Method for manufacturing bonded substrates and apparatus for manufacturing bonded substrates

Abstract

To provide a manufacturing method of a bonded substrate capable of consistently performing processing from smoothing work to super-low-damage surface activation, and a manufacturing device for the bonded substrate.SOLUTION: The present invention relates to a method for manufacturing a bonded substrate by bonding a first inorganic crystal material substrate 14 and a second inorganic crystal material substrate 13. The method includes: a smoothing processing step of using a GCIB device capable of changing an irradiation condition to make surface roughness of the first inorganic crystal material substrate 14 disposed in vacuum equal to or less than Ra several nm with which bonding is possible; a surface activating step of using the GCIB device to respectively activate in an inert gas atmosphere a bonding surface of the first inorganic crystal material substrate 14 after a super smoothing processing step and a bonding surface of the second inorganic crystal material substrate 13 in such a manner that a thickness of a damage layer formed on a bonding interface between the first inorganic crystal material substrate 14 and the second inorganic crystal material substrate 13 becomes equal to or less than 2 nm; and a bonding step of contacting and bonding the activated bonding surface of the first inorganic crystal material substrate 14 with the activated bonding surface of the second inorganic crystal material substrate 13.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a bonded substrate and an apparatus for manufacturing a bonded substrate.

Background Art

[0002] In recent years, in various industrial fields, an inorganic crystal material substrate and an inorganic crystal material substrate of the same or different kind as the inorganic crystal material substrate are bonded to manufacture a bonded substrate. In this specification, the "inorganic crystal material substrate" refers to a wafer-shaped or chip-shaped substrate made of a metal, semiconductor, ceramics, oxide, nitride, carbide, silicide, and an inorganic crystal material containing them.

[0003] For example, silicon wafers are bonded to manufacture three-dimensional semiconductor devices or MEMS sensor devices, compound semiconductors and silicon semiconductors are bonded to manufacture multilayered heterogeneous devices or multi-junction solar cell modules, oxide crystal materials are bonded to manufacture optical elements, and piezoelectric single crystal wafers are bonded to manufacture surface acoustic wave filters.

[0004] These bonds cannot be made at high temperatures (e.g., 150°C or higher) due to the heat resistance limitations of the elements and materials formed on the substrates, and also cannot be heat-treated (post-annealed) at high temperatures after bonding.

[0005] In addition, in the case of bonding the above-mentioned heterogeneous substrates, since the thermal expansion coefficients of the materials of the heterogeneous substrates are different, heat distortion and thermal stress occur during bonding at high temperatures, resulting in problems such as inability to bond or deterioration of the characteristics after bonding.

[0006] Due to the challenges described above, bonding methods that allow bonding at low temperatures of 150°C or below, or at room temperature, are now being used for bonding inorganic crystalline material substrates to inorganic crystalline material substrates of the same or different types. One such bonding method is surface-activated bonding (SAB). Surface-activated bonding involves ionizing an inert gas such as argon to create an ion beam, and irradiating the surface of the materials to be bonded with this ion beam or plasma. This removes oxide films and contaminant layers present on the surface of the materials to be bonded, activating the surface and enabling bonding at low temperatures or room temperature.

[0007] However, in surface activation bonding, it is necessary to ensure close contact between the bonding surfaces at low temperatures or room temperature, so the activated surface to be bonded must be extremely flat. For example, ultra-smoothness with a surface roughness Ra (arithmetic mean surface roughness) of less than 1 nm is required.

[0008] Furthermore, because the surface is irradiated with ions, for most crystalline inorganic materials, ion irradiation inevitably forms a damage layer nearly 5 nm thick on the activated surface. This damage layer can be directly observed using a transmission electron microscope as an amorphous or fine-grained aggregate.

[0009] For example, in silicon and compound semiconductors, amorphous layers of about 5 nm or more are formed, which reduces interfacial electrical conductivity and is known to prevent solar cells from achieving their theoretical power generation efficiency. Similarly, in piezoelectric single crystals, damage to the crystal layer is known to occur, leading to a decrease in piezoelectric properties.

[0010] On the other hand, in high-power electronic devices and high-speed communication fields such as 5G information and communication, heat dissipation of devices has become a major challenge due to the increasing power consumption. In this field, diamond, with its high thermal conductivity, is expected to be a good inorganic crystalline substrate material for use as a heat dissipation substrate, but it is difficult to create large single-crystal diamond substrates. On the other hand, polycrystalline diamond films formed on substrates such as Si by chemical vapor deposition (CVD) have recently begun to be distributed in sizes of 4 to 6 inches, and are expected to be a high thermal conductivity substrate. In order to use this diamond substrate as a high thermal conductivity substrate, it is necessary to bond it to power devices made of wide-bandgap semiconductors or high-frequency devices such as SAW filters, but even in this case, it is known that an amorphous or fine-grained damage layer is formed at the bonding interface. Therefore, a problem arises in that the interfacial thermal resistance cannot be reduced to the theoretical value.

[0011] As mentioned above, the damaged layer reduces the heat conduction effect at the junction interface; therefore, when using diamond as a heat dissipation substrate, thinning the damaged layer is an extremely important challenge. Heat dissipation technology is particularly important for future power devices. [Overview of the project] [Problems that the invention aims to solve]

[0012] As described above, in the manufacturing of bonded substrates using inorganic crystalline material substrates, 1) in order to bond at low temperatures of 150°C or below (room temperature), ultra-smoothness with a surface roughness Ra (arithmetic mean surface roughness) of less than 1 nm is required, and 2) in order to avoid impairing the properties of the bonded substrate, the damaged layer on the activated bonded surface must be made as thin as possible.

[0013] However, in the case of diamond substrates, which are an example of inorganic crystalline material substrates, the surface of CVD-grown polycrystalline diamond has irregularities of several hundred nanometers, making it impossible to bond wafer substrates that constitute devices such as GaN or LT / LN in that state. Similarly, single-crystal substrates and polycrystalline freestanding substrates also have surface roughness of several tens of nanometers or more, making them impossible to bond in that state.

[0014] Therefore, when attempting to smooth the substrate, conventional polishing methods require a long polishing time (around 1000 hours) to smooth diamond, which is the hardest material. Furthermore, conventional polishing using abrasive grains cannot stably polish to a level of roughness that allows for room-temperature bonding with the wafer substrate as described above (for example, an arithmetic mean surface roughness Ra of 1 nm or less).

[0015] Furthermore, compound semiconductors like GaN substrates, while not as hard as diamond, have chemically unstable orientations depending on the crystal direction, making mechanical polishing difficult due to the high polishing speed. Additionally, ion irradiation activation presents a problem: because Ga and N detach from the surface at different rates, defects lacking N are introduced into the activated surface.

[0016] These defects and damages can be reduced by heating the bonded substrate to over 300°C through post-annealing after bonding; however, this high-temperature heating is not possible for bonded substrates made of dissimilar materials.

[0017] Therefore, processing using a gas cluster ion beam (GCIB) (hereinafter referred to as GCIB) can be considered. GCIB processing is a molecular process, and because it processes with kinetic energy greater than the bonding energy between atoms in the workpiece, smoothing is possible regardless of the hardness of the workpiece.

[0018] However, in GCIB smoothing processes, the relationship between processing speed and surface roughness is not always consistent and is often inverse. Even in the case of diamond, under conditions where rough surfaces can be smoothed at high speed, the achievable roughness does not reach 1 nm in arithmetic mean surface roughness Ra.

[0019] However, etching the entire surface of a 4-inch (Φ4") diamond substrate with a surface roughness of approximately Ra150nm by 1μm requires 100μA / cm². 2 With GCIB irradiation, processing can be achieved in approximately 108 minutes. In this case, the achievable surface roughness is Ra 10 to several nm. On the other hand, achieving a surface roughness of Ra 0.5 nm requires approximately 3.7 hours under ultra-smoothing conditions, but this is achievable.

[0020] The object of the present invention is to provide a method for manufacturing a bonded substrate and an apparatus for manufacturing a bonded substrate that can perform smoothing and ultra-low-damage surface activation treatment in an integrated manner using a gas cluster ion beam (GCIB) apparatus. [Means for solving the problem]

[0021] The present invention relates to a method for manufacturing a bonded substrate by joining a first inorganic crystalline material substrate to a second inorganic crystalline material substrate of the same or different type as the first inorganic crystalline material substrate. In this specification, "inorganic crystalline material substrate" refers to a wafer-shaped or chip-shaped substrate made of metals, semiconductors, ceramics, oxides, nitrides, carbides, silicides, and inorganic crystalline materials containing the same.

[0022] The manufacturing method of the present invention uses a gas cluster ion beam (GCIB) apparatus capable of changing irradiation conditions to reduce the surface roughness of a first inorganic crystalline material substrate placed in a vacuum to a level of Ra of a few nanometers or less (for example, arithmetic mean surface roughness Ra of 1 nm or less), which is suitable for bonding. superA smoothing process, a surface activation process in which the bonding surfaces of the first inorganic crystal material substrate and the second inorganic crystal material substrate that have undergone a super-smoothing process are activated in an inert gas atmosphere using a GCIB apparatus so that the thickness of the damage layer formed at the bonding interface between the first inorganic crystal material substrate and the second inorganic crystal material substrate is 2 nm or less, and a bonding process in which the activated bonding surface of the first inorganic crystal material substrate and the activated bonding surface of the second inorganic crystal material substrate are brought into contact and bonded together.

[0023] According to the present invention, since it can be made with a manufacturing apparatus that consistently implements the present invention from the smoothing process of the first inorganic crystal material substrate, the surface activation processes of the first and second inorganic crystal material substrates, to the subsequent bonding, it becomes possible to rationalize the manufacturing process and improve reliability. super In the smoothing process, while monitoring the surface roughness of the first inorganic crystal material substrate placed in a vacuum, based on the monitoring result, from the irradiation conditions for performing a flattening process to reduce the rough surface with a surface roughness Ra value of 100 nm of the first inorganic crystal material substrate to about several 10 nm, the surface of the first inorganic crystal material substrate is super-smoothed based on the relationship between the surface roughness that enables bonding and the intensity of the scattered light of the optical monitor obtained by switching to the irradiation conditions for performing a super-smoothing process in advance. By doing so, the operation of switching from the irradiation conditions for performing a flattening process to the irradiation conditions for performing a super-smoothing process can be carried out with high accuracy by monitoring, so that the surface roughness of the first inorganic crystal material substrate can be surely made Ra number nm or less that enables bonding.

[0024] super Monitoring is carried out using a monitoring device that outputs an electrical signal corresponding to the surface roughness based on the fact that the ratio of the scattered light and the reflected light of the light irradiated from a light source placed in the GCIB apparatus onto the first inorganic crystal material substrate changes depending on the surface roughness, and the GCIB apparatus may be configured to switch the irradiation conditions based on the electrical signal. By doing so, automation becomes possible.

[0025]

[0026] ​Regarding the second inorganic crystal material substrate, at least the surface activation treatment and bonding may be performed according to the present invention by previously making the surface roughness Ra number nm or less suitable for bonding by a method suitable for the second inorganic crystal material substrate. That is, the second inorganic crystal material substrate is super the same as the smoothing treatment step for the first inorganic crystal material substrate super through the smoothing treatment step, the surface roughness may be made Ra number nm or less suitable for bonding, or super a separate super through the smoothing treatment step different from the smoothing treatment step for the first inorganic crystal material substrate, the surface roughness may be made Ra number nm or less suitable for bonding.

[0027] The first inorganic crystal material substrate may be a wafer-shaped or chip-shaped substrate made of metal, semiconductor, ceramics, oxide, nitride, carbide, silicide, and inorganic crystal materials containing them. For example, it may be a diamond substrate. More specifically, it may be a CVD diamond substrate having a diamond layer formed by chemical vapor deposition (CVD).

[0028] The present invention can also be specified as a manufacturing apparatus for manufacturing a bonded substrate by bonding a first inorganic crystal material substrate and a second inorganic crystal material substrate of the same or different type from the first inorganic crystal material substrate. The manufacturing apparatus for the bonded substrate of the present invention includes a gas cluster ion beam (GCIB) apparatus capable of changing irradiation conditions, a monitoring apparatus for monitoring the surface roughness of the first inorganic crystal material substrate arranged in a vacuum, and a bonding apparatus for bonding the super-smooth first inorganic crystal material substrate and the second inorganic crystal material substrate in a vacuum. The GCIB apparatus includes a super-smoothing treatment step for making the surface roughness of the first inorganic crystal material substrate arranged in a vacuum Ra number nm or less suitable for bonding, and a surface activation step for activating the bonding surface of the first inorganic crystal material substrate and the bonding surface of the second inorganic crystal material substrate that have undergone the super-smoothing treatment step in an inert gas atmosphere using the GCIB apparatus so that the thickness of the damage layer formed at the bonding interface between the first inorganic crystal material substrate and the second inorganic crystal material substrate is 2 nm or less. In the ultra-smoothing process, while monitoring the surface roughness of the first inorganic crystalline material substrate placed in a vacuum using a monitoring device, the irradiation conditions are switched from those for a planarization process that reduces the rough surface Ra of several hundred nm to several tens of nm based on the monitoring results, to those for an ultra-smoothing process. The surface of the first inorganic crystalline material substrate is then ultra-smoothed based on the relationship between the bondable surface roughness and the intensity of scattered light from the optical monitor, for which a correlation has been determined in advance. [Brief explanation of the drawing]

[0029] [Figure 1] This is a schematic diagram (cross-sectional view) of the manufacturing apparatus for bonded substrates according to this embodiment. [Figure 2] This is a schematic diagram illustrating the details of a GCIB (Ground Control Isolation Binder) device, which is part of a manufacturing apparatus for bonded substrates. [Figure 3] (a) is a schematic diagram of a porous Faraday cup apparatus, and (b) is a schematic partial cross-sectional view of the Faraday cup body. [Figure 4] This is a schematic diagram used to explain the principle of an optical surface roughness monitoring device. [Figure 5] This is a simplified graph showing the relationship between the intensity of scattered and reflected light and surface roughness. [Figure 6] This graph shows the relationship between cluster size and damage layer thickness, confirmed through simulations and experiments. [Figure 7] This graph shows that the cluster size can be changed using the cluster size change mechanism. [Figure 8] This is a schematic diagram (cross-sectional view) of the manufacturing apparatus for bonded substrates according to the second embodiment. [Modes for carrying out the invention]

[0030] Figure 1 is a schematic diagram (cross-sectional view) showing an example of an embodiment of the manufacturing apparatus for bonded substrates according to the present invention, which implements the method of the present invention. The manufacturing apparatus for bonded substrates is broadly composed of a GCIB apparatus, a process chamber, an optical surface roughness monitoring apparatus, a bonding apparatus, and a load lock chamber.

[0031] The GCIB apparatus has a gas cluster chamber 1 that generates clusters, an ion chamber 2 that ionizes and accelerates these clusters (allowing for monomer ion removal and insertion of a magnetic field for cluster size selection), and a neutralization chamber 3 that focuses and neutralizes the ionized clusters using an Einzel lens 31 as an electrostatic lens. The gas cluster chamber 1 that generates the clusters has a cluster size changing mechanism 1C that can change the relative positions of nozzle 1A and skimmer 1B to change the cluster size. The porous Faraday cup apparatus 25 in Figure 3 allows confirmation that a predetermined cluster size has been obtained by adding and removing a magnetic field from the beam path of the gas clusters. The GCIB apparatus is connected to turbopumps 6A and 6B that exhaust the area and a gas introduction system GIS.

[0032] As described later, the first inorganic crystalline material substrate 14 is irradiated with a gas cluster ion beam (hereinafter sometimes referred to as GCIB) using a GCIB apparatus to reduce the surface roughness of the first inorganic crystalline material substrate to a Ra value of several nanometers or less, which is suitable for bonding. super A smoothing process is performed. In this embodiment, the minimum surface roughness required for bonding is assumed to be 1 nm or less in terms of arithmetic mean surface roughness Ra.

[0033] The process chamber 5 has a mechanical scanning stage on which the workpiece, a first inorganic crystalline material substrate 14, is placed. In this embodiment, the first inorganic crystalline material substrate 14 is specifically a CVD diamond substrate having a diamond layer formed by chemical vapor deposition (CVD).

[0034] The optical surface roughness monitoring device 18 monitors the surface roughness of a diamond substrate.

[0035] Load lock chambers 8 and 10 are chambers that can be vacuum-separated from the process chamber 5. For example, load lock chamber 10 is a chamber used to pre-vacuum the first inorganic crystalline material substrate 14, which will undergo smoothing processing by the GCIB apparatus, before it is placed in a sample holder 16A transported by the transport mechanism 16 and introduced into the process chamber 5. A turbopump 6C is connected to load lock chamber 8, and a turbopump 9 is connected to load lock chamber 10. High vacuum bellows 11 and 12 can move back and forth while maintaining a vacuum.

[0036] The second inorganic crystalline material substrate 13 is pre-treated to be ultra-smooth, i.e., to a surface roughness of Ra several nm or less (arithmetic mean surface roughness Ra 1 nm or less) so that it can be bonded to the first inorganic crystalline material substrate 14 (ultra-smoothing may also be done within the apparatus). In this embodiment, the second inorganic crystalline material substrate 13 is a GaN substrate. Immediately before bonding, the substrate is transported by the transport mechanism 7 to the GCIB irradiation position of the GCIB apparatus, and the GCIB apparatus is used to irradiate the bonding surface with GCIB of an inert gas (e.g., Ar gas) to perform a surface activation treatment. The surface activation treatment removes deposits from the bonding surface, and at the same time, the atoms on the surface are excited and activated with ultra-low damage.

[0037] The first inorganic crystalline material substrate 14, which has been ultra-smoothed by the GCIB apparatus, is then, if necessary, subjected to surface activation treatment with an inert gas (e.g., Ar gas) using the GCIB apparatus, similar to the second inorganic crystalline material substrate 13, and then held by the sample holder 16A and transported to a position facing the second inorganic crystalline material substrate 13, which is in the same vacuum environment. The first inorganic crystalline material substrate 14 is then pressed against the second inorganic crystalline material substrate 13, which has been previously transported to the position shown in Figure 1 by the transport mechanism 7, by the pressure contact mechanisms 17 and 17', and bonded at room temperature (surface activation bonding [SAB]).

[0038] Furthermore, the statement above that the first inorganic crystalline material substrate 14 will be subjected to surface activation treatment "as needed" means that if the GCIB irradiated at the end of the ultrasmoothing treatment is an inert gas (for example, Ar gas), there is no need to perform surface activation treatment as a separate step, and does not mean that surface activation treatment is unnecessary.

[0039] The bonded first inorganic crystalline material substrate 14 and second inorganic crystalline material substrate 13 are transported to the load lock chamber 10 by the sample holder 16A, or to the load lock chamber 8 by the transport mechanism 7, and after the load lock chamber 8 and / or load lock chamber 10 are vacuum-separated from the process chamber 5, they are removed from the apparatus.

[0040] Figure 2 is a schematic diagram illustrating the details of the GCIB apparatus, which constitutes part of the manufacturing apparatus for bonded substrates, and Figure 3 is a schematic diagram showing a porous Faraday cup apparatus 25 for checking cluster size. Each of the multiple holes H formed in the Faraday cup body 25A has a diameter of approximately Φ1 mm, and multiple small-diameter Faraday cups 25B are installed corresponding to each hole H. The Faraday cups 25B are positioned in an area where the full width at half maximum of the beam diameter to be measured can be sufficiently measured. Figure 4 is a schematic diagram illustrating the principle of the monitoring apparatus, Figure 5 is a simple graph showing the relationship between the intensity of scattered and reflected light and surface roughness, and Figure 6 is a graph showing the correlation between the distance between the nozzle and the skimmer and the cluster size.

[0041] As shown in Figure 2, the GCIB apparatus has a gas introduction system GIS, a cluster generation section (gas cluster chamber 1, nozzle 1A, and skimmer 1B), and a section that ionizes, accelerates, focuses, and neutralizes these clusters using an electrostatic lens (ion chamber 2, neutralization chamber 3, extraction electrode 4, Einzel lens 31, magnet 32, neutralizer 33). The GCIB is irradiated onto a first inorganic crystalline material substrate 14 placed on a sample folder 16A extending into the process chamber 5. The apparatus also has a mechanism (transport mechanism 34, high vacuum bellows 35) that allows a magnet 32 ​​for removing monomer ions MI or sorting cluster sizes to be inserted into the cluster beam path. By installing the porous Faraday cup apparatus 25 shown in Figure 3, the GCIB irradiation position can be measured, and the size of the cluster can be determined by changing the size of the gas cluster GC using the cluster size changing mechanism 1C from that position. Specifically, since smaller clusters deflected by the magnet 32 ​​are bent more significantly, the size of the cluster is determined by utilizing the correlation between the position of the Faraday cup 25B where the cluster peak is detected and the size of the cluster. Other components are as specified in Figure 2.

[0042] In this embodiment, the GCIB apparatus is equipped with an optical surface roughness monitoring device 18 for performing a smoothing process. The optical surface roughness monitoring device 18 measures the surface roughness of the first inorganic crystalline material substrate 14 according to the principle shown in Figure 4. In Figure 4, the monitoring device 18 includes a light source 19 such as a semiconductor laser and a polarizing plate 20 , The device comprises a hemispherical concave mirror 21, a reflected light photosensor 22, and a scattered light photosensor 23. The concave mirror 21 has a hole at its apex through which reflected light passes. GCIB is a processing gas cluster ion beam, SL is scattered light, PL is polarized light that has passed through the polarizer 20, RL is reflected light, 20' is a polarizer aligned with the polarization direction of the incident light from the reflected light, and reference numeral 11 denotes the reflected light that has passed through the polarizer.

[0043] The laser light emitted from the light source 19 passes through the polarizing plate 20 to become polarized light PL, which is then irradiated onto the surface of the workpiece, the first inorganic crystalline material substrate 14. The irradiation position coincides with the position where the GCIB is irradiated. When the surface roughness is large, the polarized light PL is scattered, some of which becomes scattered light SL and is scattered from the surface to the surroundings, and some which is reflected and focused inside the perforated concave mirror 21 and received by the scattered light photosensor 23. The reflected light RL passes through the hole in the concave mirror 21 and through the polarizing plate 20', and the component in the direction of the deflection of the incident light enters the reflected light photosensor 22.

[0044] As GCIB irradiation progresses and the surface roughness of the workpiece decreases, scattered light SL decreases and reflected light RL increases. This process is shown in Figure 5.

[0045] The relationship between the surface roughness and the readings of the two photosensors (reflected light photosensor 22 and scattered light photosensor 23) is determined in advance. Once the desired roughness is achieved, the GCIB irradiation conditions are switched to the ultra-smoothing treatment conditions. For planarization, reactive gases such as SF6, NF3, CF4, or Ar, Kr, Xe, etc., may be added to the reactive gases, and the type of gas can be selected depending on the irradiation conditions. Switching from planarization to ultra-smoothing is performed by changing irradiation parameters such as the type of gas, irradiation energy, irradiation current, cluster size, irradiation angle, and substrate temperature. At this time, a magnetic field can be inserted into the GCIB beam path to remove monomer ions MI and to check the cluster size using a porous Faraday cup apparatus 25. If the change in light intensity is sufficient, either signal may be used, and if insufficient, both may be calculated and used. Furthermore, in the same manner, once an indication value showing that an ultra-smooth state has been obtained is obtained, the ultra-smoothing treatment is completed, and if necessary, the GCIB apparatus is used to perform surface activation treatment with an inert gas (e.g., Ar gas) using GCIB, and then bonding with the inorganic material substrate is performed as shown in Figure 1.

[0046] In this embodiment, by using the optical surface roughness monitoring device 18, the smoothing process is carried out in two stages: a planarization process that reduces the rough surface of the substrate, which has a surface roughness of Ra several hundred nm, to about several tens of nm, and an ultra-smoothing process that makes the surface roughness Ra below several nm, which is suitable for bonding.

[0047] Figure 6 shows a graph confirming the relationship between cluster size and damage layer thickness through simulation and experiment. This figure shows the damage layer when Ar clusters (irradiated at 5KV) of various sizes are irradiated onto a Si surface, and demonstrates that in this case, the thickness of the damage layer can be made significantly smaller than 1 nm.

[0048] Figure 7 also shows that the cluster size can be changed by the cluster size changing mechanism 1C shown in Figure 2. From this figure, it can be seen that by changing the distance between nozzle 1A and skimmer 1B by approximately 5 mm, the peak position of the cluster size can be changed from approximately 1000 to 5000.

[0049] Figure 8 is a schematic diagram (cross-sectional view) of a manufacturing apparatus for bonded substrates, showing a second embodiment of the present invention. The manufacturing apparatus for bonded substrates consists of a GCIB apparatus chamber 100, a pre-processing chamber 101, and a bonding chamber 102. The pre-processing chamber 101 and the bonding chamber 102 are each equipped with an exhaust system and separated by a gate valve, thereby independently controlling the pressure in each chamber. The bonding chamber maintains an ultra-high vacuum of 10⁻⁷ to 10⁻⁸ Pa, and when the gate valve is opened, the pre-processing chamber 101 is also evacuated to the same pressure as the bonding chamber 102. The loading and unloading of substrates between the pre-processing chamber 101 and the bonding chamber 102 is carried out by a transport mechanism (not shown).

[0050] The pre-processing chamber 101 includes a GCIB device, an XY stage 103 for holding the substrate, and a monitoring device 18 for monitoring surface roughness. The XY stage 103 allows the GCIB to scan the substrate by driving it in the XY direction. By using an XYZ stage 103, the relative distance between the GCIB device and the substrate may be varied to adjust the irradiation conditions. Furthermore, by providing an angle-adjustable mechanism for the substrate stage, the incident angle of the GCIB relative to the normal of the substrate may be optimized.

[0051] The bonding chamber 102 receives the substrates to be bonded from the pre-processing chamber 101 and holds them in the upper and lower bonding stages 106 and 106'. After aligning the substrates, the upper and lower bonding stages 106 and 106' are moved relative to each other by driving the lifting devices 105 and 105', bringing the substrates to be bonded closer together and into contact. The control device applies pressure to the substrates to be bonded for a predetermined time. The pressure and duration of the pressure should be set according to the substrates to be bonded. Heaters may be provided on the upper and lower bonding stages to control the temperature of the bonding surface.

[0052] The pre-treatment chamber 101 performs planarization, ultra-smoothing, surface activation treatment, and film deposition on the substrate before bonding. Planarization and ultra-smoothing may be performed together as a smoothing treatment. Planarization is a process that flattens a substrate having an uneven structure until the surface roughness Ra is tens of nanometers or less. Planarization is performed by irradiating the substrate surface with GCIB using a GCIB apparatus to remove a portion of the substrate material. In this embodiment, reactive gases such as SF6, CF4, NF3, and CHF3 are used for planarization to achieve high-speed processing. However, inert gases such as Ar and N2 may also be used, and the type of gas, including O2, N2O, C2F6, C3F8, C4F6, SiF4, COF2, Kr, and Xe, can be appropriately selected according to the irradiation conditions. If the surface roughness Ra of the substrate to be bonded is tens of nanometers or less, the planarization treatment may be omitted.

[0053] Ultra-smoothing is a process that smooths the surface roughness Ra of the substrate to be bonded to 1 nm or less. The same GCIB apparatus is used for planarization, but the characteristic feature is that the irradiation conditions of the GCIB are changed. During planarization, the monitoring device 18 measures the surface roughness of the substrate in situ during the planarization process. When the surface roughness meets a predetermined value, the control mechanism changes the irradiation conditions of the GCIB. In this embodiment, at the timing of switching from planarization to ultra-smoothing, the monomer ion removal magnet is extended into the beam path of the GCIB. During planarization, the processing current can be increased by retracting the monomer ion removal magnet, thereby increasing the etching speed. During ultra-smoothing, monomer ions that cause damage to the substrate surface can be reliably removed by extending the monomer ion removal magnet.

[0054] Surface activation treatment is a process that activates the bonding surface of the substrates to be bonded. The same GCIB apparatus is used for surface activation treatment as for planarization and ultra-smoothing. During ultra-smoothing, the monitoring device 18 also measures the surface roughness of the substrate in situ during processing. Since the amount of change in surface roughness during ultra-smoothing is very small, the monitoring device 18 is equipped with a highly accurate optical system that can detect the amount of change in surface roughness in sub-angstrom units. When the surface roughness meets a predetermined value, the control mechanism changes the irradiation conditions of the GCIB. In this embodiment, the gas type is changed from a reactive gas to an inert gas at the timing of switching from ultra-smoothing to surface activation treatment. Fluorine-based reactive gases have a high etching rate and are suitable for planarization and ultra-smoothing, but they remain on the bonding surface. Therefore, by using an inert gas in the surface activation treatment, the bonding surface is cleaned and activated at the same time.

[0055] The film deposition process involves depositing a material suitable for bonding onto the bonding surface of the substrates to be bonded. Examples of deposition materials include metals such as Si, Fe, Ti, Al, and Cu, as well as oxides and nitrides. The same GCIB apparatus is used for planarization, ultra-smoothing, and surface activation processes, and the process is switched from etching to deposition by changing the gas type and acceleration voltage. The film deposition process can be performed before the bonding process. Alternatively, the film deposition process may be performed after ultra-smoothing, followed by surface activation and then bonding; or, the surface activation process may be performed after ultra-smoothing, followed by film deposition and then bonding. If the substrate surface becomes inactive due to the film deposition process, then surface activation may be performed after ultra-smoothing, followed by film deposition, followed by further surface activation and then bonding. Performing surface activation before film deposition also has the effect of facilitating material deposition during the film deposition process. Furthermore, when using difficult-to-process materials for film deposition, the film deposition process may be performed before planarization or ultra-smoothing.

[0056] In this embodiment, planarization, ultra-smoothing, surface activation treatment, and film deposition can all be performed with a single GCIB apparatus, contributing to a simplification of the apparatus configuration and a reduction in cost. Furthermore, planarization, ultra-smoothing, and surface activation treatment also contribute to the cleaning of the substrate surface.

[0057] In this embodiment, the pretreatment chamber 101 is configured as a single chamber, but multiple pretreatment chambers may be provided. For example, the first pretreatment chamber may be used for planarization, and the second pretreatment chamber may be used for ultra-smoothing, surface activation treatment, and film formation treatment. If a reactive gas is used in the first pretreatment chamber and an inert gas in the second pretreatment chamber, the introduction of the reactive gas into the bonding chamber can be suppressed, thereby preventing contamination of the bonding chamber.

[0058] The irradiation conditions for GCIB should be determined according to the type of substrate and required specifications. Parameters for switching irradiation conditions include gas type, gas flow rate, current, cluster size, irradiation energy, incident angle, and substrate temperature.

[0059] In this embodiment, the GCIB irradiation conditions are switched using the monitoring device 18, but the conditions may also be determined in advance and the GCIB irradiation conditions may be switched by time control.

[0060] In ultra-smoothing and surface activation treatments, using GCIB makes it possible to obtain activated surfaces with less damage and less distortion compared to using a single-atom ion beam.

[0061] In this embodiment, diamond was used as the bonding substrate, but the type of substrate is not limited to this. This apparatus may also be used to bond piezoelectric single crystals such as LiNbO3 or LiTaO3 with acoustic layers such as sapphire or SiOx, or other inorganic materials. [Explanation of symbols]

[0062] 1. Gas cluster room 2. Ion Room 3 Neutralization room 5 Process Chambers 6A, 6B, 6C, 9 Turbo pumps 7. Conveying mechanism 8,10 Load Lock Chamber 11,12 High Vacuum Bellows 13. Second inorganic crystalline material substrate 14. First inorganic crystalline material substrate 16 Conveying mechanism 16A Sample Holder 17. Press-fitting mechanism 18 Monitoring device

Claims

1. A method for manufacturing a bonded substrate by joining a first inorganic crystalline material substrate and a second inorganic crystalline material substrate of the same or different type as the first inorganic crystalline material substrate, An ultra-smoothing process is performed using a gas cluster ion beam (GCIB) apparatus capable of changing irradiation conditions to reduce the surface roughness of the first inorganic crystalline material substrate, which is placed in a vacuum, to a minimum Ra of several nanometers, which is suitable for bonding. A surface activation step is performed to activate the bonding surface of the first inorganic crystalline material substrate that has undergone the ultra-smoothing process and the bonding surface of the second inorganic crystalline material substrate, respectively, in an inert gas atmosphere using the GCIB apparatus, such that the thickness of the damage layer formed at the bonding interface of the first inorganic crystalline material substrate and the second inorganic crystalline material substrate is 2 nm or less. The process comprises a bonding step of bringing the activated bonding surface of the first inorganic crystalline material substrate into contact with the activated bonding surface of the second inorganic crystalline material substrate and bonding them together. A method for manufacturing a bonded substrate, characterized in that, in the ultra-smoothing process, while monitoring the surface roughness of the first inorganic crystalline material substrate placed in a vacuum, the irradiation conditions are switched from those for a planarization process that reduces the rough surface Ra of several hundred nm of the first inorganic crystalline material substrate to about several tens of nm based on the monitoring results, and the surface of the first inorganic crystalline material substrate is ultra-smoothed based on the relationship between the bondable surface roughness and the intensity of scattered light from an optical monitor, for which a correlation has been determined in advance.

2. The monitoring is performed using a monitoring device that outputs an electrical signal corresponding to the surface roughness, based on the fact that the ratio of scattered light to reflected light of light irradiated onto the first inorganic crystalline material substrate from a light source placed in the GCIB apparatus changes according to the surface roughness. The method for manufacturing a bonded substrate according to claim 1, wherein the GCIB apparatus switches the irradiation conditions by the electrical signal.

3. The method for manufacturing a bonded substrate according to claim 1, wherein the second inorganic crystalline material substrate is subjected to the same ultrasmoothing process as the first inorganic crystalline material substrate, so that its surface roughness is less than or equal to a Ra of several nm, which is suitable for bonding.

4. The method for manufacturing a bonded substrate according to claim 1, wherein the second inorganic crystalline material substrate is subjected to an ultrasmoothing process separate from the ultrasmoothing process for the first inorganic crystalline material substrate, so that its surface roughness is less than or equal to a Ra of several nm, which is suitable for bonding.

5. The method for manufacturing a bonded substrate according to claim 1, wherein the first inorganic crystalline material substrate is a diamond substrate.

6. A manufacturing apparatus for manufacturing a bonded substrate by joining a first inorganic crystalline material substrate and a second inorganic crystalline material substrate of the same or different type as the first inorganic crystalline material substrate, A gas cluster ion beam (GCIB) system that allows for changes in irradiation conditions, A monitoring device for monitoring the surface roughness of the first inorganic crystalline material substrate placed in a vacuum, The system includes a bonding apparatus for bonding the first and second inorganic crystalline material substrates, which are ultra-smoothed in a vacuum, The GCIB apparatus is configured to perform an ultra-smoothing process to reduce the surface roughness of the first inorganic crystalline material substrate, which is placed in a vacuum, to a minimum Ra of several nanometers or less, which is suitable for bonding; and a surface activation process to activate the bonding surface of the first inorganic crystalline material substrate and the bonding surface of the second inorganic crystalline material substrate, which have undergone the ultra-smoothing process, in an inert gas atmosphere using the GCIB apparatus, such that the thickness of the damage layer formed at the bonding interface between the first inorganic crystalline material substrate and the second inorganic crystalline material substrate is 2 nm or less. The ultra-smoothing process is characterized in that, while monitoring the surface roughness of the first inorganic crystalline material substrate, which is placed in a vacuum, using the monitoring device, the irradiation conditions are switched from those for a planarization process that reduces the rough surface of the first inorganic crystalline material substrate, which has a surface roughness of several hundred nanometers Ra, to about several tens of nanometers, based on the monitoring results, to those for an ultra-smoothing process, thereby ultra-smoothing the surface of the first inorganic crystalline material substrate based on the relationship between the bondable surface roughness and the intensity of scattered light from an optical monitor, for which a correlation has been determined in advance.

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