JP2007301600A - Joining method and its device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joining method and its device capable of preventing a joined state from being non-uniform even when a joining area of an object to be joined is increased. <P>SOLUTION: First and second wafers (objects to be joined) 11, 12 held on a stage 5 arranged in an evacuated vacuum chamber 1 are pressurized by a joining head 4 at the predetermined pressure; the DC voltage is applied between joining surfaces in surface contact with each other, and the ultrasonic vibration is applied thereto by an X-axis ultrasonic oscillator 2 and/or a Z-axis ultrasonic oscillator 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bonding method and apparatus for improving bonding quality and bonding efficiency in anodic bonding in which a plurality of objects to be bonded are bonded to each other at their bonding surfaces.

  When a plurality of objects to be bonded such as wafers or wafers and chips are bonded to each other at the bonding surface, the bonding surfaces are surface-treated with oxygen plasma, ion beam, etc. And a method of joining between the joining surfaces by applying pressure is known. However, since it is difficult to obtain a stable bonding state only by pressurization, a more effective bonding method is required. An anodic bonding apparatus developed to meet the demand is known.

  As shown in FIG. 5, the anodic bonding apparatus is arranged in the chamber 103 in a state where the first bonding target object 101 and the second bonding target object 102 are overlapped so as to face each other on the bonding surface. Hundreds of power supplied from the DC power source 105 to the joint surfaces of the objects 101 and 102 are heated by applying a load to the objects 101 and 102 and heating the objects 101 and 102 by the heater 106. A DC voltage of volts is applied from the electrode 104 (see Patent Document 1).

When a DC voltage is applied to the bonding surface, a space charge layer is formed at the bonding interface and a high electric field is generated. An electrostatic attractive force is generated at the bonding interface pressurized by the high electric field, and the first and second bonding objects are bonded between the bonding surfaces.
JP 2000-294469 A

  However, in the anodic bonding method in the prior art, the uniformity of the bonding surface with respect to the condition load is low, and partial bonding failure occurs on the bonding surface. In particular, when the object to be bonded is a wafer, the wafer tends to increase in size. When wafers having such a large bonding surface are to be bonded to each other at the bonding surface, pressure applied to the bonding object is applied. Need to be larger. On the other hand, the wafer also tends to be thinned, and applying a large load may damage the wafer.

  An object of the present invention is to provide a bonding method and apparatus capable of improving the bonding quality even when the pressure applied to a plurality of bonding objects is kept low.

  In order to achieve the above object, the first invention of the present application is a bonding method in which a plurality of objects to be bonded are pressurized so as to come into surface contact with each other, and a plurality of objects to be bonded are bonded between the bonding surfaces. It is characterized by applying ultrasonic vibration.

  According to the above-described joining method, since ultrasonic vibration is applied to the joining surfaces in a state where a plurality of joining objects are contact-pressed on each other's joining surfaces, even if the load for pressing the joining objects is reduced, The bonding surfaces are bonded in a uniform bonding state by the action of sonic bonding. Even for wafers with a large area where uniform bonding cannot be obtained, the action of ultrasonic bonding is also added, so even bonding objects that tend to become larger and thinner like wafers are pressurized. The joining region can be uniformly joined by the action of ultrasonic joining without increasing the load and equalizing the contact with the joining surface. Accordingly, it is possible to shorten the bonding time, stabilize the bonding, and simplify the apparatus.

  In the above-described joining method, the two orthogonal axes on the joining surface are the X-axis and the Y-axis, the axis perpendicular to the joining surface is the Z-axis, and at least one axial direction of each of the X-axis, Y-axis, and Z-axis directions. By applying ultrasonic vibrations, it is possible to selectively combine the optimal excitation directions according to the joining surface material and joining surface size of the joining object.

  In addition, by synchronizing at least two of the ultrasonic vibrations in each of the X-axis, Y-axis, and Z-axis directions and applying the ultrasonic vibration while controlling the intensity, the joint surface is three-dimensional. By applying ultrasonic vibration, the action of ultrasonic bonding can be increased, and by controlling the intensity of ultrasonic vibration, it is possible to obtain a bonded state that matches the bonding surface material and bonding surface size of the object to be bonded.

  In addition, it is preferable to apply ultrasonic vibration of 20 to 70 KHz as a vibration frequency for bonding between wafers or between a wafer and a chip.

  In addition, it is preferable to apply ultrasonic vibration with a vibration amplitude of 5 μm or less, and application of ultrasonic vibration with a large vibration amplitude may cause displacement. In particular, vibration in the vertical direction perpendicular to the joint surface is If the amplitude is increased, the bonding surface may be damaged, and application of ultrasonic vibration with a small vibration amplitude is suitable when bonding precision parts such as wafers and chips.

  In addition, it is preferable to detect the impedance of the ultrasonic transducer and control to stop the application of ultrasonic vibration when the impedance increases to 20% or more from the initial application, and the bonding area by ultrasonic bonding is reduced. Impedance increases as it expands, but if vibration energy exceeding the joint area is applied, damage due to excess energy being applied to the joint and the object itself is likely to occur. It is preferable to stop the application of ultrasonic vibration when it increases above a predetermined amount.

  In addition, when applying ultrasonic vibration, it is preferable to gradually increase the pressure, and if the pressure is increased as the bonding area by ultrasonic bonding increases, the state of proper ultrasonic bonding Is obtained. If large pressure is applied from the beginning of application, it is difficult to obtain the sliding friction necessary for ultrasonic bonding between the joint surfaces, but if the pressure is gradually increased, sliding friction synchronized with the bonding area may be obtained. it can.

  Also, heating and bonding the bonding target object is effective for a bonding target object that is difficult to bond at room temperature, and the combined use of heating promotes diffusion at the bonding interface and facilitates bonding.

  In addition, it is preferable to bond the objects to be bonded in a vacuum atmosphere, and even when non-uniform bonding occurs due to bubbles generated at the bonding interface when ultrasonic bonding is performed in the air, Since no bubbles are generated, a stable bonded state can be obtained.

  Moreover, this invention 2nd invention pressurizes so that a several joining target object may surface-contact with each other's joining surface, and in a joining apparatus which joins a several joining target object between joining surfaces, surface contact between the said joining surfaces. An ultrasonic vibration applying means for applying ultrasonic vibration to a plurality of objects to be joined is provided.

  According to the above bonding apparatus, ultrasonic vibration is applied from the ultrasonic vibration applying means to the bonding surface in conjunction with the application of the DC voltage in a state where a plurality of objects to be bonded are pressed so as to be in surface contact with each other. Then, the action of ultrasonic bonding extends between the bonding surfaces, and the entire bonding surfaces are bonded uniformly. When the area of the bonding surface is increased, a portion that cannot be bonded is likely to be generated. However, by applying ultrasonic vibration, it is possible to improve the bonding quality for a bonding surface having a large area even if the pressing force is suppressed.

  In the above configuration, at least the holding means and the load applying means are disposed in the vacuum chamber, so that the objects to be joined can be held in a vacuum and contacted and pressurized, and the bonding interface can be obtained when ultrasonic bonding is performed in the atmosphere. Even in the case where non-uniform bonding occurs due to the generation of bubbles, no bubbles are generated in vacuum, so that a stable bonding state can be obtained. The ultrasonic vibration applying means can be easily applied from the outside of the vacuum chamber. However, if the ultrasonic vibration applying means is disposed in the vacuum chamber, the apparatus can be miniaturized.

  In addition, by providing at least the energy irradiation port of the surface modification means for modifying the bonding surface in the vacuum chamber, the state cleaned or activated in vacuum is maintained, and the surface is superficial with no deposits. Sonic bonding is performed, and when activated, even those that could not be bonded in the atmosphere can be ultrasonic bonded.

  According to the present invention, in joining between joining surfaces of a plurality of joining objects, a state in which joining non-uniformity is likely to occur when the area of the joining surface becomes large is an action of ultrasonic joining by applying ultrasonic vibration. Therefore, a stable bonded state can be obtained, which is effective for bonding wafers that tend to increase in area and thickness.

  FIG. 1 shows a configuration of a bonding apparatus according to the first embodiment, and a first wafer 11 and a second wafer 12 that are objects to be bonded are bonded to each other at a bonding surface using an anodic bonding method. It is configured to be able to. The configuration of the heating means and voltage application means necessary for anodic bonding is the same as in the prior art, and is not shown in the figure, and only characteristic components are shown.

  In FIG. 1, a holding means 7 that holds a second wafer 12 is disposed on a stage 5 disposed in the vacuum chamber 1, and the first wafer 11 is placed on the second wafer 12. Has been. A bonding head 4 is disposed above the stage 5 and moved downward by a load applied from the pressure shaft 8 to pressurize the first and second wafers 11 and 12, and an electrode (not shown) is the first. A DC voltage is applied in contact with the wafer 11 and the first and second wafers 11 and 12 are heated to a predetermined temperature by heating means. Further, ultrasonic vibration in the X-axis direction is applied from the X-axis ultrasonic transducer 2 to the bonding head 4, and ultrasonic vibration in the Z-axis direction is applied from the Z-axis ultrasonic transducer 3.

  The first and second wafers 11 and 12 having the bonded surfaces cleaned and activated are loaded into the vacuum chamber 1 and aligned so that the bonding positions of the first and second wafers face each other precisely. The pressure is reduced to a predetermined vacuum state, and the first and second wafers 11 and 12 are heated to a predetermined temperature by a heating means (not shown). Next, when a load is applied to the pressure shaft 8 by a pressure means (not shown), the bonding head 4 moves down, and a predetermined pressure is applied to both the bonding surfaces of the first wafer 11 and the second wafer 12. . When a DC voltage is applied to the bonding surface from a voltage applying means (not shown) in this pressurized state, a space charge layer is formed at the bonding interface, a high electric field is generated, and electrostatic attraction is generated. The wafers 11 and 12 are bonded between the bonding surfaces.

  By applying ultrasonic vibrations in the X-axis direction and the Z-axis direction from the X-axis ultrasonic transducer 2 and the Z-axis ultrasonic transducer 3 to the bonding head 4 in parallel with the application of the DC voltage, the ultrasonic vibration is Since the pressure is transmitted from the bonding head 4 to the first wafer 11 and the second wafer 12 in a pressurized state, ultrasonic vibration is applied to the bonding surface between the first wafer 11 and the second wafer 12. By increasing the stress at the bonding interface, bonding proceeds by ultrasonic vibration even when the load between the bonding surfaces is low.

  In the above bonding method, since the action of ultrasonic bonding is performed in addition to the application of the DC voltage, the pressure applied between the bonding surfaces of the first and second wafers 11 and 12 may be a low load. The load on each of the second wafers 11 and 12 can be kept small, which is suitable for bonding wafers that tend to be thin. Further, even if there is a bias in the pressurization state due to the small pressurization on the large joining surface of the wafer to be enlarged, it can be compensated by ultrasonic joining, so that a uniform joining state can be obtained over the entire joining surface.

  Further, since the bonding is performed in the vacuum chamber 1 having a reduced pressure, bubbles remain at the bonding interface and no gap is formed, and a highly uniform bonding is performed over the entire bonding surface.

  When the area of the joining surface of the object to be joined is large, there is a risk that the action of ultrasonic joining is reduced only by ultrasonic vibration in the X-axis direction (lateral direction), but even in this case, the Z-axis direction ( By jointly using (longitudinal direction) ultrasonic vibration, a uniform joining state can be obtained even for a joining surface having a large area.

  Further, the ultrasonic vibration can be applied not only in the illustrated X-axis direction and Z-axis direction but also in the Y-axis direction orthogonal to them. In addition, when bonding a semiconductor chip having a relatively small bonding area, such as a semiconductor chip, application of ultrasonic vibration in a lateral direction (X-axis direction or Y-axis direction in the illustrated state) causes mechanical damage. Sometimes there are few things. Accordingly, the ultrasonic vibration direction is selected by selecting one ultrasonic vibration in the X-axis direction, Y-axis direction, or Z-axis direction according to the type of the object to be joined, or applying a combination of ultrasonic vibrations in a plurality of directions. Such a setting is preferable.

  In addition, by synchronizing at least two directions of ultrasonic vibrations in each direction of the X axis, Y axis, and Z axis, it is possible to apply three-dimensional ultrasonic vibrations to the bonding surface, so that ultrasonic bonding Can be increased. Moreover, the joining state which adapts to the joining surface material and joining surface size of a joining target object can be obtained by applying, controlling the intensity | strength of the ultrasonic vibration of these each axial directions.

  In addition, it is preferable to apply an ultrasonic vibration of 20 to 70 KHz for bonding a precision component such as a semiconductor wafer or a chip. In addition, it is preferable to apply ultrasonic vibration of 5 μm or less as the vibration amplitude, and application of ultrasonic vibration having a large vibration amplitude may cause displacement. In particular, vibration in the Z-axis direction with respect to the joint surface is amplitude. If the height of the wafer is increased, the bonding surface may be damaged. When a precision component such as a wafer or a chip is bonded, application of ultrasonic vibration having a small vibration amplitude is suitable.

  Further, an impedance detection means for detecting the impedance of the ultrasonic transducers 2 and 3 is provided, and control is performed so that the application of ultrasonic vibration is stopped when the detected impedance increases to 20% or more from the initial application time. Is preferred. Impedance increases as the bonding area by ultrasonic bonding expands, but if vibration energy exceeding the bonding area is applied, damage due to excess energy being applied to the joint and the object to be bonded itself occurs. Since it is easy to detect the impedance, it is preferable to stop the application of the ultrasonic vibration when the impedance is increased to a predetermined amount or more.

  In addition, it is preferable that the pressure applied from the bonding head 4 to the first and second wafers 11 and 12 when applying ultrasonic vibration is gradually increased from the initial application of ultrasonic vibration. If the pressurization is increased as the bonding area increases, an appropriate ultrasonic bonding state can be obtained. When a large load is applied from the beginning of application, it is difficult to obtain the sliding friction necessary for ultrasonic bonding between the bonding surfaces, but when the pressure is gradually increased, sliding friction synchronized with the bonding area can be obtained. .

  Even if the joint surface is polished smoothly, when viewed microscopically, the joint surface has small unevenness and a difference in height of the joint part, and the joint starts from the point contact part, and they are crushed. As the bonding area expands and the bonding area expands as the bonding progresses, gradually increasing the pressure from the initial state where ultrasonic vibration is applied compensates for the expansion of the contact area. And can be joined in a shorter time.

  In addition, heating at the time of application of ultrasonic vibration is effective for an object to be bonded that is difficult to bond at room temperature. By using heating together, diffusion at the bonding interface is promoted and bonding becomes easy. In anodic bonding, heating is performed by a heating means before applying pressure so that the objects to be bonded are at a temperature suitable for bonding, but ultrasonic bonding is also performed by heating to a predetermined temperature even when ultrasonic vibration is applied. It is possible to improve the function.

  In addition, although it demonstrated that it joined in the vacuum chamber 1 in the said structure, it is also possible to join under atmospheric pressure according to the kind of joining target object, the state of a joining surface, etc.

  FIG. 2 shows the configuration of the bonding apparatus according to the second embodiment. Ultrasonic vibrators 2 and 3 are arranged in the vacuum chamber 1 to reduce the size of the entire apparatus.

  In this configuration, the horn 3a that transmits ultrasonic vibration from the Z-axis ultrasonic transducer 3 to the bonding head 4 does not need to penetrate the wall surface of the vacuum chamber 1, so that the configuration of the vacuum chamber 1 is not complicated. The structure that maintains airtightness can be simplified. Further, when a component for applying ultrasonic vibration is disposed in the vacuum chamber 1, a component for applying ultrasonic vibration to the bonding head 4 can also be disposed.

  FIG. 3 shows a configuration of a bonding apparatus according to the third embodiment. A configuration for modifying the bonding surfaces of the first and second wafers 11 and 12 is arranged in the vacuum chamber 1. ing.

  The first surface modification device 9 and the second surface modification device 10 irradiate the bonding surface of an object to be bonded with an atomic beam or an ion beam to clean and activate the bonding surface. The surface modifying device 9 modifies the bonding surface of the first wafer 11 held by the upper holding means 6, and the second surface modifying device 10 is used for the second wafer 12 held by the lower holding means 7. Modify the joint surface.

  In the configuration shown in each of the first and second embodiments, the object to be joined is carried into the vacuum chamber 1 after undergoing modification of the joining surface at a required location outside the vacuum chamber 1. Even if the bonding surface is cleaned in advance, it is exposed to the atmosphere before being carried into the vacuum chamber 1, so even if work is performed in a clean room, organic matter or some foreign matter adheres to the bonding surface even if it is small. There is a fear. In the present embodiment, the wafer to be bonded is an oxide such as silicon. However, when the bonding target is a metal, an oxide film may be generated. The adhesion of organic substances and the generation of an oxide film or the like impair the bonding uniformity over the entire bonding surface when bonded by contact pressure, so that surface modification is performed in the vacuum chamber 1 as in this embodiment. This is effective in improving the bonding quality.

  When surface modification is performed on the bonding surfaces of the objects to be bonded, the first and second wafers 11 and 12 as the objects to be bonded are held by the holding means 6 and 7 on the upper and lower sides, respectively. Since the bonding surfaces of the two surfaces face each other with a small separation distance, it becomes difficult to irradiate the bonding surfaces with an atomic beam or an ion beam for surface modification. Therefore, in this configuration, the stage 5 is configured to be movable up and down as shown, and in the surface modification step performed before the joining step, the stage 5 is moved down to move each of the first and second stages. The bonding surfaces of the wafers 11 and 12 are sufficiently opened.

  Each of the first and second surface modification devices 9 and 10 is disposed at a position where the beam irradiation direction is directed to the bonding surface of the first wafer 11 and the second wafer 12 and the beam can be irradiated evenly on the bonding surface. The By irradiating the first and second wafers 11 and 12 with the atomic beam or the ion beam from the first and second surface modification devices 9 and 10, respectively, foreign substances such as organic substances adhering to the bonding surface are removed. Simultaneously with removal and cleaning, the surface molecules are replaced by collision of ion molecules with the surface layer, and the surface layer is chemically treated by ions to activate the bonding surface.

  When the first and second surface reforming devices 9 and 10 are disposed in the vacuum chamber 1 and the vacuum chamber 1 is enlarged, the first and second surface reforming devices 9 are used. , 10 can be installed outside the vacuum chamber 1 so that their energy irradiation ports are located at predetermined positions in the vacuum chamber 1.

  Further, the same effect can be obtained by applying plasma energy or light energy as the energy used for the surface modification.

  As described above, the surface modification of the joining surface is performed in the vacuum chamber 1, so that the joining by the anodic joining is performed at the same time and the joining by the ultrasonic vibration is used together, so that the joining area of the joining object is large. Even in such a case, it is possible to improve the uniformity of bonding for bonding the first and second wafers 11 and 12 between their bonding surfaces without increasing the load for pressurization.

  FIG. 4 shows the procedure of the bonding method according to the fourth embodiment, and the configuration of the first or second embodiment shown in FIG. 1 or 2 is applied to the bonding apparatus applied to this. . In the figure, S1, S2,... Are step numbers indicating process procedures, and coincide with numbers added in the text.

  The first wafer 11 and the second wafer 12 to be bonded are subjected to a cleaning process at a predetermined cleaning place before being carried into the vacuum chamber 1 (S1). Cleaning is performed in the atmosphere using at least one of ultrasonic water, supercritical water, atmospheric pressure plasma, and light energy. By this cleaning treatment, organic substances and particles adhering to the bonding surface are removed, the surface of the bonding surface is activated, and a bonding strength at a lower temperature can be obtained.

  The first and second wafers 11 and 12 that have been subjected to the cleaning process are carried into the vacuum chamber 1 (S2), set to a predetermined bonding position (S3), and then aligned to accurately position the bonding position. Implemented (S4).

  Next, heating by the heating means is started to heat the first and second wafers 11 and 12 to a temperature suitable for bonding (S5), and the vacuum chamber 1 is evacuated to obtain a predetermined degree of vacuum. The pressure is reduced as follows. Next, the bonding head 4 is lowered by the pressurizing shaft 8 to pressurize the bonding surface of the first wafer 11 and the bonding surface of the second wafer 12 with a predetermined pressure (S6).

  Anodic bonding for applying a predetermined DC voltage from the voltage applying means to the pressurized first and second wafers 11 and 12 is started (S7), and the X-axis ultrasonic transducer 2 and the Z-axis are applied. The ultrasonic vibrator is operated to apply ultrasonic vibration between the bonding surfaces of the first and second wafers 11 and 12 (S8). By applying ultrasonic vibration in combination with the application of the DC voltage, uniform bonding is performed over the entire bonding surface (S9). In addition, since the bonding surfaces of the first and second wafers 11 and 12 are cleaned and activated in advance by a cleaning process, anodic bonding can be smoothly performed without increasing the pressure. At the same time, a uniform bonded state can be obtained by applying ultrasonic vibration.

In the embodiment described above, an example in which a wafer that is Si or SiO ₂ is applied as an object to be bonded has been described. The same applies to bonding.

  As described above, according to the present invention, in joining between joining surfaces of a plurality of joining objects, a state where joining non-uniformity is likely to occur when the joining surface area is increased is due to application of ultrasonic vibration. Since it can be compensated by the action of ultrasonic bonding, a stable bonding state can be obtained without being affected by the time of application of DC voltage or heating in anodic bonding. A bonding method that is particularly effective when a wafer to be enlarged is used as an object to be bonded, and can be bonded uniformly over the entire bonding surface when bonding large-area wafers to each other. And an apparatus thereof.

Sectional drawing which shows the principal part structure of the joining apparatus which concerns on 1st Embodiment. Sectional drawing which shows the principal part structure of the joining apparatus which concerns on 2nd Embodiment. Sectional drawing which shows the principal part structure of the joining apparatus which concerns on 3rd Embodiment. The flowchart which shows the process sequence of the joining method which concerns on 4th Embodiment. Sectional drawing which shows the outline of the joining apparatus which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 X-axis ultrasonic transducer 3 Z-axis ultrasonic transducer 4 Joining head 5 Stage 8 Pressurizing shaft 11 First wafer (joining object)
12 Second wafer (joining object)

Claims (12)

In a bonding method in which a plurality of objects to be bonded are pressurized so as to be in surface contact with each other's bonding surfaces, and a plurality of objects to be bonded are bonded between bonding surfaces.
A bonding method comprising applying ultrasonic vibration to a bonding surface.   Two orthogonal axes on the joint surface are the X-axis and Y-axis, respectively, and an axis perpendicular to the joint surface is the Z-axis, and ultrasonic vibration in at least one axial direction of each of the X-axis, Y-axis, and Z-axis directions is performed. The joining method according to claim 1 to be applied.   The bonding method according to claim 1 or 2, wherein at least two directions of ultrasonic vibration in each direction of the X axis, Y axis, and Z axis are synchronized and applied while controlling the intensity of the ultrasonic vibration.   The joining method according to claim 1, wherein ultrasonic vibration having a vibration frequency of 20 to 70 KHz is applied.   The bonding method according to claim 1, wherein ultrasonic vibration having a vibration amplitude of 5 μm or less is applied.   The joining method according to any one of claims 1 to 5, wherein the impedance of the ultrasonic vibrator is detected, and the application of the ultrasonic vibration is stopped when the impedance increases to 20% or more from the initial application time.   The joining method according to any one of claims 1 to 6, wherein the pressure is gradually increased when applying the ultrasonic vibration.   The joining method according to claim 1, wherein the joining object is heated to join the joining object.   The joining method according to claim 1, wherein the objects to be joined are joined in a vacuum atmosphere. In a bonding apparatus that pressurizes a plurality of objects to be bonded in surface contact with each other in a bonding surface, and bonds the plurality of objects to be bonded between bonding surfaces,
2. A bonding apparatus comprising ultrasonic vibration applying means for applying ultrasonic vibration to a plurality of objects to be bonded that are in surface contact between the bonding surfaces.   The bonding apparatus according to claim 10, wherein a vibrator constituting the ultrasonic vibration applying means is disposed in a vacuum chamber.   The joining apparatus according to claim 10 or 11, wherein an irradiation port for at least reforming energy of a surface modifying means for modifying the joining surface is provided in the vacuum chamber.

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