Methods of forming silicon oxide layer and semiconductor structure

Methods of forming a silicon oxide layer and a semiconductor structure are disclosed. The method of forming the silicon oxide layer includes the following steps. A silicon-containing precursor, an oxygen-containing precursor and an oxygen radical are provided to form a silicon oxide layer containing water. A thermal process is performed on the silicon oxide layer to diffuse the water into the silicon oxide layer and oxidize the silicon oxide layer by using the water as oxidizer.

BACKGROUND

Generally, shallow trench isolations (STIs) are used to separate and isolate active areas on a semiconductor wafer from each other. These STIs have historically been formed by etching trenches, sometimes referred to as gaps, overfilling the trenches with a dielectric such as an oxide, and then removing any excess dielectric with a process such as chemical mechanical polishing (CMP) or etching in order to remove the dielectric outside the trenches. This dielectric helps to electrically isolate the active areas from each other.

However, as circuit densities continue to increase, the widths of these gaps decrease, thereby increasing gap aspect ratios, which are typically defined as the gap height divided by the gap width. As a result, it is very difficult to fill these narrow and deep gaps completely with a gap-fill dielectric material. Incomplete filling results in unwanted voids and discontinuities in the gap-fill dielectric material as well as inclusion of unwanted material. These voids and inclusions result in inadequate isolation between active areas. Electrical performance of a device with inadequate isolation is poor and device yield is reduced.

DETAILED DESCRIPTION

FIG. 1is a flow chart of a method of forming a silicon oxide layer in accordance with some embodiments of the disclosure. Referring toFIG. 1, at step S10, a silicon-containing precursor and an oxygen radical are provided to a processing region to deposit a flowable silicon oxide layer in a deposition chamber. In some embodiments, the processing region is a substrate or wafer. In some embodiments, the silicon-containing precursor is a Si-core precursor (i.e., Si atom is a central atom in the structure), N-core precursor (i.e., N atom is a central atom in the structure), a precursor with N—Si—N backbone or a combination thereof. In some embodiments, the Si-core precursor can be written as a formula of SiHx(R1)y(R2)z, where R1is SiH3, R2is NH2, N(CH3)2or N(C2H5)2, and x+y+z=4, x≥0, y≥0, and z≥0. In some embodiments, the Si-core precursor is trisilylamine (TSA) (SiH(SiH3)3) or perhydropolysilazanes(SiH3(NH2)), for example. In some embodiments, the N-core precursor can be written as a formula of N(SiH3)xRyHz, where R is CH3or C2H5, and x+y+z=3, x≥1. In some embodiments, the N-core precursor is disilylamine (DSA) (NH(SiH3)2), for example. In some embodiments, the precursor with N—Si—N backbone can be written as a formula of Si(NR)xHy, where R is H, CH3or C2H5, and x+y=4, x≥2. In some embodiments, the precursor with N—Si—N backbone is SiH2(NC2H5)2, for example.

In some embodiments, the oxygen radical is generated in a remote plasma system (RPS) outside of the deposition chamber and transported into the processing region of the deposition chamber. The oxygen radical can be generated from an oxygen containing reactant gas such as molecular oxygen (O2), ozone (O3), water vapor (H2O) or hydrogen peroxide (H2O2).

In some embodiments, an oxygen-free reactant gas may be provided and include NH3, N2, H2, the like, or a combination thereof. In some embodiments, the oxygen-free reactant gas includes nitrogen such as NH3or N2and H2. In some embodiments, the oxygen-free reactant gas flows through the remote plasma system (RPS) outside of the deposition chamber and radical thereof is generated and transported into the processing region of the deposition chamber.

One or more carrier gases may also be included. The carrier gases may include helium (He), argon (Ar), nitrogen (N2), the like, or a combination thereof. In some embodiments, the deposition temperature is 40° C. to 150° C., such as 50° C. to 100° C. or 60° C. to 120° C.

Next, at step S20, an oxygen-containing precursor is provided to react with the oxygen radical in the processing region of the deposition chamber, so as to form water in the flowable silicon oxide layer. In some embodiments, the oxygen-containing precursor is free of nitrogen. In some embodiments, the oxygen-containing precursor may be oxysilane, alkoxysilane, the like, or a combination thereof. In some embodiments, the oxysilane can be written as a formula of Si(OR)x(OH)yHz, where R is CH3, C2H5, C3H7, and x+y+z=4, x≥1. In some embodiments, the oxysilane is Si(OCH3)4or Si(OC2H5)4. In some embodiments, the oxysilane can also be cyclic type such as (SiO)xH2x, where 4x8, i.e., (SiO)4H8. In some embodiments, the alkoxysilane can be written as a formula of Si(CH3)x(OR)yHz, where R is CH3, C2H5, C3H7, and x+y+z=4, x≥1, y≥1. In some embodiments, the alkoxysilane is SiH(CH3)(OC2H5)2. In some embodiments, the alkoxysilane can also be cyclic type, (SiO)xHy(CH3)z, where 3x8, y+z=2x, i.e., (SiO)3(CH3).

The water is a byproduct when the oxygen-containing precursor (such as Si—O—R) reacts with the oxygen radical. In detail, the reaction mechanisms include hydrocarbon oxidation, self-condensation and/or alcohol condensation as shown below.
Si—O—R+O or H2O→Si—OH+R′O (hydrocarbon oxidation)
Si—OH+Si—OH→Si—O—Si+H2O (self-condensation)
Si—O—R+Si—OH→Si—O—Si+ROH ROH+O→CO2+H2O(alcohol condensation)

In the processing region, the silicon-containing precursor deposits a flowable silicon oxide layer on the substrate or wafer present in the processing region, and then the oxygen-containing precursor reacts with the oxygen radical to form water in the flowable silicon oxide layer. Since the silicon layer has flowable characteristic, the formed water can easily diffuse into the flowable silicon oxide layer, and the formed water is substantially dispersed and inserted throughout the flowable silicon oxide layer. In addition, the flowable nature of the flowable silicon oxide layer allows the layer to flow into narrow gaps, trenches and other structures on the processing region of the substrate/wafer.

In some embodiments, before inserting the water into the flowable silicon oxide layer, the flowable silicon oxide layer contains nitrogen, and N—H bond and Si—O bond in the layer can be characterized by FTIR ([N—H]: 3260-3450 cm−1, FWHM=180˜220 cm−1; [Si—O]: 1010-1080 cm−1, FWHM=60˜100 cm−1) with a peak height ratio as [N—H]peak/[Si—O]: In some embodiments, the peak height ratio of [N—H]peak/[Si—O]peakis larger than 0.02, for example. In some embodiments, the peak height ratio of [N—H]peak/[Si—O]peakis 0.04 to 0.06 or 0.035 to 0.07. After the water is formed by the oxygen-containing precursor and an oxygen radical, the flowable silicon oxide layer contains H2O, and the water bond in the layer can be characterized by FTIR ([H2O]: 3250-3420 cm−1, FWHM=400˜500 cm−1) with a peak height ratio as [H2O]peak/[Si—O]peak. In some embodiments, the peak height ratio of [H2O]peak/[Si—O]peakis larger than 0.05, for example. In some embodiments, the peak height ratio of [H2O]peak/[Si—O]peakis 0.12 to 0.165 or 0.135 to 0.175.

FIG. 2shows a timing diagram of a method of forming a silicon oxide layer in accordance with some embodiments of the disclosure. The deposition process is basically formed by repeating at least one deposition cycle. The deposition cycle includes time periods t1-t3, for example. During the whole deposition cycle from the start of the time period t1to the ending of the time period t3, the silicon-containing precursor and the oxygen-containing reactant gas are provided into the deposition chamber with a constant amount, and the flowable silicon oxide layer is deposited. In addition, during the whole deposition cycle, the oxygen-containing reactant gas is provided to flow through the RPS to generate the oxygen radical and other radical(s). The oxygen-free reactant gas is provided with a constant amount during the whole deposition cycle, and the oxygen-containing reactant gas is provided with an increased amount during the time period t2. In the time period t2which is between the time period t1and the time period t3, the oxygen-containing precursor is provided into the deposition chamber with a constant amount. In some embodiments, assuming that the silicon oxide layer is formed by depositing multiple silicon oxide layers onto one another, during the time period t1, a first silicon oxide layer is formed by the silicon-containing precursor and the oxygen-containing reactant gas, for example. During the time period t2, a second silicon oxide layer is formed over the first silicon oxide layer by the silicon-containing precursor and the oxygen-containing reactant gas. In addition, during the time period t2, the oxygen-containing precursor reacts with the oxygen radical to form water in the second silicon oxide layer. The steps of the deposition of the second silicon oxide layer and the formation of the water into the second silicon oxide layer are not separated substantially, and deposition of the second silicon oxide layer and formation of the water may occur simultaneously, which allows the water to diffuse into the second silicon oxide layer easily. During the time period t3, a third silicon oxide layer is formed over the second silicon oxide layer containing the water by the silicon-containing precursor and the oxygen-containing reactant gas.

In some embodiments, the flow of oxygen radical is controlled and optimized to react with the oxygen-containing precursor to form a certain amount of water. In other words, in contrast to the silicon-containing precursor provided during the whole deposition cycle, the oxygen-containing precursor is periodically provided accompanied with the optimized flow of oxygen radical for flowability tuning and control of water amount. In some embodiments, the time periods t1-t3may have a relationship of 0.25<t2/(t1+t3)<4 such as t2/(t1+t3)=1 or 0.8, but the disclosure is not limited thereto. The deposition cycle is completed at the ending of the time period t3. In some embodiments, an idle time period tidleis between the adjacent two deposition cycles. During the idle time period tidle, the silicon-containing precursor, the oxygen-containing reactant gas, the oxygen-free reactant gas and the oxygen-containing precursor are all ceased to provide, which allows the flowable silicon oxide layer to flow, and thus the flowability of the flowable silicon oxide layer containing the water can be improved. In some alternative embodiments, the idle time period tidlemay be 0, for example. In other words, the silicon-containing precursor, the oxygen-containing reactant gas and the oxygen-free reactant gas can be consistently provided in two continuous deposition cycles without being ceased. The deposition cycle is repeated until a desired thickness of material has deposited onto the at least one substrate in the deposition chamber. InFIG. 2, three deposition cycles are illustrated, but the disclosure is not limited thereto.

Then, at step S30, after the deposition process, a thermal process is performed on the silicon oxide layer to diffuse the water into the silicon oxide layer and oxidize the silicon oxide layer by using the water as oxidizer. In some embodiments, the water in the second silicon oxide layer diffuses into the first, second and third silicon oxide layers, for example. In some embodiments, since the water is formed in the flowable silicon oxide layer before performing the thermal process, the flowable silicon oxide layer can be converted to a silicon oxide layer having high structural integrity with a high transition rate. In an embodiment, after the oxidation, the silicon oxide layer consists essentially of silicon and oxygen. In some embodiments, the thermal process makes the flowable silicon oxide layer fully transform into the silicon oxide layer with higher density, stronger mechanical strength and less wet etch loss. In some embodiments, the thermal process is an annealing process, and may be performed at temperatures larger than 300° C. The annealing process may be either a wet or dry anneal. The annealing process may be performed for a duration larger than 30 minutes. In some alternative embodiments, in the annealing process, additional oxygen containing gas such as O2, O3or H2O may be provided. In some embodiments, the thermal process is performed with a temperature ranging from 400° C. to 450° C. for 30 minutes to 60 minutes in an nitrogen ambient, and in the formed silicon oxide layer, atom percentage of carbon is less than 7% and a dielectric constant ranges from 3.65 to 4.0, for example.

In some embodiments, the thermal process is a curing process. In some embodiments, the curing process is a UV curing process, and the curing process can be performed with an oxygen-containing gas, such as O2, O3, the like, or a combination thereof and a high thermal conductive gas, such as He, Ar, the like, or a combination thereof. In some embodiments, when the thermal process is an annealing process, an additional curing process may be performed after the annealing process, so as to reduce the residual carbon concentration and increase Si—O crosslinking. In some embodiments, the thermal process is performed with a temperature ranging from 550° C. to 650° C. for 30 minutes to 60 minutes in a H2O ambient, followed by an additional UV curing process at a temperature of 300° C. to 400° C. for 3 minutes to 5 minutes in an O2or O3ambient for achieving higher density, and in the formed silicon oxide layer, atom percentage of carbon is less than 2% and a dielectric constant ranges from 3.85 to 4.05, for example.

In some embodiments, after the deposition process, a surface stabilization treatment is performed on the silicon oxide layer. In some embodiments, the surface stabilization treatment is performed by using NH3, N2, H2, or O2plasma or soaking in O3or H2O, the like, or a combination thereof.

In some embodiments, by periodically providing the oxygen-containing precursor to react with the oxygen radical, the water is formed and inserted into the formed silicon oxide layer. Therefore, addition of the water is omitted, and high temperature and long period thermal annealing process for driving H2O is not required. Furthermore, since the water homogeneously diffuses into the silicon oxide layer, high-speed and homogeneous oxidation can be achieved. Accordingly, the characteristics such as carbon content and K value of the formed silicon oxide are improved and allows a higher thermal budget for the rest of the semiconductor manufacturing process.

The above disclosed method of forming flowable layers can be utilized in forming shallow trench isolation (STI) regions and/or inter-layer dielectrics (ILDs) in Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), such as Fin Field-Effect Transistors (FinFETs) or other semiconductor devices.

FIGS. 3A to 3Dare cross-sectional views of a method of forming a semiconductor structure along a first direction in accordance with some embodiments.FIG. 4is a cross-sectional view of a semiconductor structure along a second direction perpendicular to the first direction in accordance with some embodiments, andFIGS. 3D and 4are cross-sectional view of the same semiconductor structure.

Referring toFIG. 3A, at least one opening112is formed in a material layer such as a substrate110. After removing portions of the substrate110, 3D structures such as fins114are formed in the substrate110. In some embodiments, the substrate110may be a semiconductor substrate, such as a bulk semiconductor, a semiconductor-on-insulator (SOI) substrate, or the like, which may be doped (e.g., with a p-type or an n-type dopant) or undoped. The substrate110may be a wafer, such as a silicon wafer. Generally, an SOI substrate comprises a layer of a semiconductor material formed on an insulator layer. The insulator layer may be, for example, a buried oxide (BOX) layer, a silicon oxide layer, or the like. The insulator layer is provided on a substrate, typically a silicon or glass substrate. Other substrates, such as a multi-layered or gradient substrate may also be used. In some embodiments, the semiconductor material of the substrate110may include silicon; germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. In some embodiments, the openings112may be formed by etching trenches in the substrate110. The etching may be any acceptable etch process, such as a reactive ion etch (RIE), neutral beam etch (NBE), the like, or a combination thereof. The etch may be anisotropic.

Referring toFIG. 3B, an insulating layer120is formed to fill the openings112and cover the 3D structures such as fins114. In some embodiments, the insulating layer120is formed between neighboring fins114. In some embodiments, the insulating layer120is a silicon oxide layer formed by the method described above inFIGS. 1 and 2and corresponding paragraphs. In some embodiments, a width w of the opening112is larger than 6 nm, and aspect ratio (height h to width w) of the opening112is larger than 8, for example. In some embodiments, a flowability is defined as T/T′, where T is a mean thickness of the insulating layer120filling in the opening112, and T′ is a mean thickness of the insulating layer120on a top of the 3D structure such as the fin114. In some embodiments, the flowability is larger than 5 or 5.5 when the width w is about 100 nm, for example. In some alternative embodiments, the insulating layer120may be an oxide formed by any acceptable process, a nitride, the like, or a combination thereof, and the insulating layer120may be formed by a high density plasma chemical vapor deposition (HDP-CVD), the like, or a combination thereof.

In some embodiments, the insulating layer120outside the opening112is removed. In some embodiments, a planarization process, such as a chemical mechanical polish (CMP), may remove any excess insulating layer120and form top surfaces of the insulating layer120and top surfaces of the fins114that are coplanar.

Referring toFIG. 3C, in some embodiments, the insulating layer120is recessed, such as to form Shallow Trench Isolation (STI) regions. The insulating layer120is recessed such that the fins114protrude from between neighboring silicon oxide layers120. Further, the top surfaces of the insulating layer120may have a flat surface as illustrated, a convex surface, a concave surface (such as dishing), or a combination thereof. The top surfaces of the insulating layer120may be formed flat, convex, and/or concave by an appropriate etch. The insulating layer120may be recessed using an acceptable etching process, such as one that is selective to the material of the insulating layer120. For example, dilute hydrofluoric (dHF) acid may be used.

Referring toFIGS. 3D and 4, then, a source/drain122is partially formed in the substrate110, a gate124is formed on the substrate110, and a gate dielectric layer126formed between the gate124and the substrate110. In some embodiments, the source/drain122may be epitaxial source/drain regions and may include silicon, SiC, SiCP, SiP, or the like. The gate124may be made of a metal-containing material such as TiN, TaN, TaC, Co, Ru, Al, combinations thereof, or multi-layers thereof. In some alternative embodiments, the gate124may be formed by a replacement gate process, that is, a dummy gate is first formed, and then the dummy gate is replaced by a real gate, for example.

An ILD layer128is formed in an opening/gap between the source/drain122and the gate124over the substrate110. In some embodiments, the ILD layer128fills the opening/gap between the source/drain122and the gate124over the substrate110, exposes a top surface of the gate124and covers a top surface of the source/drain122. An ILD layer130is formed to cover the ILD layer128, and at least one contact132is formed to penetrate the ILD layers128,130to electrically connect the source/drain122. In some embodiments, the ILD layer128,130may be an oxide, such as silicon oxide, a nitride, the like, or a combination thereof. In some embodiments, the ILD layer128,130is a silicon oxide layer formed by the method described above inFIG. 1and corresponding paragraphs. In other words, the silicon oxide layer formed by the method described above inFIG. 1may be formed between the source/drain122and the gate124and covers the gate124or between the contacts132. In some alternative embodiments, the ILD layer128,130may be formed by a high density plasma chemical vapor deposition (HDP-CVD), the like, or a combination thereof. Other silicon oxides formed by any acceptable process may be used.

Although not explicitly shown, a person having ordinary skill in the art will readily understand that further processing steps may be performed on the structure inFIGS. 3D and 4. For example, various Inter-Metal Dielectrics (IMD) and metal layers in the IMD may be formed over ILD130.

In some embodiments, the insulating features such as STI regions and/or ILDs in the semiconductor device such as FinFETs may be the silicon oxide layer formed by the method described above inFIG. 1. The flowable nature of the flowable silicon oxide layer allows the film to flow into narrow gaps, trenches and other structures on the deposition surface of the substrate. Accordingly, the formed insulating features have good gap filling property and thus provide good insulation. In addition, the process is simplified, and cost and time for forming the insulating features can be significant reduced.

In some embodiments, a method of forming a silicon oxide layer includes the following steps. A silicon-containing precursor, an oxygen-containing precursor and an oxygen radical are provided to form a silicon oxide layer containing water. A thermal process is performed on the silicon oxide layer to diffuse the water into the silicon oxide layer and oxidize the silicon oxide layer by using the water as oxidizer.

In some embodiments, a method of forming a silicon oxide layer includes the following steps. At least one deposition cycle is performed. The deposition cycle includes: consistently providing a silicon-containing precursor and an oxygen radical to deposit a silicon oxide layer; and periodically providing an oxygen-containing precursor and increasing amount of the oxygen radical to form water in the silicon oxide layer. A thermal process is performed on the silicon oxide layer to diffuse the water into the silicon oxide layer and oxidize the silicon oxide layer by using the water as oxidizer.

In some embodiments, a method of forming a semiconductor structure includes the following steps. An opening is filled with a silicon oxide layer, wherein a method of forming the silicon oxide layer includes the following steps. A silicon-containing precursor, an oxygen-containing precursor and an oxygen radical are provided to form a silicon oxide layer containing water. A thermal process is performed on the silicon oxide layer to diffuse the water into the silicon oxide layer and oxidize the silicon oxide layer by using the water as oxidizer.