Method for forming thermally stable organosilicon polymer film

The present invention generally relates to a method for forming a thermally stable organosilicon polymer film which is used as, for example, a gap-fill layer filling trenches.

In processes of fabricating integrated circuits such as those for shallow trench isolation, inter-metal dielectric layers, passivation layers, etc., it is often necessary to fill trenches (any recess typically having an aspect ratio of one or higher) with insulating material. However, with miniaturization of wiring pitch of large scale integration (LSI) devices, void-free filling of high aspect ratio spaces (e.g., AR≥3) becomes increasingly difficult due to limitations of existing deposition processes. Further, even if void-free filling can be accomplished, when being subjected to subsequent heat or plasma exposure such as post-deposition treatment including plasma ashing, the filled material undergoes shrinkage, thereby creating a void. Also, the void-free filling tends to have insufficient chemical resistance such as relatively high wet etching rates.

In view of the above, an embodiment of the present invention provides a post deposition treatment to make an organosilicon polymer thermally stable. This technology can be applied not only to gap-filling processes such as those disclosed in U.S. Provisional Application No. 62/619,569, but also to conformal film-formation processes. The embodiment can solve one or more of the above-discussed problems.

Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.

An object, among other objects, of the present invention is to provide a method of improving thermal stability of an organosilane polymer which is often used as gap-filling material due to its flowability but is typically thermally unstable, manifesting significant shrinkage of a film constituted by the polymer when being exposed to heat, e.g., an atmosphere having a temperature of 400° C. or higher such as those for annealing or ashing process in semiconductor fabrication. The significant shrinkage of the film interferes with semiconductor fabrication processes. The target polymer whose thermal stability is to be improved is an organosilane polymer (referred to also as “silicon-containing polymer”) having a backbone composed of silicon atoms (polysilane), a Si—C—Si backbone (polycarbosilane), a Si—N—Si backbone (polysilazane), a Si—O—Si backbone (polysiloxane), a modified backbone of any of the foregoing, or a mixture of any of the foregoing. The organosilane polymer is chemically significantly different from silicon carbide (SiC) which is already highly thermally stable and also is not categorized as a polymer constituted by many repeated subunits forming chains. In some embodiments, as a first step, such an organosilane polymer film is deposited on a substrate at a thickness of less than 10 nm, for example, and then, as a second step, the organosilane polymer film is exposed to a hydrogen plasma in a manner increasing Si—H bonds and decreasing C—H bonds in the organosilicon polymer, whereby polymer chains of the organosilane polymer are cross-linked to each other, thereby densifying the polymer and rendering the polymer thermally stable. The hydrogen plasma treatment can induce cross-linking of polymer chains under conditions specified in this disclosure.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomic layer deposition) apparatus for depositing a dielectric film usable in an embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supply system using a flow-pass system (FPS) usable in an embodiment of the present invention.

FIG. 2 shows temperature desorption analysis data of an organosilane polymer, wherein the sample was heated and the emitted species were analyzed by mass spectrometry.

FIG. 3 is a schematic representation of cross-linking of different polymer chains induced by H2 plasma treatment according to an embodiment of the present invention.

FIG. 4 illustrates a process sequence constituted by PEALD deposition cycles and H plasma treatment process according to an embodiment, wherein the width of each column does not necessarily represent the actual time length, and a raised level of the line in each row represents an ON-state whereas a bottom level of the line in each row represents an OFF-state.

FIG. 5 is a graph showing the relationship between RI and RF power for H plasma treatment according to embodiments of the present invention.

FIG. 6 is a graph showing the relationship between RI and the number of deposition cycles per H plasma treatment according to embodiments of the present invention.

FIG. 7 is a graph showing the relationship between RI and the duration of RF power application for H plasma treatment according to embodiments of the present invention.

FIG. 8 is a graph showing the relationship between dry etch ratio (DER) and RI according to embodiments of the present invention.

FIG. 9 shows Fourier Transform Infrared (FTIR) spectra of a gap-fill layer according to an embodiment of the present invention.

FIGS. 10 and 11 are charts of thermodesorption gas chromatography with mass spectrometric detection, showing emission of volatile organic compounds from a “untreated” polymer according to a comparative example and a “H2 treated” polymer according to an embodiment of the present invention.

FIG. 12 shows a graph indicating thickness reduction of untreated film according to a comparative example, and thickness reduction of H2 treated films according to embodiments of the present invention.

FIG. 13 shows a graph indicating wet etch resistivity of untreated film according to a comparative example, and thickness reduction of H2 treated films according to embodiments of the present invention.

FIG. 14 shows a graph indicating thickness changes by annealing of a deposited film according to an embodiment of the present invention, and thickness changes by annealing of a deposited film according to a comparative example.

FIG. 15 shows graphs indicating the schematic relationship between process parameters and RI improvement obtained using statistical data analysis software JMP® according to embodiments of the present invention.

FIG. 16 shows graphs indicating the schematic relationship between process parameters and RI obtained using statistical data analysis software JMP® according to embodiment of the present invention.

FIG. 17 shows STEM photographs of cross-sectional views of gap-filled wide trenches subjected to periodic hydrogen plasma treatment in (a), and gap-filled narrow trenches subjected to periodic hydrogen plasma treatment in (b) according to an embodiment of the present invention.

In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases, depending on the context. Likewise, an article “a” or “an” refers to a species or a genus including multiple species, depending on the context. In this disclosure, a process gas introduced to a reaction chamber through a showerhead may be comprised of, consist essentially of, or consist of a silicon-containing precursor and an additive gas. The additive gas may include a reactant gas for nitriding and/or carbonizing the precursor, and an inert gas (e.g., noble gas) for exciting the precursor, when RF power is applied to the additive gas. The inert gas may be fed to a reaction chamber as a carrier gas and/or a dilution gas. In this disclosure, no reactant gas for oxidizing the precursor is used. Further, in some embodiments, no reactant gas is used, and only noble gas (as a carrier gas and/or a dilution gas) is used. The precursor and the additive gas can be introduced as a mixed gas or separately to a reaction space. The precursor can be introduced with a carrier gas such as a rare gas. A gas other than the process gas, i.e., a gas introduced without passing through the showerhead, may be used for, e.g., sealing the reaction space, which includes a seal gas such as a rare gas. In some embodiments, the term “precursor” refers generally to a compound that participates in the chemical reaction that produces another compound, and particularly to a compound that constitutes a film matrix or a main skeleton of a film, whereas the term “reactant” refers to a compound, other than precursors, that activates a precursor, modifies a precursor, or catalyzes a reaction of a precursor, wherein the reactant may provide an element (such as N, C) to a film matrix and become a part of the film matrix, when RF power is applied. The term “inert gas” refers to a gas that excites a precursor when RF power is applied, but unlike a reactant, it does not become a part of a film matrix.

In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film or a non-film structure. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers. Further, in this disclosure, any two numbers of a variable can constitute a workable range of the variable as the workable range can be determined based on routine work, and any ranges indicated may include or exclude the endpoints. Additionally, any values of variables indicated (regardless of whether they are indicated with “about” or not) may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, the terms “constituted by” and “having” refer independently to “typically or broadly comprising,” “comprising,” “consisting essentially of,” or “consisting of” in some embodiments. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

In this disclosure, “continuously” refers to without breaking a vacuum, without interruption as a timeline, without any material intervening step, without changing treatment conditions, immediately thereafter, as a next step, or without an intervening discrete physical or chemical structure between two structures other than the two structures in some embodiments.

In some embodiments, the term “precursor” refers generally to a compound that participates in the chemical reaction that produces another compound, and particularly to a compound that constitutes a film matrix or a main skeleton of a film, whereas the term “reactant” refers to a compound that activates a precursor, modifies a precursor, or catalyzes a reaction of a precursor.

In this disclosure, a recess between adjacent protruding structures and any other recess pattern are referred to as a “trench.” That is, a trench is any recess pattern including a hole/via and which has, in some embodiments, a width of about 20 nm to about 100 nm (typically about 30 nm to about 50 nm) (wherein when the trench has a length substantially the same as the width, it is referred to as a hole/via, and a diameter thereof is about 20 nm to about 100 nm), a depth of about 30 nm to about 100 nm (typically about 40 nm to about 60 nm), and an aspect ratio of about 2 to about 10 (typically about 2 to about 5). The proper dimensions of the trench may vary depending on the process conditions, film compositions, intended applications, etc.

In some embodiments, a method of forming a thermally stable organosilicon polymer, comprises: (i) depositing an organosilicon polymer whose backbone is composed of silicon atoms on a substrate using a silicon-containing precursor in a reaction space; and (ii) exposing the organosilicon polymer deposited in step (i) to a hydrogen plasma in the absence of the precursor in the reaction space in a manner increasing Si—H bonds and decreasing C—H bonds in the organosilicon polymer without depositing an organosilicon polymer.

In some embodiments, in step (i), the target organosilane polymer is thermally unstable, wherein the term “thermally unstable” refers to a property of a film manifesting a shrinkage of 10% or higher as measured when being placed at a temperature of 450° C. for five minutes in an atmosphere of inert gas (e.g., noble gas such as Ar) or in conditions equivalent thereto, such as conditions for annealing or ashing. The term “thermally stable” refers to a property of a film which is not “thermally unstable” (manifesting a shrinkage of less than 10% as measured in the same manner as above), typically, manifesting a shrinkage of 5% or less, preferably, manifesting substantially no shrinkage (e.g., less than 10%, 5%, 1%, or substantially 0%).

In some embodiments, the target organosilane polymer is constituted by polysilane, polycarbosilane, polysilazane, or polysiloxane. In some embodiments, the target organosilane polymer is a flowable silicon-containing polymer which is used as, for example, a gap-fill layer filling trenches. For example, the flowable silicon-containing polymer which is disclosed in U.S. Provisional Application No. 62/619,569, the disclosure of which is incorporated herein by reference in its entirety, may be used as the target organosilane polymer wherein PEALD-like process is disclosed (the “PEALD-like process” comprises a PEALD recipe, e.g., feed/purge/plasma strike/purge, wherein the purge after feed is voluntarily severely shortened to leave high partial pressure of precursor during the plasma strike, which PEALD-like process is clearly distinguished from ALD chemistry or mechanism). In some embodiments, the target organosilane polymer constitutes a conformal film (having a conformality of 80% or higher). For example, a H 2 plasma can improve the quality (e.g., thermal stability) of film deposited on a top surface, side walls of a trench, and a bottom of the trench, uniformly, whereas a H 2 /Ar plasma or H 2 /He plasma can improve the quality (e.g., thermal stability) of film deposited on a top surface and a bottom of a trench more efficiently than that of film deposited on sidewalls of the trench, due to the contribution of heavy ion bombardment by Ar or He ions. The plasma is preferably a direct plasma (generated with capacitively coupled parallel electrodes in a reaction chamber). For a remote plasma, improvement can be topologically uniform but the treatment is less efficient than that by a direct plasma.

The target organosilane polymer can be deposited not only by plasma-enhanced atomic layer deposition (PEALD), but also by plasma-enhanced chemical vapor deposition (PECVD) with continuous plasma or pulsing plasma. Further, such polymer can also be formed thermally with the right chemistry/catalyst by thermal CVD (including pulse CVD) and thermal ALD.

Step (ii) is not part of deposition step (i), i.e., the plasma is used to reform the already existing polymer, not to deposit or form a new layer of polymer. In step (ii), no precursor (also no reactant) is fed to the reaction space, or no unreacted precursor is adsorbed on a surface of a substrate, so that substantially no new film is formed on the surface of the substrate. Further, in step (ii), at least one gas used in step (i) other than the precursor is not used, and/or at least one gas not used in step (i) is used, in order to perform the hydrogen plasma treatment. In an ALD process which comprises repeating multiple times a deposition cycle to deposit a monolayer or at least an equivalent quantity of flowable material, step (i) is constituted by one or more deposition cycles, and step (ii) is conducted after every step (i). The thickness of the film deposited in step (i) before conducting step (ii) is less than 10 nm, typically less than 5 nm, so that the film is fully reformed in the thickness direction by step (ii). In some embodiments, step (i) comprises conducting one or more cycles (e.g., 2 to 10 cycles) of plasma-enhanced atomic layer deposition (PEALD) per step (ii) conducted once, and steps (i) and (ii) are repeated as step (iii) until a desired thickness (e.g., about 20 nm to about 100 nm) of the organosilicon polymer is obtained.

In some embodiments, step (i) and step (ii) are continuously conducted in the same reaction chamber. In this disclosure, “continuously” refers to without breaking a vacuum, without interruption as a timeline, without any material intervening step, without changing treatment conditions, immediately thereafter, or as a next step, depending on the embodiment.

In some embodiments, step (ii) comprises applying RF power to the reaction space in a range of 0.07 W/cm 2 to 1.4 W/cm 2 (e.g., 0.14 to 0.7 W/cm 2 ) to generate the hydrogen plasma. In some embodiments, step (ii) is conducted for 5 seconds to 60 seconds (e.g., 10 seconds to 30 seconds). In some embodiments, step (ii) comprises supplying hydrogen gas and noble gas to the reaction space at a ratio of hydrogen gas flow to total flow of gases including hydrogen gas and noble gas, which is 0.1 to 0.9 (e.g., 0.5 to 0.8). In some embodiments, step (ii) comprises supplying only hydrogen gas to the reaction space to generate the hydrogen plasma.

In some embodiments, in step (ii), the hydrogen plasma is a pulsed plasma generated by applying RF power to the reaction space in pulses with intervals of about 10 milliseconds to about 500 milliseconds (e.g., about 50 milliseconds to about 200 milliseconds).

The present invention is explained in more detail below using examples, but the present invention is not intended to be limited to the examples.

As discussed above, the material to be reformed is an organosilane polymer which is not considered to be constituted by silicon carbide (SiC) which is normally thermally stable and not flowable. In some embodiments, the organosilane polymer has a polysilane-based structure, which may or may not be flowable, but has low thermal stability. Although both silicon carbide and silicon-containing polymer contain silicon atoms and carbon atoms, silicon-containing polymer has lower density than does silicon carbide and has less resistance to heat than does silicon carbide, and thus, silicon-containing polymer has less thermal stability than silicon carbide, thereby being vulnerable to shrinkage and dry etching, for example. Silicon-containing polymer properties depend greatly on polymer cross-linking state which is crucial for polymer thermal stability. Hydrogen plasma treatment can induce crosslinking with positive influence on film properties such as thermal stability and resistance to dry etching.

FIG. 3 is a schematic representation of cross-linking of different polymer chains induced by H2 plasma treatment according to an embodiment of the present invention. Although there is a high degree of randomness in plasma polymerization, as shown in FIG. 3 , different polymer chains (they can be the same chains) are cross-linked by hydrogen plasma treatment, thereby promoting densification (increasing RI) and improving thermal stability and resistance to dry etching or other chemical treatment.

In some embodiments, since silicon-containing polymer deposition need not be flowable or bottom-up deposition, process parameters for depositing silicon-containing polymer can be selected and set more leniently than those for bottom-up deposition such as those disclosed in U.S. Provisional Application No. 62/619,569. Since the parameters and set points for deposition of SiC may be those shown in Table 1 below, silicon-containing polymer can be formed under conditions having one or more set points different from those shown in Table 1, in which the “SUS temp” (susceptor temperature) and “purge” (purge after feed of a precursor) may be the most impactful parameters. In Table 1, “total He” refers to the total flow rate of He gas including a He carrier gas, a He seal gas, a He dilution gas, etc., “gap” refers to a gap between capacitively coupled parallel electrodes, “pressure” refers to a pressure of the reaction space, and “feed” refers to feed of the precursor. A skilled artisan in the art can readily provide such conditions to optimize the process conditions, in view of the present disclosure in its entirety and the disclosure of U.S. Provisional Application No. 62/619,569, the disclosure of which is incorporated herein by reference in its entirety, as a matter of routine experimentation.

The organosilane polymer is then subjected to hydrogen plasma treatment to improve thermal stability. FIG. 4 illustrates a process sequence constituted by PEALD deposition cycles and H plasma treatment process according to an embodiment, wherein the width of each column does not necessarily represent the actual time length, and a raised level of the line in each row represents an ON-state whereas a bottom level of the line in each row represents an OFF-state. In this sequence, “Gas Stab 1” refers to a first gas stabilization step which is conducted before each deposition step, where feeding of a plasma-generating gas (e.g., He) begins without feeding a precursor and without applying RF power. “Depo” refers to a deposition step comprising one or more deposition cycles, each deposition cycle depositing a monolayer or at least an equivalent quantity of flowable material, where each cycle is constituted by feeding a precursor, purging, applying RF power, and purging (in this sequence, the cycle is repeated once, i.e., two cycles are performed, but the number of cycles is not limited thereto and any suitable number of cycles can be performed).

Thereafter, a hydrogen plasma treatment step begins. In this sequence, “Gas Stab 2” refers to a second gas stabilization step which is conducted before the hydrogen plasma treatment step, where feeding of the plasma-generating gas (e.g., He) is stopped, while feeding of hydrogen and an additional plasma-generating gas (e.g., Ar) begins without feeding a precursor and without applying RF power. In “H treat” which refers to a hydrogen plasma treatment step, RF power is applied in the absence of any precursor. Although a H 2 /Ar plasma is more effective in improving thermal stability (inducing cross-linking of polymers) than a H 2 /He plasma, the H2/He plasma can be used. Also, solely a H 2 plasma can be used. In some embodiments, a workable flow ratio of He to total plasma-generating gas (including He and/or Ar) is not limited as long as there is no arcing and the plasma is stable, and the workable flow ratio is highly hardware-dependent. In some embodiments, the hydrogen plasma treatment is conducted in a manner similar to that illustrated in FIG. 4 under the conditions shown in Table 2 below.

In the above, the “RF power (for a 300-mm wafer)” can be converted to units of W/cm 2 for different sizes of wafers, in both PEALD-like process and PECVD with continuous or pulsing plasma. In the above, the “Thickness of deposited organosilane polymer exposed to H2 plasma” refers to the thickness of the polymer on a top surface of a substrate.

In some embodiments, the deposition step and the hydrogen plasma treatment are conducted continuously in the same reaction chamber. For example, FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomic layer deposition) apparatus for depositing a dielectric film usable in an embodiment of the present invention. In this figure, by providing a pair of electrically conductive flat-plate electrodes 4 , 2 in parallel and facing each other in the interior 11 (reaction zone) of a reaction chamber 3 , applying HRF power (50 Hz or 2 GHz) 20 to one side, and electrically grounding the other side 12 , a plasma is excited between the electrodes. A temperature regulator is provided in a lower stage 2 (the lower electrode), and a temperature of a substrate 1 placed thereon is kept constant at a given temperature. The upper electrode 4 serves as a shower plate as well, and a plasma-generating gas (and a dilution gas if any) and a precursor gas (with a carrier gas if any) are introduced into the reaction chamber 3 through a gas line 21 and a gas line 22 , respectively, and through the shower plate 4 . Additionally, in the reaction chamber 3 , a circular duct 13 with an exhaust line 7 is provided, through which gas in the interior 11 of the reaction chamber 3 is exhausted. Additionally, a transfer chamber 5 disposed below the reaction chamber 3 is provided with a seal gas line 24 to introduce a seal gas into the interior 11 of the reaction chamber 3 via the interior 16 (transfer zone) of the transfer chamber 5 wherein a separation plate 14 for separating the reaction zone and the transfer zone is provided (a gate valve through which a wafer is transferred into or from the transfer chamber 5 is omitted from this figure). The transfer chamber is also provided with an exhaust line 6 . In some embodiments, the deposition of multi-element film and surface treatment are performed in the same reaction space, so that all the steps can continuously be conducted without exposing the substrate to air or other oxygen-containing atmosphere.

The continuous flow of the carrier gas can be accomplished using a flow-pass system (FPS) wherein a carrier gas line is provided with a detour line having a precursor reservoir (bottle), and the main line and the detour line are switched, wherein when only a carrier gas is intended to be fed to a reaction chamber, the detour line is closed, whereas when both the carrier gas and a precursor gas are intended to be fed to the reaction chamber, the main line is closed and the carrier gas flows through the detour line and flows out from the bottle together with the precursor gas. In this way, the carrier gas can continuously flow into the reaction chamber, and can carry the precursor gas in pulses by switching the main line and the detour line. FIG. 1B illustrates a precursor supply system using a flow-pass system (FPS) according to an embodiment of the present invention (black valves indicate that the valves are closed). As shown in (a) in FIG. 1B , when feeding a precursor to a reaction chamber (not shown), first, a carrier gas such as Ar (or He) flows through a gas line with valves b and c, and then enters a bottle (reservoir) 20 . The carrier gas flows out from the bottle 20 while carrying a precursor gas in an amount corresponding to a vapor pressure inside the bottle 20 , and flows through a gas line with valves f and e, and is then fed to the reaction chamber together with the precursor. In the above, valves a and d are closed. When feeding only the carrier gas (noble gas) to the reaction chamber, as shown in (b) in FIG. 1B , the carrier gas flows through the gas line with the valve a while bypassing the bottle 20 . In the above, valves b, c, d, e, and f are closed.

After the deposition step (which may be constituted by 2 to 6 cycles of PEALD, for example) is complete, the hydrogen plasma treatment step begins in a manner similar to that for the deposition step, except that no precursor gas is fed, and process parameters are adjusted for the hydrogen plasma treatment.

A skilled artisan will appreciate that the apparatus includes one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) are communicated with the various power sources, heating systems, pumps, robotics and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.

In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed close to each other) can be used, wherein a reactant gas and a noble gas can be supplied through a shared line whereas a precursor gas is supplied through unshared lines.

The film having filling capability can be applied to various semiconductor devices including, but not limited to, cell isolation in 3D cross-point memory devices, self-aligned Via, dummy gate (replacement of current poly Si), reverse tone patterning, PC RAM isolation, cut hard mask, and DRAM storage node contact (SNC) isolation.

In the following examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. A skilled artisan will appreciate that the apparatus used in the examples included one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) were communicated with the various power sources, heating systems, pumps, robotics and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.