RU2615099C1 - Method for europium disilicide epitaxial film growing on silicon - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method for europium disilicide epitaxial film production on a silicon substrate, and can be used to create source/drain contacts in MOSFET technology with a Schottky barrier (SB-MOSFET), and to create spintronic devices as contact injector/detector of spin-polarized carriers. The method consists in atomic europium flow deposition under pressure P_Eu=(0.55÷)×10^-8 Torr on a clean Si(001) substrate surface, heated to T_s=400±20°C, until a europium disilicide film of the desired thickness is formed. When the film thickness reaches 100 Å or more, further deposition is performed at T_s=560±20°C to form a europium disilicide film of the desired thickness.

EFFECT: formation of epitaxial EuSi² films by molecular-beam epitaxy, which allows to achieve the required quality of contacts in microelectronics.

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Description

Technical field

The invention relates to methods for producing epitaxial thin-film materials, namely europium disilicide. In contact with silicon, this material forms the minimum Schottky barrier among silicides of rare-earth metals. Due to this fact, the EuSi ₂ / Si epitaxial contact has great potential in microelectronics, and the proposed procedure for its formation can be used to create source / drain contacts in the production technology of Schottky field-effect transistors (SB-MOSFET). At the same time, in the antiferromagnetic phase at temperatures below 40 K, EuSi ₂ can be used to create spintronics devices as an injector contact / detector of spin-polarized carriers in silicon.

State of the art

The invention is known "A method for producing mesotoxic layers of cobalt disilicide in silicon" (Patent SU 1795821 A1), in which cobalt disilicide layers embedded in silicon are obtained by ion implantation of Co into silicon and subsequent annealing. The disadvantage of this method is the difficulty of creating thin (<10 nm) layers required in microelectronics.

A known method of forming metal silicides, including the deposition of a metal layer on silicon and its subsequent melting under the influence of a compression plasma stream (Patent RU 2405228 C2). The disadvantage of this method is the low crystalline quality of the obtained silicide layers, as well as the concentration gradient of the elements along the film thickness.

The invention is known "Method of forming a film of metal silicide" (Patent No. US 5047111 A), which consists in creating a layered metal / silicon superstructure and subsequent annealing of this structure, leading to the formation of a single crystal layer of silicide. The disadvantage of this method is the need to use a flux of Si atoms, as well as the impossibility of obtaining epitaxial EuSi ₂ structures with it.

The invention is known "Method for the formation of metal silicide films on silicon substrates by deposition of an ion beam" (Patent No. US 4908334 A), in which homogeneous stoichiometric, having a large grain size and low resistance of a metal silicide film are obtained by depositing low-energy metal ions on a heated surface (for increase diffusion rate) silicon wafer. The disadvantage of this method is the more laborious (in comparison with thermal evaporation) process of ion beam formation.

Also known is RF patent 2557394 "Method for growing epitaxial films of europium monoxide on silicon", in which the europium silicide submonolayer is formed by molecular beam epitaxy at a substrate temperature T _s = 640 ÷ 680 ° C and a pressure of the stream of europium atoms P _Eu = (1 ÷ 7 ) ⋅10 ^-8 Torr, after which the deposition is carried out at a substrate temperature T _s = 340 ÷ 380 ° C, oxygen flow pressure P _Ox = (0.2 ÷ 3) ⋅10 ^-8 Torr and europium atom flux pressure P _Eu = ( 1 ÷ 4) ⋅10 ^-8 Torr, then the deposition is carried out at the substrate temperature T _s = 430 ÷ 490 ° C, oxygen flow with pressure P _Ox = (0.2 ÷ 3) ⋅10 ^-8 T orp, and the flux of europium atoms with a pressure P _Eu = (1 ÷ 7) ⋅ 10 ^-8 Torr. The procedure also provides for a number of vacuum anneals:

- intermediate annealing after the first stage (T _s = 340 ÷ 380 ° C) of growth, carried out at a temperature T _s = 490 ÷ 520 ° C;

- final annealing in the temperature range T _s = 500 ÷ 560 ° C

However, the claimed formation conditions do not allow obtaining high-quality EuSi2 films in contact with silicon.

Known inventions are “Heterostructures of metal-silicon silicide” and “Method for the production of metal-silicon-silicide heterostructures” (Patents Nos. US 4,492,971 A and US 4,554,045 A), in which a metal silicide layer is formed by simultaneous deposition on a silicon surface heated to T _s = 550 ÷ 850 ° C, silicon atoms and metal from the corresponding atomic fluxes or by deposition on the silicon surface of only metal atoms. The disadvantage of the first method described in this method is the need to use an additional stream of silicon atoms. The second method is the closest analogue of our technical solution. However, the claimed formation conditions do not allow to obtain high-quality EuSi ₂ films in contact with silicon.

Disclosure of invention

The technical result of the present invention is the formation of epitaxial EuSi ₂ films by molecular beam epitaxy, which allows to achieve the required contact quality in microelectronics.

To achieve a technical result, a method is proposed for growing EuSi ₂ epitaxial films on a silicon substrate by molecular beam epitaxy, which consists in the deposition of an atomic stream of europium with a pressure of P _Eu = (0.5 ÷ 5) × 10 ^-8 Torr on a previously cleaned surface of the Si substrate ( 001), heated to T _s = 400 ± 20 ° C until a europium disilicide film is formed of the required thickness.

Moreover, upon reaching a film thickness of 100 Å or more, further deposition is carried out at T _s = 560 ± 20 ° C until a europium disilicide film of the required thickness is formed.

In molecular beam epitaxy units, an ambiguous interpretation of substrate temperatures usually takes place. In the present invention, the temperature of the substrate is considered to be the temperature determined by the readings of an infrared pyrometer. The flow pressure is the pressure measured by the ionization pressure gauge in the position of the substrate.

Brief Description of the Drawings

The invention is illustrated by drawings:

In FIG. Figure 1 shows the images of diffraction of fast electrons along the [110] azimuth of the Si (001) substrate at different stages of Eu disilicide formation: (a) - Original Si (001) surface: reconstruction (2 × 1) + (1 × 2); (b) - 30 A of grown EuSi ₂ at 400 ° C; (c) - 50 A grown EuSi ₂ at 400 ° C; (d) the end of growth at 400 ° C, 530 A grown EuSi ₂ ; (e) the end of growth at 560 ° C, 560 A grown EuSi ₂ .

In FIG. Figure 2 shows an X-ray diffraction pattern of a SiO _x / EuSi ₂ / Si (001) sample. The tab of the figure shows the region containing the peak of EuSi ₂ (004). Intensity oscillations indicate atomically sharp EuSi ₂ / Si (001) and SiO _x / EuSi ₂ interfaces. Reflexes marked with * refer to diffraction from a silicon substrate.

In FIG. Figure 3 shows the structure of the EuSi ₂ / Si (001) contact in the SiO _x / EuSi ₂ / Si (001) system obtained by transmission electron microscopy (TEM). a, Bright field TEM image of a cross section with a low magnification along the axis of the [110] zone of the Si (001) substrate, showing the absence of side phases. b, Electron diffraction image on a EuSi ₂ film combined with diffraction from a Si (001) substrate, showing their relative orientation, c, Bright-field image of a TEM of a cross section with an average increase in the EuSi ₂ / Si interface. d, High-magnitude TEM image of a high-magnitude cross-sectional TEM showing the atomic level EuSi ₂ / Si (001) interface.

In FIG. Figure 4 shows the current – voltage characteristics of the Schottky barrier formed in the EuSi ₂ / n-Si structure, measured for a number of temperatures from 160 K to 300 K with a step of 20 K. The linearized temperature dependence of the saturation current on the inverse temperature, used to determine Schottky barrier heights.

The implementation of the invention

Example 1 of the method of the invention.

The Si (001) substrate is placed in an ultrahigh vacuum chamber (residual vacuum P <1⋅10 ^-10 Torr). Then, to remove the layer of natural oxide from the surface of the substrate, the substrate is heated to a temperature of T _s = 900 ÷ 1100 ° C. The fact of cleaning the surface of oxide is established by diffraction of fast electrons: in the [110] directions, a reconstruction picture of (1 × 2) + (2 × 1) appears. After this, the substrate cools down to T _s = 400 ± 20 ° C and the Eu cell shutter opens, heated to such a temperature (~ 500 ° C) to provide a pressure of the atom flux Eu Р _Eu = (0.5 ÷ 5) × 10 ^{- 8} Torr. The growth cycle lasts until a film of the required thickness is obtained. We have grown films up to 150 nm thick. To prevent exposure of EuSi _{2 to} air when the sample is removed from the chamber, at the end of growth, the film is closed with a continuous protective layer, for example, Al or silicon oxide with a thickness of 2 nm or more.

Example 2

The growth cycle at the substrate temperature T _s = 400 ± 20 ° C, described in Example 1, lasts until the formation of the EuSi ₂ film with a thickness of 100 Å or more, then the temperature of the substrate rises to 560 ± 20 ° C, at which subsequent growth occurs. In the process of temperature rise, the growth process may not be interrupted. The duration of the second stage at elevated temperature is 10 minutes or more. After this, the sample is also covered with a protective layer.

The film is monitored in situ using fast electron diffraction. The dynamics of diffraction patterns during growth is shown in FIG. 1. Exceeding the limits of the described modes can lead to the formation of a polycrystalline EuSi ₂ film, an Eu layer, or other phases of Eu silicides, which is unacceptable in the manufacture of the contact.

Studies of manufactured samples using x-ray diffractometry (Fig. 2) showed that EuSi ₂ films are single-crystal and have an orientation (001), like a silicon substrate. The lattice parameter of EuSi ₂ determined from the peak position is d = 13.633 ± 0.006 Å, which corresponds to the lattice parameter of bulk three-dimensional EuSi ₂ samples. It should also be noted that intensity oscillations near the EuSi ₂ (004) peak (tab of Fig. 2) indicate atomic smoothness of the EuSi ₂ / Si and SiO _x / EuSi ₂ interfaces.

The study of the samples using transmission electron microscopy proves the absence of extraneous phases, the uniformity of the films along the thickness (Fig. 3a), the orientation of the crystal structure of EuSi ₂ relative to the substrate (Fig. 3b), i.e. epitaxial growth of the EuSi ₂ film, as well as the sharpness of the EuSi ₂ / Si and SiO _x / EuSi ₂ interfaces (Fig. 3a, Fig. 3c, Fig. 3d).

The asymmetric current – voltage characteristics of the EuSi ₂ / n-Si structure, measured in the temperature range 160–300 K, are shown in FIG. 4. With a small bias voltage, the characteristics are exponential. The Schottky barrier height determined by the linear dependence of the saturation current on the reciprocal temperature is 0.21 ± 0.1 eV, which is significantly less than the values obtained for other rare-earth metal silicides.

Example 2

The surface of silicon substrates is cleaned of atmospheric oxide by heating them to a temperature T _s = 770–800 ° C and exposing them in a stream of Eu atoms with a pressure P _Eu = (0.1–5) × 10 ^-8 Torr. The rest of the method is implemented as in Examples 1, 2.

Example 3

The silicon substrate is cleaned of natural oxide before it is loaded into the chamber by washing in a 5% aqueous HF solution, and passivation of silicon bonds by H ⁺ ions is achieved, which subsequently desorb from the surface upon heating. The rest of the method is implemented as in Examples 1, 2.

Thus, the invention allows to obtain films of EuSi ₂ on Si (001), which:

- are epitaxial;

- do not contain extraneous phases;

- have sharp EuSi ₂ / Si interfaces and a protective layer / EuSi ₂ ;

- are uniform along the thickness;

- in contact with n-type silicon form a Schottky barrier with a height of 0.21 ± 0.1 eV, which is significantly less than the values obtained for other rare-earth metal silicides.

Claims (1)

A method of growing an epitaxial film of europium disilicide on a silicon substrate, including the deposition of an atomic stream of europium by molecular beam epitaxy, characterized in that the surface of the silicon substrate Si (001) is pre-cleaned, heated to Ts = 400 ± 20 ° C, and the atomic stream of europium is deposited with pressure P _Eu = (0.5 ÷ 5) × 10 ^-8 Torr until a film thickness of 100 Å or more is reached, and then the substrate temperature is increased to Ts = 560 ± 20 ° C and deposition is performed until a europium disilicide film is formed of a given thickness.

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