JP3435633B2 - Thin film laminate, thin film capacitor, and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductor thin film epitaxially formed on a silicon substrate via a buffer layer, and a method for manufacturing the same. More specifically, the present invention relates to a conductor thin film used for a thin film capacitor and the like, and an epitaxial conductor thin film having a function of improving the film quality (crystallinity) of a dielectric thin film, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Recently, BaTiO ₃ , SrTiO ₃ , (B
a, Sr) TiO ₃ , PbTiO ₃ , Pb (Zr, Ti) O
A technique for forming a thin film of a dielectric / ferroelectric material such as ₃ , (Pb, La) (Zr, Ti) O ₃ on a silicon substrate has been actively researched. Especially, PZT and PLZ with large remanent polarization
If a Pb-based perovskite ferroelectric material such as T can be epitaxially grown, spontaneous polarization can be aligned in one direction, and a larger polarization value and good switching characteristics can be realized. As a result, the applicability to a high density recording medium is dramatically increased, and therefore, it is strongly desired to establish a method for forming a ferroelectric thin film having good crystallinity on a silicon substrate.

By the way, in order to form a thin film capacitor or the like using a dielectric thin film such as PZT or PLZT, a so-called MIM in which a dielectric thin film is sandwiched between conductor thin films from above and below.
(Metal-Insulater-Metal) structure is commonly used. However, in this structure, it is difficult to improve the crystallinity of the ferroelectric thin film for the reason described below, and a ferroelectric thin film having sufficiently satisfactory crystallinity has not yet been obtained.

That is, when a metal material such as Al, Cu, Ag, and Au is used as the conductor thin film (lower electrode) formed on the silicon substrate, the conductor thin film is formed when the ferroelectric thin film is formed on the lower electrode. A metal oxide film is formed at the interface with the dielectric thin film. The presence of this metal oxide film hinders the crystal growth of the dielectric thin film. In addition, the above-mentioned metal material is likely to cause mutual diffusion with the silicon substrate, and when a semiconductor element or the like is formed on the silicon substrate, the characteristics thereof may be changed.

A method using Pt as the conductor thin film is also conceivable. However, although Pt is epitaxially grown on an oxide single crystal substrate such as MgO or SrTiO _3, it cannot be directly epitaxially grown on a silicon substrate. Therefore, it is inappropriate to use Pt as a conductor thin film when forming a ferroelectric thin film having high crystallinity on a silicon substrate (generally, the conductor thin film located in the lower layer has good crystallinity). The better the crystallinity of the ferroelectric thin film formed thereon can be improved.

[0006]

Therefore, the present inventors have found that
First, as a buffer layer on a silicon substrate, first, Ti _1-x A
l _x N thin film is grown epitaxially (Ti _1-x Al _x N
Easily grows epitaxially on a silicon substrate), then Ti
We proposed a method of epitaxially growing a Pt thin film as a conductor thin film on a _1-x Al _x N thin film (Pt is Ti _1-x Al _x
Epi growth is easy on N). As a result, it has become possible to form a ferroelectric thin film having relatively good crystallinity on a conductor thin film made of an epitaxial Pt thin film.

However, even in this method, the composition element of the ferroelectric thin film reacts with the Pt thin film of the lower electrode particularly when the ferroelectric thin film is formed by a film forming method such as a CVD method at a high temperature. However, a phenomenon such as diffusion along the crystal grain boundaries of the Pt thin film occurred, and the crystallinity of the ferroelectric thin film could not be improved as intended.

Therefore, an object of the present invention is to provide an epitaxial conductor thin film (lower electrode) having a function of forming a ferroelectric thin film having good crystallinity on a silicon substrate, and a method for manufacturing the same.

[0009]

In view of the above technical problems, the inventors of the present invention have conducted extensive studies and as a result, as a metal material used for a conductor thin film, a platinum group element having a face-centered cubic structure,
Specifically, in order to use Ir and Rh and to epitaxially grow Ir and Rh, a TiN layer or a Ti _1-x Al _x N / TiN layer (where 0 <x ≦ 0.4) as a buffer layer on a silicon substrate. By interposing
It was found that a ferroelectric thin film having good crystallinity can be formed on the conductor thin film.

Pt used as a material for the conductor thin film in the above-mentioned prior art has advantages that it is not easily oxidized even in the atmosphere and that it is easily lattice-matched with ferroelectrics such as PZT, PLZT and BST. . But Pt
Has a property of easily forming a compound with an element such as silicon or Pb. Therefore, the characteristics of a semiconductor element formed on a silicon substrate are changed, or a compound is formed at the interface with a ferroelectric containing Pb. However, there is a possibility that the crystallinity of the dielectric thin film formed above may deteriorate. In addition, there is also a phenomenon in which oxygen passes through the grain boundaries of the Pt thin film and diffuses to the lower layer of the Pt thin film, and although Pt itself is difficult to oxidize, the characteristics of elements and films located in the lower layer of the Pt thin film, such as semiconductor elements, are not observed. Could have an adverse effect on.

In view of this, Ir and Rh, which are platinum group elements having a face-centered cubic structure, have high electric conductivity similarly to Pt, are easier to process than Pt, and have an oxygen diffusion barrier function. Therefore, the phenomenon that oxygen passes through the Ir thin film and diffuses to the lower layer does not occur. Further, since it hardly reacts with other elements, it is possible to suppress the problems such as the change of the characteristics of the semiconductor element and the deterioration of the crystallinity of the dielectric thin film when Pt is used.

Thus, it can be said that Ir and Rh are suitable materials (as materials for the lower electrode) in order to form a ferroelectric thin film having good crystallinity. However, when forming a thin film of Ir and Rh on a silicon substrate, it has been difficult to grow epitaxially by the conventional method.
For example, Nakamura et al. Formed an Ir thin film as a lower electrode of a PZT thin film capacitor on a SiO ₂ / Si substrate by an RF magnetron sputtering method (JJAP. Vol 34 (1995), 5).
184), the obtained Ir thin film was a (111) preferential alignment film. In addition, Horii et al. Formed an Ir thin film on a YSZ / Si substrate by a sputtering method (The 45th Joint Lecture on Applied Physics (1998), Lecture Proceedings 29a-Zf-11). Was obtained only with a film having a mixture of (100) and (111) orientations.

Therefore, the present inventors have found that I on a silicon substrate.
In order to epitaxially grow a conductor thin film composed of r and Rh, a TiN layer as a buffer layer on a silicon substrate,
Alternatively, Ti _1-x Al _x N / TiN layer (where 0 <x ≦
The present invention has been completed by discovering that Ir and Rh can be epitaxially grown on a silicon substrate by forming the film with 0.4) interposed therebetween.

That is, the lattice length of the silicon substrate is 0.5.
43 nm, TiN has a lattice length of 0.424 nm, and a TiN thin film can be epitaxially grown on a silicon substrate in a long period matching mode between lattices. On the other hand, the lattice length of Ir is 0.384 nm, which is very similar to that of TiN, and it is possible to epitaxially grow it on a TiN thin film.

Incidentally, in order to further enhance the orientation of the epitaxial Ir thin film, the Ir thin film may be formed in a high temperature oxygen atmosphere. In this case, as a characteristic required for the buffer layer, in addition to the lattice matching with Ir, a high temperature oxidation resistance characteristic is further required. In this respect, the high temperature oxidation resistance can be improved by interposing Ti _1-x Al _x N in which Ti is partially replaced by Al in TiN (however, the crystallinity gradually deteriorates as the x value increases. ). Ti _1-x Al _x N has a higher T than that on the silicon substrate.
Epitaxial growth easily occurs on iN, and TiN epitaxially grows on the silicon substrate with good crystallinity.
Thus, on a silicon substrate by first forming a TiN thin film, followed by forming a Ti _1-x Al _x N thin film on the TiN film was realized high-temperature oxidation resistance while maintaining high crystallinity Ti _1- it is possible to form a buffer layer having a two-layer structure of the _x Al _x N / TiN. Since the lattice length of Ti _1-x Al _x N is sufficiently close to the lattice length of Ir even if the x value is changed within the above numerical range, there is no concern that the epitaxial growth of the Ir thin film is deteriorated. Absent.

When the TiN thin film is used as a buffer layer for forming the epitaxial Ir thin film, it is desirable that not only the crystallinity of the TiN thin film but also the flatness of the surface thereof has high flatness. As a result of repeated experiments on this point, 50 to 3 at a film forming rate of 1 to 10 nm / min.
By forming a TiN-based buffer layer (TiN layer and Ti _1-x Al _x N / TiN layer) with a film thickness of 00 nm, sufficient flatness (specifically, surface average) for forming an epitaxial Ir thin film is obtained. It has been found that a roughness of 0.1 to 0.5 nm can be realized.

When the Ir thin film is used as the lower electrode to form a ferroelectric thin film having good crystallinity, not only the crystallinity of the Ir thin film but also the flatness of its surface is high. Is desirable. As a result of repeated experiments on this point, a film formation rate of 1 to 10 nm / min was 50 to 5
By forming an Ir thin film with a thickness of 00 nm, the flatness is sufficient to form a ferroelectric thin film with good crystallinity (specifically, the average surface roughness is 0.1 to 1.0 nm). I found that can be realized.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION [First Embodiment, FIG. 1] A thin film capacitor formed by using the thin film laminate of the present invention and a method for manufacturing the same will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a thin film capacitor 10 of this embodiment. In the figure, 1 is a Si substrate, 2
Is a TiN thin film epitaxially grown on the Si substrate 1,
3 is Ti _0.9 epitaxially grown on the TiN thin film 2.
The Al _0.1 N thin film, 4 is an Ir thin film which is epitaxially grown on the Ti _0.9 Al _0.1 N thin film 3 and serves as a lower electrode of the thin film capacitor 5, 5 is a PZT thin film epitaxially grown on the Ir thin film 4, and 6 is formed on the PZT thin film 5. The Pt thin film used as the upper electrode of the thin film capacitor 10 is shown, respectively. Here, the TiN thin film 2 and the Ti _0.9 Al _0.1 N thin film 3 constitute a buffer layer 7 for epitaxially growing the Ir thin film 4.

Next, a method of manufacturing the thin film capacitor 10 having the above structure will be described in detail.

First, as the Si substrate 1, S having a diameter of 2 inches is used.
An i (100) substrate is prepared. Then, this Si substrate is subjected to ultrasonic cleaning in an organic solvent such as acetone or ethanol, and immersed in a solution of HF: H ₂ O: ethanol = 1: 1: 10 to oxidize naturally formed on the surface of the Si substrate. Remove the membrane.

Then, the surface-cleaned Si substrate is fixedly arranged in a vacuum container of a laser ablation device,
A TiN thin film 2 having a film thickness of 10 nm is formed on the surface of the Si substrate under the film forming conditions summarized in Table 1 below. Since TiN easily grows epitaxially on the Si substrate, the TiN thin film 2 obtained at this time becomes an epitaxial film.

Further, by changing the target used for film formation, a Ti _0.9 Al _0.1 N thin film 3 in which a part of Ti site of TiN is replaced with Al 10% is continuously formed on the TiN thin film 2 obtained above. The film is formed to 90 nm. This Ti _0.9 A
The l _0.1 N thin film 3 also becomes an epitaxial film because the crystallinity of the TiN thin film 2 is maintained. At this time, it was confirmed that the Ti _0.9 Al _0.1 N thin film 3 was epitaxially grown even when the degree of vacuum in the vacuum container was in the order of 10 ⁻⁵ Torr, but in order to realize an epitaxial film having higher crystallinity, it is 10 ^−6.
It is desirable to secure the vacuum level of the Torr table. The other film forming conditions are the same as those for forming the TiN thin film 2. Further, each target (TiN sintered body, and Ti _{0. 9} Al _0.1 N sintered body) to be used for the deposition of TiN film 2, and Ti _0.9 Al _0.1 N film 3, a relative density of 90% or more It is desirable to use one, more preferably 95% or more.

Next, the target used for film formation was changed, and the above-mentioned Ti _0.9 Al _0.1 N / TiN layer was replaced with the buffer layer 7.
Then, the Ir thin film 4 is continuously formed to a film thickness of 100 nm. At this time, the lattice lengths of TiN and Ti _0.9 Al _0.1 N and the lattice length of Ir are very close to each other, and the Ir thin film 4 to be deposited is epitaxially grown on the Ti _0.9 Al _0.1 N thin film 3. An Ir metal target is used for forming the Ir thin film 4, and its purity is preferably 99.9% or more.

The above-mentioned TiN thin film 2 and Ti _0.9 Al
_{The 0.1} N thin film 3 and the Ir thin film 4 were continuously formed in the same film forming apparatus by switching the target corresponding to the thin film to be formed. Here, the film forming conditions of the above-mentioned thin films are summarized in Table 1 below.

[0026]

[Table 1]

Epitaxial I thus obtained
By forming a PZT thin film on the r thin film 4, an epitaxially grown PZT thin film 5 can be obtained. This PZT
By depositing, for example, a Pt thin film 6 as an upper electrode of the thin film capacitor 10 on the thin film 5 by a method such as vapor deposition,
The Ir thin film 4, the PZT thin film 5, and the Pt thin film 6 can realize the thin film capacitor 10 having the MIM structure.

In this embodiment, Ti is used as a buffer layer for epitaxially growing the Ir thin film 4.
_{Although the} buffer layer composed of two layers of _0.9 Al _0.1 N / TiN is used, the buffer layer may be composed of only one TiN thin film layer. It can be understood from FIG. 2 showing the analysis result (described later) regarding the crystallinity of each thin film that the Ir thin film formed on the buffer layer also grows epitaxially in this case.

Now, the analysis result of the crystallinity of each thin film of the thin film capacitor 10 obtained by the above-described manufacturing method will be described. First, Ir formed on a Si substrate
The XRD diffraction patterns of two kinds of thin film laminates of / Ti _0.9 Al _0.1 N / TiN and Ir / TiN are shown in FIG. As is clear from this figure, only the peaks due to TAN (002) (TiN or Ti _0.9 Al _0.1 N / TiN) and Ir (002) were detected on Si (001) in any of the thin film laminates. And each thin film is (00
It can be seen that the film is oriented in l).

Further, a pole figure analysis was carried out to confirm the orientation of the Ir thin film in the film plane. The results are shown in Fig. 3. As can be seen from the figure, a four-fold symmetrical peak is obtained, and the Ir thin film 4 has Ti _0.9 Al _0.1 N / TiN / S.
It can be confirmed that the epitaxial growth is fine on the i substrate.

For comparison with the prior art, a comparative example was prepared in which the portion corresponding to the Ir thin film 4 of this example was replaced with Pt. The thin film structure and film forming conditions other than the Pt thin film portion are the same as those in the first embodiment. The Pt thin film is formed by RF sputtering using a Pt metal target having a purity of 99.9% or more, with an RF power of 200 W,
Gas composition ratio Ar / O ₂ = 9/1, vacuum degree during film formation 5 × 1
The film was formed under the conditions of 0 ^-5 Torr and the film forming temperature of 600 ° C. The results of crystallinity analysis of the thin film laminate of this comparative example and the thin film laminate of the first embodiment are summarized in Table 2 below.

[0032]

[Table 2]

As can be seen from Table 2 above, the Ir thin film of this example has better crystallinity than the Pt thin film of the comparative example (because the half width of the (002) peak is small). Moreover, it can be seen that a conductor thin film having a more flat surface and a dense film quality can be obtained. The full width at half maximum of the (002) peak was obtained from the XRD rocking curve. The surface average roughness is measured by using an AFM for an area of the thin film surface of 5 μm × 5 μm. Further, FIG. 4 shows the surface AFM images of the Pt thin film and the Ir thin film of this comparative example.
As can be seen from this figure, it can be seen that the comparative example has a mesh-like shape and is relatively rough, whereas the surface of the comparative example is flat and more dense.

Although the Si (100) substrate is used in the above embodiment, the present invention is not limited to this, and Si (111), Si
A silicon substrate such as (110) may be used.

In the present embodiment, an example in which the Ir thin film epitaxially grown is used as the lower electrode of the thin film capacitor 10 has been described.
_The thin film laminate having a structure of _0.9 Al _0.1 N / TiN / Si substrate can be applied to other than the thin film capacitor, and can also be used for an electrode film of DRAM or the like. . [Second Embodiment] The second embodiment of the present invention is the same as the first embodiment.
The feature is that the portion corresponding to the r thin film 4 is replaced with the Rh thin film. Purity of 99.9% when forming the Rh electrode
The above Rh metal target was used. The other thin film structures and film forming conditions are the same as those of the thin film capacitor 10 of the first embodiment, and therefore their explanations are omitted.

Also in the present example in which the Ir electrode 4 was replaced with the Rh electrode, the analysis by XRD diffraction confirmed that the Rh thin film was epitaxially grown. Further, when the surface condition of the Rh thin film of this example was observed by AFM, it was confirmed that the surface was a flat and dense film.

[0037]

As is apparent from the above description, Si
Epitaxial T i _1-x Al _x as a buffer layer on the substrate
By adopting a thin film laminated structure in which a platinum group element having a face-centered cubic structure is formed on the buffer layer with an N / TiN layer interposed, a ferroelectric thin film having good crystallinity can be formed on a Si substrate. An epitaxial conductor thin film having the function of obtaining can be formed. Further, on this epitaxial conductor thin film (specifically, a platinum group element such as Ir or Rh),
By utilizing the good crystallinity of the conductor thin film, it becomes possible to form a functional thin film such as a ferroelectric substance having a high uniaxial or higher orientation.

Ir and Rh do not easily diffuse or react with the composition elements of the ferroelectric thin film or the Si substrate. Therefore, for example, when a thin film capacitor using a ferroelectric substance is formed on a Si substrate, if an epitaxial Ir thin film is used as a lower electrode of the thin film capacitor, the characteristics of semiconductor elements such as FETs formed on the Si substrate will be improved. Without affecting
Further, it becomes possible to form a ferroelectric thin film having good crystallinity (that is, without forming a compound and deteriorating the crystallinity).

With these, it becomes possible to epitaxially grow a functional thin film such as a ferroelectric thin film on a Si substrate, and not only DRAM and FeRAM but also a pyroelectric element, a microactuator, a thin film capacitor, and other small size It can be applied to piezoelectric elements.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a thin film capacitor of a first embodiment of the present invention.

FIG. 2 is an XRD diffraction result of the thin film laminate obtained in Example 1.

FIG. 3 is a pole figure analysis result showing the in-plane orientation of the Ir thin film of the first example.

FIG. 4 is an AFM image showing the surface of each of the conductor thin films of the comparative example and the first example.

[Explanation of symbols]

1 ・ ・ ・ Si substrate 2 ・ ・ ・ TiN thin film 3 ・ ・ ・ Ti _0.9 Al _0.1 N thin film 4 ・ ・ ・ Ir thin film 5 ・ ・ ・ PZT thin film 6 ・ ・ ・ Pt thin film 7 ・ ・ ・ Buffer layer

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI H01L 21/285 H01L 27/10 451 301 37/02 21/8242 27/04 C 27/04 H01G 4/06 102 27/10 451 H01L 27/10 651 27/108 37/02 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/822 C30B 29/02 H01G 4/12 H01G 4/33 H01L 21/285 H01L 21 / 82 H01L 21/8242 H01L 27/04 H01L 27/10 H01L 27/108 H01L 37/02

Claims (6)

(57) [Claims] 1. A thin film stack comprising a silicon substrate, a buffer layer epitaxially formed on the silicon substrate, and a conductive thin film epitaxially formed on the buffer layer , wherein the buffer layer is TiN. And a layer formed on the TiN layer.
A Ti _1-x Al _x N layer (where 0 <x ≦ 0.4)
The conductive thin film is made of a platinum group element having a face-centered cubic structure. 2. A silicon substrate, a buffer layer epitaxially formed on the silicon substrate, a conductor thin film epitaxially formed on the buffer layer, a dielectric thin film formed on the conductor thin film, and a dielectric thin film on the dielectric thin film. A thin film capacitor having a formed upper electrode, wherein the buffer layer is formed on the TiN layer and the TiN layer.
A Ti _1-x Al _x N layer (where 0 <x ≦ 0.4)
A thin film capacitor , wherein the conductive thin film is made of a platinum group element having a face-centered cubic structure. 3. The thin film laminated body according to claim 1, wherein the platinum group element is any one of Ir and Rh, or the thin film capacitor according to claim 2. Having a first step of wherein epitaxially forming a buffer layer on a silicon substrate, a second step of epitaxially forming a platinum group conductive thin film of a face-centered cubic structure on the buffer layer, wherein the buffer A layer is formed on the TiN layer and on the TiN layer.
Ti _1-x Al _x N layer (where 0 <x ≦ 0.4)
A method for manufacturing a thin film laminate, comprising: 5. The buffer layer is formed at a growth rate of 1 to 10 nm / min and has a surface average roughness of 0.1 to 0.5 n.
m, and the film thickness is 50-300 nm, The manufacturing method of the thin film laminated body of Claim 4 characterized by the above-mentioned. 6. The platinum group conductor thin film has a thickness of 1 to 10 nm /
Formed at a growth rate of 10 minutes and a surface average roughness of 0.1 to 1.
The method for producing a thin film laminate according to claim 4 or 5 , wherein the thickness is 0 nm and the film thickness is 50 to 500 nm.