Loading etch effect mitigation for reactive ion etching

Abstract

A method for etching a substrate includes pulsing an RF power at a given frequency to generate a plasma for etching the substrate where each pulse period has an ON-state and an OFF-state comprising a duty cycle, selecting an ON-state duration of the duty cycle based on, at least in part, a first duration for restriking the plasma, a second duration for a minimum on-time per a given RF power source providing the RF power, and a third duration for the plasma to reach a steady state, selecting an OFF- state duration of the duty cycle for each pulse period to alter a profile loading, a iso-dense depth loading, or a critical dimension (CD) loading etching effect associated with a feature to be formed on the substrate, and forming the feature by using the duty cycle for the RF power to etch the substrate.

Description

PATENTAttorney Docket No.: 44024641 WO1Loading Etch Effect Mitigation for Reactive Ion EtchingFIELD

[0001] Embodiments of the present principles generally relate to semiconductor processing of semiconductor substrates.BACKGROUND

[0002] Etching processes or removal of material from a substrate are used in the formation of semiconductor structures. One type of etching process uses plasma to form a neutral reactive species that is used along with ions to anisotropically etch substrates. In order to form uniform features of the semiconductor structures, the etch rate of the substrate material should be the same across the entire surface of the substrate. However, the inventors have observed that when areas of dense features are interspersed in isolation or open areas, the etch rates differ between the dense areas and the isolation or open areas, causing unwanted feature changes and unwanted isolation profile changes, leading to defects in the structures. The defects lower the performance of the structures and cause lower manufacturing yields.

[0003] Accordingly, the inventors have provided methods for reducing the impacts of iso-dense depth and profile loading etching effects on substrate structures.SUMMARY

[0004] Methods for iso-dense depth loading, profile loading, and critical dimension (CD) loading etching effects mitigation are provided herein.

[0005] In some embodiments, a method for reactive ion etching of a substrate may comprise pulsing an RF power at a given frequency to generate a plasma for etching the substrate where each pulse period has an ON-state and an OFF-state comprising a duty cycle, selecting an ON-state duration of the duty cycle based on, at least in part, a first duration for restriking the plasma, a second duration for a minimum on-time for a given RF power source providing the RF power, and a third duration for the plasma to reach a steady-state, selecting an OFF-state duration of the duty cycle for each pulse period to alter a profile loading etching effect, an iso-dense depth loading etching effect, or a critical dimension (CD) loading etching effect associated with a feature to be11593262 1PATENTAttorney Docket No.: 44024641 WO1 formed on the substrate, and forming the feature by using the duty cycle for the RF power to etch the substrate.

[0006] In some embodiments, the method may further include selecting the OFF-state duration which includes, at least in part determining a rate of removal of by-product in the feature to be formed on the substrate for a given reactive ion etch chamber and selecting the OFF-state duration for the given reactive ion etch chamber based on, at least in part, on the rate of removal of by-product, a given reactive ion etch chamber that uses a bias to direct ions to etch the feature and where the bias has at least one power level, a given reactive ion etch chamber that is an inductively coupled plasma chamber or a capacitively coupled plasma chamber, a duty cycle that is approximately 1 % and an RF power that is pulsed at approximately 10Hz, a duty cycle that is approximately 0.5% and the RF power is pulsed at approximately 10Hz, an RF power that is pulsed at a frequency approximately 10Hz or higher, an OFF-state duration that is based, at least in part, on forming approximately 90-degree sidewalls on the feature, an ON-state duration which includes more than one RF power level, an ON-state duration that is greater than 200 nanoseconds, and / or a duty cycle that is less than approximately 10% and the RF power is pulsed at approximately 10Hz or higher.

[0007] In some embodiments, a method for reactive ion etching of a substrate may comprise pulsing an RF power at a given frequency to generate a plasma for etching the substrate where each pulse period has an ON-state and an OFF-state comprising a duty cycle, selecting an ON-state duration of the duty cycle based on, at least in part, a first duration for restriking the plasma, a second duration for a minimum on-time for a given RF power source providing the RF power, and a third duration for the plasma to reach a steady state where the ON-state duration includes more than one RF power level and the ON-state duration is greater than 200 nanoseconds, selecting an OFF- state duration of the duty cycle for each pulse period to alter a profile loading etching effect, an iso-dense depth loading etching effect, or a critical dimension (CD) loading etching effect associated with a feature to be formed on the substrate, and forming the feature by using the duty cycle for the RF power to etch the substrate.

[0008] In some embodiments, the method may further include selecting the OFF-state duration which includes, at least in part determining a rate of removal of by-product in the feature to be formed on the substrate for a given reactive ion etch chamber and21593262 1PATENTAttorney Docket No.: 44024641 WO1 selecting the OFF-state duration for the given reactive ion etch chamber based on, at least in part, on the rate of removal of by-product, a given reactive ion etch chamber that uses a bias to direct ions to etch the feature and where the bias has at least one power level, a duty cycle that is approximately 1 % and an RF power that is pulsed at approximately 10Hz, a duty cycle that is approximately 0.5% and an RF power that is pulsed at approximately 10Hz, an RF power that is pulsed at a frequency approximately 10Hz or higher, an OFF-state duration that is based, at least in part, on forming approximately 90-degree sidewalls on the feature, and / or a duty cycle that is less than approximately 10% and an RF power that is pulsed at approximately 10Hz or higher.

[0009] In some embodiments, a non-transitory, computer readable medium having instructions stored thereon that, when executed, cause a method for reactive ion etching of a substrate to be performed, the method may comprise pulsing an RF power at a given frequency to generate a plasma for etching the substrate where each pulse period has an ON-state and an OFF-state comprising a duty cycle, selecting an ON- state duration of the duty cycle based on, at least in part, a first duration for restriking the plasma, a second duration for a minimum on-time for a given RF power source providing the RF power, and a third duration for the plasma to reach a steady state, selecting an OFF-state duration of the duty cycle for each pulse period to alter a profile loading etching effect, an iso-dense depth loading etching effect, or a critical dimension (CD) loading etching effect associated with a feature to be formed on the substrate, and forming the feature by using the duty cycle for the RF power to etch the substrate.

[0010] Other and further embodiments are disclosed below.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the present principles, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the principles depicted in the appended drawings. However, the appended drawings illustrate only typical embodiments of the principles and are thus not to be considered limiting of scope, for the principles may admit to other equally effective embodiments.

[0012] Figure 1 is a method for reactive ion etching of a substrate in accordance with some embodiments of the present principles.31593262 1PATENTAttorney Docket No.: 44024641 WO1

[0013] Figure 2 depicts a waveform for a pulsed RF power that generates plasma for etching a substrate in accordance with some embodiments of the present principles.

[0014] Figure 3 depicts a waveform for a pulsed RF power that generates plasma for etching a substrate with multiple power levels in accordance with some embodiments of the present principles.

[0015] Figure 4 depicts an ON-state duration selection process and an OFF-state duration selection process for a pulsed RF power that generates plasma for etching a substrate in accordance with some embodiments of the present principles.

[0016] Figure 5 depicts another ON-state duration selection process and another OFF-state duration selection process for a pulsed RF power that generates plasma for etching a substrate in accordance with some embodiments of the present principles.

[0017] Figure 6 depicts a cross-sectional view of a desired etching profile of a substrate in accordance with some embodiments of the present principles.

[0018] Figure 7 depicts a cross-sectional view of a dense feature etching rate less than an isolation or open area etching rate in accordance with some embodiments of the present principles.

[0019] Figure 8 depicts a cross-sectional view of a dense feature etching rate greater than an isolation or open area etching rate in accordance with some embodiments of the present principles.

[0020] Figure 9 depicts a cross-sectional view of an isolation or open area profile loading etching effect in accordance with some embodiments of the present principles.

[0021] Figure 10 depicts a side profile view of a sidewall of an isolation or open area profile and the effects of an increased ratio of OFF-state duration to ON-state duration in accordance with some embodiments of the present principles.

[0022] Figure 11 are graphs which depict impacts of increased OFF-state durations in accordance with some embodiments of the present principles.

[0023] Figure 12 is a cross-sectional view of an inductively coupled plasma chamber in accordance with some embodiments of the present principles.

[0024] Figure 13 is a cross-sectional view of a critical dimension (CD) loading etching effect in accordance with some embodiments of the present principles.41593262 1PATENTAttorney Docket No.: 44024641 WO1

[0025] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.DETAILED DESCRIPTION

[0026] The methods provide iso-dense depth and profile loading etching effect reduction by tuning the OFF-state of a duty cycle for a pulsed RF power source that generates plasma for etching substrates. The tuning advantageously increases the etching uniformity across dense feature areas and isolation or open areas of a substrate. The tuning can also be used to prevent or reduce profile issues such as tapering and bowing of sidewalls of open area features and the like. Adjustments of the OFF-state duration based on the ON-state duration can be used to tune etching processes that use a wide-range of chemistries and / or semiconductor etching chambers, affording substantial flexibility to improve the etching rate uniformity across the substrate. The techniques may be applied not only to dense feature areas combined with isolation or open areas but also to substrates having features with different critical dimensions (CDs) and the like. The methods mitigate the different etch rates due to the differences in CDs (CD loading etching effect) such that the CD loading has significantly less impact on the etch processes, increasing etch rate uniformities.

[0027] Atomic layer etching (ALE) functions by removing material at an atomic level using reactive ion etching (RIE) processes. Plasma is used to form ions and a highly reactive neutral species from a reactive gas or gases. The ions are guided towards a substrate surface using a bias to anisotropically etch the surface of the substrate. The accelerated ions strike the surface of the substrate, causing atomic level collisions. The neutral reactive species diffuse into the surface of the substrate producing an etch front saturation region in the surface of the substrate. The etching of the surface of the substrate is caused by both a chemical reaction from the flux of ions and the neutral reactive species. The combined species and ion effects cause some of the substrate material to be released from the surface of the substrate by chemical reaction and by collision of ions with the substrate surface which sputters some of the substrate material off the surface of the substrate. Heat may also be applied during the etching to aid in51593262 1PATENTAttorney Docket No.: 44024641 WO1 the etching of the substrate. The chemical reactions, applied heat, and collisions form etching by-products that can undesirably cause redeposition of the removed material onto other surfaces of the substrate during the etching process, producing defects.

[0028] The inventors discovered that, by adjusting the duty cycle of the power applied to the plasma during etching, a more uniform etch rate across the surface of the substrate can be achieved, reducing the impact of iso-dense depth loading, CD loading, and / or profile loading on the etching process. The inventors observed that when etching a substrate surface that has both dense feature areas and isolation or open areas, the etching rates in the dense feature areas may be different than the etching rates in the isolation or open areas (iso-dense depth loading effect and / or iso-dense profile loading effect). In addition, the inventors observed that other profile changes occur outside of just depth changes (lower or increased comparative etch rate impact) such as, but not limited to, base profile tapering or sidewall bowing and the like of features, leading to defects in the semiconductor structures on the substrate. The inventors also observed that substrates with feature sets having different CDs leads to nonuniform etching rates for the different feature sets. When power is applied to the plasma, ions are present and strike the substrate surface causing etching along with a given flux at the etch point at the substrate surface. When power is removed, the ions are no longer being formed but a certain level of flux is still present at the etching surface along with the diffused neutral reactive species. The longer that the power is not applied, the more time that is afforded to the neutral reactive species to saturate the bottom etch front. The inventors found that with careful adjustment of the duty cycle of the power applied to the plasma, the iso-dense depth loading, the CD loading impact on the etch rate, and the distortions of the profile can be controlled to reduce defects in the features, increasing yields.

[0029] Fig. 1 is a method 100 for reactive ion etching of a substrate. In some embodiments, the goal of the etching process is to achieve structures formed with uniform etching rates as depicted in a view 600 of Fig. 6. In Fig. 6, the substrate 602 has a dense feature area 604 in combination with an isolation or open area 608 adjacent to the dense feature area 604, causing iso-dense depth loading challenges and profile loading challenges. Other examples of substrates with CD loading challenges are discussed later (see, e.g., Fig. 13). In block 102, an RF power 202 is pulsed at a given frequency (e.g., 10Hz with a pulse period of 100ms, etc.) to generate61593262 1PATENTAttorney Docket No.: 44024641 WO1 a plasma for etching the substrate 602 as depicted in a view 200 of Fig. 2. The pulsed RF power 202 has a pulse period 204 with a duty cycle comprising an ON-state 206 and an OFF-state 208. The ON-state 206 has an ON-state duration 210, T1 , and the OFF-state 08 has an OFF-state duration 212, T2.

[0030] The RF power 202 may be pulsed at any frequency. In some embodiments, the pulse frequency may be from approximately 10Hz to approximately 10kHz. In some embodiments, the pulse frequency may be approximately 10Hz. In some embodiments, the pulse frequency may be approximately 1kHz (+ / -500Hz). The example depicted in Fig. 2 is merely for the sake of brevity, and the 100ms pulse period (10Hz frequency) will change as the pulse frequency changes. In some embodiments, the supplied RF power may be from approximately 15W to approximately 5000W. In some embodiments, the delivered power level of the ON-state 206 may not be constant. Fig. 3 in a view 300 depicts the ON-state 206 with more than one power level occurring within the ON-state 206. A first power level duration 302, T1 , has a first power level 308, a second power level duration 304, T2, has a second power level 310, and a third power level 312 has a third power level duration 306, T3. The present principles may be applied to any number of power levels.

[0031] In block 104 of Fig. 1 , an ON-state duration 210 of a duty cycle for the pulsed RF power to the plasma is selected based on, at least in part, a first duration for restriking the plasma, a second duration for a minimum on-time for a given RF power source (RF power generator) providing the RF power to generate the plasma, and a third duration for the plasma to reach a steady state. When generating plasma with a pulsed RF power, the power to the plasma is interrupted during the OFF-state of the duty cycle. The plasma must then be restarted at the beginning of the next ON-state for the next pulse period. The restriking of the plasma takes several hundred nanoseconds and presents a lower limit of the ON-state duration (e.g., ON-state duration is at least approximately 200ns to allow for the restriking of the plasma, etc.). As depicted in a view 400 of Fig. 4, a first duration 402 of the ON-state 206 is allotted to the restriking of the plasma after an OFF-state has occurred in a prior pulse period. In some embodiments, the first duration 402 may include the restrike time along with other processes necessary to perform the restriking (e.g., removing faraday shields of a process chamber to allow for a capacitive field to build up electrons to permit plasma71593262 1PATENTAttorney Docket No.: 44024641 WO1 striking in an ICP chamber, etc.). In some embodiments, the first duration 402 may be from approximately 100ns to approximately 600ns and the like.

[0032] A given RF power source (e.g., pulsed RF power source 1216 of Fig. 12 and the like) has a minimum on-time requirement based on hardware specifications or requirements. The time required by the hardware specifications for the given RF power source is represented by a second duration 404 within the ON-state 206 (see Fig. 4). The second duration 404 may vary based on, at least in part, on the type of chamber (e.g., ICP, CCP, etc.), the plasma load seen by a given RF power source, and other hardware related parameters / requirements. Each given RF power source may have a different minimum on-time that is established by the manufacturer and disclosed within the specifications for the given RF power source. In some embodiments, the second duration 404 may be from approximately 20 microseconds to approximately 50 microseconds in duration. In some embodiments, the second duration 404 may be approximately 25 microseconds in duration. A third duration 406 of the ON-state 206 is an amount of time for the plasma to reach a steady state. In some embodiments, the third duration 406 may overlap with the second duration 404 or occur within the second duration 404. In some instances, the third duration 406 may be from approximately 40 microseconds to approximately 100 microseconds in duration. In some embodiments, the completion of the first duration 402, the second duration 404, and the third duration 406 may be used to select the ON-state duration 210 of the ON-state 206. In some embodiments, a fourth duration 408 may be used to allow for other processes to complete or to allow for further tunability (e.g., adjustment of ON-state to OFF-state ratios and the like) of the overall reduction of the iso-dense depth loading etch rate effect and / or the profile loading etch rate effect and the like. In some embodiments, the ON-state duration is limited at an upper range by a 5% duty cycle for a given pulse frequency.

[0033] With reference to Fig. 6, as the neutral reactive species interact at the etch front 620 of the features 606 being etched into the substrate 602, the neutral reactive species diffuse into the etch front 620 and into the substrate 602. Although the etch front 620 is depicted at the very bottom of the features 606, the etch front 620 moves from the tops of the features to the bottoms of the features as material is removed (etched) from the substrate 602 to form the features 606. Thus, the depiction of the81593262 1PATENTAttorney Docket No.: 44024641 WO1 etch front 620 and the neutral reactive species diffusion 622 into the bottoms of the features 606 is not meant to be limiting. The diffusion duration may vary based on, at least in part, on the diffusion rate of the type of neutral reactive species (chemistry used in conjunction with the plasma) and also the type of material used for the substrate 602. The diffusion duration may also vary based on the pressure and other parameters of a given etch process and the like. In some embodiments, the diffusion may be several milliseconds in duration. As the neutral reactive species diffuses into the substrate at the etch front 620, the etch front 620 is saturated with the neutral reactive species. The saturation duration may vary based on, at least in part, the saturation rate of the type of neutral reactive species (chemistry used in conjunction with the plasma) and also the type of material used for the substrate 602. In some instances, the saturation may be instantaneous or approximately zero (saturation occurs within an insignificantly small amount of time compared to the other events such as the time taken to evacuate a process chamber of by-products, etc.).

[0034] In block 106 of Fig. 1 , an OFF-state duration 212 of a duty cycle for each pulse period of the pulsed RF power to the plasma is selected based on, at least in part, to alter a profile loading etching effect, an iso-dense depth loading etching effect, and / or a CD loading etching effect associated with one or more features to be formed on a substrate (see, e.g., loading etching effects depicted in Figs. 7-9 and 13). Chemistries used in the etching processes may present different tuning challenges for loading etching effects. In a view 600 of Fig. 6, an optimum example for a dense feature set in combination with an isolation or open area is depicted where a feature etch depth 610 in a dense feature area 604 is approximately equal to an isolation etch depth 612 of an isolation or open area 608. In the example of Fig. 6, the etch rates for both areas are the same with no iso-dense depth loading or profile loading etching effects. In a view 700 of Fig. 7, an example of a dense feature etching rate of the dense feature area 604 being less than an isolation or open area etching rate (featureless area etching rate) of the open area 608 (feature etch depth 710 is less than 714 the isolation etch depth 712). The differing etch rates in the example may be due to neutral reactive species diffusion issues (e.g., neutral reactive species etching is limited due to Knudsen diffusion) and / or may be due to clogging or necking of the dense features by redeposition of etch by-products causing ion and neutral reactive species shadowing in the features 606.91593262 1PATENTAttorney Docket No.: 44024641 WO1

[0035] In a view 800 of Fig. 8, an example of a dense feature etching rate of the dense feature area 604 being greater than an isolation or open area etching rate (featureless area etching rate) of the open area 608 (feature etch depth 810 is greater than 814 the isolation etch depth 812). The differing etch rates in the example may be due to heavy redeposition of by-products in open areas which results in a slower etch rate of the open area 608 or even a complete halting of the etching in the open area 608. In a view 900 of Fig. 9, an example of a dense feature etching rate of the dense feature area 604 being less than an isolation or open area etching rate (featureless area etching rate) of the open area 608 (feature etch depth 910 is less than 904 the isolation etch depth 912). Chemistries used along with the material of the substrate 602 produce etch heavy by-products that form in the transition area between the dense feature area 604 and the open area 608, causing tapering 902, bowing, and / or other defects to form on the feature or isolation sidewalls from profile loading etching effects.

[0036] In a view 1000 of Fig. 10, in etching processes where the isolation profile loading is problematic, the inventors found that the isolation profile loading etching effects could be mitigated by tuning the OFF-state duration of the duty cycle in light of the ON-state duration. As the OFF-state duration 1010 is increased (increased ratio of OFF-state duration to ON-state duration), the tapering of a tapered sidewall 1002 is reduced and with proper tuning of the OFF-state duration in light of the ON-state duration, a vertical or an approximately 90-degree sidewall 1004 (right angle 1006) can be achieved. The inventors also found, however, that if the OFF-state duration is too long in light of the ON-state duration (i.e., ratio is too high), bowed sidewalls 1008 are formed. The inventors also found through further tests that when chemistries such as hydrogen bromide and argon are used to etch silicon materials, heavy etching byproducts are produced. However, as depicted in a graph 1100A of Fig. 11 , as the OFF- state duration 1102 is increased, the by-products 1104 deposited at the mouth of the features (necking) 1106 was substantially reduced as well as less redeposition of byproducts in isolation or open areas. The inventors found that a longer OFF-state duration breaks the iso-dense depth loading versus mask selectivity trade-off as depicted in a graph 1100B of Fig. 11 . As the OFF-state duration 1102 is increased, the iso-dense depth loading 1108 decreases 1110. In some embodiments, up to a 45% improvement 1112 or more in iso-dense depth loading can be achieved.101593262 1PATENTAttorney Docket No.: 44024641 WO1

[0037] In a view 1300 of Fig. 13, in etching processes where feature sets may have different CDs on a substrate 1302, the inventors found that the CD loading etching effect could be mitigated by tuning the OFF-state duration of the duty cycle in light of the ON-state duration. As the OFF-state duration is increased, the etch depth delta 1308 caused by a first CD 1314 of a first feature set 1304 being larger than a second CD 1312 of a second feature set 1306. The reduced etch rate for the second feature set 1306 may be caused by by-product production from the first feature set 1304 is undesirably redeposited at the openings 1310 of the second feature set 1306 causing clogging or necking issues in the second feature set 1306. For example, a longer OFF- state duration may be selected in conjunction with a shorter ON-state duration such that less by-product is produced during the ON-state which is more easily removed during the longer OFF-state to prevent the necking / clogging of smaller CD feature sets and the like. In some instances (not shown), the smaller CD may have a faster etch rate than a larger CD for which adjustments to the OFF-state duration and / or ON-state duration may be accomplished to provide for more uniform etch rates between the different CD feature sets.

[0038] Returning to Fig. 4, when the ON-state duration 210 produces heavy byproducts (due to chemistries, materials, etch process, etc.), in some embodiments, the OFF-state duration 212 may be selected based on the evacuation duration of a given reactive ion etch chamber. In some embodiments, a by-product evacuation-based OFF-state duration 420 is selected. The by-product evacuation-based OFF-state duration 420 may yield iso-dense depth loading etch effect reductions and / or profile loading etch effect reductions and the like. The rate of production of the by-product and the ON-state duration 210 yields an amount of by-product that needs to be removed from the etch chamber. The time needed to evacuate the by-product is dependent not only on the process volume size of the etch chamber but also the rate at which the process volume can be evacuated which is also dependent on the etch chamber design. Care must be taken as the amount of by-product, or the process volume size may be too large for a given etch process chamber to evacuate within a given OFF- state duration 212 based on the pulse frequency of the RF power. Satisfactory results may not be achievable if the ON-state 206 of the pulse period produces too much byproducts which redeposit onto other substrate surfaces before the by-products can be removed, causing defects from the by-product deposits on the substrate. Thus, the111593262 1PATENTAttorney Docket No.: 44024641 WO1 selection of the OFF-state duration 212 must be made in light of the ON-state duration 210, and the given etching process and by-products produced during the ON-state duration 210.

[0039] In some embodiments, an iso-dense depth loading reduction-based OFF-state duration 422 is selected. The iso-dense depth loading reduction-based OFF-state duration 422 may be selected to increase the etching depth of the features compared to the isolation or open areas of the substrate and may be the same, less than, or more than the duration of the by-product evacuation-based OFF-state duration 420 (a single duration dotted line is used for each OFF-state duration type for the sake of clarity but is not meant to be limiting). Similarly, in some embodiments, a CD loading reductionbased OFF-state duration 450 may be selected. The CD loading reduction-based OFF- state duration 450 may be selected to increase etch rate uniformity between different feature set CDs and may be the same, less than, or more than the duration of the byproduct evacuation-based OFF-state duration 420. In some embodiments, a profile loading reduction-based OFF-state duration 424 is selected. The profile loading reduction-based OFF-state duration 424 may be selected to increase the etching depth of the isolation or open areas compared to the dense feature areas of the substrate and may be the same, less than, or more than the duration of the by-product evacuation-based OFF-state duration 420 and / or iso-dense depth loading reductionbased OFF-state duration 422 (a single duration line is used for each OFF-state duration type for the sake of clarity but is not meant to be limiting).

[0040] As indicated in Fig. 4, the various types of OFF-state durations fall within a pulse period which means that the OFF-state duration must be selected in light of the ON-state etching process and timing. For example, given a frequency of 10Hz and a duty cycle of 1 %, the ON-state 206 would have an ON-state duration 210 of 1 ms and an OFF-state 208 would have an OFF-state duration 212 of 99ms which may give satisfactory etching results (e.g., etching profiles and depths as depicted in Fig. 6, etc.). Should the ON-state duration 210 be increased to 50ms (50% duty cycle), the byproducts produced may be too great for a given etch chamber to evacuate within a 50ms OFF-state duration, leading to undesired etching effects and substrate defects. Similarly, the etch chemistries may produce a large amount of by-products in a short amount of time within the ON-state duration for a given etch process and etch chamber.121593262 1PATENTAttorney Docket No.: 44024641 WO1For example, given an ON-state duration of 1ms for a 1 % duty cycle (10Hz pulse frequency), a 99ms OFF-state duration may not prove adequate to achieve, by-product evacuation, iso-dense depth loading reduction, and / or profile loading reduction.

[0041] In a view 500 of Fig. 5, an example of selecting the OFF-state duration 212 based on profile loading is depicted. As discussed above for Fig. 10, a too short OFF- state duration 520 may lead to tapering of isolation or open area sidewalls and the like. A too long OFF-state duration 524 may lead to bowing of isolation or open area sidewalls and the like. In the example, the vertical sidewall OFF-state duration 522 can be selected to produce approximately 90-degree sidewalls of isolation or open area sidewalls. The selection of the OFF-state duration to reduce profile loading in the amount to yield vertical sidewalls is dependent, in part, on the etch chemistries, the materials being etched, the etch process, the etch chamber, and / or the ON-state duration 210.

[0042] Referring back to Fig. 1 , in block 108, a feature is formed on the substrate using the duty cycle for the pulsed RF power based on the selected ON-state duration and the selected OFF-state duration to etch the substrate. The methods of the present techniques are applicable to inductively coupled plasma chambers as well as capacitively coupled plasma chambers. The techniques provide extreme flexibility in fine tuning of the duty cycle to overcome etching challenges using any type of etch chemistry, etched materials, and hardware configurations, and the like.

[0043] Fig. 12 is a view 1200 of an inductively coupled plasma (ICP) chamber 1202 in which the present techniques may be used. The techniques may also be used with capacitively coupled plasma (CCP) chambers (not shown). The ICP chamber 1202 has a process volume 1228 where plasma 1240 is generated inductively by one or more pulsed RF power source 1216 via a first match network 1218 into a set of coils 1210. A substrate 1206 is positioned on a substrate support 1204 for processing. One or more process gases are supplied by a gas supply 1212 which is ionized by the plasma 1240 to produce ions and neutral reactive species for etching of the substrate. In some embodiments, the ICP chamber may have more than one bias power source 1220 that is connected via a second match network 1222 to the substrate support 1204 to facilitate in guiding the ions to the surface of the substrate 1206. A vacuum pump 1224 is used to evacuate the process volume 1228 during the OFF-state of the pulsed RF131593262 1PATENTAttorney Docket No.: 44024641 WO1 power source 1216. The rate of flow, direction of flow 1226, pressure, and volume of gases to be evacuated are dependent on a given etching chamber design and a given etching process. The diameter 1214 of the chamber may vary along with the type of pump used as well as the etching process parameters. The characteristics of the chamber and etching process are used to determine, at least in part, the duration required to evacuate the by-product gases produced during the ON-state of the pulsed RF power source 1216. The duration may then be used to assist in selecting the OFF- state duration to achieve various etching results as described above.

[0044] The ICP chamber 1202 uses a controller 1230 to control the operation of any of the systems of the ICP chamber 1202 described herein. The controller 1230 may use a direct control of the ICP chamber 1202, or alternatively, by controlling the computers (or controllers) associated with the ICP chamber 1202. In operation, the controller 1230 enables data collection and feedback from the ICP chamber 1202 to optimize performance of the ICP chamber 1202 and to control the power sources and etching processes according to the methods described herein. The controller 1230 generally includes a central processing unit (CPU) 1232, a memory 1234, and a support circuit 1236. The CPU 1232 may be any form of a general-purpose computer processor that can be used in an industrial setting. The support circuit 1236 is conventionally coupled to the CPU 1232 and may comprise a cache, clock circuits, input / output subsystems, power supplies, and the like. Software routines, such as methods as described herein may be stored in the memory 1234 and, when executed by the CPU 1232, transform the CPU 1232 into a specific purpose computer (controller 1230). The software routines may also be stored and / or executed by a second controller (not shown) that is located remotely from the ICP chamber 1202.

[0045] The memory 1234 is in the form of computer-readable storage media that contains instructions, when executed by the CPU 1232, to facilitate the operation of the semiconductor processes and equipment. The instructions in the memory 1234 are in the form of a program product such as a program that implements methods of the present principles. The program code may conform to any one of a number of different programming languages. In one example, the disclosure may be implemented as a program product stored on a computer-readable storage media for use with a computer system. The program(s) of the program product define functions of the aspects141593262 1PATENTAttorney Docket No.: 44024641 WO1(including the methods described herein). Illustrative computer-readable storage media include, but are not limited to: non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, flash memory, ROM chips, or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and writable storage media (e.g., floppy disks within a diskette drive or hard-disk drive or any type of solid-state random access semiconductor memory) on which alterable information is stored. Such computer- readable storage media, when carrying computer-readable instructions that direct the functions of the methods described herein, are aspects of the present principles.

[0046] Embodiments in accordance with the present principles may be implemented in hardware, firmware, software, or any combination thereof. Embodiments may also be implemented as instructions stored using one or more computer readable media, which may be read and executed by one or more processors. A computer readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing platform or a “virtual machine” running on one or more computing platforms). For example, a computer readable medium may include any suitable form of volatile or non-volatile memory. In some embodiments, the computer readable media may include a non-transitory computer readable medium.

[0047] While the foregoing is directed to embodiments of the present principles, other and further embodiments of the principles may be devised without departing from the basic scope thereof.151593262 1

Claims

PATENTAtorney Docket No.: 44024641WO1CLAIMS1 . A method for reactive ion etching of a substrate, comprising: pulsing an RF power at a given frequency to generate a plasma for etching the substrate, wherein each pulse period has an ON-state and an OFF-state comprising a duty cycle; selecting an ON-state duration of the duty cycle based on, at least in part, a first duration for restriking the plasma, a second duration for a minimum on-time for a given RF power source providing the RF power, and a third duration for the plasma to reach a steady-state; selecting an OFF-state duration of the duty cycle for each pulse period to alter a profile loading etching effect, an iso-dense depth loading etching effect, or a critical dimension (CD) loading etching effect associated with a feature to be formed on the substrate; and forming the feature by using the duty cycle for the RF power to etch the substrate.

2. The method of claim 1 , wherein selecting the OFF-state duration includes, at least in part: determining a rate of removal of by-product in the feature to be formed on the substrate for a given reactive ion etch chamber; and selecting the OFF-state duration for the given reactive ion etch chamber based on, at least in part, on the rate of removal of by-product.

3. The method of claim 2, wherein the given reactive ion etch chamber uses a bias to direct ions to etch the feature and wherein the bias has at least one power level.

4. The method of claim 2, wherein the given reactive ion etch chamber is an inductively coupled plasma chamber or a capacitively coupled plasma chamber.

5. The method of claim 1 , wherein the duty cycle is approximately 1 % and the RF power is pulsed at approximately 10Hz.161593262_1PATENTAttorney Docket No.: 44024641WO16. The method of claim 1 , wherein the duty cycle is approximately 0.5% and the RF power is pulsed at approximately 10Hz.

7. The method of claim 1 , wherein the RF power is pulsed at a frequency approximately 10Hz or higher.

8. The method of claim 1 , wherein the OFF-state duration is based, at least in part, on forming approximately 90-degree sidewalls on the feature.

9. The method of claim 1 , wherein the ON-state duration includes more than one RF power level.

10. The method of claim 1 , wherein the ON-state duration is greater than 200 nanoseconds.11 . The method of claim 1 , wherein the duty cycle is less than approximately 10% and the RF power is pulsed at approximately 10Hz or higher.

12. A method for reactive ion etching of a substrate, comprising: pulsing an RF power at a given frequency to generate a plasma for etching the substrate, wherein each pulse period has an ON-state and an OFF-state comprising a duty cycle; selecting an ON-state duration of the duty cycle based on, at least in part, a first duration for restriking the plasma, a second duration for a minimum on-time for a given RF power source providing the RF power, and a third duration for the plasma to reach a steady state, wherein the ON-state duration includes more than one RF power level and wherein the ON-state duration is greater than 200 nanoseconds; selecting an OFF-state duration of the duty cycle for each pulse period to alter a profile loading etching effect, an iso-dense depth loading etching effect, or a critical dimension (CD) loading etching effect associated with a feature to be formed on the substrate; and forming the feature by using the duty cycle for the RF power to etch the substrate.171593262_1PATENTAttorney Docket No.: 44024641WO113. The method of claim 12, wherein selecting the OFF-state duration includes, at least in part: determining a rate of removal of by-product in the feature to be formed on the substrate for a given reactive ion etch chamber; and selecting the OFF-state duration for the given reactive ion etch chamber based on, at least in part, on the rate of removal of by-product.

14. The method of claim 13, wherein the given reactive ion etch chamber uses a bias to direct ions to etch the feature and wherein the bias has at least one power level.

15. The method of claim 12, wherein the duty cycle is approximately 1 % and the RF power is pulsed at approximately 10Hz.

16. The method of claim 12, wherein the duty cycle is approximately 0.5% and the RF power is pulsed at approximately 10Hz.

17. The method of claim 12, wherein the RF power is pulsed at a frequency approximately 10Hz or higher.

18. The method of claim 12, wherein the OFF-state duration is based, at least in part, on forming approximately 90-degree sidewalls on the feature.

19. The method of claim 12, wherein the duty cycle is less than approximately 10% and the RF power is pulsed at approximately 10Hz or higher.

20. A non-transitory, computer readable medium having instructions stored thereon that, when executed, cause a method for reactive ion etching of a substrate to be performed, the method comprising: pulsing an RF power at a given frequency to generate a plasma for etching the substrate, wherein each pulse period has an ON-state and an OFF-state comprising a duty cycle;181593262_1PATENTAtorney Docket No.: 44024641WO1 selecting an ON-state duration of the duty cycle based on, at least in part, a first duration for restriking the plasma, a second duration for a minimum on-time for a given RF power source providing the RF power, and a third duration for the plasma to reach a steady state; selecting an OFF-state duration of the duty cycle for each pulse period to alter a profile loading etching effect, an iso-dense depth loading etching effect, or a critical dimension (CD) loading etching effect associated with a feature to be formed on the substrate; and forming the feature by using the duty cycle for the RF power to etch the substrate.191593262_1

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