JP2014201506A - Laminating method of substrate, substrate, and laminated substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminating method of substrates, with which joining of a low temperature co-fired ceramics (LTCC) substrate and a glass substrate is made possible.SOLUTION: A laminating method of substrates at least includes sequentially: a step α to form a silicon oxide film 3 on a face of a low temperature co-fired ceramics (LTCC) substrate 2; a step β to polish a face of the silicon oxide film; and a step γ to join a glass substrate 11 onto the silicon oxide film.

Description

  The present invention relates to a substrate bonding method, a substrate, and a bonded substrate, which enable bonding of a low temperature fired ceramics (LTCC) substrate and a glass substrate.

  In the fields of MEMS devices, biochips, interposers, etc., there has been a demand for packages and device structures that have both an electrical wiring structure and high airtightness.

Ceramics, low-temperature fired ceramic (LTCC) substrates, etc. can be made into a wiring structure by the built-up method, but are required to transmit light and are required to be anodic bonded to a silicon substrate. Can not be used. Or, sufficient bonding characteristics are not obtained.
Thus, there has been a demand for bonding between a glass substrate and a ceramic substrate or LTCC substrate from the field where permeability and anodic bonding are required.

However, it has been difficult to perform precise polishing necessary for direct bonding with ceramic substrates or LTCC substrates, and bonding with glass has been impossible.
As an important point that enables direct bonding, it is necessary to create a surface that has been finely polished (Ra 0.3 nm level). However, with a composite material such as LTCC, precise polishing is difficult because of different polishing rates depending on the components, and it is difficult to process with ceramics as well, and precision polishing is also difficult.

JP 2009-280417 A

The present invention has been devised in view of such conventional circumstances, and it is a first object to provide a method for bonding substrates, which enables bonding of a low-temperature fired ceramic (LTCC) substrate and a glass substrate. The purpose.
The second object of the present invention is to provide a substrate containing low-temperature fired ceramics (LTCC) that can be bonded to a glass substrate.
Furthermore, a third object of the present invention is to provide a bonded substrate in which a low-temperature fired ceramic (LTCC) substrate and a glass substrate are bonded.

The method for bonding substrates according to claim 1 of the present invention includes a step α for forming a silicon oxide film on one surface of a low-temperature fired ceramic (LTCC) substrate, a step β for polishing the surface of the silicon oxide film, And a step γ of bonding a glass substrate on the silicon oxide film at least in order.
The substrate bonding method according to claim 2 of the present invention is characterized in that, in claim 1, the step β uses an abrasive containing cerium oxide.
The substrate bonding method according to claim 3 of the present invention is characterized in that, in claim 1 or 2, in the step β, the surface roughness Ra of the silicon oxide film is 0.5 nm or less. To do.
According to a fourth aspect of the present invention, there is provided the method for bonding substrates according to any one of the first to third aspects, wherein the step γ is performed in a reduced pressure atmosphere.

According to a fifth aspect of the present invention, there is provided a method for bonding substrates, comprising: applying a resist on one surface of a low-temperature fired ceramic substrate to form a pattern; and the low-temperature fired ceramic substrate on which the resist pattern is formed. A step B of forming a silicon oxide film on one side, a step C of peeling the resist from the low-temperature fired ceramic substrate, a step D of polishing the surface of the silicon oxide film, and a glass on the silicon oxide film And a step E of bonding the substrates in order.
The substrate bonding method according to claim 6 of the present invention further comprises a step F of forming a metal film on one surface of the low-temperature fired ceramic substrate prior to the step A in claim 5. Features.
The method for bonding substrates according to claim 7 of the present invention is characterized in that, in claim 6, further comprising a step G of removing the metal film between the step D and the step E. To do.

The substrate according to claim 8 of the present invention is characterized in that a silicon oxide film is disposed on one surface of a low-temperature fired ceramic substrate.
The substrate according to claim 9 of the present invention is characterized in that, in claim 8, the silicon oxide film has a surface roughness Ra of 0.5 nm or less.

The bonded substrate according to claim 10 of the present invention is a low-temperature fired ceramic substrate, a silicon oxide film disposed on one surface of the low-temperature fired ceramic substrate, a glass substrate directly bonded on the silicon oxide film, It is characterized by providing.
A bonded substrate according to an eleventh aspect of the present invention is characterized in that the bonded substrate according to the tenth aspect is bonded by the method according to any one of the first to seventh aspects.

In the present invention, a silicon oxide film capable of the same precision polishing as glass is formed on one surface of a low-temperature fired ceramic (LTCC) substrate. By polishing the surface of this silicon oxide film, the surface roughness required for bonding to the glass substrate can be realized. Thereby, in this invention, the bonding method of a board | substrate which enabled the joining of a LTCC board | substrate and a glass substrate can be provided.
Moreover, in this invention, the board | substrate which can be joined to a glass substrate can be provided by arrange | positioning a silicon oxide film on one surface of a low-temperature baking ceramic substrate.
In addition, according to the present invention, it is possible to provide a bonded substrate in which a low-temperature fired ceramic substrate and a glass substrate are bonded to each other through a silicon oxide film.

Sectional drawing which shows the example of 1 structure of the board | substrate which concerns on 1st embodiment. Sectional drawing which shows the example of 1 structure of the bonding board | substrate which concerns on 1st embodiment. The figure which shows the process of the bonding method of the board | substrate which concerns on 1st embodiment in order. The photograph which image | photographed the substrate surface after performing each process using AFM. The evaluation result (photograph) with respect to the surface of the LTCC board | substrate with which the silicon oxide film was formed. The evaluation result (photograph) with respect to the surface of the polished silicon oxide film. Sectional drawing which shows the example of 1 structure of the board | substrate which concerns on 2nd embodiment. Sectional drawing which shows the example of 1 structure of the bonding board | substrate which concerns on 2nd embodiment. The figure which shows the process of the bonding method of the board | substrate which concerns on 2nd embodiment in order. The figure which shows one structural example at the time of applying a bonded substrate board to a wiring board. The figure which shows one structural example at the time of applying a bonded substrate board to a wiring board. The figure which shows one structural example at the time of applying a bonded substrate board to a wiring board.

  Hereinafter, an embodiment of a substrate bonding method, a substrate, and a bonded substrate according to the present invention will be described with reference to the drawings.

<First embodiment>
FIG. 1 is a cross-sectional view schematically showing a configuration example of a substrate according to the present embodiment.
In the substrate 1A (1) of this embodiment, a silicon oxide film 3 (for example, a SiO ₂ film) is disposed on one surface 2a of a low-temperature fired ceramic (LTCC) substrate 2.
In this substrate 1A (1), the surface roughness Ra of the silicon oxide film 3 is preferably 0.5 nm or less, and more preferably 0.35 nm or less. Thereby, this board | substrate 1A (1) can join with a glass substrate, for example.

FIG. 2 is a cross-sectional view showing an example of the configuration of the bonded substrate 10A (10) according to this embodiment.
This bonded substrate 10A (10) includes an LTCC substrate 2, a silicon oxide film 3 disposed on one surface 2a of the LTCC substrate 2, and a glass substrate 11 directly bonded on the silicon oxide film 3.
The bonded substrate 10A (10) is bonded by the following method.

FIG. 3 is a diagram sequentially illustrating the steps of the substrate bonding method according to the present embodiment.
The substrate bonding method of the present embodiment includes a step α for forming a silicon oxide film 3 on one surface 2 a of the LTCC substrate 2, a step β for polishing the surface of the silicon oxide film 3, and the silicon oxide film 3. Step γ for bonding the glass substrate 11 is provided at least in order.

  In order to directly bond the LTCC substrate 2 and the glass substrate 11, it is necessary to precisely polish the substrate so that the surface roughness Ra is 0.5 nm or less. However, ceramics cause brittle fracture. Because it is easy, precise polishing is difficult. Moreover, LTCC is a composite material of ceramics and glass, and precise polishing is difficult because the polishing rates of ceramics and glass are different. In the ordinary glass polishing method, only the glass melts and the ceramic becomes convex and remains. In the case of the LTCC substrate 2, Ra has a limit of several nm level, and precise polishing which is one order of magnitude smaller is not achieved.

  Therefore, in the present invention, a silicon oxide film 3 similar to glass is formed on one surface 2a of the LTCC substrate 2, and the surface roughness of the silicon oxide film 3 is polished so as to be bonded to the glass substrate 11. Can be realized. Thereby, in the bonding method of this invention, joining of the LTCC board | substrate 2 and the glass substrate 11 is attained.

Hereinafter, it demonstrates in order of a process.
Here, FIG. 4 is a photograph of the LTCC substrate surface after each process is performed using an atomic force microscope (AFM). FIG. 4A shows an AFM photograph of the surface of the LTCC substrate before processing. Before processing (polished), the LTCC substrate surface had irregularities such as polishing marks (sweeping marks), and the surface roughness Ra was about 3 nm.

(1-1) First, as shown in FIG. 3A, a silicon oxide film 3 is formed on one surface 2a of a low-temperature fired ceramic (LTCC) substrate (step α).
The method for forming the silicon oxide film 3 is not particularly limited, and for example, a sputtering method, a vapor deposition method, a coating method (SOG or the like) can be used.
In this embodiment, the SiO ₂ film is formed to a thickness of 1500 mm by RF sputtering at a substrate temperature of 100 ° C.

  FIG. 4B is a view showing an AFM photograph of the surface of the LTCC substrate 2 on which the silicon oxide film 3 is formed. Even if the silicon film 3 is formed, the unevenness on the surface of the LTCC substrate 2 cannot be covered, and the surface roughness Ra is not improved.

(1-2) Next, as shown in FIG. 3B, the surface of the silicon oxide film 3 is polished (step β).
In this step, for example, it is preferable to use an abrasive 20 containing cerium oxide. Thereby, fine polishing becomes possible and a smoother surface can be obtained. If a smoother surface is required, a polishing step using an abrasive containing colloidal silica can be added.
In this embodiment, for example, the surface of the silicon oxide film 3 is polished by performing single-side polishing using an abrasive 20 containing cerium oxide for 5 minutes.
In this step, the surface roughness Ra of the silicon oxide film 3 is preferably 0.5 nm or less, and more preferably 0.35 nm or less. Thereby, the surface roughness required for joining with the glass substrate 11 is realizable.

  FIG. 4C is a view showing an AFM photograph of the surface of the polished silicon oxide film 3. By precision polishing, the unevenness due to the difference in polishing rate between the ceramic particles and the glass, the original polishing trace of the LTCC substrate 2 and the like completely disappear, and the surface roughness Ra of the LTCC substrate 2 is reduced before processing (FIG. 4 ( Compared with a)), it was able to be about 1/10 (0.5 nm or less).

  On the other hand, FIG. 4D is a view showing an AFM photograph in the case where the surface of the LTCC substrate 2 is precisely polished using an abrasive containing cerium oxide without forming the silicon oxide film 3. Only the glass is polished and the ceramics are raised.

(1-3) Next, as shown in FIG. 3C, the glass substrate 11 is bonded onto the silicon oxide film 3 (step γ).
The joining method of the glass substrate 11 is not specifically limited, A well-known method can be used.

  As described above, in the present invention, the surface roughness Ra required for direct bonding is 0 by polishing the silicon oxide film 3 formed on the LTCC substrate 2 by using a precision glass polishing method. A surface having a smoothness of 5 nm or less could be obtained (hereinafter referred to as “production method according to the present invention”). Moreover, it became joining of glassy surfaces and it became possible to join using the conventional joining method of glass.

  In order to confirm the action and effect of the production method according to the present invention described above, the present inventor made detailed evaluations using various analysis techniques. In the following, SEM means “scanning electron microscope”, and EDX means “X-ray spectroscopy using an energy dispersive X-ray spectrometer”.

  FIG. 5 shows the evaluation results for the surface of the LTCC substrate 2 on which the silicon oxide film 3 is formed. FIG. 5A is an AFM photograph (uneven image) and corresponds to FIG. 5B is an SEM photograph (secondary electron image), FIG. 5C is an EDX photograph (aluminum element), and FIG. 5D is an EDX photograph (silicon element), both of which are shown in FIG. 5A. Is the result of observing the same angle of view.

The following points became clear from FIG.
(A) According to the AFM photograph (uneven image), “an irregular grain shape (confirmed to be concave)” is discrete on the surface on which the silicon oxide film 3 is formed on the LTCC substrate 2. [Fig. 5 (a)].
(B) “Parts having an irregular grain shape” according to the AFM photograph are observed as white according to the SEM photograph (secondary electron image). “Other parts” were observed in black [FIG. 5 (b)].
(C) According to the EDX photograph (observing Kα from the aluminum element), the “part observed in white” in FIG. 5B was observed faintly white. It was found that “(part forming an irregular grain shape)” contains aluminum as a main element [FIG. 5 (c)].
(D) According to the EDX photograph (observing Kα from the silicon element), the “parts observed in black” in FIG. 5B were faintly observed in white. It was found that the region excluding (a portion having an irregular grain shape) contained silicon as a main element [FIG. 5 (d)].

  FIG. 6 shows the evaluation results for the surface of the silicon oxide film 3 polished by the manufacturing method according to the present invention. FIG. 6A is an AFM photograph (uneven image) and corresponds to FIG. 6B is an SEM photograph (secondary electron image), FIG. 6C is an EDX photograph (aluminum element), and FIG. 6D is an EDX photograph (silicon element), both of which are shown in FIG. 5A. Is the result of observing the same angle of view.

The following points became clear from FIG.
(E) According to the AFM photograph (uneven image), the surface of the silicon oxide film 3 polished by the manufacturing method according to the present invention has the “irregular shape (concave shape)” observed in FIG. It disappeared and was observed to be flat over the entire picture [FIG. 6 (a)].
(F) However, according to the SEM photograph (secondary electron image), there are “parts where the irregular grain shape is observed in white (although flat according to the AFM photograph)”, and “other parts” are observed in black. [FIG. 6B].
(G) According to the EDX photograph (observing Kα from the aluminum element), the “parts observed in white” in FIG. 6B were observed to be faintly white. It was found that “the part of” includes aluminum as a main element [FIG. 6 (c)].
(H) According to the EDX photograph (observing Kα from the silicon element), the “parts observed in black” in FIG. It was found that “the part excluding the part of“ includes silicon ”as a main element [FIG. 6 (d)].
(I) That is, from the evaluation results of (a) to (h) described above, according to the manufacturing method according to the present invention, the silicon oxide film 3 formed on the LTCC substrate 2 is subjected to a technique for precise polishing of glass. By using and polishing, it was confirmed that a surface having a smoothness of Ra of 0.5 nm or less required for direct bonding can be obtained.

<Second embodiment>
FIG. 7 is a cross-sectional view schematically showing one configuration example of the substrate according to the present embodiment.
In the substrate 1B (1) of this embodiment, a silicon oxide film 3 (for example, a SiO ₂ film) is disposed on one surface 2a of the LTCC substrate 2.
In the substrate 1B (1) of this embodiment, the silicon oxide film 3 has a predetermined pattern.
In the substrate 1B (1), the surface roughness Ra of the silicon oxide film 3 is preferably 0.5 nm or less. Thereby, this board | substrate 1B (1) can join with a glass substrate, for example.

FIG. 8 is a cross-sectional view showing a configuration example of the bonded substrate board according to the present embodiment.
This bonded substrate 10 B (10) is disposed on the LTCC substrate 2, the one surface 2 a of the LTCC substrate 2, a silicon oxide film 3 formed in a predetermined pattern, and a glass substrate 11 directly bonded on the silicon oxide film 3. And comprising.

When the bonded substrate 10B (10) of the present embodiment is actually used, on the LTCC substrate 2 side, for example, a laminated wiring formed by using a built-up method, film formation, and photolithography are used. A surface wiring pattern is formed. On the other hand, a pattern having spaces such as flow paths and cavities is formed on the glass substrate 11 side. These are joined, and the electrode, the flow path, and the cavity itself have a function, or a device such as a MEMS waiting for the function is incorporated in this space.
That is, some pattern is formed on both the LTCC substrate 2 side and the glass substrate 11 side, and the silicon oxide film 3 that mediates bonding also has a pattern that matches the bonding pattern.
When the silicon oxide film 3 has a predetermined pattern, the bonded substrate 10B (10) is bonded by the following method.

FIG. 9 is a diagram sequentially illustrating the steps of the substrate bonding method according to the present embodiment.
(2-1) First, as shown in FIG. 9A, a metal film 4 is formed on one surface 2a of the LTCC substrate 2 (step F).
Since LTCC is a composite material containing glass, when a pattern is formed on one surface 2a of the LTCC substrate 2 and polishing using a glass abrasive is performed, the portion where the LTCC is exposed is polished, resulting in a rough surface. There is a risk of surface formation [FIG. 4 (d)].
Therefore, it is preferable to form the metal film 4 on the one surface 2 a of the LTCC substrate 2. By polishing while protecting the surface of the LTCC substrate 2 with the metal film 4, it is possible to prevent surface roughness.

The material of the metal film 4 is not particularly limited, but, for example, chromium, nickel or the like is used.
The method for forming the metal film 4 is not particularly limited, and for example, a sputtering method or the like can be used.
The thickness of the metal film 4 is not particularly limited. For example, the nickel film is about 5000 mm in the embodiment, but it may be thinner.

(2-2) Next, as shown in FIG. 9B, a resist 5 is applied on one surface 2a (metal film 4) of the LTCC substrate 2 to form a pattern (step A).
When bonding to a glass substrate 11 having a pattern, if the substrate material is a material having high hydrofluoric acid resistance, a silicon oxide film 3 is formed on one surface 2a of the substrate, and the pattern is formed by etching using hydrofluoric acid. Can be formed. However, LTCC is a material inferior in hydrofluoric acid resistance. Therefore, a resist 5 is applied to one surface 2a of the LTCC substrate 2, and a pattern is formed, for example, by photolithography. As will be described later, the silicon oxide film 3 having the pattern can be formed by forming the silicon oxide film 3 on the resist pattern and lifting it off.

(2-3) Next, as shown in FIG. 9C, the silicon oxide film 3 is formed on the one surface 2a side of the LTCC substrate 2 on which the resist pattern is formed (step B).
The method for forming the silicon oxide film 3 is not particularly limited, and for example, a sputtering method, a vapor deposition method, a coating method (SOG or the like) can be used.
In this embodiment, the SiO ₂ film is formed to a thickness of 1500 mm by RF sputtering at a substrate temperature of 100 ° C.

(2-4) Next, as shown in FIG. 9D, the resist 5 is removed from the LTCC substrate 2 (step C).
The resist 5 was peeled off (lifted off) from the LTCC substrate 2 together with the silicon oxide film 3.
In this embodiment, for example, the resist 5 is removed by immersing the substrate in a 3% NaOH aqueous solution for 10 minutes. As a result, a pattern was obtained in which the silicon oxide film 3 was left only in the portion bonded to the glass substrate 11.

(2-5) Next, as shown in FIG. 9E, the surface of the silicon oxide film 3 is polished (step D).
In this step, for example, it is preferable to use an abrasive 20 containing cerium oxide. Thereby, fine polishing becomes possible and a smoother surface can be obtained. If a smoother surface is required, a polishing step using an abrasive containing colloidal silica can be added.
In this embodiment, for example, the surface of the silicon oxide film 3 is polished by performing single-side polishing using an abrasive 20 containing cerium oxide for 5 minutes.
At this time, since the metal film 4 is formed on the one surface 2a of the LTCC substrate 2, the surface of the LTCC substrate 2 can be protected and the roughening of the surface can be prevented.
In this step, the surface roughness Ra of the silicon oxide film 3 is preferably 0.5 nm or less, and more preferably 0.35 nm or less. Thereby, the surface roughness required for joining with the glass substrate 11 is realizable.

(2-6) Next, as shown in FIG. 9F, the metal film 4 is removed (step G).
The method for removing the metal film 4 is not particularly limited, but in this embodiment using a nickel film as the metal film 4, the nickel film is removed by, for example, immersing in a ferric chloride solution for 60 seconds. did.

(2-7) Then, as shown in FIG. 9G, the glass substrate 11 is bonded onto the silicon oxide film 3 (step E).
The joining method of the glass substrate 11 is not specifically limited, A well-known method can be used.
In this step, it is preferable to perform heat treatment in a reduced pressure atmosphere or an inert gas atmosphere. Thereby, when it is set as the structure of FIGS. 10-12 mentioned later, the oxidation of the metal used for wiring can be prevented.

  As described above, even when a pattern is formed on the substrate surface, the silicon oxide film 3 formed on the LTCC substrate 2 is polished by using a precision glass polishing method, so that direct bonding can be achieved. The required surface having smoothness with Ra of 0.5 nm or less was obtained. Moreover, it became joining of glassy surfaces and it became possible to join using the conventional joining method of glass.

10 to 12 are diagrams showing a configuration example when the bonded substrate 10B (10) of the present embodiment is applied to a wiring substrate (interposer) or the like. 10 to 12, “bent lines shown inside the LTCC substrate 2” represent wirings.
In the example shown in FIG. 10, wiring is formed on the LTCC substrate 2, and a space 30 is formed on the glass substrate 11. In addition, as shown in FIG. 11, a functional device 31 may be incorporated in the space 30.
Furthermore, as shown in FIG. 12, the other surface side of the glass substrate 11 may be anodically bonded to the silicon wafer 32, and the functional device 31 may be incorporated in the space 30.

The substrate bonding method, the substrate, and the bonded substrate according to the present invention have been described above, but the present invention is not limited to this, and can be appropriately changed without departing from the spirit of the invention. .
For example, in the above description, the case where the LTCC substrate is used has been described as an example. However, for example, the present invention can be similarly applied to the case where a ceramic substrate is used.

  The present invention can be widely applied to a substrate bonding method, a substrate, and a bonded substrate used in, for example, semiconductor packages and devices.

  1A, 1B (1) substrate, 2 LTCC substrate, 3 silicon oxide film, 4 metal film, 5 resist, 10A, 10B (10) bonded substrate, 11 glass substrate.

Claims (11)

Forming a silicon oxide film on one surface of a low-temperature fired ceramic (LTCC) substrate;
Polishing the surface of the silicon oxide film β,
A substrate bonding method comprising: a step γ of bonding a glass substrate on the silicon oxide film at least in order.   The substrate bonding method according to claim 1, wherein the step β uses an abrasive containing cerium oxide.   3. The method for bonding substrates according to claim 1, wherein in the step β, the surface roughness Ra of the silicon oxide film is 0.5 nm or less.   The substrate bonding method according to claim 1, wherein in the step γ, heat treatment is performed in a reduced pressure atmosphere or an inert gas atmosphere. Applying a resist on one surface of a low-temperature fired ceramic substrate to form a pattern; and
Forming a silicon oxide film on one side of the low-temperature fired ceramic substrate on which the resist pattern is formed; and
Step C of peeling the resist from the low-temperature fired ceramic substrate;
Polishing step D of the surface of the silicon oxide film;
A step E of bonding a glass substrate on the silicon oxide film;
Are provided in order. The board | substrate bonding method characterized by the above-mentioned.   The substrate bonding method according to claim 5, further comprising a step F of forming a metal film on one surface of the low-temperature fired ceramic substrate prior to the step A.   The substrate bonding method according to claim 6, further comprising a step G of removing the metal film between the step D and the step E.   A substrate characterized in that a silicon oxide film is disposed on one surface of a low-temperature fired ceramic substrate.   The substrate according to claim 8, wherein the silicon oxide film has a surface roughness Ra of 0.5 nm or less. A low-temperature fired ceramic substrate;
A silicon oxide film disposed on one surface of the low-temperature fired ceramic substrate;
And a glass substrate directly bonded on the silicon oxide film.   The bonded substrate according to claim 10, wherein the bonded substrate is bonded by the method according to claim 1.