MXPA97003234A

MXPA97003234A - Treatment of crystal substrates to compensate combadura and distors

Info

Publication number: MXPA97003234A
Application number: MXPA/A/1997/003234A
Authority: MX
Inventors: Boek Heather; Marcel Jean Beguin Alain; Orr Maschmeyer Richard; M Trouchet Denis
Original assignee: Corning Incorporated
Priority date: 1996-04-30
Filing date: 1997-04-29
Publication date: 1998-04-01

Abstract

A method for forming a flat, substantially smooth optical wave circuit having a substantially smooth flat silica substrate and a crystalline wave guide layer concreted on the silica substrate, a post-structure treatment at an elevated temperature is given for a time sufficient to smooth said structure and compensate for distortion, alternatively, the silica substrate may be heated and pre-warped to a predetermined degree to compensate for the distortion or warpage occurring in later processing.

Description

TREATMENT OF CRYSTAL SUBSTRATES TO COMPENSATE COMBADURA AND DISTORTION FIELD OF THE INVENTION The present invention relates in general to a method of treating substrates to compensate for warpage and, more specifically, to a method for compensating for warping in multi-layer optical and electronic devices having a plurality of overlapping glass layers which are sealed between yes. Tension is generated when two cps + ales that have different coefficients of thermal expansion (CTEs) are sealed together. For example, flat waveguide crystal layers are formed on silica substrates to make light-wave optical circuits (LOC). The differences of CTEs in + re the silica and the waveguide layer, and between this layer and a layer of workers + irn ento, can cause the substrate < It is deformed unacceptably. In addition, the pattern of the waveguides can influence the shape of the substrate. A warped substrate can lead to poor resolution during the subsequent steps of photolithography and etching, or it can contribute to losses by deforming or bending waveguides and can degrade other optical properties. This problem with respect to warping, caused by layers of glass having different CTEs in optical and electronic structures of mixed layers, has not been handled or solved by the technique in a significant manner. One of the few published articles dealing with this problem is the article Polarsation-Insensiti e Arrayed-Waveguide Gratmg riultiplexer with S? 2-on-S? Os Structure by S. Suzuki et al. In Electronics Letters, 14 bpl 1994, Vol. 30, No. 8, pages. 642-643. In the Suzuki et al. Article, it was suggested that one approach to solving this problem was to replace 2 with S as a substrate to allow the use of a higher consolidation temperature and consolidate without deformation or warpage of the substrate. This approach is rather limiting and does not solve the problem when S1O2 co or the substrate must be used. Therefore, it can be seen from the above that in the formation of mixed crystal structures, such as flat waveguide crystal layers for use as optical circuits, the approach suggested by S. Suzuki et al. Severely limits the procedure and the Available materials options for the fabpcan + e of flat optical and electronic devices that have multiple layers of different glass layers that are sealed in + re yes. In another teaching of the prior art, in the EPO Patent Application, EP 0 697 605 A2"Optical Decive with Substrate and Uaveguide Structure Having Thermal Matching Interfaces", applicants teach an optical device and waveguide structure that +? Ene matched thermal interfaces that are achieved by trying to match the thermal expansion coefficients of the substrate and the waveguide layer with each layer appropriately impurified. This approach seems to be expensive and requires additional treatment that consumes time. Therefore, an object of the present invention is to provide a method for treating glass substrates to solve the distortion and warping problems of the prior art described above.

BRIEF DESCRIPTION OF THE INVENTION The present invention is directed to the treatment of substrates to compensate for warpage that results in final distortion in the optical and electrical properties in flat devices of the type having two or more crystals that are sealed together, and having different coefficients. thermal expansion (CTESs). In one embodiment of the present invention, a waveguide flat crystal layer is formed on a silica substrate to make a light wave optical circuit (LOC). The differences in CTE between the silica, the waveguide layer, and the upper overcoat crystal layer can cause the substrate to unacceptably deform. In addition, the formation of the circuit or pattern of the waveguides can also influence the shape of the substrate. In an embodiment of the present invention, a subsequent heat treatment is carried out to correct the camber caused by the formation of the waveguide crystal layer on the silica substrate. In this embodiment, the silica substrate containing the waveguide crystal layer is heated on a smooth flat surface in an oxygen-free atmosphere or environment, depending on the support plate used, at a temperature between the annealing temperature and the softening point of the silica layer for a sufficient time to allow the warped substrate to be smoothed. In an alternative embodiment, an uncoated silica substrate is heated or warped in advance to compensate for cambering that occurs predictably during formation of the specified waveguide layer on the silica substrate. A further embodiment of the first embodiment described above includes heat treatment after over coating the crystalline waveguide layer following conventional photolithography and etching steps that form the appropriate circuit on the waveguide layer. Conventional photolithography and etching techniques are well known in the art. The book "Semiconductor Lithography Principles, Practices and Materials" by U. M. Moreau, Plenurn Press, 1988 teaches suitable procedures that can be used, and is incorporated herein by reference.

BRIEF DESCRIPTION OF THE DTBUJOS For a more complete understanding of the nature and objects of the invention, reference should be made to the following detailed description of a preferred embodiment of practicing the invention, in relation to the accompanying drawings in which: Figure 1 illustrates measurement traces taken through substrate samples of the present invention. Figure 2 illustrates a side view of a coated substrate which is treated by the present invention. Figure 3 illustrates a side view of a second coated substrate that is treated by the present invention. Figure 4 illustrates a side view of a coated substrate that has been treated by the present invention. Figure 5 illustrates a perspective view of an uncoated substrate to be treated by the present invention. Figure 6 is a view of Figure 5 along line 6-6. Figure 7 is an enlarged view of Figure 2. Figure 8 is an enlarged view of Figure 3.

DESCRIPTION OF THE LEFL OF THE LEFL RNVFNCTON Heat after treatment Substrates suitable for use in the present invention are also known as slices or discs for waveguide crystal layers, and are made of silica (S1O2). They are typically straight cylinders with a diameter of 10 cm and a millimeter thick. The upper and lower surfaces of the substrate are flat (typically <5 μm over 10 c) and highly polished with beveled edges. The deviation of 5 μrn is the total roughness or the largest deviation of a perfectly smooth surface. A light waveguide layer typically of 5-7 μm (microns) thick is formed on the substrate by first forming a layer of oxide soot by hydrolysis to the flame followed by concretion of the soot layer to form a layer. of oxide crystal on the substrate. The wave guide or crystal core layers in a modality are within the quaternary Ge? 2 -B2O3 -P2O5 -S1O2 to achieve a high percent delta. U.S. Patent Nos. 5043,002 and ,154,744 illustrate conventional methods of flame and baked or concreted hydrolysis which can be used to form the glass waveguide layers on the silica substrate, and are incorporated herein by reference. The waveguide layers may also be formed with other conventional techniques such as CVD; CVD of low pressure; electronic beam deposition and ion exchange technology, which are readily available in the art ca. In the embodiment of the present invention, smooth silica substrates made of high purity fused quartz, of 10 crn in diameter and 1 m of esp > Available from General Electric, under the designation GE 124. A soot layer of 13.9% Ge? 2, 3.4% B2O3, 1.4% P2O5 and 81.3% S1O2 (all% by weight) was formed on the silica substrate. by flame hydrolysis. The oxide soot layer was then concreted at 1290 ° C to form a crystal layer of about 5 to 7 microns thick. Three additional samples were made by the same method. It should be understood that any other suitable silica substrates can be used. For example, silica substrates made of high purity fused quartz from Corning, Tnc. under Codes 7980 and 7940. When a complete device is made, following the formation of the circuit by conventional techniques described above, the gr-abated device is then overcoated with a crystal layer having a refractive index that equals that of the silica substrate. For this application, a suitable coating crystal composition comprises 8.6% D2O3, 4.6% P2O5 and 86.8% S1O2 (all% by weight). As illustrated in Figures 2 and 3, the silica substrates 10 contain the concreted glass layers 12 formed as described above, warped upwardly or downwardly, as shown in Figures 2 and 3, respectively. The maximum camber height or distance for each sample was measured and recorded. This distance d is illustrated in Figures 7 and 8 which are elongated views of Figures 2 and 3, respectively. Cambering was measured with a Taylor-Hobson profilometer. Three strokes were made through each sample (fl a B, C a ü, E a F); the lines were taken edge by edge and are illustrated in diagramatic form in Figure 1 of the drawings. Then the four samples were given a heat treatment that is hot enough to deform the sub-stratum, but cold enough to avoid-damage to the glass layers. A suitable temperature scale for that treatment is between 1200 to 1300 ° C for about 15 minutes to 7 hours. The samples were heated to the treatment temperature at about 10-17 ° C / min, and after the treatment they were cooled at a rate of about 17 ° C / min. The substrate or slice is supported on a support plate that is made of crystalline carbon; This material is polished to be extremely flat (at least as flat as the silica substrate). The graphite plate requires an oxygen-free baking atmosphere. A temperature of 1290 ° C for 1 hour was found suitable for this combination of materials. For glass layers having different compositions and configurations other heat treatment conditions may be required.

The following are examples of 4 coated r-odes described above which have been heat treated (TC at 1290 ° C for 1 hour in He) on a graphite plate. Three strokes were made through each sample (fl-B, C-D, E-F). (see Fig. 1). The data in the table are in microwaves for cambering, before and after treatment.

TABLE 1 Example 1 fl-B C-D E-F media Initial 166.0 146.2 134. 6 148 9 After TC 37.0 29.6 64. 1 4 3 - 6 Example 2 Initial 132.8 126.9 125.8 128.5 After TC 39.0 42.5 54.2 45.2 Example 3 Initial 130.3 132.5 121.4 128.1 After TC 51.1 34.0 42.2 42.4 Example 4 Initial 127.8 137.9 127.6 1.31.1 After TC 23.5 42.4 49.7 38.5 As can be seen from the above data, these samples have been successfully smoothed to be within a white scale of approximately 40 microns, which is a maximum of nominal distortion tolerable for applications and optical processes. The regulation of the heat treatment step may vary depending on the competition or closeness of the CTEs of the different layers of glass, i.e., substrate, light guide layer and reversal, or the effect of the formation of the circuit or pattern on the substrate, depending on when correction is required. For example, a single heat treatment step can occur to smooth the substrate after the formation of the light waveguide crystal; after engraving to form the optical circuit; or after coating. Optionally, more than one heating step may occur if unacceptable warpage of the substrate occurs after more than one rattling step. In another embodiment, uncoated silica slices (GE 124) were treated while resting on a silica ring 16 (See figures 5 and 6). The heat treatments consisted of heating from room temperature to a temperature higher than 1210 ° C, to approximately 10 to 17 ° C / m ?n, maintaining for a given time at that higher temperature, and cooling to the speed of the oven that it is typically 17 ° C / m? n. Substrates were drawn for plan and after heat treatment. The traces were taken through each sample (fl-B, C-D, E-F). The data for cambering d are in microns.

TABLE 2 Treatment Example fl-B C-D E-F medium heat 1 Initial 0.3 1.4 0.8 0.8 1200 ° C / 0.5 After hr of TC 19.4 5.7 10.91 12.0 Example A- C-D E-F media Initial 0.6 0.3 0.8 0.6 1200 ° C / 0.75 After HR of TC 0.8 23.3 1.3 8.5 Example fl-B C-D E-F edia 3 Initial 1.4 0.9 l.l 1.1 1210 ° C / 0.5 After hr of TC 19.7 4.4 12.1 12.1 The substrates were repeatedly (descending) warped during these heat treatments, but the amount of warpage is small. The above data demonstrate that these samples can then be used in soot deposition / consolidation in which the initial camber can compensate for the stress generated by the concreted glass layers formed on the silicon substrate. Although the preferred application of the present invention is directed to silica substrates (SIO2), it should be understood that it can also be applied to other substrates such as silicon (Si) and sapphire (AI2O3). Although the present invention has been shown and described particularly with reference to the preferred mode as illustrated in the drawing, the. A person skilled in the art will understand that several changes can be made in the detail of the same without departing from the spirit and scope of the invention as defined by the reivifications.

Claims

NOVELTY OF THE INVENTION CLAIMS

1. - A method for forming a smooth substantially flat optical waveguide circuit, comprising: a) providing a substantially smooth flat silica substrate; b) forming a layer of a plurality of oxide compounds on said substrate; c) concreting said oxide layer to form a crystalline light guide layer on said silica substrate; d) heating the structure formed in c) above at an elevated temperature for a sufficient time to smooth said structure; e) forming an optical circuit in said crystalline layer by means of conventional photolithography and etching; and f) coating the surface formed in step e) above with a superimposed glass layer having a refractive index substantial and equal to that of the substrate. ? . - The method according to claim 1, further characterized in that the structure is supported on smooth graphite support during the heating step d). 3. The method according to claim 1, further characterized in that the heating step of d) is repeated after step f). 4. A method of forming a substantially smooth light wave plane circuit comprising: a) providing a substantially smooth flat silica substrate; b) pre-warp the substrate to a predetermined degree to compensate for future warping that will occur during the formation of other glass layers on the substrate by heating said substrate to a high temperature; c) forming a layer of a plurality of oxide compounds on said substrate; d) concreting said oxide layer to form a crystalline light guide layer on said silica substrate; e) forming a circuit or pattern in said crystalline layer; and f) coating the surface formed in step e) above with a superimposed glass layer. 5. The method according to claim 1 or 4, characterized in that the oxide layer of step b) is formed by an oxide soot. 6. The method according to claim 1 or 4, further characterized in that the soot comprises a mixture of Ge? 2-fl2? 3-P2? S- ??

2. 7. The method according to claim 1 or 4, further characterized in that the substrate comprises a circular slice. 8. A method for forming a flat light wave optical circuit, substantially smooth, comprising a) providing a flat, substantially flat silica substrate; b) forming a layer of a plurality of oxide compounds on said substrate; c) concreting said oxide layer to form a crystalline light guiding layer on said silica substrate; d) forming an optical circuit in said crystalline layer by means of conventional photolithography; e) coating the surface formed in step d) above with a superimposed glass layer having a refractive index substantially equal to that of the substrate; and f) heating the structure formed in step e) at an elevated temperature for a sufficient time to smooth said structure. 9. A method for forming a flat luminous wave optical circuit, substantially smooth, comprising: a) providing a smooth substantially flat silica substratum; It will form a layer of a plurality of oxide compounds on said substrate; c) concreting said oxide layer to form a crystalline light guide layer on said silica substrate; d) forming an optical circuit in said crystalline layer by means of photolithography; e) heating the structure formed in d) above at an elevated temperature for a sufficient time to smooth said structure and overcome any distortion caused by the formation of the optical circuit; and f) coating the surface formed in step e) above with a superimposed glass layer having a refractive index substantially equal to that of the substrate; g) optionally repeat step e) of heating. 10. A method of compensating for warpage and / or distortion caused by the difference in the coefficient of thermal expansion of a flat structure having at least two layers of glass that have been sealed or fused together; said method comprises heating said structure to an elevated temperature for a sufficient time to soften and smooth at least the layers of glass, and overcome said warpage or distortion; one of said layers is optionally silica.