Silicon substrate integration method of single crystal magneto-optical film

Abstract

The invention belongs to the field of silicon-based photoelectrons, and particularly relates to a silicon-based integration method of a single-crystal magneto-optical film. The method comprises the following steps: depositing a protective layer on a single crystal magneto-optical film through a low-kinetic-energy film preparation process such as inclination magnetron sputtering or atomic layer deposition, activating the surface of the protective layer and a silicon-based substrate through plasma, and aligning the activated protective layer film with the silicon-based substrate. And finally, bonding the single crystal magneto-optical film to the silicon-based substrate in a heating and pressurizing manner. The protection layer is used for assisting bonding, the single crystal magneto-optical film is bonded to the silicon-based substrate on the premise that the performance of the single crystal magneto-optical film is not affected, the bonding method is compatible with the subsequent high-temperature process, the non-destructive bonding vacancy of the single crystal magneto-optical film is filled up, and the bonding method has great significance in further industrial application of the single crystal magneto-optical film bonding technology.

Description

Technical Field

[0001] The present invention belongs to the field of silicon-based optoelectronics, and particularly relates to a silicon-based integration method for single-crystal magneto-optical thin films. Background Art

[0002] Silicon-based optoelectronic technology has developed rapidly in recent years. Most active devices can achieve silicon-based integration. Only photon devices based on the non-reciprocal principle, such as optical circulators and optical isolators, are still discrete devices that need to be developed. Magneto-optical materials are one of the three methods to achieve non-reciprocity due to their special asymmetric dielectric constant tensor. Therefore, the silicon-based integration of magneto-optical thin films is a popular research direction in current silicon-based optoelectronics.

[0003] Currently, the main methods for realizing the silicon-based integration of magneto-optical materials are direct deposition and bonding.

[0004] For direct deposition, due to the large gap between the lattice constants of the silicon-based substrate and the magneto-optical material thin film, the magneto-optical material thin film will exist in a polycrystalline form on the silicon-based substrate. Polycrystalline materials have high optical transmission losses due to grain boundary scattering and a large number of defects inside the lattice, while single-crystal materials do not have the above problems.

[0005] Currently, the mainstream methods for transferring single-crystal materials to silicon-based substrates are direct bonding and assisted bonding. Direct bonding requires activating the surfaces of the magneto-optical thin film and the silicon-based substrate through plasma, then bringing the two surfaces into contact, and firmly bonding the two in a vacuum environment through high-temperature and high-pressure methods. However, the process of surface plasma activation will damage the surface of the magneto-optical thin film, resulting in an increase in the surface roughness of the thin film, an increase in the transmission loss of the thin film material, and a weakening of the magneto-optical effect. The loss of single-crystal magneto-optical materials directly bonded to the target substrate via surface activation can be as high as 64 dB / cm.

[0006] In addition, assisted bonding is also a common bonding technique. Assisted bonding is a technique for bonding different materials through an intermediate layer material such as benzocyclobutene (BCB). This technique effectively avoids the damage to the surface of the magneto-optical thin film during the plasma activation process. At a wavelength of 1550 nm, compared with silicon (n = 3.48), the refractive indices of the BCB layer (n = 1.53) and Ce:YIG (n = 2.3) are relatively low. Therefore, the thickness of the BCB layer used in the assisted bonding technique should be relatively thin and requires precise control. Moreover, the BCB layer itself has problems of incompatibility with subsequent high-temperature processes and poor long-term stability. After a period of time, the single-crystal magneto-optical thin film is prone to peeling off. Therefore, BCB-assisted bonding cannot be widely applied to the field of bonding single-crystal magneto-optical materials.

[0007] Therefore, to better meet the requirements of large-scale industrial production, there is an urgent need for an assisted bonding protective layer and deposition method that neither damages the surface of the thin film nor is incompatible with subsequent high-temperature processes. Summary of the Invention

[0008] In view of the above problems or deficiencies, to solve the silicon-based bonding of existing single-crystal magneto-optical thin films, the present invention provides a silicon-based integration method for single-crystal magneto-optical thin films, a magneto-optical thin film-assisted bonding protective layer, and a deposition method for this protective layer. This method deposits a bonding protective layer on the surface of the single-crystal magneto-optical thin film by means of inclined angle sputtering, atomic layer deposition, etc., and then uses this protective layer as a bonding layer after surface activation to bond the single-crystal magneto-optical thin film to a silicon-based substrate; compared with coaxial sputtering and PECVD, the particle kinetic energy produced by the deposition methods of inclined angle sputtering and atomic layer deposition is lower. Therefore, these methods are used to deposit the auxiliary bonding protective layer first to avoid damage to the surface of the magneto-optical thin film during the process of surface plasma activation when the single-crystal magneto-optical thin film is subsequently bonded to the target substrate.

[0009] A silicon-based integration method for single-crystal magneto-optical thin films is as follows:

[0010] Step 1: Deposit a protective layer film with a thickness of 5 - 40 nm on the surface of the single-crystal magneto-optical thin film through a low-kinetic energy thin film preparation process.

[0011] The low-kinetic energy thin film preparation process means that the optical transmission loss and magneto-optical effect of the single-crystal magneto-optical thin film will not be lower than the industry application standard after the preparation of the protective layer.

[0012] Step 2: Plasma-activate both the protective layer side of the single-crystal magneto-optical thin film obtained in Step 1 and the surface of the target silicon-based substrate, and then bond these two surfaces by high-temperature pressing in a vacuum environment, thereby realizing the integration of the single-crystal magneto-optical thin film onto the silicon-based substrate.

[0013] Further, the low-kinetic energy thin film preparation process is inclined angle magnetron sputtering or atomic layer deposition, etc.

[0014] Further, the protective layer film is a film material with an optical transmission loss lower than 100 dB / cm.

[0015] Further, the protective layer film is a SiO2 film.

[0016] Further, the thickness of the SiO2 film is 5 - 40 nm.

[0017] In summary, in the present invention, a low-kinetic energy thin film preparation process such as inclined angle magnetron sputtering or atomic layer deposition is first used to deposit a protective layer on the single-crystal magneto-optical thin film, and then the surface of the protective layer and the silicon-based substrate are activated by plasma. Then, the activated protective layer thin film is aligned with the silicon-based substrate, and finally, the single-crystal magneto-optical thin film is bonded to the silicon-based substrate by heating and pressurizing. In the present invention, the protective layer is used to assist bonding, and the single-crystal magneto-optical thin film is bonded to the silicon-based substrate without affecting the performance of the single-crystal magneto-optical thin film, and is compatible with subsequent high-temperature processes, filling the gap in the lossless bonding of single-crystal magneto-optical thin films, which has great significance for the further industrial application of single-crystal magneto-optical thin film bonding technology. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of the single-crystal Ce:YIG magneto-optical thin film in the embodiment.

[0019] Figure 2 It is a high-resolution X-ray diffraction pattern of the single-crystal Ce:YIG magneto-optical thin film in the embodiment.

[0020] Figure 3 It is a schematic diagram of depositing the SiO2 protective layer thin film using the inclined angle sputtering technique in the embodiment.

[0021] Figure 4 It is a schematic diagram of oxygen plasma activation on the surface of the SiO2 protective layer thin film.

[0022] Figure 5 It is the micro-ring structure of the silicon-based substrate used in the embodiment.

[0023] Figure 6 It is the test pattern of the micro-ring structure after the final silicon-based integration in the embodiment. Detailed Embodiment

[0024] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0025] A method for silicon-based integration of a single-crystal magneto-optical thin film, the specific steps are as follows:

[0026] Step 1. In this embodiment, the magnetron sputtering technique is used to deposit an amorphous Ce:YIG magneto-optical thin film on a gadolinium gallium garnet (GGG) substrate, and the sample thin film is crystallized into a single-crystal thin film by high-temperature annealing in an oxygen atmosphere of 2 Torr at a temperature of 850 °C in an annealing furnace as Figure 1 shown in the structure. The XRD pattern of the single-crystal Ce:YIG thin film crystallized after annealing is as Figure 2 shown.

[0027] Then, the inclined angle magnetron sputtering technique is used, the angle between the sputtering source and the vertical line is 35°, and a SiO2 with a thickness of 30 nm is deposited on the surface of the single-crystal Ce:YIG thin film as an auxiliary bonding protective layer with a sputtering power of 90 W, asFigure 3 as shown

[0028] Not all of the low - kinetic - energy thin - film preparation processes are applicable. For example, in the direct - current sputtering deposition method, since the garnet target is a dielectric target, under direct current, the dielectric target can be equivalent to an infinite capacitor. At this time, although there is a voltage on the dielectric target, there is no current, and the target cannot be normally ignited.

[0029] Other negative effects of the protective layer should also be considered. For example, the material type and its thickness, such as the refractive index and thickness of different protective - layer material types, as well as the precision of the related preparation process, will all affect the optical transmission performance after the final integration of the single - crystal magneto - optical thin film on the silicon substrate to varying degrees.

[0030] Step 2: Activate the SiO2 protective - layer side of the single - crystal magneto - optical thin film obtained in Step 1 and the surface of the SOI silicon substrate through plasma, and then bond these two surfaces under high temperature and pressure in a vacuum environment, so as to integrate the single - crystal magneto - optical thin film onto the silicon substrate.

[0031] The SiO2 protective layer is activated by oxygen plasma to enhance the surface activity, as Figure 4 shown. The surface - activated protective layer contacts the SOI non - garnet substrate. Through heating and pressing, the two materials are locally attracted to each other by van der Waals forces and can be directly bonded to the surface of the target waveguide core layer. Figure 5 The micro - ring structure of the SOI silicon substrate used in the embodiment is shown. The micro - ring structure is obtained by etching silicon - on - insulator (SOI). The single - crystal magneto - optical thin film with a protective layer prepared in this embodiment is surface - activated and then bonded to the micro - ring structure, and relevant test characterizations are carried out.

[0032] The test spectrum of the micro - ring with the magneto - optical material after bonding in this embodiment is as Figure 6 shown. According to the micro - ring frequency - response curve, it can be calculated that the Q value of the micro - ring at 1550 nm is about 38750, and the loss of the single - crystal Ce:YIG material obtained by fitting is about 25 dB / cm, which is much smaller than the material loss (64 dB / cm) of directly activating the surface of the single - crystal Ce:YIG magneto - optical thin film reported in the prior art. This is because directly activating the surface of the magneto - optical thin film with plasma will cause irreversible damage to the magneto - optical thin film. Pits appear on the surface of the magneto - optical material directly activated by plasma, and the roughness increases, resulting in a significant increase in the transmission loss of the thin - film material.

[0033] As can be seen from the above embodiments, by depositing a protective layer on the surface of the magneto-optical thin film by means of low-kinetic-energy particle coating, direct damage to the surface of the magneto-optical thin film can be avoided, and the problem of increased transmission loss caused by surface damage of the magneto-optical thin film can be reduced. After the SiO2 protective layer provided by the present invention is plasma-activated, the surface of the SiO2 protective layer is activated, while the surface of the single-crystal magneto-optical material thin film is protected and not damaged by the plasma. Therefore, the transmission loss of the finally bonded material is much smaller than the material loss (64 dB / cm) of directly activating the surface of the single-crystal magneto-optical thin film reported in the literature, and it can be compatible with subsequent high-temperature processes, providing a new method for the non-destructive bonding of single-crystal magneto-optical thin films.

Claims

1. A silicon-based integration method for a single-crystal magneto-optical thin film, characterized in that The specific steps are as follows: Step 1: Deposit a protective layer film on the surface of the single-crystal magneto-optical thin film through a low-kinetic-energy thin film preparation process; The low-kinetic-energy thin film preparation process means that after the preparation of the protective layer, the optical transmission loss and magneto-optical effect of the single-crystal magneto-optical thin film will not be lower than the industry application standard; Step 2: Plasma-activate both the protective layer side of the single-crystal magneto-optical thin film obtained in Step 1 and the surface of the target silicon-based substrate, and then bond these two surfaces by high-temperature pressing in a vacuum environment, so as to integrate the single-crystal magneto-optical thin film onto the silicon-based substrate.

2. The silicon-based integration method of the single-crystal magneto-optical thin film according to claim 1, wherein: The low-kinetic-energy thin film preparation process is inclined magnetron sputtering or atomic layer deposition.

3. The silicon-based integration method of the single-crystal magneto-optical thin film according to claim 1, characterized in that: The angle between the sputtering source of the inclined magnetron sputtering and the vertical line is 35°.

4. The silicon-based integration method of the single-crystal magneto-optical thin film according to claim 1, characterized in that: The protective layer film is a thin film material with an optical transmission loss lower than 100 dB / cm.

5. The silicon-based integration method of the single-crystal magneto-optical thin film according to claim 1, characterized in that: The protective layer film is a SiO2 film.

6. The silicon-based integration method of the single-crystal magneto-optical thin film according to claim 5, characterized in that: The thickness of the SiO2 film is 5 - 40 nm.

7. The silicon-based integration method of the single-crystal magneto-optical thin film according to claim 1, wherein: The silicon-based substrate is SOI.

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