere by chemical vapor deposition. Thus, the homogeneous film of a uniform thickness can be formed on the whole surface of the steel sphere except the support points of the support rods in simplified stages. In Patent Abstracts of Japan, vol. 8, no. 176 (E-260) (1613), 14.08.1984; & JP-A-59 072 127 it is disclosed to prevent a sliding on the fitting of a wafer while obviating the adhesion of a pollutant on the surface of the water by forming a tapered degassing groove to the surface of a base body. Double latticed grooves are formed on a plate and arranged at intervals L₁ smaller than the diameter of the wafer and an interval L₂ with the groove just under an adjacent wafer is set to a larger value. The width D₁ and depth D₂ of the groove are set in response to the kinds of gases used for vapour growth and the size of the wafer. Since the sectional form of the groove takes a V shape, the reactive gas is made escape rapidly from a section just under the wafer while the adhesion of a large amount of a reaction residue in the groove is prevented. Accordingly to the constitution, the sliding of the wafer can be prevented, the wafer can be placed positively at a predetermined position by one operation, workability is improved, the adhesion of extraneous matter on the hot plate on the wafer accompanied by a sliding can be obviated, and a high-quality thin-film with no defect can be formed. Therefore a need remains in the art for a method of applying a uniform coating, such as an AR coating, to an article of manufacture, such as a spherical lens member. Summary of the Invention The need remaining in the prior art is addressed by the resent invention which relates to a method of applying a coating to an article of manufacture and, more particularly, to a vapor deposition process for the application of such a coating as defined by the appended claims. In one exemplary embodiment of the present invention, a plurality of articles are loaded onto a carrier and subjected to chemical vapor deposition (CVD) of a suitable material for a time and temperature sufficient to provide a substantially uniform coating of the desired thickness. The uniformity is achieved by utilizing CVD processes that favor heterogeneous film growth (which are minimally affected by gas flow dynamics) as compared to gas phase reactions and processes. For a specific embodiment, the articles may comprise spherical members. When utilized with spheres, a carrier may be formed to include a grid of trenches in the top surface thereof such that the lenses may be placed upon the top surface and rest upon only four individual points of contact (the contacts being << 1 µm and formed by the intersection of the trenches). The utilization of such a carrier results in coating essentially the entire outer surface of each spherical member. Spheres of various sizes may be simultaneously coated. In fact, a number of separate carriers, each including grids for supporting lenses of different sizes, may be processed simultaneously. When utilized to apply an AR coating to a plurality of spherical lenses, the method may employ the chemical vapor deposition of an SiO₂ material such as DADBS (diacetoxyditertiarybutoxysilane). Advantageously, the method of the present invention may also be utilized to apply a reflective coating to a spherical member. In this case, the thickness of the deposited material is chosen to provide the desired degree of reflectivity. Alternatively, metals may be deposited from organometallic precursors to yield reflective metallic films. An advantage of the technique of the present invention is that a large number of articles of manufacture may be simultaneously processed to form a coating layer with a predetermined uniformity, the CVD process resulting in an extremely high yield for the coated articles. Other and further advantages of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings. Brief Description of the Drawing FIG. 1 illustrates a plurality of exemplary articles of manufacture, in the form of lenses, disposed on a carrier suitable for use in the method of the present invention; FIG. 2 is a top view of a portion of the arrangement of FIG. 1; and FIG. 3 is a cut-away side of the arrangement of FIG. 1. Detailed Description FIG. 1 illustrates a plurality of spherical lenses 10 as positioned upon a carrier member 12 suitably formed to be used in association with the inventive method. It is to be understood that the coating process to be described hereinbelow is suitable for use with any desired article of manufacture and the following discussion directed to spherical members is for exemplary purposes only. Referring back to FIG. 1, member 12 contains a plurality of "horizontal" trenches 14 and a plurality of "vertical" trenches 16 formed in top surface 18 of member 12. The pluralities of trenches intersect to form the grid-like structure as shown in FIG. 1. The dimensions and spacing of trenches 14,16 are such that lenses 10 will rest therebetween with only four points of contact, denoted A, B, C and D in FIG. 1. As will be discussed hereinafter in association with FIGs. 2 and 3, trenches 14,16 may be formed as a bi-level structure to improve the stability of spheres 10 in carrier 12. After spherical lenses 10 are loaded on carrier 12, carrier 12 is inserted in a reactor chamber (not shown) to begin the chemical vapor deposition of the coating material. Once the coating has been deposited to the desired thickness (as determined by processing parameters such as time and ambient temperature), the carrier is removed from the chamber. Coated lenses 10 may then be removed from carrier 12, using a "pick and place" tool, for example. Although points of contact A, B, C and D will not be coated, such has not been found to affect the optical properties of the coated lens, perhaps due to the relatively small contact point size (e.g., << 1 µm for a 300 µm sphere). It is to be noted that spheres of various dimensions may be simultaneously contacted and, further, several carriers may be processed simultaneously to further increase throughput. EXAMPLE Approximately 1000 sapphire spheres, each approximately 300µm in diameter, were loaded onto a carrier (approximately one inch square) as depicted in FIG. 1. The loaded carrier was transferred into a reactor chamber and a DADBS SiO₂ layer was deposited. In practice, one reactor chamber may easily handle 10 to 50 carriers during each run. The chamber was maintained at a temperature of approximately 500°C and the deposition was performed for approximately 26.5 minutes. The time and temperature parameters were calculated to yield an AR coating layer (for λ = 1.3 µm) approximately 225 nm thick. Ellipsometry measurements on coated witness slides yielded an actual thickness of approximately 222 nm. Optical transmission and reflection measurements on the spheres gave results consistent with theory (i.e., transmissivity > 98% and reflectivity < 1%). Under optical microscope examination, no contact points were visible (with magnification greater than 400x). Measurements of several thousand spheres yielded spheres with transmissivity greater than 98%, regardless of orientation. It has been found, through experimentation, that improved stability of spheres on the trench structure of carrier 12 may result from the utilization of sets of bi-level trenches, as illustrated in particular in FIGs. 2 and 3. In the top view of FIG. 2, an exemplary sphere 10 i,j is illustrated as resting in the intersection of horizontal trench 14 i and vertical trench 16 j . Each trench, in actuality, comprises a lower trench of width w₁ and an upper trench of width w₂, where w₁ is less than w₂. The widths are chosen such that a sphere of diameter D rest upon four points of contact A, B, C and D (A and B being the only visible points of contact in FIG. 3). The difference in width being chosen such that only slight motion of the spheres (indicated by the arrows in FIG. 2) will be tolerated before the spheres contact points A', B', C'or D' associated with the upper trenches. As seen by the view in FIG. 3, lower horizontal trench 14' i is formed to comprise a depth d₁ below top surface 18 of carrier 12. This depth is chosen such that sufficient flow of material through the trench during the CVD coating process is maintained. Depth d₂ for upper trench 14'' i may be chosen such that approximately half of sphere 10 i,j remains above surface 18 of carrier 12. It is to be noted that the above-described technique is equally applicable to forming a reflective coating on an article of manufacture, where such a reflective coating may be useful for some applications. Any suitable coating material, for example a metal such as aluminum or tungsten deposited from an organo-metallic precursor, may be used to form a reflective coating utilizing the vapor deposition method of the present invention.

Claims: A method of coating a plurality of spherical members comprising the steps of: a) providing a plurality of articles of manufacture (10); b) loading said plurality of articles of manufacture onto a carrier support member (12); c) inserting the loaded carrier support member into a reactor chamber; and d) depositing, using a chemical vapor deposition process, a coating material on the outer surface of each article of manufacture, the deposition performed at a temperature and for a time sufficient to form an essentially uniform coating of a desired thickness. CHARACTERISED IN THAT in performing step a), a plurality of spherical lenses is provided; and in performing step b), the carrier support member comprises a grid of intersecting trenches formed in the top surface thereof such that each spherical lens is disposed at an intersection of a pair of trenches and is supported by four points of contact with the carrier support member. A coating method as defined in claim I wherein in performing step d), depositing an anti-reflective coating as the coating material. A coating method as defined in claim 2 wherein in performing step d), depositing a coating of silicon dioxide. A coating method as defined in claim 3 wherein in performing step d), DADBS (diacetoxy ditertiary butoxysilane) is utilized to form the silicon dioxide. A coating method as defined in claim 1 wherein in performing step d), the deposition temperature is approximately 500°C. A coating method as defined in claim I wherein in performing step d), the deposition is performed for a time sufficient to form a coating in the range of 200-300 nm. A coating method as defined in claim 6 wherein the predetermined time is in the range of 20-30 minutes. A coating method as defined in claim 1, wherein in performing step d), depositing a reflective coating. A coating method as defined in claim 8 wherein in performing step d), depositing a metallic coating from an organo-metallic precursor. A coating method as defined in claim 8 wherein in performing step d), aluminium is deposited. A coating method as defined in claim 1 wherein in performing step b), the intersecting trenches are bi-level in form, comprising a lower trench width of w1 and an upper trench width of w2, where w1 < w2.

Inventors: BLONDER GREG E, DAUTARTAS MINDAUGAS FERNAND, BLONDER, GREG E., DAUTARTAS, MINDAUGAS FERNAND
Applicants: AT & T CORP, AT&T CORP.
Application year: 1992
Main classification: C23C16
IPC codes: C23C16, C03C17, G02B1, C04B41, C03C4