Method for forming aluminum-containing dielectric layer

The present disclosure provides a method of forming an aluminum-containing layer. The method includes providing a substrate in an atomic layer deposition (ALD) process chamber; and performing a cycle of a first step and a second step one or more times in the ALD process chamber to provide a composite layer, wherein performing the first step of the cycle includes: applying a first precursor that includes a non-aluminum-based component having a first molecular weight onto the substrate; and applying a second precursor that that includes an aluminum-based component having a second molecular weight onto the substrate, wherein the second molecular weight is lower than the first molecular weight; and wherein performing the second step of the cycle includes applying the first precursor onto the substrate.

BACKGROUND

In semiconductor technology, higher-k materials such as ZrO2and HfO2are being implemented in order to achieve lower effective oxide thickness without compromising the ability to prevent dopant migration between the gate and channel region. A gate dielectric layer consisting of a high-k dielectric film with a thickness of less than 20 angstroms is difficult to control by a CVD technique which usually has a relatively fast deposition rate. Accordingly, atomic layer deposition (ALD) has been proposed to provide a more controllable deposition rate.

While a variety of techniques to use ALD to form a film have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.

DETAILED DESCRIPTION

A variety of high dielectric constant dielectric materials (high-k dielectric) have been investigated as possible replacements for silicon dioxide. Potential candidates of such high-k dielectric materials include titanium oxide (TiO2), tantalum oxide (Ta2O5, k value between 9 and 27), aluminum oxide (Al2O3, k value about 9), zirconium oxide (ZrO2, k value between 10 and 25), hafnium oxide (HfO2, k value between 10 and 25), and various combinations and mixtures such as multilayers, multicomponents, and nanolaminates. Moreover, incorporating a trivalent metal such as aluminum (Al) into a high dielectric constant material such as zirconium oxide (ZrO2) or hafnium oxide (HfO2) advantageously increases the crystallized temperature so that the resulting film remains amorphous under high temperature processing conditions. However, in order to form a film with a percentage of the trivalent metal at about 50% or less, it generally requires forming a composite layer that includes plural non-trivalent metal-containing layers (e.g., HfO2) and trivalent metal layers (e.g., Al2O3). In an example, multiple non-trivalent metal-containing layers (e.g., more than 9 layers of HfO2) may be required to average down the high percentage of the aluminum in the trivalent metal-containing layer (e.g., 90% or more in the Al2O3layer) in order to form a composite layer with about 5% ratio of aluminum atom, which in turn results in a relative thick composite layer (e.g., 2 nanometers or more). The present disclosure provides methods of forming an aluminum-containing composite high-k dielectric material layer with a substantially thin thickness (e.g., about 2 angstroms) while keeping the percentage of aluminum low (e.g., about 5% atomic ratio of aluminum or less).

FIG. 1is a flowchart of a method100to form a composite film according to one or more embodiments of the present invention.FIGS. 2A, 2B, 2C, 2D, 2E, 2F, and 2Gillustrate sectional views of an exemplary composite film200during various fabrication stages of the method100. With reference toFIG. 1throughFIG. 2Gand other figures, the method100and the exemplary composite film200are described below.

The method100begins at102by providing or receiving a substrate202in an atomic layer deposition chamber that includes a top surface203as illustrated inFIG. 2A. In some embodiments, the substrate202includes silicon. Alternatively, the substrate202may include other elementary semiconductor such as germanium in accordance with some embodiments. In some embodiments, the substrate202additionally or alternatively includes a compound semiconductor such as silicon carbide, gallium arsenic, indium arsenide, and indium phosphide. In some embodiments, the substrate202includes an alloy semiconductor such as silicon germanium, silicon germanium carbide, gallium arsenic phosphide, and gallium indium phosphide.

The substrate202may include an epitaxial layer formed on the top surface, such as an epitaxial semiconductor layer overlying a bulk semiconductor wafer. In some embodiments, the substrate202includes a semiconductor-on-insulator (SOI) structure. For example, the substrate may include a buried oxide (BOX) layer formed by a process such as separation by implanted oxygen (SIMOX). In various embodiments, the substrate202includes various p-type doped regions and/or n-type doped regions, such as p-type wells, n-type wells, p-type source/drain features and/or n-type source/drain features, formed by a process such as ion implantation and/or diffusion. The substrate202may include other functional features such as a resistor, a capacitor, diode, transistors, such as field effect transistors (FETs). The substrate202may include lateral isolation features configured to separate various devices formed on the substrate202. The substrate202may further include a portion of a multilayer interconnection (MLI) structure. The multilayer interconnection structure includes metal lines in a plurality of metal layers. In the current embodiment, the substrate202may include an active channel region of a transistor. As such, a subsequently formed layer/film on the substrate/top surface203may be a gate dielectric layer.

The method100proceeds to operation104by applying/injecting a first precursor204into the chamber thereby forming a hydrogen-terminated surface203as illustrated inFIG. 2B. In the illustrated embodiment ofFIG. 2B, such a hydrogen-terminated surface203may be implemented by injecting an oxygen-based precursor (e.g., H2O) into the chamber and accordingly the surface203may be covered by a plurality of hydroxyl groups206. However, any of a variety of oxygen-based precursors may be used to form such a hydrogen-terminated surface while remaining within the scope of the present disclosure. Typically, before the injection of the oxygen-based precursor into the chamber, the chamber and/or the substrate202has been maintained at an elevated temperature, for example, about 80° C. to about 150° C. and the chamber has a pressure that ranges from about 0.1 mbar to about 2 mbar. In some embodiments, this elevated temperature and pressure range are maintained throughout subsequent operations (e.g., up to operation112). The injection of the oxygen-based precursor into the chamber may last for a short interval (e.g., about 0.1 seconds to about 0.5 seconds) and is followed by a purge with an inert gas such as, for example, Ar, He, and/or H2. This purging process purges any excessive or unreacted first precursor(s).

The method100proceeds to operation106by applying/injecting a second precursor208into the chamber as illustrated inFIG. 2C. In some embodiments, the second precursor208may include TetrakisDiMethylAminoHafnium(TDMAHf) with a molecular weight of about 355 Daltons and/or TetrakisEthylMethylAmidoZirconium(TEMAZr) with a molecular weight about 324 Daltons. In other embodiments, the second precursor208may include TetrakisDiMethylAminoHafnium(TDMAHf) with a molecular weight ranging from about 300 Daltons to about 400 Daltons and/or TetrakisEthylMethylAmidoZirconium(TEMAZr) with a molecular weight from about 300 Daltons to about 400 Daltons.

While the substrate/chamber is maintained at the above-mentioned elevated temperature and pressure, the injection of the second precursor208may include flowing the second precursor into the chamber with a flow rate of about 100 to about 300 standard cubic centimeters per minute (sccm) for a short interval (e.g., about 0.1 seconds to about 2 seconds). As such, the second precursor208, at least in part, may react and combine with the hydroxyl group206on the substrate202(as illustrated inFIG. 2D). Following the injection of the second precursor208into the chamber, an inert gas such as, for example, Ar, He, and/or H2may be injected into the chamber. This purging process purges any excessive or unreacted second precursor(s).

Referring toFIGS. 1 and 2D, method100includes an operation108by applying/injecting a third precursor210into the chamber. In some embodiments, the third precursor210may include TriMethylAluminium(TMAl) with a molecular weight about 70 Daltons. In other embodiments, the third precursor210may include TriMethylAluminium(TMAl) with a molecular weight ranging from about 30 Daltons to about 150 Daltons. In the example in which the second precursor208has a molecular weight ranging between about 300 Daltons to about 400 Daltons and the third precursor210has a molecular weight ranging between about 30 Daltons to about 150 Daltons, a substantial difference of the molecular weights between the second and the third precursors may range between about 50% to about 93%.

Such a third precursor may be an aluminum-containing precursor. For example, the third precursor may be an aluminum-containing precursor selected from the group consisting of aluminum chloride, aluminum iodide, etc. While the substrate/chamber is maintained at the above-mentioned elevated temperature and pressure, the injection of the third precursor210may include flowing the third precursor into the chamber with a flow rate of about 50 to about 300 standard cubic centimeters per minute (sccm) for a short interval (e.g., about 0.1 seconds to about 0.5 seconds). As such, the third precursor210, at least in part, may react and combine with a remaining portion of hydroxyl groups206that do not react/combine with the second precursor208on the substrate202(as illustrated inFIG. 2E). Following the injection of the third precursor210into the chamber, an inert gas such as, for example, Ar, He, and/or H2may be injected into the chamber so to purge any excessive or unreacted third precursor(s).

Referring still toFIG. 2E, after the second precursor208and the third precursor210react/combine with the hydroxyl groups206, a layer209is formed on the substrate202. More particularly, due to the fact of a substantial difference of the molecular weights and physical sizes between the second precursor208and the third precursor210, a first portion of the hydroxyl groups206may react/combine with the second precursors208and a second portion of the hydroxyl groups206may react/combine with the third precursors210(aluminum-containing precursor). The formed layer209consists of precursor208and210at a ratio of 2/1 resulting in a total atomic percentage/ratio (or concentration) of aluminum in the dielectric layer at about 10%. In some embodiments, the layer209may have a thickness that is about 1 angstrom.

The method100then proceeds to operation110by applying/injecting the first precursor204into the chamber thereby causing the layer209to be covered by another plurality of hydroxyl groups206′ as illustrated inFIG. 2F. As shown, hydroxyl groups206′ are disposed over layer209and bond with the second and third precursor materials208and210that are already bonded with hydroxyl groups206. Following the injection of the first precursor204into the chamber, an inert gas such as, for example, Ar, He, and/or H2may be injected into the chamber so to purge any excessive or unreacted first precursor(s).

The method100continues to operation112with applying/injecting the second precursor208′ into the chamber thereby forming a layer211over the layer209as illustrated inFIG. 2G. In some embodiments, the second precursor208′ may include TetrakisDiMethylAminoHafnium(TDMAHf) with a molecular weight of about 355 Daltons and/or TetrakisEthylMethylAmidoZirconium(TEMAZr) with a molecular weight about 324 Daltons. In other embodiments, the second precursor208′ may include TetrakisDiMethylAminoHafnium(TDMAHf) with a molecular weight ranging from about 300 Daltons to about 400 Daltons and/or TetrakisEthylMethylAmidoZirconium(TEMAZr) with a molecular weight from about 300 Daltons to about 400 Daltons. In some embodiments, the second precursor208′ is formed of the same material as the second precursor208. Alternatively, in other embodiments, the second precursor208′ is formed of a different material than second precursor208.

While the substrate/chamber is maintained at the above-mentioned elevated temperature and pressure, the injection of the second precursor208at operation112may include flowing the second precursor208′ into the chamber with a flow rate of about 100 to about 300 standard cubic centimeters per minute (sccm) for a short interval (e.g., about 0.1 seconds to about 2 seconds). As such, the second precursor208′, at least in part, may react and combine with the hydroxyl group206′ (as illustrated inFIG. 2G) and thus the layer211(a non-aluminum-containing layer) is formed. Thus, the formed layer211may include a percentage of aluminum that is about 0%. In some embodiments, the layer211may have a thickness that is about 1 angstrom. Following the injection of the second precursor208′ into the chamber, an inert gas such as, for example, Ar, He, and/or H2may be injected into the chamber so to purge any excessive or unreacted second precursor(s).

After operation112, method100may continue with an annealing step. Such an annealing step may be performed to improve the quality of the formed layers209/211and in turn form a composite layer that includes the layers209and211. In some embodiments, such an annealing step may include heating up the substrate202and the formed layers209and211in nitrogen to an elevated temperature (e.g., about 250° C.) for about 30 seconds.

Referring toFIG. 1, after the operation112, method100may route back to operation104for one or more cycles. By “cycle”, in the current embodiments, it is meant that a series of operations from104to112is sequentially performed. In some embodiments, any number of cycles may be performed until a desired thickness of a composite layer is reached. For example, in the illustrated embodiment ofFIG. 2G, one cycle is performed. That is, an aluminum-containing dielectric layer209(about 10% atomic ratio of aluminum, 1 angstrom) and a non-aluminum-containing layer211(0% aluminum, 1 angstrom) are formed, which results in a composite layer that has an aluminum percentage of about 5% atomic ratio with a total thickness of about 2 angstrom. If a desired thickness of a composite layer is about 4 angstrom and with an aluminum percentage of about 5% atomic ratio, 2 cycles may be performed to reach such a goal.

The method100illustrated inFIG. 1is merely an example, one or more operations in the method100may be added, omitted, or exchanged for a suitable use and while remaining within the scope of the present disclosure. In an example, if a desired thickness of a composite layer is about 4 angstrom and with an aluminum percentage of about 2% to 3% atomic ratio, the composite layer may include one aluminum-containing layer and three non-aluminum-containing layers. In order to form such a composite layer, an aluminum-containing layer may be formed first and followed/covered by a non-aluminum-containing layer by using one cycle (operations104-112), and subsequently by performing 3 iterations of operations from110to112. In another example, if a desired thickness of a composite layer is about 10 angstrom and with an aluminum percentage of about 5% atomic ratio, the composite layer may include five aluminum-containing layers and five non-aluminum-containing layers. In order to form such a composite layer, an aluminum-containing layer may be formed first and followed/covered by a non-aluminum-containing layer by using one cycle (operations104-112), and subsequently by performing 4 iterations of operations from104to112to form other four aluminum-containing layers/non-aluminum-containing layers.

FIG. 3illustrates an embodiment of an exemplary semiconductor device300that includes an aluminum-containing composite layer308that is formed by using the method100with respect toFIG. 3. In the illustrated embodiment ofFIG. 3, the semiconductor device300includes a semiconductor substrate302that includes an active channel region303, source/drain features304/306, and a gate stack312formed over the active channel region303. The gate stack312includes the aluminum-containing layer composite308and a gate electrode310. In the specific embodiment ofFIG. 3, the aluminum-containing composite layer308may serve as a gate dielectric layer for the semiconductor device300, and more particularly, the gate dielectric layer (the aluminum-containing composite layer308) may further multiple layers as described above. In the illustrated embodiment, the gate dielectric layer308includes two aluminum-containing layers309and two non-aluminum-containing layers311. According to the embodiments of the present disclosure, such aluminum-containing composite layer308may thus have an aluminum percentage of about 5% atomic ratio and a thickness of about 4 angstroms.

The embodiments of the present disclosure provide a variety of advantages to form an aluminum-containing film. In an example, by sequentially applying/injecting two precursors with substantially different molecule weights into an ALD chamber, a self-limiting layer may be formed with a relatively low percentage of aluminum (e.g., about 10% atomic ratio) while keeping the layer with a thin thickness that is about 1 angstrom. Conventionally, in order to form a layer or a composite layer that has such a low percentage of aluminum, a multi-layer approach may be required to average down a relatively high percentage of aluminum by lamination with layers containing no aluminum. Generally, this may cause the formed composite layer to have a relatively thick thickness, which may disadvantageously arise issues if the composite layer is used as a gate dielectric layer such as, poor gate control ability, scalability, etc.

Thus, the present disclosure provides a method of forming an aluminum-containing film in accordance with some embodiments. The method includes providing a substrate in an atomic layer deposition (ALD) process chamber; and performing a cycle of a first step and a second step one or more times in the ALD process chamber to provide a composite layer, wherein performing the first step of the cycle includes: applying a first precursor that includes a non-aluminum-based component having a first molecular weight onto the substrate; and applying a second precursor that that includes an aluminum-based component having a second molecular weight onto the substrate, wherein the second molecular weight is lower than the first molecular weight; and wherein performing the second step of the cycle includes applying the first precursor onto the substrate.

The present disclosure also provides a method of forming an aluminum-containing film in accordance with some embodiments. The method includes providing a substrate in an atomic layer deposition (ALD) process chamber; injecting a first precursor that includes a first molecule with a first molecular weight into the ALD chamber for a first interval; and injecting a second precursor that includes a second molecule containing aluminum and having a second molecular weight into the ALD chamber for a second interval thereby forming a first aluminum layer on the substrate, wherein the second molecular weight is less than the first molecular weight.

The present disclosure also provides a method of forming an aluminum-containing film in accordance with some embodiments. The method includes providing a substrate in an atomic layer deposition (ALD) process chamber; injecting a first precursor that includes a first molecule with a first molecular weight into the ALD process chamber for a short interval; injecting a second precursor that includes a second molecule containing aluminum and having a second molecular weight into the ALD process chamber for a short interval thereby forming a first aluminum-containing layer on the substrate, wherein the second molecular weight is less than the first molecular weight by about 80%; and injecting the first precursor into the ALD process chamber for a short interval thereby forming a second non-aluminum-containing layer over the first aluminum-containing layer.