Bonding device and bonding method

Abstract

To provide a technique for improving the accuracy of joint of substrates.SOLUTION: A joint device comprises: a first holding part; a second holding part; a first interferometer; a housing; a gas supply part; and an air flow control cover. The first holding part sucks and holds the first substrate. The second holding part sucks and holds the second substrate. The first interferometer irradiates the second holding part or a first object moving together with the second holding part in a first horizontal direction with light to measure a distance in the first horizontal direction to the second holding part or the first object. The housing houses the first holding part, the second holding part, and the first interferometer. The gas supply part is provided at a side surface of the housing and supplies gas into an inner part of the housing. The air flow control cover is provided at the inner part of the housing, and converts a direction of a part of a flow of the gas supplied from the gas supply part toward a first path of light radiated from the first interferometer.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a bonding apparatus and a bonding method. [Background technology]

[0002] In order to meet the demand for high integration of semiconductor devices, the use of 3D integration technology for stacking semiconductor devices in three dimensions has been proposed. One of the 3D integration technologies is a bonding technology for bonding substrates such as semiconductor wafers together. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 088094 Summary of the Invention [Problem to be solved by the invention]

[0004] One aspect of the present disclosure provides a technique for improving the bonding accuracy between substrates. [Means for solving the problem]

[0005] A bonding device according to an embodiment of the present disclosure bonds a first substrate and a second substrate. The bonding device includes a first holding unit, a second holding unit, a first moving unit, a first interferometer, a housing, a gas supply unit, and an airflow control cover. The first holding unit adsorbs and holds the first substrate. The second holding unit adsorbs and holds the second substrate. The first moving unit moves the second holding unit in a first horizontal direction relative to the first holding unit. The first interferometer measures a distance in the first horizontal direction to the second holding unit or the first object by irradiating light onto the second holding unit or a first object moving together with the second holding unit in the first horizontal direction. The housing accommodates the first holding unit, the second holding unit, the first moving unit, and the first interferometer. The gas supply unit is provided on a side surface of the housing and supplies gas to the inside of the housing. The airflow control cover is provided inside the housing and redirects a portion of the gas flow supplied from the gas supply unit toward a first path of light irradiated from the first interferometer. The joining device includes a support frame inside the housing that supports the first holding unit, the second holding unit, the first moving unit, the first interferometer, and the airflow control cover. The airflow control cover redirects a portion of the gas flow from above the support frame toward the first path. Effect of the Invention

[0006] According to one aspect of the present disclosure, the accuracy of the position control of the second holding part can be improved, and the joining accuracy of the substrates can be improved. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a plan view showing a joint system according to one embodiment. [Diagram 2] FIG. 2 is a side view of the joint system of FIG. [Diagram 3] FIG. 3 is a side view showing an example of the first substrate and the second substrate. [Figure 4] FIG. 4 is a flow chart illustrating a bonding method according to one embodiment. [Diagram 5] FIG. 5 is a plan view showing an example of a bonding apparatus. [Figure 6] FIG. 6 is a side view of the joining device of FIG. [Figure 7]FIG. 7 is a cross-sectional view showing an example of an upper chuck and a lower chuck. [Figure 8] FIG. 8 is a flowchart showing the details of step S109 in FIG. [Figure 9] FIG. 9(A) is a side view showing an example of the operation in step S112, FIG. 9(B) is a side view showing the operation following FIG. 9(A), and FIG. 9(C) is a side view showing the operation following FIG. 9(B). [Figure 10] FIG. 10(A) is a cross-sectional view showing an example of the operation in step S113, FIG. 10(B) is a cross-sectional view showing an example of the operation in step S114, and FIG. 10(C) is a cross-sectional view showing the operation following FIG. 10(B). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding configurations are denoted by the same reference numerals, and the description may be omitted. In addition, the X-axis direction, the Y-axis direction, and the Z-axis direction are mutually perpendicular directions, the X-axis direction and the Y-axis direction are horizontal directions, and the Z-axis direction is vertical directions.

[0009] First, a bonding system 1 according to the present embodiment will be described with reference to Figs. 1 and 2. The bonding system 1 bonds a first substrate W1 and a second substrate W2 shown in Fig. 3 to produce a laminated substrate T. At least one of the first substrate W1 and the second substrate W2 is a semiconductor substrate such as a silicon wafer or a compound semiconductor wafer on which a plurality of electronic circuits are formed. One of the first substrate W1 and the second substrate W2 may be a bare wafer on which no electronic circuits are formed. The first substrate W1 and the second substrate W2 have approximately the same diameter. The compound semiconductor wafer is not particularly limited, but may be, for example, a GaAs wafer, a SiC wafer, a GaN wafer, or an InP wafer. A glass substrate may be used instead of the semiconductor substrate.

[0010] Hereinafter, the first substrate W1 may be referred to as the "upper wafer W1", the second substrate W2 may be referred to as the "lower wafer W2", and the overlapped substrate T may be referred to as the "overlapped wafer T". As shown in Fig. 3, of the surfaces of the upper wafer W1, the surface that is to be joined to the lower wafer W2 is referred to as the "joining surface W1j", and the surface opposite the bonding surface W1j is referred to as the "non-bonding surface W1n". Also, of the surfaces of the lower wafer W2, the surface that is to be joined to the upper wafer W1 is referred to as the "joining surface W2j", and the surface opposite the bonding surface W2j is referred to as the "non-bonding surface W2n".

[0011] 1, the bonding system 1 includes a loading / unloading station 2 and a processing station 3. The loading / unloading station 2 and the processing station 3 are arranged in the negative direction of the Y axis in the order of the loading / unloading station 2 and the processing station 3. The loading / unloading station 2 and the processing station 3 are connected together.

[0012] The carry-in / out station 2 includes a mounting table 10 and a transfer area 20. The mounting table 10 includes a plurality of mounting plates 11. Cassettes C1, C2, and C3, which accommodate a plurality of substrates (e.g., 25 substrates) in a horizontal state, are mounted on each of the mounting plates 11. The cassette C1 accommodates an upper wafer W1, the cassette C2 accommodates a lower wafer W2, and the cassette C3 accommodates a laminated wafer T. In the cassettes C1 and C2, the upper wafer W1 and the lower wafer W2 are accommodated with their bonding surfaces W1j and W2j facing upwards and aligned in the same direction.

[0013] The transfer region 20 is disposed adjacent to the mounting table 10 on the negative side of the Y axis. The transfer region 20 is provided with a transfer path 21 extending in the X axis direction and a transfer device 22 movable along the transfer path 21. The transfer device 22 is also movable in the Y axis direction and rotatable about the Z axis, and transfers the upper wafer W1, lower wafer W2, and overlapped wafer T between cassettes C1 to C3 mounted on the mounting table 10 and a third processing block G3 of the processing station 3, which will be described later.

[0014] The number of cassettes C1 to C3 placed on the mounting table 10 is not limited to that shown in the figure. In addition to the cassettes C1, C2, and C3, a cassette for recovering defective substrates or the like may be placed on the mounting table 10.

[0015] For example, three processing blocks G1, G2, and G3 are provided in the processing station 3. For example, a first processing block G1 is provided on the rear side (positive X-axis direction in FIG. 1) of the processing station 3, and a second processing block G2 is provided on the front side (negative X-axis direction in FIG. 1) of the processing station 3. Furthermore, a third processing block G3 is provided on the loading / unloading station 2 side of the processing station 3 (positive Y-axis direction in FIG. 1).

[0016] A transfer region 60 is formed in an area surrounded by the first processing block G1 to the third processing block G3. A transfer device 61 is disposed in the transfer region 60. The transfer device 61 has a transfer arm that is movable, for example, in the vertical direction, the horizontal direction, and around the vertical axis.

[0017] The transfer device 61 moves within the transfer region 60 to transfer the upper wafer W1, the lower wafer W2, and the overlapping wafer T to predetermined devices within the first processing block G1, the second processing block G2, and the third processing block G3 adjacent to the transfer region 60.

[0018] In the first processing block G1, for example, a surface modification device 33 and a surface hydrophilization device 34 are arranged. The surface modification device 33 modifies the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2. The surface hydrophilization device 34 hydrophilizes the modified bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2.

[0019] For example, the surface modification device 33 breaks the SiO2 bonds on the bonding surfaces W1j and W2j to form dangling bonds of Si, enabling subsequent hydrophilization. In the surface modification device 33, for example, oxygen gas, which is a processing gas, is excited to be plasmatized and ionized in a reduced pressure atmosphere. Then, the oxygen ions are irradiated onto the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2, whereby the bonding surfaces W1j and W2j are plasma-processed and modified. The processing gas is not limited to oxygen gas, and may be, for example, nitrogen gas.

[0020] The surface hydrophilization device 34 hydrophilizes the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2 with a hydrophilization treatment liquid such as pure water. The surface hydrophilization device 34 also has a role of cleaning the bonding surfaces W1j and W2j. In the surface hydrophilization device 34, pure water is supplied onto the upper wafer W1 or the lower wafer W2 while rotating the upper wafer W1 or the lower wafer W2 held by, for example, a spin chuck. As a result, the pure water diffuses onto the bonding surfaces W1j and W2j, and OH groups are attached to the dangling bonds of Si, thereby hydrophilizing the bonding surfaces W1j and W2j.

[0021] In the second processing block G2, for example, a bonding device 41, a first temperature adjustment device 42, and a second temperature adjustment device 43 are arranged. The bonding device 41 bonds the hydrophilized upper wafer W1 and the lower wafer W2 to produce a laminated wafer T. The first temperature adjustment device 42 adjusts the temperature distribution of the upper wafer W1 before bonding, that is, before contact with the lower wafer W2. The second temperature adjustment device 43 adjusts the temperature distribution of the lower wafer W2 before bonding, that is, before contact with the upper wafer W1. In this embodiment, the first temperature adjustment device 42 and the second temperature adjustment device 43 are provided separately from the bonding device 41, but may be provided as part of the bonding device 41.

[0022] In the third processing block G3, for example, a first position adjustment device 51, a second position adjustment device 52, and transition devices 53 and 54 are stacked in this order from top to bottom (see FIG. 2). The locations of the devices in the third processing block G3 are not limited to those shown in FIG. 2. The first position adjustment device 51 adjusts the horizontal orientation of the upper wafer W1 by rotating the upper wafer W1 around a vertical axis, and turns the upper wafer W1 upside down so that the bonding surface W1j of the upper wafer W1 faces downward. The second position adjustment device 52 adjusts the horizontal orientation of the lower wafer W2 by rotating the lower wafer W2 around a vertical axis. The upper wafer W1 is temporarily placed on the transition device 53. In addition, the lower wafer W2 and the overlapped wafer T are temporarily placed on the transition device 54. In this embodiment, the first position adjustment device 51 and the second position adjustment device 52 are provided separately from the joining device 41, but they may be provided as part of the joining device 41.

[0023] The bonding system 1 includes a control device 90. The control device 90 is, for example, a computer, and includes a CPU (Central Processing Unit) 91 and a storage medium 92 such as a memory. The storage medium 92 stores programs that control various processes executed in the bonding system 1. The control device 90 controls the operation of the bonding system 1 by causing the CPU 91 to execute the programs stored in the storage medium 92.

[0024] Next, the bonding method of this embodiment will be described with reference to Fig. 4. The bonding method includes, for example, steps S101 to S109. Steps S101 to S109 are performed under the control of the control device 90. Note that the bonding method does not need to include all of steps S101 to S109, and for example, does not need to include steps S104 and S108. Furthermore, the bonding method may include processes other than steps S101 to S109.

[0025] First, the cassette C1 accommodating a plurality of upper wafers W1, the cassette C2 accommodating a plurality of lower wafers W2, and the empty cassette C3 are placed on the placement table 10 of the carry-in / out station 2.

[0026] Next, the transfer device 22 takes out the upper wafer W1 in the cassette C1 and transfers it to the transition device 53 in the third processing block G3 of the processing station 3. Thereafter, the transfer device 61 takes out the upper wafer W1 from the transition device 53 and transfers it to the surface modification device 33 in the first processing block G1.

[0027] Next, the surface modification device 33 modifies the bonding surface W1j of the upper wafer W1 (step S101). The modification of the bonding surface W1j is performed with the bonding surface W1j facing upward. Thereafter, the transfer device 61 takes out the upper wafer W1 from the surface modification device 33 and transfers it to the surface hydrophilization device .

[0028] Next, the surface hydrophilization device 34 hydrophilizes the bonding surface W1j of the upper wafer W1 (step S102). The hydrophilization of the bonding surface W1j is performed with the bonding surface W1j facing upward. Thereafter, the transfer device 61 takes out the upper wafer W1 from the surface hydrophilization device 34 and transfers it to the first position adjustment device 51 of the third processing block G3.

[0029] Next, the first position adjustment device 51 rotates the upper wafer W1 around the vertical axis to adjust the horizontal orientation of the upper wafer W1, and turns the upper wafer W1 upside down (step S103). As a result, the notch of the upper wafer W1 is oriented in a predetermined direction, and the bonding surface W1j of the upper wafer W1 faces downward. Thereafter, the transfer device 61 takes out the upper wafer W1 from the first position adjustment device 51 and transfers it to the first temperature adjustment device 42 in the second processing block G2.

[0030] Next, the first temperature adjustment device 42 adjusts the temperature of the upper wafer W1 (step S104). The temperature adjustment of the upper wafer W1 is performed with the bonding surface W1j of the upper wafer W1 facing downward. Thereafter, the transfer device 61 takes out the upper wafer W1 from the first temperature adjustment device 42 and transfers it to the bonding device 41.

[0031] In parallel with the above-mentioned processing for the upper wafer W1, the following processing for the lower wafer W2 is performed. First, the transfer device 22 takes out the lower wafer W2 from the cassette C2 and transfers it to the transition device 54 in the third processing block G3 of the processing station 3. Then, the transfer device 61 takes out the lower wafer W2 from the transition device 54 and transfers it to the surface modification device 33 in the first processing block G1.

[0032] Next, the surface modification device 33 modifies the bonding surface W2j of the lower wafer W2 (step S105). The modification of the bonding surface W2j is performed with the bonding surface W2j facing upward. Thereafter, the transfer device 61 takes out the lower wafer W2 from the surface modification device 33 and transfers it to the surface hydrophilization device .

[0033] Next, the surface hydrophilization device 34 hydrophilizes the bonding surface W2j of the lower wafer W2 (step S106). The hydrophilization of the bonding surface W2j is performed with the bonding surface W2j facing upward. Thereafter, the transfer device 61 takes out the lower wafer W2 from the surface hydrophilization device 34 and transfers it to the second position adjustment device 52 in the third processing block G3.

[0034] Next, the second position adjustment device 52 rotates the lower wafer W2 around the vertical axis to adjust the horizontal orientation of the lower wafer W2 (step S107). As a result, the notch of the lower wafer W2 is oriented in a predetermined direction. Thereafter, the transfer device 61 takes out the lower wafer W2 from the second position adjustment device 52 and transfers it to the second temperature adjustment device 43 in the second processing block G2.

[0035] Next, the second temperature control device 43 adjusts the temperature of the lower wafer W2 (step S108). The temperature control of the lower wafer W2 is performed with the bonding surface W2j of the lower wafer W2 facing upward. Thereafter, the transfer device 61 takes out the lower wafer W2 from the second temperature control device 43 and transfers it to the bonding device 41.

[0036] Next, the bonding device 41 bonds the upper wafer W1 and the lower wafer W2 to manufacture the overlapped wafer T (step S109). Thereafter, the transfer device 61 takes out the overlapped wafer T from the bonding device 41 and transfers it to the transition device 54 in the third processing block G3.

[0037] Finally, the transfer device 22 takes out the overlapped wafer T from the transition device 54, and transfers it to the cassette C3 on the mounting table 10. This completes a series of processes.

[0038] Next, an example of the bonding device 41 will be described with reference to Fig. 5 and Fig. 6. The bonding device 41 includes, for example, a housing 100, an upper chuck 110, a lower chuck 120, a moving unit 130, a gas supply unit 140, an exhaust unit 150, a first interferometer 161, a second interferometer 162, and an airflow control cover 170.

[0039] The housing 100 is, for example, a box having a rectangular shape in a plan view. An unillustrated loading / unloading port is formed on the side of the housing 100 on the side of the transfer area 60, and an opening / closing shutter is provided at the loading / unloading port. The upper wafer W1, the lower wafer W2, and the overlapped wafer T are loaded and unloaded through the loading / unloading port.

[0040] The housing 100 houses, for example, a support frame 101, an upper chuck 110, a lower chuck 120, a moving unit 130, a gas supply unit 140, an exhaust unit 150, a first interferometer 161, a second interferometer 162, and an airflow control cover 170.

[0041] The support frame 101 supports, for example, the upper chuck 110, the lower chuck 120, the moving part 130, the first interferometer 161, the second interferometer 162, and the airflow control cover 170. The support frame 101 includes a mounting table 102, a plurality of support columns 103 erected on the upper surface of the mounting table 102, and an upper frame 104 fixed to the upper ends of the plurality of support columns 103.

[0042] The upper frame 104 supports the upper chuck 110 from above. The upper chuck 110 suction-holds the upper surface (non-bonding surface W1n) of the upper wafer W1 from above. On the other hand, the lower chuck 120 is provided below the upper chuck 110 and suction-holds the lower surface (non-bonding surface W2n) of the lower wafer W2 from below.

[0043] The moving unit 130 moves the lower chuck 120 in the horizontal direction. For example, the moving unit 130 includes a first moving unit 131 that moves the lower chuck 120 in the X-axis direction. The moving unit 130 also includes a second moving unit 132 that moves the lower chuck 120 in the Y-axis direction.

[0044] The first moving part 131 is configured to move along a pair of first rails 131a extending in the X-axis direction. The pair of first rails 131a is provided on an upper surface of the second moving part 132. The moving part 130 moves the lower chuck 120 in the X-axis direction by moving the first moving part 131 in the X-axis direction.

[0045] The second moving part 132 is configured to move along a pair of second rails 132a extending in the Y-axis direction. The pair of second rails 132a are provided on the upper surface of the mounting table 102. The moving part 130 moves the second moving part 132 in the Y-axis direction, thereby moving the first moving part 131 and the lower chuck 120 in the Y-axis direction.

[0046] The lower chuck 120 is attached to a first moving unit 131 and moves in the X-axis and Y-axis directions together with the first moving unit 131. The first moving unit 131 may be configured to move the lower chuck 120 in the vertical direction. Furthermore, the first moving unit 131 may be configured to rotate the lower chuck 120 around a vertical axis. The direction of rotation about the vertical axis may be referred to as the θ direction.

[0047] The moving unit 130 moves the lower chuck 120 in the X-axis direction, the Y-axis direction, and the θ direction, thereby aligning the upper wafer W1 held by the upper chuck 110 with the lower wafer W2 held by the lower chuck 120 in the horizontal direction. In addition, the moving unit 130 moves the lower chuck 120 in the Z-axis direction, thereby aligning the upper wafer W1 held by the upper chuck 110 with the lower wafer W2 held by the lower chuck 120 in the vertical direction.

[0048] The moving unit 130 only needs to be able to relatively move the upper chuck 110 and the lower chuck 120 in the X-axis direction, the Y-axis direction, and the θ direction. For example, the moving unit 130 may move the upper chuck 110 in the X-axis direction, the Y-axis direction, and the θ direction. The moving unit 130 may also move the lower chuck 120 in the X-axis direction and the Y-axis direction, and move the upper chuck 110 in the θ direction.

[0049] Of the upper chuck 110 and the lower chuck 120, the one moved in the X-axis direction by the moving unit 130 (the lower chuck 120 in this embodiment) corresponds to the second holding unit described in the claims, and the remaining one (the upper chuck 110 in this embodiment) corresponds to the first holding unit described in the claims. The X-axis direction corresponds to the first horizontal direction described in the claims, and the Y-axis direction corresponds to the second horizontal direction described in the claims.

[0050] The moving unit 130 moves the relative positions of the upper chuck 110 and the lower chuck 120 between a substrate transfer position and a bonding position. The substrate transfer position is a position where the upper chuck 110 receives the upper wafer W1 from the transfer device 61, the lower chuck 120 receives the lower wafer W2 from the transfer device 61, and the lower chuck 120 transfers the overlapped wafer T to the transfer device 61. The substrate transfer position is a position where the overlapped wafer T produced in the nth (n is a natural number of 1 or more) bonding is continuously carried out, and the upper wafer W1 and the lower wafer W2 to be bonded in the n+1th bonding are carried in. The substrate transfer position is, for example, a position shown in FIG. 5 and FIG. 6.

[0051] The transfer device 61 enters directly below the upper chuck 110 when transferring the upper wafer W1 to the upper chuck 110. The transfer device 61 also enters directly above the lower chuck 120 when receiving the overlapped wafer T from the lower chuck 120 and transferring the lower wafer W2 to the lower chuck 120. To facilitate the entry of the transfer device 61, the upper chuck 110 and the lower chuck 120 are shifted laterally, and the vertical distance between the upper chuck 110 and the lower chuck 120 is also large.

[0052] On the other hand, the bonding position is a position where the upper wafer W1 and the lower wafer W2 are faced to each other with a predetermined gap therebetween and bonded. The bonding position is, for example, the position shown in Fig. 7. At the bonding position, the gap G between the upper wafer W1 and the lower wafer W2 in the vertical direction is narrower than at the substrate transfer position. Also, at the bonding position, unlike the substrate transfer position, the upper wafer W1 and the lower wafer W2 overlap when viewed in the vertical direction.

[0053] The gas supply unit 140 supplies gas to the inside of the housing 100. The gas is, for example, dry air or an inert gas such as nitrogen gas or argon gas. The gas supply unit 140 is, for example, an FFU (Fan Filter Unit), and supplies purified gas.

[0054] The gas supply unit 140 supplies gas adjusted to a set temperature. The set temperature is, for example, room temperature, 23° C. The gas supply unit 140 is connected to a gas supply source 143 via a temperature sensor 149, a temperature regulator 141, and a valve 142. The temperature sensor 149 measures the temperature of the gas and outputs the measured data to the control device 90. The control device 90 controls the temperature regulator 141 so that the temperature measured by the temperature sensor 149 becomes the set temperature.

[0055] The gas supply unit 140 may supply gas that is adjusted to a set humidity.

[0056] Gas supply unit 140 is provided on side surface 100a, which is orthogonal to the Y-axis direction, among a plurality of side surfaces of housing 100, and discharges gas in the Y-axis direction (specifically, the positive Y-axis direction).

[0057] The exhaust unit 150 is provided on a side surface 100b, which is opposite to the side surface 100a to which the gas supply unit 140 is attached, among a plurality of side surfaces of the housing 100. The exhaust unit 150 is connected to a suction device (not shown) such as a vacuum pump, and evacuates the inside of the housing 100 by utilizing the suction force of the suction device.

[0058] The gas supply unit 140 and the exhaust unit 150 form a side flow inside the housing 100 .

[0059] The first interferometer 161 measures the distance in the X-axis direction from a reference point of the first interferometer 161 to the first object 163 by irradiating light onto the first object 163, which moves in the X-axis direction together with the lower chuck 120, which is the second holding part. The first object 163 is attached to the first moving part 131, for example.

[0060] The first interferometer 161 is provided at the same height as the first object 163. The first object 163 is, for example, a mirror, and has a light reflecting surface perpendicular to the X-axis direction. The first interferometer 161 receives light reflected by the first object 163, thereby measuring the distance in the X-axis direction from a reference point of the first interferometer 161 to the first object 163.

[0061] The first interferometer 161 may measure the distance in the X-axis direction to the lower chuck 120, which is the second holding part, by irradiating the lower chuck 120 with light.

[0062] The first interferometer 161 outputs the measured data to the control device 90. The control device 90 controls the moving part 130 using the measured data of the first interferometer 161, and controls the position of the lower chuck 120 in the X-axis direction. The position control includes speed control. The control device 90 may also use a linear scale (not shown) when controlling the position of the lower chuck 120 in the X-axis direction.

[0063] The first interferometer 161 is disposed between the first moving part 131 and a side surface 100c perpendicular to the X-axis direction among multiple side surfaces of the housing 100. The first interferometer 161 irradiates light in a direction (X-axis direction, specifically, the positive X-axis direction) perpendicular to the flow direction of the side flow (Y-axis direction, specifically, the positive Y-axis direction). In other words, the first path LP1 of the light irradiated from the first interferometer 161 is perpendicular to the direction in which the gas is discharged from the gas supply part 140 (Y-axis direction, specifically, the positive Y-axis direction).

[0064] The second interferometer 162 measures the distance in the Y-axis direction from a reference point of the second interferometer 162 to the second object 164 by irradiating light onto the second object 164, which moves in the Y-axis direction together with the lower chuck 120, which is the second holding part. The second object 164 is attached to the first moving part 131, for example.

[0065] The second interferometer 162 is provided at the same height as the second object 164. The second object 164 is, for example, a mirror, and has a light reflecting surface perpendicular to the Y-axis direction. The second interferometer 162 receives light reflected by the second object 164, thereby measuring the distance in the Y-axis direction from a reference point of the second interferometer 162 to the second object 164.

[0066] The second interferometer 162 may measure the distance in the Y-axis direction to the lower chuck 120, which is the second holding part, by irradiating light onto the lower chuck 120.

[0067] The second interferometer 162 outputs the measured data to the control device 90. The control device 90 controls the moving part 130 using the measured data of the second interferometer 162, and controls the Y-axis direction position of the lower chuck 120. The position control includes speed control. Note that the control device 90 may also use a linear scale (not shown) when controlling the Y-axis direction position of the lower chuck 120.

[0068] The second interferometer 162 is disposed between the first moving part 131 and a side surface 100a of the housing 100 that is perpendicular to the Y-axis direction, among the multiple side surfaces the housing 100 has, and is disposed between the gas supply part 140 and the first moving part 131. The second interferometer 162 irradiates light in the same direction as the flow direction of the side flow (the Y-axis direction, specifically the positive Y-axis direction). In other words, the second path LP2 of the light irradiated from the second interferometer 162 is parallel to the direction in which the gas is discharged from the gas supply part 140.

[0069] The first interferometer 161 and the second interferometer 162 are, for example, laser interferometers, and irradiate laser light. Note that the light irradiated from the first interferometer 161 and the second interferometer 162 does not have to be laser light, and may be directional light having a certain period.

[0070] However, when the temperature, humidity, or air pressure fluctuates in the first path LP1, the refractive index of the air fluctuates, and the optical path length (the product of the path length and the refractive index) fluctuates. As a result, the measurement value of the first interferometer 161 fluctuates, causing a measurement error. For example, when the length of the first path LP1 is 300 mm and the temperature fluctuation range is 0.1° C., the theoretical fluctuation range of the measurement value is about 28 nm. Here, the fluctuation range is the difference between the maximum value and the minimum value.

[0071] In order to reduce the measurement error of the first interferometer 161, it is effective to reduce the fluctuations in temperature, humidity, and air pressure on the first path LP1, and it is effective to form a stable air flow. Similarly, in order to reduce the measurement error of the second interferometer 162, it is effective to reduce the fluctuations in temperature, humidity, and air pressure on the second path LP2, and it is effective to form a stable air flow.

[0072] Electrical equipment such as a motor, an amplifier, a laser light source, or a camera is provided at the same height as the first path LP1 and the second path LP2. The electrical equipment can be a heat source that changes the temperature of the gas, or an obstacle that disturbs the flow of gas. In addition to the electrical equipment, the support columns 103 of the support frame 101 can also be obstacles. Obstacles include not only stationary objects but also movable objects. An example of a movable object is the first moving part 131. A movable object can not only be an obstacle when stopped, but can also generate a new gas flow when moving.

[0073] The gas supply unit 140 discharges gas in the positive direction of the Y axis, forming a side flow that flows in the positive direction of the Y axis. The side flow has a temperature distribution in the X axis direction due to heat from electrical components or heat transfer from outside the housing 100. The direction of the side flow may be disturbed by an obstacle. Therefore, the temperature and direction of the side flow are constantly fluctuating.

[0074] While the second path LP2 is parallel to the side flow, the first path LP1 is perpendicular to the side flow. Since the first path LP1 crosses the side flow, it is easily affected by the fluctuation of the side flow. Therefore, in the past, the measurement error of the first interferometer 161 was larger than the measurement error of the second interferometer 162.

[0075] Therefore, in this embodiment, the airflow control cover 170 is used to redirect a part of the gas flow supplied from the gas supply unit 140 to the first path LP1. The gas that is less affected by heat sources and obstacles can be redirected toward the first path LP1, and an airflow with stable temperature and direction can be formed on the first path LP1. As a result, the fluctuation range of the measurement value of the first interferometer 161 can be reduced, and the measurement error of the first interferometer 161 can be reduced. Therefore, the accuracy of the position control of the lower chuck 120 can be improved, and the bonding accuracy of the lower wafer W2 and the upper wafer W1 can be improved. By using the airflow control cover 170, it is also possible to suppress the fluctuation range of the measurement value of the first interferometer 161 to less than 10 nm.

[0076] As a technique different from the technique of the present disclosure, for example, it is possible to surround the first path LP1 with a cylindrical cover. In this case, the cylindrical cover needs to be moved together with the lower chuck 120, and the structure of the joining device 41 may become complicated so as to prevent interference between the cylindrical cover and other components. In addition, the movable range of the lower chuck 120 is likely to be limited.

[0077] As another technique different from the technique of the present disclosure, it is also possible to surround the first path LP1 with a cylindrical spot airflow. In this case, a second gas supply unit that forms the spot airflow is required in addition to the gas supply unit 140. In addition, a temperature difference or a pressure difference between the spot airflow and the side flow may become a problem.

[0078] Furthermore, as a technique different from the technique of the present disclosure, it is also possible to form a downflow throughout the entire interior of the housing 100. In this case, there are many obstacles that prevent the formation of the downflow, and the airflow is likely to become turbulent. In addition, it is not realistic to provide exhaust units 150 at all four corners of the lower surface of the housing 100 in order to stabilize the downflow.

[0079] In contrast to these, according to one aspect of the present disclosure, the airflow control cover 170 is used to redirect a part of the gas flow supplied from the gas supply unit 140 to the first path LP1, and an airflow with a stable temperature and direction is formed in the first path LP1. Therefore, compared to the case where a cylindrical cover surrounding the first path LP1 is used, the movable range of the lower chuck 120 is less restricted, and the structure of the joining device 41 is simple. Also, unlike the case where a cylindrical spot airflow surrounding the first path LP1 is formed, the temperature difference or pressure difference between the spot airflow and the side flow does not become a problem, and a second gas supply unit is not required. Furthermore, compared to the case where a downflow is formed throughout the entire interior of the housing 100, there are fewer obstacles and a stable airflow is easily formed.

[0080] 6, the airflow control cover 170 may redirect a part of the gas flow from diagonally above the first path LP1 toward the first path LP1. There are few heat sources and obstacles (including both stationary and moving objects) at heights different from the first path LP1. Therefore, gas with stable temperature and direction can be redirected toward the first path LP1.

[0081] For example, the airflow control cover 170 redirects part of the gas flow from above the support frame 101 toward the first path LP1. There are particularly few heat sources and obstacles above the support frame 101. Therefore, gas with particularly stable temperature and direction can be redirected toward the first path LP1.

[0082] The airflow control cover 170 may include, for example, an inclined plate 171 that is inclined downward toward the gas discharge direction (positive direction of the Y axis) of the gas supply unit 140. The inclined plate 171 allows the flow of gas to be smoothly redirected. In this embodiment, the inclined plate 171 is a flat plate, but it may be a curved plate.

[0083] An opening 105 through which the inclined plate 171 is inserted is formed in the upper frame 104 of the support frame 101. The gas changed in direction by the inclined plate 171 passes through the opening 105 of the upper frame 104 and is guided to the first path LP1.

[0084] An upper end of the inclined plate 171 is disposed above the upper frame 104 and below the ceiling of the housing 100. On the other hand, a lower end of the inclined plate 171 is disposed below the upper frame 104 and above the lower surface of the upper chuck 110 that suction-holds the upper wafer W1.

[0085] If the lower end of the inclined plate 171 is disposed above the lower surface of the upper chuck 110, it is possible to prevent interference between the upper wafer W1 and the inclined plate 171 when the upper wafer W1 is loaded or unloaded. In addition, it is possible to prevent interference between the lower chuck 120 or the lower wafer W2 held by the lower chuck 120 and the inclined plate 171 when the lower chuck 120 moves.

[0086] The airflow control cover 170 may include a horizontal plate 172 and a vertical plate 173 in addition to the inclined plate 171. The vertical plates 173 are arranged perpendicular to the X-axis direction and are provided as a pair with a gap in the X-axis direction. The vertical plates 173 are, for example, in the shape of a right-angled trapezoid.

[0087] The horizontal plate 172, the pair of vertical plates 173, and the upper frame 104 form a gas inlet 174. The gas discharged from the gas supply unit 140 passes through the inlet 174 and then flows obliquely downward along the inclined plate 171.

[0088] 5, the dimension in the X-axis direction of the airflow control cover 170 may be smaller than the dimension in the X-axis direction of the upper frame 104. A space for electrical wiring and the like can be secured above the upper frame 104.

[0089] As shown in Fig. 5, when viewed from above, the airflow control cover 170 may overlap with the second path LP2 of the light irradiated from the second interferometer 162. When the first moving part 131 is far from the second interferometer 162 and the length of the second path LP2 is long, as shown by the dashed line in Fig. 6, the gas redirected by the airflow control cover 170 can be supplied to the second path LP2 as well. Therefore, an airflow with stable temperature and direction can be formed in the second path LP2 as well. As a result, the fluctuation range of the measurement value of the second interferometer 162 can be reduced, and the measurement error of the second interferometer 162 can be reduced.

[0090] Next, the upper chuck 110 and the lower chuck 120 will be described with reference to Fig. 7. The upper chuck 110 is partitioned into a plurality of (e.g., three) regions 110a, 110b, and 110c. These regions 110a, 110b, and 110c are provided in this order from the center to the periphery of the upper chuck 110. The region 110a has a circular shape in a plan view, and the regions 110b and 110c have annular shapes in a plan view.

[0091] Suction pipes 111a, 111b, and 111c are provided independently for the respective regions 110a, 110b, and 110c. Different vacuum pumps 112a, 112b, and 112c are connected to the respective suction pipes 111a, 111b, and 111c. The upper chuck 110 can vacuum-suck the upper wafer W1 for each of the regions 110a, 110b, and 110c.

[0092] The upper chuck 110 is provided with a plurality of holding pins 115 that can be raised and lowered in the vertical direction. The plurality of holding pins 115 are connected to a vacuum pump 116, and vacuum-suck the upper wafer W1 by operation of the vacuum pump 116. The upper wafer W1 is vacuum-sucked to the lower ends of the plurality of holding pins 115. Ring-shaped suction pads may be used instead of the plurality of holding pins 115.

[0093] The multiple holding pins 115 move downward to protrude from the holding surface of the upper chuck 110. In this state, the multiple holding pins 115 vacuum-suck the upper wafer W1 and receive it from the transfer device 61. Thereafter, the multiple holding pins 115 move upward, and the upper wafer W1 is brought into contact with the holding surface of the upper chuck 110. Next, the upper chuck 110 horizontally vacuum-sucks the upper wafer W1 in each of the regions 110a, 110b, and 110c by operation of the vacuum pumps 112a, 112b, and 112c.

[0094] Further, a through hole 113 that passes through the upper chuck 110 in the vertical direction is formed in the center of the upper chuck 110. A pressing part 190, which will be described later, is inserted into the through hole 113. The pressing part 190 presses down the center of the upper wafer W1, which is disposed at a distance from the lower wafer W2, to bring the upper wafer W1 into contact with the lower wafer W2.

[0095] The pushing part 190 has a pushing pin 191 and an outer cylinder 192 which serves as a lifting guide for the pushing pin 191. The pushing pin 191 is inserted into the through hole 113 by, for example, a drive part (not shown) having a built-in motor, protrudes from the holding surface of the upper chuck 110, and pushes down the center of the upper wafer W1.

[0096] The lower chuck 120 is partitioned into a plurality of (for example, two) regions 120a and 120b. These regions 120a and 120b are provided in this order from the center toward the periphery of the lower chuck 120. The region 120a has a circular shape in a plan view, and the region 120b has an annular shape in a plan view.

[0097] Suction pipes 121a and 121b are provided independently for the respective regions 120a and 120b. Different vacuum pumps 122a and 122b are connected to the respective suction pipes 121a and 121b. The lower chuck 120 can vacuum-suck the lower wafer W2 for each of the regions 120a and 120b.

[0098] A plurality of holding pins 125 that can be raised and lowered in the vertical direction are provided on the lower chuck 120. The lower wafer W2 is placed on the upper ends of the plurality of holding pins 125. The lower wafer W2 may be vacuum-sucked to the upper ends of the plurality of holding pins 125.

[0099] As the multiple holding pins 125 rise, they protrude from the holding surface of the lower chuck 120. In this state, the multiple holding pins 125 receive the lower wafer W2 from the transfer device 61. Thereafter, the multiple holding pins 125 descend, and the lower wafer W2 is brought into contact with the holding surface of the lower chuck 120. Next, the upper chuck 110 horizontally vacuum-sucks the lower wafer W2 in each of the regions 120a and 120b by operation of the vacuum pumps 122a and 122b.

[0100] Next, details of step S109 in Fig. 4 will be described with reference to Fig. 8 to Fig. 10. First, the transfer device 61 carries in the upper wafer W1 and the lower wafer W2 into the bonding device 41 (step S111). In step S111, the relative positions of the upper chuck 110 and the lower chuck 120 are the substrate transfer positions shown in Figs. 5 and 6.

[0101] Next, the moving part 130 moves the relative positions of the upper chuck 110 and the lower chuck 120 from the substrate transfer position shown in Fig. 5 and Fig. 6 to the bonding position shown in Fig. 7 (step S112). In step S112, the upper wafer W1 and the lower wafer W2 are aligned. For the alignment, a first camera S1 and a second camera S2 are used as shown in Fig. 9.

[0102] The first camera S1 is fixed to the upper chuck 110 and captures an image of the lower wafer W2 held by the lower chuck 120. A plurality of reference points P21 to P23 are formed in advance on the bonding surface W2j of the lower wafer W2. Patterns of electronic circuits or the like are used as the reference points P21 to P23. The number of reference points can be set arbitrarily.

[0103] On the other hand, the second camera S2 is fixed to the lower chuck 120 and captures an image of the upper wafer W1 held by the upper chuck 110. A plurality of reference points P11 to P13 are formed in advance on the bonding surface W1j of the upper wafer W1. Patterns of electronic circuits or the like are used as the reference points P11 to P13. The number of reference points can be set arbitrarily.

[0104] First, as shown in Fig. 9(A), the moving unit 130 adjusts the relative horizontal positions of the first camera S1 and the second camera S2. Specifically, the moving unit 130 moves the lower chuck 120 in the horizontal direction so that the second camera S2 is positioned substantially directly below the first camera S1. Then, the first camera S1 and the second camera S2 capture an image of a common target X, and the moving unit 130 finely adjusts the horizontal position of the second camera S2 so that the horizontal positions of the first camera S1 and the second camera S2 match. This completes the alignment of the first camera S1 and the second camera S2.

[0105] Next, as shown in Fig. 9(B), the moving unit 130 moves the lower chuck 120 vertically upward, and then adjusts the horizontal positions of the upper chuck 110 and the lower chuck 120. Specifically, while the moving unit 130 moves the lower chuck 120 horizontally, the first camera S1 sequentially captures images of the reference points P21 to P23 of the lower wafer W2, and the second camera S2 sequentially captures images of the reference points P11 to P13 of the upper wafer W1. Note that Fig. 9(B) shows how the first camera S1 captures the image of the reference point P21 of the lower wafer W2, and the second camera S2 captures the image of the reference point P11 of the upper wafer W1.

[0106] The first camera S1 and the second camera S2 transmit the captured image data to the control device 90. The control device 90 controls the moving part 130 based on the image data captured by the first camera S1 and the image data captured by the second camera S2, and adjusts the horizontal position of the lower chuck 120 so that the reference points P11 to P13 of the upper wafer W1 and the reference points P21 to P23 of the lower wafer W2 coincide with each other when viewed in the vertical direction.

[0107] Next, as shown in Fig. 9(C), the moving part 130 moves the lower chuck 120 vertically upward. As a result, the gap G (see Fig. 7) between the bonding surface W2j of the lower wafer W2 and the bonding surface W1j of the upper wafer W1 becomes a predetermined distance, for example, 80 µm to 200 µm. The first displacement gauge S3 and the second displacement gauge S4 are used to adjust the gap G.

[0108] The first displacement meter S3 is fixed to the upper chuck 110, similar to the first camera S1, and measures the thickness of the lower wafer W2 held by the lower chuck 120. The first displacement meter S3, for example, irradiates light onto the lower wafer W2, receives light reflected from both the upper and lower surfaces of the lower wafer W2, and measures the thickness of the lower wafer W2. The thickness measurement is performed, for example, when the moving unit 130 moves the lower chuck 120 in the horizontal direction. The measurement method of the first displacement meter S3 is, for example, a confocal method, a spectral interference method, a triangulation method, or the like. The light source of the first displacement meter S3 is an LED or a laser.

[0109] On the other hand, the second displacement meter S4 is fixed to the lower chuck 120 like the second camera S2, and measures the thickness of the upper wafer W1 held by the upper chuck 110. The second displacement meter S4, for example, irradiates light onto the upper wafer W1, receives light reflected from both the upper and lower surfaces of the upper wafer W1, and measures the thickness of the upper wafer W1. The thickness measurement is performed, for example, when the moving unit 130 moves the lower chuck 120 in the horizontal direction. The measurement method of the second displacement meter S4 is, for example, a confocal method, a spectral interference method, a triangulation method, or the like. The light source of the second displacement meter S4 is an LED or a laser.

[0110] The first displacement gauge S3 and the second displacement gauge S4 transmit the measured data to the control device 90. The control device 90 controls the moving part 130 based on the data measured by the first displacement gauge S3 and the data measured by the second displacement gauge S4, and adjusts the vertical position of the lower chuck 120 so that the gap G becomes a set value.

[0111] Next, the operation of the vacuum pump 112a is stopped, and the vacuum suction of the upper wafer W1 in the region 110a is released, as shown in Fig. 10(A). After that, the pushing pin 191 of the pushing part 190 descends, pushing down the center of the upper wafer W1 and bringing it into contact with the lower wafer W2 (step S113). As a result, the centers of the upper wafer W1 and the lower wafer W2 are bonded together.

[0112] Since the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2 have been modified, van der Waals forces (intermolecular forces) are generated between the bonding surfaces W1j and W2j, and the bonding surfaces W1j and W2j are bonded to each other. Furthermore, since the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2 have been hydrophilized, hydrophilic groups (e.g., OH groups) form hydrogen bonds, and the bonding surfaces W1j and W2j are firmly bonded to each other.

[0113] Next, the operation of the vacuum pump 112b is stopped, and the vacuum suction of the upper wafer W1 in the region 110b is released as shown in Fig. 10(B). Subsequently, the operation of the vacuum pump 112c is stopped, and the vacuum suction of the upper wafer W1 in the region 110c is released as shown in Fig. 10(C).

[0114] In this manner, the vacuum suction of the upper wafer W1 is released stepwise from the center to the periphery of the upper wafer W1, and the upper wafer W1 drops stepwise onto and comes into contact with the lower wafer W2. Then, the bonding of the upper wafer W1 and the lower wafer W2 progresses sequentially from the center to the periphery (step S114). As a result, the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2 come into contact over their entire surfaces, the upper wafer W1 and the lower wafer W2 are bonded together, and an overlapped wafer T is obtained. After that, the pushing pin 191 is raised to its original position.

[0115] Next, the moving unit 130 moves the relative position of the upper chuck 110 and the lower chuck 120 from the joining position shown in Fig. 7 to the substrate transfer position shown in Fig. 5 and Fig. 6 (step S115). For example, the moving unit 130 first lowers the lower chuck 120 to widen the vertical distance between the lower chuck 120 and the upper chuck 110. Next, the moving unit 130 moves the lower chuck 120 laterally to laterally shift the lower chuck 120 and the upper chuck 110.

[0116] Next, the transfer device 61 carries out the overlapped wafer T to the bonding device 41 (step S116). Specifically, first, the lower chuck 120 releases the hold of the overlapped wafer T. Then, the multiple holding pins 125 rise and deliver the overlapped wafer T to the transfer device 61. After that, the multiple holding pins 125 fall to their original positions.

[0117] Although the embodiments of the joining device and joining method according to the present disclosure have been described above, the present disclosure is not limited to the above embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure. [Explanation of symbols]

[0118] 41 Joining equipment 100 Case 110 Upper chuck (first holding part) 120 Lower chuck (second holding part) 140 Gas Supply Section W1 Upper wafer (first substrate) W2 Lower wafer (second substrate)

Claims

1. A bonding apparatus for bonding a first substrate and a second substrate, comprising: a first holding unit that suction-holds the first substrate; a second holding portion that suction-holds the second substrate; a first moving unit configured to move the second holding unit in a first horizontal direction relative to the first holding unit; a first interferometer that measures a distance in the first horizontal direction to the second holding unit or the first object by irradiating light onto the second holding unit or a first object that moves together with the second holding unit in the first horizontal direction; a housing that houses the first holding unit, the second holding unit, the first moving unit, and the first interferometer; a gas supply unit provided on a side surface of the housing and supplying a gas to an inside of the housing; an airflow control cover that is provided inside the housing and redirects a part of the flow of the gas supplied from the gas supply unit toward a first path of the light irradiated from the first interferometer; Equipped with a support frame for supporting the first holding portion, the second holding portion, the first moving portion, the first interferometer, and the airflow control cover within the housing, The airflow control cover redirects a portion of the gas flow from above the support frame toward the first path.

2. the support frame includes a mounting table, a plurality of support columns erected on an upper surface of the mounting table, and an upper frame horizontally provided on upper ends of the support columns; the airflow control cover includes an inclined plate that is inclined downward toward a direction in which the gas is discharged from the gas supply unit, The joining device according to claim 1 , wherein the upper frame is formed with an opening through which the inclined plate is inserted.

3. the upper frame holds the first holding portion from above, the first holding portion holds the first substrate from above, and the second holding portion holds the second substrate from below, The bonding device according to claim 2 , wherein a lower end of the inclined plate is provided above a lower surface of the first holding part that suction-holds the first substrate.

4. The joining device according to claim 2 or 3, wherein a dimension of the airflow control cover in the first horizontal direction is smaller than a dimension of the upper frame in the first horizontal direction.

5. the gas supply unit discharges the gas into the housing in a second horizontal direction perpendicular to the first horizontal direction, The bonding apparatus according to any one of claims 1 to 4, wherein the first path is perpendicular to a direction in which the gas is discharged from the gas supply unit.

6. 6. The bonding apparatus according to claim 1, wherein the first interferometer is a laser interferometer.

7. a second moving unit provided inside the housing and configured to move the second holding unit in a second horizontal direction perpendicular to the first horizontal direction relative to the first holding unit; a second interferometer that is provided inside the housing and that measures a distance in the second horizontal direction to the second holding part or the second object by irradiating light onto the second holding part or a second object that moves together with the second holding part in the second horizontal direction; The joining device according to any one of claims 1 to 6, comprising:

8. The bonding device according to claim 7 , wherein the airflow control cover overlaps with a second path of light emitted from the second interferometer when viewed from above.

9. A method for bonding a first substrate and a second substrate, comprising the steps of: suction-holding the first substrate by a first holding part; suction-holding the second substrate by a second holding portion; moving the second holding unit using a first moving unit that moves the second holding unit in a first horizontal direction relative to the first holding unit; measuring a distance in the first horizontal direction from the first interferometer to the second holding unit or the first object by irradiating light from a first interferometer to the second holding unit or a first object moving in the first horizontal direction together with the second holding unit; supplying a gas into an interior of a housing that houses the first holding unit, the second holding unit, the first moving unit, and the first interferometer by a gas supply unit provided on a side of the housing; Using an airflow control cover provided inside the housing, redirecting a portion of the gas flow supplied from the gas supply unit to a first path of light irradiated from the first interferometer; having a support frame supporting the first holding portion, the second holding portion, the first moving portion, the first interferometer, and the airflow control cover is provided inside the housing; The airflow control cover redirects a portion of the gas flow from above the support frame toward the first path.

Images