Patent Description:
In the field of electronic components, for example, solid materials are bonded together during wafer bonding wherein silicon substrates, substrates having an oxide layer or nitride layer formed on a silicon or other substrate, or substrates of glass material are bonded together, during bonding of metal materials between electronic components in flip-chip processes, and during package sealing when preparing MEMS (Micro Electro Mechanical Systems).

When bonding substrates, it is common to raise the strength of the bonding interface by heating to a high temperature after contact to promote chemical reactions between the bonding substrates and atomic diffusion in the vicinity of the bonding interface (bonding with heat treatment).

For example, in a method for bonding silicon wafers, the surfaces of silicon wafers may be hydrophilized, the pair of wafers joined by a van der Waals force, then subjected to a heat treatment at about <NUM> to obtain a firm bond. Additionally, in anodic bonding, silicon and heat-resistant glass can be firmly bonded by applying a high voltage of <NUM> kV at <NUM>.

However, bonding methods involving heat treatments are limited by the types of substrates to which they can be applied. In particular, when bonding together substrates of different materials, the differences in the coefficients of thermal expansion between the materials may result in increased residual thermal stresses and cause mechanical damage to the bonded materials as the temperature falls to room temperature (standard temperature), and as the residual stress becomes higher, the bonded materials may be destroyed. Additionally, bonding methods involving heat treatments are difficult to apply to bonding of components having elements with low heat resistance and voltage resistance, such as MEMS.

Standard-temperature bonding methods have been proposed for performing substrate bonding at room temperature, in order to overcome the detrimental influence that bonding methods involving heat treatments have on substrate materials. In this type of room temperature bonding method, the substrate surface is treated to a surface treatment such as cleaning or activation by irradiating the substrate with a particle beam, and the surface-treated substrate surfaces are brought into contact in a vacuum at room temperature for bonding.

Such room temperature bonding methods extend the types of substrate materials that can be applied compared to bonding methods involving heat treatments, and have met with a degree of success. However, such room temperature bonding methods have constraints on their bonding environment conditions, such as needing to keep the atmosphere at a high vacuum after surface activation and transition to the bonding process within an extremely short period of time in order to minimize reoxidation of the substrate surface which has been surface-activated. Additionally, since the bonding mechanism must be provided as a portion of the processing vacuum system, the bonding mechanism tends to be complicated and expensive.

<CIT> relates to a method for bonding of substrates having a steps of irradiating surfaces of the substrates respectively in a vacuum with both an inert gas beam and a metal beam thereby forming island shaped thin metal films on the surfaces of the substrates, and surface-activated bonding of the substrates through the island shaped thin metal films by contacting the surfaces of the substrates each other.

<CIT> relates to a method of room-temperature bonding a plurality of substrates via an intermediate member, including forming the intermediate member on a surface to be bonded of the substrate by physically sputtering a plurality of targets and activating the surface to be bonded by an ion beam.

The present invention is an attempt to respond to the need for an improved substrate bonding technology by relaxing the required bonding environment conditions.

Specifically, the present invention has the purpose of offering a method of fabricating a bonding substrate capable of forming a bonding surface that ensures sufficient bonding strength even if the atmosphere at the time of bonding is not a high vacuum.

Furthermore, the present invention has the purpose of offering a bonding substrate fabricated with a bonding surface having a sufficient bonding strength capability even if the atmosphere at the time of bonding is not a high vacuum. Similarly, it has the purpose of offering a substrate assembly obtained by bonding such bonding substrates.

Furthermore, the present invention has the purpose of producing a bonding substrate having a bonding surface with a sufficient potential bonding strength, and offering an apparatus wherein bonding mechanisms and process chambers for surface treatment can be separately and flexibly arranged.

One aspect of the present invention offers a bonding substrate fabrication method for fabricating a substrate ("bonding substrate") on which a bonding surface is formed, the bonding substrate fabrication method comprising:.

The method is characterised in that implementation of the first surface treatment step is performed before the second surface treatment step so that the metal particles are distributed in a base material of a surface layer of the bonding substrate with higher concentration than in the remaining of the bonding substrate.

Additionally, another aspect of the present invention offers a bonding substrate fabrication apparatus for fabricating a substrate, bonding substrate, on which a bonding surface is formed, the bonding substrate fabrication apparatus comprising:an energetic particle source for surface-treating a surface of a substrate by irradiation with radiated particles including energetic particles; and a metal particle source for surface-treating the substrate surface by irradiation with radiated particles including metal particles;a process condition memory for storing process conditions satisfying targeted properties, target properties, of a targeted bonding substrate; and a control device for referring to the memory and controlling the energetic particle source and the metal particle source based on process conditions satisfying the target properties; and an orientation control device for controlling an orientation of the energetic particle source; wherein the orientation control device is configured to, in an energy-based surface treatment mode, arrange the energetic particle source in a first orientation to direct radiated particles from the energetic particle source to the substrate surface; in a metal-based surface treatment mode, arrange the energetic particle source in a second orientation to direct radiated particles from the energetic particle source to the metal particle source; wherein the metal particle source, in the metal-based surface treatment, is arranged in an orientation for radiating metal particles toward the substrate surface in response to radiated particles from the energetic particle source. The bonding substrate fabrication apparatus is characterised in that it is configured to perform irradiation with radiated particles including energetic particles before irradiation with radiated particles including metal particles so that the metal particles are distributed in a base material of a surface layer of the bonding substrate with higher concentration than in the remaining of the bonding substrate.

First, the basic terminology used in the present specification will be explained. The term "substrate" is synonymous with "solid-state material", and a substrate may be of any shape. In the preferred embodiments explained below, the substrate may take the form of a wafer. However, this is no more than an example, and is not limiting. An "energetic particle" may be an inert gas ion and/or a neutral atom. A "metal particle" may be a metal ion, a neutral metal atom and/or a cluster. An energetic particle source is a device that radiates energetic particles. The term "radiate" is synonymous with "emit". An "energetic radiated particle" or a "radiated energetic particle" is a particle radiated or emitted from an energetic particle source. For example, in a typical energetic particle source, the particles present in a plasma space (plasma particles) are accelerated by an electric field to capture energy, forming energetic particles that are then emitted (radiated) outside the plasma space. A "metal particle source" is a device for radiating or emitting metal particles. For example, a metal body will react with energetic particle radiation and radiate or emit metal particles. In that case, the combination of a metal body and an energetic particle source that radiates energetic particles onto the metal body constitutes a metal particle source. This type of metal particle source is known as a sputtering-type metal particle source.

Herebelow, the present invention will be explained in detail by referring to preferred embodiments. However, these specific embodiments are merely exemplary, and are not intended to limit the present invention. The principles of the present invention, the above-described and other purposes, characteristics and advantages will become more apparent from the detailed description provided below with reference to the drawings.

<FIG> shows the outward appearance of a substrate bonding system G00. Such a system G00 typically includes a load-lock apparatus G02, a bonding substrate fabrication apparatus G01, and a substrate bonding apparatus G03. The outward appearance itself and the specifics of the outward appearance of the system G00 do not constitute a part of the present invention.

The load-lock apparatus G02 is an entry port for substrates and an exit port for bonding substrates or substrate assemblies. The bonding substrate fabrication apparatus G01 performs a process (bonding substrate fabrication method) for forming a bonding surface on a loaded substrate to fabricate a bonding substrate. In general, such a process requires a high-vacuum environment. For this reason, the bonding substrate fabrication apparatus G01 performs the processes with the inside of the process chamber H02 in a high-vacuum state (e.g., gas pressure <NUM>-<NUM> Pa). Normally, before introducing substrates into the process chamber H02, the inside of the load-lock apparatus G02 into which a substrate has been loaded is subjected to a depressurization operation to lower the pressure from atmospheric pressure to a predetermined vacuum.

The substrate bonding apparatus G03 is for fabricating a substrate assembly by bonding together bonding substrates. In a typical substrate bonding system G00 (<FIG>), the substrate bonding apparatus G03 is coupled to a bonding substrate fabrication apparatus G01 so that their atmospheres are in communication, and is capable of receiving a supply of bonding substrates from the bonding substrate fabrication apparatus G01 and transferring the fabricated substrate assemblies through the bonding substrate fabrication apparatus G01 to the load-lock apparatus G02 which is the exit port. Normally, in a substrate bonding system G00, the exchange of substrates, bonding substrates, substrate assemblies and the like between processing devices are performed by a robot.

According to the conventional art, a substrate bonding apparatus G03 requires an atmosphere in a vacuum state, and bonding (adhesion) of bonding substrates is performed in a vacuum. As described below, according to one aspect of the present invention, the substrate bonding apparatus G03 does not require a vacuum atmosphere. In a preferred embodiment of the present invention, a bonding substrate fabricated by a bonding substrate fabrication apparatus G01 does not require bonding in a vacuum atmosphere. Therefore, in an embodiment of the present invention, the substrate bonding apparatus G03 may be an independent apparatus separate from the bonding substrate fabrication apparatus G01.

As described above, the bonding substrate fabrication apparatus G01 fabricates bonding substrates by forming bonding surfaces on the received substrates. Herebelow, some embodiments shall be explained regarding the bonding substrate fabrication method performed by the bonding substrate fabrication apparatus G01, and associated portions of the bonding substrate fabrication apparatus involved in performance of the method.

<FIG> is a flow chart showing several processes (bonding substrate fabrication methods) for forming a silicon thin film-implanted bonding surface on a substrate based on different embodiments of the present invention. These processes are performed by the bonding substrate fabrication apparatus G01. In a first step, a starting substrate is obtained (F01), then preprocessing (F02) is performed to result in a substrate on which a bonding surface is to be formed.

In a specific example, commercially available silicon substrates for industrial use with a diameter of <NUM> were used as the starting substrate. Additionally, during pre-processing, an oxide film was formed on the surface of the silicon substrate by subjecting the silicon substrate to conventional thermal oxidation.

Returning to the flow diagram of <FIG>, after the pre-processing F02, a bonding substrate fabrication process for forming a silicon thin film-implanted bonding surface on the substrate is performed according to different embodiments of the present invention. As selectable processes, <FIG> shows five processes A to E.

Process A is a process (bonding substrate fabrication method) wherein the substrate surface is subjected to only a surface treatment ("irradiation" step F03). Unlike the other processes B-E, a silicon thin film is not formed (F04) on the bonding surface. The substrate fabricated by this process will be referred to as the bonding substrate A. Therefore, process A is a comparative reference process, and substrate A is a comparative reference substrate.

Process E is a process in which surface treatment (F03) of the substrate surface is followed by formation of a silicon thin film on the surface-treated substrate surface (F04), then by surface treatment of the formed silicon thin film surface (F05). The substrate fabricated by this process will be referred to as substrate E. In a specific example, as shown in <FIG>, the bonding substrate E (L00) is such that the surface of the silicon oxide film L01 is surface-treated (L02), a silicon thin film (L03) is formed on the surface, and the silicon thin film is surface-treated (L04).

Process C is the same as process E up to the surface treatment F03 of the substrate surface and the silicon thin film formation F04, but the final silicon thin film surface treatment F05 is not performed. The result will be referred to as the bonding substrate C. In the specific example, bonding substrate C is a substrate having a silicon oxide film surface that is surface-treated, and a silicon thin film formed on the surface thereof.

Process D is a process wherein the substrate surface is not subjected to a surface treatment F03, a silicon thin film is formed directly thereon (F04), and the formed silicon thin film surface is surface-treated (F05). The substrate fabricated in this way will be referred to as bonding substrate D. In a specific example, bonding substrate D is a substrate wherein the silicon oxide film surface is not surface-treated, a silicon thin film is formed, and further subjected to a surface treatment.

Process B is a process wherein a silicon thin film is formed (F04) directly on the substrate surface. The substrate obtained in this way will be referred to as bonding substrate B.

As shown in <FIG> to be described below, the bonding strengths of bonding substrates B to E according to the embodiments exhibited unexpected differences with respect to the comparative reference substrate A.

In the following explanation, the surface treatment F03 of the substrate surface may be referred to as "step <NUM>", the silicon thin film formation process F04 may be referred to as "step <NUM>", and the surface treatment F05 of the silicon thin film surface may be referred to as "step <NUM>".

<FIG> schematically shows the relevant portions of a bonding substrate fabrication apparatus G01, along with a process chamber H02, suitable for performing steps <NUM> and <NUM>, and step <NUM> (surface treatment, and silicon thin film formation process) of <FIG>. Basically, in order to perform a surface treatment, a particle source for irradiating the substrate with energetic particles is needed (see H03). Additionally, the silicon thin film may be formed with a silicon source by CVD using a CVD apparatus or PVD using a PVD apparatus, but <FIG> shows a sputtered silicon source (see H10).

As shown in <FIG>, the process chamber H02 is set to a pressure of <NUM>-<NUM> Pa as a vacuum before processing is started. Inside the process chamber H02, the substrate H06 is supported on the substrate supporting portion H08. Furthermore, an energetic particle source H03 is provided so as to be capable of irradiating the substrate H6 with radiated particles H05 including energetic particles or metal particles. The energetic particle source H03 has an axis of rotation H04 in a direction perpendicular to the drawing, and the orientation of the energetic particle source H03 may be controlled about the axis of rotation H04. This constitutes a simple orientation control apparatus. If desired, the orientation control apparatus may control the orientation of the energetic particle source H03 about multiple axes.

Therefore, in <FIG>, the bonding substrate fabrication apparatus includes an energetic particle source H03 for emitting radiated particles including energetic particles, a silicon source H10, and an orientation control apparatus H04 for controlling the orientation of the energetic particle source H03. The orientation control apparatus H04, in a surface treatment mode according to steps <NUM> and <NUM>, puts the energetic particle source H03 in a first orientation to direct the radiated particles from the energetic radiation source H03 toward the substrate H06 surface, and in a silicon thin film formation mode for forming a silicon thin film on the substrate surface according to step <NUM>, orients the energetic particle source in a second orientation to direct radiated particles from the energetic particle source H03 toward the silicon source H10. In the silicon thin film formation mode, the silicon source H10 responds to the radiated particles from the energetic particle source H03, and is oriented to radiate silicon particles toward the surface of the substrate H06.

Additionally, the substrate supporting portion H08 should preferably support a plurality of substrates in addition to the substrate H06. For example, in <FIG>, a substrate H07 is further supported.

More preferably, the substrate supporting portion H08 includes a mechanism H09 that moves in the lateral direction in <FIG>, and by translation of the substrate supporting portion H08 with respect to the energetic particle source H03 by the movement mechanism H09, the substrates H06 and H07 are able to be sequentially irradiated by the radiated particles.

Having a movement mechanism H09 provides various advantages in the process.

For example, due to the movement mechanism H09, the substrate H06 can be moved outside the range of irradiation of the radiated particles H05 at the time of ignition of the energetic particle source H03. Irradiation of the substrate H06 under unfavorable conditions such as instability immediately following ignition of the energetic particle source H03 can be avoided.

Additionally, for example, after processing of the substrate H06, the movement mechanism H09 may consecutively or continuously subject another substrate H07 held by the substrate supporting portion H08 to irradiation by the radiated particles H05. As a result, the speed and efficiency of the overall process may be improved.

Furthermore, for example, a linear particle source that is long in the position direction (linear ion source) may be used as shown in <FIG>, and by arranging it in the direction perpendicular to the paper surface in <FIG>, a substrate of large dimensions may be efficiently processed.

The energetic particle source H03 can emit radiated particles including energetic particles. These energetic particles may be inert particles, preferably including argon.

The energetic particle source H03 may further emit radiated particles including metal particles. These metal particles are preferably transition metals, more preferably iron.

A particle source H03 (energetic particle source and metal particle source) emitting both energetic particles and metal particles may have various structures.

In one structural example, this type of particle source H03 which emits both energetic particles and metal particles generates a plasma of inert particles (argon), and by applying an electric field E to this plasma, the plasma inert particles are accelerated in the direction of the electric field, causing radiation of energetic particles including inert particles. Inside the particle source H03, an exposable metal body including a desired metal is arranged in the area where the plasma of the inert particles (argon) is generated, so that the energetic particles from the plasma also cause radiation of metal particles from the metal body, which form a portion of the radiated particles. The particle source of this structure functions mainly as the particle source for radiating energetic particles when the metal body is in a retracted position by selection of an active mode, and functions as a particle source for radiating metal particles together with energetic particles when the metal body is in an exposed position (positioned in the plasma space).

In this type of particle source H03, the proportion of metal particles contained in all radiated particles or the quantity relative to the energetic particles (here, inert particles) may be enhanced or controlled by various methods.

In one structural example, a conical metal body is further provided at the exit of the particle source H03, and the energetic particles (here, inert particles in a plasma state) sputter the metal body, thereby increasing the quantity of metal particles radiated from the particle source.

In another structural example, a grid-shaped metal body is further provided at the exit of the particle source H03, so that the energetic particles (here, inert particles in a plasma state) sputter the metal grid, thereby increasing the quantity of metal particles emitted.

The proportion of metal particles contained in all the radiated particles or the amount relative to the energetic particles (e.g., inert energetic particles) are not limited to those for the above structural examples. For example, the metal body for generating the metal particles may be provided at any position, even a position distanced from the particle source, as long as the position is between the particle source and the substrate which is the irradiation target, and exposed to irradiation by particles including energetic particles. Additionally, the shape of the metal body may be any shape capable of achieving the same objective.

Next, an embodiment of a method and apparatus for sputter deposition of a silicon thin film according to the present invention will described with reference to <FIG>.

<FIG> shows a structure having a silicon source H10 further inside the process chamber H02 shown in <FIG>. Here, the silicon source H10 is positioned so as to be capable of radiating silicon H11 in the direction of the substrate H06 on which the silicon is to be deposited, and is further arranged to be capable of receiving radiated particles H05 from the particle ion beam H03 for radiating silicon. Here, the particle ion beam H03 rotates about the axis of rotation H04 from the position shown in <FIG>, and is radiated in the direction of the silicon source H10.

In the embodiments shown in <FIG>, the energetic particle source H03 and silicon source H10 are arranged with respect to the substrate H06 inside the process chamber H02, enabling a single energetic particle source H03 to be used to irradiate the substrate H06 with radiated particles and perform sputter deposition of a silicon thin film onto the substrate H06. By doing so, the arrangement of components inside the process chamber H02 can be simplified.

As described above, the substrate bonding apparatus G03 is for bonding together bonding substrates. The substrate bonding mechanism G03 is not limited, but a mechanism functioning, for example, as shown in <FIG> is preferred. In other words, the substrate supporting portion H08 has a supporting portion H08a and a supporting portion H08b for respectively supporting the substrate H06 and the substrate H07. The supporting portion H08a and the supporting portion H08b respectively pivot about an axis of rotation H12 that is perpendicular to the paper surface of <FIG>, enabling the bonding surfaces of the substrate H06 and the substrate H07 to come into planar contact. Because the bonding fabrication apparatus G00 has this mechanism, the substrates can be bonded together in a desired time and conditions inside the process chamber H02 or other vacuum chamber (not shown) without being removed from the bonding surface fabrication apparatus G00.

In a specific example, after fabricating bonding substrates with the bonding substrate fabrication apparatus G01 based on processes A to E in <FIG>, pairs of substrates A to E obtained by the same process can be bonded in the substrate bonding apparatus G03 as shown in <FIG> using the mechanism shown in <FIG>. The pairs of bonded substrates will be referred to hereafter as substrate assemblies A to E.

The structure of substrate assembly E is shown in <FIG>. In specific examples, for substrate E, the surface of the silicon oxide film L01 is irradiated (L02) in step <NUM>, a silicon thin film (L03) is formed on the surface thereof, and the silicon thin film is irradiated (L04) according to step <NUM>. By bonding together a pair of substrates E processed in the same way, the surfaces L04 are bonded together, forming the substrate assembly E (L10).

After the bonding process, the substrate assemblies A to E were removed from the substrate bonding system G00 into air, and the bonding energies of the substrate assemblies were measured by a blade insertion method. The average values over a plurality of measurements of substrate assemblies A to E are shown in <FIG>.

The measurement results for bonding strength will be explained with reference to <FIG>. First, the substrate assembly A obtained by bonding together substrates on which a silicon film was not formed and wherein the silicon oxide film was irradiated by step <NUM> exhibited the lowest bonding strength ( <NUM> J/m<NUM> or less). Next, substrate assembly B obtained by bonding together substrates on which a silicon film was formed without performing step <NUM> at all exhibited a bonding strength (<NUM> J/m<NUM>) which is higher than substrate assembly A. This is a bonding strength of about <NUM>% of the breaking strength (<NUM> J/m<NUM>) of bulk silicon. Next, the substrate assembly D obtained by bonding together substrates on which a silicon film was formed without performing step <NUM>, then followed by step <NUM>, exhibited a bonding strength (<NUM> J/m<NUM>) which is higher than the bonding strength of the substrate assembly B. This is a bonding strength which is about <NUM>% the breaking strength (<NUM> J/m<NUM>) of bulk silicon. Next, the substrate assembly C obtained by bonding together substrates on which a silicon film was formed after performing step <NUM>, then not followed by step <NUM>, exhibited a bonding strength (<NUM> J/m<NUM>) which is even higher than that of substrate assembly D. This is a bonding strength which is about <NUM>% of the breaking strength (<NUM> J/m<NUM>) of bulk silicon. Finally, the substrate assembly E obtained by bonding together substrates on which a silicon film was formed after performing step <NUM>, then followed again by step <NUM>, exhibited the highest bonding strength (<NUM> J/m<NUM>). This is a bonding strength that is about <NUM>% of the breaking strength (<NUM> J/m<NUM>) of bulk silicon.

The results for bonding strength shown in <FIG> show that substrates on which a silicon film is formed clearly exhibit higher bonding strength than substrates on which a silicon film is not formed, and that the bonding strength becomes greater the more step <NUM> is performed before and after formation of the silicon film.

In the above examples, pairs of substrates subjected to the same processes were bonded together to compare the bonding strengths of the substrate assemblies depending on the processing methods, but similar effects are clearly achieved even when processing only one substrate.

In the above examples, silicon oxide was used as the substrate (surface layer portion), but there is clearly no need for such a limitation. Additionally, by forming the silicon thin films inside the bonding surface layers, the broadness of the range of application wherein there are fundamentally no limitations on the materials of the substrates themselves can be observed. As a result, the present invention may be applied to the material of any substrate as long as irradiation of the substrate surface by energetic particles and generation of a silicon thin film is possible.

Additionally, in the above examples, radiated particles including energetic particles and metal particles were used as the particle source H03. However, it is clear from the results of room temperature bonding methods performed until now that similar results can be obtained even when metal particles are not included, or when metal particles are intentionally left out of the energetic particles by installing a grid or horn-shaped metal body.

While visible light cannot pass through a silicon substrate, infrared light can. Therefore, the state of bonding can be analyzed by using a technique of observation of transmission of infrared rays. The portions where the substrates are not closely bonded form spaces, or so-called voids, where the optical path lengths of infrared rays differ from those where the substrates are closely bonded. When viewing an image of infrared rays transmitted through the substrates, the places where the substrates are and are not closely bonded appear as differences in darkness and lightness of the transmitted light.

The formation of voids suggests that undesirable particles adhering to the bonding surface are present in the bonding interface, forming gaps between the substrates, or that the bonding strength is weak.

<FIG> shows an infrared ray transmission image of substrate assembly A (M11), and <FIG> shows an infrared ray transmission image of substrate assembly E (M21). In <FIG>, voids can be observed to have formed in the areas denoted by M12. On the other hand, in <FIG>, the formation of voids such as those indicated by M12 in <FIG> was not observed.

Substrate E involves many steps compared to substrate A, and therefore can be expected to have a higher probability of adherence of undesirable particles to the bonding surface before bonding. The fact that voids nevertheless did not form on the substrate assembly E suggests that the bonding strength of the substrate assembly E is much higher than that of substrate assembly A, which agrees with the results of bonding strength shown in <FIG>.

<FIG> shows the microscopic structure in the vicinity of the bonding interface of substrate assembly E as viewed by transmission electron microscopy. In this specific example, the substrate was obtained by forming a surface of a silicon oxide film L01 on a silicon substrate (L10) as a starter material, irradiating by step <NUM> (L02), forming a silicon thin film on the surface (L03), then irradiating the silicon thin film by step <NUM> (L04). By bonding together a pair of similarly processed substrates E, the surfaces L04 bond together to form a substrate assembly E (L10).

Furthermore, the iron concentration in the vicinity of the bonding interface of the substrate assembly E was measured using a technique called EELS in transmission electron microscopy. EELS scanning enables the concentration of atoms to be measured for extremely small areas of atomic size. <FIG> shows the concentration profile of iron in a direction perpendicular to the bonding interface (K31), measured by line-scanning the bonding interface L04 in a perpendicular direction.

In this specific example, with an EELS line scan in a direction perpendicular to the bonding interface L04, iron was found to be present at positions L02 and L04 which were irradiated with energetic particles in step <NUM>, but was not measured in any other areas. Furthermore, the concentration of iron at the bonding interface L04 was higher than at the area L02 irradiated by energetic particles before deposition of the silicon thin film L03. This is believed to correspond to the fact that twice as much iron is contained by joining surfaces irradiated with energetic particles under the same conditions in step <NUM>.

In the above example, the iron concentration distribution in the direction perpendicular to the bonding interface is shown in the vicinity of the bonding interface of a substrate assembly E obtained by bonding together a pair of substrates E subjected to similar processes, but a similar iron distribution can clearly be obtained even when just one substrate is processed as shown in <FIG>.

<FIG> will be explained. In this case, the surface of one substrate L01 is irradiated by step <NUM> (L02), a silicon thin film (L03) is formed on the surface thereof, the silicon thin film is irradiated by step <NUM> (L04), then the substrate is bonded with another substrate L41. However, aside from when the substrate L01 and L41 can be distinguished, it is difficult to determine whether the bonding interface is in L02 or in L04 by observation of the interface structure alone, and it does not matter whether step <NUM> and step <NUM> are performed on substrate L01 or substrate L41.

Additionally, in the relevant portions of L02 and L04, the metals included in other energetic particles are present at a higher concentration than other portions.

These metals are preferably transition metals, more preferably iron.

Regarding the activation conditions for the particle source, in a specific example, step <NUM> is performed with an acceleration voltage of <NUM> to <NUM> kV and a current of <NUM> to <NUM> mA, and step <NUM> is performed with an acceleration voltage of <NUM> to <NUM> kV and a current of <NUM> to <NUM> mA.

Hereinabove, a method and apparatus for fabricating a bonding substrate of a type having a "silicon thin film layer" formed inside the bonded layer (see <FIG>), a bonding substrate which is the product thereof (<FIG>), and a substrate assembly (<FIG>) have been explained. As shown in <FIG>, the bonding substrate was found to have a higher bonding capacity compared to other cases when forming a silicon thin film in the bonded layer as shown in <FIG>. Additionally, the present method and apparatus have no limitations on the materials of the substrate to which they can be applied, and they are very highly effective.

Herebelow, the approach of forming a "silicon thin film layer" in the bonded layer is set aside, and sufficient bonding strength is achieved by making improvements to the surface treatments of the substrate (see <FIG>, layers L02 and L04).

Herebelow, the surface treatment will be explained in detail with reference to embodiments.

These embodiments offer a bonding substrate fabrication method for fabricating substrates on which a bonding surface has been formed ("bonding substrates"). This method according to the claimed invention, includes a first surface treatment step of surface-treating the surface of a substrate by irradiation with radiated particles including energetic particles, and a second surface treatment step of surface-treating the substrate surface by irradiation with radiated particles including metal particles. As a result of performing these steps, the aforementioned bonding substrates are produced, and the performance of the steps is controlled so that the metal particles are distributed within the base material of the surface layer of the bonding substrate. In a comparative example outside the scope of the appended claims but useful for understanding the invention, the first surface treatment step and the second surface treatment step may be performed simultaneously. This was already explained in connection with the energetic particle source and metal particle source H03 shown in <FIG>. Instead of simultaneous processes, the claimed invention requires that a sequential process is used wherein the substrate surface is subjected to energetic particle radiation, after which the substrate surface is subjected to metal particle radiation. Depending on the application, an energetic particle source and metal particle source H03 may be used, or the action of an energetic particle source may be followed by the action of a metal particle source.

As a bonding substrate fabrication apparatus G01 for forming a bonding surface of a substrate, <FIG> shows a bonding substrate fabrication apparatus comprising an energetic particle source FG20 for surface-treating a surface of a substrate by irradiation with radiated particles including energetic particles, a metal particle source FG30 for surface-treating the surface of the substrate by irradiation with radiated particles including metal particles, a processing condition memory SS01 for storing processing conditions satisfying the targeted properties of the bonding substrate ("target properties"), and a control device SS02 for referring to the memory SS01 and controlling the energetic particle source FG20 and the metal particle source FG30 based on the processing conditions satisfying the target properties.

The above-mentioned target properties include a distribution of metal particles inside the base material of the surface layer of the bonding substrate, and the actions of the energetic particle source FG20 and the metal particle source FG30 may be controlled based on the processing conditions satisfying the target properties under the control of the control device SS02.

The target properties may include, according to an example outside the scope of the invention as claimed, (A) absence of a metal layer on the surface layer of the bonding substrate or, according to the claimed invention, (B) distribution of the metal particles inside the base material of the surface layer of the bonding substrate, and the actions of the energetic particle source FG20 and the metal particle source FG30 may be controlled based on the processing conditions satisfying the above-mentioned target properties under the control of the control device SS02.

In one example, the above-mentioned processing conditions may include energy conditions to be acquired by the energetic particles from the energetic particle source FG20. The energy conditions may be <NUM> eV or more.

In another example, the above-mentioned target properties include "the bonding substrate having a certain bonding strength capability", and the actions of the energetic particle source FG20 and the metal particle source FG30 may be controlled based on processing conditions satisfying the above-mentioned target properties under the control of the control device SS02. For example, lookup tables T01, T02 such as those shown in <FIG> may be stored in the processing condition memory SS01, capable of displaying bonding strengths (expressed, for example, as substrate breaking strength ratios).

As an alternative, as shown in <FIG>, the control portion S01 illustrated in the form of a PC may contain therein a memory storing processing requirements relating to the energy requirements, and a power supply S02 may be provided with voltage instructions corresponding to required acceleration energies via the data bus S03. Upon receipt thereof, the energetic particle source H03 is activated at voltages corresponding to the required acceleration energies from the power supply S02 through the power supply line S04.

The surface treatment based on one embodiment is a process of irradiating the substrate surface with energetic radiated particles. Generally, the surface of the solid material originally on the substrate has a certain amount of oxides and compounds other than oxides formed or adsorbed thereto. The oxides are often formed by the substrate material reacting with oxygen in the air or with water in a wet process. In the case of silicon, they are mostly SiO<NUM>. Aside from oxides, microparticles from the air may be adsorbed, or chemical substances from various processes may adsorb to the surface or react with and form on the substrate material. There are many forms and types, but they will be referred to simply as "impurities" in the present specification.

The purpose of "surface treatment" is first to remove the above-mentioned oxides and impurities by collisions of radiated particles including energetic particles, and exposing the clean surface of the substrate material itself. The surface of the substrate material itself has dangling bonds and is in a high-energy, unstable state. By avoiding oxidation and adsorption of impurities and bringing into contact another energetically unstable clean surface, the dangling bonds can be bound together and become energetically stable, resulting in a strong bond.

The second purpose of "surface treatment" is to disrupt the crystallinity of the substrate material by further irradiating the clean surface with radiated particles including energetic particles, thereby accelerating the formation of dangling bonds and further raising the surface energy. Therefore, by joining these surfaces together, an even stronger bond can be obtained.

In the below-given examples, an inert gas, especially argon, was used for the radiated particles including energetic particles used for the "surface treatment", but the invention is not limited thereto. For example, other inert gases may be used, and aside from inert gases, any particles, such as nitrogen molecules and oxygen molecules, capable of transmitting to the substrate material kinetic energy obtained by being accelerated by the particle source, may be used. Additionally, instead of having kinetic energy, they may be chemically reactive with the substrate material.

Furthermore, the particle used for the particle radiation in the "surface treatment" may include multiple types of particles. For example, as described above or below, metal particles may be included. In that case, the metal particles that have reached the surface of the substrate material can be considered to undergo some kind of chemical reaction at the time of bonding, as a result of which the bonding strength is increased.

The "surface treatment" may be performed on both or on just one of the pair of substrate surfaces to be bonded.

The surface treatment method of the present embodiment was confirmed by measurements to contain metal particles in the surface-treated substrate surface layer (bonding surface layer). While the specifics of the phenomena actually occurring in the substrate surface layer during surface treatment are unclear, judging from the measurement results, it appears that irradiation by the energetic particles and metal particles removes oxides and impurities present on the substrate surface, the energy from the particles amorphizes the substrate surface layer, and the metal particles are bonded to the base material of the amorphized layer. The descriptions of these phenomena are merely hypothesized from the measurements as an attempt at a simple explanation. Phenomena per se, theories on phenomena per se and physical/chemical analysis per se cannot be protected by patents, and therefore do not constitute a portion of the present invention, nor are they intended to be used to interpret the scope of the present invention. The scope of the present invention, as defined by law, should be determined based on the claims.

A specific example of a surface treatment method based on the present embodiment wherein silicon is used as the substrate material, argon is used for the energetic particles and iron atoms are used as the metal will be described with reference to <FIG>. In other words, in the substrate FG01, the silicon atoms FF11 are arranged in a diamond crystal structure. As a result of a surface treatment method under the present embodiment, the silicon substrate surface layer FG04 can be considered to lose its diamond crystal structure and the silicon atoms FF21 to form an amorphous layer FG04. The iron atoms FF22 can be considered to be present mainly in this amorphous layer FG04.

<FIG> shows the results of compositional analysis in the depth direction of a silicon substrate after irradiation by energetic particles and iron particles by RF glow discharge spectroscopy. These results show that there is an iron concentration peak in the surface layer and the peak concentration is <NUM> atomic% (hereinafter referred to as "at%").

Aside from the amorphous layer FG04, the iron atoms may, for example, be present on the substrate FG01. This is because the diffusion coefficients of transition metals in semiconductor materials are generally high, and for example, the diffusion coefficient of iron in silicon is extremely high (<NPL>). Therefore, even at room temperature, the diffusion coefficient of transition metals represented by iron is high. Additionally, even if the temperature of the substrate overall is held at room temperature or a temperature lower than room temperature, during irradiation with energetic particles, the energy of the energetic particles is converted into thermal energy by collisions, causing the temperature near the surface to rise locally within a range of a few atoms. Therefore, the diffusion distance of iron can be expected to increase near the surface. However, only the iron atoms positioned near the substrate surface are involved in the bonding process, while the iron atoms at positions deeper than the amorphous layer FG04 when viewed from the surface are not directly involved in the bonding process.

Additionally, the acceleration energy of iron atoms may be lower than the acceleration energy of argon which is an energetic particle. The diffusion rate of iron atoms is higher in amorphous silicon than in crystalline silicon, so the diffusion of iron atoms can be expected to be sufficient.

In order to obtain sufficient bonding strength, the surface layer FG04 made by the surface treatment method of the present embodiment should preferably comprise metals by <NUM> to <NUM> at%.

Furthermore, the surface layer FG04 formed by the surface treatment method according to the present embodiment should preferably comprise metals by <NUM> to <NUM> at%.

If the metal content is lower than the designated amount, then a sufficient bonding strength that can be expected by the presence of metals cannot be obtained.

Additionally, it may not be preferable for the metal content to be greater than the designated amount.

First, if the metal content is greater than the designated amount, then sufficient bonding strength may not be able to be obtained.

For example, a high bonding strength was obtained when, after the surface treatment, the substrate with an iron content of <NUM> at% in the surface layer FG04 was bonded after changing the gas pressure from vacuum to atmospheric pressure.

Additionally, a substrate having an iron content of <NUM> at% in the surface layer FG04, as a result of measurement, was found to have a slower oxidation rate than an iron metal film.

Various mechanisms may be contemplated as the reason for the slow iron oxidation rate. For example, when the iron content in the silicon is low, the probability of iron atoms being close to each other becomes extremely small, so the iron atoms can be considered to be isolated from other iron atoms. In that case, the iron atoms will bind with silicon atoms and form a silicon alloy. Silicon alloys are believed to be less susceptible to oxidation than when adjacent irons forms a metal film. Furthermore, when an iron atom is located at the surface layer FG04, one end of these iron atoms binds with silicon atoms, while the other end is exposed to the surface, and is not bound to silicon atoms or the like and therefore has a certain degree of activity. In other words, due to the fact that the amount of iron atoms on the outermost surface after the surface treatment does not exceed a certain amount, they can be considered to have the property of being less susceptible to oxidation, while having sufficient activity to generate a strong bond when contacting other substrate surfaces.

Additionally, the feature of the metal content being greater than a certain amount, in an unfavorable second case, generates conductivity.

For example, by increasing the metal content of the surface layer FG04, the metal atoms become continuous, forming metallic bonds. As a result of the continuous metallic bonds in surface layer FG04, the layer has conductivity. Additionally, even if not completely continuous, if metal atoms are present nearby at the atomic level, conductivity may arise as a result of the tunneling effect. Alternatively, even if the surface layer FG04 alone does not have conductivity, conductivity may arise as a result of bonding a pair of similar surface layers FG04.

In one example of the present embodiment, energetic particles and metal particles are radiated from the particle source, so the energy of the energetic particles and metal particles is defined by the particle source driving conditions. However, as mentioned above, the energetic particles and metal particles can be considered to play different roles in acting on the substrate material. If the amount of metal particles reaching the substrate material surface exceeds the amount of substrate material removed by energetic particles, then the metal particles will be deposited on the substrate material surface. In this case, a metal film is formed. On the other hand, if the amount of metal particles reaching the substrate material surface is less than the amount of substrate material removed by the energetic particles, then the metal particles will not be deposited onto the substrate material surface, and the substrate material will be progressively removed. In other words, the balance between the kinetic energy of the energetic particles and the amount of metal particles arriving at the substrate material surface is a factor in forming a desired thin film.

Next, experimental results relating to the relationship between bonding strength and the acceleration energy of energetic particles when using a <NUM> silicon wafer as the substrate material, specifically acceleration voltages of <NUM> V and <NUM> V, will be demonstrated.

First, the amount of substrate material removed by energetic particles was measured in the case of the above-described two acceleration voltages as shown in <FIG> is a side view showing the positional relationship between the substrate H06, the energetic particle source H03 and the direction of emission of the energetic particles H05. <FIG> is a plan view of the same. As the substrate H06, a thermal oxide film was formed on a silicon substrate, the thickness of this thermal oxide film was measured before and after irradiation by energetic particles, and the difference in thickness was recorded as the etched amount. Energetic particles H05 were radiated from the energetic particle source H03 in an oblique direction with respect to the substrate surface so as to contain the center <NUM> of the substrate. Additionally, the thickness of the thermal oxide film was measured from point <NUM> to <NUM> in the direction of the diameter of the substrate H06, in other words, along the direction of radiation <NUM> of the energetic particles H05. At this time, the positions of the measurement points <NUM> to <NUM> were determined by positioning a notch O06 as shown in <FIG>.

First, <FIG> shows the amount etched (nm) at measurement points <NUM> to <NUM> at <NUM> V and <NUM> V. At <NUM> V, the etched amounts were measured under the two conditions of radiation amounts <NUM> A-min and <NUM> A-min, and the etched amounts were confirmed to be roughly proportional to the amount of radiation. At <NUM> V, roughly the same results of etching amount as for <NUM> V and <NUM> A-min were obtained at measurement points <NUM> to <NUM>, while etching amounts intermediate between the results for the two conditions at <NUM> V described above were measured at positions <NUM> and <NUM>. In both cases, energetic particle radiation at the above-described <NUM> V and <NUM> V was found to provide roughly equivalent etching amounts in the thermal oxide film.

Silicon substrates were surface-treated with the same energetic particle acceleration voltages, and bonded together. In this case, no oxide film or any other thin film of anything other than silicon was formed on the silicon substrate surface, and the silicon materials were bonded together. Sufficient bonding strength was not obtained when the surface treatment was performed by accelerating the energetic particles at an acceleration voltage of <NUM> V, while sufficient bonding strength was obtained when the surface treatment was performed by accelerating the energetic particles at an acceleration voltage of <NUM> V. The measurement results show that even under energetic particle irradiation conditions providing similar amounts of etching, the bonding strength can differ depending on the acceleration voltage of a certain particle source, in other words, the kinetic energy of the energetic particles.

While the above example demonstrates the difference in bonding strength between energetic particle acceleration voltages of <NUM> V and <NUM> V using a predetermined particle source, this can change depending on various conditions. For example, depending on the irradiated material, the acceleration voltage may be <NUM> V (see <FIG>). Additionally, for example, the kinetic energy of the energetic particles specifically depends on the arrangement of the particle source that is used. Furthermore, while silicon was used in the above example, the bonding strength depends on the type (semiconductor, ceramic, dielectric material, organic material, etc.) and form (monocrystalline material, crystal orientation at the material surface, polycrystallinity, size of crystal grains, etc.) of the material to be irradiated with energetic particles as well as the kinetic energy (energy of the particles). Therefore, the resulting bonding strength can be considered to depend on parameters such as the energy of the particles, materials irradiated and the particle source.

For example, as shown in <FIG>, lookup tables T01, T02 can be prepared beforehand, showing the acceleration voltages E(V) necessary for obtaining a designated bonding strength BS (%) (= bonding strength (J/m<NUM>)/bulk breaking strength (J/m<NUM>)) for various materials such as SiO<NUM>, Si, SiN and M4 depending on the particle source G1, G2 used.

By storing these lookup tables in a memory of a computer S01 as shown in <FIG>, a user may enter desired parameters, whereupon the computer S01 will output to the power supply S02 an instruction S03 regarding the necessary acceleration voltage value. The power supply S02 will apply the instructed voltage to the voltage plate S05 of the acceleration voltage of the energetic particle source H03. As a result, the particles H05 accelerated by the predetermined voltage will be radiated form the energetic particle source H03. By providing a metal body S06 on the path of the particles H05, the energetic particles can be made to include metal particles.

As described above, by choosing the above-described parameters appropriately according to the present invention, a sufficient bonding strength can be achieved when the metal content in the surface layer of the substrate is within a predetermined range.

Next, as another example of the present invention, a method of adjusting the proportion between the radiation amount of energetic particles and metal particles in two different steps will be demonstrated. With reference to <FIG>, the difference between the above-described example (<FIG>) and the present example (<FIG>) will be explained.

In the above example, energetic particles are radiated from a single particle source FG10 to remove an oxide film FG02 and impurities FG03 on the surface of the substrate FG01 (<FIG>), forming the bonding layer FG04 on the substrate FG01 (<FIG>). When the energetic particles include metal particles, the metals will be contained in the formed bonding layer FG04.

In another example, as a first step, energetic particles were radiated from one particle source FG20 to remove an oxide film FG02 and impurities FG03 on the surface of the substrate FG01 (<FIG>), forming a bonding layer FG05 on the substrate FG01 (<FIG>). Next, as a second step, a particle source FG30 with a different amount of radiation of metal particles was used to irradiate the substrate FG01 with metal particles FG31, to form a final bonding layer FG04 (<FIG>). In the present example, the energetic particles in the first step may or may not include metal particles. Additionally, the particle source FG30 in the second step may simultaneously radiate energetic particles and metal particles as used in the above-described example. The amount of metal particles radiated can be increased or decreased by various methods. Additionally, this particle source FG30 need not have a mechanism for accelerating the particles. Basically, the embodiments exemplified by the present example enable the energetic particle irradiation conditions and metal particle irradiation conditions to be relatively freely set between a first step and a second step, so that their functions can be better controlled.

With the apparatus arrangement shown in <FIG>, the energetic particle source does not radiate energetic particles toward the substrate H06, but rather toward the metal particle source FG30. The metal particle source FG30 reacts with the energetic particles FG21 so that metal particles FG31 are sputtered and radiated toward the substrate H06.

Therefore, the metal particle source FG30 is a sputtering target for the energetic particles FG21. A sputtering target wherein sputtering is appropriately switched between metal particles and silicon depending on the process is effective. For example, the sputtering target may be of a polygonal prism shape having multiple faces and capable of rotation, provided with a silicon target on at least one surface, and a metal particle on at least one other surface. By using such a rotary sputtering target instead of a metal particle source FG30, after forming a silicon film on the substrate by radiating energetic particles at a silicon target to sputter silicon, the rotary sputtering target can be rotated so as to radiate the energetic particles onto the metal particle target to sputter metal particles (e.g., iron particles) and easily radiate metal particles onto the substrate.

In connection with <FIG>, formation of a silicon thin film insertion type substrate was explained. In particular, the substrate (surface layer) material was silicon oxide in the example shown in <FIG>. In other words, while the material of the starting substrate was silicon, the surface was thermally oxidized to form silicon oxide, and in terms of the features of the present invention, the example used silicon oxide as the substrate. On the other hand, in the following specific examples wherein silicon thin film insertion was not performed on the bonding surface, a material other than silicon oxide was used as the substrate.

In all of the specific examples below, the substrates were bonded after performing treatments for both under the same steps as the bonding surface fabrication process of substrate E shown in <FIG>. Therefore, the structure of the interface of the substrate assembly is the same structure as the above-described substrate assembly E. After bonding, the bonding strength of the substrate assembly was measured by a blade insertion method which is the same as the measurement of bonding strength in <FIG>.

The present example used, as one substrate, a silicon substrate on which a bonding surface was produced without undergoing thermal oxidation, and as the other substrate, a silicon substrate wherein silicon nitride was formed on the silicon substrate surface, and a bonding surface was formed. Therefore, the present example essentially demonstrates the formation of a bonding surface, bonding, and measurement results for bonding strength between silicon and silicon nitride.

As indicated by N02 in <FIG>, the bonding strength of the present example was estimated at <NUM> J/m<NUM>. In fact, when inserting a blade between the two substrates in a normal method of blade insertion, the substrates did not separate, and the silicon substrate was fractured, so the actual bonding strength of the present example was not measured. However, the fracture of the silicon substrate shows that a very strong bonding surface was formed. In other words, the bonding strength in the present example has at least the breaking strength of bulk silicon. In the drawings, the bonding strength at this time was estimated by the lowest limit value, so the breaking strength of bulk silicon, <NUM> J/m<NUM>, was recorded.

The substrate assembly N01 indicated at the far left of <FIG> is the same as the substrate assembly shown in <FIG>, and is presented for the purposes of comparison.

Based on the measurements and estimates of the bonding strength, the strength of the substrate assembly N02 in the present example was found to be greater than that of substrate assembly E (N01 in <FIG>), and at least as much as the bonding strength of a silicon substrate assembly.

The present example used, as one substrate, a silicon substrate wherein the silicon substrate surface was thermally oxidized, then a bonding surface was formed, and as the other substrate, a silicon substrate wherein a silicon nitride was formed on the silicon substrate surface, then a bonding surface was formed. Therefore, the present example essentially demonstrates the formation of a bonding surface, bonding, and measurement results for bonding strength between silicon oxide and silicon nitride.

As indicated by N03 in <FIG>, the bonding strength of the present example was estimated at <NUM> J/m<NUM>. As with N02, the substrates did not separate during blade insertion, as a result of which the silicon substrate was fractured, so the estimate was recorded as <NUM> J/m<NUM> which is the bonding interface strength of silicon materials.

Based on the measurements and estimates of the bonding strength, the strength of the substrate assembly N03 in the present example was found to be greater than that of substrate assembly E (N01 in <FIG>), and at least as much as the bonding strength of a silicon substrate assembly.

In the present example, silicon substrates were used for both substrates, on each of which silicon nitride was formed on the silicon substrate surface, then a bonding surface was produced. Therefore, the present example essentially demonstrates the formation of a bonding surface, bonding, and measurement results for bonding strength between silicon nitride and silicon nitride.

As indicated by N04 in <FIG>, the bonding strength of the present example was measured as <NUM> J/m<NUM>. The silicon substrate was not fractured during blade insertion. This is a bonding strength of about <NUM>% of the breaking strength of bulk silicon (<NUM> J/m<NUM>).

Based on these measurements of the bonding strength, the strength of the substrate assembly N04 in the present example was found to be higher than that of substrate assembly E (N01 of <FIG>).

As shown in <FIG>, the measurement results for bonding strength of substrate assemblies N02, N03 and N04 in the above examples were all higher than that of substrate assembly N01. This shows that the method of the present invention is capable of obtaining a high bonding strength independent of the type of substrate.

In all of the above examples, the substrates were bonded in a vacuum after performing the bonding surface fabrication processes of the present invention. In the following example, the substrates were bonded at atmospheric pressure after producing bonding surfaces in the same manner as the above-described example for silicon nitride - silicon nitride (N04 in <FIG>).

The bonding strength of the substrate assembly N05 produced by bonding at atmospheric pressure was <NUM> J/m<NUM> as shown at the far right of <FIG>. This is a bonding strength of about <NUM>% with respect to the breaking strength of bulk silicon (<NUM> J/m<NUM>). As shown in <FIG>, the bonding strength of substrate assembly N05 was lower than the bonding strength of substrate assembly N04, but higher than the bonding strengths of substrate assemblies A and B shown in <FIG>. Therefore, as a result of these bonding strength measurements, it was found that a sufficiently high bonding strength can be obtained by using the method of the present invention, even if the pressure at bonding is atmospheric pressure. Furthermore, one would naturally expect that the bonding strength when the pressure at bonding was lower than atmospheric pressure to be even greater than that of bonding assembly N05.

At the beginning of the detailed description, an example of an apparatus structure for performing surface treatments and bonding surface fabrication, and bonding substrates together was described. Herebelow, examples of other apparatus structures will be explained.

An example of an apparatus structure is shown in <FIG>. In the present example, a pair of substrates H06a, H06b is arranged so that their bonding surfaces face each other inside a process chamber H02 that can be set to a vacuum atmosphere. The energetic particle source H03 radiates energetic particles H05 in a horizontal direction towards the surfaces of the substrates H06a, H06b and the space between the substrate bonding surfaces, thereby simultaneously surface-treating the bonding surfaces of the substrates H06a, H06b. In the present example, a bonding mechanism H13 is further provided, enabling the surface-treated substrates to be brought into contact and bonded together. Since surface treatments can be performed on a pair of substrates with a single energetic particle source H03 and the distance between substrates is small, the apparatus structure is simple and economical. Additionally, the substrates can be bonded immediately after the surface treatment, reducing the chances of impurities adhering again after the surface treatment.

The apparatus structure for another example is shown in <FIG>. In the apparatus structure shown in <FIG>, the substrate surface is roughly parallel to the direction of the energetic particles H05, so there is a large difference in the intensity distribution of energetic particles on the substrate surface, and the energetic particle irradiation of the substrate surface cannot be considered to be uniform. Additionally, since the distance between substrates is small, there is a problem of impurities removed from one substrate surface adhering to the other substrate surface. Therefore, in the apparatus structure shown in <FIG>, an energetic particle source H03 is provided for each substrate H06a, H06b, and the distance between the substrates is widened so that the energetic particles H05 irradiate the substrate from a higher angle. As a result, with the apparatus structure of the present example, the intensity distribution difference at the substrate surface of the energetic particles is smaller than in the above example. Furthermore, a bonding mechanism H13 may be provided to bring the substrates into contact and bond them together immediately after the surface treatment.

Another example of an apparatus structure is shown in <FIG>. A single energetic particle source H03 is positioned facing the surface of the substrate H06 inside the process chamber H02. This energetic particle source H03 is capable of achieving a better intensity distribution of energetic particles than in the above examples by radiating energetic particles H03 roughly perpendicularly with respect to the surface of the substrate H06. As the bonding mechanism, a bonding chamber H14 is coupled to the process chamber H02 without breaking the vacuum, and each time the surface treatment of a substrate is completed in the process chamber H02, it is conveyed to the bonding chamber H14, where substrates H06 can be brought into contact and bonded using a bonding mechanism H13. Since this is a single-wafer process, more time is required from the treatment to bonding than for the above examples.

Another example of an apparatus structure is shown in <FIG>. Inside the process chamber H02, the substrates H06a, H06b are arranged with their bonding surfaces facing each other. A mobile linear energetic particle source H03 is provided between the substrates. For example, as shown in <FIG>, energetic particles are radiated not from a single point, but from a linear radiation source, making it suitable for performing surface treatments of wide substrates. In <FIG>, the linear particle source is assumed to be in the form of a line that is long in the direction perpendicular to the paper surface. The energetic particle source H03 can be moved in the direction indicated by the single-dotted chain line, to scan the substrates H06a, H06b with energetic particles H05. When the energetic particle source H03 arrives at the end of one substrate H06a, the linear beam source H03 is inverted to scan energetic particles across another substrate H06b. According to the structure of this example, a surface treatment with a uniform energetic particle intensity can be performed, thereby also making the thickness of the bonding surface layer uniform. Furthermore, a bonding mechanism H13 may be provided to enable the substrates to be brought into contact and bonded immediately after the surface treatment.

Another example of an apparatus structure is shown in <FIG>. Like the apparatus structure of <FIG>, substrates H06a, H06b are arranged inside the process chamber H02 so that their bonding surfaces face each other. Furthermore, a mobile linear energetic particle source H03 is provided between the substrates. However, in the apparatus structure of <FIG>, a mechanism for inverting the linear beam source H03 is needed. The apparatus structure of the present example does not use such an inverting mechanism, but instead uses a pair of particle sources. In other words, a pair of energetic particle sources H03c, H03d is provided, and each particle source irradiates respective substrates with energetic particles H05c, H05d. The energetic particle sources H03c, H03d may be moved in the direction indicated by the single-dotted chain line to scan the substrates H06a, H06b with energetic particles H05c, H05d. As with the previous example, due to the structure of the present example, a surface treatment with uniform energetic particle intensity can be performed, thereby also making the thickness of the bonding surface layer uniform. Furthermore, a bonding mechanism H13 may be provided to enable the substrates to be brought into contact and bonded immediately after the surface treatment. Additionally, the upper and lower substrates can be simultaneously processed, reducing the exposure time from surface treatment to bonding compared with the apparatus structure of <FIG>.

Another example of the apparatus structure is shown in <FIG>. A linear energetic particle source H03 is immobilized inside the process chamber H02, and the substrate H06 is moved to the right in the drawing, thereby scanning the energetic particles H05 across the substrate H06. Surface treatments can further be performed by similarly moving other substrates H06 to the right in the drawing. One of the pair of substrates can be inverted so that the bonding surfaces of the substrates face each other, and they can be brought into contact and bonded by means of the bonding mechanism H13. Additionally, surface treatments can be performed during handling, using means for conveying the wafers to the bonding chamber, for example, a robot, making the process more efficient and simplifying the apparatus.

Another example of an apparatus structure is shown in <FIG>. Inside the process chamber H02, a pair of substrates H06a, H06b is arranged in parallel with the surfaces to be surface-treated on the outside. The energetic particle sources H03c, H03d are arranged to face the substrates H06a, H06b from the outside of the pair of substrates, and are immobilized with respect to the process chamber H02. Due to the substrates H06a, H06b moving to the right in the drawing, the substrate H06 is scanned by energetic particles H05 to perform the surface treatment. The present example does not require a mechanism for inverting the substrates. The substrates whose surface treatments have been completed are bonded using a bonding mechanism H13 inside a bonding chamber H14.

<FIG> is a vertical section view of a bonding apparatus <NUM> (also referred to as 1A) according to a first embodiment of the present invention. In the drawings, the direction is indicated using an orthogonal XYZ coordinate system for the sake of convenience.

This bonding apparatus <NUM> is an apparatus that activates a bonding surface of an object to be bonded <NUM> and a bonding surface of an object to be bonded <NUM> with an atomic beam or the like inside a chamber (vacuum chamber) <NUM> under reduced pressure, to bond together the objects to be bonded <NUM>, <NUM>. According to this apparatus <NUM>, a surface activation treatment can be performed on the bonding surfaces of both the objects to be bonded <NUM>, <NUM>, while also enabling solid-state bonding of the objects to be bonded <NUM>, <NUM>. Various materials (e.g., semiconductor wafers, etc.) can be used as the objects to be bonded <NUM>, <NUM>.

The bonding apparatus <NUM> includes a vacuum chamber <NUM> which is a processing space for the objects to be bonded <NUM>, <NUM>, and a load-lock chamber <NUM> coupled to the vacuum chamber <NUM>. The vacuum chamber <NUM> is connected to the vacuum pump <NUM> via an exhaust pipe <NUM> and an exhaust valve <NUM>. By reducing (depressurizing) the pressure inside the vacuum chamber <NUM> with an evacuation operation by the vacuum pump <NUM>, the vacuum chamber <NUM> is put into a vacuum state. Additionally, the exhaust valve <NUM> is capable of adjusting the degree of vacuum inside the vacuum chamber <NUM> by means of an opening/closing action and adjustment of the exhaust flow rate.

After the objects to be bonded <NUM>, <NUM> are held by a clamping chuck 4c at the tip portion of a feed pipe <NUM> inside the load-lock chamber <NUM>, they are moved inside the vacuum chamber <NUM>. Specifically, the upper object to be bonded <NUM> is held by the tip portion of a feeding rod <NUM>, then moved in the X direction to a position PG2 directly under the head <NUM>, then picked up by the head <NUM>. Similarly, the lower object to be bonded <NUM> is held at the tip portion of the feeding rod <NUM> and moved toward stage <NUM> in the X direction to position PG1, then held by the stage <NUM>.

The head <NUM> and the stage <NUM> are both provided inside the vacuum chamber <NUM>.

The head <NUM> is moved (translated) in the X direction and the Y direction by an alignment table <NUM>, and rotated in the θ direction (direction of rotation about the Z axis) by a rotary drive mechanism <NUM>. The head <NUM> is driven by the alignment table <NUM> and the rotary drive mechanism <NUM> based on the positional detection results or the like from a position recognition portion <NUM> to be described below, to perform alignment in the X direction, Y direction and θ direction.

Additionally, the head <NUM> is moved (elevated) in the Z direction by a Z axis lift drive mechanism <NUM>. The Z axis lift drive mechanism <NUM> is capable of controlling the applied pressure at the time of bonding based on signals detected by a pressure detecting sensor which is not shown.

Additionally, the stage <NUM> can be moved (translated) in the X direction by a slide movement mechanism <NUM>. The stage <NUM> is moved in the X direction between a standby position near the beam irradiation portion <NUM> (around position PG1) and a bonding position immediately below the head <NUM> (around position PG2). The slide movement mechanism <NUM> has a high-precision position detector (linear scale), whereby the stage <NUM> can be positioned with high precision.

Additionally, the bonding apparatus <NUM> includes position recognition portions <NUM>, <NUM> for recognizing the positions of the objects to be bonded <NUM>, <NUM>. The position recognition portions <NUM>, <NUM> respectively have imaging portions (cameras) 18b, 28b for acquiring light images of the objects to be bonded as image data. Additionally, the objects to be bonded <NUM>, <NUM> are respectively provided with position recognition marks (hereafter referred to simply as marks). For example, two position recognition marks may be provided on one object to be bonded <NUM>, and two position recognition marks may be provided on the other object to be bonded <NUM>. These marks preferably have a specific shape. However, the invention is not so limited, and an orientation flat of a wafer or a part of the circuit pattern formed on a wafer may serve as an alternative to the position recognition mark.

The positioning actions of the objects to be bonded <NUM>, <NUM> are performed by the position recognition portions (cameras etc.) recognizing the positions of marks appended to the objects to be bonded <NUM>, <NUM>.

For example, the position recognition portion <NUM> acquires a light image of an object to be bonded <NUM> present at position PG1 as image data. Specifically, light emitted from a light source 18a positioned outside and above the vacuum chamber <NUM> passes through a window portion 2a of the vacuum chamber <NUM> and reaches the object to be bonded (position PG1) where it is reflected. Additionally, the light reflected by the object to be bonded <NUM> propagates again through the window portion 2a of the vacuum chamber <NUM> and reaches the imaging portion 18b. In this way, the position recognition portion <NUM> acquires a light image of the object to be bonded <NUM> as image data. Then, the position recognition portion <NUM> extracts the marks from the image data, recognizes the positions of the marks, and thereby recognizes the position of the object to be bonded <NUM>.

Similarly, the position recognition portion <NUM> acquires a light image of an object to be bonded <NUM> present at position PG2 as image data. Specifically, light emitted from light source 28a positioned outside and below the vacuum chamber <NUM> passes through a window portion 2b of the vacuum chamber <NUM> and reaches the object to be bonded <NUM> (position PG2) where it is reflected. Additionally, the light reflected by the object to be bonded <NUM> (specifically a portion thereof) propagates again through the window portion 2b of the vacuum chamber <NUM> and reaches the imaging portion 28b. In this way, the position recognition portion <NUM> acquires a light image of the object to be bonded <NUM> as image data. Additionally, the position recognition portion <NUM> extracts marks based on this image data, recognizes the positions of these marks, and thereby recognizes the position of the object to be bonded <NUM>.

Furthermore, as will be described below, in this bonding apparatus <NUM>, the stage <NUM> moves in the X direction, causing the object to be bonded <NUM> to move to position PG2, transitioning to a state in which the objects to be bonded <NUM>, <NUM> face each other. As shown in <FIG>, the position recognition portion <NUM> can acquire light images of the objects to be bonded <NUM>, <NUM> as image data with the objects to be bonded <NUM>, <NUM> facing each other. Specifically, the light emitted from the light source 28a positioned outside and below the vacuum chamber <NUM> passes through the window portion 2b of the vacuum chamber <NUM> and is reflected by the objects to be bonded <NUM>, <NUM> (specifically a portion thereof), then propagates again through the window portion 2b of the vacuum chamber <NUM> and reaches the imaging portion 28b. The position recognition portion <NUM> acquires light images (images of the reflected light) of the objects to be bonded <NUM>, <NUM> obtained in this way, and recognizes the positions of the marks based on the image data. As the light source 28a, light (such as infrared light) that is transmitted by both objects to be bonded <NUM>, <NUM> and the stage <NUM> may be used.

Additionally, in this embodiment, as shown in <FIG>, the position recognition portion <NUM> also has other light sources 28c, 28d. The position recognition portion <NUM> is capable of recognizing the positions of both objects to be bonded <NUM>, <NUM> using image data of transmitted light from the light sources 28c, 28d with both objects to be bonded <NUM>, <NUM> facing each other. Specifically, the light emitted from the light sources 28c, 28d positioned outside and to the side of the vacuum chamber <NUM> passes through the window portions 2c, 2d of the vacuum chamber <NUM>, then is reflected by mirrors 28e, 28f which change the direction of propagation, and propagates downward. After further passing through the objects to be bonded <NUM>, <NUM> (specifically a portion thereof), the light passes through the window portion 2b and reaches the imaging portion 28b. The position recognition portion <NUM> acquires light images (images of transmitted light) of both objects to be bonded <NUM>, <NUM> obtained in this way as image data and recognizes the positions of the marks based on the image data.

Thus, the bonding apparatus <NUM> is equipped with two types of imaging systems, these being an imaging system using reflected light (including light source 28a and an imaging portion 28b) and an imaging system using transmitted light (including light sources 28c, 28d and an imaging portion 28b). The bonding apparatus <NUM> is capable of recognizing the positions of the marks by appropriately switching between and using these two types of imaging systems as conditions require.

The positions of the objects to be bonded <NUM>, <NUM> are recognized by the position recognition portions <NUM>, <NUM> in the above manner. Additionally, based on the recognized position information, the head <NUM> is driven in the X direction, Y direction and/or θ direction by the alignment table <NUM> and the rotary drive mechanism <NUM> to move relative to the objects to be bonded <NUM>, <NUM> in carrying out the alignment action. For example, by moving the objects to be bonded <NUM>, <NUM> microscopically so that the two marks provided on object to be bonded <NUM> and the two marks provided on object to be bonded <NUM> overlap, the objects to be bonded <NUM>, <NUM> can be finely positioned.

Additionally, the bonding apparatus <NUM> includes three beam emitting portions <NUM>, <NUM>, <NUM>. In the bonding apparatus <NUM>, the surface activation process is performed using these three beam emitting portions <NUM>, <NUM>, <NUM>. As shown in <FIG>, the beam emitting portions <NUM> and <NUM> are provided on a side wall surface at the far end (+Y side) of the vacuum chamber <NUM>, and the beam emitting portion <NUM> is provided on a side wall surface at the right side (+X side) of the vacuum chamber <NUM>. The beam emitting portions <NUM>, <NUM> and <NUM> respectively emit beams of specific substances toward corresponding positions inside the vacuum chamber <NUM>.

More specifically, as shown in <FIG>, the beam emitting portion <NUM> is provided near position PG1 relatively to the left side (-X side) inside the vacuum chamber, and the beam emitting portion <NUM> is positioned near position PG2 relatively to the right side (+X side) inside the vacuum chamber <NUM>.

As shown also by the section view of <FIG>, the beam emitting portion <NUM> is arranged parallel to the horizontal plane on the +X side wall surface of the vacuum chamber <NUM>. As a result, with the object to be bonded <NUM> held on the stage <NUM> and the object to be bonded <NUM> held by the head <NUM> facing each other at position PG2, the beam emitting portion <NUM> emits a beam from the side of the space SP across which the objects <NUM>, <NUM> oppose each other and toward the opposition space SP. The beam emitting direction of the beam emitting portion <NUM> is a direction parallel to the X axis.

In this bonding apparatus <NUM>, by emitting specific substances (such as argon) from the beam emitting portions <NUM>, <NUM> in a slide arrangement state to be described below, a surface activation process for activating the bonding surfaces of the objects to be bonded <NUM>, <NUM> is performed. Additionally, the bonding apparatus <NUM> brings the objects to be bonded <NUM>, <NUM> which have been subjected to a surface activation treatment into a proximate opposed state, then brings them together to bond the objects to be bonded <NUM>, <NUM>.

Additionally, in this embodiment, the beam emitting portion <NUM> further emits specific substances (such as argon) after the objects to be bonded <NUM>, <NUM> have been put into a proximate opposed state, thereby also carrying out a surface activation treatment for activating the bonding surfaces of the objects to be bonded <NUM>, <NUM>.

Here, the beam emitting portions <NUM>, <NUM>, <NUM> activate the bonding surfaces of the objects to be bonded <NUM>, <NUM> by accelerating the ionized specific substance (argon in this case) with an electric field and emitting the specific substances toward the bonding surfaces of the objects to be bonded <NUM>, <NUM>. In other words, the beam emitting portions <NUM>, <NUM> and <NUM> activate the bonding surfaces of the objects to be bonded <NUM>, <NUM> by emitting energy waves. Additionally, the pair of beam emitting portions <NUM>, <NUM> and <NUM> may be separated by particle beam and metal beam. For example, the beam emitting portions <NUM>, <NUM> may emit a neutral atomic beam (fast atom beam, or FAB) not containing metal particles, and the beam emitting portion <NUM> may emit an ion beam such as shown in <FIG> containing large quantities of metal particles. Additionally, the beam emitting portions <NUM>, <NUM> may emit ion beams as shown in <FIG>, in which the amount of metal particles contained therein may be adjusted as compared with the beam emitting portion <NUM>.

As shown in <FIG>, a beam emitting portion 31D includes an anode <NUM>, a cathode <NUM> and a magnet <NUM>. The anode <NUM> and the cathode <NUM> are electrodes (also called electrode members or metal members) composed of respectively appropriate metal materials. For example, the anode <NUM> is composed of iron (Fe), and the cathode <NUM> is composed of tungsten (W). Additionally, the anode <NUM> is horn-shaped (roughly conical), while the cathode <NUM> is filament-shaped (coil-shaped). Additionally, the main body portion <NUM> of the beam emitting portion 31D is roughly cylindrical, and has a concave portion <NUM> in a front central portion. This concave portion <NUM> is formed as a space surrounded by the horn-shaped (megaphone-shaped) anode <NUM>. The anode <NUM> and the cathode <NUM> are electrically insulated from each other, the anode <NUM> having an anode potential and the cathode <NUM> having a cathode potential.

In the vicinity of the emission port of the beam emitting portion 31D, electrons supplied from the cathode <NUM> are trapped by the magnetic field of the magnet <NUM>, and begin circling in the vicinity of the emission port (see the circular dashed line in <FIG>). Additionally, further supplied argon is acted upon by the electrons and is present in a plasma state. Then, argon ions in a plasma state are accelerated by an electric field E generated by a voltage applied between the electrodes <NUM>, <NUM> (particularly due to the repulsive force of the anode <NUM>), and move toward the cathode <NUM>, going past the position of the cathode <NUM> and being cast outside the beam emitting portion 31D. At this time, the argon ions collide with the anode <NUM> and the cathode <NUM>, sputtering parts of the anode <NUM> and the cathode <NUM>. Additionally, the sputtered metal atoms move toward the bonding surfaces of the objects to be bonded <NUM>, <NUM>, where they adsorb to and are deposited on the bonding surfaces.

In the above embodiments, the beam emitting portion 31D was exemplified by one having a relatively compact anode <NUM>, but the beam emitting portion 31D may be replaced by a beam emitting portion 31E as shown in <FIG>. In this beam emitting portion 31E, a roughly conical anode <NUM> is elongated in the direction of the cathode <NUM>. More specifically, the beam emitting portion 31E includes an anode <NUM> (51E) that extends from the end (front end) 59f of the aperture side of the main body portion <NUM> to a forward (-X side) position. In other words, the anode 51E has a guide portion <NUM> protruding forward from the front end surface 59f of the main body portion <NUM> of the emitting portion 31E near the emission port of the beam emitting portion 31E.

For this reason, the anode 51E of the beam emitting portion 31E is capable of raising the directionality of the scattering range (irradiation range) of argon and metals compared to the anode <NUM> (51D) of the beam emitting portion 31D. This prevents argon and metals from scattering to unwanted parts (portions of the objects to be bonded <NUM>, <NUM> apart from the bonding surfaces). Additionally, by using an anode 51E having a guide portion <NUM>, the area of collision between the argon ions and the anode can be increased, so that a relatively large amount of metal can be removed, and the relatively large amount of metal moved in the direction of the bonding surface. As a result, with the beam emitting portion 31E, a larger amount of metal atoms than the beam emitting portion 31D can be efficiently supplied toward the objects to be bonded <NUM>, <NUM>. In view thereof, it is preferable to use the beam emitting portion 31E rather than beam emitting portion 31D. Additionally, the cathode <NUM> may be provided with an electron emitter (hollow cathode) separate from the beam emitting portion. The electrons emitted from the cathode also function to make the irradiated surface ionically neutral.

Additionally, as shown in <FIG>, the present example achieved a relatively high bonding strength when the acceleration voltage of the energetic particles was <NUM> or <NUM> V, while bonding was not possible at <NUM> V (bonding strength = <NUM> J/m<NUM>).

Several causes may be considered for the reason why the bonding strength falls so much that bonding is not possible at a certain threshold value. One cause may be that, due to the irradiation conditions, the removal of impurities may not be sufficient and the amorphization may also be insufficient, as a result of which the bonding strength between the iron and the substrate may be insufficient, or the iron atoms contained in the surface layer may be susceptible to oxidation, as a result of which the iron atoms may oxidize before bonding and reduce the bonding strength.

Additionally, <FIG> shows the results of measurement of the iron 2p spectrum on the surface of a substrate obtained by re-separating bonded substrates, as in the case of the bonding strength measurement. The substrate surface after the surface treatment is protected from oxidation and re-adsorption of impurities, thereby mostly retaining the condition after surface treatment. Therefore, the state of the substrate surface after surface treatment can be known by studying the state of the substrate surface after separation of the bonded substrates. <FIG> shows the iron 2p spectrum on the substrate surface after separation of a substrate assembly when holding the particle source drive conditions the same but changing two other conditions (C1, C2). The condition C1 indicates the conditions for providing a high bonding strength and the condition C2 indicates the conditions for providing a relatively low bonding strength. When observing the spectral components corresponding to FeO and Fe<NUM>O<NUM>, it can be observed that the iron on the substrate surface when applying a surface treatment (C2) providing a relatively low bonding strength is oxidized compared to a surface treatment (C1) providing a high bonding strength. Therefore, one cause of the decrease in bonding strength can be considered to be the fact that the iron of the substrate surface layer is oxidized before bonding.

Additionally, in the embodiments of the present invention, the bonding process is preferably performed at room temperature, but the bonding substrates can also be heated. As long as the temperature is kept low at about <NUM> or less, there are considerable merits compared to conventional thermal bonding. Additionally, the temperature should more preferably be equal to or less than <NUM> which is the melting point of conventional solder.

Claim 1:
A bonding substrate fabrication method for fabricating a substrate, bonding substrate, on which a bonding surface is formed, the bonding substrate fabrication method comprising:
a first surface treatment step of surface-treating a surface of a substrate by irradiation with radiated particles including energetic particles; and
a second surface treatment step of surface-treating the substrate surface by irradiation with radiated particles including metal particles;
wherein the bonding substrate is fabricated as a result of implementing the first surface treatment step and second surface treatment step; and
characterised in that
implementation of the first surface treatment step is performed before the second surface treatment step so that the metal particles are distributed in a base material of a surface layer of the bonding substrate with higher concentration than in the remaining of the bonding substrate.