JP2001097787A - Method for forming flattened film, ceramic substrate, and electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a flattened film of uniform thickness on a ceramic substrate with recesses on its surface so as to hard to cause cracking of the film and be capable of sufficiently flattening the recesses. SOLUTION: This method comprises the following steps: step 1 wherein a 1st flattening solution is applied on a ceramic substrate so as to fill recesses on the substrate therewith and to form a 1st flattened film, step 2 wherein the 1st flattened film is removed by a portion corresponding to a specified film thickness while leaving the film in the recesses, and step 3 wherein a 2nd flattening solution is applied on the 1st flattened film to form a 2nd flattened film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a flattening film for flattening a surface of a ceramic substrate having irregularities.

[0002]

2. Description of the Related Art Irregularities are usually present on the surface of a ceramic substrate. The circuit pattern formed on the ceramic substrate having such irregularities can be miniaturized, and the yield and durability of a thin film capacitor can be improved. Therefore, attempts have been made to smooth the surface of the ceramic substrate. As one of the methods, there is a method in which a flattening solution is applied to the substrate surface to form a flattening film, thereby filling the unevenness on the substrate surface and flattening the substrate.

[0003] As a flattening film, for example, SOG (Sp
(On On Glass) solution. SOG is mainly formed of a silicon compound having at least one silanol bond (Si-OH) in a molecule, and is formed by dissolving this in an organic solvent such as alcohol, or by applying and firing this solution. It is a general term for insulating films. SOG is roughly classified into an organic SOG containing (SiR ₂ O) n as a main component and an inorganic SOG containing (nSiO ₂ · m (H ₂ O)) as a main component. Thus, a SiO ₂ insulating film can be formed, and because of its simplicity, it has been widely put into practical use in the field of semiconductors such as embedding steps between wirings.

Hereinafter, a conventional method for flattening a ceramic substrate using SOG will be described with reference to FIG. First, an SOG solution is spin-coated on the ceramic substrate 21 to fill the recesses 23 of the substrate 21 to some extent (FIG. 4A). in this case,
The larger the supply amount of the SOG solution, the better the filling property of the concave portion 23 of the substrate becomes. Therefore, it is necessary to apply the SOG solution layer 22 thicker. In order to sufficiently fill the substrate recess, specifically, the thickness of the SOG solution layer 22 needs to be 1 μm or more. Next, the substrate 21 is heat-treated at about 100 to 300 ° C. In this temperature range, the SOG exhibits reflow properties, and the SOG flows into the concave portions 24 on the surface of the SOG solution layer 22 to further improve the flatness (FIG. 4).
(B)). Finally, by heat-treating (curing) the substrate at about 450 ° C., the silanol bonds in the molecules are converted into siloxane bonds (Si—O—Si), and the SiO ₂ insulating film 26 is formed (FIG. 4C). ).

[0005]

The conventional method of flattening a ceramic substrate using SOG has the following problems. That is, in the conventional method, it is necessary to apply the SOG solution thickly in order to sufficiently fill the concave portion of the substrate. However, the applied SOG solution contracts greatly during curing, and generates a large stress inside. In particular, when the SOG solution is applied thickly, since the volume of the SOG is large, the stress generated inside is large, and as shown in FIG.
Many cracks will occur in itself.

In order to apply a thick SOG solution, S
It is necessary to set the rotation speed at the time of spin coating of the OG solution to a low speed. However, when spin coating is performed at a low speed, the SOG solution tends to accumulate at the edge of the substrate, and thus there is a problem that a large difference occurs in the SOG film thickness between the center and the edge of the substrate. Specifically, the average thickness of SOG is 1.7 μm
In this case, the variation (3σ) of the film thickness is as large as about 27%.

To solve these problems, SOG
A method of applying a thin solution is conceivable. However, if the SOG solution is applied thinly in the conventional method, the supply amount of the SOG solution to the substrate becomes insufficient, and the concave portion of the substrate cannot be sufficiently filled.

The method of forming a flattening film according to the present invention has been made in view of the above-mentioned problems, and solves these problems. Thus, cracks are less likely to occur, the film thickness is uniform, and unevenness of the substrate is reduced. It is an object of the present invention to provide a method for forming a planarization film which can sufficiently planarize.

[0009]

According to the present invention, there is provided a method for forming a flattening film for flattening a ceramic substrate having a concave portion on the surface, wherein the flattening film is filled in the concave portion of the ceramic substrate. Forming a first planarizing film by applying a first planarizing solution so that the first planarizing film has a predetermined thickness while leaving the first planarizing film in the concave portion of the ceramic substrate. And a step of applying a second planarizing solution on the first planarizing film to form a second planarizing film.

As described above, in the present invention, the flattening film is formed twice. First, a first planarizing film is formed on a substrate and removed by a predetermined thickness to reduce the depth of the concave portion of the substrate. Even if the supply amount of the substrate is small, the concave portion of the substrate can be sufficiently filled. Therefore, the thickness of the second flattening film can be reduced, and a flattening film with less cracks and a uniform thickness can be obtained.

The step of forming the first flattening film and the step of removing the first flattening film by a predetermined thickness may be alternately repeated a plurality of times. Subsequent to the step of forming the flattening film, a step of removing the second flattening film by a predetermined thickness while leaving the second flattening film in the concave portion of the ceramic substrate may be further performed. Further, the step of forming the second planarization film and the step of removing the second planarization film by a predetermined thickness may be alternately repeated a plurality of times.

As described above, the step of forming the flattening film and removing it by a predetermined thickness is repeated a plurality of times, so that the concave portion of the substrate can be made shallower.
Even when the amount of the planarizing solution supplied when forming the planarizing film is extremely small, the concave portion of the substrate can be sufficiently buried, and the second
It is possible to further reduce the thickness of the flattening film.

Preferably, the first and second planarizing solutions are applied by spin coating. When spin coating is used, not only is it easy to obtain a relatively uniform flattening film by filling the recesses of the substrate, but also it is possible to obtain a flattening film having a desired film thickness by adjusting the rotation speed. is there.

It is desirable that the rotation speed at the time of applying the first planarizing solution is lower than the rotation speed at the time of applying the second planarizing solution. As described above, the first planarizing solution can be applied thickly by reducing the rotation speed at the time of applying the first planarizing solution. That is, by sufficiently supplying the first planarizing solution, even if there is a large concave portion on the surface of the ceramic substrate, it can be sufficiently filled. In addition, since the concave portion of the substrate is already somewhat shallow by embedding the first planarizing film in the concave portion of the substrate, the supply amount of the planarizing solution is small when the second planarizing solution is applied. However, the unevenness of the substrate can be sufficiently filled. Therefore, even when the second planarizing solution is applied thinly, the substrate is rotated at a higher rotational speed at the time of applying the second planarizing solution than at the time of applying the first planarizing solution. Can be sufficiently filled, and the thickness of the second flattening film can be reduced.

It is desirable that the rotation speed at the time of applying the first planarizing solution is not more than 500 rpm. If the rotation speed is as low as 500 rpm or less, the first planarizing solution can be sufficiently supplied, and even if there is a large concave portion on the ceramic substrate, it can be sufficiently buried.

As the first and second planarizing solutions, for example, SOG solutions can be used. The SOG solution is applied to the substrate and then heat-treated (cured) to form an SOG film. The SOG film contracts greatly during the curing, and generates a large stress inside. Therefore, when the SOG solution is applied thickly, a problem that cracks are generated in the SOG film easily occurs.

The removal of the flattening film is preferably performed by reactive ion etching. This is because reactive ion etching can perform selective etching, and therefore, by using an etching gas capable of selectively etching the flattening film, only the flattening film can be accurately etched.

Further, the first planarizing film has a thickness of 1.
Desirably, it is 2 to 3.0 μm. The purpose of forming the first planarizing film is to bury the concave portion of the substrate, but by applying the planarizing solution thickly, the concave portion of the substrate can be sufficiently buried. On the other hand, the second
The flattening film preferably has a thickness of 0.1 to 1.0 μm. By embedding the first planarizing film in the concave portion of the substrate, the concave portion of the substrate is already somewhat shallow,
When the second planarizing solution is applied, the supply amount of the planarizing solution is small, and even if the planarizing film has a thickness of 0.1 to 1.0 μm, the unevenness of the substrate can be sufficiently filled. That's why.

For example, when an SOG solution is used as the planarizing solution, the present invention desirably follows the following steps. That is, the present invention is a method of forming a flattening film for flattening a ceramic substrate having a concave portion on the surface,
A step of spin-coating the SOG solution on the ceramic substrate at a low speed and performing a heat treatment to form a first SOG film; and, while leaving the first SOG film in the concave portion of the ceramic substrate,
The method includes a step of etching back the first SOG film, and a step of spin-coating the SOG solution on the ceramic substrate at a high speed and performing a heat treatment to form a second SOG film.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a flattening film according to an embodiment of the present invention will be described below with reference to FIGS. FIG.
3 to 3 are cross-sectional process diagrams showing a method of forming a flattening film in the present invention. (Embodiment 1) In this embodiment, a case where an SOG solution is used as a planarizing solution will be described. First,
The first SOG solution layer 2 is formed by spin-coating the SOG solution on the substrate 1 at a rotation speed of 200 rpm for 30 seconds so as to fill the concave portions 3 on the surface of the ceramic substrate 1 (FIG. 1).
(A)). Since the rotation speed is low, the first SOG solution is applied thickly, and the SOG solution is sufficiently supplied. Therefore, even if there is a large recess of about 10 μm on the surface of the ceramic substrate, this can be sufficiently filled. on the other hand,
Since the spin coating is performed at a low speed, the SOG solution easily accumulates at the edge of the substrate.
A large difference occurs in the thickness of the solution layer 2.

Next, the substrate 1 is placed on a direct hot plate at 150 ° C. and heat-treated for 60 seconds, and then placed on a direct hot plate at 250 ° C. and heat-treated for 60 seconds. Since SOG exhibits reflow properties at these temperatures, the SOG is placed in the recess 4 on the surface of the SOG solution layer 2.
Flow to improve the flatness (FIG. 1B).

Subsequently, the first SOG film 6 (SiO ₂ insulating film) having an average film thickness of about 1.7 μm is formed by subjecting the substrate 1 to a heat treatment (curing) in a nitrogen atmosphere at 450 ° C. for 30 minutes (FIG. 2B). FIG. 1 (c)). At this time, the first SO
Since the G film 6 is thick, a large stress is generated due to shrinkage during curing, and the SOG film 6 itself has cracks. Further, since the SOG solution is spin-coated at a low speed in the above process, the SOG solution is formed at the center and the end of the substrate.
A large difference occurs in the thickness of the G film 6. Specifically, the variation in the film thickness is as high as 27%.

Next, the first SOG film 6 is etched back using CF ₄ plasma in a parallel plate reactive ion etching apparatus. By leaving the first SOG film buried in the concave portion 3 of the substrate and removing other portions, the concave portion 3 of the substrate is partially buried with the first SOG film 6 and
A shallow recess 8 is formed on the upper portion (FIG. 1D). Further, since most of the first SOG film 6 is removed in this step, there is no problem even if the SOG film 6 has cracks in the step before the removal and there is a large variation in the film thickness. The etching gas may be any gas that can etch SOG, and specifically, CF ₄ , CH
_{F 3, F 2, NF 3} , CClF 3, C 2 F 6, CBrF 3, C
_{H 2 F 2, CHClF 2,} C 3 F 8, CCl 2 F 2, C 4 F 8,
A gas containing one or more of CHCl ₂ F, CBr ₂ F ₂ , and CCl ₃ F can be used.

Next, the SOG solution is spin-coated on the substrate 1 again so as to fill the recess 8. 1000 rpm
m for 30 seconds to form a second SOG solution layer 7 (FIG. 1E). Since the rotation speed is high, the second SOG solution layer 7 is formed thin. However, in the above-described process, the concave portion 3 of the substrate becomes the shallow concave portion 8 due to the formation of the first SOG film 6 and the etch back. The concave portion 8 can be sufficiently filled even when the supply amount of the SOG solution is smaller than when the first SOG film is formed. Further, since the second SOG solution layer 7 can be formed thin as described above, the SOG solution does not easily accumulate at the end of the substrate. Therefore, it is possible to achieve a flatter planarized film without a large difference in film thickness between the central portion and the end portion of the substrate.

Next, the substrate is placed on a direct hot plate at 150 ° C. and heat-treated for 60 seconds, and then placed on a direct hot plate at 250 ° C.
Heat treatment is performed for 0 seconds. Since SOG exhibits reflow properties at these temperatures, SOG flows into the concave portions 9 on the surface of the SOG solution layer, and the flatness is further improved (FIG. 1F).

Subsequently, the substrate is heat-treated (cured) in a nitrogen atmosphere at 450 ° C. for 30 minutes to form a _second SOG film 10 (SiO ₂ insulating film) having an average thickness of about 0.8 μm. (FIG. 1 (g)). The SOG contracts during curing, but the second SOG film 10 is thinner than the first SOG film, so that the stress generated during the contraction is small. Therefore, flattening of the SOG film can be realized without generating cracks in the SOG itself. Further, since the SOG solution is spin-coated at a high speed in the above process, the SOG solution is formed at the center and the end of the substrate.
There is no large difference in the thickness of the G film 10. Specifically, the variation in the film thickness can be suppressed to 14%.

(Embodiment 2) A case where an SOG solution is used as a planarizing solution as in the case of Embodiment 1 will be described. First, a first SOG film is formed on a substrate and etched back in the same process as in the first embodiment. That is, as shown in FIGS. 2A to 2D, after forming a first SOG film 6 (SiO ₂ insulating film) having an average film thickness of about 1.7 μm on a ceramic substrate 1, a concave portion 3 on the substrate surface is formed. The other portions are removed, leaving the first SOG film 6 embedded in the first. Thereby, the recess 3 is buried to some extent by the SOG film 6, and a shallower recess 8 is formed on the substrate 1.

Next, a first SOG film is formed on the substrate and etched back in the same process as in the first embodiment. That is, the SOG solution is spin-coated on the substrate 1 at a rotation speed of 200 rpm for 30 seconds so as to fill the recess 8,
The first SOG solution layer 12 is formed (FIG. 2E). Next, the substrate is placed on a direct hot plate at 150 ° C. and heat-treated for 60 seconds. Then, the substrate is placed on a direct hot plate at 250 ° C. and heat-treated for 60 seconds. SOG flows into the substrate, and the flatness is further improved (FIG. 3A). Subsequently, the substrate 1 is subjected to a heat treatment (curing) in a nitrogen atmosphere at 450 ° C. for 30 minutes so that the average film thickness is about 1.7.
A 1 μm first SOG film 16 (SiO ₂ insulating film) is formed (FIG. 3B).

Next, the first SOG film 16 is etched back using CF ₄ plasma in a parallel plate reactive ion etching apparatus (FIG. 3C). By leaving the SOG film 16 buried in the concave portion 3 of the substrate and removing other portions, the concave portion 3 of the substrate is buried with the SOG films 6 and 16, and a substantially flat concave portion 18 shallower than the concave portion 8 is formed. You.

Next, a second SOG film is formed on the substrate by the same process as in the first embodiment. That is, first, the SOG solution is spin-coated on the substrate 1. Spin coating is performed for 30 seconds at a rotation speed of 1000 rpm to form a second SOG solution layer 17 (FIG. 3D). Next, the substrate 1 was placed on a direct hot plate at 150 ° C. and heat-treated for 60 seconds.
Subsequently, the SOG solution layer 1 was set on a direct hot plate at 250 ° C. and heat-treated for 60 seconds.
The SOG flows into the concave portion 19 on the surface of the substrate 7, and the flatness is further improved (FIG. 3E). Finally, the substrate 1 is heat-treated (cured) in a nitrogen atmosphere at 450 ° C. for 30 minutes, so that the second SOG film 20 having an average thickness of about 0.8 μm is formed.
(SiO ₂ insulating film) is formed (FIG. 3F).

In the present embodiment, the process of forming the first SOG film and removing it by a predetermined thickness is repeated twice successively, so that the concave portion of the substrate can be sufficiently filled with the SOG film. The recess can be made shallower and almost flat as compared with the case where the process is performed only once as in the case of (1). Therefore, when the second SOG film is formed in the final step, the concave portion can be buried sufficiently with a smaller supply amount of the SOG solution, so that the SOG film can be further thinned, and the generation of cracks can be reduced. It is possible to obtain a flattened film having a small thickness variation.

The step of forming the first SOG film and removing it by a predetermined thickness may be repeated three or more times. By repeating the above process many times, the concave portion can be sufficiently filled, and a flatter SOG film can be obtained. Similar effects can be obtained for the second SOG film by repeating the process of forming the SOG film and removing it by a predetermined thickness a plurality of times.

Further, in the above embodiment, when removing the SOG film, other portions were removed except for the SOG film buried in the concave portion of the substrate, but it is not always necessary to remove all other portions. For example, in the case where a convex portion exists on the ceramic substrate, the SOG is so thick that the convex portion is covered with the SOG film.
Other portions may be removed while leaving the G film.

It should be noted that the SOG used in the above embodiment may be any material that can fill the recesses of the ceramic substrate.
Organic SOG and inorganic SOG do not matter. In the above embodiment, the case where the SOG solution is used as the planarizing solution has been described. However, the present invention is not limited to this, and any material that can embed the concave portion of the ceramic substrate can be used.

The ceramic substrate flattened by the method for forming a flattening film according to the present invention can be used for forming an electronic component. By using the ceramic substrate having the flattening film formed according to the present invention, the electronic component can be formed. Performance can be greatly improved. For example, when a circuit pattern or a thin film capacitor is formed on a ceramic substrate on which the planarizing film of the present invention is formed, it is possible to easily achieve the miniaturization of the circuit pattern and the improvement of the yield and durability of the thin film capacitor. Become.

[0036]

As described above, according to the present invention, the flattening film is formed in a plurality of times, and the concave portions of the substrate are sufficiently buried in advance to reduce the thickness of the flattening film formed in the final step. It becomes possible. Therefore, not only can a flattening film free of cracks be formed, but also the number of revolutions can be set high during coating, so that the flattening solution does not easily accumulate at the substrate edge, and the film thickness varies. And a flattened film can be obtained.

[Brief description of the drawings]

FIGS. 1A to 1G are cross-sectional process diagrams illustrating a method of forming a planarization film according to a first embodiment of the present invention.

FIGS. 2A to 2E are cross-sectional process diagrams illustrating a method of forming a planarizing film according to a second embodiment of the present invention.

FIGS. 3A to 3F are cross-sectional process diagrams illustrating a method of forming a planarization film according to a second embodiment of the present invention, following FIG. 2E.

FIGS. 4A to 4C are cross-sectional process views showing a conventional method for forming a planarizing film.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 ceramic substrate 2 first SOG solution layer 3 recess 6 first planarization film 7 second SOG solution layer 10 second SOG film

Claims (14)

[Claims] 1. A method for forming a flattening film for flattening a ceramic substrate having a concave portion on the surface, the method comprising applying a first planarizing solution so as to fill the concave portion of the ceramic substrate. (1) forming a flattening film; removing the first flattening film by a predetermined thickness while leaving the first flattening film in the concave portion of the ceramic substrate; Forming a second flattening film by applying the flattening solution of No. 2 above. 2. A method of forming a flattening film, wherein the step of forming the first flattening film and the step of removing the first flattening film by a predetermined thickness are alternately repeated a plurality of times. . 3. The method according to claim 1, further comprising the step of removing the second flattening film by a predetermined thickness while leaving the second flattening film in the concave portion of the ceramic substrate.
The method for forming a flattening film according to item 1. 4. The method according to claim 3, wherein the step of forming the second planarizing film and the step of removing the second planarizing film by a predetermined thickness are alternately repeated a plurality of times. A method for forming a planarizing film. 5. The method according to claim 1, wherein the first and second planarizing solutions are applied by spin coating. 6. The method according to claim 5, wherein a rotation speed at the time of applying the first planarizing solution is lower than a rotating speed at the time of applying the second planarizing solution. A method for forming a planarizing film. 7. The method according to claim 5, wherein a rotation speed at the time of applying the first flattening solution is 500 rpm or less.
Or the method for forming a flattening film according to 6. 8. The method of claim 1, wherein the first and second planarizing solutions are SO
8. The method for forming a flattening film according to claim 1, wherein the solution is a G solution. 9. The method according to claim 1, wherein the removal of the first planarizing film is performed by reactive ion etching.
9. The method for forming a flattening film according to any one of items 8 to 8. 10. The first flattening film has a thickness of 1.2 to 1.2.
The method according to claim 1, wherein the thickness is in a range of 3.0 μm. 11. The film thickness of the second flattening film is 0.1 to 0.1.
The method for forming a flattening film according to claim 1, wherein the thickness is within a range of 1.0 μm. 12. A method for forming a flattening film for flattening a ceramic substrate having a concave portion on its surface, wherein a first SOG film is formed by spin-coating an SOG solution on the ceramic substrate at a low speed and performing heat treatment. Forming the first SOG film while leaving the first SOG film in the concave portion of the ceramic substrate; and spin-coating the SOG solution on the ceramic substrate at a high speed, followed by heat treatment. Performing a step of forming a second SOG film;
A method for forming a flattening film, comprising: 13. A ceramic substrate on which a flattening film is formed by using the method for forming a flattening film according to claim 1. 14. An electronic component formed using the ceramic substrate according to claim 13.