CN1217036C

CN1217036C - Method for preparing crystalline alkaline earth metal oxide on silicon substrate

Info

Publication number: CN1217036C
Application number: CN 00121617
Authority: CN
Inventors: Z·于; J·A·哈尔马克; J·K·阿伯瓦; C·D·奥加德; R·德罗帕德
Original assignee: Freescale Semiconductor Inc
Current assignee: Motorola Solutions Inc; NXP USA Inc
Priority date: 2000-07-21
Filing date: 2000-07-21
Publication date: 2005-08-31
Anticipated expiration: 2020-07-21
Also published as: CN1334361A

Abstract

The present invention relates to a method for preparing crystallization alkaline earth oxide on a Si substrate, wherein a Si substrate with noncrystal silicon dioxide is supplied on the surface. The substrate is heated to a temperature of 700 to 800 DEG C. Moreover, the substrate is exposed to an alkaline earth metal beam under the pressure of 10<-9> to 10<-10> torr in a molecular beam epitaxy chamber. RHEED technology is used for monitoring the surface during the epitaxy of a molecular beam so as to confirm the conversion from noncrystal silicon oxide to crystallization alkaline earth oxide. After the alkaline earth oxide is formed, an additional material layer is formed; for example, the alkaline earth oxide with additional thickness can be applied to silicon on a nonvolatile memory device with high density, and monocrystal ferroelectric oxide or oxide with high dielectric constants.

Description

Method for preparing crystalline alkaline earth metal oxides on silicon substrates

The invention relates to a method for producing crystalline alkaline earth metal oxides on silicon substrates for further production processes.

For many device applications, an ordered and stable silicon (Si) surface is most desirable for subsequent epitaxial growth of single crystal thin films on silicon, such as various ferroelectric or high dielectric constant oxides for non-volatile and high density memory devices. Especially for the subsequent growth of monocrystalline oxides such as perovskites, it is important to build an ordered transition layer on the Si surface. There have been some reports: with respect to, for example, BaO and BaTiO₃The basis for the successful growth of these oxides on Si (100) is the deposition of a quarter monolayer of Ba in BaSi on Si (100) by reactive epitaxy at temperatures above 850 deg.C₂(cube) template. See, for example: an article by r.mckee et al, appl.phys.lett.59(7), pages 782 and 784 (1991, 8, 12); an article by r.mckee et al, appl.phys.lett.63(20), page 2818-2820 (1993, 11/15); an article by R.Mckee et al, Mat.Res.Soc.Symp.Proc.Vol.21, page 131-; united states patent 5225031 entitled "method for epitaxial deposition of oxide on silicon substrate and structures made by the method" granted on 6.7.1993; U.S. patent 5482003 entitled "method for depositing epitaxial alkaline earth metal oxides on a substrate and structures made using the method" was issued on 9.1.1996. Molecular beam epitaxy surface preparation and templating (e.g. BaSi)₂) The high temperatures required to be established actually turn the above process into a high temperature process. The main problem is that such high temperaturemethods require a high thermal budget, which promotes diffusion in the structure, often undesirable or unacceptable.

It would therefore be particularly desirable to have a molecular beam epitaxy process that is amenable to low temperature processes, which can be performed simply, and which provides an ordered wafer surface for subsequent thin film epitaxy.

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

It is a further object of the present invention to provide a new and improved method for preparing crystalline alkaline earth metal oxides on Si substrates using molecular beam epitaxy suitable for low temperatures.

It is a further object of the present invention to provide a new and improved method for preparing crystalline alkaline earth metal oxides on Si substrates using a simplified method requiring little monitoring during the process.

It is a further object of the present invention to provide a new and improved method for preparing crystalline alkaline earth metal oxides on Si substrates to provide an ordered wafer surface.

It is a further object of the present invention to provide a new and improved method for preparing crystalline alkaline earth metal oxides on Si substrates without complicating subsequent process steps.

The above and other objects can be at least partially solved and the above and other objects can be accomplished by a method for preparing a crystalline alkaline earth metal oxide on a Si substrate, wherein the Si substrate having a silicon dioxide layer on a surface of the substrate is provided. The temperature of the substrate is heated to a temperature below the temperature at which the silicon dioxide rises and the substrate surface is exposed to a beam of alkaline earth metal to convert the amorphous silicon dioxide to crystalline alkaline earth metal oxide. Then, depending on the application, additional thicknesses of alkaline earth oxides, single crystal ferroelectrics for non-volatile and high density memory device applications, or high dielectric constant oxides may be conveniently formed on the alkaline earth oxides.

Reference is made to the accompanying drawings

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

FIG. 2 is a cross-sectional view of the Si substrate shown in FIG. 1 with a silicon dioxide layer converted to an alkaline earth oxide; and

fig. 3 is a cross-sectional view of the Si substrate shown in fig. 2 with additional material formed on the surface of the alkaline earth oxide.

Referring now to the drawings, whereinSimilar features are indicated by similar numerals and fig. 1 shows a silicon (Si) substrate 10 with silicon dioxide 11 formed on a surface thereof. Once the silicon substrate 10 is exposed to air (oxygen), silicon oxide (typically SiO) naturally exists₂) Or purposefully grown in a controlled manner as is known in the art. In silicon technology, good SiO is usually obtained₂The interface of/Si. However, the silicon dioxide layer 11 is amorphous, rather than single crystalline, and in order to grow additional single crystalline material on the substrate, it is desirable to provide a single crystalline oxide, excluding the amorphous silicon layer 11 at the oxide/silicon interface.

The epitaxial transition layer is important for the subsequent growth of the single crystal oxide on the Si substrate 10. Alkaline earth metals such as barium, strontium, calcium, etc. have proven to be stable on silicon substrates. For example BaSi₂the/BaO transition layer has been formed using molecular beam epitaxy as described in the article and patent application mentioned above(MBE) is grown on a silicon substrate. These transition layers were grown on a clean Si substrate surface using reactive epitaxy and MBE. However, a sub-monolayer of BaSi₂The thickness needs to be precisely controlled and the subsequent growth of BaO also depends on the barium flux and oxygen pressure. Precise thickness and pressure control complicates the growth process, substantially increases process costs, and increases process time.

The Si substrate 10 and the amorphous silicon dioxide layer 11 are heated to below the sublimation temperature of the oxide layer 11. Typically, the silicon dioxide is sublimed at temperatures above 850 deg.C, and it is preferred that the substrate 10 be heated to a temperature of 700 deg.C and 800 deg.C. This may be done in a molecular beam epitaxy chamber, or the substrate 10 may be at least partially heated in a preparation chamber, and then the substrate 10 is transferred to a growth chamber and the heating is completed.

The pressure in the growth chamber is reduced to about 10^-9To 10^-10And (5) torr.

After the substrate 10 is appropriately heated and the pressure in the growth chamber is appropriately reduced, the surface of the substrate 10 having the silicon dioxide layer 11 thereon is exposed to an alkaline earth metal beam, as shown in fig. 2. In a preferred embodiment, the beam is barium, strontium, or both produced by resistively heated interstitial chambers or by e (electron) beam evaporation sourcesA combination of elements. In one specific example, the substrate 10 and the oxide layer 11 are exposed to a barium beam. Barium replaces the silicon in the silicon dioxide and transforms the layer 11 into a BaO crystalline buffer layer 12. The silicon being replaced either forms volatile silicon monoxide (SiO) or is combined with pure silicon of the substrate 10, but not exclusively, BaSi at the Si/BaO interface₂。

The conversion of silicon dioxide to alkaline earth metal oxide layer 12 is based on the fact that the enthalpy change (or heat formation ah) of the alkaline earth metal oxide is higher for each oxygen atom than for silicon dioxide. For example, see table I below, which also lists the lattice constants of the cubic alkaline earth metal oxides.

Oxide SiO₂BaO SrO CaO MgO

Δ H (per oxygen) (kJ/mole) -455.4-548.0-592.0-643.9-601.6

a₀(Angstrom) 5.5425.1604.7994.208

This indicates that alkaline earth metal oxides such as barium oxide are thermodynamically more noble than SiO₂More stable and the following reactions occur:

and

due to cubic single crystal BaO (a)₀Equal to 5.542 angstroms) is made of silicon (a)₀Equal to 5.432 angstroms) is well matched (1.6% mismatch) if the temperature of the Si is kept high enough (typically 700-₂At the sublimation temperature of (b), a BaO epitaxial layer is easily formed on the Si surface. Reported lowest SiO₂The sublimation temperature was 850 ℃. A perfect lattice match can be provided by mixing the flows of Ba and strontium to form a (Ba, Sr) O layer.

In general, the amorphous silicon dioxide layer 11 on the silicon substrate 10 is about 50 angstroms thick, providing an acceptable transition layer 12. It is understood that thinner or thicker layers may be used depending on the particular application. However, if a thicker oxide layer is used, it may take longer to convert to an alkaline earth metal oxide layer, since the thicker oxide layer must be exposed to the alkaline earth metal molecular beam for a long time. Since the thickness of the amorphous silicon dioxide layer is easily and very precisely controlled, the alkaline earth oxide layer can be controlled very precisely in the end.

The surface is monitored using the RHEED (reflection high energy electron diffraction) technique, which is well known in the art and can be used in situ while the exposure step is being performed in the growth chamber, while the amorphous silicon dioxide layer 11 is exposed to the alkaline earth metal beam. The surface crystalline structure is detected or probed using the RHEED technique, which in the present process represents a rapid change from no characteristic line of amorphous silicon dioxide to a strong and sharp stripe after the transition is complete. Naturally, it should be understood that once a specialized manufacturing process is formed, it is not necessary to perform the RHEED technique for each substrate.

Thus, a new and improved method for preparing crystalline alkaline earth metal oxides on Si substrates using molecular beam epitaxy suitable for low temperatures and a simplified method requiring little monitoring during the process is disclosed. The method is essentially a self-limiting process, allowing better control of uniformity and thickness. In addition, this is a low temperature process compared to prior art processes. In addition, the method provides a crystalline ordered wafer surface for growing alkaline earth metal oxide, single crystal ferroelectric or high dielectric constant oxide of additional thickness (layer 15 shown in fig. 3) on silicon for non-volatile and high density memory device applications depending on the application.

While particular embodiments of the present invention have been shown and described herein, further modifications and improvements will occur to those skilled in the art. It is intended that the invention not be limited to the particular forms shown, but that it will be covered by the appended claims without departing from the spirit and scope of the invention.

Claims

1. A method of preparing a crystalline alkaline earth metal oxide on a Si substrate, comprising the steps of:

providing a Si substrate having silicon dioxide on a surface of the substrate, the silicon dioxide having a sublimation temperature;

heating the substrate to a temperature below the sublimation temperature of the silicon dioxide;

after heating, the silica is exposed to alkaline earth metal beams, converting the silica layer to an alkaline earth metal oxide layer.

2. The method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 1, wherein the alkaline earth metal comprises one of barium, strontium, calcium, magnesium and each combination thereof.

3. The method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 2, wherein the alkaline earth metal comprises barium.

4. The method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 2, wherein the alkaline earth metal includes barium and strontium.

5. The method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 1, wherein the step of providing the Si substrate with silicon dioxide on a surface of the substrate comprises one of the following steps: providing a Si substrate having a native oxide on a surface thereof, or providing a Si substrate and forming an oxide on a surface thereof.

6. The method for producing a crystalline alkaline earth metal oxide on a Si substrate as claimed in claim 1, wherein the step of heating said substrate to a temperature lower than said sublimation temperature of silicon dioxide comprises heating said substrate to a temperature of 700 ℃ and 800 ℃.

7. A method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 1, wherein the step of exposing the silicon dioxide to an alkaline earth metal beam is performed in a molecular beam epitaxy chamber.

8. The method for preparing a crystalline alkaline earth metal oxide on a Si substrate as claimed in claim 7, wherein the step of exposing the silicon dioxide to an alkaline earth metal beam in a molecular beam epitaxy chamber comprises reducing the pressure in the chamber to about 10 f^-9To 10^-10And (5) torr.

9. The method of preparing a crystalline alkaline earth oxide on a Si substrate as claimed in claim 1, comprising monitoring said silicon dioxide with RHEED technique during the exposing step to determine the step of converting the silicon dioxide to the crystalline alkaline earth oxide.

10. The method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 1, further comprising an additional step of forming an additional material layer on the substrate after said exposing step.

11. The method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 1, wherein the Si substrate comprises amorphous silicon dioxide; heating the substrate to a temperature of 700-; the amorphous silicon dioxide is added at about 10 deg.C^-9To 10^-10Exposure to a torr pressure; and monitoring the amorphous silicon dioxide with a RHEED technique during the exposing step to determine the transition from amorphous silicon dioxide to crystalline alkaline earth metal oxide.

12. The method for producing a crystalline alkaline earth metal oxide on a Si substrate as claimed in claim 11, wherein the alkaline earth metal comprises one of barium, strontium, calcium, magnesium and each combination thereof.

13. The method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 12, wherein the alkaline earth metal comprises barium.

14. The method for producing a crystalline alkaline earth metal oxide on a Si substrate as claimed in claim 12, wherein the alkaline earth metal includes barium and strontium.

15. The method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 11, wherein the step of providing the Si substrate with silicon dioxide on a surface of the substrate includes one of the following steps:providing a Si substrate having a native oxide on a surface thereof, or providing a Si substrate and forming an oxide on a surface thereof.

16. The method for producing a crystalline alkaline earth metal oxide on a Si substrate as claimed in claim 11, further comprising an additional step of forming an additional material layer after converting the amorphous silicon dioxide into the crystalline alkaline earth metal oxide.

17. A method of preparing a crystalline alkaline earth metal oxide on a Si substrate as claimed in claim 11, wherein the amorphous silicon dioxide is exposed to a beam of one of barium, strontium and barium-strontium; monitoring the amorphous silica with a RHEED technique to determine a transition from the amorphous silica to one of crystalline barium oxide, strontium oxide and barium-strontium oxide; and forming an additional material layer after converting the amorphous silicon dioxide into one of crystalline barium oxide, strontium oxide, and barium-strontium oxide.

18. The method for producing a crystalline alkaline earth metal oxide on a Si substrate according to claim 17, wherein the step of providing the Si substrate with silicon dioxide on a surface of the substrate includes one of the following steps: providing a Si substrate having a native oxide on a surface thereof, or providing a Si substrate and forming an oxide on a surface thereof.