WO2004068568A1

WO2004068568A1 - Structure, especially a semi-conductor structure, in addition to a method for the production said structure

Info

Publication number: WO2004068568A1
Application number: PCT/DE2004/000038
Authority: WO
Inventors: Clemens Först; Christopher Ashman; Peter Blöchl
Original assignee: Technische Universität Clausthal
Priority date: 2003-01-31
Filing date: 2004-01-15
Publication date: 2004-08-12
Also published as: DE10303875B4; DE10303875A1

Abstract

The invention relates to a structure, especially a semi-conductor structure, comprising a substrate which has a diamond or zinc-selenium type lattice structure, and at least one insulating layer disposed on said substrate. The structure is characterised in that, in the region of the insulating layer, essentially all atoms of the substrates are positioned on the lattice of the substrate, the atoms of the highest substrate layer are dimerized, and the substrate surface is devoid of silicide; at least one ion intermediate layer is directly adjacent to the substrate surface; and at least one ion covering layer is arranged on the ion intermediate layer.

Description

Structure, in particular semiconductor structure, and method for producing a structure

The invention relates to a structure, in particular a semiconductor structure, with a substrate which has a diamond or zinc selenide-like lattice structure, and with at least one insulating layer on the substrate.

Such structures are used, for example, for non-volatile data memories with high density and logic circuits, for example when ferroelectric or high dielectric constants are required. Single crystal thin films are grown epitaxially on a stable and orderly substrate structure, for example silicon.

The invention further relates to a method for producing such a structure, comprising the steps:

- Application of an intermediate ion layer on a substrate surface; and

- Applying at least one ion cover layer to the intermediate ion layer.

US Pat. No. 5,225,031 describes a method and a structure with a silicon substrate, on the surface of which an oxide layer is epitaxially applied, for example barium oxide BaO and barium titanate BaTiO ₃ . Here, a quarter monolayer of barium is applied to the (001) plane of the silicon substrate based on a cubic BaSi ₂ structure by reaction epitaxy at temperatures greater than 850 ° C.

US Pat. No. 6,241,821 and US Pat. No. 6,248,459 describe methods for producing a semiconductor structure and the semiconductor structure itself, in which an intermediate ion layer is produced from a material of the composition XSiO ₂ , where X is a metal. These known structures are metallic and therefore conductive. They are also not sufficiently stable. The conventional structures either form a silicide or a structure with silicon atoms that are not directly bound to the substrate.

For example, in the case of semiconductor components, it is necessary to create insulating layers which are as thin as possible and which, for. B. can be used as a so-called gate oxide in MOS-FET transistors. This gate oxide has the function of a dielectric of a capacitor with which line carriers are brought into the channel of a MOS-FET transistor. The transistor is switched by applying and switching off a voltage at the gate. The gate oxide conventionally has a thickness of approximately 2 to 3 nm. This corresponds to only a few atomic layers. If the thickness is reduced to less than 1.5 nm, the oxide is so thin that it loses its insulating properties and the function of the components is severely impaired. Therefore, as in the prior art mentioned above, oxides with a higher dielectric constant are used, which are called high-K oxides. These high-K oxides must have thermodynamic stability, a small number of interface states, a sufficiently large band offset and a low density of impurities. Oxides with strontium Sr, barium Ba, yttrium Y, zirconium Zr, hafnium Hf, aluminum Al and lanthanides appear to be suitable. With a significant reduction in the thickness of the insulating oxide layer, the use of crystalline oxides may become necessary.

The object of the invention is therefore to create an improved structure with an insulating layer which has a small thickness and high stability.

The object is achieved according to the invention with the structure of the generic type in that in the region of the insulating layer essentially all atoms of the substrate are on the lattice positions of the substrate lattice, the atoms of the uppermost substrate layer are dimerized, and the substrate surface is free of silicide;

at least one intermediate ion layer directly adjoins the substrate surface, and

there is at least one ion cover layer on the intermediate ion layer.

According to the invention, an intermediate ion layer is thus used which directly adjoins the substrate surface. It is essential that the substrate surface remains free of silicide. This ensures that the substrate surface and the intermediate ion layer do not metallize, but rather form a dielectric and are insulating. The actual ion cover layer, which is, for example, an oxide or nitride, can then be applied to the intermediate ion layer.

The substrate used for the structure according to the invention has a diamond or zinc selenide-like lattice structure. The top layer of substrate is dimerized either by direct bonds or oxygen bridges. The substrate can also contain oxygen atoms which are bound to the uppermost layer of substrate. Oxygen bridges only occur within the top substrate layer.

In the case of silicon as a substrate, the number of silicon atoms in the uppermost substrate layer corresponds to a monolayer, which is also called a monoatomic layer. The same applies to other substrate materials.

The intermediate ion layer preferably contains metal cations. It has the function of electronically saturating the open bonds of the substrate. In the case of silicon as the substrate atom, an electronically saturated structure is achieved by adding one electron for each silicon atom to the uppermost substrate layer.

The intermediate ion layer should preferably have a number of cations which corresponds to a proportion of the number of cations located on the uppermost layer of the substrate surface, the number of cations being chosen such that all open bonds of the substrate are filled with electrons. An open bond can contain a maximum of two electrons. The number of electrons provided by the cations corresponds to the valence minus the electrons which are consumed by bonds in the intermediate ion layer and to the ion cover layer. If the intermediate ion layer is formed from a monovalent metal, the intermediate ion layer should thus form a monolayer. Accordingly, a half monolayer should be provided for a divalent metal and a third monolayer for a trivalent metal.

The intermediate ion layer should preferably have metal ions, in particular alkaline earth metal ions or lanthanoids. The alkaline earth metal ions can be selected, for example, from the group of the elements barium Ba and strontium Sr.

It is particularly advantageous if the uppermost substrate layer is oxidized. It is now possible to set the band offset, since the selective oxidation of the silicon atoms of the uppermost substrate layer leads to dipoles that shift the potential and thus the band offset.

The atoms of the intermediate ion layer can either over the surface formed by the uppermost atoms of the substrate, or into this surface be lowered. As a rule, the atoms of the intermediate ion layer are located in the gaps in the lattice structure of the substrate surface.

The dimers on the OOD substrate surface can be arranged in rows. Then the cations of the intermediate ion layer should be arranged between the rows of the dimers.

It is particularly advantageous if the atoms of the intermediate ion layer and the atoms of the substrate form a two-dimensional periodic lattice with substrate atoms bound to dimers and with atoms of the intermediate layer between two dimers or in the middle of four dimers. In this way, a long-term stable symmetrical structure is created.

The ion cover layer should preferably have a lattice structure which is matched to the lattice of the intermediate ion layer and should not have any excess or deficiency of electrons. This means that the binding electrons should be saturated so that an electron flow is avoided and the ion cover layer and the ion intermediate layer form an insulator.

It is furthermore advantageous if an oxygen-containing, ion-conducting material structure is provided in a border area to the intermediate ion layer or the ion cover layer. The ion cover layer can be part of the material structure. The oxygen-containing, ion-conducting material structure serves as an oxygen reservoir and should be selected and installed in such a way that oxygen ions that diffuse out of the oxygen-containing, ion-conducting material structure are largely replaced. In this way, the long-term stability of the structure can be improved. The material structure can also be used to compensate for the lack of oxygen in the ion cover layer, for example in the gate oxide. The oxygen-containing, ion-conducting material structure should contain an auxiliary oxide with a low formation energy for empty oxygen parts. The auxiliary oxide should be stored in an area in which the circuit properties are not influenced, e.g. in spacer layers. The auxiliary oxide and the materials between the auxiliary oxide and the gate oxide should have a sufficiently high oxygen diffusion constant so that the oxygen atoms can reach the gate oxide efficiently.

The intermediate ion layer according to the invention in connection with the silicide-free substrate surface ensures that the binding electrons of the substrate surface are saturated and can be directly exposed to a non-polar oxide layer without the substrate surface itself forming a silicide. The substrate surface is thus electronically saturated by the intermediate ion layer.

Another object of the invention is to provide an improved method for adjusting the band offset of a structure according to the invention described above. The band offset is conventionally carried out by changing the chemical composition of the oxides used.

According to the invention, oxygen is introduced to the substrate surface and a desired energetic distance of the band edges of the insulating layer relative to the band edges of the substrate is set by adjusting the oxygen content on the substrate surface.

The selective oxidation of the interface of the substrate to the ion interlayer introduces dipoles that shift the potential and thus the band offset. In the method, the partial pressure of oxygen is preferably increased during or after the production of the substrate in order to set the desired distance between the strip edges.

The invention is explained below with reference to the accompanying drawings. Show it:

Figure 1 a - sketch of a side view of the atomic structure of a pure silicon (OOD substrate surface in a dimer reconstruction in the [110] direction;

Figure 1 b - sketch of a side view of the atomic structure of a pure silicon

(OOD substrate surface in a dimer reconstruction in the [110] direction;

FIG. 2a - sketch of a side view of the atomic structure of an embodiment of an ion intermediate layer of strontium atoms in the gaps of the lattice structure of a silicon substrate surface in the [1 10] direction;

Figure 2b- Sketch of a side view of the atomic structure of an embodiment of an ion intermediate layer of strontium atoms according to the invention in the gaps of the lattice structure of a silicon substrate surface

che in the [110] direction;

3 shows a top view of the atom structure from FIG. 2, the intermediate ion layer and the dimerized silicon atoms of the uppermost substrate layer being shown;

4 shows a top view of the atomic structure from FIG. 2, the intermediate ion layer and the two upper atomic layers of the substrate being shown; 5 shows a top view of the charge pattern of the intermediate ion layer and the uppermost substrate layer according to FIGS. 2 to 4;

6a - sketch of a side view of a structure according to the invention with an ion cover layer on the intermediate ion layer according to FIG. 2 in the [110] direction;

Figure 6b - Sketch of a side view of a structure according to the invention with an ion cover layer on the intermediate ion layer according to Figure 2

in the [110] direction;

FIG. 7a - side view of an ion cover layer on an intermediate ion layer according to FIG. 2 with an additional oxygen monolayer, which is simply bound to the uppermost substrate layer, in the [110] direction;

FIG. 7b - side view of an ion cover layer on an intermediate ion layer according to FIG. 2 with an additional oxygen monolayer,

which is simply bound to the uppermost layer of substrate, in the [110] direction.

FIG. 1 a shows a side view of the atomic structure of a pure silicon

Recognize the substrate surface in the plane spanned by the [001] and [110] direction, the uppermost substrate layer being dimerized in a dimer reconstruction. The silicon substrate has a diamond-like lattice structure.

Such a high-purity (001) substrate surface with a dimer reconstruction can be achieved with conventional cleaning methods, e.g. B. by thermal desorption of silicon oxide SiO ₂ at a temperature greater than or equal to 850 ° C., or by removing hydrogen from a silicon substrate surface reconstructed by hydrogen (1x1) at a temperature greater than or equal to 300 ° C. in an ultra-high vacuum. The hydrogen termination is a known method in which hydrogen is loosely bound to the so-called “dangling bonds” of silicon on the substrate surface in order to saturate the crystal structure.

Instead of the silicon substrate shown in FIG. 1, a structure can likewise be constructed based on other suitable substrates.

In order to form the thinnest possible insulating layer on the substrate, metal ions are preferably deposited as an intermediate ion layer on the substrate surface. The growth of the intermediate ion layer can be monitored, for example, by a high-energy electron reflection diffraction measurement method (reflection high energy electron defraction - RHEED). This method can be used in the deposition chamber for the ion interlayer during the development step and serves to detect or measure the surface crystal structures.

The degree of coverage of the intermediate ion layer can also be checked by changing the band spectra by [making the positions of the hull energy levels as is well known from the prior art. Below a degree of coverage of half a monolayer of an alkaline earth metal as an intermediate ion layer, the Fermi level lies in the lower region of the silicon band gap, while with a larger covering it is in the upper region of the conduction band. FIGS. 2a and 2b show the atomic structure in the plane of a silicon substrate spanned by the [001] and [110] direction with an intermediate ion layer made of strontium atoms directly adjacent to the substrate surface. It becomes clear that the strontium atoms of the intermediate ion layer are embedded in the gaps in the lattice structure of the substrate surface. The mean lateral distances between the strontium atoms of the intermediate ion layer and the respectively adjacent silicon atoms of the substrate on the (OOD substrate surface) are the same.

The intermediate ion layer ensures that the electronic structure of the substrate surface is saturated, so that an ion cover layer can be applied to an inert intermediate ion layer or substrate surface. In this way, a very thin insulating layer can be achieved, in particular with high-K oxides, which is also stable.

The application of the intermediate ionic layer according to the invention can be carried out by applying an alkaline earth metal to the high-purity substrate surface using known methods, e.g. Epitaxy. Preferably, the deposition begins at a high temperature to desorb any remaining oxygen and hydrogen. Then the substrate temperature is preferably reduced to about 650 to 750 ° C. This can be done, for example, in a molecular beam epitaxy chamber or the silicon substrate can be at least partially heated in a preparation chamber and then transferred to a growth chamber, in which the heating process is completed.

As soon as the silicon substrate has been suitably heated and the pressure in the growth chamber has been reduced to an appropriate level, the surface of the silicon substrate is exposed to a metal jet, preferably an alkaline earth metal jet. In a preferred embodiment, barium or strontium is added sets, which leads to an intermediate ion layer with a low number of lattice defects.

The strontium atoms of the intermediate ion layer outlined in FIG. 2 are partially embedded in the substrate surface of the silicon substrate and form a surface with the dimers of the substrate surface. Such an intermediate ion layer can be achieved at temperatures between approximately 650 to 750 ° C. using a vapor deposition process.

The two valence electrons of the strontium atoms are each transferred into the only partially filled “dangling bonds” of the silicon atoms on the substrate surface. As a result, the substrate surface is electronically saturated and the band gap is set to a value in the region of the band gap of the substrate.

FIGS. 3 and 4 show top views of the atomic structure with the dimerized silicon atoms of the uppermost substrate layer and the strontium atoms of the intermediate ion layer. FIG. 4 also shows the atomic layer of the substrate lying under the uppermost substrate layer.

It becomes clear that the strontium atoms of the intermediate ion layer in the gaps in the lattice structure of the substrate are regularly installed in half a monolayer based on the number of silicon atoms on the uppermost substrate layer.

FIG. 5 shows a top view of the charge pattern of the intermediate ion layer and the uppermost substrate layer according to FIG. 3. It becomes clear that the charge of the double positively charged strontium atoms compensates for that of the single negatively charged silicon atoms if the intermediate ion layer contains half a monolayer of the strontium atoms. After the intermediate ion layer is formed, one or more ion cover layers, preferably made of a single crystal oxide, are applied to the intermediate ion layer.

FIGS. 6a and 6b show such a completed structure with substrate surface, intermediate ion layer and ion cover layer, the ion cover layer being formed from strontium atoms, titanium atoms and oxygen atoms.

Optionally, the ion cover layer can have an intermediate layer adjacent to the ion intermediate layer made of an alkaline earth metal oxide, such as barium oxide BaO or SrO.

The ion cover layer can be formed, for example, by reducing the temperature while the intermediate ion layer is maintained, for example in the case of at least half a monolayer of alkaline earth metal atoms. The reduced temperature may be required to avoid desorption of the alkaline earth metals. Oxygen and strontium are then introduced either simultaneously or alternately in order to achieve a cover layer with a monolayer of strontium and a monolayer of oxygen. Alternatively, the partial pressure of oxygen can be raised to a value which, however, has to be lower than is required for oxidizing the silicon substrate. As a result, a (1 × 1) reconstructed alkaline earth metal oxide is formed on the substrate surface covered with half a monolayer of the intermediate ion layer. Depending on the temperature and the composition, the alkaline earth metal oxide monolayer can distort. The RHEED pattern is thereby indefinite. After depositing additional ion cover layers, which do not necessarily have to have the same material composition, the distortion becomes unstable and the structure is reconstructed in the desired pattern. For example, as additional oxide layer titanium oxide can be used in the case of the growth of SrTiO ₃ .

It is advantageous if the ion composition of the ion cover layer ensures a lattice structure adapted to the ion interlayer and the uppermost substrate layer and an apolar (uncharged) interface to the ion interlayer.

The finished structure with substrate, intermediate ion layer and at least one ion cover layer is then exposed to an oxygen partial pressure which is so low that no silicon oxide SiO _{2 is} formed and which is so large that the oxide of the ion cover layer is of good quality, in particular one low oxygen vacancy concentration. Oxidation of the substrate should be avoided while the layers are being applied. The deposition should therefore be carried out at an oxygen partial pressure which is not sufficient to form SiO ₂ but is large enough to avoid silicide formation on the substrate surface. This means that the oxide of the ion cover layer is oxygen-rich and a good insulator.

FIGS. 7a and 7b show the side view of an ion cover layer on an intermediate ion layer with an additional monolayer of oxygen bound to the substrate surface in the [110] direction and [11D] direction. The intermediate ion layer has half a monolayer of strontium. The ion cover layer contains strontium atoms, titanium atoms and oxygen atoms.

Oxygen can be introduced during or after the production of the intermediate ion layer. However, it is also advisable to introduce oxygen in a final step after applying the ion cover layer, for example using a gas annealing process. The oxygen content in the Oxide adjusted and free lattice positions and bonds are filled with oxygen and possibly the top substrate layer is selectively oxidized.

The selection of a suitable oxygen partial pressure for setting the oxygen content is well known to the person skilled in the art. If the partial pressure is too low, the quality of the ion cover layer is impaired, so that it is not a good insulator. If the partial pressure is too high, the substrate is also oxidized below the uppermost substrate layer, which impairs the dielectric properties (capacitance) of the structure.

During the life of the structure, oxygen atoms can diffuse out of the insulating layer, which leads to a reduction in quality. Released oxygen positions can cause electrical defects due to leakage currents and chemical processes that reduce the lifespan of the structure. The oxygen loss can be compensated for by introducing an oxygen reservoir with a low formation energy of oxygen vacancies. The material structure for the oxygen reservoir should be stored in an area in which an impoverished oxygen reservoir does not adversely affect functionality. The oxygen reservoir and the material with the oxygen material and the insulating layer should have a sufficiently high oxygen diffusion constant so that oxygen atoms can reach the insulating layer efficiently.

Claims

Claims:

1 . Structure, in particular semiconductor structure, with a substrate which has a diamond or zinc selenide-like lattice structure, and with at least one insulating layer on the substrate, characterized in that in the region of the insulating layer

essentially all atoms of the substrate are on the lattice positions of the substrate lattice, the atoms of the uppermost substrate layer are dimerized, and the substrate surface is free of silicide;

at least one intermediate ion layer directly adjoins the substrate surface; and

there is at least one ion cover layer on the intermediate ion layer.

2. Structure according to claim 1, characterized in that the intermediate ion layer has such a number of cations that all open bonds of the substrate are filled with electrons.

3. Structure according to claim 1 or 2, characterized in that the intermediate ion layer has metal ions, in particular alkaline earth metal ions or lanthanoids.

4. Structure according to claim 3, characterized in that the intermediate ion layer forms approximately a monolayer of a monovalent metal, approximately half a monolayer of a divalent metal, or approximately a third monolayer of a trivalent metal, the number of atoms being one ner monolayer corresponds to the number of atoms in an (OOD network plane of the substrate.

5. Structure according to claim 3 or A, characterized in that the alkaline earth metal ions are selected from the group of the elements barium (Ba) and / or strontium (Sr).

6. Structure according to one of the preceding claims, characterized in that the uppermost substrate layer is oxidized.

7. Structure according to one of the preceding claims, characterized in that the dimer bonds of the uppermost substrate layer are replaced by oxygen bridges.

8. Structure according to claim 6 or 7, characterized in that the oxygen atoms are simply bound to the substrate atoms of the substrate surface.

9. Structure according to one of the preceding claims, characterized in that the dimers of the substrate are aligned line by line on the [O01] substrate surface and the cations of the ion intermediate layer are arranged between the lines of the dimers.

10. Structure according to one of the preceding claims, wherein the atoms of the intermediate ion layer and the atoms of the substrate form a two-dimensional periodic lattice with substrate atoms bound to dimers and with atoms of the intermediate ion layer in each case between two dimers or in the middle of four dimers.

1 1. Structure according to one of the preceding claims, characterized in that the ion cover layer is an oxide and / or nitride.

12. Structure according to one of the preceding claims, characterized in that the ion cover layer has a lattice structure adapted to the lattice of the intermediate ion layer and no electron excess or electron deficiency.

13. Structure according to one of the preceding claims, characterized by an oxygen-containing, ion-conducting material structure immediately subsequent to the ion intermediate layer, the oxygen-containing, ion-conducting material structure being selected and incorporated in such a way that oxygen ions which diffuse out of the oxygen-containing, ion-conducting material are largely replaced.

14. Structure according to one of the preceding claims, characterized by an oxygen-containing, ion-conducting material structure immediately after the ion cover layer, the oxygen-containing, ion-conducting material structure being selected and installed in such a way that an oxygen deficit in the ion cover layer is compensated for.

15. Structure according to one of claims 13 or 14, characterized in that the material structure contains an interface between two materials which have a different oxygen content from each other.

16. A method for producing a structure according to one of the preceding claims, comprising the steps:

- Application of an intermediate ion layer on a substrate surface - Applying at least one ion cover layer to the intermediate ion layer, characterized by introducing oxygen into the substrate surface and adjusting a desired energetic distance of the band edges of the insulating layer relative to the band edges of the substrate by adjusting the oxygen content of the substrate surface.

17. The method according to claim 16, characterized by adjusting the oxygen partial pressure during or after the manufacture of the structure for adjusting the desired spacing of the band edges.