JP4543572B2 - Silicon wafer processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silicon wafer processing method for etching a part of a silicon wafer to make it thin in the thickness direction.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, resonators and infrared sensors that use ceramic thin film piezoelectricity and pyroelectricity by forming an element composed of a ceramic thin film and electrodes on a substrate have been used.
In order to prevent such a resonator or infrared sensor from affecting the element on the substrate, only the element portion of the resonator or infrared sensor and its periphery are etched from the back surface of the substrate to reduce the substrate thickness, or It is a common practice to remove the substrate, leave only the elements, and form a diaphragm structure.
[0003]
This etching is preferably anisotropic etching that proceeds only in the thickness direction of the substrate without etching other than necessary portions. For this reason, a single crystal substrate that is easily anisotropically etched, particularly a silicon wafer, is often used as a substrate material.
[0004]
This etching is preferably performed after an element is formed on the silicon wafer.
This is because, for example, if a diaphragm structure is formed by etching before forming an element, it is difficult to handle a silicon wafer in the element forming process due to a decrease in mechanical strength, and silicon is heated to about 500 ° C. or more when forming a ceramic thin film. This is because damage such as breakage may occur due to thermal distortion of the wafer.
[0005]
However, even when etching is performed after the element is formed, there is a problem that the element is also damaged by dissolution because the silicon etchant is a strong base.
To solve this problem, a silicon oxide film, a silicon nitride film, or a silicon oxynitride film that functions as a protective film including elements and electrodes on the surface of the silicon wafer is formed after the elements are formed. There is a solution to prevent dissolution. Note that if this protective film is left formed even after etching the back surface of the silicon wafer, it affects the characteristics of the elements and the like, so it is desirable to remove it after etching the back surface of the silicon wafer. The removal is performed using a protective film etching solution that can remove the protective film without etching the silicon wafer.
[0006]
There is also a method of forming a protective film made of a metal such as Mo that is resistant to a silicon etching solution on a portion other than the pad of the electrode. In this case, the protective film is removed by dipping in an acid such as a nitric acid solution.
[0007]
[Problems to be solved by the invention]
However, the removal of the protective film described above cannot completely eliminate damage to the ceramic thin film of the element due to etching or reaction. Although this damage occurs only on the thin surface layer, the end of the ceramic thin film of the element is thin, and this damage tends to cause a defect, which causes electrical leakage.
[0008]
The silicon wafer processing method of the present invention has been made in view of the above-mentioned problems. When the back surface of a silicon wafer is etched after forming an element, the surface of the silicon wafer is covered with a protective film, and the element is damaged. An object of the present invention is to provide a silicon wafer processing method capable of easily removing a protective film without giving it.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, in the silicon wafer processing method according to the first aspect of the present invention, one main surface is an etched surface, the other main surface is a non-etched surface, and part or all of the etched surface. Is a silicon wafer processing method for etching an etching processing portion of a silicon wafer, which is an etching processing portion, and thinning the silicon wafer, wherein the first film soluble in an organic solvent is formed on at least the non-etching processing surface. A step of forming the entire surface or a part thereof, a step of forming a second film made of a resin resistant to strong base and hydrofluoric acid and protecting the silicon wafer from etching, on at least the first film; Is immersed in a silicon etchant to etch the etched portion, and the silicon wafer is immersed in an organic solvent to obtain a first Removing the film, by removing the first film, a silicon wafer processing method characterized by comprising the step of removing the second film peeling becomes easier, at least.
[0010]
In the silicon wafer processing method of the present invention according to claim 2, one main surface is an etched surface, the other main surface is a non-etched surface, and a part of the etched surface is an etched portion. A silicon wafer processing method for etching a wafer etching portion and thinning a silicon wafer, wherein the silicon wafer is heated to form a silicon oxide film on both main surfaces of the silicon wafer, and against hydrofluoric acid. A process of providing a hydrofluoric acid film made of a highly resistant material on the silicon oxide film excluding the etched portion, and immersing the silicon wafer in a hydrofluoric acid solution to remove the silicon oxide film formed on the etched portion. A step of removing the hydrofluoric acid resistant film by immersing in a stripping solution, and a first film soluble in an organic solvent. A step of forming the entire surface or a part of the chin processing surface, and a step of forming a second film made of a resin resistant to strong base and hydrofluoric acid and protecting the silicon wafer from etching at least on the first film. Immersing the silicon wafer in a silicon etchant to etch the etched portion, immersing the silicon wafer in an organic solvent to remove the first film, and removing the first film And a step of removing the second film that has been easily peeled off.
[0011]
According to a third aspect of the present invention, there is provided a silicon wafer processing method according to the present invention, wherein a first film that is soluble in an organic solvent is formed on a non-etched surface at least before the step of forming the first film. 3. The silicon wafer processing method according to claim 1, wherein a step of forming either or both of an electrode and a ceramic thin film is provided on the etched surface.
[0012]
According to a fourth aspect of the present invention, there is provided a silicon wafer processing method of the present invention, wherein a second film made of a resin resistant to a strong base and hydrofluoric acid is formed on at least the first film formed on the entire non-etched surface. The step of forming the second film is characterized in that the second film is also formed on at least part of the side surface of the silicon wafer, or at least part of the side surface and part of the etched surface. 4. A silicon wafer processing method according to any one of 3 above.
[0013]
The silicon wafer processing method of the present invention according to claim 5 is the silicon wafer processing method according to any one of claims 1 to 4, wherein the first film is a resist.
[0014]
Further, in the silicon wafer processing method of the present invention according to claim 6, in addition to the second film being resistant to a strong base and hydrofluoric acid, the second film is soluble, peelable or swellable in an organic solvent. The silicon wafer processing method according to any one of claims 1 to 5, wherein the silicon wafer processing method is characterized in that the resin has a resin.
[0015]
As described above, according to the present invention, the first film is made soluble in an organic solvent, and the second film is resistant to a strong base, thereby damaging the device or the silicon wafer. In addition, desired etching and removal of the second film as the protective film can be performed. Further, by making the second film resistant to hydrofluoric acid, an element or silicon wafer made of hydrofluoric acid used for removing a minute silicon oxide film naturally formed on the etched portion of the silicon wafer. It will also be possible to prevent damage.
[0016]
Etching of the backside of the silicon wafer after element formation results in damage to the silicon wafer due to a decrease in mechanical strength, damage due to thermal distortion of the silicon wafer due to heating to about 500 ° C. or more during ceramic thin film formation, etc. The occurrence of damage can be prevented.
[0017]
In the step of forming the second film resistant to strong base and hydrofluoric acid on the first film, the second film is formed on at least a part of the side surface of the silicon wafer or at least a part of the side surface. In addition, by forming also on a part of the etched surface, it is possible to almost certainly prevent a problem that the part other than the etched part is undesirably etched.
[0018]
Moreover, the effect of being easily dissolved in an organic solvent can be easily obtained by using the first film as a resist.
[0019]
In addition to being resistant to strong bases and hydrofluoric acid, the second film is made of a resin that is soluble, peelable, or swellable in an organic solvent. Further, it can be easily removed.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a silicon wafer processing method according to an embodiment of the present invention will be described with reference to FIGS. The first half of the embodiment will be described with reference to FIGS. 1 and 2, and the second half of the embodiment will be described with reference to FIGS. 3 and 4. FIG.
FIGS. 1A to 1D are longitudinal sectional views showing steps of forming the silicon oxide film 10 and the element 3 on the silicon wafer 1. FIG. 2 is a perspective view showing the silicon wafer 1 in which the element 3 is formed on the surface 11. 1 is a longitudinal sectional view taken along the line AA ′ in FIG.
[0021]
As shown in FIG. 1A, first, silicon oxide films 10 are respectively formed on the entire surface 11 and back surface 12 of the silicon wafer 1. As a forming method, for example, a method of heating the silicon wafer 1 and oxidizing the front surface 11 and the back surface 12 of the silicon wafer is used.
[0022]
Subsequently, as shown in FIGS. 1B and 2, an element 3 including an upper electrode 31, a lower electrode 33, and a ceramic thin film 32 is formed on the silicon oxide film 10 on the silicon wafer surface 11. Hereinafter, the structure of the element 3 will be described.
[0023]
The lower electrode 33 includes, for example, an electrode pad portion 33a formed in a substantially rectangular shape at one end portion (left side in FIGS. 1 and 2) of the silicon wafer 1, and from the electrode pad portion 33a toward the center of the silicon wafer 1. The wiring portion 33b extends and an element forming portion (not shown) connected to the wiring portion 33b and formed in a substantially rectangular shape near the center of the silicon wafer 1. The lower electrode 33 has a laminated structure in which, for example, the first layer is made of a Ti film and the second layer is made of a Pt film.
[0024]
A ceramic thin film 32 is formed in a substantially rectangular shape so as to cover an element forming portion of the lower electrode 33 and a part of the wiring portion 33b. As a ceramic material, if a piezoelectric material such as PZT or ZnO is used, it becomes a resonator, and if a pyroelectric material such as PbTiO ₃ is used, it becomes an infrared sensor. In this embodiment, a resonator using PZT is taken as an example. I will explain.
[0025]
The upper electrode 31 is formed, for example, at the other end of the silicon wafer 1 (on the right side in FIGS. 1 and 2) in a substantially rectangular shape, and from the electrode pad 31a to the center of the silicon wafer 1. A wiring portion 31b extending toward the upper surface of the ceramic thin film 32, a part of which is in contact with the ceramic thin film 32 on the upper surface of the ceramic thin film 32, and the center of the silicon wafer 1 on the upper surface of the ceramic thin film 32 It is composed of an element forming portion 31c formed in the vicinity of a substantially rectangular shape. The upper electrode 31 has a laminated structure in which, for example, the first layer is made of a Ti film and the second layer is made of an Au film.
[0026]
As a method for forming the upper electrode 31, the lower electrode 33, and the ceramic thin film 32 described above, a free method can be selected from known methods such as a dry process such as sputtering, vapor deposition, and CVD, or a wet process such as sol-gel plating. It is.
[0027]
Subsequently, as shown in FIG. 1C, a substance resistant to hydrofluoric acid, for example, a commercially available resist 2 is formed on the front surface 11 of the silicon wafer 1 and the back surface 12 of the silicon wafer 1 in the thickness direction. It is applied to a portion other than a portion to be etched thinly (hereinafter referred to as an etching processed portion 5).
[0028]
Thereafter, the silicon wafer 1 is immersed in a hydrofluoric acid solution. By doing so, as shown in FIG. 1D, the silicon oxide film 10 of the etched portion 5 is removed by hydrofluoric acid, and the portion where the resist 2 is applied is protected by the resist. Thereafter, the resist 2 is removed with a commercially available stripping solution.
[0029]
By performing the above-described steps, the silicon oxide film 10 that functions as a protective film can be formed on the back surface 12 of the silicon wafer 1 with respect to the portion that is not etched, and the silicon is exposed in the etched portion 5. Therefore, only that portion can be reliably etched. In the case where the entire back surface 12 of the silicon wafer 1 is etched and thinned, the silicon oxide film 10 forming step as described above is not necessary.
[0030]
The portions other than the etched portion 5 on the back surface 12 of the silicon wafer 1 and the portions other than the elements on the front surface 11 of the silicon wafer 1 are protected from unwanted etching by providing the silicon oxide film 10. The element 3 formed on the surface is not protected and may be damaged by the silicon etching solution. In order to prevent the occurrence of this damage, it is necessary to provide a protective film resistant to strong base and hydrofluoric acid on the surface 11 including the element 3 of the silicon wafer 1. In the silicon wafer processing method of the present invention, a paste-like resin resistant to strong base and hydrofluoric acid is used as a protective film (the reason why the resin is resistant to hydrofluoric acid will be described later). By using a paste-like resin as the protective film, the film thickness can be increased to about 0.5 mm, and damage to the element 3 can be reliably prevented.
[0031]
If a protective film made of a paste-like resin resistant to strong base and hydrofluoric acid is formed directly on the silicon wafer 1, the silicon wafer 1 is damaged when removed. Therefore, a film soluble in an organic solvent is provided below the protective film, and the silicon wafer 1 is immersed in the organic solvent to remove the film soluble in the organic solvent, thereby removing the protective film. I made it easy.
[0032]
FIGS. 3A to 3C are longitudinal sectional views showing the etching process of the silicon wafer 1 after the silicon oxide film 10 is removed from the etching processed portion 5.
[0033]
After removing the silicon oxide film 10 in the etched portion 5, as shown in FIG. 3A, the portions other than the etched portion 5 on the front surface 11 and the back surface 12 of the silicon wafer 1, that is, the silicon oxide film in this embodiment. A first film 21 that is soluble in an organic solvent is formed on 10 and the element 3. As the material of the first film 21, it is preferable to use a resist that is relatively easily available, but is not particularly limited. In this example, the first film made of resist was formed to 2 μm on the silicon oxide film 10 and the element 3.
[0034]
Subsequently, a resin that is resistant to strong base and hydrofluoric acid is applied to at least the first film 21 formed on the surface 11 of the silicon wafer 1 with a spin coater, a spatula, or the like to form a second protective film. The film 22 is formed. As shown in FIG. 2B, the second film 22 is preferably provided so as to cover the side surface of the silicon wafer 1 and the end portion of the back surface 12 in order to further strengthen the protective force. In this example, the second film 22 was formed to have a thickness of 0.5 mm. Thereafter, after air drying for 4 hours, heat treatment was performed at 100 ° C. for 30 minutes to cure the second film 22.
[0035]
Subsequently, the minute silicon oxide film naturally formed on the etching processed portion 5 of the silicon wafer 1 in the curing process of the second film 22 is removed by dipping in a hydrofluoric acid solution for a short time. At this time, since the second film 22 is a resin resistant to hydrofluoric acid, the second film 22 is not affected by dissolution and the immersion time is short. There is no influence on the silicon oxide film 10 formed on the back surface 12 of the substrate.
[0036]
Subsequently, the etching processing part 5 of the silicon wafer 1 is etched. This etching is performed by heating the TMAH aqueous solution to 90 ° C. and immersing the silicon wafer 1 in the TMAH aqueous solution. The etching time is adjusted according to the wafer thickness, the dimension of the diaphragm, and the remaining silicon wafer (silicon oxide film) thickness. Through the above steps, the diaphragm structure D of the silicon wafer 1 shown in FIG.
[0037]
FIG. 4 is a completed longitudinal sectional view of a resonator using the silicon wafer 1.
The silicon wafer 1 after the formation of the diaphragm structure D is immersed in acetone as an organic solvent and left for 8 hours. As a result, the resist which is the first film 21 is dissolved, and the second film 22 can be easily removed without damaging the element 3 or the silicon wafer 1. In order to more efficiently remove the second film, a resin material that is soluble, peelable, or swellable in an organic solvent is used, or a certain elasticity after curing. It is more preferable to use a resin having a. Furthermore, if the part formed in the back surface 12 and side surface of the silicon wafer 1 of the 2nd film | membrane 22 is opened before immersing in an organic solvent, immersion time can be shortened.
As described above, a resonator using the silicon wafer 1 as shown in FIG. 4 could be produced.
[0038]
【The invention's effect】
As described above, according to the present invention, the first film is made soluble in an organic solvent, and the second film is resistant to a strong base, thereby damaging the device or the silicon wafer. In addition, desired etching and removal of the second film as the protective film can be performed. Further, by making the second film resistant to hydrofluoric acid, an element or silicon wafer made of hydrofluoric acid used for removing a minute silicon oxide film naturally formed on the etched portion of the silicon wafer. It will also be possible to prevent damage.
[0039]
Also, etching of the backside of the substrate after element formation causes damage to the silicon wafer due to a decrease in mechanical strength, and damage due to thermal distortion of the silicon wafer due to heating to about 500 ° C. or more during ceramic thin film formation. Damage can be prevented from occurring.
[0040]
In the step of forming the second film resistant to strong base and hydrofluoric acid on the first film, the second film is formed on at least a part of the side surface of the silicon wafer or at least a part of the side surface. Further, by forming it on a part of the etched surface, it is possible to almost certainly prevent a problem that the non-etched surface is undesirably etched.
[0041]
Moreover, the effect of being easily dissolved in an organic solvent can be easily obtained by using the first film as a resist.
[0042]
In addition to being resistant to strong bases and hydrofluoric acid, the second film is made of a resin that is soluble, peelable, or swellable in an organic solvent. Further, it can be easily removed.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a process of forming a silicon oxide film 10 and an element 3 on a silicon wafer 1 of the present embodiment. FIG. 2 shows the silicon wafer 1 of the present embodiment in which an element 3 is formed on a surface 11. FIG. 3 is a longitudinal sectional view of the silicon wafer 1 of the present embodiment showing the etching process of the silicon wafer 1 after the removal of the silicon oxide film 10 in the etching processing section 5. FIG. 4 is a vertical sectional view of the silicon wafer 1 of the present embodiment. Completion longitudinal cross-sectional view of a resonator using a laser [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Silicon wafer 3 Element 5 Etching process part 10 Silicon oxide film 21 1st film | membrane 22 2nd film | membrane

Claims (6)

One of the main surfaces is an etched surface, the other main surface is a non-etched surface, and a part or all of the etched surface is an etched portion. A silicon wafer processing method comprising:
Forming a first film that is soluble in an organic solvent on at least the entire surface of the non-etched surface;
Forming a second film made of a resin that is resistant to strong base and hydrofluoric acid and protects the silicon wafer from etching, on at least the first film;
A step of immersing a silicon wafer in a silicon etchant and etching the etched portion;
Immersing the silicon wafer in an organic solvent to remove the first film;
Removing the first film and removing the second film that has been easily peeled;
The silicon wafer processing method characterized by including at least. A silicon wafer that thins the silicon wafer by etching the etched portion of the silicon wafer, where one main surface is an etched surface, the other main surface is a non-etched surface, and part of the etched surface is an etched portion. A processing method,
Forming a silicon oxide film on both main surfaces of the silicon wafer by heating the silicon wafer;
Providing a hydrofluoric acid resistant film made of a material resistant to hydrofluoric acid on the silicon oxide film excluding the etched portion;
A step of immersing the silicon wafer in a hydrofluoric acid solution and removing the silicon oxide film formed on the etched portion;
A step of removing the hydrofluoric acid resistant film by immersing in a stripping solution;
Forming a first film that is soluble in an organic solvent over the whole or part of the non-etched surface;
Forming a second film made of a resin that is resistant to strong base and hydrofluoric acid and protects the silicon wafer from etching, on at least the first film;
A step of immersing a silicon wafer in a silicon etchant and etching the etched portion;
Immersing the silicon wafer in an organic solvent to remove the first film;
Removing the first film and removing the second film that has been easily peeled;
The silicon wafer processing method characterized by including at least. Prior to the step of forming the first film soluble in the organic solvent on at least the entire surface of the non-etched surface, either or both of the electrode and the ceramic thin film are formed on the non-etched surface of the silicon wafer. The silicon wafer processing method according to claim 1, wherein a forming step is provided. In the step of forming the second film made of a resin resistant to strong base and hydrofluoric acid on the first film formed on the entire surface of at least the non-etched surface,
The second film is also formed on at least a part of the side surface of the silicon wafer, or at least a part of the side surface and a part of the etched surface. Silicon wafer processing method. The silicon wafer processing method according to claim 1, wherein the first film is a resist. The second film is a resin having any one of solubility, releasability, and swelling in an organic solvent in addition to resistance to a strong base and hydrofluoric acid. Item 6. The silicon wafer processing method according to any one of Items 5 to 6.

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