JP2013194320A - METHOD FOR PRODUCING AlN THIN FILM - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an AlN thin film with C-axis orientation properties, the AlN thin film having a polarity aligned in an Al polarity on a lower electrode, while suppressing surface oxidation of the lower electrode by depositing next AlN immediately after the deposition of the lower electrode, since a thin film formation technique by means of general sputtering methods is difficult to satisfy such requirements that, in order to obtain an AlN thin film having good piezoelectric properties, it is required not only that the AlN thin film is subjected to c-axis orientation but also that a polarity thereof is aligned in a fixed direction, and it is known that the polarity of AlN is significantly affected by oxidation at the outermost surface of a metal layer as the lower electrode, so that, in order to align the polarity of AlN, the deposition of AlN is to be started before the lower electrode is contaminated by oxygen.SOLUTION: In an AlN thin film formed on an Al layer as a lower electrode, the deposition of the AlN thin film is started without interrupting the deposition by starting introduction of nitrogen in a rectangular manner during deposition of the Al layer.

Description

  The present invention relates to a method for producing an AlN thin film. Specifically, the present invention relates to a method for manufacturing a C-axis oriented AlN thin film that can be applied as a piezoelectric thin film resonator or a piezoelectric element and that has the same polarity as the Al polarity.

  AlN, which is a wurtzite material, has piezoelectricity and pyroelectricity in the C-axis direction. For this reason, C-axis oriented AlN thin films (C-axis oriented AlN thin films) are applied as piezoelectric thin film resonators and MEMS components by utilizing their piezoelectric properties, and as sensors by utilizing their pyroelectric properties. ing.

  Therefore, many studies have been made to obtain a C-axis oriented AlN thin film. When forming an AlN thin film by sputtering, it is known that if the film is formed at a low gas pressure, it tends to be C-axis oriented. Specifically, the gas pressure is preferably about 0.5 Pa, but it is not always a gas pressure that can be easily realized.

  On the other hand, an attempt has been made to obtain a C-axis oriented AlN thin film by orienting the underlying layer when depositing the AlN thin film. The underlayer is generally a metal thin film. This is because the underlayer needs to function as a lower electrode when using the piezoelectric characteristics of the AlN thin film. When the metal thin film as the underlayer is made of, for example, a metal having a face-centered cubic structure and is (111) oriented, the AlN thin film tends to be C-axis oriented.

  By the way, in order to obtain an AlN thin film having good piezoelectric characteristics, it is required that the AlN crystal grains in the thin film have C-axis orientation and that the polarity is aligned in a certain direction. However, it is known that it is difficult to align the polarity of the AlN thin film.

  For example, it is pointed out that when AlN is deposited on clean Ru (ruthenium), and when AlN is deposited on Ru contaminated with oxygen, the polarity of the growing AlN crystal is different (non-non). Patent Document 1).

  J. et al. A. Ruffner, P.A. G. Clem, B.M. A. Tuttle, D.C. Dimos, D.D. M.M. Gonzales, “Effect of Substrate composition on the piezoelectric response of reactively putted AlN thin films”, Thin Solid Films, Netherlands, Elsevier B. V. , November 10, 1999, 354, 1-2, pages 256-261

  Therefore, in order to produce a C-axis oriented AlN thin film with uniform polarity, it is necessary to deposit the AlN thin film after the lower electrode is deposited and before the surface is contaminated with oxygen.

  However, it is difficult to prevent the outermost surface of the lower electrode from oxygen contamination by a general multilayer thin film manufacturing technique. This is because there is a time during which the film formation is interrupted (hereinafter referred to as a film formation interruption time) between the formation of the lower electrode and the deposition of the next AlN thin film, and the outermost surface of the lower electrode in the meantime. This is because is in the direction of oxidation. In general, Ar gas is used when forming the metal thin film as the lower electrode, and a mixed gas of Ar and nitrogen is used when forming the AlN thin film. Therefore, each time the thin film to be formed is changed, it is introduced into the vacuum vessel. This is because it is necessary to replace the gas used, and further, after the gas replacement, pre-sputtering is required to stabilize the target surface. Therefore, it is considered good to use a metal that is difficult to oxidize as the underlayer, but such a metal is expensive.

  In addition, there is a report that when the oxygen partial pressure in the vacuum vessel is changed, the polarity of the growing AlN crystal is changed, and when the oxygen is introduced excessively, the polarity is dispersed (non-native). Patent Document 2).

  Morito Akiyama, Toshihiro Kamohara, Kazuhiko Kano, Akihiko Teshigahara, and Nobuaki Kawahara, "Influence of oxygen concentration in sputtering gas on piezoelectricresponse of aluminum nitride thin films", APPLIED PHYSICS LETTERS, the United States, American Institute of Physics, Inc., 2008 July 14 Sun, Volume 93, No. 1, 021903

  In particular, it is known that the oxygen partial pressure at the start of AlN deposition is important, and it is reported that when the oxygen partial pressure is high, crystals cannot be formed and deposition is started as amorphous ( Non-patent document 3).

  V. Brien, P.M. Pigeat, “Microstructures diagram of magnetron sputtered AlN deposits: Amorphous and nanostructured films”, Journal of Crystal Growth, Netherlands, Else. V. , January 5, 2007, 299, 1, 1, 189-194

  By the way, there are two types of C-axis oriented AlN thin films having the same polarity: an Al-polar C-axis oriented AlN thin film and an N-polar C-axis oriented AlN thin film. In general, a C-axis oriented AlN thin film grown in N polarity is relatively easily obtained, whereas it is known that it is difficult to obtain an Al polar C-axis oriented AlN thin film (Non-patent Document 4). ).

  E. Mileutin, S.M. Harada, D .; Martin, J.M. F. Carlin, N .; Grandjean, V.M. Savu, O .; Vaszquez-Mena, J.A. Brugger, P.A. Multalt, “Sputtering of (001) AlN thin films: Control of polarity by a seed layer,” Journal of Vacuum Science and Technology B, June, L page

  Therefore, in order to produce a C-axis oriented AlN thin film with uniform polarity, the deposition interruption time should be shortened as much as possible after the deposition of the lower electrode, before the outermost surface of the electrode is contaminated with oxygen. It is necessary to deposit a thin AlN film. More desirably, there is a need for a method that initiates the deposition of AlN at a low oxygen partial pressure. There is also a need for a method of growing an Al-polar C-axis oriented AlN thin film.

Therefore, the main object of the present invention is to provide a method for manufacturing a C-axis oriented AlN thin film with uniform polarity on the lower electrode by immediately depositing the next AlN immediately after the lower electrode is deposited. is there.
A subordinate object of the present invention is to provide a method for producing a C-axis oriented AlN thin film having good crystallinity and uniform polarity on the lower electrode by starting the deposition of AlN at a low oxygen partial pressure. That is.
Yet another secondary objective of this study is to provide a method for growing Al polar C-axis oriented AlN thin films.
Still another object of the present invention is to provide a method for producing a C-axis oriented AlN thin film having a uniform polarity on a lower electrode in a short time and easily using a lower cost lower electrode.

  In the method for producing a C-axis oriented AlN thin film with uniform polarity according to the present invention, in the AlN thin film formed on the Al layer as the lower electrode, nitrogen is introduced in a rectangular manner during the deposition of the Al layer. Thus, the deposition of the AlN thin film is started without interrupting the film formation.

  According to the present invention, a C-axis-oriented AlN thin film with uniform polarity can be stably produced on an Al layer as a lower electrode. In addition, a C-axis oriented AlN thin film having the same polarity can be easily produced in a short time. Furthermore, an Al-polar C-axis oriented AlN thin film can be grown. In addition, even an inexpensive lower electrode of Al can produce a C-axis oriented AlN thin film with uniform polarity.

  The above-described object, other objects, features, and effects of the present invention will be specifically clarified from the following examples.

This is a film forming procedure when an AlN layer, an Al layer, and an AlN layer are sequentially deposited on a substrate according to the present invention and an application form of the present invention. It is the result of having observed the cross section with the transmission electron microscope about the sample manufactured by the film-forming procedure of FIG. It is the result of having observed the cross section by STEM-HAADF about the AlN thin film formed on the Al layer in the sample manufactured by the film-forming procedure of FIG. It is a cross-sectional schematic diagram of the sample manufactured by the film-forming procedure of FIG. The arrow points to the + c direction of the AlN crystal grains. Using the present invention, an application form of the present invention, and a film forming method described in Patent Document 1, an Al polar C-axis oriented AlN thin film and an N polar C-axis oriented AlN thin film are grown in the same multilayer thin film. FIG. The arrow points to the + c direction of the AlN crystal grains. FIG. 6 is a circuit diagram showing that the same amount of deformation can be obtained even with a conventional half voltage by using the multilayer thin film of FIG. 5.

  According to the present invention and the application form of the present invention, an AlN thin film as a buffer layer is formed on a substrate, an Al layer as a lower electrode is formed on the AlN thin film, and a piezoelectric thin film is formed on the Al layer. FIG. 1 shows a film forming procedure when a C-axis oriented AlN thin film having a uniform polarity is formed. The present invention is applied at t2 in the figure. Further, at t1 in the figure, as an application form of the present invention, the deposition of the next Al layer is started without interrupting film formation by canceling the introduction of nitrogen in a rectangular manner during the deposition of AlN. .

  The result of observing the cross section of the multilayer thin film thus produced with a transmission electron microscope is shown in FIG. Moreover, the STEM-HAADF observation result in the AlN thin film on the Al layer is shown in FIG.

  As can be seen from FIG. 2, even if the introduction of nitrogen is started or canceled in a rectangular manner, it can be understood that a multilayer thin film having a structure corresponding to that is produced. From FIG. 3, it was found that the AlN thin film on the Al layer exhibited C-axis orientation and had the same polarity as the Al polarity. In addition, it was the same orientation and the same polarity irrespective of the in-plane position of the manufactured thin film. The Al layer was (111) oriented. Furthermore, AlN on the Al layer was deposited without forming an amorphous phase. These are summarized as shown in FIG. 4, and the + c direction of the AlN crystal is indicated by an arrow.

  Therefore, as shown in FIG. 1, it is possible to start the deposition of AlN on the Al layer without interrupting the film formation by starting the introduction of nitrogen gas in a rectangular manner. The AlN thin film is a C-axis oriented AlN thin film having the same polarity as the Al polarity. In this embodiment, the amount of Ar gas introduced is changed along with the amount of nitrogen gas introduced, but this is for keeping the sputtering gas pressure constant and is not the essence of the present invention.

By combining the present invention and the application form of the present invention and the manufacturing method described in Patent Document 1, as shown in FIG. 5, in the same multilayer thin film, an Al polar C-axis oriented AlN thin film and an N polar C axis An oriented AlN thin film can be formed. This is actually confirmed from the STEM-HAADF image. And such a thin film can obtain the same deformation amount even if it is a conventional 1/2 voltage by applying an electric field as shown in FIG. In this example, although the manufacturing method described in Patent Document 1 was used, it is known that an N-polar C-axis oriented AlN thin film can be obtained relatively easily. It is not necessary to use the described production method.

  JP 2011-117059

  According to the present invention, since a C-axis oriented AlN thin film having a uniform polarity can be formed on a metal electrode without passing through an amorphous layer, a piezoelectric thin film resonator of several hundred GHz band (in this case, the thickness of the AlN layer is several Can be 10 nm).

10 C-axis oriented AlN thin film 21 whose polarity is aligned with Al polarity 21 Substrate 22 AlN thin film 23 as buffer layer (111) oriented Al layer 24 as lower electrode (111) oriented Pt layer 25 Polarity to N polarity C-axis oriented AlN thin film 26 aligned Upper electrode 31 Power supply

Claims (9)

An AlN thin film formed on an Al layer, wherein the deposition of the AlN thin film is started without interruption by starting the introduction of nitrogen in a rectangular manner when the Al layer is being deposited. A method for producing an AlN thin film. Al film is formed on the AlN thin film, and when the AlN thin film is deposited using the Al target, deposition of the Al thin film is started without interruption by stopping the introduction of nitrogen in a rectangular manner. A method for producing an AlN thin film, characterized by comprising: 3. The AlN thin film according to claim 1, wherein the AlN thin film is formed by a sputtering method using a mixed gas of Ar and nitrogen having a gas pressure in a range of 0.5 Pa to 1.0 Pa. 4. Manufacturing method. 3. The AlN film according to claim 1, wherein the AlN thin film is formed by a sputtering method using a mixed gas of Ar and nitrogen with a flow rate ratio of nitrogen gas in the range of 20% to 40%. Thin film manufacturing method. The method for producing an AlN thin film according to any one of claims 1 to 2, wherein the AlN thin film is C-axis oriented. The method for producing an AlN thin film according to claim 5, wherein the AlN thin film has a uniform polarity. The method for producing an AlN thin film according to claim 6, wherein the AlN thin film is grown with Al polarity. The method of manufacturing an AlN thin film according to any one of claims 5 to 7, wherein the thickness of the AlN thin film is 1 nm or more. By combining the method for producing an AlN thin film according to any one of claims 1 to 8 and a method for producing a general AlN thin film, an Al polar C-axis oriented AlN thin film and an N polar C A multilayer thin film made of AlN and a metal, characterized in that an axially oriented AlN thin film is laminated via a metal layer.