Wafer alignment method, wafer bonding method, wafer alignment apparatus, and wafer bonding apparatus

Abstract

The present invention provides a wafer alignment method, a wafer bonding method, a wafer alignment apparatus, and a wafer bonding apparatus that improve alignment accuracy by accurately recognizing the wafer in the imaging unit, and simultaneously improve wafer bonding accuracy. [Solution] A wafer alignment method for adjusting the alignment of two wafers W1 and W2, which are at different distances from the imaging unit 18, when joining them, using a single imaging unit 18, wherein the alignment mark of one wafer W1, which is located at a short distance from the imaging unit 18, is imaged without passing the light from the imaging unit 18 through the glass, and with the positions of the imaging unit 18 and one wafer W1 fixed, the alignment mark of the other wafer W2, which is located at a long distance from the imaging unit 18, is imaged by passing the light from the imaging unit 18 through the glass 22.

Description

Technical Field

[0001] The present invention relates to a wafer alignment method, a wafer bonding method, a wafer alignment apparatus, and a wafer bonding apparatus for wafers such as semiconductor wafers.

Background Art

[0002] Conventionally, a technique for bonding substrates such as semiconductor wafers and glass substrates has been known. For example, a bonding apparatus includes a first holding unit, a second holding unit, a stage, an imaging unit, a light source, a horizontal position adjustment unit, and a control unit. The first holding unit adsorbs and holds a first substrate. The second holding unit adsorbs and holds a second substrate to be bonded to the first substrate. The imaging unit is disposed outside the stage and images alignment marks provided on the first substrate and the second substrate through through-holes formed in the stage and the first holding unit from outside the stage. The light source is disposed outside and inside the stage and irradiates light through through-holes formed in the stage and the second holding unit from outside the stage. The control unit causes the imaging unit to perform an imaging process of imaging the alignment marks of the first substrate and the second substrate inside the stage, and then causes the horizontal position adjustment unit to perform an adjustment process of adjusting the horizontal position of the first holding unit based on the imaging result of the imaging unit (Patent Document 1).

[0003] Furthermore, a method for joining a first substrate and a second substrate, comprising: a pre-alignment step of the first substrate, in which, at a first position of the imaging unit, the first substrate is within the depth of field range of the imaging unit and the second substrate is outside the depth of field range of the imaging unit, and with the light source turned on, the imaging unit captures the alignment marks of the first substrate and pre-aligns the first substrate; a pre-alignment step of the second substrate, in which, at a second position of the imaging unit, the first substrate is outside the depth of field range of the imaging unit and the second substrate is within the depth of field range of the imaging unit, and with the second light source turned on, the imaging unit A known method for joining substrates is provided (Patent Document 2), which includes: a position misalignment confirmation step of imaging the alignment marks of the first substrate at the first position and with the first light source lit, and confirming the misalignment by comparing it with the result of imaging the alignment marks in the pre-alignment step of the first substrate; a simultaneous imaging step of the imaging unit simultaneously imaging the alignment marks of the first substrate and the alignment marks of the second substrate with the imaging unit while the first substrate and the second substrate are close together and with the light source lit; and a joining step of joining the first substrate and the second substrate while the first substrate and the second substrate are close together and with the light source lit. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-134459 [Patent Document 2] Patent No. 7125190 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in all of the above-mentioned conventional technologies, the imaging unit is configured to move at least in the Z-axis direction, or the two wafers (substrates) must be moved in order to fix the imaging unit and adjust the focal length. As a result, the imaging accuracy tends to deteriorate with the movement of the imaging unit. Consequently, there was a technical problem of reduced bonding accuracy between the substrates.

[0006] Therefore, the present invention aims to provide a wafer alignment method, a wafer bonding method, a wafer alignment apparatus, and a wafer bonding apparatus that improve alignment accuracy by accurately recognizing the wafer with an imaging unit, in order to solve the above problems. [Means for solving the problem]

[0007] The first invention is a wafer alignment method that uses a single imaging unit to adjust the alignment of two wafers at different distances from the imaging unit during bonding, For the alignment mark of one wafer located at a short distance from the imaging unit, the light from the imaging unit is imaged without passing through the glass. With the imaging unit and one of the wafers fixed in place, the light from the imaging unit is passed through the glass to image the alignment marks of the other wafer, which is located at a distance from the imaging unit.

[0008] The second invention is a wafer alignment method that uses a single imaging unit to adjust the alignment of two wafers at different distances from the imaging unit during bonding, For the alignment mark of one wafer located at a distance from the imaging unit, the light from the imaging unit is passed through the glass to take an image. With the imaging unit and one of the wafers fixed in place, the alignment marks of the other wafer, which is located at a short distance from the imaging unit, are imaged without passing the light from the imaging unit through the glass.

[0009] The third invention is a wafer joining method for joining two wafers at different distances from a single imaging unit, wherein the imaging unit is used to join two wafers at different distances from the imaging unit. For the alignment mark of one wafer located at a short distance from the imaging unit, the light from the imaging unit is imaged without passing through the glass. With the imaging unit and one of the wafers fixed in place, the light from the imaging unit is passed through the glass to image the alignment mark of the other wafer, which is located at a distance from the imaging unit. The wafers are joined together by moving only one of the two wafers so that the alignment marks overlap.

[0010] The fourth invention is a wafer joining method for joining two wafers at different distances from a single imaging unit, wherein the imaging unit is used to join two wafers at different distances from the imaging unit. For the alignment mark of one wafer located at a distance from the imaging unit, the light from the imaging unit is passed through the glass to take an image. With the positions of the imaging unit and one of the wafers fixed, the alignment marks of the other wafer, which is located at a short distance from the imaging unit, are imaged without passing the light from the imaging unit through the glass. The wafers are joined together by moving only one of the two wafers so that the alignment marks overlap.

[0011] The fifth invention is a wafer alignment method for adjusting the alignment of a first wafer and a second wafer during bonding using a single imaging unit, A first alignment step is performed by imaging the first wafer and the second wafer that is relatively close to the imaging unit with respect to the wafer, without using a focus changing unit to change the focal length of the imaging unit with respect to the wafer, The system includes a second alignment step, in which, with the positions of the imaging unit and the one wafer fixed, the imaging unit uses the focus changing unit to image the other wafer of the second wafer, which is at a relative distance from the imaging unit, with the imaging unit, thereby adjusting the alignment.

[0012] The sixth invention is a wafer alignment method for adjusting the alignment of a first wafer and a second wafer during bonding using a single imaging unit, A first alignment step involves adjusting the alignment by imaging the first wafer and the second wafer, which is at a relative distance from the imaging unit, via a focus changing unit that changes the focal length of the imaging unit with respect to the wafer; The system includes a second alignment step, in which, with the positions of the imaging unit and the one wafer fixed, the imaging unit performs alignment adjustment by imaging the other wafer of the second wafer that is relatively close to the imaging unit, without using the focus changing unit, thereby adjusting the alignment between the first wafer and the other wafer.

[0013] The seventh invention is a wafer joining method for joining a first wafer and a second wafer using a single imaging unit, A first alignment step is performed by imaging the first wafer and the second wafer that is relatively close to the imaging unit with respect to the wafer, without using a focus changing unit to change the focal length of the imaging unit with respect to the wafer, A second alignment step involves fixing the positions of the imaging unit and one of the wafers, and then using the focus changing unit to image the other wafer of the second wafer that is at a relative distance from the imaging unit, thereby performing alignment adjustment. The process includes a bonding step of joining the first wafer and the second wafer after the alignment adjustment described above.

[0014] The eighth invention is a wafer bonding method for bonding a first wafer and a second wafer using a single imaging unit, comprising: a first alignment step of performing alignment adjustment by imaging, with an imaging unit, one of the first wafer and the second wafer that is relatively far from the imaging unit via a focus changing unit that changes the focal length of the imaging unit with respect to the wafer; a second alignment step of performing alignment adjustment by imaging, with the imaging unit, the other of the first wafer and the second wafer that is relatively close to the imaging unit without passing through the focus changing unit while the positions of the imaging unit and the one wafer are fixed respectively; and a bonding step of bonding the first wafer and the second wafer that have undergone the alignment adjustment.

[0015] The ninth invention is a wafer alignment apparatus for adjusting alignment during bonding of a first wafer and a second wafer, comprising: a first holding unit for holding the first wafer; a second holding unit for holding the second wafer; a single imaging unit for imaging the first wafer and the second wafer; and performing alignment adjustment by imaging, with the imaging unit, one of the first wafer and the second wafer that is relatively close to the imaging unit without passing through a focus changing unit that changes the focal length of the imaging unit with respect to the wafer, and performing alignment adjustment by imaging, with the imaging unit, the other of the first wafer and the second wafer that is relatively far from the imaging unit via the focus changing unit while the positions of the imaging unit and the one wafer are fixed respectively.

[0016] The tenth invention is a wafer alignment apparatus for adjusting alignment during bonding of a first wafer and a second wafer, comprising: a first holding part for holding the first wafer; a second holding part for holding the second wafer; a single imaging part for imaging the first wafer and the second wafer; and having alignment adjustment is performed by imaging, with the imaging part, one of the first wafer and the second wafer that is relatively far from the imaging part through a focus changing part that changes the focal length of the imaging part with respect to the wafer,

[0017] An eleventh invention is a wafer bonding apparatus for bonding a first wafer and a second wafer, comprising a first holding part for holding the first wafer; a second holding part for holding the second wafer; a single imaging part for imaging the first wafer and the second wafer; and having alignment adjustment is performed by imaging, with the imaging part, one of the first wafer and the second wafer that is relatively close to the imaging part without passing through a focus changing part that changes the focal length of the imaging part with respect to the wafer, alignment adjustment is performed by imaging, with the imaging part, the other of the first wafer and the second wafer that is relatively far from the imaging part through the focus changing part while the positions of the imaging part and the one wafer are fixed respectively, the first holding part and the second holding part are brought close to each other, and the first wafer and the second wafer that have undergone the alignment adjustment are bonded; a wafer bonding apparatus.

[0018] ​The twelfth invention is a wafer joining apparatus for joining a first wafer and a second wafer, A first holding part for holding the first wafer, A second holding portion for holding the second wafer, A single imaging unit for imaging the first wafer and the second wafer, It has, Alignment adjustment is performed by imaging the first wafer and the second wafer, which is at a relative distance from the imaging unit, via a focus adjustment unit that changes the focal length of the imaging unit with respect to the wafer. With the positions of the imaging unit and the one wafer fixed, alignment adjustment is performed by imaging the other wafer of the second wafer that is relatively close to the imaging unit with the first wafer, without using the focus changing unit. The first holding portion and the second holding portion are brought close together, and the first wafer and the second wafer, which have undergone the alignment adjustment, are joined together. [Effects of the Invention]

[0019] According to the present invention, by accurately recognizing the wafer in the imaging unit, alignment accuracy can be improved, and at the same time, wafer bonding accuracy can be improved. [Brief explanation of the drawing]

[0020] [Figure 1] This figure shows the state in which the lower stage of the bonding apparatus of the present invention has retracted from its opposing position to the upper stage, resulting in a relative positional misalignment. [Figure 2] This figure shows the lower stage of the bonding apparatus of the present invention positioned opposite the upper stage. [Figure 3] This figure shows a mounting portion for housing a focus adjustment unit, which is formed on the upper stage of the bonding device of the present invention. [Figure 4] This diagram shows the positional relationship between the imaging unit of the bonding apparatus of the present invention, the first wafer located above it, and the second wafer located below it. [Figure 5] This figure shows the change in distance to the focal point when a focus changing unit is interposed between the imaging unit and the first wafer located above it in the bonding apparatus of the present invention. [Figure 6] This is a plan view showing an example of a focus adjustment holder that holds multiple focus adjustment parts with different plate thicknesses. [Figure 7] This is a conceptual diagram showing the imaging unit of the bonding apparatus of the present invention focusing on the first wafer located above it, without the intervening focus change unit. [Figure 8] This is a conceptual diagram showing the imaging unit of the bonding apparatus of the present invention focusing on a second wafer located below it, with a focus change unit in between. [Figure 9] This is a flowchart showing the wafer alignment adjustment process and wafer bonding process of the present invention. [Modes for carrying out the invention]

[0021] This document describes a wafer alignment method, a wafer bonding method, a wafer alignment apparatus, and a wafer bonding apparatus according to one embodiment of the present invention.

[0022] The wafer bonding method of the present invention is an invention that utilizes the wafer alignment method of the present invention. Furthermore, the wafer bonding apparatus of the present invention is an invention that utilizes the wafer alignment apparatus of the present invention.

[0023] In this specification, "wafer" refers to semiconductor wafers (silicon wafers) and other materials used in semiconductor manufacturing. A semiconductor substrate is also referred to as a wafer. Generally, a wafer is a disc-shaped plate made by thinly slicing a single crystal column of silicon (Si) or gallium arsenide (GaAs), and is an essential material for semiconductor manufacturing. Its surface is mirror-finished to eliminate minute irregularities and fine particles.

[0024] [Wafer alignment and bonding equipment] First, we will explain wafer alignment equipment and bonding equipment. Wafer alignment equipment refers to the same device as wafer bonding equipment, but it is a device that extracts the wafer alignment adjustment function from a wafer bonding device. Wafer bonding equipment also refers to the same device as wafer alignment equipment, but it includes a wafer bonding function for joining wafers together, in addition to the wafer alignment adjustment function. In the following explanation, we will refer to it as wafer bonding equipment.

[0025] As shown in Figures 1, 2, 3, 7, and 8, the wafer bonding apparatus 10 comprises a housing 12, a first holding unit 14 for holding a first wafer W1, a second holding unit 16 for holding a second wafer W2, a single imaging unit 18 for imaging the first wafer W1 and the second wafer W2, and a focus adjustment unit 20 for adjusting the focal length of the imaging unit 18 for each wafer W1 and W2. The wafer bonding apparatus 10 is also called a wafer alignment apparatus 11.

[0026] The first holding part 14 is attached to the housing 12. The first holding part 14 is fixed so as not to move in the vertical direction (also called the height direction, defined as the Z direction). Furthermore, the first holding part 14 is fixed so as not to move in the horizontal direction (defined as the X direction and the Y direction). The first holding part 14 is attached to the first shaft (not shown). The first shaft is attached to the housing 12 so as to be rotatable around its axis. Therefore, the first holding part 14 is configured to rotate around the axis of the first shaft (the Θ direction) along with the rotation of the first shaft. The first holding part 14 may also be fixed and not rotate around the axis of the first shaft (the Θ direction). The first holding part 14 may also be referred to as the first stage.

[0027] The first retaining portion 14 is located, for example, on the upper side in the vertical direction.

[0028] The principle by which the first holding part 14 holds the first wafer W1 is the same as the principle of substrate adsorption in conventional bonding apparatuses.

[0029] Specifically, the first holding unit 14 includes, for example, an electrostatic chuck, a heating unit, a cooling unit (all not shown), etc. The electrostatic chuck has an internal electrode and a dielectric, and uses the electrostatic force generated by applying a voltage to the internal electrode to attract the first wafer W1.

[0030] The heating element is a heater, such as a ceramic heater, and is built into the electrostatic chuck. By heating the electrostatic chuck, the heating element heats the first wafer W1 held in the electrostatic chuck.

[0031] The cooling unit is an existing one, and after the bonding of the first wafer W1 and the second wafer W2, it cools the polymerized wafer that is formed by the bonding of the first wafer W1 and the second wafer W2.

[0032] The second holding part 16 is mounted on the housing 12 so as to be movable along the vertical direction (also called the height direction, defined as the Z direction) and the horizontal direction (defined as the X direction and the Y direction). For example, rails may be arranged on the housing 12, and the second holding part 16 may slide along the rails to move along the horizontal direction. The second holding part 16 does not rotate around the second axis (Θ direction). The second holding part 16 may be supported by a second axis (not shown) and mounted so as to be rotatable around the second axis. The second holding part 16 may also be referred to as the second stage.

[0033] The second retaining portion 16 is located, for example, on the downward side in the vertical direction.

[0034] The principle by which the second holding part 16 holds the second wafer W2 is the same as the principle of substrate adsorption in conventional bonding apparatuses.

[0035] Specifically, the second holding unit 16 includes, for example, an electrostatic chuck, a heating unit, a cooling unit (all not shown), etc. The electrostatic chuck has an internal electrode and a dielectric, and uses the electrostatic force generated by applying a voltage to the internal electrode to attract the second wafer W2.

[0036] The heating element is a heater, such as a ceramic heater, and is built into the electrostatic chuck. By heating the electrostatic chuck, the heating element heats the second wafer W2 held in the electrostatic chuck.

[0037] The cooling unit is an existing one, and after the bonding of the first wafer W1 and the second wafer W2, it cools the polymerized wafer that is formed by the bonding of the first wafer W1 and the second wafer W2.

[0038] The imaging unit 18 captures alignment marks on the first wafer W1 and the second wafer W2. The imaging results are stored in the storage unit of the imaging unit 18 as image data of the first wafer W1 and the second wafer W2. The imaging unit 18 is attached to the first holding unit 14. This fixes the relative position of the imaging unit 18 with respect to the first holding unit 14. When the first holding unit 14 moves along the vertical direction, the imaging unit 18 moves along the vertical direction together with the first holding unit 14.

[0039] The imaging unit 18 is preferably an optical camera, for example. In particular, an infrared camera (IR camera) is used for the imaging unit 18. The depth of field of the imaging unit 18 is, for example, ±1.25 μm. The imaging unit 18 may also have a built-in control unit capable of performing alignment or joining processing based on imaging data. Furthermore, the imaging unit 18 may be configured to transmit imaging data to an external control system, which then performs wafer alignment or joining processing.

[0040] The imaging unit 18 includes, for example, a light source (not shown) that emits infrared light. The light source is illuminated at least during the alignment of the first wafer W1, enabling imaging. In this way, the imaging unit 18 is capable of coaxial illumination.

[0041] The light source used will be a conventionally known infrared LED element or halogen lamp. Furthermore, the light source will emit light with a wavelength of, for example, 1000 to 1200 nanometers (nm). The light source used will be capable of emitting light with a wavelength that can penetrate substrates such as semiconductor wafers, including silicon wafers.

[0042] The focus adjustment unit 20 is attached to the first holding unit 14. Specifically, the first holding unit 14 has a recessed mounting portion 26. The focus adjustment unit 20 is attached to this mounting portion 26. The focus adjustment unit 20 is positioned on the optical axis L of the light emitted from the imaging unit 18. As a result, the light emitted from the imaging unit 18 enters the focus adjustment unit 20, passes through the interior of the focus adjustment unit 20, and illuminates the second wafer W2.

[0043] The imaging unit 18 and the focus changing unit 20 may also be attached to the second holding unit 16 instead of the first holding unit 14.

[0044] The focus adjustment unit 20 changes the focal length of light from the imaging unit 18 to wafers W1 and W2. The focus adjustment unit 20 is made of, for example, glass. Quartz glass is particularly preferred as the glass. The focus adjustment unit 20 has the function of changing the focal length of light depending on the refractive index (material) and the plate thickness. Furthermore, since the focal length of light differs depending on the refractive index (material) and the plate thickness, by preparing multiple focus adjustment units 20 with different refractive indices (materials) or plate thicknesses, the focal length of light from the imaging unit 18 to wafers W1 and W2 can be changed to multiple distances, and the optimal focal length can be selected to improve imaging accuracy.

[0045] Regarding the refractive index of light, light refracts when it passes through a different medium. When light passes through air and enters, for example, glass, the refractive index of glass is higher than that of air, so the speed of light slows down inside the glass. Therefore, even if the physical distance is the same, the optical distance (the path the light travels) when light passes through glass is shorter. In other words, the theoretical focusing time is shortened.

[0046] The focal length of the imaging unit 18 relative to wafers W1 and W2 changes depending on the thickness of the focus changing unit 20. For example, when glass is used, the optically observed focal position becomes closer to the imaging unit 18. In detail, if the thickness of the glass is t and the refractive index of the glass is n, the amount of change in the focal position (amount of shortening of the optical path) Δ is calculated as follows. Δ = t(1 - 1 / n). For example, if the refractive index of the glass is 1.5 and the thickness of the glass is 1 mm, Δ = 1 mm × (1 - 1 / 1.5) = 0.33 mm. Therefore, the focal point shifts by 0.33 mm. In this way, as the thickness of the glass plate increases, the distance the focal point shifts also increases.

[0047] For the reasons stated above, when light passes through glass, a phenomenon occurs where the so-called travel distance changes depending on the refractive index of the light and the thickness of the glass. Therefore, when imaging a wafer by passing light from the imaging unit 18 through glass, by varying the thickness of the glass according to the distance from the imaging unit 18 to the wafer, the focus of the imaging unit 18 on the wafer can be adjusted while the position of the imaging unit 18 is fixed. As a result, positional and focus errors of the imaging unit 18 can be avoided, and the accuracy of wafer imaging is improved.

[0048] Here, as shown in Figures 4, 5, and 7, when the imaging unit 18 images the first wafer W1 which is located relatively closer to the second wafer W2, the light from the imaging unit 18 illuminates the first wafer W1 without passing through the focus changing unit 20.

[0049] On the other hand, as shown in Figures 4, 5, and 8, when the imaging unit 18 images a second wafer W2 that is located at a relatively greater distance than the first wafer W1, the light from the imaging unit 18 passes through the focus changing unit 20 and illuminates the second wafer W2.

[0050] Therefore, it is preferable to have a focus change unit moving mechanism (not shown) for moving the focus change unit 20 so that when the imaging unit 18 images the first wafer W1, the focus change unit 20 is moved away from the optical axis L of the light emitted from the imaging unit 18, and when the imaging unit 18 images the second wafer W2, the focus change unit 20 is positioned on the optical axis L of the light emitted from the imaging unit 18.

[0051] Alternatively, the imaging unit 18 may be equipped with multiple light sources and multiple camera lenses, and the focus changing unit 20 may not be positioned on the optical axis L of the light emitted from one light source, but rather on the optical axis L of the light emitted from the other light source. In this configuration, the light emitted from one light source illuminates the first wafer W1 without passing through the focus changing unit, and the light emitted from the other light source illuminates the second wafer W2 after passing through the focus changing unit. This eliminates the need for a focus changing unit movement mechanism.

[0052] As shown in Figure 6, for example, a focus change holder 24 may be provided, which has multiple focus change units 20 arranged in a planar direction, each having at least one of different refractive indices (materials) or plate thicknesses. Preferably, the focus change holder 24 is detachably attached to a mounting portion 26 formed on the first holding portion 14. The focus change holder 24 may be configured to be rotatable around a central axis. Depending on the material of the wafer to be imaged or the surface condition of the wafer, the focus change holder 24 rotates around the central axis to select the optimal focus change unit 20. The rotation of the focus change holder 24 around the central axis may be performed manually by an operator, or it may be automatically controlled using a rotation control mechanism (not shown).

[0053] Here, the focus change holder 24 has, for example, five pieces of glass (e.g., quartz glass) 22 of different thicknesses arranged on it. For example, pieces of glass 22 with thicknesses of 3.0 mm, 1.0 mm, 0.3 mm, 0.1 mm, and 0.05 mm are arranged on it. Also, the part with a plate thickness of 0.0 mm means that no glass is placed and it is hollow. In this way, by rotating the focus change holder 24 around its central axis, each piece of glass 22 (e.g., quartz glass) of 3.0 mm, 1.0 mm, 0.3 mm, 0.1 mm, and 0.05 mm can be positioned on the optical axis L of the imaging unit 18, and the pieces of glass 22 (e.g., quartz glass) can be moved away from the optical axis L of the imaging unit 18.

[0054] Furthermore, the material (composition) of the glass 22 is not limited to quartz. By changing the material (composition) of the glass 22, the refractive index of light can be changed. For example, glass 22 of different materials with the same thickness may be arranged side by side. Alternatively, glass 22 of different materials (composition) and thicknesses may also be arranged side by side.

[0055] In a configuration where a 3.0 mm thick glass 22 (e.g., quartz glass) is placed on the optical axis L of the imaging unit 18, the focal length is extended by approximately 1000 μm. In a configuration where a 1.0 mm thick glass 22 (e.g., quartz glass) is placed on the optical axis L of the imaging unit 18, the focal length is extended by approximately 300 μm. In a configuration where a 0.1 mm thick glass 22 (e.g., quartz glass) is placed on the optical axis L of the imaging unit 18, the focal length is extended by approximately 30 μm. In a configuration where a 0.05 mm thick glass 22 (e.g., quartz glass) is placed on the optical axis L of the imaging unit 18, the focal length is extended by approximately 15 μm.

[0056] The thickness of the glass 22 (for example, quartz glass) is preferably in the range of 0.02 mm or more and 1.0 mm or less, but is not limited to this range.

[0057] When imaging a first wafer W1 that is 12.5 mm away from the camera lens of the imaging unit 18, the glass 22 (for example, quartz glass) (focus change unit) is not placed on the optical axis L of the imaging unit 18. The light from the imaging unit 18 does not pass through the glass 22 but shines onto the first wafer W1, and the alignment marks on the A-side are imaged (recognized). This performs alignment adjustment of the first wafer W1 (first alignment step S100 in Figure 9).

[0058] Next, a glass 22 (for example, quartz glass) with a thickness of 1.0 mm is placed on the optical axis L of the imaging unit 18. This extends the focal length of the imaging unit 18 with respect to the wafer by approximately 300 μm. If the second wafer W2 is approximately 300 μm further away from the imaging unit 18 than the first wafer W1, then placing the glass 22 (for example, quartz glass) with a thickness of 1.0 mm on the optical axis L of the imaging unit 18 cancels out the extension of the focal length and the displacement D (see Figures 4 and 5), allowing the camera lens to focus. In other words, the positional displacement D of the second wafer W2 relative to the first wafer W1 (see Figures 4 and 5) cancels out the value of the optical path shortening, thereby fixing the positions of the imaging unit 18 and the first wafer W1 (especially the vertical position). The light from the imaging unit 18 passes through the glass 22 and illuminates the second wafer W2, capturing (recognizing) the alignment marks on the B-plane. This performs alignment adjustment of the second wafer W2 (second alignment step S200 in Figure 9).

[0059] This adjustment method allows for adjusting the focal position of the imaging unit 18 relative to the second wafer W2 using, for example, glass 22 (e.g., quartz glass) with a thickness in the range of 0.02 mm or more and 1.0 mm or less. By selecting glass 22 with a plate thickness corresponding to the positional misalignment D (see Figures 4 and 5) between the A-plane on the first wafer W1 and the B-plane on the second wafer W2, it is possible to focus on both the A-plane on the first wafer W1 and the B-plane on the second wafer W2 using a single imaging unit 18 and a single camera lens.

[0060] Once the alignment adjustment of the first wafer W1 and the second wafer W2 is complete, the first holding part 14 and the second holding part 16 are brought relatively close together, and the first wafer W1 and the second wafer W2 are joined (wafer joining process S300 in Figure 9). At this time, one of the holding parts (for example, the first holding part 14) is fixed along the horizontal and vertical directions, and only the other holding part (for example, the second holding part 16) is moved along the horizontal and vertical directions, thereby fixing one wafer W1 and moving only one wafer W2 to join wafers W1 and W2 together. This improves the positional accuracy during joining.

[0061] As a result, the alignment adjustment of the first wafer W1 and the second wafer W2 is completed while the position of the imaging unit 18 is fixed. Compared to the method of adjusting the wafer alignment by moving the position of the imaging unit 18, positional displacement and vibration are eliminated, and the alignment accuracy is improved. As a result, by joining wafers with high alignment accuracy, relative displacement between wafers is eliminated, and the wafer joining accuracy is also improved.

[0062] In particular, by simply using the focus change unit 20, two focal lengths can be achieved with a single imaging unit 18 and one camera lens, contributing to the miniaturization and cost reduction of the bonding device 10.

[0063] Next, we will describe the wafer alignment adjustment process and wafer bonding process using the wafer bonding apparatus 10 (alignment apparatus 11).

[0064] As shown in Figure 9, the wafer alignment adjustment process and bonding process mainly consist of a first alignment process S100, a second alignment process S200, and a wafer bonding process S300.

[0065] The explanation will assume that the first wafer W1 is held by the first holding part 14 and the second wafer W2 is held by the second holding part 16.

[0066] In the first alignment process S100, as shown in Figures 4, 5, and 7, the light source of the imaging unit 18 is turned on, and light (e.g., infrared light) is irradiated from the imaging unit 18 toward the first wafer W1, which is located at a relatively closer distance than the second wafer W2, to image the alignment marks on the first wafer W1. At this time, the light emitted from the imaging unit 18 does not pass through the glass 22 (e.g., quartz glass) which is the focus change unit 20, but irradiates the first wafer W1. Since the positions of the imaging unit 18 and the first wafer W1 are fixed by the first holding unit 14, the imaging accuracy is high. After the imaging unit 18 images the alignment marks on the first wafer W1, the imaging unit 18 stores the alignment marks as image data.

[0067] In the second alignment process S200, as shown in Figures 4, 5, and 8, with the positions of the imaging unit 18 and the first wafer W1 fixed, the light source of the imaging unit 18 is turned on, and light (e.g., infrared light) is irradiated from the imaging unit 18 toward the second wafer W2, which is located at a relative distance from the first wafer W1, to image the alignment marks on the second wafer W2. At this time, a glass 22 (e.g., quartz glass), which is the focus change unit 20, is placed on the optical axis L of the light emitted from the imaging unit 18. Therefore, the light emitted from the imaging unit 18 passes through the glass 22 (e.g., quartz glass), which is the focus change unit 20, and irradiates the second wafer W2. Since the positions of the imaging unit 18 and the second wafer W2 are fixed by the second holding unit 16, the imaging accuracy is high. After the imaging unit 18 captures the alignment marks on the second wafer W2, the imaging unit 18 stores the image data of the alignment marks.

[0068] Furthermore, the focal length of the light emitted from the imaging unit 18 extends by approximately 30% of the thickness of the glass 22 (e.g., quartz glass). For example, if a glass 22 (e.g., quartz glass) with a thickness of 0.1 mm is used, the focal length of the light extends by approximately 30 μm.

[0069] Here, while the imaging unit 18 reads the alignment marks of the second wafer W2, the second holding unit 16 is moved in the horizontal and Θ directions to superimpose the alignment marks of the second wafer W2 with the alignment marks of the first wafer W1.

[0070] In the wafer bonding process S300, when the alignment marks of the first wafer W1 and the second wafer W2 coincide, the second holding part 16 moves vertically (height direction) to approach the first holding part 14, and the first wafer W1 and the second wafer W2 are bonded. At this time, the first holding part 14 and the first wafer W1 are fixed vertically, and only the second holding part 16 and the second wafer W2 are moved horizontally and vertically to bond the first wafer W1 and the second wafer W2. This improves the positional accuracy during bonding.

[0071] In the first alignment step S100, the alignment adjustment is performed first on the first wafer W1, which is located relatively closer to the imaging unit 18 than the second wafer W2. However, the procedure is not limited to this. For example, the alignment adjustment may be performed first on the second wafer W2, which is located relatively further away from the imaging unit 18 than the first wafer W1.

[0072] Specifically, the light source of the imaging unit 18 is turned on, and light (e.g., infrared light) is irradiated from the imaging unit 18 toward the second wafer W2, which is located at a relative distance from the first wafer W1, to image the alignment marks on the second wafer W2. At this time, a glass 22 (e.g., quartz glass), which is the focus change unit 20, is placed on the optical axis L of the light emitted from the imaging unit 18. Therefore, the light emitted from the imaging unit 18 passes through the glass 22 (e.g., quartz glass), which is the focus change unit 20, and irradiates the second wafer W2. After the imaging unit 18 images the alignment marks on the second wafer W2, the imaging unit 18 stores the image data of the alignment marks.

[0073] Subsequently, in the second alignment process S200, alignment is performed on the first wafer W1, which is located at a relatively closer distance from the imaging unit 18 than the second wafer W2. The light source of the imaging unit 18 is turned on, and light (e.g., infrared light) is irradiated from the imaging unit 18 toward the first wafer W1, which is located at a closer distance than the second wafer W2, to image the alignment marks on the first wafer W2. At this time, the glass 22 (e.g., quartz glass), which is the focus change unit 20, is moved away from the optical axis L of the imaging unit 18, and the light emitted from the imaging unit 18 irradiates the first wafer W1 without passing through the glass 22. After the imaging unit 18 images the alignment marks on the first wafer W1, the imaging unit 18 stores the alignment marks as image data.

[0074] Here, while the imaging unit 18 reads the alignment marks of the first wafer W1, the second holding unit 16 is moved appropriately in the horizontal and Θ directions to align the alignment marks of the first wafer W1 and the second wafer W2. Then, the wafer bonding process S300 is performed, and the first wafer W1 and the second wafer W2 are bonded together.

[0075] As described above, according to this embodiment, after imaging the alignment mark of one wafer, the alignment mark of the other wafer is imaged while the positions of the imaging unit 18 and the one wafer are fixed, thereby improving the wafer alignment accuracy. In contrast, in the conventional technology, the imaging unit is moved in the vertical direction, resulting in two errors: the driving accuracy of the imaging unit and the positional accuracy of one wafer, which led to a problem of reduced alignment accuracy. Therefore, in this embodiment, the focal length of the imaging unit 18 can be freely adjusted by the glass material (refractive index of light) and the thickness of the glass plate, so the position of the imaging unit 18 does not need to be moved and can be fixed. As a result, the alignment accuracy of wafers W1 and W2 is improved, and consequently, the bonding accuracy of wafers W1 and W2 is improved.

[0076] It should be noted that this embodiment and the examples illustrate one aspect of the present invention, and the present invention is not limited thereto. Differences in the degree of design modifications from this embodiment and the examples are naturally included within the scope of the technical idea of ​​the present invention. [Explanation of symbols]

[0077] 10 Bonding equipment 11 Alignment device 12 cabinets 14. First holding part (upper stage) 16. Second holding section (lower stage) 18 Imaging Unit 20 Focus adjustment section 22 Glass (quartz glass) 24 Focus adjustment holder 26 Mounting part D. Positional misalignment between the first wafer and the second wafer. L optical axis W1 First wafer (upper wafer) W2 Second wafer (lower wafer)

Claims

1. A wafer alignment method for adjusting the alignment of two wafers at different distances from a single imaging unit during bonding, wherein the imaging unit is used to adjust the alignment of the two wafers at different distances from the imaging unit. For the alignment mark of one wafer located at a short distance from the imaging unit, the light from the imaging unit is imaged without passing through the glass. With the imaging unit and one of the wafers fixed in place, the light from the imaging unit is passed through the glass to image the alignment mark of the other wafer, which is located at a distance from the imaging unit. Wafer alignment method.

2. A wafer alignment method for adjusting the alignment of two wafers at different distances from a single imaging unit during bonding, wherein the imaging unit is used to adjust the alignment of the two wafers at different distances from the imaging unit. For the alignment mark of one wafer located at a distance from the imaging unit, the light from the imaging unit is passed through the glass to take an image. With the imaging unit and one of the wafers fixed in place, the alignment marks of the other wafer, which is located at a short distance from the imaging unit, are imaged without passing the light from the imaging unit through the glass. Wafer alignment method.

3. When imaging the wafer by passing light from the imaging unit through the glass, the thickness of the glass is varied according to the distance from the imaging unit to the wafer. A wafer alignment method according to claim 1 or 2.

4. A wafer joining method for joining two wafers at different distances from a single imaging unit, wherein For the alignment mark of one wafer located at a short distance from the imaging unit, the light from the imaging unit is imaged without passing through the glass. With the imaging unit and one of the wafers fixed in place, the light from the imaging unit is passed through the glass to image the alignment mark of the other wafer, which is located at a distance from the imaging unit. The wafers are joined together by moving only one of the two wafers so that the alignment marks overlap. Method for joining wafers.

5. A wafer joining method for joining two wafers at different distances from a single imaging unit, wherein For the alignment mark of one wafer located at a distance from the imaging unit, the light from the imaging unit is passed through the glass to take an image. With the positions of the imaging unit and one of the wafers fixed, the alignment marks of the other wafer, which is located at a short distance from the imaging unit, are imaged without passing the light from the imaging unit through the glass. The wafers are joined together by moving only one of the two wafers so that the alignment marks overlap. Method for joining wafers.

6. When imaging the wafer by passing light from the imaging unit through the glass, the thickness of the glass is varied according to the distance from the imaging unit to the wafer. A method for joining wafers according to claim 4 or 5.

7. A wafer alignment method for adjusting the alignment of a first wafer and a second wafer during bonding using a single imaging unit, A first alignment step is performed by imaging the first wafer and the second wafer that is relatively close to the imaging unit with respect to the wafer, without using a focus changing unit to change the focal length of the imaging unit with respect to the wafer, The system includes a second alignment step, in which, with the positions of the imaging unit and one of the wafers fixed, the imaging unit uses the focus changing unit to image the other wafer of the second wafer, which is at a relative distance from the imaging unit, with the imaging unit, thereby performing alignment adjustment. Wafer alignment method.

8. A wafer alignment method for adjusting the alignment of a first wafer and a second wafer during bonding using a single imaging unit, A first alignment step involves adjusting the alignment by imaging the first wafer and the second wafer, which is at a relative distance from the imaging unit, via a focus changing unit that changes the focal length of the imaging unit with respect to the wafer, The system includes a second alignment step, in which, with the positions of the imaging unit and the one wafer fixed, the imaging unit performs alignment adjustment by imaging the other wafer of the second wafer that is relatively close to the imaging unit, without using the focus changing unit, thereby adjusting the alignment between the first wafer and the other wafer. Wafer alignment method.

9. In the first alignment step or the second alignment step, glass is used as the focus changing part. The wafer alignment method according to claim 7 or 8.

10. The focal length of the imaging unit relative to the wafer is adjusted by the optical refractive index or thickness of the glass. The wafer alignment method according to claim 9.

11. As the aforementioned glass, quartz glass is used. The wafer alignment method according to claim 10.

12. A wafer joining method for joining a first wafer and a second wafer using a single imaging unit, A first alignment step is performed by imaging the first wafer and the second wafer that is relatively close to the imaging unit with respect to the wafer, without using a focus changing unit to change the focal length of the imaging unit with respect to the wafer, A second alignment step involves fixing the positions of the imaging unit and one of the wafers, and then using the focus changing unit to image the other wafer of the second wafer that is at a relative distance from the imaging unit, thereby performing alignment adjustment. The process includes a bonding step of joining the first wafer and the second wafer after the alignment adjustment described above. Wafer alignment bonding method.

13. A wafer joining method for joining a first wafer and a second wafer using a single imaging unit, A first alignment step involves adjusting the alignment by imaging the first wafer and the second wafer, which is at a relative distance from the imaging unit, via a focus changing unit that changes the focal length of the imaging unit with respect to the wafer, A second alignment step is performed by fixing the positions of the imaging unit and one of the wafers, and without using the focus changing unit, imaging the other wafer of the second wafer that is relatively close to the imaging unit with the first wafer, thereby adjusting the alignment. The process includes a bonding step of joining the first wafer and the second wafer after the alignment adjustment described above. Wafer alignment bonding method.

14. In the first alignment step or the second alignment step, glass is used as the focus changing part. A method for joining wafers according to claim 12 or 13.

15. The focal length of the imaging unit relative to the wafer is adjusted by the optical refractive index or thickness of the glass. The wafer joining method according to claim 14.

16. As the aforementioned glass, quartz glass is used. The wafer joining method according to claim 15.

17. A wafer alignment device for adjusting the alignment of a first wafer and a second wafer during bonding, A first holding part for holding the first wafer, A second holding part for holding the second wafer, A single imaging unit for imaging the first wafer and the second wafer, It has, Alignment adjustment is performed by imaging the first wafer and the second wafer that is relatively close to the imaging unit with respect to the wafer, without using a focus adjustment unit to change the focal length of the imaging unit with respect to the wafer. With the positions of the imaging unit and one of the wafers fixed, alignment adjustment is performed by imaging the other wafer of the second wafer, which is at a relative distance from the imaging unit, with the imaging unit via the focus changing unit. Wafer alignment device.

18. A wafer alignment device for adjusting the alignment of a first wafer and a second wafer during bonding, A first holding part for holding the first wafer, A second holding part for holding the second wafer, A single imaging unit for imaging the first wafer and the second wafer, It has, Alignment adjustment is performed by imaging the first wafer and the second wafer, which is at a relative distance from the imaging unit, via a focus adjustment unit that changes the focal length of the imaging unit with respect to the wafer. With the positions of the imaging unit and the one wafer fixed, alignment adjustment is performed by imaging the other wafer of the second wafer, which is relatively closer to the imaging unit than the first wafer, with the imaging unit, without using the focus changing unit. Wafer alignment device.

19. The aforementioned focus changing part is made of glass. A wafer alignment apparatus according to claim 17 or 18.

20. The optical refractive index and thickness of the glass are used to adjust the focal length of the imaging unit relative to the wafer. Wafer alignment apparatus according to claim 19.

21. A glass holding portion having a plurality of the aforementioned glass pieces with different optical refractive indices and / or plate thicknesses, Wafer alignment apparatus according to claim 20.

22. The imaging unit is attached to either the first holding unit or the second holding unit. A wafer alignment apparatus according to claim 17 or 18.

23. The focus changing unit is the first holding unit or the second holding unit, and is mounted on the optical axis of the imaging unit through which the light from the imaging unit passes. The wafer alignment apparatus according to claim 22.

24. The glass in question is quartz glass. Wafer alignment apparatus according to claim 19.

25. A wafer bonding apparatus for bonding a first wafer and a second wafer, A first holding part for holding the first wafer, A second holding part for holding the second wafer, A single imaging unit for imaging the first wafer and the second wafer, It has, Alignment adjustment is performed by imaging the first wafer and the second wafer that is relatively close to the imaging unit with respect to the wafer, without using a focus adjustment unit to change the focal length of the imaging unit with respect to the wafer. With the positions of the imaging unit and the one wafer fixed, alignment adjustment is performed by imaging the other wafer of the second wafer, which is at a relative distance from the imaging unit, with the imaging unit via the focus changing unit. The first holding portion and the second holding portion are brought close together to join the first wafer and the second wafer after the alignment adjustment has been performed. Wafer bonding equipment.

26. A wafer bonding apparatus for bonding a first wafer and a second wafer, A first holding part for holding the first wafer, A second holding part for holding the second wafer, A single imaging unit for imaging the first wafer and the second wafer, It has, Alignment adjustment is performed by imaging the first wafer and the second wafer, which is at a relative distance from the imaging unit, via a focus adjustment unit that changes the focal length of the imaging unit with respect to the wafer. With the positions of the imaging unit and the one wafer fixed, alignment adjustment is performed by imaging the other wafer of the second wafer that is relatively close to the imaging unit with the first wafer, without using the focus changing unit. The first holding portion and the second holding portion are brought close together to join the first wafer and the second wafer after the alignment adjustment has been performed. Wafer bonding equipment.

27. The aforementioned focus changing part is made of glass. A wafer bonding apparatus according to claim 25 or 26.

28. The optical refractive index and thickness of the glass are used to adjust the focal length of the imaging unit relative to the wafer. A wafer bonding apparatus according to claim 27.

29. A glass holding portion having a plurality of the aforementioned glass pieces with different optical refractive indices and / or plate thicknesses, A wafer bonding apparatus according to claim 28.

30. The imaging unit is attached to either the first holding unit or the second holding unit. A wafer bonding apparatus according to claim 25 or 26.

31. The focus changing unit is the first holding unit or the second holding unit, and is mounted on the optical axis of the imaging unit through which the light from the imaging unit passes. A wafer bonding apparatus according to claim 30.

32. The glass in question is quartz glass. A wafer bonding apparatus according to claim 27.

Images