KR0170195B1 - Low temperature consollidation process and system for silica soot - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-temperature densification process and apparatus for silica fine particles for easily forming a glass film that forms a waveguide on a separate substrate for a passive component used in optical communication to form an optical signal flow and implements an optical circuit. Flame hydrolysis is a method derived from the VAD method, which is a manufacturing method of optical fiber, to form oxide fine particles by reacting raw materials in a torch at atmospheric pressure and high temperature to obtain a densified glass film by heat treatment. The conventional method has a flame temperature of 1200 to 1250 ° C. The problem of birefringence and cracking caused by the high temperature torch reaction and the high melting process temperature of 1250 ~ 1380 ℃ cannot be ruled out, and the viscosity of the over clad film is not easily controlled at the same densification process temperature. There was a problem of poor flatness after deposition.

The present invention devised to solve such a problem is to form a high quality glass film to fundamentally improve the loss of optical components and to improve the quality of various optical components to be used in optical communication in the future. FHD (Flame Hydrolysis Deposition) method to solve the problems of birefringence and cracks caused by the difference in thermal expansion coefficient between the substrate and the glass film, and to manufacture optical passive components with very low loss by constructing optical circuits on substrates such as silicon and quartz. Is used to melt and homogenize particulate silica to produce a low loss silica waveguide on a silicon substrate.

The present invention is to reduce the problems of birefringence, cracks, etc. by processing the densification of the silica fine particles formed by the low temperature flame at a lower temperature than conventional methods to increase the size of the substrate which is most problematic in the FHD method, and also the existing horizontal type The high-density electric furnace used as a vertical design eliminates the warpage of quartz tubes at high temperatures and allows processing of a large number of substrates even in narrow heating zones.

Description

Low Temperature High Density Process of Silica Particles and Its Apparatus

1 is a schematic view of a silica film forming process by flame hydrolysis.

2 is a configuration diagram of an electric furnace of a low temperature densification system.

3 is a schematic view of a gas line configuration of the present invention.

4 is a graph showing a low temperature densification method through composition control.

* Explanation of symbols for main parts of the drawings

1: silicon substrate 2: torch (quartz tube torch)

3: oxide fine particles 4: oxyhydrogen flame

5: Seoyoung tube tube 6: Super kanthal heat resistance to heat the electric furnace

7: Loading Beam for Loading Substrate

8: Pyrometer for checking the temperature of the electric furnace

9: Loading Frange

10: Automatic air driving unit that can load / unload substrate

11: water cooling line 12: viton ring for vacuum sealing of electric furnace

13: N2 Blower for Rapid Cooling Substrate

14: densification detector 15: particulate filter

16: Pirani Gauge to measure the degree of vacuum

17: gate valve to protect the vacuum pump in case of emergency

18: Scrub to Dispose of Exhaust Gas

19: Bypass line for exhausting scrub in case of emergency

20: laser for detecting the temperature and density of the electric furnace

21: Gas Injection Port through which gas is introduced

22: Oil Trap to prevent oil from the vacuum pump from flowing back to the electric furnace

23: reflector for reflecting the laser 24: vacuum pump

25: tube for T / C dummy substrate 9 for measuring the temperature of the substrate

26: Clamp to support Loading Beam (7)

27: substrate for process

28: Dummy Wafer with Thermo-Couple for Measuring Accurate Temperature of Substrate

29: gas flow controller (MFC) 30: 0.25 inch general piping of helium mixing line

31: 0.5 inch mixed pipe of helium mixing line

32: high density filter for improving mixing characteristics 33: gas manifold

34: Optical device mounting port for scanning and detecting the laser on the substrate

The present invention relates to a low-temperature densification process of silica fine particles and a device for easily forming a glass film that forms a waveguide on a separate substrate for a passive component used for optical communication to form an optical signal flow and implement an optical circuit.

With the development of optical communication technology, various planar waveguide technologies have been developed to manufacture various integrated optical components such as an optical coupler, an optical switch, and a wavelength divider.

Conventional waveguide forming technology defines a core layer by a reaction ion etching method of a silica membrane (buffer clad, core layer) prepared by flame hydrolysis, and forms a silica layer (over clad layer) to induce the flow of an optical signal. It is made of structure.

Flame hydrolysis is a method derived from the VAD method, which is an optical fiber manufacturing method, in which raw materials are reacted in a torch at atmospheric pressure and high temperature to form oxide fine particles to obtain a glass film densified by heat treatment.

For the method of depositing glass on such a substrate, see Chemical Vapor Deposition (CVD): B. H. Verbeek, C. H. Henry, et. al., Integrated Four Mach-Zender Multi- Demultiplexer Fabricated with Phosphorous Doped SiO 2 Waveguides on Si, '' J. Lightwave Technol. Vol. 6, No. 6. 1011 (1988), and Flame Hydrolysis Deposition (FHD): M. Kawachi, Silica Waveguide on Silicon and Their Application to Integrated-Optic omponents, Optical and Quantum Electronics, Vol. 22, 391 (1990).

The main parameters of the waveguide characteristics are the transparency of the glass film, the uniform refractive index and the uniform thickness of the waveguide.

The traditional FHDM of the need for such variable control. Kawachi, Silica Waveguide on Silicon and Their Application to Integrated-Optic omponents, Optical and Quantum Electronics, Vol. 22, 391 (1990) has not completely eliminated the problems of birefringence and cracking caused by the fact that the flame temperature is a high temperature torch reaction of 1200 to 1250 ° C and the melting process temperature of the particles is 1250 to 1380 ° C. .

The defect of the silica film is a phenomenon of bending of the substrate due to the high temperature process, and the existing substrate is provided with a significant stress with a radius of curvature of about 10 to 30 m.

In addition, since the viscosity is not easily controlled at the same densification process temperature, there is a problem of poor flatness after deposition of the over clad film.

The waveguide loss of the prior art is relatively low, such as 0.1 dB / cm, but the loss portion of the birefringence problem and a long waveguide of several meters, etc. is relatively large.

In the conventional FHD method, the densification process causes a significant shrinkage imbalance between the silicon substrate and the silica film at a high temperature of about 1250 to 1380 ° C, which is relatively higher than the flame process temperature.

In particular, the low temperature flame process has recently been tried, but if the densification temperature is high, the effect of trying the low temperature flame process cannot be expected.

In addition, in the existing horizontal densification furnace, since the substrate cannot be mounted vertically, it requires a lot of process area by mounting horizontally.

In this case, the heating part wound with heat resistance should be wide to maintain accurate temperature.

In order to solve such a problem, the present invention provides a high-density process system for melting and homogenizing particulate silica to prepare a low loss silica waveguide on a silicon substrate using FHD (Flame Hydrolysis Deposition). The object is to provide a low temperature densification process and an apparatus thereof.

In order to achieve the above object, the present invention provides a device for manufacturing a waveguide optical component, comprising: a high temperature and low density vertical electric furnace comprising a vertical quartz tube as a heating means to maximize the thermal efficiency and productivity of the heating unit; Temperature control means having a double control function by a dummy wafer coupled to an external pyrometer and a thermo-couple to measure an accurate temperature of the substrate mounting part of the vertical furnace; A gas line configured with a flow controller (MFC) 29, a bypass valve, and a mixing pipe, and the inlet of all the gases is introduced through the manifold 33; The upper part of the electric furnace is composed of a vacuum exhaust part composed of a vacuum exhaust line, a pyrometer (8), a high density detector (14), a particulate filter (15), and the like. It is characterized by suppressing residual stress in the silica film and forming a silica film with high flatness and low birefringence.

The present invention can increase the size of the substrate which is most problematic in the FHD method by reducing the problems such as birefringence, cracks by processing the densification of the silica fine particles formed by the low temperature flame at a lower temperature than conventional methods.

In preparation for stress, the thickness of the substrate is processed to about 900-1000 μm, which includes economic problems, and the size of the waveguide substrate can be extended to 6 to 8 inches.

In addition, if the degree of viscosity of the silica film at the same temperature can have the flatness of the film, semiconductor processing to define a thin film heater, such as Mach-Zehnder interferometer will be facilitated.

In addition, the present invention intends to open by applying an in-situ detection function using a laser in order to reduce the trial and error that occurs because it can not accurately measure the densification temperature of the silica film in the existing densification system.

In particular, the accurate detection of the densification temperature is to form a high quality silica film without distortion when the melting point is processed on a substrate of a season similar to the silica film, such as a quartz substrate.

In addition, the high density electric furnace, which was used as a horizontal type, was vertically designed to eliminate the warpage of the quartz tube at high temperatures and to process a large amount of substrates even in a narrow heating area.

Substrate used is silicon, quartz, sapphire, etc., and is used according to each function.

The present invention solves various problems arising from the existing densification method and forms a high-quality glass film to fundamentally improve the loss of optical parts and to improve the quality of various optical parts for future optical communication. And a system.

The present invention solves problems such as birefringence and cracking due to the difference in thermal expansion coefficient between a silicon substrate and a glass film, and can manufacture an optical passive component having extremely low loss by constructing an optical circuit on a substrate such as silicon and quartz.

In addition, it is intended to extend the size of the waveguide substrate to 6 to 8 inches to enable the production of molten parts having a mass production side and a long waveguide structure.

In addition, by sensing the precise densification temperature it can be melted in the polarization maintaining device by a substrate process of a material similar to the silica film melting point, such as a quartz substrate.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a high-temperature heat treatment process using high temperature flame hydrolysis and silica densification (3) deposited on the substrate such as silicon (1), quartz, ceramic, etc. Shows a method of forming a silica) film.

The basic composition of the silica fine particles is SiO ₂ and is composed of GeO ₂ , B ₂ O ₃ , P ₂ O _5, etc., which are additives for controlling the refractive index and melting point.

The raw materials used are SiCl ₄ , GeCl ₄ , BCl ₃ , POCl ₃ (PCl ₃ ), and most of them are liquid materials with low vapor pressure. Unlike general gas for semiconductors, they have strong corrosion resistance at low pressure.

The densification process is a process of removing the hydroxyl groups and pores by heat-treating the silica fine particles deposited by the flame hydrolysis method in a high-temperature electric furnace to increase the density of the silica fine particle layer to obtain a high-density glass film.

Through this process, the glass film can be prevented from cracking or bubble phenomenon, and a transparent glass layer can be formed to manufacture optical components with low loss.

In the present invention, four characteristics of the existing densification methods are designed to improve the core, first, to effectively remove the OH groups contained in the fine particles when forming silica particles, and second, to reduce the process temperature through the composition control to reduce the warpage of the substrate. Minimization; Third, homogeneous silica film formation by oxide stabilization of Phosphorous, Boron, Germanium, etc. through chemical reaction during the process; Fourth, various densities at high temperature were solved by devising the densification device shape vertically.

2 is a schematic of the furnace part of the densification system, which is designed vertically.

In the conventional horizontal densification furnace, a process zone equal to the substrate diameter is required to densify one sheet, but in the present invention, the process is designed to be possible even by securing a process zone equal to the substrate thickness.

In the existing horizontal densification furnace, since the substrate cannot be mounted vertically, it requires a lot of process area by mounting horizontally.

In this case, the heating part wound with heat resistance should be wide to maintain accurate temperature.

In the present invention, the heating part can be drastically reduced by devising the electric furnace vertically and mounting the substrate 27 horizontally.

This can prevent the warpage of the quartz tube (5) at a high temperature, can reduce the overall size of the electric furnace to increase the vacuum efficiency, accurate temperature control as well as to secure the economic advantages in manufacturing.

In the present invention, the quartz tube is used as the tube (5) and the heat source is configured in the form of resistance heating using the supercantal (6).

The mounting of the substrate 27 was precisely mounted by three Loading Beams 7 made of SiC, quartz, etc., and the heating part was configured with a precise temperature control mechanism of ± 1 ° C in a 200 to 300mm vertical region.

Temperature control of the electric furnace can be controlled by a pyrometer (8) from the outside, and a thermo-couple dummy wafer (28) inside to control the precise temperature in the heating zone.

The loading beam 7 on which the substrate 27 is mounted is coupled to the loading flange 9 and moved to the center of the furnace by the automatic air driving unit 10.

Since the loading flange 9 has a high temperature of the heating portion, the water cooling line 11 is configured to lower the local temperature of the metal portion, and the major sealing constitutes the viton ring 12 on which the metal is deposited.

In the present invention, by mounting the Loading Flange (9) in the lower part of the furnace, even if the substrate is broken during the process, the effect on the vacuum pump 24 can be reduced and maintenance is convenient.

After the densification process, the slow cooling of the sample causes crystal growth in the silica film, and it is necessary to prevent the deformation of the silica film by quenching.

Since rapid unloading of the sample exerts thermal shock on the electric furnace, in the present invention, the N2 blower (13) line guided to the substrate mounting part was configured for the rapid cooling process to induce cooling by high purity N2 when unloading the sample.

All the gases used in the densification process are supplied to the Gas Injection Port 21 through the pipe of FIG.

The upper part of the electric furnace is composed of a vacuum exhaust line, a pyrometer (8), a densification detector (14), and the like, and the vacuum exhaust is equipped with a particulate filter (15) to protect the silica particles.

The degree of vacuum of the densification system was about 10 ^-3 to 10 ^-4 Torr, and T / C and Pirani gauges 16 were formed at the gate valve 17 front end.

The by-products after the reaction of the raw materials used in the process are disposed of and exhausted by a scrubber 18 configured at the rear of the pump.

At this time, because the temperature of the furnace in the process is a high temperature, the vacuum exhaust pipe is protected by the water cooling line (11), and in case of emergency constituted a line (19) bypassed by a scrubber.

In order to detect the densification initiation and the completion of the densification, a laser beam of 6328 Å wavelength is irradiated to the substrate at an angle of 30 ° and the intensity of the reflected light is measured by the detector 14 and compared with the intensity of the silica substrate. The mounting port 34 was configured.

3 shows the gas line piping diagram of the densification system.

The low temperature densification furnace system is composed of gas lines such as BCl ₃ , helium, oxygen, nitrogen, etc. for the purpose of improving the above characteristics, all the gas is introduced into the furnace through the Manifold (33).

The gas line consists of a flow regulator (MFC) 29, a bypass valve, and a mixing pipe. The mixing pipe has a composition in which high pressure gas, helium and oxygen, is highly mixed in the pipe. After using the tube of (31) and the high-density (0.01μm) filter 32 of 0.5 inches (32) was configured of the Delay Line connected to the 0.25 (30) inch tube again.

Manifold (33) constructed an extension line from 0.25 inch tube to 0.5 inch tube to increase the conductance in the pipe.

4 is a graph of low temperature densification through composition control.

Removal of OH groups is described by VAD [S. Sudo, M. Kawachi, et. al., Low-OH-content Optical Fiber Fabricated by Vapour-phase Axial-Deposition, Electronics Letters. Vol. 14, No. 17. 534-535 (1978)], many studies have shown that up to 30 p.m. containing silica particles and SOCl2 can be reduced to 0.4 p.m.m by induction of dehydration (Eq. 1).

The type of gas used for this purpose is SF ₆ [H. Murata, Recent Developments in Vapor Phase Axial Deposition, J. Lightwave Technol. Vol. 4, No. 8. 1026 (1986)], CCl ₄ , CCl ₂ F _2, etc., and react with hydrogen to exhaust the volatile gas to form a basic reaction.

The reaction temperature was 800 ° C. in which the OH group and the added raw material were pyrolyzed. Cl ₂ , SiCl _4, and the like were used in the FHD method.

The dehydrogenation reaction was not necessarily applied during the densification process in the FHD method, and helium was used at an actual densification temperature of 1250-1380 ° C.

[S. Sudo, M. Kawachi, et. al., Low-OH-content Optical Fiber Fabricated by Vapour-phase Axial-Deposition, Electronics Letters. Vol. 14, No. 17. 534-535 (1978)]

In the present invention, BCl ₃ (CCl ₂ F ₂ ) and helium having excellent reactivity with hydrogen for dehydrogenation of OH group are used for GeO ₂ and B ₂ O _{3 in} the membrane together with dehydrogenation at a high temperature of 750-850 ° C. for 15-30 minutes. Stable and preferential melting process of addition oxides such as, P ₂ O _{5 was} induced.

The melting point of each oxide is shown in Table 1 below, and the dehydrogenation and the formation of B ₂ O ₃ proceed simultaneously to induce smoothening of the silica film and stabilize the formation of oxides such as P ₂ O ₅ . The heterogeneity can be improved and the densification temperature can be lowered.

The low temperature densification main process increases the temperature to 1000 to 1100 ° C. in the same furnace after the above dehydrogenation reaction to maintain a smooth mixing of helium and SiO, the main composition, with other densified oxides for 1-2 hours.

At this time, the addition of helium inhibits bubble formation of the film and the role of oxygen helps to form stable and homogeneous silica film by capping the desorption of light weight P, B, and Ge to the surface.

After the low temperature densification main process is completed, the annealing process is used to heat the silica film at 950-1000 ℃ for 5-10 hours in a helium and oxygen atmosphere to stabilize the silica film and to remove residual stress generated during the heat treatment process.

The low temperature densification process of the silica film reduces the bowing of the substrate, thereby reducing problems such as cracking.

The present invention as described above has the following effects.

According to the present invention, the conventional densification method causes the warpage of the substrate caused by the difference in thermal expansion coefficient between the silicon substrate and the glass (silica) layer due to the higher temperature than the flame upon deposition of the glass film, and thus deteriorates the characteristics of the silica film. Attempt to low temperature densification through control to improve the characteristics.

In addition, the conventional horizontal densification device was devised as a vertical type to solve various problems occurring in the horizontal type densification device.

Through the present invention, it is possible to implement an optical component of a low loss room when implementing various direct type optical components, and to increase the size of a substrate, thereby obtaining economic effects in mass production.

Through this technology, it can be utilized as a base technology for manufacturing various direct type optical components such as optical coupler, optical splitter, optical wavelength splitter, optical frequency divider, optical switch, optical amplifier.

Claims (13)

An apparatus for manufacturing a waveguide optical component, comprising: a high temperature and low density vertical electric furnace using a vertical quartz tube as a heating means to maximize thermal efficiency and productivity of a heating part; Temperature control means having a double control function by a dummy wafer coupled to an external pyrometer and a thermo-couple to measure an accurate temperature of the substrate mounting part of the vertical furnace; A gas line configured with a flow regulator (MGC) 29, a bypass valve, and a mixed pipe, and the inlet of all the gases is introduced through the manifold 33; The upper part of the furnace is composed of vacuum exhaust lines consisting of a vacuum exhaust line, a pyrometer (8), a densification detector (14), a particulate filter (15), and the like. Low temperature densification apparatus of silica fine particles for suppressing residual stress in film and forming silica film with high flatness and low birefringence. According to claim 1, the mixing line of the gas line is a high pressure gas of helium and oxygen in the configuration to increase the mixing in the pipe 0.25 inch (30) to 0.5 inch (31) tube and 0.5 inch high density (0.01μm) filter Low temperature densification device of silica particles, characterized in that the configuration of the Delay Line connected to the 0.25 inch tube again after using (32). 2. The apparatus for compacting low temperature silica fine particles according to claim 1, wherein the heating means of the vertical electric furnace uses a quartz tube as a tube and the heat source uses a supercantal (6). In order to manufacture waveguide type optical parts, silica particles of low temperature hydrolysis deposition method are prepared by using a high temperature, low density vertical electric furnace having a temperature control means, a gas line, a vacuum vent, and a vertical quartz tube as heating means. A low temperature high-densification process of silica fine particles, characterized in that to suppress residual stress in the silica film at a low temperature and to form a silica film having high flatness and low birefringence. 5. The low temperature densification process of silica fine particles according to claim 4, wherein a high purity N ₂ gas is introduced into the substrate mounting portion of the low temperature high density vertical electric furnace at high speed to rapidly cool the silica substrate to inhibit crystal formation. 6. The method of claim 4, wherein the low temperature of the fine silica particles to control the precise temperature by irradiating a laser and sensing the intensity of the reflected light to confirm the completion time of the high density of the fine particles on the low-temperature densification vertical electric furnace Densification process. 5. The low temperature densification process of silica fine particles according to claim 4, wherein a gate valve and a particulate filter are formed in the upper vacuum pipe of the low temperature densification vertical furnace to block abrasion of the pump and inflow of impurities. 5. The low temperature densification process of silica fine particles according to claim 4, characterized in that a line is bypassed with a scrubber in the upper vacuum pipe of the low temperature densification vertical furnace to discharge toxic gas from the electric furnace in case of emergency. [5] The method of claim 4, wherein in the densification process, BCl ₃ and helium having excellent reactivity with hydrogen are used to dehydrogenate at a temperature of 750 to 850 DEG C for 15 to 30 minutes for dehydrogenation of OH groups. Low temperature high density process of silica fine particles. According to claim 4, GeO ₂ , B ₂ O ₃ , P ₂ O _{5 in} the film in a process of 15 to 30 minutes at a temperature of 750 ~ 850 ℃ using BCl ₃ and helium excellent in hydrogen reactivity in the densification process method Low temperature densification process of silica fine particles, characterized by inducing a preferential melting process for stabilization of added oxides. 5. The method of claim 4, wherein after the dehydrogenation reaction is performed in a high-densification process, the temperature is controlled to 1000 to 1100 ° C. in the same furnace to achieve a smooth mixing of helium and castable SiO ₂ with other densified oxides. Low temperature densification process of silica fine particles, characterized in that it is maintained for 2 hours to suppress the bubble formation of the film and capping desorption of light weight P, B, and Ge to achieve stable and homogeneous silica film formation. The fine particles of claim 4, wherein the silica fine particles are heated by heating at 950-1000 ° C. for 5-10 hours in an helium and oxygen atmosphere to stabilize the silica film and remove residual stresses generated during the heat treatment. Low temperature densification process. The method of claim 12, wherein the low temperature of the silica fine particles, characterized in that to stabilize the silica film in the humidified atmosphere and to effectively remove the reaction by-products after heating for 5 to 10 hours at 950 ~ 1000 ℃ in the helium and oxygen atmosphere during the annealing process Densification process.