JP2004047690A - Forming method of wiring and method for manufacturing surface acoustic wave equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method of wiring in surface acoustic wave equipment with high electric power resistance in the wiring forming method by a lift-off method. <P>SOLUTION: A substrate is processed by using etchant containing surface active agent. Thus, a damage layer on a surface of the substrate can be removed while peeling of resist is prevented. Wiring in surface acoustic wave equipment with high electric power resistance can be formed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming wiring of an electronic component, and particularly to a method for forming an electrode of a surface acoustic wave device.
[0002]
[Prior art]
A lift-off method is known as a method for forming wiring of an electronic component. In the lift-off method, a metal film is formed after applying a resist on a substrate, patterning the resist by exposing and developing, but when immersing the resist in a developing solution to remove a part of the resist, a resist is applied to the developing solution. The dissolved organic matter may adhere to the substrate surface and remain. Reactive ion etching (RIE) may be performed in order to remove the organic matter.
[0003]
Further, there is a wiring forming method by a lift-off method disclosed in Japanese Patent Application Laid-Open No. 2002-64054. In this method, a first resist layer having high solubility in a stripping solution such as an organic solvent, a second resist layer having high absorbance to an exposure wavelength and having heat resistance, and a resistance to dry etching are provided on a substrate. A third resist layer having high heat resistance is formed in order, and exposure and development are performed on the third resist layer to form an opening, and the first and second resist layers are formed through the opening. A resist pattern is formed by removal by dry etching, and a metal film to be a wiring is formed on the substrate via the resist pattern.
[0004]
[Problems to be solved by the invention]
In the above two techniques, a dry etching step is included before forming a metal film to be a wiring. Therefore, the surface of the substrate is damaged by the dry etching process, and the damage affects the quality of the metal film formed on the substrate. In particular, when a metal film accompanied by epitaxial growth is formed on a single crystal substrate, damage to the substrate surface significantly affects the film quality and leads to deterioration of characteristics. That is, in epitaxial growth, the metal film grows with the same crystal structure as the crystal structure of the substrate surface. Therefore, if the crystallinity of the substrate surface is disturbed by dry etching, the crystal structure of the metal film is significantly affected. It will be lost. For example, in the method of forming an electrode of a surface acoustic wave device disclosed in Japanese Patent Application Laid-Open No. Hei 7-162255, an improvement in power durability and the like is achieved by forming an Al film serving as an electrode by epitaxial growth. In order to form such an electrode, it is necessary to remove the damaged layer on the substrate surface.
[0005]
In order to solve this problem, there is a method of removing the damaged layer on the substrate surface by wet etching, but at this time, the etchant may enter the interface between the substrate and the resist, and peeling of the resist from the substrate may occur. is there.
[0006]
Therefore, there is a need for a method of removing a damaged layer on the substrate surface while preventing the resist from peeling off the substrate.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the method of forming a wiring according to claim 1 includes a step of applying a resist on a substrate, a step of patterning the resist, and the step of removing an organic residue on the substrate. A step of dry-etching the substrate, a step of treating the surface of the substrate with an etchant containing a surfactant, a step of forming a metal film on the substrate, and the step of depositing the resist on the resist Lifting off together with the metal film.
[0008]
By treating the surface of the substrate with an etchant containing a surfactant, it is possible to prevent the resist from peeling off from the substrate and to remove a damaged layer on the substrate surface generated in a dry etching step for removing organic residue. it can.
[0009]
3. The method of forming a wiring according to claim 2, wherein at least two or more resist layers are formed on the substrate, and among the resists, a top resist is patterned by photolithography; Removing the resist other than the uppermost resist by dry etching using the resist as a mask, treating the surface of the substrate with an etchant containing a surfactant, and forming a metal film on the substrate And lifting off the resist together with the metal film on the resist.
[0010]
By treating the surface of the substrate with an etchant containing a surfactant, it is possible to prevent a resist from peeling off from the substrate and remove a damaged layer on the substrate surface generated in a dry etching step for patterning the resist. .
[0011]
According to a third aspect of the present invention, there is provided a method for manufacturing a surface acoustic wave device, wherein a wiring is formed by the wiring forming method according to the first or second aspect.
[0012]
The electrodes of the surface acoustic wave device are repeatedly applied with a stress by the propagation of the surface acoustic wave, so that stress migration easily occurs and the power durability is poor. Therefore, according to the present invention, since the damage layer on the surface of the substrate can be removed while preventing the resist from being stripped, an electrode having high power durability can be formed, and the power durability of the surface acoustic wave device is improved. .
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1) A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows steps in this embodiment.
[0014]
An organic material having high solubility in organic solvents and good heat resistance, such as polydimethylglutarimide (PMGI), is applied on a substrate 10 made of a single crystal of LiNbO ₃ by spin coating and baked, and the first resist is baked. The layer 21 is formed. Next, a material having high absorbance to the exposure wavelength is applied by spin coating and baked to form a second resist layer 22. Here, since the exposure wavelength is 365 nm, XHRi-16 manufactured by BrewerScience is preferred. Next, an organic material having high resistance to reactive ion etching and high heat resistance, such as Fi-SP2 manufactured by Fujifilm Arch Co., is applied by spin coating and baked to form a third resist layer 23. . The resist having the three-layer structure shown in FIG. 1A formed by the above method is exposed to i-line (wavelength 365 nm) of a high-pressure mercury lamp and developed, and the third resist is formed as shown in FIG. Is patterned.
[0015]
Next, a part of the first resist layer 21 and the second resist layer 22 is removed by reactive ion etching using oxygen plasma, and patterning is performed as shown in FIG. At this time, since the third resist layer 23 has high resistance to reactive ion etching, the etching rate is lower than that of the first and second resist layers 21 and 22, so that the cross section of the resist has an inversely tapered shape. Due to this reactive ion etching, a damaged layer having disordered crystallinity is formed on the surface of the substrate 10.
[0016]
Next, the substrate 10 is immersed in a surfactant-containing BHF (buffered hydrofluoric acid) 1200BHF-SE manufactured by Morita Chemical Co., Ltd. to remove a damaged layer generated on the surface of the substrate 10 by reactive ion etching. The time for immersing the substrate 10 was 300 seconds.
[0017]
By using an etchant containing a surfactant, the resist can be prevented from peeling off the substrate 10 during removal of the damaged layer. This is because the surface tension is reduced by the effect of the surfactant, and the acid contained in the etchant is prevented from entering the interface between the substrate 10 and the first resist 21 by the capillary action.
[0018]
The surface tension of the surfactant-containing BHF used in this example is 36 dyne / cm at 20 ° C. On the other hand, the surface tension of 1200 BHF manufactured by Morita Chemical Co., which is the same concentration of BHF containing no surfactant, is 92 dyne / cm at 20 ° C. The surfactant-containing etchant is not limited to the above, and any other etchant may be used, but the surface tension is desirably as low as the above.
[0019]
In order to confirm the effect of adding a surfactant to prevent resist peeling, an experiment was conducted to examine the correlation between the time during which the substrate 10 was immersed in an etchant and the resist peeling. The result of this experiment is shown in FIG. In the figure, “○” indicates that resist peeling did not occur, and “x” indicates that resist peeling occurred. The time is expressed as a ratio with respect to the minimum time required to remove the damaged layer from the surface of the substrate 10 as 1.0. When the etchant containing the surfactant was used, the resist was not stripped even when the time was 2.0, whereas when the etchant without the surfactant was used, the time was 0.3. Even in this case, the resist is partially removed.
[0020]
Next, as shown in FIG. 1D, a Ti film 31 having a thickness of 10 nm is formed on the substrate 10 by vapor deposition, and an Al film 32 having a thickness of 190 nm is further formed by vapor deposition. Thereafter, the substrate 10 is immersed in an organic solvent, and the resist is lifted off from the substrate 10 together with the metal film on the resist to obtain a desired wiring as shown in FIG.
[0021]
By the reactive ion etching, a damaged layer whose crystallinity is disturbed is formed on the surface of the substrate 10, but by performing the surface treatment on the substrate 10, the surface of the substrate 10 is exposed to oxygen as shown in FIG. The atoms 41 are arranged at intervals of 0.297 nm. Next, the formed Ti film 42 is epitaxially grown as shown in FIG. 3B, and has a hexagonal close-packed structure with an atomic spacing of 0.292 nm. The Ti film 31 is formed to improve the crystallinity of the Al film 32. This is because the difference in atomic spacing between the oxygen atoms 41 and the Al atoms 43 is large, so that if the Al film 32 is formed directly on the substrate 10, it is difficult to perform epitaxial growth. Although only one atomic layer of Ti atoms 42 is shown in FIG. 3B, several to several hundred atomic layers are actually formed. Next, the formed Al film is epitaxially grown on the Ti film, and has a face-centered cubic structure with an atomic spacing of 0.286 nm. As a result, an Al film having a crystal structure having two kinds of crystal orientations, which are rotated by 180 degrees with each other, is formed depending on how the Al atoms 43 enter. That is, the Al film has a twin structure in which the line indicated by XY in FIG. 3C is a crystal grain boundary, that is, a twin plane.
[0022]
FIG. 4A shows an XRD pole figure of the Al film 32 formed according to this embodiment in order to confirm that the Al film 32 is a triaxially oriented film having a twin structure. Al belongs to a face-centered cubic structure crystallographically, and the diffraction of the (200) pole figure of single crystal Al is three-fold symmetric, but FIG. 4A shows a pole figure of six-fold symmetry, and the Al film It can be seen that 32 is a triaxially oriented film having a twin structure. On the other hand, FIG. 4B shows, as a comparative example, an XRD pole figure when the Ti film 31 and the Al film 32 are formed without removing the damaged layer. In this case, the pole figure has a ring shape, and it can be seen that the Al film 32 is a uniaxially oriented film.
[0023]
Since the mechanical strength of a metal is higher in a polycrystal than in a single crystal, by forming the Al film into a twin structure, plastic deformation is less likely to occur and power durability is improved.
[0024]
Generally, it is said that when a crystal grain boundary is present in an Al electrode, Al self-diffuses through the crystal grain boundary and defects called hillocks and voids grow, resulting in short-circuit between the electrodes and destruction of the electrodes. However, in the Al film 31 obtained according to the present invention, the crystal grain boundaries are smaller than one atomic interval, and self-diffusion through the crystal grain boundaries does not substantially occur. It does not cause characteristic deterioration.
[0025]
By forming the Al film 32 as a triaxially oriented film having a twin crystal structure, the effect of preventing the growth of hillocks and voids due to the self-diffusion of the atoms constituting the electrode through the crystal grain boundaries, and the high resistance to plastic deformation. An electrode having both power properties can be obtained.
[0026]
(Embodiment 2) Next, a second embodiment of the present invention will be described below with reference to the drawings. In this embodiment, the same parts as those in the first embodiment will not be described in detail. FIG. 5 shows the steps in this embodiment.
[0027]
First, as shown in FIG. 5A, a resist 24 is applied on a substrate 10 made of a single crystal of LiNbO ₃ . Next, as shown in FIG. 5B, the resist 24 is patterned by photolithography. At the time of development in the photolithography process, organic substances dissolved in the developer adhere to the substrate 10. If a metal film is formed in a state where an organic substance is adhered on the substrate 10, a metal film cannot be formed by epitaxial growth. Therefore, the substrate 10 is etched by reactive ion etching to remove the organic substance. At this time, a damaged layer whose crystallinity is disturbed is formed on the surface of the substrate 10 by the reactive ion etching.
[0028]
Next, the substrate is immersed in a surfactant-containing BHF (buffered hydrofluoric acid) 1200BHF-SE manufactured by Morita Chemical Co., Ltd. to remove a damaged layer generated on the surface of the substrate 10 by reactive ion etching. As described in detail in the first embodiment, the resist 24 can be prevented from peeling off from the substrate 10 by the effect of the surfactant.
[0029]
Next, as shown in FIG. 5C, a 10 nm thick Ti film 31 is formed on the substrate 10 by vapor deposition, and a 190 nm thick Al film 32 is further formed by vapor deposition. Thereafter, the substrate 10 is immersed in an organic solvent to lift off the resist 24 and the metal film on the resist 24 together from the substrate 10 to obtain a desired wiring as shown in FIG. As described in detail in the first embodiment, the Al film 32 is a triaxially oriented film having a twin structure and has high power durability.
[0030]
(Embodiment 3) Next, a method for manufacturing a surface acoustic wave device according to the present invention will be described. The surface acoustic wave device has a piezoelectric substrate such as LiNbO ₃ or LiTaO ₃ and wiring such as an IDT electrode formed on the substrate. This wiring is formed by the method of the first or second embodiment described above. By treating the surface of the substrate with an etchant containing a surfactant, the wiring becomes a triaxially oriented film having a twin structure, and a wiring with high power resistance can be obtained. Thus, a surface acoustic wave device having high power durability can be obtained.
[0031]
It is common to use Al having low electric resistivity and low specific gravity for the wiring of the surface acoustic wave device, particularly for the electrodes, but since stress is repeatedly applied by the propagation of the surface acoustic wave, stress migration is likely to occur. Poor power. Therefore, according to the present invention, since the damage layer on the surface of the substrate can be removed while preventing the resist from being stripped, an electrode having high power durability can be formed, and the power durability of the surface acoustic wave device is improved. .
[0032]
【The invention's effect】
As described above, according to the wiring forming method of the present invention, by treating the surface of the substrate with an etchant containing a surfactant, while preventing the resist formed on the substrate from peeling from the substrate, The damaged layer generated by the dry etching can be removed. By removing the damaged layer on the substrate surface, the quality of the metal film formed on the substrate can be improved, and the effect is particularly remarkable in the case of forming a metal film accompanied by epitaxial growth.
[0033]
Further, when the surface of the substrate is treated according to the present invention, a triaxially oriented film having a twin structure can be formed on the substrate as described above, and a wiring having high power resistance due to the difficulty of plastic deformation. Can be formed.
[0034]
According to the surface acoustic wave device manufacturing method of the present invention, by forming the wiring after treating the surface of the substrate with an etchant containing a surfactant, it is possible to obtain a wiring having high power resistance, The power durability of the surface acoustic wave device is improved.
[Brief description of the drawings]
FIG.
FIG. 4 is a process chart illustrating a first embodiment of the present invention.
FIG. 2
FIG. 9 is a diagram showing the results of an experiment for examining the relationship between the time during which a substrate is immersed in an etchant and the removal of resist.
FIG. 3
FIG. 3 is a plan view showing an atomic arrangement on the surface of a substrate, a Ti film, and an Al film in the present invention.
FIG. 4
FIG. 4 is an XRD pole figure of an Al film.
FIG. 5
FIG. 6 is a process diagram illustrating a second embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 10 substrate 21 first resist layer 22 second resist layer 23 third resist layer 24 resist 31 Ti film 32 Al film 41 oxygen atom 42 Ti atom 43 Al atom

Claims (3)

A step of applying a resist on the substrate,
Patterning the resist,
Dry etching the substrate to remove organic residues on the substrate,
Treating the surface of the substrate with an etchant comprising a surfactant,
Forming a metal film on the substrate,
Lifting off the resist together with the metal film overlying the resist. Forming at least two or more layers of resist on the substrate, and patterning the uppermost resist of the resist by photolithography;
Removing the resist other than the uppermost resist by dry etching using the uppermost resist as a mask,
Treating the surface of the substrate with an etchant comprising a surfactant,
Forming a metal film on the substrate,
Lifting off the resist together with the metal film overlying the resist. A method for manufacturing a surface acoustic wave device, comprising: forming a wiring by the wiring forming method according to claim 1.

Images