Method for depositing dielectric film in trenches by PEALD

Abstract

A method for depositing a dielectric film in a trench by plasma-enhanced atomic layer deposition (PEALD) includes depositing a dielectric film in a trench of a substrate by PEALD under conditions wherein the wet etch rate of the depositing film on a top surface of the substrate is substantially equivalent to or higher than the wet etch rate of the depositing film at a sidewall of the trench, wherein a precursor fed into the reaction space has N(CH.sub.3).sub.2 as a functional group.

Claims

1. A method for depositing a dielectric film in a trench by plasma-enhanced atomic layer deposition (PEALD), comprising: (i) (a) obtaining multiple substrates on each of which a dielectric film is formed in a trench of each substrate in a reaction space by PEALD under deposition conditions wherein RF power varies as a sole variable in RF power application for the respective substrates, said trench being a recess from a top surface of the substrate and having a bottom and a sidewall connecting the top surface and the bottom; (b) subjecting the multiple substrates to wet etching of the dielectric films formed thereon under common etching conditions for etching the dielectric films; and (c) obtaining a first standard curve representing a first relationship between RF power applied to the reaction space and a wet etch rate of a part of the film, at a given location of interest, deposited on the sidewall of the trench as measured under wet etching conditions where an etching solution is a hydrofluoric acid diluted at 1:100, a temperature is 17 C., a sample size is 55 cm, and an etching time is 5 minutes, and a second standard curve representing a second relationship between the RF power and a wet etch rate of a part of the film deposited on the top surface of the substrate as measured under the wet etching conditions, wherein a precursor fed into the reaction space has N(CH.sub.3).sub.2 as a functional group, said PEALD being conducted under deposition conditions wherein the RF power is used as a sole variable in a range such that the first standard curve and the second standard curve intersect; (ii) selecting RF power which corresponds to a first wet etch rate of the part of the film deposited on the sidewall of the trench and a second wet etch rate of the part of the film deposited on the top surface of the substrate where the second wet etch rate is more than 90% of the first wet etch rate based on the first and second standard curves obtained in step (i); and (iii) depositing a dielectric film in a trench of a substrate by PEALD under the deposition conditions used in step (i) where RF power is the one determined in step (ii).

2. The method according to claim 1, wherein the RF power used in step (iii) is selected such that the second wet etch rate is equal to the first wet etch rate according to the first and second relationships in step (i).

3. The method according to claim 1, wherein the precursor is a dimethylamido metal complex.

4. The method according to claim 3, wherein the metal in the metal complex is titanium.

5. The method according to claim 1, wherein RF power used in step (iii) is in a range of about 0.07 W/cm.sup.3 to about 0.7 W/cm.sup.3 per area of the substrate.

6. The method according to claim 1, wherein the trench has a depth of about 100 nm to about 500 nm and an aspect ratio of about 1 to about 5.

7. The method according to claim 1, wherein the dielectric film deposited in step (iii) has a thickness of about 10 nm to about 100 nm.

8. The method according to claim 1, further comprising (iv) etching the dielectric film deposited in step (iii).

9. The method according to claim 8, wherein the dielectric film deposited in step (iii) has a first conformality and the dielectric film etched in step (iv) has a second conformality, wherein the second conformality is higher than the first conformality.

10. The method according to claim 9, wherein the second conformality is about 90% to about 110%.

11. A method for depositing a dielectric film in a trench of a substrate by plasma-enhanced atomic layer deposition (PEALD), said trench being a recess from a top surface of the substrate and having a bottom and a sidewall connecting the top surface and the bottom, said method comprising depositing an initial dielectric film in the trench of the substrate, followed by wet etching the initial dielectric film, wherein the step of depositing the initial dielectric film is conducted by PEALD under conditions wherein RF power is a sole variable in RF power application and selected in a range of about 0.07 W/cm.sup.3 to about 0.7 W/cm.sup.3 per area of the substrate such that a wet etch rate of the depositing film on the top surface of the substrate is more than 90% of a wet etch rate of the depositing film at a given location of interest of the sidewall of the trench as measured under etching conditions where an etching solution is a hydrofluoric acid diluted at 1:100, a temperature is 17 C., a sample size is 55 cm, and an etching time is 5 minutes, wherein a precursor fed into the reaction space has N(CH.sub.3).sub.2 as a functional group.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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.

(2) 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.

(3) 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.

(4) FIG. 2 illustrates a PEALD process sequence according to an embodiment of the present invention.

(5) FIG. 3A is a graph showing the relationship between N concentration of a film and RF power used for deposition of the film according to an embodiment of the present invention.

(6) FIG. 3B is a graph showing the relationship between the wet etch rate of a deposited film relative to that of oxide film and RF power used for deposition of the film according to an embodiment of the present invention.

(7) FIG. 4 is a graph showing the relationship between the wet etch rate (arbitrary unit) of a deposited film at the sidewall and on the top surface relative to that of thermal oxide film, and RF power used for deposition of the film according to an embodiment of the present invention.

(8) FIG. 5 shows Scanning transmission electron microscopy (STEM) photographs of cross-sectional views of conformal dielectric films formed according to a comparative example, wherein (a) shows a film as deposited, and (b) shows a film after wet etching.

(9) FIG. 6 shows Scanning transmission electron microscopy (STEM) photographs of cross-sectional views of conformal dielectric films formed according to an embodiment of the present invention, wherein (a) shows a film as deposited, and (b) shows a film after wet etching.

DETAILED DESCRIPTION OF EMBODIMENTS

(10) In this disclosure, gas may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases. Likewise, an article a or an refers to a species or a genus including multiple species. 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 precursor and a reactant gas. The reactant gas includes a gas for oxidizing the precursor when RF power is applied to the reactant gas. The reactant gas can be introduced continuously to a reaction space if it is not reactive to the precursor without RF power. The precursor can be introduced with a carrier gas such as a noble 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 noble gas. 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. A film 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. The terms constituted by and having refer independently to typically or broadly comprising, comprising, consisting essentially of, or consisting of in some embodiments.

(11) In the present disclosure 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 experimentation.

(12) In all of the disclosed embodiments, any element used in an embodiment can be replaced with any elements equivalent thereto, including those explicitly, necessarily, or inherently disclosed herein, for the intended purposes. Further, the present invention can equally be applied to apparatuses and methods.

(13) In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

(14) 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.

(15) The dielectric film includes, but is not limited to, a metal oxide film constituted such as titanium oxide, or multi-element materials, etc., having a dielectric constant of about 10 to about 100, typically about 50 to about 60. In some embodiments, the dielectric film is formed in trenches, vias, or other recesses including side walls and bottom surfaces (collectively referred to as trenches) by plasma-enhanced ALD or other plasma-assisted cyclic deposition methods. The trench may have a depth of about 10 nm to about 1,000 nm, typically about 100 nm to about 500 nm, and an aspect ratio of about 1 to about 10, typically about 2 to about 3. The thickness of the deposited dielectric film may be in a range of about 2 nm to about 500 nm, typically about 10 nm to about 100 nm, more typically about 15 nm to about 30 nm (a desired film thickness can be selected as deemed appropriate according to the application and purpose of film, etc.).

(16) The embodiments will be explained with respect to preferred embodiments. However, the present invention is not limited to the preferred embodiments.

(17) In an embodiment, a method for depositing a dielectric film in a trench by plasma-enhanced atomic layer deposition (PEALD), comprises: (i) determining a first relationship between RF power applied to a reaction space where a dielectric film is being deposited in a trench of a substrate by PEALD and a wet etch rate of a part of the film deposited on a sidewall of the trench, and a second relationship between the RF power and a wet etch rate of a part of the film deposited on a top surface of the substrate, wherein a precursor fed into the reaction space has N(CH.sub.3).sub.2 as a functional group; (ii) determining RF power which corresponds to a first wet etch rate of the part of the film deposited on the sidewall of the trench and a second wet etch rate of the part of the film deposited on the top surface of the substrate where the second wet etch rate is substantially equivalent to or higher than the first wet etch rate according to the first and second relationships in step (i); and (iii) depositing a dielectric film in a trench of a substrate by PEALD under conditions equivalent to those used in the first and second relationships where RF power is the one determined in step (ii).

(18) In this disclosure, substantially the same, substantially equivalent, or the like may refer to an immaterial difference or a difference recognized by a skilled artisan such as those of less than 10%, less than 5%, less than 1%, or any ranges thereof in some embodiments (typically, the difference is 5%). Also, in the disclosure, substantially higher, substantially different, or the like may refer to a material difference or a difference recognized by a skilled artisan such as those of at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any ranges thereof in some embodiments.

(19) In some embodiments, the wet etch rate of a film deposited on a top surface of a substrate changes as a function of RF power used for deposition of the film, and when a precursor having N(CH.sub.3).sub.2 as a functional group is used, the wet etch rate of the film changes along a downward parabola with a vertex as RF power increases. That is, when RF power is relatively weak, the wet etch rate decreases as RF power increases, i.e., the quality of a depositing film is improved. However, when RF power further increases, more plasma reaches the top surface, and impurity concentration also begins increasing. In general, the changes of the wet etch rate are correlated to the changes of impurity concentration. As a result, the wet etch rate begins increasing after reaching a minimum value (the lowest vertex). The quality of the film on the top surface obtained at the lowest vertex appears to be the highest. However, when the quality of the film on the top surface is the highest at the lowest vertex, the quality of the film at the sidewall is not high, i.e., the wet etch rate of the film at the sidewall is relatively high. Since plasma does not easily reach the sidewall, the quality of the film at the sidewall is not significantly affected by the intensity of RF power, in contrast with the quality of the film on the top surface. In some embodiments, the wet etch rate of the film at the sidewall gradually decreases as RF power increases. Thus, although the wet etch rate of the film at the sidewall is higher than that of the film on the top surface when RF power is relatively low, as RF power increases, at a certain point after the lowest vertex point of the wet etch rate of the film on the top surface, the wet etch rate of the film on the top surface and that of the film at the sidewall become substantially equivalent because the wet etch rate of the film on the top surface continues increasing while the wet etch rate of the film at the sidewall gradually decreases (the line representing the relationship between the wet etch rate of the film on the top surface and RF power, and the line representing the relationship between the wet etch rate of the film at the sidewall and RF power, intersect).

(20) In some embodiments, only by adjusting RF power for depositing a film (other process parameters are unchanged), the second wet etch rate (i.e., the wet etch rate of a film deposited on the top surface) is rendered substantially equivalent to or higher than the first wet etch rate (i.e., the wet etch rate of a film deposited at the sidewall), so that the conformality of the film after wet etching can be improved. In some embodiments, the conformality of the film after wet etching is in a range of about 90% to about 110%, ideally about 95% to about 100%. The conformality is defined as a ratio of thickness of a film at a sidewall of a trench of a substrate (or at the bottom surface) to thickness of the film on a top surface of the substrate. The first wet etch rate is selected depending on the conformality of the film deposited on the substrate. If the conformality is about 100%, the first and second wet etch rates may be substantially equivalent so that the conformality of the film after wet etching can remain about 100%. In some embodiments, the conformality of the film deposited is in a range of about 80% to about 100%. Conventionally, the conformality after wet etching is lower than that of the deposited film by about 5% to about 10%. In contrast, in some embodiments of the present invention, the conformality after wet etching is higher than that of the deposited film by about 5% to about 15% (typically around 10%). In some embodiments, the above is achieved by degrading the quality of the film on the top surface of the substrate, instead of improving the quality of the film at the sidewall of the trench of the substrate.

(21) In some embodiments, the precursor is a dimethylamido metal complex. In some embodiments, the metal in the metal complex is titanium. Other metals such as germanium can be used. In some embodiments, the precursor is one or more compounds selected from the group consisting of tetrakis(dimethylamido)titanium, tetrakis(dimethylamido)germanium.

(22) In some embodiments, RF power used in step (iii) (i.e., RF power-determining step) is in a range of about 0.02 W/cm.sup.3 to about 1.4 W/cm.sup.3, typically about 0.07 W/cm.sup.3 to about 0.7 W/cm.sup.3, more typically 0.3 W/cm.sup.3 to about 0.4 W/cm.sup.3 per area of the substrate.

(23) In this disclosure, the wet etch rate is evaluated by subjecting the film to wet etching under the conditions shown in Table 1 below:

(24) TABLE-US-00001 TABLE 1 Conditions for wet etching Etching solution 1:100 diluted HF (hydrofluoric acid) Temperature 17 C. Sample size 5 5 cm Etching time 5 min

(25) In the above, the measuring steps are as follows: (1) cutting a substrate on which a film is deposited into a piece having a size of 55 cm; (2) measuring the thickness of the film by spectroscopic ellipsometry; (3) submerging the substrate piece in a solution having a hydrofluoric acid concentration of 1:100 for five minutes; (4) thoroughly washing the substrate piece using pure water and drying it by a blower; and (5) measuring the thickness of the film by spectroscopic ellipsometry, and calculating the wet etch rate which is defined as a ratio of the difference between the thickness measured in step (2) and that in step (5) to the film thickness measured in step (2). Also, a substrate on which a thermal oxide film (TOX) is deposited is subjected to the same steps as above, and the ratio of the wet etch rate of the film to that of TOX is calculated.

(26) In some embodiments, since the degree of wet etch rate is related to the impurity concentration in the film, the method can be conducted based on the impurity concentration as follows: (a) depositing a film under first conditions, and measuring impurity concentration of the film on the top surface (T1) and that at the sidewall (S1), wherein T1<S1; (b) depositing a film under second conditions wherein process parameters such as RF power are changed from those of the first conditions (e.g., increasing RF power), and measuring impurity concentration of the film on the top surface (T2) and that at the sidewall (S2), wherein T1<T2, and S1>S2; and (c) repeating step (b) until optimal conditions where T2S2 are determined ( denotes substantially the same).

(27) In some embodiments, the film is deposited by PEALD under conditions shown in Table 2 below.

(28) TABLE-US-00002 TABLE 2 Conditions for Deposition Cycle Substrate temperature 70 to 250 C. (preferably 150 to 200 C.) Pressure 200 to 600 Pa (preferably 300 to 400 Pa) Precursor e.g., Tetrakis(dimethylamido)titanium Precursor pulse 0.1 to 5 sec Precursor purge 0.1 to 5 sec Reactant e.g., oxygen plasma Flow rate of reactant (continuous) 250 to 2000 sccm (preferably 1000 to 2000 sccm) Carrier gas e.g., argon Dilution gas e.g., argon Flow rate of carrier gas (continuous) 500 to 2000 sccm (preferably 1000 to 2000 sccm) Flow rate of dilution gas (continuous) 250 to 1000 sccm (preferably 500 to 1000 sccm) RF power (13.56 MHz) for a 300-mm 50 to 500 W (preferably 200 to 300 W) wafer RF power pulse 0.1 to 5 sec Purge 0.1 to 5 sec Growth rate per cycle 0.060 to 0.076 nm/cycle Total thickness [nm] 18 to 23 nm

(29) FIG. 2 illustrates a PEALD process sequence according to an embodiment of the present invention. In this disclosure, 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. The deposition cycle includes steps of feeding a precursor to a reaction zone, purging the reaction zone, applying RF power to the reaction zone, and purging the reaction zone in this order, wherein a purge/carrier gas is supplied continuously to the reaction zone throughout the entire steps of deposition cycle, and a reactant gas for deposition is supplied continuously to the reaction zone throughout the entire steps of deposition cycle. In the deposition cycle, steps of feeding the precursor, purging the reaction zone, applying RF power to the reaction zone, and purging the reaction zone can be repeated p times (p is an integer of 150 to 350, typically 250 to 300), depending on the target film thickness and the target compositions and quality of the film, although repeating is not required.

(30) In this disclosure, the word continuously refers to at least one of the following: without breaking a vacuum, without being exposed to air, without opening a chamber, as an in-situ process, without interruption as a step in sequence, and without changing main process conditions, depending on the embodiment. In some embodiments, an auxiliary step such as a delay between steps or other step immaterial or insubstantial in the context does not count as a step, and thus, the word continuously does not exclude an intervening auxiliary step.

(31) In the sequence illustrated in FIG. 2, the precursor is supplied in a pulse using a carrier gas which is continuously supplied. This 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.

(32) The precursor may be provided with the aid of a carrier gas. Since ALD is a self-limiting adsorption reaction process, the number of deposited precursor molecules is determined by the number of reactive surface sites and is independent of the precursor exposure after saturation, and a supply of the precursor is such that the reactive surface sites are saturated thereby per cycle. A plasma for deposition may be generated in situ, for example, in an ammonia gas that flows continuously throughout the deposition cycle. In other embodiments the plasma may be generated remotely and provided to the reaction chamber.

(33) As mentioned above, each pulse or phase of each deposition cycle is preferably self-limiting. An excess of reactants is supplied in each phase to saturate the susceptible structure surfaces. Surface saturation ensures reactant occupation of all available reactive sites (subject, for example, to physical size or steric hindrance restraints) and thus ensures excellent step coverage. In some embodiments the pulse time of one or more of the reactants can be reduced such that complete saturation is not achieved and less than a monolayer is adsorbed on the substrate surface.

(34) The process cycle can be performed using any suitable apparatus including an apparatus illustrated in FIG. 1A, for example. FIG. 1A is a schematic view of a PEALD apparatus, desirably in conjunction with controls programmed to conduct the sequences described below, usable in some embodiments 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 (13.56 MHz or 27 MHz) 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 reactant gas (and noble gas) and precursor gas 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 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. In some embodiments, a remote plasma unit can be used for exciting a gas.

(35) In some embodiments, in the apparatus depicted in FIG. 1A, the system of switching flow of an inactive gas and flow of a precursor gas illustrated in FIG. 1B (described earlier) can be used to introduce the precursor gas in pulses without substantially fluctuating pressure of the reaction chamber.

(36) In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed closely 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.

(37) 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.

(38) The present invention is further explained with reference to working examples below. However, the examples are not intended to limit the present invention. In the 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. Also, the numbers applied in the specific examples can be modified by a range of at least 50% in some embodiments, and the numbers are approximate.

EXAMPLES

Example 1

(39) A titanium oxide film was formed on a 300-mm substrate having a patterned surface having an aspect ratio of about 2 and an opening depth of about 320 nm under the conditions shown in Table 3 below using the sequence illustrated in FIG. 2 and the PEALD apparatus illustrated in FIGS. 1A and 1B.

(40) TABLE-US-00003 TABLE 3 Conditions for Deposition Cycle Substrate temperature 200 C. Pressure 250 Pa Precursor Tetrakis(dimethylamido)titanium Precursor pulse 0.4 sec Precursor purge 0.3 sec Reactant oxygen plasma Flow rate of reactant (continuous) 500 sccm Carrier gas argon Dilution gas argon Flow rate of carrier gas (continuous) 1000 sccm Flow rate of dilution gas (continuous) 500 sccm RF power (13.56 MHz) for a 300-mm See FIG. 3B wafer RF power pulse 0.4 sec Purge 0.1 sec Growth rate per cycle 0.062 to 0.065 nm/cycle Total thickness [nm] 18.6 to 19.4 nm

(41) The wet etch rate of a part of each film deposited on the top surface of the substrate was measured. The results are shown in FIG. 3B wherein the wet etch rate is expressed as WERR/[TOX], i.e., the ratio of the wet etch rate of the film to that of a thermal oxide film. As shown in FIG. 3B, the wet etch rate of the film changed along a downward parabola with a vertex as RF power increased. That is, when RF power was relatively weak, the wet etch rate decreased as RF power increased, i.e., the quality of the depositing film was improved. The wet etch rate began increasing after hitting the minimum value (the lowest vertex). The quality of the film on the top surface obtained at the lowest vertex appears to be the highest, and thereafter, the wet etch rate increased as RF power increased, degrading the quality of the film deposited on the top surface. The nitrogen concentration was also measured for some of the films, and the results are shown in FIG. 3A. The changes of the wet etch rate were generally correlated to the changes of impurity concentration.

Example 2

(42) Films were deposited under the same conditions as in Example 1, and the wet etch rate of each film not only on the top surface but also at the sidewall was measured. The results are shown in FIG. 4. As shown in FIG. 3B, the wet etch rate began increasing after hitting the minimum value (the lowest vertex), and FIG. 4 shows the wet etch rate after the lowest vertex. The quality of the film on the top surface obtained at the lowest vertex appears to be the highest. Although the quality of the film on the top surface was the highest at the lowest vertex, the quality of the film at the sidewall was not high, i.e., the wet etch rate of the film at the sidewall was relatively high. Since plasma does not easily reach the sidewall, the quality of the film at the sidewall is not significantly affected by the intensity of RF power, in contrast with the quality of the film on the top surface. The wet etch rate of the film at the sidewall gradually decreased as RF power increased as shown in FIG. 4. Thus, although the wet etch rate of the film at the sidewall was higher than that of the film on the top surface when RF power was relatively low, as RF power increased, at a certain point after the lowest vertex point of the wet etch rate of the film on the top surface, the wet etch rate of the film on the top surface and that of the film at the sidewall became substantially equivalent because the wet etch rate of the film on the top surface continued increasing while the wet etch rate of the film at the sidewall gradually decreased as shown in FIG. 4. That is, the line representing the relationship between the wet etch rate of the film on the top surface and RF power, and the line representing the relationship between the wet etch rate of the film at the sidewall and RF power, intersect at about 500 W.

Example 3

(43) The film deposited in a trench when RF power was 200 W was analyzed by Scanning transmission electron microscopy (STEM). FIG. 5 shows STEM photographs of cross-sectional views of the film, wherein (a) shows the film as deposited, and (b) shows the film after wet etching. As shown in FIG. 5, the conformality of the film as deposited was 89% at the upper sidewall, 96% at the lower sidewall, and 97% at the bottom, whereas the conformality of the film after wet etching was 83% at the upper sidewall, 90% at the lower sidewall, and 89% at the bottom, i.e., the conformality of the film decreased after wet etching by about 6% to about 8%.

(44) Also, the film deposited in a trench when RF power was 500 W was analyzed by Scanning transmission electron microscopy (STEM). FIG. 6 shows STEM photographs of cross-sectional views of the film, wherein (a) shows the film as deposited, and (b) shows the film after wet etching. As shown in FIG. 6, the conformality of the film as deposited was 83% at the upper sidewall, 89% at the lower sidewall, and 90% at the bottom, whereas the conformality of the film after wet etching was 93% at the upper sidewall, 100% at the lower sidewall, and 99% at the bottom, i.e., the conformality of the film increased after wet etching by about 10% to about 12%. As described above, by lowering the quality of the film on the top surface by increasing RF power (here, a reduction of thickness after wet etching was greater when RF power was 500 W than that when RF power was 200 W), the conformality of the film after wet etching was successfully improved.

(45) It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention.