JP7476720B2 - Substrate bonding apparatus and method for manufacturing bonded substrate - Google Patents

Description

The present invention relates to a substrate bonding device and a method for manufacturing a bonded substrate.

Silicon carbide is a compound semiconductor material composed of silicon and carbon. Silicon carbide has a dielectric breakdown field strength ten times that of silicon, and a wide band gap three times that of silicon, making it an excellent semiconductor material. Furthermore, it is possible to control the p-type and n-type required for device fabrication over a wide range, and so it is expected to be a material for power devices that exceeds the limitations of silicon.

In addition, silicon carbide has the advantage that it can achieve high voltage resistance even with a thinner thickness, so by making it thinner, it is possible to obtain a semiconductor with low on-resistance and low loss.

However, compared to silicon semiconductors, which have been widely used up to now, it is difficult to obtain large-area silicon carbide single crystal substrates, and the manufacturing process is complicated. For these reasons, silicon carbide semiconductors are more difficult to mass-produce and more expensive than silicon semiconductors.

Various efforts have been made to reduce the cost of silicon carbide semiconductors. For example, Patent Document 1 describes a method for manufacturing a silicon carbide substrate, which includes at least preparing a silicon carbide single crystal substrate and a silicon carbide polycrystalline substrate having a micropipe density of 30 pieces/cm2 or ^less , performing a step of bonding (joining) the silicon carbide single crystal substrate and the silicon carbide polycrystalline substrate, and then performing a step of thinning the single crystal substrate to manufacture a substrate in which a single crystal layer is formed on the polycrystalline substrate.

Furthermore, Patent Document 1 describes a method for manufacturing a silicon carbide substrate in which a step of implanting hydrogen ions into the single crystal substrate to form a hydrogen ion implanted layer is performed before the step of bonding the single crystal substrate and the polycrystalline substrate, and after the step of bonding the single crystal substrate and the polycrystalline substrate, and before the step of thinning the single crystal substrate, a heat treatment is performed at a temperature of 350°C or less, and the step of thinning the single crystal substrate is a step of mechanically peeling it off at the hydrogen ion implanted layer.

This method makes it possible to produce many more bonded silicon carbide substrates from a single silicon carbide single crystal ingot.

JP 2009-117533 A

The method of manufacturing a silicon carbide wafer described in Patent Document 1 involves bonding a silicon carbide single crystal substrate, on which a thin ion-implanted layer has been formed by implanting hydrogen ions, to a silicon carbide polycrystalline substrate, and then heating and peeling the two together.

In bonding a wide band gap semiconductor substrate such as a silicon carbide single crystal substrate and a handle substrate such as a silicon carbide polycrystalline substrate, the substrates are bonded by a method called room temperature bonding. In general, first, argon (Ar) ions or neutral argon particles are irradiated to the bonding surfaces of each substrate under a high vacuum atmosphere to remove interface termination components such as oxygen, hydrogen, and hydroxyl groups (OH groups) on the bonding surfaces of the substrates, thereby activating the surfaces. Then, the activated bonding surfaces are brought into contact with each other to bond the substrates.

Conventionally, as mentioned above, surface activation processing has been performed by irradiating the substrate with argon ions or neutral argon particles. However, when irradiating the substrate with these particles, the particles have mass and attack the substrate surface, which in principle causes the sputtering phenomenon. For this reason, during irradiation, two problems can occur: (1) particles that are repelled by sputtering and ejected from the substrate or vacuum chamber aggregate to form particles, and particles that are ejected from the substrate or vacuum chamber adhere to the chamber walls and then peel off to form particles, resulting in the generation of particles; and (2) metal contamination of materials in the vacuum chamber.

Furthermore, if the generated particles become trapped between the bonding surfaces, voids may form at the bonding surface after bonding. It has also been confirmed that contamination by particles ejected from the substrates or vacuum chamber due to the sputtering phenomenon can cause defects as impurities in the bonded substrates. For these reasons, suppressing these problems has been a major challenge.

Therefore, an object of the present invention is to provide a substrate bonding apparatus and a method for manufacturing a bonded substrate that can reduce voids and contamination in an apparatus for manufacturing a bonded substrate that bonds a wide band gap semiconductor substrate and a handle substrate.

The substrate bonding apparatus of the present invention is a substrate bonding apparatus for manufacturing a bonded substrate by bonding a wide band gap semiconductor substrate and a handle substrate, and includes: a bonding chamber for bonding the wide band gap semiconductor substrate and the handle substrate; a first holding part provided inside the bonding chamber and having a first holding surface for holding either the wide band gap semiconductor substrate or the handle substrate; a second holding part having a second holding surface for holding the other of the wide band gap semiconductor substrate or the handle substrate; and an arm for changing the first holding surface and the second holding surface to a vertically downward direction and to a direction facing each other; an ultraviolet irradiation device for irradiating ultraviolet light onto at least one of the bonding surfaces of the wide band gap semiconductor substrate and the handle substrate held by the substrate holder; and a vacuum device for creating a vacuum inside the bonding chamber.

The substrate bonding apparatus of the present invention may further include a heater for heating the wide band gap semiconductor substrate and the handle substrate held by the substrate holder.

In the substrate bonding apparatus of the present invention, the substrate holder may have an adsorption mechanism that electrostatically adsorbs the wide band gap semiconductor substrate and the handle substrate on the first and second holding surfaces.

The substrate bonding device of the present invention may be such that the arm of the substrate holder has a first arm that moves the first holding part and a second arm that moves the second holding part, and the first arm and the second arm each have an upper arm portion extending horizontally, a forearm portion connected to one end of the upper arm portion and supporting the first holding part or the second holding part, and a joint shaft portion that serves as a rotation axis for rotating the forearm portion relative to the upper arm portion.

The substrate bonding apparatus of the present invention may be configured such that the ultraviolet irradiation device has an irradiation source that irradiates ultraviolet light with a wavelength of 170 nm to 260 nm.

In the substrate bonding apparatus of the present invention, the wide band gap semiconductor substrate may be a single crystal substrate, and the handle substrate may be a polycrystalline substrate.

In the substrate bonding apparatus of the present invention, both the wide band gap semiconductor substrate and the handle substrate may be silicon carbide substrates.

The manufacturing method of the bonded substrate of the present invention is a method of manufacturing a bonded substrate using the substrate bonding apparatus of the present invention, and includes an activation treatment step of holding the bonding surface of the wide band gap semiconductor substrate and the bonding surface of the handle substrate facing vertically downward with the first holding surface and the second holding surface facing vertically downward by the arm, and irradiating ultraviolet light under vacuum to at least one of the bonding surface of the wide band gap semiconductor substrate and the bonding surface of the handle substrate by the ultraviolet irradiation device, and a bonding step of driving the arm after the activation treatment step to cause the bonding surface of the wide band gap semiconductor substrate to face the bonding surface of the handle substrate and to overlap and bond the wide band gap semiconductor substrate and the handle substrate.

In the method for producing a bonded substrate of the present invention, in the bonding step, the bonding surfaces of the wide band gap semiconductor substrate and the handle substrate may face each other in a horizontal direction.

The substrate bonding apparatus of the present invention can reduce voids and contamination in a bonded substrate produced by bonding a wide band gap semiconductor substrate and a handle substrate.

According to the method for manufacturing a bonded substrate of the present invention, when a bonded substrate is manufactured by bonding a wide band gap semiconductor substrate and a handle substrate, voids and contamination in the bonded substrate can be reduced.

1 is a side view showing a schematic view of an interior of a bonding chamber of a substrate bonding apparatus according to an embodiment of the present invention; 2 is a diagram showing the inside of a bonding chamber of the substrate bonding apparatus shown in FIG. 1, and is a plan view showing typically the operation of a transfer robot. FIG. 2 is a side view showing a state in which a substrate is held by a transfer robot and is being transferred toward a substrate holder in the substrate bonding apparatus shown in FIG. 1 . FIG. 2 is a side view showing a state in which the transported substrates are held by a substrate holder in the substrate bonding apparatus shown in FIG. 1 ; 2 is a side view showing a state in which the substrates held by the substrate holders are irradiated with ultraviolet light in the substrate bonding apparatus shown in FIG. 1 ; FIG. 2 is a side view showing a state in which substrates held by substrate holders are opposed to each other in the substrate bonding apparatus shown in FIG. 1 ; 2 is a side view showing a schematic state in which the substrates are placed opposite each other and then overlapped in the substrate bonding apparatus shown in FIG. 1 . FIG. 2 is a side view showing a schematic state after the substrates have been bonded in the substrate bonding apparatus shown in FIG. 1 ; FIG. 4 is a side view showing a schematic diagram of a state in which a bonded substrate is being transported in the substrate bonding apparatus shown in FIG. 1. FIG. FIG. 10A is a plan view that shows a bonded substrate in which voids have occurred, and FIG. 10B is a plan view that shows a method for cutting the bonded substrate into chips and evaluating them.

[Substrate bonding device]
A substrate bonding apparatus according to an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiment. Note that in the drawings, the arrow X direction is the horizontal direction and indicates the width direction of the substrate bonding apparatus, the arrow Y is the vertical direction from bottom to top, and the arrow Z direction is the direction perpendicular to the arrows X and Y and indicates the depth direction of the substrate bonding apparatus.

The substrate bonding apparatus of this embodiment can be applied to the manufacture of a bonded substrate W, in which a wide band gap semiconductor substrate S and a handle substrate P are stacked together to obtain a bonded substrate W in which the wide band gap semiconductor substrate S and the handle substrate P are stacked together.

Furthermore, in manufacturing the bonded substrate W using the substrate bonding apparatus of this embodiment, a single crystal substrate can be used as the wide band gap semiconductor substrate S, and a polycrystalline substrate can be used as the handle substrate P. This embodiment can be suitably applied to the case of manufacturing a bonded substrate W in which both the wide band gap semiconductor substrate S and the handle substrate P are any of a silicon carbide (SiC) substrate, a silicon (Si) substrate, and a gallium nitride (GaN) substrate.

Specifically, for example, when obtaining a silicon carbide substrate as the bonded substrate W, a silicon carbide single crystal substrate can be used as the wide band gap semiconductor substrate S, and a silicon carbide polycrystalline substrate can be used as the handle substrate P.

The silicon carbide single crystal substrate used as the wide band gap semiconductor substrate S may be, for example, a 4H-SiC single crystal substrate obtained by processing a bulk single crystal of silicon carbide produced by a sublimation method, or a 4H-SiC single crystal substrate obtained by epitaxial growth on a single crystal wafer by a chemical vapor deposition method. The silicon carbide single crystal substrate used as the wide band gap semiconductor substrate S may contain a dopant such as nitrogen or aluminum.

The silicon carbide polycrystalline substrate used as the handle substrate P can be, for example, a 3C-SiC polycrystalline substrate obtained by forming a silicon carbide polycrystalline film by chemical vapor deposition.

The shape of the wide band gap semiconductor substrate S and the handle substrate P can be, for example, a circular parallel plate shape. The thickness of the wide band gap semiconductor substrate S and the handle substrate P is not particularly limited, and can be, for example, about 200 μm to 500 μm, respectively.

The substrate bonding apparatus 100 of this embodiment includes a bonding chamber 10, a substrate holder 20, a heater 30, a transport robot 40, an ultraviolet irradiation device 50, a suction mechanism 60, a vacuum device (not shown), and a pressurizing means (not shown). As shown in FIG. 1, the substrate holder 20, the heater 30, the transport robot 40, the ultraviolet irradiation device 50, the suction mechanism 60, the vacuum device, and the pressurizing means are provided in the bonding chamber 10. In addition, each device in the bonding chamber 10 of the substrate bonding apparatus 100 is made of stainless steel. In this embodiment, the direction of the arrow A in FIG. 1 is the left-right direction (horizontal direction), and the directions of the arrows E and F are the up-down direction (vertical direction).

Figures 1 and 3 to 9 are side views that show the inside of the bonding chamber of the substrate bonding apparatus 100, and Figure 2 is a plan view that shows the inside of the bonding chamber of the substrate bonding apparatus 100 as seen from above. Also, in Figures 5 to 9, the first conveyor table 411, the second conveyor table 421, part of the first arm 412, and part of the second arm 422 are not shown.

The bonding chamber 10 is a place where the wide band gap semiconductor substrate S and the handle substrate P are bonded therein.

The substrate holder 20 is provided inside the bonding chamber 10 and holds the wide band gap semiconductor substrate S and the handle substrate P. The substrate holder 20 has a first holder 21 having a first holding portion 211 and a second holder 22 having a second holding portion 221. As described later, the first holder 21 and the second holder 22 of the substrate holder 20 have the first holding portion 211 that holds either the wide band gap semiconductor substrate S or the handle substrate P, the second holding portion 221 that holds the other of the wide band gap semiconductor substrate S or the handle substrate P, and arms (first arm and second arm described later) that change the orientation of the first holding surface 211a and the second holding surface 221a to a vertically downward direction and to a direction facing each other.

Furthermore, the substrate holder 20 has an adsorption mechanism 60 that electrostatically adsorbs the wide band gap semiconductor substrate S and the handle substrate P on the first holding surface 211a and the second holding surface 221a, as will be described later.

By changing the orientation of the first holding surface 211a and the second holding surface 221a so that they face vertically downward, when ultraviolet light is irradiated onto the bonding surfaces S1, P1 of the wide band gap semiconductor substrate S and the handle substrate P held by the substrate holder 20, the substrates can be held so that the bonding surfaces S1, P1 face vertically downward.

In this embodiment, the first holding surface 211a and the second holding surface 221a are configured to face each other in the horizontal direction. There is no particular limitation as to whether the wide band gap semiconductor substrate S or the handle substrate P is held by the first holding part 211, and in the following description, the first holding part 211 will be described as holding the wide band gap semiconductor substrate S, and the second holding part 221 will be described as holding the handle substrate P.

The first holder 21 has a first holding part 211 having a first holding surface 211a for holding the wide band gap semiconductor substrate S, and a first arm for moving the first holding part 211. The first arm has a forearm part 212 connected to one end of an upper arm part 213 and the first holding part 211, the upper arm part 213 extending in a horizontal direction, and a joint shaft part 214 for rotating the first holding part 211 and the forearm part 212 with respect to the upper arm part 213. The first arm can move the first holding part 211 by expanding and contracting the first holding part 211 along the direction of the arrow A in FIG. 1. The joint shaft part 214 can change the orientation of the first holding part 211 so that it faces vertically downward and horizontally toward the second holder 22.

The second holder 22 has a second holding part 221 having a second holding surface 221a that holds the handle substrate P, and a second arm that moves the second holding part 221. The second arm has a forearm part 222 that connects one end of the upper arm part 223 to the second holding part 221, the upper arm part 223 that extends horizontally, and a joint shaft part 224 that rotates the second holding part 221 and the forearm part 222 relative to the upper arm part 223. In addition, the joint shaft part 224 allows the second holding part 221 to be oriented vertically downward and horizontally toward the first holder 21.

In this embodiment, when the wide band gap semiconductor substrate S and the handle substrate P are stacked, the first holding portion 211 moves toward the second holding portion 221, but the second holding portion may move toward the second holding portion, or the first holding portion and the second holding portion may move so as to approach each other.

In addition, inside the first holding part 211 and the second holding part 221, there are provided an adsorption mechanism 60 for holding the wide band gap semiconductor substrate S and the handle substrate P, and a heater 30 for heating the held wide band gap semiconductor substrate S and handle substrate P.

The heater 30 heats the wide band gap semiconductor substrate S and the handle substrate P held by the substrate holder 20. The heater 30 has a first heater 31 provided in the first holding portion 211 of the substrate holder 20 and a second heater 32 provided in the second holding portion 221. By providing the heater 30, the wide band gap semiconductor substrate S and the handle substrate P can be heated in the step of bonding the wide band gap semiconductor substrate S and the handle substrate P, thereby increasing the bonding strength.

The transfer robot 40 transfers the wide band gap semiconductor substrate S, the handle substrate P, and the bonded substrate W within the bonding chamber 10 .

The transport robot 40 has a first robot 41 that transports the substrate toward the first holder 21, and a second robot 42 that transports the substrate toward the second holder 22.

The first robot 41 has a first transport table 411 that holds and transports the wide band gap semiconductor substrate S, a first arm 412 that moves the first transport table 411, and a first arm shaft portion 413 that serves as the axis about which the first arm 412 rotates.

The second robot 42 has a second transport table 421 that holds and transports the handle substrate P, a second arm 422 that moves the second transport table 421, and a second arm shaft portion 423 that serves as the shaft about which the second arm 422 rotates.

The first conveying table 411 and the second conveying table 421 are provided with an adsorption mechanism 60, which is capable of adsorbing and transporting the wide band gap semiconductor substrate S, the handle substrate P, and the bonded substrate W to the adsorption surface 411a, which is the upper surface of the first conveying table 411, and the adsorption surface 421a, which is the upper surface of the second conveying table 421.

2, the first arm 412 can rotate around the first arm shaft 413, and the second arm 422 can rotate around the second arm shaft 423. That is, the first arm 412 moves along the arrow G in FIG. 2, and can transport a substrate adsorbed and held on the first transport stage 411. The second arm 422 moves along the arrows H and I, and can transport a substrate adsorbed and held on the second transport stage 421. Note that the position a of the first transport stage 411 shown in FIG. 2 is the initial position, and the position b is the position where the substrate is transferred to the substrate holder 20. The position c of the second transport stage 421 is the initial position, the position d is the position where the substrate is transferred to the substrate holder 20, and the position e is the position where the bonded substrate W is retrieved.

The ultraviolet irradiation device 50 irradiates ultraviolet rays onto the bonding surfaces S1, P1 of the wide band gap semiconductor substrate S and the handle substrate P held by the substrate holder 20. The ultraviolet irradiation device 50 may irradiate ultraviolet rays onto at least one of the bonding surfaces S1, P1 of the wide band gap semiconductor substrate S and the handle substrate P held by the substrate holder 20, but in order to more reliably activate the bonding surfaces of the substrates, it is preferable that the ultraviolet irradiation device 50 is configured to irradiate ultraviolet rays onto both of the bonding surfaces S1, P1 of the wide band gap semiconductor substrate S and the handle substrate P held by the substrate holder 20 as in this embodiment.

The ultraviolet irradiation device 50 has a first irradiation device 51 that irradiates ultraviolet light toward the first holding part 211 to irradiate the wide band gap semiconductor substrate S, and a second irradiation device 52 that irradiates ultraviolet light toward the first holding part 211 to irradiate the handle substrate P.

The first irradiation device 51 has a frame 511 that is open only at the top, an ultraviolet lamp 512 housed in the frame 511, and an ultraviolet arm 513 that moves the frame 511 and the ultraviolet lamp 512 in the direction of the arrow E (up and down) in Figure 1. The second irradiation device 52 has a frame 521 that is open only at the top, an ultraviolet lamp 522 housed in the frame 521, and an ultraviolet arm 523 that moves the frame 521 and the ultraviolet lamp 522 in the direction of the arrow F (up and down) in Figure 1. The ultraviolet arms 513 and 523 allow the substrate held by the substrate holder and the ultraviolet lamps 512 and 522 to be positioned at an appropriate distance, allowing efficient irradiation of ultraviolet light.

The frames 511 and 521 are configured so that ultraviolet light is not irradiated in any direction other than the open upward direction. This allows ultraviolet light to be efficiently irradiated onto the substrate held by the substrate holder 20.

The ultraviolet lamps 512 and 522 can be irradiation sources that irradiate ultraviolet rays with wavelengths of 10 nm to 280 nm, and preferably use irradiation sources that irradiate ultraviolet rays with wavelengths of 170 nm to 260 nm, which are particularly easy to obtain. In this embodiment, the ultraviolet lamps 512 and 522 are each composed of five cylindrical Xe excimer lamps, and the five lamps are arranged in a line in the width direction. The ultraviolet irradiation source can be changed in various ways according to the desired ultraviolet wavelength, and is not limited to Xe excimer lamps (172 nm), and for example, low-pressure mercury lamps (254 nm, 185 nm) can be used.

In this embodiment, the ultraviolet lamps 512, 522 are moved by the ultraviolet arms 513, 523 of the ultraviolet irradiation device 50, but the substrate holder may be moved to position the substrate holder and the ultraviolet lamps at an appropriate distance. Also, the substrate holder and the ultraviolet irradiation device may be moved closer to each other.

The suction mechanism 60 electrostatically suctions the wide band gap semiconductor substrate S and the handle substrate P, thereby enabling the substrates to be held. The suction mechanism 60 is provided on the first holding part 211 and the second holding part 221 of the substrate holder 20 and the first transport table 411 and the second transport table 421 of the transport robot 40.

By providing an adsorption mechanism 60 that electrostatically adsorbs the substrate, the substrate can be held more securely and transported or joined.

The suction mechanism 60 may be provided only on the first holding part 211 and the second holding part 221 that hold the substrate on the underside. As in this embodiment, the suction mechanism 60 is also provided on the first conveying table 411 and the second conveying table 421, so that the substrate can be held more reliably.

The vacuum device is for creating a vacuum in the bonding chamber 10. The vacuum device is configured with a pump. The type of pump is not particularly limited as long as it can create a predetermined vacuum state in the bonding chamber 10. Here, when manufacturing a bonded substrate W in which both the wide band gap semiconductor substrate S and the handle substrate P are silicon carbide substrates, a high degree of vacuum may be required. In this way, when high vacuum conditions are required, for example, a turbo molecular pump can be used. The vacuum device may be provided near the substrate holder in order to more reliably create a high vacuum around the substrate activation and bonding field.

The pressurizing means applies a predetermined pressure to the inside of the bonding chamber 10. The pressurizing method is not particularly limited, and for example, a hydraulic method or the like can be used. The wide band gap semiconductor substrate S held by the first holder 21 and the handle substrate P held by the second holder 22 are pressed in an overlapping state, whereby the wide band gap semiconductor substrate S and the handle substrate P can be bonded to each other.

By using the substrate bonding apparatus of this embodiment, activation of the bonding surfaces S1, P1 of the wide band gap semiconductor substrate S and the handle substrate P, and bonding of the wide band gap semiconductor substrate S and the handle substrate P can be performed in one apparatus. That is, the time from the activation process of the bonding surfaces S1, P1 to bonding can be shortened, and bonding can be performed while more reliably maintaining the activated state of the bonding surfaces S1, P1.

[Method of manufacturing bonded substrate]
Next, a method for manufacturing the bonded substrate of this embodiment will be described.

The manufacturing method of the bonded substrate of the present embodiment is a method of manufacturing a bonded substrate W using the substrate bonding apparatus 100 of the above-described embodiment, and includes an activation treatment step of holding the first holding surface 211a and the second holding surface 221a facing vertically downward with the arm of the substrate holder 20, and holding the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P facing vertically downward, and irradiating ultraviolet rays under vacuum to at least one of the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P by the ultraviolet irradiation device 50, and a bonding step of overlapping and bonding the wide band gap semiconductor substrate S and the handle substrate P after the activation treatment step by driving the arm of the substrate holder 20 to face the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P.

In the activation treatment step, the wavelength of the ultraviolet light is preferably 10 nm to 280 nm, and the vacuum is preferably 1×10 ⁻⁴ Pa or less.

That is, in the activation treatment step, it is preferable not to irradiate particles having mass such as Ar, as has been conventionally done, and instead of irradiating particles having mass, activation of the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P is performed by irradiating ultraviolet light.

In addition, it is preferable to mirror-polish and clean the bonding surfaces S1, P1 of the wide band gap semiconductor substrate S and the handle substrate P beforehand, prior to the activation treatment step.

Next, the operation of the substrate bonding apparatus 100 and the method for manufacturing the bonded substrate W will be described. The method for manufacturing the bonded substrate W described below is one example of a method for manufacturing a bonded substrate using the substrate bonding apparatus 100 of this embodiment, and various conditions can be changed without causing any problems.

(Activation Treatment Step)
Next, the activation treatment step will be described in detail.

The activation process is a process of irradiating at least one of the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P with ultraviolet light having a wavelength range of 10 nm to 280 nm, i.e., VUV (10 nm to 200 nm) to UV-C (200 to 280 nm) under vacuum to activate them. In this embodiment, ultraviolet light is irradiated to both the bonding surfaces S1 and P1. By irradiating both surfaces with ultraviolet light, the bonding surfaces can be more reliably activated to increase the bonding strength.

Here, activation of the bonding surfaces S1, P1 refers to removing interface termination components such as oxygen, hydrogen, and hydroxyl groups (OH groups), as well as oxide films, present on the bonding surfaces S1, P1 between the wide band gap semiconductor substrate S and the handle substrate P to form dangling bonds.

The wavelength of the ultraviolet light in the activation process can be 170 nm to 260 nm, which is within the range of 10 nm to 280 nm and is the range where lamps that serve as the irradiation source are easily available. If the wavelength of the ultraviolet light is longer than 260 nm, the amount of energy is small, and it may not be possible to provide sufficient energy to the bonding surfaces S1 and P1 to promote surface activation.

In the activation process, the activation process time for irradiating ultraviolet light may be any time that can provide sufficient energy to the bonding surfaces S1 and P1. Since the amount of energy is the product of the intensity of the ultraviolet light and the irradiation time, the time required for irradiation can be calculated from the intensity of the ultraviolet light to be irradiated. Specifically, when the intensity of the ultraviolet light to be irradiated is, for example, 5 mW/ ^cm2 , the time can be set to about 2 minutes or more.

In the activation process, the degree of vacuum can be set to 1×10 ⁻⁴ Pa (N/m ² ) or less, and more preferably, ultra-high vacuum (JIS Z 8126-1) of 1×10 ⁻⁶ Pa or less. If the degree of vacuum in the activation process is low, the amount of activity of the activated surfaces (bonding surfaces S1, P1) after irradiation with ultraviolet light may be low, and sufficient bonding strength may not be obtained in the bonding process.

The activation process using the substrate bonding device 100 of this embodiment is carried out according to the following procedure.

Prior to the activation process, the inside of the bonding chamber 10 is evacuated to a predetermined vacuum level (for example, 5×10 ⁻⁶ Pa) by a vacuum device, and the vacuum state is maintained.

First, the wide band gap semiconductor substrate S and the handle substrate P are held by the substrate holder 20. At this time, the first holding surface 211a and the second holding surface 221a are oriented vertically downward by the arm of the substrate holder 20. First, the wide band gap semiconductor substrate S is placed on the adsorption surface 411a of the first conveyance table 411 and held by electrostatic adsorption of the adsorption mechanism 60, and the handle substrate P is placed on the adsorption surface 421a of the second conveyance table 421 and held by electrostatic adsorption of the adsorption mechanism 60. At this time, the first conveyance table 411 is at the position a in Fig. 2, and the second conveyance table 421 is at the position c in Fig. 2. The positions a and c are respectively assumed to be initial state positions.

Thereafter, the first arm 412 is rotated toward the substrate holder 20 to position b along the direction of arrow G in Fig. 2, and the second arm 422 is rotated toward the substrate holder 20 to position d along the direction of arrow H in Fig. 2. As a result, the wide band gap semiconductor substrate S moves directly below the first holding portion 211 of the substrate holder 20, and the handle substrate P moves directly below the second holding portion 221 of the substrate holder 20 (Fig. 3).

4, the electrostatic adsorption of the adsorption mechanisms 60 of the first and second conveyance tables 411 and 421 is switched to the electrostatic adsorption of the adsorption mechanisms 60 of the first and second holding parts 211 and 221 of the substrate holder 20, so that the wide band gap semiconductor substrate S is electrostatically adsorbed to the first holding part 211, and the handle substrate P is electrostatically adsorbed to the second holding part 221 and held thereon. At this time, the bonding surfaces S1 and P1 of the wide band gap semiconductor substrate S and the handle substrate P face downward (FIG. 3). Thereafter, the first and second conveyance tables 411 and 43 are rotated in the opposite direction to the previous one to retreat to their initial positions (positions a and c in FIG. 2).

5, the ultraviolet arm 513 of the first irradiation device 51 of the ultraviolet irradiation device 50 is extended in the direction of the arrow E1, and the ultraviolet arm 523 of the second irradiation device 52 is extended in the direction of the arrow F1 to bring the ultraviolet lamps 512, 522 closer to the bonding surfaces S1, P1 of the wide band gap semiconductor substrate S and the handle substrate P. At this time, the wide band gap semiconductor substrate S and the first irradiation device 51, and the handle substrate P and the second irradiation device 52 are positioned vertically and linearly aligned, respectively.

Furthermore, the ultraviolet lamps 512, 522 irradiate the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P with ultraviolet light at a predetermined intensity (e.g., 172 nm ultraviolet light at 10 mW/ ^cm2 ) for a predetermined time (e.g., 2 minutes) (FIG. 4). As a result, the bonding surfaces S1, P1 are activated, and the activation process is completed.

Here, since the wide band gap semiconductor substrate S and the handle substrate P face downward in the activation process, it is possible to prevent dust and the like from adhering to the activated bonding surfaces S1 and P1.

In the above explanation, an example is shown in which ultraviolet light is irradiated to both the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P, but it is sufficient to irradiate ultraviolet light to at least one of the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P.

(Joining process)
Next, the joining step will be described.

The bonding step is a step of, after the activation treatment step, opposing the bonding surface S1 of the wide band gap semiconductor substrate S to the bonding surface P1 of the handle substrate P and bonding the bonding surface S1 of the wide band gap semiconductor substrate S to the bonding surface P1 of the handle substrate P to obtain a bonded substrate W. In the bonding step described below, the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P are surfaces irradiated with ultraviolet light in the activation treatment step.

It is preferable to bond the wide band gap semiconductor substrate S and the handle substrate P while the activation state of the bonding surfaces S1 and P1 is maintained, and the time between the activation treatment step and the bonding step is preferably within a few seconds to one minute.

In addition, the temperatures of the wide band gap semiconductor substrate S and the handle substrate in the bonding process may be, for example, about 200° C. to 400° C., although the optimal conditions vary depending on the types and combinations of the wide band gap semiconductor substrate S and the handle substrate P.

If the temperatures of the wide band gap semiconductor substrate S and the handle substrate in the bonding process are too low, such as lower than 200° C., it may be impossible to obtain sufficient bonding strength between the wide band gap semiconductor substrate S and the handle substrate P, and the occurrence of voids may not be sufficiently reduced. If the temperatures of the wide band gap semiconductor substrate S and the handle substrate in the bonding process are too high, such as higher than 400° C., distortion may occur between the wide band gap semiconductor substrate S and the handle substrate P, and one or both of the substrates may crack during cooling after the bonding process.

In the bonding step, the pressure applied to the wide band gap semiconductor substrate S and the handle substrate P by the pressure means can be set to 50 kgf to 500 kgf (0.49 kN to 4.90 kN).

The degree of vacuum in the bonding chamber 10 during the bonding process can be the same as that during the activation process.

Furthermore, the processing time in the bonding step is not particularly limited as long as the wide band gap semiconductor substrate S and the handle substrate P are bonded sufficiently, and can be, for example, 10 seconds to 5 minutes.

The bonding process using the substrate bonding device 100 of this embodiment is carried out according to the following procedure.

6, the ultraviolet arm 513 of the first irradiation device 51 is retracted in the direction of arrow E2, and the ultraviolet arm 523 of the second irradiation device 52 is retracted in the direction of arrow F2 to retract the ultraviolet irradiation device 50. Then, the forearm 212 of the first holder 21 of the substrate holder 20 is rotated 90 degrees in the direction of arrow C1 around the joint shaft 214, and the forearm 222 of the second holder 22 is rotated 90 degrees in the direction of arrow D1 around the joint shaft 224. As a result, the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P face each other in the horizontal direction (FIG. 6).

By horizontally opposing the bonding surfaces S1, P1 of the wide band gap semiconductor substrate S and the handle substrate P, adhesion of dust and the like can be suppressed, and the occurrence of voids can be suppressed.

Furthermore, as shown in FIG. 7, the upper arm portion 213 of the first holder 21 is extended in the direction of the arrow A1, and the wide band gap semiconductor substrate S held by the first holding portion 211 is moved to a position where the bonding surfaces S1 and P1 come into contact and overlap.

After the wide band gap semiconductor substrate S is moved to a position where the bonding surfaces S1 and P1 come into contact and overlap, the wide band gap semiconductor substrate S and the handle substrate P are further heated by the first heater 31 and the second heater 32. While the substrates are heated, the overlapped wide band gap semiconductor substrate S and the handle substrate P are pressurized to a predetermined pressure (e.g., 100 kgf (0.98 kN)) by the pressurizing means inside the bonding chamber 10 and maintained for a predetermined time (e.g., 3 minutes), thereby bonding the wide band gap semiconductor substrate S and the handle substrate P. As a result, a bonded substrate W is formed.

Next, the bonded substrate W that has been formed is collected. Only the electrostatic chucking of the chucking mechanism 60 of the first holding part 211 is switched off, and only the electrostatic chucking of the chucking mechanism 60 of the second holding part 221 is switched on, causing the second holding part 221 to hold the bonded substrate W. Then, as shown in FIG. 8, the upper arm 213 of the first holder 21 is contracted in the direction of arrow A2, and the forearm 212 is rotated 90 degrees in the direction of arrow C2 around the joint shaft 214 to face downward. Furthermore, the forearm 222 of the second holder 22 is rotated 90 degrees in the direction of arrow D2 around the joint shaft 224 to face downward.

9, the second conveyance table 421, which is at position c in FIG. 2, is moved to a position directly below the second holding unit 221 by rotating the second arm 422 along the direction of the arrow H to position d. Furthermore, the electrostatic attraction of the suction mechanism 60 of the second holding unit 221 is switched to the electrostatic attraction of the suction mechanism 60 of the second conveyance table 421, and the bonded substrate W is electrostatically attracted to and held on the second conveyance table 421.

Furthermore, the second arm 422 is rotated in the direction of arrow I to move the second transport table 421 holding the bonded substrate W from position d in FIG. 2 to position e. The bonded substrate W is then collected. This completes the production of the bonded substrate W.

(Comparison with conventional bonded substrate manufacturing methods and manufacturing equipment)
In conventional methods and apparatus for manufacturing bonded substrates, in order to activate the bonding surfaces, argon (Ar) ions or neutral argon particles are irradiated onto the bonding surfaces of the respective substrates, thereby removing interface termination components such as oxygen, hydrogen, and hydroxyl groups (OH groups) present on the bonding surfaces of the substrates, thereby activating the surfaces.

However, irradiation with argon ions or argon particles is an attack by particles with mass, and in principle, a sputtering phenomenon occurs, which causes problems such as (1) the generation of particles resulting from particles repelled by sputtering, and (2) the generation of metal contamination of materials in the vacuum chamber. In addition, the sputtering phenomenon at the bonding surface caused by particles with mass makes the bonding surface uneven, which causes gaps (voids, for example, void V in bonded substrate 700 in FIG. 10(A)) at the bonding surface after bonding. In addition, contamination caused by particles that fly out of the substrate or vacuum chamber due to the sputtering phenomenon causes defects in the bonded substrate.

The voids that occur in the bonded substrate can be observed using an optical microscope or a laser microscope.

The inventors have discovered that by activating the bonding surface between the wide band gap semiconductor substrate and the handle substrate by irradiating the bonding surface with ultraviolet light, an activated bonding surface can be obtained without generating particles or metal contamination due to sputtered particles such as argon particles.

The substrate bonding apparatus of this embodiment can activate the bonding surface S1 of the wide band gap semiconductor substrate S and the bonding surface P1 of the handle substrate P without using particles having mass such as argon, and can obtain a bonded substrate W with reduced voids and contamination. Furthermore, since dust and the like that can cause voids may be generated when ultraviolet light is irradiated onto the bonding surfaces of the substrates, by holding the first holding surface 211a and the second holding surface 221a facing downward, it is possible to suppress adhesion of dust and the like to the bonding surfaces of the substrates and further reduce voids and contamination compared to the case of facing upward.

The present invention is not limited to the above-described embodiment, but includes other configurations that can achieve the object of the present invention, and also includes modifications of the above-described embodiment.

In the manufacturing method of the bonded substrate in the embodiment described above, a portion of the first arm and a portion of the second arm rotate at the joint shaft portions 214, 224. However, it is also possible to adopt an embodiment in which the entire arm rotates without providing a joint shaft portion, and the orientation of the first holder and the second holder is changed so that the first holding surface and the second holding surface face vertically downward and face each other.

In addition, in the above-described embodiment, the arm is configured to have an upper arm portion, a forearm portion, and a joint shaft portion, but the configuration is not limited as long as the orientation of the holding surface of the holding portion of the board can be changed. For example, the holding portion of the board and the joint shaft portion may be directly connected.

In the manufacturing method of the bonded substrate of the above-mentioned embodiment, a method has been described in which the bonding surfaces S1, P1 of the wide band gap semiconductor substrate S and the handle substrate P are opposed to each other in the horizontal direction in the bonding process, but they may be opposed to each other in another direction.

In addition, in the above-described embodiment, an apparatus for processing wide band gap semiconductor substrates S and handle substrates P one by one was described. However, by using a substrate holder or transport robot that handles multiple wide band gap semiconductor substrates S and handle substrates P, multiple substrates may be processed in a single production batch.

Although the best configurations and methods for implementing the present invention have been disclosed above, the present invention is not limited thereto. That is, the present invention has been described mainly with respect to specific embodiments, but those skilled in the art can make various modifications to the above-described embodiments in terms of shape, material, quantity, and other detailed configurations without departing from the scope of the technical idea and purpose of the present invention. Therefore, the descriptions limiting the shapes, materials, etc. disclosed above are provided as examples to facilitate understanding of the present invention, and do not limit the present invention. Therefore, descriptions of the names of components that have some or all of the limitations on the shapes, materials, etc. removed are included in the present invention.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

In this embodiment, a silicon carbide single crystal substrate was used as the wide band gap semiconductor substrate, and a silicon carbide polycrystalline substrate was used as the handle substrate, and a silicon carbide bonded substrate was manufactured in which a silicon carbide single crystal substrate and a silicon carbide polycrystalline substrate were bonded. In addition, the substrate bonding apparatus 100 of the above-mentioned embodiment was used as the manufacturing apparatus. The substrate bonding apparatus 100 includes Xe excimer lamps as the ultraviolet lamps 512 and 522.

[Example 1]
(Manufacture of silicon carbide bonded substrates)
The silicon carbide single crystal substrate used was a 4H-SiC single crystal substrate with a diameter of 4 inches produced by sublimation. The silicon carbide polycrystalline substrate used was a 3C-SiC polycrystalline substrate with a diameter of 4 inches obtained by depositing a silicon carbide polycrystalline film by chemical vapor deposition.

First, prior to the activation process, the bonding surfaces of the silicon carbide single crystal substrate and the silicon carbide polycrystalline substrate were mirror-polished and cleaned. Next, as an activation process, the mirror-polished and cleaned bonding surfaces of the silicon carbide single crystal substrate and the silicon carbide polycrystalline substrate were irradiated with ultraviolet light without irradiating with Ar ions or Ar particles.

That is, the silicon carbide single crystal substrate and the silicon carbide polycrystalline substrate were held by the substrate holder 20, and the inside of the bonding chamber 10 was made into an ultra-high vacuum atmosphere with a degree of vacuum of 5×10 ⁻⁶ Pa or less. Furthermore, the bonding surfaces of the silicon carbide single crystal substrate and the silicon carbide polycrystalline substrate were irradiated with ultraviolet light having a wavelength of 172 nm at an intensity of 10 mW/cm ² for 2 minutes by the Xe excimer lamps (ultraviolet lamps 512 and 522).

Next, a bonding process was performed. The silicon carbide single crystal substrate and the silicon carbide polycrystalline substrate were stacked so that the activated bonding surfaces were in contact with each other, and the bonding chamber 10 was heated to 300°C under the same vacuum conditions as in the activation process. A pressure of 100 kgf (0.98 kN) was applied to the stack of silicon carbide single crystal substrate and silicon carbide polycrystalline substrate, and the substrate was held for 3 minutes. In this manner, a bonded substrate of a silicon carbide single crystal substrate and a silicon carbide polycrystalline substrate was obtained. Furthermore, the temperature in the bonding chamber 10 was lowered to room temperature, and the pressure in the bonding chamber 10 was restored to atmospheric pressure, and the bonded substrate was removed. The production of the bonded substrate was repeated 50 times, and the bonded substrate was evaluated.

(Evaluation of Silicon Carbide Bonded Substrates)
The resulting bonded substrate was evaluated for the presence or absence of voids, the presence or absence of contamination, and the bonding strength.

To check for the presence or absence of voids, microscopic observation was performed using an optical microscope to check whether voids had occurred in the resulting bonded substrate. If voids had occurred in the bonded substrate, point-like voids V could be confirmed, as in the bonded substrate 700 shown in Figure 10.

The bonded substrate was also subjected to X-ray fluorescence analysis to check whether it contained impurities and to evaluate the presence or absence of contamination. The X-ray fluorescence analysis device used was a NANOHUNTER II (manufactured by Rigaku).

The bonding strength was also evaluated by cutting the resulting bonded substrate into 5 mm square chips and checking for the presence or absence of peeling between the silicon carbide single crystal substrate and the silicon carbide polycrystalline substrate.

Even if the bonding strength of the bonding substrate is sufficient, if voids V occur in the bonding substrate as in the bonding substrate 800 shown in FIG. 10(B), a chip that does not contain voids V (e.g., chip 810 in FIG. 10(B)) is a good product, but a chip that contains voids V (e.g., chips 820, 830, 840 in FIG. 10(B)) can cause defects when used in a later process. Therefore, it can be evaluated that the more chips that contain voids V, the lower the yield.

As a result of evaluating the bonded substrate, no voids were found, and measurements of metal impurities showed that they were below the inspection limit, meaning no contamination was found. In addition, when the bonded substrate was cut into 270 5 mm square chips, no peeling was found in the chips formed from 50 bonded substrates produced from 50 production runs, and it was determined that the bonding strength was sufficient.

[Comparative Example 1]
As Comparative Example 1, the substrate bonding apparatus 100 was installed upside down, and the first holding surface 211a of the first holding portion 211 of the substrate holder 20 and the second holding surface 221a of the second holding portion 221 of the substrate holder 20 were arranged to face upward when irradiating ultraviolet light, and the manufacturing and evaluation of the bonded substrates were performed in the same manner as in Example 1. As a result of evaluating the obtained bonded substrates, no peeling was confirmed in the chips formed from 50 bonded substrates manufactured from 50 manufacturing runs. However, voids were confirmed in one chip per bonded substrate in five bonded substrates.

In Example 1 using the substrate bonding apparatus 100, which is an exemplary embodiment of the present invention, it was shown that a bonded substrate having reduced voids and contamination in the bonded substrate can be obtained by irradiating the bonding surfaces of the wide band gap semiconductor substrate and the handle substrate with ultraviolet light without irradiating particles having a mass such as Ar, thereby activating the bonding surfaces and not generating particles or metal contamination due to sputtered particles such as argon particles. In addition, it was shown that when ultraviolet light is irradiated to the bonding surfaces of the substrates, since the first holding surface and the second holding surface are downward, it is possible to suppress adhesion of dust and the like to the bonding surfaces of the substrates and to further reduce voids and contamination compared to the case where they are upward.

100 Substrate bonding apparatus 10 Bonding chamber 20 Substrate holder 211 First holding portion 211a First holding surface 221 Second holding portion 221a Second holding surface 212, 222 Forearm portion 213, 223 Upper arm portion 214, 224 Joint shaft portion 30 Heater 40 Transport robot 50 Ultraviolet irradiation device 60 Suction mechanism S Wide band gap semiconductor substrate S1 Bonding surface P of wide band gap semiconductor substrate Handle substrate P1 Bonding surface W of handle substrate Bonding substrate

Claims (8)

A substrate bonding apparatus for manufacturing a bonded substrate by bonding a wide band gap semiconductor substrate and a handle substrate, comprising:
a bonding chamber for bonding the wide band gap semiconductor substrate and the handle substrate therein;
a substrate holder provided inside the bonding chamber, the substrate holder including a first holding part having a first holding surface for holding either the wide band gap semiconductor substrate or the handle substrate, a second holding part having a second holding surface for holding the other of the wide band gap semiconductor substrate or the handle substrate, and an arm for changing the orientation of the first holding surface and the second holding surface to a vertically downward orientation and to an orientation facing each other;
an ultraviolet irradiation device that irradiates ultraviolet light onto at least one of the bonding surfaces of the wide band gap semiconductor substrate and the handle substrate held by the substrate holder;
a vacuum device for creating a vacuum in the bonding chamber ;
the arm of the substrate holder includes a first arm that moves the first holding part and a second arm that moves the second holding part,
a first arm and a second arm each having an upper arm extending horizontally, a forearm connected to one end of the upper arm and supporting the first holding portion or the second holding portion, and a joint shaft portion that serves as a rotation axis for rotating the forearm relative to the upper arm. The substrate bonding apparatus of claim 1 , further comprising a heater for heating the wide band gap semiconductor substrate and the handle substrate held by the substrate holder. 3. The substrate bonding apparatus according to claim 1, wherein the substrate holder has an adsorption mechanism that electrostatically adsorbs the wide band gap semiconductor substrate and the handle substrate on the first and second holding surfaces. 4. The substrate bonding apparatus according to claim 1 , wherein the ultraviolet ray irradiation device has an irradiation source that irradiates ultraviolet rays having a wavelength of 170 nm to 260 nm. 5. The substrate bonding apparatus according to claim 1 , wherein the wide band gap semiconductor substrate is a single crystal substrate, and the handle substrate is a polycrystalline substrate. 6. The substrate bonding apparatus according to claim 1 , wherein the wide band gap semiconductor substrate and the handle substrate are both silicon carbide substrates. A method for manufacturing a bonded substrate using a substrate bonding apparatus, comprising:
The substrate bonding apparatus is a substrate bonding apparatus for manufacturing a bonded substrate by bonding a wide band gap semiconductor substrate and a handle substrate,
a bonding chamber for bonding the wide band gap semiconductor substrate and the handle substrate therein;
a substrate holder provided inside the bonding chamber, the substrate holder including a first holding part having a first holding surface for holding either the wide band gap semiconductor substrate or the handle substrate, a second holding part having a second holding surface for holding the other of the wide band gap semiconductor substrate or the handle substrate, and an arm for changing the orientation of the first holding surface and the second holding surface to a vertically downward orientation and to an orientation facing each other;
an ultraviolet irradiation device that irradiates ultraviolet light onto at least one of the bonding surfaces of the wide band gap semiconductor substrate and the handle substrate held by the substrate holder;
a vacuum device that creates a vacuum in the bonding chamber,
an activation process in which the first holding surface and the second holding surface are oriented vertically downward by the arm, the bonding surface of the wide band gap semiconductor substrate and the bonding surface of the handle substrate are held vertically downward, and at least one of the bonding surface of the wide band gap semiconductor substrate and the bonding surface of the handle substrate is irradiated with ultraviolet light by the ultraviolet irradiation device under vacuum;
a bonding step of driving the arm after the activation treatment step to cause a bonding surface of the wide band gap semiconductor substrate to face a bonding surface of the handle substrate, and overlapping and bonding the wide band gap semiconductor substrate and the handle substrate. The method for manufacturing a bonded substrate according to claim 7 , wherein in the bonding step, the bonding surfaces of the wide band gap semiconductor substrate and the handle substrate face each other in a horizontal direction.

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