JP3474352B2 - Thin film capacitor and semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film capacitor and a semiconductor device, and more particularly to a base barrier layer of a semiconductor memory device using an epitaxial ferroelectric thin film.

[0002]

2. Description of the Related Art Recently, a storage device (ferroelectric memory) using a ferroelectric thin film as a storage medium has been actively developed and partly put to practical use. Since the ferroelectric memory is non-volatile, the storage capacity is not lost even after the power is turned off, and when the film thickness is thin enough, the spontaneous polarization reverses quickly, enabling high-speed writing and reading similar to DRAM. It has characteristics such as being. In addition, a 1-bit memory cell can be manufactured with one transistor and a ferroelectric capacitor, which is suitable for large capacity.

A ferroelectric thin film suitable for a ferroelectric memory has a large remanent polarization, a small temperature dependency of the remanent polarization, a long-term retention of the remanent polarization, and repeated polarization inversion. It is necessary that the deterioration of remanent polarization is small.

At present, lead zirconate titanate (PZT) is mainly used as a ferroelectric material. Despite the high Curie temperature (300 ° C. or higher) and the magnitude of spontaneous polarization, It is said that Pb, which is the main component, cannot be applied to miniaturization because it is likely to diffuse and evaporate at a relatively low temperature (500 ° C.).

On the other hand, the present inventors have found that Pt / MgO
By using a ferroelectric thin film epitaxially grown on the above, it was found that barium titanate (hereinafter abbreviated as BaTiO ₃ ) originally having a Curie temperature of about 120 ° C. has a Curie temperature of 200 ° C. or more at a film thickness of 60 nm. . BaTiO ₃ was considered to be difficult to apply to a practical memory due to its small remanent polarization and large temperature dependence of the remanent polarization. However, if the Curie temperature can be increased by the effect of this epitaxial growth, the ferroelectricity will increase. It may be used as a storage medium for body memory. further,
By using Pt as the lower electrode and using the composition region x = 0.3 to 0.9 of barium strontium titanate (Ba _x Sr _1-x TiO ₃ hereafter referred to as BSTO) as the ferroelectric substance, It has been experimentally confirmed that the ferroelectricity is expressed (x ≦ 0.7) even in the composition region where the property should not be exhibited. According to this report, the film thickness is 200n
Strain-induced ferroelectricity due to epitaxial growth was confirmed even with a relatively thick film thickness of about m. This confirms the ferroelectricity in the film thickness region where the remanent polarization is relatively large, and is expected to be put to practical use.

[0006]

However, when a semiconductor substrate on which a switching transistor is actually formed and a memory cell made of a perovskite ferroelectric substance are combined, the elements such as Sr and Ba forming the high dielectric constant thin film are combined. However, if it diffuses into the transistor, it adversely affects the switching operation, so that a barrier layer that prevents mutual diffusion with the semiconductor substrate is required. Further, in order to obtain the above-mentioned epitaxial effect, this barrier layer also needs to be epitaxially grown on the semiconductor substrate. However, it is extremely difficult to incorporate the MgO substrate into the silicon device.

Titanium nitride (hereinafter TiN) as a barrier layer
Can be used. TiN has a lattice constant close to that of MgO (misfit 0.3%), and is also used as a barrier metal in current Si devices. Further, since it is a high melting point compound (3000 ° C. or higher), it is also very strong in terms of heat. Also, the specific resistance is polycrystalline and is about 50 μΩ.
When the electric characteristics in the film thickness direction are to be utilized, it is considered that there is an advantage that the contact resistance can be lowered.

However, TiN has a very large mismatch with the (100) or (111) Si substrate of about 30%, and it has been considered difficult to epitaxially grow it by the conventional sputtering method.

However, in recent years, J. Narayan et
al, Appl. Phys lett 61 (11)
(1992) 1290, J. Appl. Phys. 75
(2) (1994) 860 using laser deposition method
Epitaxial growth of iN on Si (100) or (111) substrates has been reported. In addition, the inventors also
Si (10) of TiN was formed using the reactive ion beam deposition method.
Successful epitaxial growth on 0) or (111) substrates. Furthermore, we have this TiN (100) //
Substrate temperature 600 on Si (100) epitaxial film
Pt and BS by rf sputtering at ℃
It was found that TO grows epitaxially.

However, BSTO on this Si substrate
When the polarization versus electric field (PE) hysteresis of the thin film capacitor was measured for the (Ba: Sr = 1: 1) epitaxial film, the value of the residual polarization obtained from this hysteresis curve was as small as 0.01 C / m ^2. Only the value was obtained. It is considered that this is because the strain that should be introduced due to the mismatch of lattice constants is relaxed by the oxygen deficiency. At this time, the sputtering gas composition was such that the O ₂ / Ar ratio was 25% to form the film.
In fact, in the Pt / BSTO film on the MgO substrate, if the sputtering gas composition is O ₂ 100%, the value of remanent polarization becomes O.
Compared with the case of ₂ / Ar ratio of 25%, it is about 3 times.

However, when Pt and BSTO are deposited on the TiN (100) // Si (100) epitaxial film at a substrate temperature of 600 ° C. by the rf sputtering method using a sputtering gas composition of 100% O ₂ .
There is a problem that the TiN portion is oxidized, and neither Pt / BSTO thereon grows epitaxially and becomes a polycrystalline film.

The present invention has been made in view of the above points, and an object of the present invention is to provide a thin film capacitor structure capable of epitaxially growing a perovskite dielectric layer with few oxygen defects.

[0013]

The present invention comprises a single crystal substrate; Ti epitaxially grown on the single crystal substrate.
A barrier layer made of a solid solution of N and MN (where M is at least one selected from Al, V, Mo, Nb and Ta); a lower electrode epitaxially grown on this barrier layer; an epitaxial growth on this lower electrode A thin film capacitor, comprising: a dielectric layer having a perovskite type crystal structure described above; and an upper electrode formed on the dielectric layer. Further, it is a semiconductor device in which this thin film capacitor is formed on a semiconductor substrate on which active elements such as transistors are formed, for example, FRAM (ferroelectric memory).

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION TiN has a B1 rock salt structure (Na
Cl type), and various B1 type structures form stable nitrides and solid solutions. The nitride capable of having the B1 type structure includes 3A group: ScN, YN 4A group: ZrN, HfN 5A group: VN, NbN, TaN 6A group: CrN Lanthanoid: LaN, CeN, PrN, NdN, Sm.
N, EuN, GdN, TbN, DyN, HoN, Er
N, TmN, YbN, LuN actinoids: ThN, UN, PuN and the like. Each of these has a coordination number of 6: 6,
Easy to form a solid solution. Also, as a special example, it is known to form a solid solution with aluminum nitride (AlN) having a wurtzite structure. These compounds are epitaxially grown on a single crystal semiconductor substrate by using a thermal non-equilibrium reaction such as a sputtering method, an ion beam method, or laser deposition.

Among these compound solid solutions, particularly Al,
The reason why it is limited to the (Ti _1-x M _x ) N epitaxial layer containing V, Mo, Nb, and Ta is that the free energy of oxide formation of these elements is equal to or lower than TiN. .

Therefore, by using these solid solutions, it is possible to suppress the oxidation of the barrier layer itself at the time of forming the dielectric layer and form the barrier layer maintaining the epitaxial structure. This makes it possible to provide an epitaxial dielectric layer with few oxygen vacancies. Therefore, in the case of a ferroelectric substance, the value of remanent polarization becomes large, and it becomes possible to form a good ferroelectric memory on a semiconductor substrate.

The dielectric material having a perovskite type crystal structure that can be used in the present invention includes barium titanate (BaTiO ₃ ) and strontium titanate (S).
rTiO ₃ ), calcium titanate (CaTiO ₃ ),
Simple perovskite type oxides such as barium stannate (BaSnO ₃ ) and barium zirconate (BaZrO ₃ ), barium magnesium niobate (Ba (Mg _1/3
Nb _2/3 ) O ₃ ), barium magnesium tantalate (Ba (Mg _1/3 Ta _2/3 ) O ₃ ), and other complex perovskite-type oxides, and a plurality of these oxides are simultaneously solid-dissolved. It is needless to say that the above system is exemplified and further, some deviation from the stoichiometric ratio is allowed.

When a dielectric film made of such a dielectric material is epitaxially grown on a conductive substrate, the growth orientation is a tetragonal (001) plane or a cubic system of the dielectric film and the conductive substrate. Are preferably grown so that their (100) planes are parallel to each other. Examples of the method for forming the dielectric film include reactive vapor deposition, rf sputtering, laser ablation, MOCVD, and the like. Sputtering is particularly preferred for forming the.

Further, the thickness of the dielectric film is preferably 70 nm or more from the viewpoint of obtaining a sufficient remanent polarization or effective dielectric constant when used in a ferroelectric memory, and practically 70 nm or more and 1 μm or less. It is desired to be within the range. However, the paraelectric dielectric film used for DRAM and the like can be sufficiently applied to the capacitor and the like of the memory cell of DRAM even if the film thickness is less than 70 nm.

When the barrier layer is represented by (Ti _1-x M _x ) N, X must be set within the solid solution range. Also the substrate,
In particular, it is necessary to select so as to grow epitaxially on the Si substrate. Preferably, O <X ≦ 0.15. Also M
The effect of the element appears in a small amount of solid solution, but preferably 0.01 ≦ X ≦ 0.15.

The thickness of the (Ti _1-x M _x ) N barrier layer is preferably as thin as possible in the range where the effect of preventing diffusion can be obtained, and is preferably about 10 nm to 100 nm. The lower electrode needs to have an appropriate lattice constant for epitaxially growing the dielectric film, and Pt or the like can be given as an example.
It is also possible to add an alloy element as needed. It is also possible to use Pt or the like as the electrode.

[0022]

EXAMPLES Examples of the present invention will be described below. 1A and 1B are schematic views of a thin film capacitor. FIG. 1A is a plan view and FIG. 1B is a sectional view. A barrier layer (5), a lower electrode (2), a dielectric layer (3) and an upper electrode (4) are sequentially laminated on a substrate (1). In this example, the upper electrode (4) is separated, and the regions corresponding to the individual electrodes become individual capacitors.

First, the Si (100) substrate which had been surface-etched with a 1 vol% hydrofluoric acid solution for 3 minutes and rinsed off with ultrapure water for 30 minutes was used as the substrate (1) in this example.

On this, a (Ti _1-x Al _x ) N film was formed by reactive rf sputtering using Ti and Al targets (barrier layer (5)). At this time, a sputtering gas was a mixed gas of N2: 3 sccm and Ar: 30 sccm, and the substrate temperature was 600 ° C. When the crystallinity of this film was confirmed by RHEED equipped in a vacuum chamber, it was confirmed that the diffraction pattern was the same as that of TiN and streaks were observed, and a flat epitaxial film was formed.

Furthermore, when the composition of this film was measured by RBS, it was confirmed that x of (Ti _1-x Al _x ) N was 0.1. In the case where Al is solid-dissolved in TiN for epitaxial growth, _x in (Ti _1-x Al _x ) N is preferably 0.15 or less. This is because the coordination number when originally forming a nitride is 4 for Al, and it is difficult to form a TiN solid solution.

On this Ti _0.9 Al _0.1 N film, Pt was formed by rf magnetron sputtering at a substrate temperature of 500 ° C. to form a base electrode (3). At this time, the thickness of the Pt film was set to about 100 nm. On top of this, Ba _0.5 Sr
_0.5 TiO ₃ film (dielectric layer (4)) with a thickness of about 200n
m, rf magnetron sputtering method. At this time, the substrate temperature is 600 ° C., and the sputtering gas is O ₂ 100.
%. A sintered body (4 inches, 5 mm thick) of the same composition was used as the sputter target. Further, the upper electrode Pt (5) was formed at room temperature by the rf sputtering method using lift-off.

In order to examine the oxidation state of the underlying barrier film in this thin film, the composition analysis profile in the depth direction was measured by Auger electron spectroscopy. As a result, Ti _0.9 Al was obtained.
The oxygen atom concentration in the _0.1 N film portion was below the detection limit of Auger electrons as shown in FIG. 2, and almost no oxidation was observed.

As a comparative example, FIG. 3 shows a profile under the same conditions when a TiN epitaxial film is used as a barrier layer. From this, it was found that the oxidation resistance is improved by using the epitaxially grown solid solution.

The results of evaluating the crystallinity of this thin film by the X-ray diffraction method are shown in FIG. It is to be noted that this is generally called the φ-scan method, and the gonio axis is fixed at an angle of θ-2θ corresponding to the plane with respect to an axis positioned at a predetermined angle with respect to the axis perpendicular to the substrate, By rotating in the in-plane direction, the peak based on the axial symmetry is detected. In addition, here, φ-sca with respect to the <110> axis
n have gone. As seen in FIG. 4, Pt, Ti _0.9
Epitaxial growth of all (100) faces of Al _0.1 N and BSTO was confirmed.

Further, the polarization versus electric field (PE) hysteresis curve of the thin film capacitor using this BSTO film was measured. 500Hz using a Sawyer tower circuit for measurement
Was measured at room temperature (22 ° C.). As a result, the magnitude of the remanent polarization obtained from the hysteresis curve was as large as 0.2 C / m ^2, and it was confirmed that the ferroelectric memory can be formed on the semiconductor substrate.

Further, M elements other than Al (V, Nb, M
The same effect was obtained with o). FIG. 5 is a sectional view showing an example of a dynamic access memory (DRAM) semiconductor memory device of the present invention. 41 is a first conductivity type semiconductor substrate, 42 is an element isolation oxide film, 43 is a gate oxide film, 4
4 is a word line, 45 and 47 are interlayer insulating films, 46 is a second conductivity type impurity diffusion layer, 48 is a bit line, 49 is a planarizing insulating film, 50 is a polishing stopper layer, 51 is a single crystal silicon storage node, 52 is an epitaxial barrier metal, 53 is an epitaxial lower electrode, 54 is an epitaxial dielectric film, and 55 is an upper electrode.

FIG. 6 shows a schematic cross-sectional view in the order of steps of the example shown in FIG. FIG. 6A is a cross-sectional view after forming the transistor portion of the memory cell and the bit line 48, and then forming the planarization insulating film 49 and the polishing stopper layer 50. Here, an etch back method may be used to planarize the insulating film, or a CMP method or the like may be used. An insulating film such as aluminum oxide can be used as the polishing stopper layer 50.

Next, as shown in FIG. 6B, a contact hole to the second conductivity type impurity diffusion layer 46 is continuously formed in the opening of the polishing stopper layer 50 by known photolithography and plasma etching. The storage node 51 was formed by the selective growth technique of single crystal silicon. The storage node 51 is grown at a growth temperature of 820 by, for example, an LPCVD method using dichlorosilane as a source gas.
This can be performed by selectively embedding single crystal silicon at ℃.

Next, as shown in FIG. 6C, CMP is performed.
Alternatively, the single crystal silicon formed on the polishing stopper layer 50 is removed by mechanical polishing. Then, FIG. 6 (d)
As shown in FIG. 6, after forming a shallow trench by photolithography and plasma etching, a platinum thin film to be the epitaxial barrier metal 52 and the lower electrode 53 was formed by a sputtering method (FIG. 6E).

Then, the polishing stopper layer 5 is again formed by the CMP method.
After removing the epitaxial barrier metal and the platinum thin film formed on 0, the epitaxial dielectric film 54 and the upper electrode 55 are sequentially formed. Note that a known magnetron sputtering method, MOCVD method, or the like can be used for forming the dielectric film.

[0036]

As is apparent from the above description, by using the solid solution having the composition of the present invention, it is possible to suppress the oxidation of the barrier metal itself at the time of forming the dielectric layer and form the barrier layer maintaining the epitaxial structure. be able to. As a result, it is possible to provide an epitaxial dielectric layer with few oxygen vacancies, and therefore, the value of remanent polarization in the ferroelectric becomes large, and it becomes possible to form a good ferroelectric memory on a semiconductor substrate. .

[Brief description of drawings]

FIG. 1 is a schematic view showing a thin film capacitor structure of the present invention.

FIG. 2 is a depth profile diagram in Auger electron spectroscopy of an epitaxial film when a Ti _0.9 Al _0.1 N film is used as a barrier layer.

FIG. 3 is a profile diagram in the depth direction in Auger electron spectroscopy of an epitaxial film when a TiN film is used as a barrier layer.

FIG. 4 is an X-ray diffraction diagram of an epitaxial film in an example.

FIG. 5 is a schematic sectional view showing an embodiment of a semiconductor device of the present invention.

FIG. 6 is a schematic process sectional view showing an embodiment of the semiconductor device of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H01L 29/788 29/792 (56) References JP-A-8-64786 (JP, A) JP-A-9-82913 (JP, A) JP-A-6-196648 (JP, A) JP-A-9-289297 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/8242 H01L 21/822 H01L 21 / 8247 H01L 27/04 H01L 27/108 H01L 29/788 H01L 29/792 JISC file (JOIS)

Claims (2)

(57) [Claims] 1. A single crystal substrate; TiN and MN epitaxially grown on this single crystal substrate (where M is Al,
(At least one selected from V, Mo, Nb and Ta)
And a lower electrode epitaxially grown on the barrier layer; a dielectric layer having a perovskite crystal structure epitaxially grown on the lower electrode; and an upper portion formed on the dielectric layer. A thin-film capacitor comprising an electrode. 2. A semiconductor device comprising the thin film capacitor according to claim 1, and the active element, wherein the single crystal substrate is a semiconductor substrate on which an active element is formed.