Patent Grant
6998286
1. Field of the Invention
This invention relates a thin film-structure and a method for producing the same, and more particularly the same structure and the same method suitable for parts constituting micro machines such as a micro actuator, cats, various sensors such as a micro sensor, various probes such as a sensor for a scanning probe-microscope, etc.
2. Description of the Prior Art
Micro machines, various sensors, various probes, etc. are needed to detect outward powers from a substrate surface, various proximity effects in a substrate surface, flows of liquids, voltages of other electronic circuits. Thus, thin film-structures, made by three-dimensionally deforming plane structures such as beams composed of various thin films through applied micro machining of thin film-forming techniques and micro processing techniques in manufacturing semiconductors, have been used.
In the past, a thin film-structure was produced as follows:
In producing the thin film structure by taking advantage of the above bimorph effect (the above (1)), the thin film structure has had layers with different thermal expansion coefficient after its production. Thus, on account of temperature change in using, the shape of the thin film structure changes with time through the bimorph effect in nearby room temperature.
In producing the thin film structure by heating and deforming the polysilicon (the above (2)), the thin film structure has difficulty having a desired strength and elastic limit, etc. because a material for it is limited to the polysilicon. Moreover, the plane structure requires to be held by a microprobe, which results in degradation of its productivity.
In producing the thin film structure by taking advantage of the remaining stresses in film-forming (the above (3)), its reproducibility is degraded and its shape change with time due to the change with time of the remaining stresses.
It is an object of the present invention to provide a thin film-structure having good productivity, reproducibility and good shape-stability after its production and a method for producing the same.
This invention relates to a thin film-structure composed of a three-dimensional deformed thin film made of an amorphous material having an supercooled liquid phase region.
This invention also relates to a method for producing a thin film-structure comprising the steps of:
To iron out the above problems, this inventors has been intensely studied to develop a new material constituting the thin film-structure and a method for producing it. At last, they have found a way to solve the above problems as follows:
The thin film-structure is formed of an amorphous material having an supercooled liquid phase region. First of all, a thin film is formed of the amorphous material and is heated to a temperature within the supercooled liquid phase region. Then, the thin film is deformed to a given shape at the temperature with the supercooled liquid phase region.
That is, when the thin film made of the amorphous material having the supercooled liquid phase region is heated, it exhibits glass-transition phenomenon. Just then, the once solid and high rigid thin film becomes semisolid (supercooled liquid) and becomes in viscous flow of a viscosity of 108–1013 Pa·S. Thus, the thin film can be deformed through its weight as well as force from outside. Moreover, the thin film become soft at the region, so that it can be easily deformed to every kind of shape desired.
Then, when the thin film is cooled to a temperature below the super-cooled liquid phase region, it becomes solid again and exhibits large stiffness. Thus, the thin film formed in a desired shape at the temperature within the region becomes solid and has large stiffness with its shape being maintained.
This invention has been realized through this inventors' finding and attention of the above natures of the amorphous material having the supercooled liquid phase region and taking advantage of the natures.
According to the thin film-structure and the method for producing the same, only when the thin film made of the amorphous material is heated to a temperature within the supercooled liquid phase region, the thin film becomes in a viscous flow. Thus, the thin film can be easily deformed to form the thin film-structure. Since the thin film has a very large stiffness in a normal use nearby room temperature, the thin film dose not almost change in its shape.
Consequently, the thin film-structure having a high productivity, reproducibility and good shape-stability after its production can be provided.
Herein, the wording “supercooled liquid phase region” is a temperature region from a glass-transition temperature (Tg) to a crystallization-starting temperature (Tx).
The invention will be more particularly described with reference to the accompanying drawings:
The invention will be described in detail as follows, with reference to the above drawings.
The thin film-structure requires to be made of an amorphous material having an supercooled liquid phase region.
The amorphous material is not restricted if it can achieve the above object of the present invention. As the amorphous material is exemplified an oxidic glass (SiO2, Pyrex glass, etc.) or a metallic glass made of a chalcogenide semiconductor (As—S, Si—As—Te, etc.), some amorphous alloy (Zr—Cu—Al, Pd—Cu—Si, etc.) or the like.
The amorphous material preferably has a glass-transition temperature of 200–600° C. in its supercooled liquid phase region, more preferably 250–400° C. The lower glass-transition temperature of the amorphous material enables the heating step of the thin film made of it to be simplified. Moreover, it can vary materials of a substrate on which the thin film is formed and of a jig to hold a substrate. Generally, the amorphous material has viscosity of 1011–1013 Pa·S at nearby its glass-transition temperature. Therefore, the thin film made of the above amorphous material is prevented from being deformed excessively and being destroyed due to its large deformation during short time as its viscosity falls down too low.
The amorphous material has a very large stiffness at nearby room temperature. Thus, the thin film deformed in the supercooled liquid phase region does not almost change its shape in use. Consequently, the thin film-structure having an excellent shape-stability can be provided.
The supercooled liquid phase region preferably has a temperature width more than 20° C. The relatively large temperature width enables the heating step of the thin film to be simplified. Moreover, it can reduce influence due to the temperature fluctuation in the heating.
Concretely, Zr66Cu39Al, Pd76Cu6Si18, boron oxide etc. are exemplified as the amorphous material.
The thin film-structure of the present invention requires to be produced by heating the thin film made of like the above amorphous material to a temperature within its supercooled liquid phase region. The heating of the thin film may be carried out by a well known means such as infrared heating, inductive heating, resistive heating.
Besides, the thin film-structure of the present invention requires to be produced by deforming the thin film into a given shape with the thin film being maintained at a temperature within the supercooled liquid phase region after the thin film is heated to the above temperature.
The deforming of the thin film may be carried out by applying mechanical external force, electrostatic external force, magnetic external force for the thin film or taking advantage of the bimorph effect or the weight of the thin film.
Each method is explained hereinafter.
(A Method to Deform the Thin Film Through Its Weight)
Normally, the above thin film having dimension of μm order does not almost change in its shape. However, when it is heated to a temperature within its supercooled liquid phase region, it easily change in its shape through its weight. Moreover, the thin film does not become in a viscous flow at a temperature below the region, it does not almost change. Thus, the deformation degree of the thin film depends upon its viscosity and its heat-holding time in the region. That is, as the viscosity is small and the heat-holding time is long, the deformation degree rises up.
Furthermore, the thin film may be processed in beam-like shape by etching or the like it, and a wide portion or a bump-like protuberance may be formed on the tip of the thin film. It can increase the weight of the tip and thereby increase the deformation degree of the thin film.
(A Method to Deform the Thin Film Through Mechanical External Force)
In this case, the thin film is deformed by applying external force for it by using a micro pin before heating it to a temperature within its supercooled liquid phase region, and during the heating, the external force is maintained. When the thin film is heated to the temperature on that condition, it softens and generates permanent strain therein to relax its stress due to the external force. The permanent strain corresponds to the deformation degrees of the thin film.
In using an appropriate micro pin-driving machine such as a micro manipulator, the thin film may be directly deformed during the heat-holding through the micro pin attached to the machine after it heated to the temperature of the supercooled liquid phase region.
(A Method to Deform the Thin Film Through Electrostatic External Force)
If the thin film is made of a conductive amorphous material having an supercooled liquid phase region such as Zr66Cu33Al, an opposite electrode having an insulated layer is formed opposing to the thin film. Then, an external power supply is connected between the thin film and the opposite electrode and the voltage from the power supply is supplied therebetween. Just then, an electrostatic field is generated and electrostatic force is generated therebetween. The thin film in viscous flow, heated to a temperature within its supercooled liquid phase region, is easily deformed into a given shape by the attraction or repulsion of the electrostatic force.
If the thin film is made of a nonconductor such as an oxidic glass, an electrode layer made of conductive material such as Au is formed nearby the thin film by a well known film-forming method such as sputtering. Then, an outer power supply is connected between the electrode layer and the opposite electrode and the voltage from the power supply is supplied therebetween. Consequently, the thin film maintained in the supercooled liquid phase region is deformed through the electrostatic force generated therebetween as above-mentioned.
The deformation degree of the thin film can be controlled by adjusting the gap between the thin film and the opposite electrode, the supplied voltage, the heating temperature and the heating time.
The electrostatic force may be generated before or after heating the thin film.
(A Method to Deform the Thin Film Through Magnetic External Force)
If the thin film is deformed through magnetic external force, a magnetic layer is formed nearby the thin film. Then, an opposite magnet such as a permanent magnet or an electromagnet is installed in opposition to the magnetic layer. The thin film is deformed through the attraction or the repulsion of the magnetic force generated between the magnetic layer and the opposite magnet.
If the thin film is deformed through such a magnetic external force, the magnetic material of which the magnetic layer is made requires to have a larger Curie temperature than the glass-transition temperature of the thin film having an supercooled liquid phase region. Thereby, when the thin film is heated to a temperature within its supercooled liquid phase region, the magnetic layer can maintain its magnetism, so that the thin film can be deformed.
The deformation degree of the thin film can be controlled by adjusting the gap between the thin film and the above magnetic, the magnetic flux, the heating temperature, or the heating time.
In this method, the magnetic material constituting the magnetic layer preferably has a Curie temperature within 210–1200° C., more preferably 350–1150° C. Thereby, when the thin film is heated to the temperature with the supercooled liquid phase region, it can be easily deformed into a given shape through only the magnetic external force determined by the gap or the magnetic flux since it has a sufficiently large magnetization.
Fe, Ni, Co, Ni3Fe, etc. may be preferably used as the magnetic material.
(A Method to Deform the Thin Film Through its Bimorph Effect)
For deforming the thin film through its bimorph effect, a subsidiary layer having a difficult thermal expansion coefficient or internal stress from the thin film is formed nearby the thin film. When the thin film is heated to a temperature within its supercooled liquid phase region, a stress occurs at the interface between the thin film and the subsidiary layer. Just then, the thin film is deformed through the stress.
Concretely, the subsidiary layer nearby the thin film may be formed directly of a material having a different thermal expansion coefficient from the thin film. Moreover, it may be composed of an internal stress-layer formed by adjusting film-forming conditions such as a pressure of sputtering atmosphere or a mixed layer of the materials of a substrate and the thin film.
In the former, the material of the subsidiary layer is requires to have a thermal resistance to stand the heating to a temperature within the supercooled liquid phase region of the amorphous material of the thin film. Concretely, the material preferably has a thermal expansion coefficient of not more than 5×10−6 or 15×10−6–40×10−6 at a temperature over 200° C. As the material, SiO2, Si3N4, Cr, Ni, Al are exemplified.
The internal stress-layer preferably has an compressive or tensile stress of which absolute value is 1 MPa to 3 GPa, more preferably 10 MPa to 100 MPa. It may be composed of a Cr-layer formed by DC sputtering under an Ar atmosphere-pressure of 0.3 Pa and a sputtering voltage of 500V.
In this case, if the subsidiary layer is formed too thick, the shape of the thin film-structure often change with time due to its bimorph effect near room temperature, as above-mentioned. Thus, the subsidiary is preferably thinner. The thickness of the subsidiary layer is determined depending upon Young's modulus of itself and the thin film. If both have similar Young's modulus, the subsidiary layer preferably has a thickness of not more than one-hundredth of the thin film, more preferably has a thickness of 10–200 nm.
Moreover, if there is a difference in etching resistance between the subsidiary layer and the thin film having its supercooled liquid phase region, the subsidiary layer may be removed through an etchant not to etch the thin film and the substrate. Thereby, the shape of the thin film-structure does not change with time since its bimorph effect near room temperature is prevented.
The mixed layer constituting the subsidiary layer may be formed as follows:
First of all, the substrate is counter-sputtered by controlling sputtering conditions such as an atmosphere pressure and a sputtering output power during forming process of the thin film through sputtering. Just then, particles constituting the substrate are incorporated into the thin film to form the mixed layer.
In this case, too, if the mixed layer is formed too thick for the thin film, the shape of the thin film-structure often change with time through its bimorph effect near room temperature. Thus, the thickness of the mixed layer is preferably restricted within a given value, as above-mentioned.
In thin method, the deformation degree of the thin film is determined by the Young's modulus, the thickness, and a difference in thermal expansion coefficients of the thin film and the subsidiary layer, the heating temperature and heating time.
After the thin film is deformed to form the thin film-structure, it is cooled down to room temperature by voluntary cooling such as heat emission, introducing a cooling gas, contacting with a cooling board or the like. In deforming through the magnetic external force, the thin film may be cooled down by contacting with water-cooled electromagnet.
The thin film may be formed of an amorphous material having an supercooled liquid phase region by a sputtering method, a physical vapor deposition method such as a vacuum vapor deposition, a chemical vapor deposition method such as a CVD method.
The thin film constituting the thin film-structure of the present invention is not limited in its thickness, but may have any thickness depending upon the use of the thin film-structure. However, in applying the thin film-structure for various sensors or various probes, the thin film has a thickness of 1–20 μm, generally.
The thin film may be processed by wet-etching, dry-etching, lift-off, etc. to form a plane structure having a desired shape, in accordance with the use of the thin film-structure.
This invention is concretely described on the examples, with reference to the drawings.
In this example, the thin film made of an amorphous material having an supercooled liquid phase region was deformed through its weight.
A substrate 10 was composed of a single crystalline silicon wafer having a thickness of 200 μm and a crystal orientation <100>.
First of all, as shown in
Then, as shown in
Next, as shown in
The vacuum chamber 19 has a quartz glass-window 20, above which an infrared heater 21 is installed. The infrared heater 21 and the thermocouple 17 are connected to a thermoregulator 22 so that the thin film 14 can be heated to a determined temperature through the infrared heater 21 with the temperature of the thin film being directly monitored through the thermocouple 17. Since the cover 18 is made of Ti material which is active at a high temperature range, it can absorb the remaining oxygen during the heating and thereby prevent the thin film 14, being active at the high temperature range as well as the cover 18, from being oxidized. Moreover, it can average the heating irregularity of the infrared heater 21 and thereby the thin film 14 can be heated uniformly.
Based on the measurement of
As is apparent from
Although in this example, the thin film 14 was made of the Zr-based metallic glass, it may be of another metallic glass such as Pd76Cu6 Si18, an oxidic glass such as SiO2.
Moreover, instead of the paddle 12 as shown in
In this example and the examples shown in
In this example, the thin film made of an amorphous material having an supercooled liquid phase region was deformed by mechanical external force.
A substrate 40 was composed of a single crystalline silicon wafer having a thickness of 200 μm and a crystal orientation <100>.
As shown in
Then, the substrate 40 was etched by dipping it in a 40 wt %-K(OH) solution at 80° C. for 1.6 hours to form a pierced hole 44 reaching to the provisional layer 41.
Next, as shown in
Then, as shown in
Thereafter, the thin film 42 was cooled down to room temperature at a cooling rate of 10° C./min by voluntary cooling through controlling the heating degree and the heating equipment 47 and the jig 46 were taken off. Just then, as shown in
In this example, the thin film made of an amorphous material having an supercooled liquid phase region was deformed by electrostatic external force.
A substrate 50 was composed of a single crystalline silicon wafer having a thickness of 250 μm and a crystal orientation <100>. First of all, as shown in
Next, as shown in
Then, a protect layer (not shown) made of resist was formed on the backside surface 50B of the substrate 50 and thereafter the substrate 50 was etched by dipping it into a 40 wt %-K(OH) solution for two hours to form etch pit 54.
Then, as shown in
Then, a heater 62 was installed on the backside surface 50 of the substrate 50. The substrate 50 was heated to 560° C. at a heating rate 10° C./min and held at that temperature for two minutes. Herein, the boron oxide had a glass-transition temperature Tg of 553° C.
Thereafter, the substrate 50 was cooled down to room temperature at a cooling rate of 10° C./min by voluntary cooling through controlling the heater 62. As a result, a thin film-structure was obtained as shown in
As above mentioned, in thin example, between the substrate 50 and the electrode 59 for forming was supplied a relatively large voltage and was generated a relatively large electrostatic force. Accordingly, the thin film 52 was attracted to the electrode 59 for forming before heating it a temperature within its supercooled liquid phase region. However, when a relatively small voltage is supplied between the substrate 50 and the electrode 59 for forming, the thin film 52 is attracted to the electrode 59 to be able to form the thin film-structure 63 since it become in viscous flow by heating it to a temperature within its supercooled liquid phase region.
In this example, the thin film made of an amorphous material having an supercooled liquid phase region was deformed by magnetic external force.
A substrate 70 was composed of a single crystalline silicon wafer having a thickness of 250 μm and a crystal orientation <100>.
First of all, as shown in
Next, as shown in
Subsequently, as shown in
Next, as shown in
When the thin film 73 had a temperature of 425° C., a permanent magnetic 80 joined to a shaft 79 was approached to the magnetic layer 74 by operating a vertical driving system (not shown) along the shaft 79.
In thin case, the gap between the substrate 70 and the permanent magnetic 80 is determined based on data of a displacement sensor attached to the vertical driving system. In the polarity of the permanent magnetic 80, its part in the side of the thin film 73 was N pole and the other part in the opposite side was S pole. Moreover, for protecting the permanent magnetic 80 against heat, a cooling tube 81 is provided in it.
Herein, since the Co material had a Curie Temperature of 1131° C., its ferromagnetic did not diminish as it was heated to 425° C. as above-mentioned.
When the thin film 73 was heated to the above temperature, it was soften in its supercooled liquid phase region. Thus, it was deformed as the magnetic layer 74 was attracted to the permanent magnetic.
When the magnetic layer 74 was, as the deformation of the thin film 73 continues, attracted to the permanent magnetic 80, the thin film 73 was cooled and its deformation stopped at a temperature not more than 357° C. Thereby, a thin film-structure 82 was obtained as shown in
Herein, the magnetic layer 74 may be etched and removed by a solution of hydrochloric acid as needed after forming the thin film-structure 82.
In this example, the thin film made of an amorphous material having an supercooled liquid phase region was deformed by its bimorph effect.
A substrate 90 was composed of a single crystalline silicon wafer having a thickness of 200 μm and a crystal orientation <100>.
First of all, as shown in
Next, as shown in
Then, as shown in
Subsequently, as shown in
The assembly was heated to 425° C. at a heating rate of 10° C./min and a Cr-layer 98 was formed, by a sputtering method, in a thickness of about 0.1 μm on the one side-fixed thin film 95 as the assembly was heated to a temperature over 355° C. Herein, the metallic glass of Pd61Pt15Cu6Si18 composition had a glass-transition temperature (Tg) of 357° C., as above-mentioned.
When the thin film 95 was heated to a temperature over 357° C., forces to pull down the thin film 95, resulting from the compressive stress generated in the Cr-layer 98, acted on between the thin film 95 and the Cr-layer 98. As a result, the thin film 95 hung down toward the heater 97.
The heating was stopped at the same time when the Cr-layer 98 was finished and the assembly was cooled down to room temperature at a cooling rate of 10° C./min by emission cooling through controlling the heater 97.
When the thin film 95 was cooled down to a temperature below the supercooled liquid phase region of the metallic glass constituting the thin film 95, it stop deforming itself. Lastly, a thin film-structure 99 was obtained as shown in
The Cr-layer 98 may be etched and removed by a solution of hydrochloric acid as needed after forming the thin film-structure 99.
In this example, the thin film made of an amorphous material having an supercooled liquid phase region was deformed by its bimorph effect. However, different from Example 5, a mixed layer was formed of a material of a substrate and the amorphous material of the thin film. Then, the bimorph effect between the mixed layer and the thin film was taken advantage of.
A substrate 100 was composed of a single crystalline silicon wafer having a thickness of 200 μm and a crystal orientation <100>.
First of all, as shown in
Next, as shown in
Moreover, a protect layer 106 was formed in a thickness of about 1 μm on the backside surface 100B of the substrate 100 by spin-coating.
Then, as shown in
Subsequently, as shown in
Just then, the stress, resulting from the difference in thermal expansion coefficient between the mixed layer 105 and the thin film 104, occurred in their interface. The thermal expansion coefficient of the mixed layer 105 was smaller than that of the thin film 104, so that the thin film 104 had the compressive stress from the mixed layer 105 and was deformed downward.
As is apparent from
Although the present invention was described in detail with reference to the above examples, this invention is not limited to the above disclosure and every kind of variation and modification may be made without departing from the scope of the present invention.
The thin film-structure is formed of an amorphous material having an supercooled liquid phase region and takes advantage of the specific natures of the amorphous material below and within the supercooled liquid phase region. Thus, the thin film-structure having excellent shape-stability after its formation can be obtained under good productivity and good reproducibility.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11-126680 | May 1999 | JP | national |
This is a Continuation of application Ser. No. 09/556,795 filed Apr. 25, 2000 now U.S. Pat. No 6,759,281. The entire disclosure of the prior application is hereby incorporated by reference herein in its entirety.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5827343 | Engelke et al. | Oct 1998 | A |
| 5950704 | Johnson et al. | Sep 1999 | A |
| 5994159 | Aksyuk et al. | Nov 1999 | A |
| 6759261 | Shimokohbe et al. | Jul 2004 | B1 |
| Number | Date | Country |
|---|---|---|
| 0 762176 | Mar 1997 | EP |
| 0 783108 | Jul 1997 | EP |
| A-9-126833 | May 1997 | JP |
| A-9-237906 | Sep 1997 | JP |
| A-9234630 | Sep 1997 | JP |
| A-11-58244 | Mar 1999 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20040166664 A1 | Aug 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09556795 | Apr 2000 | US |
| Child | 10788337 | US |
