JP2923811B2 - How to make beams - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam having a displacement element formed using a semiconductor wafer, and more particularly to a beam having a probe at a free end of the beam for detecting a weak physical interaction such as a tunnel microscope. And a method for producing the same.

[0002]

2. Description of the Related Art Recently, a semiconductor pressure sensor using a semiconductor as a mechanical structure against the background of semiconductor process technology,
Mechanical and electrical elements (micromechanics devices) such as semiconductor acceleration sensors and microactuators have come into the spotlight.

[0003] The features of these devices are that they can provide small and high-precision mechanical mechanism parts, and furthermore, since a semiconductor wafer is used, the device and the electronic circuit can be integrated on one wafer. Further, by manufacturing based on a semiconductor process, improvement in productivity by batch processing of the semiconductor process can be expected. As an example of a beam having a displacement element that best represents the characteristics of the beam, an ST for micro-measurement proposed by Kuwait of Stanford University, etc.
M probe (IEEE MicroElectro M
technical Systems, pp188-
199, Feb. , 1990). FIG. 6 is a perspective view of the above-described STM probe. In this method, bimorph beams sandwiching ZnO 5 and 7 are used for electrodes 4, 6, and 8 as displacement elements on a silicon wafer, a probe 11 is disposed at the tip of the beam, and a tunnel current is read by an extraction electrode 12. . FIG. 7 shows a manufacturing method thereof. A part of the silicon nitride film on the back surface of the silicon wafer 1 on which the silicon nitride film 2 is formed on both sides is removed, and a silicon membrane is formed by anisotropic etching (aqueous KOH solution) using a difference in etching rate between crystal orientation planes. ((A) in FIG. 7). Next, Al electrodes 4, 6, 8 and ZnO thin films 5, 6 are sequentially laminated on the surface to form a bimorph beam-shaped layer 9 ((b) in FIG. 7). Thereafter, the silicon membrane and the silicon nitride film on the wafer surface are removed from the back surface by dry etching using a reactive gas to produce a bimorph beam 9 for displacement of the STM probe ((c) in FIG. 7).

When observing the surface of a sample surface using this STM probe, the probe 11 is displaced by the bimorph beam 10 along irregularities on the sample surface. The speed of following the irregularities is determined by the mechanical resonance frequency of the beam, and the beam is displaced at least below the resonance frequency. For this reason, the length of the beam is one of the important factors for determining the upper limit of the surface observation speed, and minimizing the beam length error as much as possible is important in assembling the system.

The beam length error that occurs during fabrication depends on the alignment error between the beam-shaped layer and the silicon membrane on both sides of the wafer, the plasma etching conditions, and the unevenness of the silicon membrane thickness. The unevenness of the thickness of the silicon membrane is caused by etching conditions such as the thickness accuracy of the wafer, the non-uniformity of the heating temperature in the wafer surface during the anisotropic etching, and the aging of the etching solution. As for the etching by plasma, CF ₄ , SF _{6 and the} like are used as main reactive gases used for dry etching of Si, but it is known that the etching shape changes variously depending on plasma etching conditions. (Goto et al., 1
990 Autumn Meeting of the Japan Society for Precision Engineering
72, pp1041). Further, in plasma etching, if etching is performed for a long time, the wafer temperature rises and the etching rate changes, and unevenness in the etching rate in the wafer surface occurs. Therefore, it is necessary to control the plasma etching.

Therefore, in order to manufacture a beam having a desired length, it is necessary to strictly control the etching conditions and the plasma etching conditions for improving the reproducibility of the thickness of the silicon membrane.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide a simple manufacturing method that provides a manufacturing method for obtaining a desired beam length. It is another object of the present invention to provide a method of manufacturing a beam having a displacement element that can simultaneously satisfy the above and the above.

[0008]

Means for Solving the Problems A first aspect of the present invention is a method for manufacturing a beam having a displacement element formed on a semiconductor wafer.
Forming a thin film on both surfaces of the wafer to prevent anisotropic etching utilizing a difference in the etching rate of the semiconductor crystal orientation; and providing an opening in the thin film on the first main surface of the wafer. , and the wafer on the thin film of the second major surface of the front Symbol wafer on the opposite side, a plurality of conductive constituting the beam
Forming an electrode layer and a piezoelectric layer sandwiched between these electrode layers; and forming the thin film membrane by removing the wafer from the first main surface exposed to the opening by anisotropic etching. child when the membrane of the thin film removal
And a plurality of electrode layers and sandwiched between these electrode layers
Forming a beam made of a piezoelectric layer . A second aspect of the present invention is that a semiconductor wafer
A method for producing a beam having a displacement element to be formed, comprising:
Utilizing etching rate difference of semiconductor crystal orientation on both sides of EHA
Of forming a thin film to prevent anisotropic etching
Providing an opening in the thin film on the first main surface of the wafer
And a first main surface exposing the wafer to the opening.
Partially removed by anisotropic etching and semiconductor membrane
Forming a lens; and forming a second main surface of the wafer on the wafer.
On the opposite side of the thin film from the wafer, a plurality of beams
Forming an electrode layer and a piezoelectric layer sandwiched between these electrode layers;
Removing the semiconductor membrane from the opening.
Removed by reactive etching to form a membrane of the thin film
And removing the membrane of the thin film.
A plurality of electrode layers and a piezoelectric body sandwiched between these electrode layers
Forming a beam consisting of layers.
I do.

The components of the present invention have been described above, and details and functions thereof will be described in the following embodiments.

[0010]

The present invention will be described below in detail with reference to examples.

FIG. 1 shows a process schematic diagram of a fabrication method that best illustrates the features of the present invention.

A silicon nitride film 2 is formed on both surfaces of a silicon wafer 1 having a crystal orientation (100) plane as main surfaces by a low pressure CVD (LPCVD) method using a mixed gas of SiCl ₂ H ₂ and NH ₃ at 0.2 Torr and 850 ° C. (FIG. 1A), and the silicon nitride film on one side of the wafer is formed by photolithography and reactive ion etching.
After forming a pattern using F ₄ gas and opening the opening, 1
Anisotropic etching of silicon was performed using a 27% by weight aqueous solution of KOH at 10 ° C. to form a 30 μm silicon membrane 3 ((b) in FIG. 1). Next, a bimorph beam-shaped layer 9 using a piezoelectric thin film was produced ((c) in FIG. 1). Au electrodes 4, 6, 8 and ZnO thin films 5, 7 were sequentially formed on the surface of the wafer while being patterned to form a bimorph beam-shaped layer 9 pattern. The Au electrode film is formed to a thickness of 0.1 μm by vacuum resistance heating evaporation, and the ZnO piezoelectric film is formed by sputtering a ZnO target in a mixed atmosphere of oxygen and argon by magnetron sputtering and heating the silicon wafer to 200 ° C. A film having a thickness of 0.3 μm was formed. Bimorph patterning was performed by photolithography. As an etching solution, an aqueous solution of potassium iodide was used for the Au electrode, and an aqueous solution of acetic acid was used for the ZnO film. However, in order to improve the adhesion between Au and silicon, Cr was deposited by a 20 ° vacuum evaporation method before depositing the first layer of Au4.

Next, the silicon membrane 3 is removed by the anisotropic etching described above, and the silicon nitride film 13 is removed.
Was formed ((d) in FIG. 1). FIG. 2 shows a schematic view of an apparatus for producing a silicon nitride film membrane. The ZnO thin film is dissolved by an etchant used for anisotropic etching. For this reason, the silicon wafer having the membrane prepared in FIG.
Is fixed to the container 16 with KOH 27%
The anisotropic etching is performed while the aqueous solution 17 is put in the heater 18 and heated to 80 ° C. by the heater 18. The temperature of the aqueous solution is thermocouple 1
The measurement is performed according to 9 and the electric power of the heater is adjusted. Even if the silicon nitride film becomes an etching stop layer for anisotropic etching, and the thickness unevenness of the silicon membrane 3, the difference in the etching rate in the wafer surface, the change in the etching rate with the lapse of time, and the like occur, FIG. The etching surface along the obtained crystal direction is maintained, and the position of the etching end face can be guaranteed.

The silicon nitride film membrane 13 is etched and removed by the same method as that for removing the silicon nitride film to obtain a bimorph beam of a ZnO thin film ((e) in FIG. 1).

Although not shown in the figure, as a method of manufacturing the probe, a thin film cathode method (CA Spindt, CA) using a vacuum deposition method after forming a bimorph beam in FIG.
J. Appl. Phys. , 47, pp5248, 19
76) or an electron beam evaporation method (Y. Akayama. 4th Int) after the step (e) in FIG.
electronic Conference on
Scanning Tunneling Micros
copy / Spectroscopy, '89, P2-
39, pp 126) and a method of adhering metal fine particles. In the present invention, a probe was manufactured by decomposing CH ₄ gas by an electron beam evaporation method in a CH ₄ gas atmosphere.

FIG. 3 is a schematic view of the STM probe obtained by the above-described manufacturing method, and FIG. 4 is a cross-sectional view thereof. By arranging the electrodes as shown in FIG. 3, S is displaced in the direction of A in FIG.
When a plurality of STM probes are used on a silicon wafer as shown in FIG. 5 and used as a probe for TM, a unit 100 having an end face defined by a crystal orientation plane and having a uniform beam length is formed. It has become possible.

In the present embodiment, the step of forming a silicon membrane shown in FIG. 1B was performed, but the time required for forming the silicon membrane was reduced by KOH.
The temperature of the aqueous solution was set to be as high as 110 ° C. to reduce the temperature. The silicon membrane forming step was omitted, and the silicon nitride film was formed without forming the silicon membrane by the apparatus of FIG. Needless to say, there is no problem.

As an etchant for anisotropic etching, a crystal anisotropic solution such as an aqueous solution of potassium hydroxide, ammonium hydroxide, hydrazine, ethylenediamine pyrocatechol or the like which produces a difference in etching rate depending on the crystal orientation of the semiconductor is used. Any etchant is applicable. Further, it goes without saying that the present invention can be applied as long as it has a sufficient etching selectivity as compared with a semiconductor and can form a membrane when the above-described etchant such as a silicon oxide film or SiC is used instead of the silicon nitride film.

[0019]

As described above, when a beam is manufactured by the method of the present invention, a desired beam length can be obtained with good reproducibility even if there is uneven membrane thickness in the wafer surface or uneven etching speed. It became possible.

The beam manufactured using the method of the present invention guarantees reproducibility of mechanical element characteristics such as resonance frequency and high yield.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a fabrication process that best illustrates the fabrication method of the present invention.

FIG. 2 is a schematic view of an apparatus for manufacturing a silicon nitride film membrane.

FIG. 3 is a schematic view of an STM probe having a bimorph displacement element according to the present invention.

FIG. 4 is a cross-sectional view of an STM probe having a bimorph displacement element according to the present invention.

FIG. 5 is a schematic view of a unit of a plurality of STM probes.

FIG. 6 is a perspective view of an STM probe manufactured by a conventional method.

FIG. 7 is a schematic view of a manufacturing process showing a conventional manufacturing method.

[Description of Signs] 1 silicon 2 silicon nitride film 3 silicon membrane 4,6,8 electrode 5,7 ZnO 9 beam-shaped layer 10 bimorph beam 11 probe 12 lead electrode 13 silicon nitride film membrane 14 O-ring 15 stopper 16 container 17 KOH aqueous solution 18 Heater 19 Thermocouple

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Osamu Takamatsu 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroshi Hirai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-4-343009 (JP, A) JP-A-3-162602 (JP, A) JP-A-63-309802 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/66 C23F 1/00 C23F 1/02 H01L 21/3065 H01L 29/84

Claims (3)

(57) [Claims] 1. A method for manufacturing a beam having a displacement element that is formed on a semiconductor wafer, forming a thin film for preventing anisotropic etching on both surfaces of the wafer utilizing a difference in etching rate between the semiconductor crystal orientation Providing an opening in the thin film on a first major surface of the wafer; and providing a beam on a second major surface of the wafer on the opposite side of the thin film from the wafer.
Constituting a plurality of electrode layers and sandwiched between these electrode layers
Forming a piezoelectric layer ; and placing the wafer in the opening.
A step of removing the first main surface by Rikoto isotropic etching exposed to form a membrane of the thin film, by removing the membrane of the thin film, a plurality of electrode layers and these
Forming a beam consisting of a piezoelectric layer sandwiched between different electrode layers
And a method for producing a beam. 2. A method for manufacturing a beam having a displacement element that is formed on a semiconductor wafer, forming a thin film for preventing anisotropic etching on both surfaces of the wafer utilizing a difference in etching rate between the semiconductor crystal orientation Providing an opening in the thin film on the first main surface of the wafer;
Forming a semiconductor membrane by partially removing the first main surface exposed to the opening by anisotropic etching;
The wafer on the thin film on the second main surface of the wafer
On the opposite side, a plurality of electrode layers constituting the beam and these electrodes
Forming a piezoelectric layer sandwiched between the layer and forming a membrane of the thin film to remove the semiconductor membrane by anisotropic etching from the opening by removing the membrane of the thin film, a plurality Electrode layer and this
Forming a beam consisting of a piezoelectric layer sandwiched between these electrode layers
And a method for producing a beam. 3. A method for manufacturing a beam of to claim 1 or 2 serial <br/> mounting, characterized in that it has a tunnel current detecting terminal to the free end of the beam.