JP2002050623A - METHOD FOR PRODUCING ON SILICON(Si) SUBSTRATE CRYSTALLINE ALKALINE-EARTH-METAL OXIDE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new improve method for creating a crystalline alkaline- earth-metal oxide on an Si substrate. SOLUTION: This new improved method is the method, where, from an Si substrate accompanied on its surface by an amorphous silicon dioxide, a crystalline alkaline-earth-metal oxide is obtained on the Si substrate. The substrate is heated to a temperature within a range of 700-800 deg.C, and is exposed to the molecular beam of alkaline-earth-metal elements in a molecular-beam epitaxy-chamber, under a pressure which is within a range of about 10-9-10-10 Torr. During its molecular-beam epitaxy, its surface is monitored by a RHEED method for deciding the conversion of the amorphous silicon dioxide into an alkaline-earth-metal oxide. When the alkaline-earth-metal oxide is produced, a supplementary material layer, e.g. an alkaline-earth-metal oxide having a supplementary thickness, a single-crystal ferroelectric, or a high dielectric- constant oxide is produced on Si for the application of a nonvolatile high-density memory device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for forming a crystalline alkaline earth metal oxide on a silicon substrate in preparation for a subsequent manufacturing process.

[0002]

2. Description of the Related Art Orderly stable silicon (Si) surfaces have been used in many device applications, such as ferroelectrics or high-k oxides for non-volatile high density memory devices. It is highly desirable for subsequent epitaxial growth of single crystal thin films on silicon. In particular, for continued growth of single crystal oxides such as perovskite,
It is important to place a regular transition layer on the surface.
BaO on Si (100), the good growth of these oxides, such as BaTiO _3, Ba and deposition 1/4 monolayer on Si (100) using reactive epitaxy at 850 ° exceeds C Some have been reported to be based on BaSi ₂ (cubic) templates. For example, see the following document. R. McKee et al. Appl.Phys.Lett. 59 (7), pp.782-784
(August 12, 1991); R. McKee et al., Appl. Phys. Lett.
63 (20), pp. 2818-2820 (November 15, 1993); R. Mc
Kee et al. Mat.Res.Soc.Symp.Proc., Vol.21, pp.131-135
(1991); U.S. Patent No. 5,225,01 filed July 6, 1993, "PROCESS FOR DEPOSITING AN OXID
E EPITAXIALLY ONTO A SILICON SUBSTRATE AND STRUCTU
RES PREPARED WITH THE PROCESS ”; January 9, 1996
U.S. Pat.
R DEPOSITING EPITAXIAL ALKALINE EARTH OXIDE ONTO A
SUBSTRATE AND STRUCTURES PREPARED WITH THE PROCES
S ". Due to the need for high temperatures for the preparation of molecular beam epitaxy planes and template (eg, BaSi ₂ )
The above process is truly a high temperature process. The main problem is that this high temperature process requires much higher heat supply and promotes diffusion within the structure, which is often undesirable or not possible.

[0003] It is therefore highly desirable to have a low temperature process that is simple to implement and that provides a regular wafer surface for subsequent thin film epitaxy and is compatible with molecular beam epitaxy.

[0004] It is an object of the present invention to provide a new and improved method of making crystalline alkaline earth metal oxides on Si substrates.

It is another object of the present invention to provide a new and improved method of making crystalline alkaline earth metal oxides on Si substrates using low temperatures compatible with molecular beam epitaxy.

Yet another object of the present invention is to provide a simple method that requires little monitoring during the process,
It is to provide a new and improved method of making a crystalline alkaline earth metal oxide on a substrate.

It is yet another object of the present invention to provide a new and improved method of making a crystalline alkaline earth metal oxide on a Si substrate that provides a regular wafer surface.

It is yet another object of the present invention to provide a new and improved method of making a crystalline alkaline earth metal oxide on a Si substrate without unnecessarily complicating subsequent process steps. is there.

[0009]

SUMMARY OF THE INVENTION In the method of forming a crystalline alkaline earth metal oxide on a Si substrate, the above and other problems are at least partially solved and the above and other objects are achieved. In this method, a Si substrate with silicon dioxide on the substrate surface is provided. The substrate is heated to a temperature lower than the sublimation temperature of the silicon dioxide, the substrate surface is exposed to an alkaline earth metal lines, converting amorphous silicon dioxide to the crystalline alkaline earth metal oxides. Depending on the application, an alkaline earth metal oxide, a single crystal ferroelectric or a high dielectric constant oxide having a further thickness for nonvolatile high density memory device application may be formed on silicon on the alkaline earth metal oxide. Can be conveniently formed.

[0010]

Referring to the drawings, in which like elements are designated with like numerals throughout the drawings, FIG. 1 shows a silicon (Si) substrate 10 having silicon dioxide 11 formed on its surface.
Is illustrated. Silicon oxide (usually SiO ₂ ) may be naturally present when the silicon substrate 10 is exposed to air (oxygen), or may be intentionally converted to oxide in a controlled manner by methods well known in the art. It can also be grown. Very good SiO ₂ / Si interface can be obtained routinely in silicon technology. However, since the silicon dioxide layer 11 is not single crystal but amorphous, to grow another single crystal material on the substrate, the oxide /
It is desirable to provide a single crystal oxide without including the amorphous silicon layer 11 at the silicon interface.

In order to continuously grow a single crystal oxide on the Si substrate 10, an epitaxial transition layer is extremely important. Alkaline earth metals such as barium, strontium and calcium have been found to be stable on silicon substrates. For example, a BaSi ₂ / BaO transition layer is grown on a silicon substrate by molecular beam epitaxy (MBE) as described in the references and patent applications cited above. These transition layers grow on clean Si substrates by reactive epitaxy and MBE. However, the growth of a single layer or less of BaSi ₂ requires precise thickness control, and the subsequent growth of BaO also depends on barium flux and oxygen pressure. Precise control of thickness and pressure complicates the growth process, substantially increasing cost and increasing processing time.

Si substrate 10 and amorphous silicon dioxide layer 11
Is heated to a temperature lower than the sublimation temperature of the oxide layer 11. In general, silicon dioxide sublimes at temperatures greater than 850 degrees Celsius, so that substrate 10 may be 700 to 800 degrees Celsius.
Preferably, it is heated to a temperature in the range of degrees. This can be done in a molecular beam epitaxy chamber. Alternatively, the substrate 10 is at least partially heated in the preparation chamber, after which the substrate 10 is transferred to the growth chamber to complete the heating.

[0013] The pressure in the growth chamber is reduced to a range of about 10 ^-9 to 10 ^-10 Torr.

When the substrate 10 is properly heated and the pressure in the growth chamber is properly reduced, the surface of the substrate 10 having the silicon dioxide layer 11 thereon is exposed to the alkaline earth metal lines. This is shown in FIG. In a preferred embodiment, the wire is barium, strontium, or a combination thereof generated by resistively heating the emission cell or from an electron beam evaporation source. In one example,
Substrate 10 and oxide layer 11 are exposed to a barium wire. Barium replaces the silicon in the silicon dioxide and converts layer 11 to BaO crystalline buffer layer 12.
The replaced silicon is volatile silicon monoxide (Si
O) or bond with the pure silicon of the substrate 10, but the formation of BaSi _{2 at} the Si / BaO interface is ignored.

The conversion of silicon dioxide to alkaline earth metal oxide layer 12 is due to the fact that the change in enthalpy (ie, heat of formation ΔH) for alkaline earth metal oxides is higher than silicon dioxide per oxygen atom. See, for example, Table 1 below, which also lists the lattice constants of cubic alkaline earth metal oxides.

[0016]

[Table 1] This means that thermodynamically, alkaline earth metal oxides such as barium oxide are more stable than SiO ₂ and the following reactions occur.

Ba + SiO ₂ → BaO + SiO and 2Ba + SiO ₂ → 2BaO + Si BaO (a ₀ = 5.542Å) of a cubic single crystal is Si (a ₀
= 5.432Å), which indicates (1.
If the temperature of Si is sufficiently high (typically in the range of 700-800 degrees Celsius) and maintained below the sublimation temperature of SiO ₂ , an epitaxial layer of BaO will easily form on the surface of Si. I do. The lowest sublimation temperature reported for SiO ₂ is 850 degrees Celsius. Perfect lattice matching can be obtained by mixing (Ba, Sr) O layers with a mixture of Ba and Sr fluxes.

Generally, the amorphous silicon dioxide layer 11 on the silicon substrate 10 is approximately 50 ° thick and forms a reasonable transition layer 12. It goes without saying that, depending on the application, thinner or thicker layers can be used. However, if a thicker oxide layer is used, the conversion to an alkaline earth metal oxide layer may take longer. This is because thicker oxide layers have to be exposed to alkaline earth metal molecular beams for longer periods of time. The thickness of the amorphous silicon dioxide layer can be easily and very precisely controlled, so that finally the alkaline earth metal oxide layer can be very precisely controlled.

When the amorphous silicon dioxide layer 11 is exposed to an alkaline earth metal line, it causes reflection high energy electron diffraction (RHEED).
The surface is monitored using the on) method. This method is well documented in the art and
That is, it can be used while performing the exposure step in the growth chamber. The RHEED method is used to detect or detect the crystal structure of a surface, in which the end of the conversion process sharply changes from nothing for amorphous silicon dioxide to a strong, sharp light beam. Changes to Of course, it should be understood that if a particular fabrication process is provided and performed, it is not necessary to perform the RHEED method on all substrates.

Thus, a new improvement in the preparation of crystalline alkaline earth metal oxides on Si substrates using low temperatures compatible with molecular beam epitaxy and employing a simplified method requiring little monitoring during the process. The provided method is provided. This process is basically a self-control process that allows better control of uniformity and thickness.
In addition, the process is lower in temperature than the process according to the related art. In addition, the process depends on the application
For non-volatile, high density memory device applications, an additional thickness of alkaline earth metal oxide, single crystal ferroelectric or high-k oxide (shown as layer or layer group 15 in FIG. 3) on silicon Provides a crystalline ordered wafer surface that can be used to grow

While a particular embodiment of the present invention has been shown and described, further modifications and improvements will occur to those skilled in the art. Therefore, it is to be understood that the invention is not to be limited to the specific forms illustrated, but is to include in the appended claims all modifications that do not depart from the spirit and scope of the invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a Si substrate having a silicon dioxide layer on a surface.

2 is a cross-sectional view of the Si substrate of FIG. 1 in which a silicon dioxide layer has been converted to an alkaline earth metal oxide.

FIG. 3 is a cross-sectional view of the Si substrate of FIG. 2 in which another material is added on the surface of the alkaline earth metal oxide.

[Explanation of symbols]

 Reference Signs List 10 silicon substrate 12 crystalline buffer layer 15 additional layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H01L 21/203 H01L 21/203 Z (72) Inventor Gerald A. Halmark East, Gilbert, Arizona, USA Bawn Avenue 1544 (72) Inventor Jonathan K. Abrokwa East Ranch Road, Tempe, Arizona, U.S.A. 1963 (72) Inventor Corley Dee Obagard West Mulberry Drive, Phoenix, Arizona, U.S.A. 2034 (72) Inventor Rabbit Drawpad East Gemini Drive, Arizona, USA 1854 F-term (reference) 4G076 AA02 AB16 BF05 DA03 4G077 AA03 BB02 BB10 DA05 ED06 EE06 EF01 H A12 5F058 BA11 BC03 BD05 BF20 BJ01 5F103 AA04 DD27 GG01 HH03 LL08 NN01 NN04 PP02

Claims (10)

[Claims] 1. A method of making a crystalline alkaline earth metal oxide on a Si substrate, comprising: providing a Si substrate with silicon dioxide having a sublimation temperature on a surface of the substrate; Heating the substrate surface to below the sublimation temperature; and exposing the substrate surface to an alkaline earth metal wire. 2. The method of claim 1 wherein said alkaline earth metal comprises one of barium, strontium, calcium, magnesium and combinations thereof. 3. Si with silicon dioxide on the substrate surface
The step of providing a substrate may include removing native oxide (1) on the surface.
2. The step of claim 1 including the step of providing a Si substrate with 1) or the step of providing an Si substrate to produce an oxide on the surface. 4. The method of claim 1, wherein heating the substrate to a temperature below the sublimation temperature of the silicon dioxide comprises heating the substrate to a temperature in a range of 700 to 800 degrees Celsius. Item 7. The method according to Item 1. 5. The method of claim 1, wherein said exposing said substrate surface to said alkaline earth metal line is performed in a molecular beam epitaxy chamber. 6. The method according to claim 6, wherein the surface of the substrate is formed by molecular beam epitaxy
The step of exposing the alkaline earth metal wire in the chamber increases the pressure in the chamber from about 10 ^-9 to 10
The method of claim 5 including reducing the pressure to a range of ^-10 Torr. 7. The method of claim 1, further comprising the step of monitoring said surface by RHHED during said exposing step to determine the conversion of said silicon dioxide to crystalline alkaline earth metal oxide (12). Item 7. The method according to Item 1. 8. The method of claim 1, further comprising, following the exposing step, forming an additional layer of material on the substrate. 9. A method for producing a crystalline alkaline earth metal oxide (15) on a Si substrate, comprising: providing a Si substrate (10) with amorphous silicon dioxide (11) on the surface of said substrate. Heating the substrate to a temperature in the range of 700 to 800 degrees Celsius; about 10 ^-9 to 10 ^-10 Tor
exposing said substrate surface to an alkaline earth metal line in a molecular beam epitaxy chamber at a pressure in the range of r; and monitoring said surface by RHEED during said exposing step; Determining the conversion of (11) to crystalline alkaline earth metal oxide (12). 10. A method for producing a crystalline alkaline earth metal oxide (15) on a Si substrate, comprising: providing a Si substrate (10) with amorphous silicon dioxide (11) on a surface of said substrate. Heating the substrate to a temperature in the range of 700 to 800 degrees Celsius; about 10 ^-9 to 10 ^-10 Tor;
exposing the substrate surface to a line of one of barium, strontium and barium-strontium in a molecular beam epitaxy chamber at a pressure in the range of r; monitoring the surface by RHEED during the exposure step; Determining the conversion of said amorphous silicon dioxide to one of crystalline barium oxide (12), strontium oxide and barium oxide-strontium oxide; and crystalline barium oxide of said amorphous silicon dioxide;
Forming a further layer of material following conversion to said one of strontium oxide and barium-strontium oxide.