Patent Description:
Functional complex oxides may be incorporated into semiconductor stacks, for instance, into silicon-based architectures. Typically, for achieving a crystallization of the complex oxide layers, a high-temperature complex oxide growth under oxidizing conditions is required. However, the high oxygen content and the mobility in these materials at the elevated temperatures may lead to an undesired oxidization of underlying layers, in particular, electrode layers already formed in the stack. These oxide layers may then act as dielectric layers to the detriment of the performance of the semiconductor device comprising the stack. Thus, an oxygen barrier layer is needed to prevent the formation of such oxide layers that can cause voltage drops across the functional complex oxide layer and can increase the operational voltages.

As an example, platinum may be used to form an oxygen barrier layer between the complex oxide layers and underlying layers, and works reasonably well in an intermediate temperature range of temperatures between <NUM>-<NUM>. However, at higher temperatures, oxygen can migrate down grain boundaries to oxidize the underlying layers. Several other options exist for the intermediate temperature range, but there are very few options for oxygen barrier layers suitable for growth at higher temperatures, i.e., temperatures above <NUM> or even higher as required for the growth of high-quality complex oxides. <CIT> discloses such an oxygen barrier layer, but stacked between the semiconductor substrate and the electrode.

In view of the above, an objective of this disclosure is to provide an oxygen barrier layer, which prevents the oxidization of underlying layers in a stack in which also at least one complex oxide layer is formed. An objective is that the oxygen barrier layer is grain boundary free, and is suitable to truly block all oxygen migration up to at least a temperature of <NUM>. Further objectives are that the oxygen barrier layer provides good adhesion for a complex oxide layer, and that it can be made conductive, in order to achieve a good electrical contact to one or more complex oxide layers.

These and other objectives are achieved by the solutions of this disclosure as provided in the independent claims. Advantageous implementations are defined in the dependent claims.

A first aspect of this disclosure provides a method of forming a stack for a semiconductor device, the method comprising: providing a semiconductor substrate; forming a conductive electrode layer on the semiconductor substrate; forming a conductive oxygen barrier layer on the electrode layer; and forming at least one complex oxide layer on the oxygen barrier layer; wherein forming the oxygen barrier layer includes forming a silicon layer on the electrode layer and forming a platinum layer on the silicon layer; and wherein forming the at least one complex oxide layer comprises heating to a temperature in a range of <NUM>-<NUM> or higher.

In particular, the forming of the complex oxide layers, e.g. by deposition, may be done at a temperature of <NUM>, but may even be done at higher temperatures like <NUM> or more.

The growth of the oxygen barrier layer including the silicon layer and the platinum layer leads to the formation of an alloy of platinum and silicon, when the at least one complex oxide layer is formed at the high temperatures of <NUM> or more. This silicon-platinum-alloy layer is effective in blocking all oxygen migration up to at least a temperature of <NUM>, which may be explained by the stack having only a small number of grain boundaries.

In an implementation of the method, a thickness of the silicon layer is in a range of <NUM>-<NUM> or in a range of <NUM>-<NUM>; and a thickness of the platinum layer is in a range of <NUM>-<NUM>.

For instance, the silicon layer may have a thickness of <NUM>, or may have a thickness of <NUM>. For example, if the thickness of the silicon layer is <NUM>, the thickness of the platinum layer may be <NUM>. For instance, in a stack that includes at least one ferroelectric complex oxide, this may result in a lower coercive electric field. As another example, if the thickness of the silicon layers is <NUM>, the thickness of the platinum layer may be <NUM>. For example, in a stack that includes at least one ferroelectric complex oxide, this may result in a relatively higher coercive electric field and also in a relatively higher remnant polarization than for the former example. Overall, in terms of improvement of ferroelectricity the complex oxide, e.g., if the complex oxide includes a barium titanate layer, the latter example maybe more ideal.

In an implementation of the method, the at least one complex oxide layer is formed under oxidizing conditions.

This may lead to a high quality of the one or more complex oxide layers.

In an implementation of the method, a thickness of the conductive layer is in a range of <NUM>-<NUM>, and/or a thickness of the at least one complex oxide layer is in a range of <NUM>-<NUM> or more.

In an implementation of the method, the oxygen barrier layer is used as a template for forming the at least one complex oxide layer and/or for electrically contacting the at least one complex oxide layer to the electrode layer.

In an implementation of the method, the complex oxide layer is conductive.

The oxygen barrier layer may thus provide good adhesion for the at least one complex oxide layer. If the at least one complex oxide layer is conductive, it may be electrically contacted by the conductive barrier layer to the electrode layer. Notably, the at least one complex oxide layer does not have to be conductive. Since the oxygen barrier layer is conductive, it may act as an electrode itself.

A second aspect of this disclosure provides a stack for a semiconductor device, the stack comprising: a semiconductor substrate; a conductive electrode layer arranged on the semiconductor substrate; a conductive oxygen barrier layer arranged on the electrode layer; and at least one complex oxide layer arranged on the oxygen barrier layer; wherein the oxygen barrier layer comprises an alloy of platinum and silicon.

In an implementation of the stack, the oxygen barrier layer is crystalline.

In an implementation of the stack, a platinum content of the oxygen barrier layer is in a range of <NUM>-<NUM>%, and a silicon content of the oxygen barrier layer is in a range of <NUM>-<NUM>%.

For instance, Pt<NUM>Si or Pt<NUM>Si or a mix of both may be formed.

In an implementation of the stack, a thickness of the oxygen barrier layer is in a range of <NUM>-<NUM>.

This range may result from a combination of a <NUM> silicon layer and a <NUM> platinum layer, which are formed in the method of the first aspect.

In an implementation of the stack, the at least one complex oxide layer comprises a perovskite oxide layer.

As other examples, the at least one complex oxide layer may comprise a tetragonal tungsten bronze layer, or also one or more layers of brownmillerite, corrundum, spinel, and/or mellilite.

In an implementation of the stack, the at least one complex oxide layer comprises at least one of a barium titanate layer and a lanthanum nickelate layer.

The barium titanate layer could be combined with the lanthanum nickelate layer, but may also be combined with any perovskite or other complex oxide layer.

In an implementation of the stack, the electrode layer comprises a titanium nitride layer.

That is, the stack may comprise a layer sequence of a titanium nitride layer, a platinum-silicon-alloy layer, and a complex oxide layer.

In an implementation of the stack, the semiconductor substrate comprises a silicon or silicon-based substrate surface layer.

A third aspect of this disclosure provides a semiconductor device comprising one or more stacks according to the second aspect or any implementation thereof.

The semiconductor device of the third aspect thus enjoys the advantages of the stack of the second aspect or its implementations. The semiconductor device may comprise a capacitor stack and/or a ferroelectric stack. For instance, the semiconductor device may be a ferroelectric field effect transistor device.

The above described aspects and implementations are explained in the following description of embodiments of this disclosure with respect to the following drawings:.

<FIG> and <FIG> show a method <NUM> of forming a stack <NUM> (e.g., as it is shown in <FIG>). The stack <NUM> can be used in a semiconductor device. <FIG> shows a flow-diagram of the steps of the method <NUM>, while <FIG> shows the layers of the stack <NUM>, which are formed one on top of the other in the respective method steps (as indicated by the arrows).

The method <NUM> comprises a step <NUM> of providing a semiconductor substrate <NUM>. The semiconductor substrate <NUM> may be or may comprise a silicon or silicon-based substrate surface layer.

The method <NUM> further comprises a step <NUM> of forming a conductive electrode layer <NUM> on the semiconductor substrate <NUM>. The electrode layer <NUM> may be or may comprise a titanium nitride layer.

The method <NUM> further comprises a step <NUM> of forming a conductive oxygen barrier layer on the electrode layer <NUM>. As shown in <FIG>, this step <NUM> includes a sub-step 13a of forming a silicon layer <NUM> on the electrode layer <NUM>, and a sub-step 13b of forming a platinum layer <NUM> on the silicon layer <NUM>.

The method <NUM> further comprises a step <NUM> of forming at least one complex oxide layer <NUM> on the oxygen barrier layer, in particular, on the platinum layer <NUM>. The forming of the at least one complex oxide layer <NUM> comprises heating to a temperature in a range of <NUM>-<NUM> or even higher, which also heats the previously formed layers <NUM>, <NUM>, <NUM> of the stack <NUM> to that temperature. Moreover, at least typically, the at least one complex oxide layer <NUM> is formed under highly oxidizing conditions.

As can be gathered from <FIG>, the conductive oxygen barrier layer may thus be used as a template for forming the at least one complex oxide layer <NUM>, and could also be used for electrically contacting the at least one complex oxide layer <NUM> to the electrode layer <NUM>, if the at least one complex oxide layer <NUM> is conductive.

<FIG> shows a stack <NUM> according to an embodiment of the disclosure. The stack <NUM> may be the result of the method <NUM> performed in <FIG> and <FIG>.

Accordingly, the stack <NUM> comprises the semiconductor substrate <NUM>, the conductive electrode layer <NUM> arranged on the semiconductor substrate <NUM>, the conductive oxygen barrier layer <NUM> arranged on the electrode layer <NUM>, and the at least one complex oxide layer <NUM> arranged on the oxygen barrier layer <NUM>.

The oxygen barrier layer <NUM> comprises an alloy of platinum and silicon, wherein this alloy may be the result of forming the silicon layer <NUM> and the platinum layer <NUM> in the method <NUM>, and of the subsequent high temperature of <NUM> or more occurring during the forming of the at least one complex oxide layer <NUM> in the method <NUM>. The oxygen barrier layer <NUM> may be formed such that it is crystalline.

<FIG> shows an exemplary stack <NUM> as fabricated according to the method <NUM>, but before the step <NUM> of forming the at least one complex oxide layer <NUM>. <FIG> shows the same exemplary stack <NUM> after the step <NUM> of forming the at least one complex oxide layer <NUM>. <FIG> both show a schematic of the respective stack <NUM> and a transmission electron microscopy image of the respective stack <NUM>.

As an example, <FIG> shows that a <NUM> silicon layer <NUM> followed by a <NUM> platinum layer <NUM> may be deposited at room temperature on a titanium nitride electrode layer <NUM>, which is arranged on a silicon substrate <NUM>. Generally, the thickness of the silicon layer <NUM> may be in a range of <NUM>-<NUM>, or may be in a range of <NUM>-<NUM>. The thickness of the platinum layer <NUM> may generally be in a range of <NUM>-<NUM>. The thickness of the titanium nitride electrode layer <NUM> is about <NUM> in this example.

The deposition of the silicon layer <NUM> and the platinum layer <NUM> creates a structure that, under the high temperatures of <NUM> or more occurring during the subsequent growth of the at least one complex oxide <NUM> (see <FIG>), forms an alloy of platinum and silicon (Pt-Si). This alloy may generally have a platinum content in a range of <NUM>-<NUM>%, and a silicon content in a range of <NUM>-<NUM>%. In the example of <FIG>, this alloy may have a silicon content of about <NUM>% and a platinum content of about <NUM>%. A thickness of the oxygen barrier layer <NUM> is notably about <NUM> in this example.

The Pt-Si alloy prevents the migration of oxygen to the underlying layers, i.e., particularly to the electrode layer <NUM>. Thus, it is beneficial for the performance of the stack <NUM> and the semiconductor device including the stack <NUM>. The absence of observed grain boundaries in the Pt-Si alloy of the oxygen barrier layer <NUM> seems to aid in the inhibition of oxygen migration. The Pt-Si alloy may be crystalline, and may show strong X-ray diffraction peaks.

The at least one complex oxide layer <NUM> may generally comprise a perovskite oxide layer, or at least one of a barium titanate layer <NUM> and a lanthanum nickelate layer <NUM>. In the example of <FIG>, the complex oxide layer <NUM> includes the lanthanum nickelate layer <NUM> on the oxygen barrier layer <NUM>, and the barium titanate layer <NUM> on the lanthanum nickelate layer <NUM>. Generally, a thickness of the at least one complex oxide layer can be in a range of <NUM>-<NUM> or more. In the example of <FIG>, the thickness of the lanthanum nickelate layer <NUM> is about <NUM>, and the thickness of the barium titanate layer <NUM> is at least larger than <NUM>.

Notably, a thin oxide layer <NUM> (here silicon oxide) may form at the interface of the oxygen barrier layer <NUM> and the at least one complex oxide layer <NUM>. Note that this oxide layer <NUM> is an artifact of the type of complex oxide layer used in this example, and may be eliminated with the used of other complex oxides.

Claim 1:
A method (<NUM>) of forming a stack (<NUM>) for a semiconductor device, the method (<NUM>) comprising:
providing (<NUM>) a semiconductor substrate (<NUM>);
forming (<NUM>) a conductive electrode layer (<NUM>) on the semiconductor substrate (<NUM>);
forming (<NUM>) a conductive oxygen barrier layer (<NUM>) on the electrode layer (<NUM>); and
forming (<NUM>) at least one complex oxide layer (<NUM>) on the oxygen barrier layer (<NUM>);
wherein forming (<NUM>) the oxygen barrier layer (<NUM>) includes forming (13a) a silicon layer (<NUM>) on the electrode layer (<NUM>) and forming (13b) a platinum layer (<NUM>) on the silicon layer (<NUM>); and
wherein forming (<NUM>) the at least one complex oxide layer (<NUM>) comprises heating to a temperature in a range of <NUM>-<NUM> or higher.