Method and apparatus for etching a semiconductor substrate in a plasma etch chamber

Abstract

Methods and apparatus for etching a substrate in a plasma etch chamber are provided. In one example, the method includes exposing a substrate disposed on a substrate supporting surface of a substrate support to a plasma within a processing chamber, and applying a voltage waveform to an electrode disposed in the substrate support while the substrate is exposed to the plasma during a plurality of macro etch cycles. Each macro etch cycle includes a first macro etch period and a second macro etch period. The macro etch period includes a plurality of micro etch cycles. Each micro etch cycle has a bias power on (BPON) period and a bias power off (BPOFF) period, wherein a duration of the BPON period being less than a duration of the BPOFF period. Bias power is predominantly not applied to the electrode during the second macro etch period.

Description

BACKGROUND

Field

Embodiments of the present disclosure generally relate to a system and methods used in semiconductor device manufacturing. More specifically, embodiments provided herein generally include an apparatus and methods for etching a semiconductor substrate in a plasma etch chamber.

Description of the Related Art

Reliably producing high aspect ratio features is one of the key technology challenges for the next generation of semiconductor devices. One method of forming high aspect ratio features uses a plasma assisted etching process, such as a reactive ion etch (RIE) plasma process, to form high aspect ratio openings in a material layer, such as a dielectric layer, of a substrate. In a typical RIE plasma process, a plasma is formed in a processing chamber and ions from the plasma are accelerated towards a surface of a substrate to form openings in a material layer disposed beneath a mask layer formed on the surface of the substrate.

A typical Reactive Ion Etch (RIE) plasma processing chamber includes a radio frequency (RF) generator, which supplies an RF power to a power electrode, such as a metal plate positioned adjacent to an “electrostatic chuck” (ESC) assembly, more commonly referred to as the “cathode”. The power electrode can be capacitively coupled to the plasma of a processing system through a thick layer of dielectric material (e.g., ceramic material), which is a part of the ESC assembly. In a capacitively coupled gas discharge, the plasma is created by using a radio frequency (RF) generator that is coupled to the power electrode, or a separate power electrode that is disposed outside of the ESC assembly and within the processing chamber, through an RF matching network (“RF match”) that tunes the apparent load to 50 Ω to minimize the reflected power and maximize the power delivery efficiency.

In high aspect ratio etch applications, it often challenging to maintain the verticality of the etched features. Asymmetries in any one of ground return paths, RF power application, pattern density, flow conductance, and substrate charging, among other, often contributes to loss of vertically (also known as tilting) of the sidewalls of the etched feature. In some cases, tilting of the sidewalls has a detrimental impact on device performance, and may even lead to device failure.

Thus, there is a need for an improved method and apparatus for plasma etching.

SUMMARY

Methods and apparatus for etching a semiconductor substrate in a plasma etch chamber are provided. In one example, the method includes exposing a substrate disposed on a substrate supporting surface of a substrate support to a plasma within a processing chamber, and applying a voltage waveform to an electrode disposed in the substrate support while the substrate is exposed to the plasma during a plurality of macro etch cycles. Each macro etch cycle includes a first macro etch period and a second macro etch period. The macro etch period includes a plurality of micro etch cycles. Each micro etch cycle has a bias power on (BPON) period and a bias power off (BPOFF) period, wherein a duration of the BPON period is less than a duration of the BPOFF period. Bias power is predominantly not applied to the electrode during the second macro etch period.

In another example, a method for etching a semiconductor substrate in a plasma etch chamber is provided that includes forming a plasma from a processing gas containing carbon and at least one halogen, exposing a dielectric layer disposed on the semiconductor substrate to the plasma within the plasma etch chamber, and applying bias power to the semiconductor substrate while exposed to the plasma during a plurality of macro etch cycles until an end point is reached. Each macro etch cycle includes a first macro etch period and a second macro etch period. The macro etch period includes a plurality of micro etch cycles. Each micro etch cycle has a bias power on period and a bias power off period. A duration of the BPON period is less than a duration of the BPOFF period. Bias power is predominantly not applied to the electrode during the second macro etch period. In at least the macro etch cycle, the bias power on period is at least two orders of magnitude less in duration than the first macro etch period, the bias power off period is at least two orders of magnitude less in duration than the second macro etch period.

In yet another example, a plasma etch chamber is provided. The plasma etch chamber includes a chamber body having an interior volume, a substrate support disposed in the interior volume of the chamber body, a bias power control system, a gas panel, and a controller. The substrate support is configured to retain a semiconductor substrate thereon during processing. The substrate support has a biasing electrode. The bias power control system is coupled to the biasing electrode. The gas panel is configured to provide a processing gas to the interior volume. The controller is configured to maintain a plasma within the plasma etch chamber formed from the processing gas, and apply bias power to the biasing electrode while the semiconductor substrate disposed on the substrate support is exposed to the plasma during a plurality of macro etch cycles. Each macro etch cycle includes a first macro etch period and a second macro etch period. The macro etch period includes a plurality of micro etch cycles. Each micro etch cycle has a bias power on period and a bias power off period. A duration of the BPON period is less than a duration of the BPOFF period. Bias power is predominantly not applied to the electrode during the second macro etch period.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

FIG. 1 is a flow diagram of one example of a method for etching a substrate.

FIGS. 2A-2D are partial sectional views of a substrate during various stages of an etch process, such as but not limited to the method described with reference to FIG. 1.

FIG. 3 is one example of a bias power timing diagram illustrating a plurality of macro etch cycles utilized to reach an endpoint during performance of a method for etching a substrate.

FIG. 4 is one example of a bias power timing diagram further detailing one macro etch cycle.

FIG. 5 is a schematic cross-sectional view of an exemplary plasma etch chamber configured to practice the methods described herein.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

Embodiments of the present disclosure generally relate to a system used in semiconductor device manufacturing. More specifically, embodiments provided herein generally include apparatus and methods for etching a substrate in a plasma etch chamber in manners that reduce tilting of the vertical sidewalls of the etched features. Such improvements have been realized by modulating a waveform used to apply bias power to an electrode of a substrate support utilized to support the substrate during etching in both macro and micro regimes. In the macro regime, a plurality of macro etch cycles are utilized to etch the substrate. The waveform includes periods where the bias power is essentially stopped during a portion of each macro etch cycle to allow etch by-products to be exhausted from the plasma etch chamber. By periodically clearing the etch by-products from the chamber, etchants may more effectively be delivered to the feature being etched with a vertical trajectory. In the micro regime of the waveform, a plurality of micro etch cycles are utilized during a portion of each macro etch cycle. Each micro etch cycle includes a first period in which the bias power is on and a second period in which the bias power is essentially stopped. The duration of the second period is greater than a duration of the first period to provide time for etch by-products to exit the feature being etched (such as a hole, a trench, or the like). By periodically clearing the etch by-products from the etched feature, etchants may more effectively be delivered to the bottom of the etched feature with a vertical trajectory. The reduced number of collisions between etchants and the etch by-products enables the etchants maintain a substantially vertical trajectory all the way to the bottom of the etched feature, thus beneficially resulting in a reduced etching of the sidewalls and consequently, excellent verticality of the sidewalls of the etched feature. The enhanced verticality is particularly desirable when forming high aspect ratio features by etching.

Turning now to FIG. 1, a flow diagram of one example of a method 100 for etching a substrate is illustrated. The method 100 may be practiced in a plasma etch chamber, an example of which is later depicted in FIG. 5. The method 100 may alternatively be practiced in other suitable plasma processing chambers. The method 100 is best described with additional reference to FIGS. 2A-2D that illustrate partial sectional views of a substrate 200 during various stages of the etch method 100. The method 100 may be utilized to etch contact vias and trenches, among other features. The method 100 is particularly useful when etching high aspect ratio (height to width ratio greater than 10) features, where verticality of the etched features has a high impact on device performance.

The method 100 begins at operation 102 by exposing a substrate 200 disposed on a substrate supporting surface of a substrate support to a plasma within a plasma etch chamber. As depicted in FIG. 2A, the substrate 200 generally includes a patterned mask 204 disposed on a top surface 210 of a target material 202 to be etched. The mask 204 may be a photoresist, hardmask, combination thereof or other suitable mask. The patterned mask 204 includes an opening 206 that leaves a portion 208 of the top surface 210 of the target material 202 exposed to the plasma within the plasma etch chamber for etching. The substrate 200 may have one or more additional layers (not shown) disposed below a bottom surface 212 of the target material 202.

In one example, the target material 202 is a dielectric layer. For example, the target material 202 may be an oxide layer. In yet other examples, the target material 202 may be a metal or semiconductor material.

In other examples, the target material 202 may include multiple layers. In FIG. 2A, the target material 202 includes a first material 202A disposed on a second material 202B. The first material 202A and the second material 202B are different materials. For example, one of the first material 202A is an oxide layer or a nitride layer, while the second material 202B is the other of an oxide layer or a nitride layer. In still other examples, target material 202 includes a plurality of alternating oxide and nitride layer pairs.

The plasma may be formed within the plasma etch chamber, or formed remote from and delivered into the plasma etch chamber. The plasma is generally formed from a process gas suitable for etching the target material 202. For example when the target material 202 is a dielectric material, the processing gas may comprise a carbon and halogen containing gas. Examples of suitable carbon and halogen containing gases include variants of C_XH_YF_Z, wherein X, Y and Z are integers. Other examples of suitable carbon and halogen containing gases include variants of C_XF_Z, wherein X and Z are integers. In still other examples wherein the target material 202 includes one or more metals, the processing gas may comprise Cl and/or oxygen. In still other examples wherein the target material 202 is silicon, the processing gas may comprise CI and/or fluorine, such as carbon tetrachloride (CCl₄), trifluoromethane (CHF₃), and the like. In any of the above examples, one or more polymer cleaning gases (such as O2, N2, NF3, etc.) and/or one or more inert gases (such as He, Ar, Kr etc.) may optionally be provided as part of the process gas.

At operation 104, a voltage waveform is applied to an electrode disposed in the substrate support while the substrate 200 is exposed to the plasma during a plurality of macro etch cycles to etch the substrate 200, as depicted in FIG. 2B. Each macro etch cycle including a first macro etch period and a second macro etch period. The first macro etch period is generally is used to etch the portion 208 of the target material 202 of the substrate 200 that is exposed through the opening 206 in of the patterned mask 204. Each macro etch cycle may be milliseconds in duration. Within macro etch cycle, the first macro etch period is generally longer than the second macro etch period. For example, the first macro etch period may be three times or longer than the second macro etch period.

During the first macro etch period, the voltage waveform includes a plurality of micro etch cycles. Each micro etch cycle may be microseconds in duration. Thus, the duration of macro etch period is generally an order of magnitude more, for example, 2 to 3 or more orders of magnitude more, than the duration of the micro etch cycle.

Each micro etch cycle includes of a bias power on period and a bias power off period. During the bias power on period, DC power is applied to the electrode disposed in the substrate support. During the bias power off period, DC power is predominately not applied to the electrode disposed in the substrate support, where predominately not applying DC power is defined as not applying DC power from a DC power source coupled to the electrode between zero and 10 percent of the duration of the bias power off period. In one example, essentially no DC power is applied to the electrode disposed in the substrate support for the entire duration of the bias power off period.

The DC power applied to the electrode during the bias power on period effectively directs etchants from the plasma vertically into the feature 224 to etch the exposed portion 208 of the target material 202. Similarly, with DC power predominantly not applied to the electrode during the bias power off period, the target material 202 of the substrate 200 is not etched, thus allowing etch by-products to exit the etched feature 224. Advantageously, as the bias power off period allows the etch by-products to be substantially removed from feature 224, the DC power applied in next bias power on period allows etchants to be directed vertically to the bottom 220 of the etched feature 224 with reduced probability of collision with by-products in feature 224 resulting in the bottom 220 of the feature being vertically etch with little etching of the sidewalls 222 of the feature 224. The reduced etching of the sidewalls 222 of the feature 224 beneficially results in a high degree of verticality of the sidewalls 222.

Similarly during the second macro etch period, DC power is predominately not applied to the electrode disposed in the substrate support, such that DC power is applied from a DC power source coupled to the electrode between zero and 10 percent of the duration of the second macro etch period. In one example, essentially no DC power is applied to the electrode disposed in the substrate support for the entire duration of the second macro etch period.

As with the bias power off period of the second micro etch cycle where DC power predominantly not applied to the electrode, during the second macro etch period the target material 202 of the substrate 200 is also not etched. The millisecond duration of the second macro etch period allows etch by-products, that have exited from etched feature 224 during the bias power off periods of the previously completed first macro etch cycle, to be removed from the region directly above the substrate 200 and pumped out of the plasma etch chamber. With the etch by-products removed from the region directly above the substrate 200, the next macro etch cycle may be performed with a reduced number of collisions between residual etch by-products and the etchant being directed into the feature 224, thus further enhancing the verticality the etched feature 224. By comparison, the duration of the second macro etch period is 100 to 1000 or more times longer than the duration of the second micro etch period, as more time is needed to pump out by-products from the chamber as compared to pumping out by-products from the feature 224.

The macro etch cycles are repeated until an endpoint is reached at operation 106 when a depth of the etched feature 224 reaches a predefined depth D. As illustrated in FIG. 2B, the endpoint of the process for etching the target material 202 at a depth D that does not break through the target material 202. The endpoint of the process for etching the target material 202 may be determined by monitoring optical spectra of the plasma composition, interferometry, or timed etch, among other techniques.

In some examples where the target material 202 includes multiple layers, such as a first material 202A disposed on a second material 202B, the endpoint depth D may be beyond the thickness of the first material 202A but does not break through the second material 202B, as illustrated in FIG. 2C. In still other examples where the target material 202 includes a single layer or multiple layers, the depth D at each the endpoint is reached is when the etched feature 224 breaks through the target material 202 such that the bottom 220 of the feature 224 is defined by the layer (not shown) underlying the target material 202, as illustrated in FIG. 2D.

FIG. 3 is one example of a bias power timing diagram illustrating a waveform 320 that comprises a plurality of macro etch cycles 302 utilized to reach an endpoint at time (TE) during performance of a method for etching a substrate 200, such as the method 100 described above or other similar etch process. Although not illustrated in FIG. 3, the last of the plurality of macro etch cycles 302 may be truncated upon reaching the endpoint at time (TE), for example at operation 106 described above. In the bias power timing diagram depicted in FIG. 3, the vertical axis is representative of DC power applied to the electrode disposed in the substrate support, while the horizontal axis is representative of time. A duration 310 of the entire etch process to reach the endpoint depth D extends from time (To) to the endpoint at time (TE).

Each macro etch cycle 302 generally has, but is not limited to, a duration of 1 to 250 milliseconds. As discussed above, each macro etch cycle 302 includes a first macro etch period 304 and a second macro etch period 306. Although not required, the first macro etch period 304 occurs prior to the second macro etch period 306. The first macro etch period 304 has a duration longer than a duration of the second macro etch period 306. In one example, the first macro etch period 304 has a duration that is at least percent of the total duration of the macro etch cycle 302. In another example, the first macro etch period 304 has a duration that is at least 80 percent of the total duration of the macro etch cycle 302. In one example, the duration of the second macro etch period 306 is selected to be sufficient enough to pump out most of the etch by-products in the process volume above the substrate support.

In some examples, the amount of etch by-products in the process volume above the substrate support may change at different times over the duration 310 of the entire etch process. For example, as the etched feature 224 becomes deeper, the mount the amount of etch by-products in the process volume above the substrate support per unit time may diminish. As such the ratio of the duration of the first macro etch period 304 to the second macro etch period 306 may increase over the course of the duration 310, particularly closer to the endpoint at time (TE). Alternatively, the ratio of the duration of the first macro etch period 304 to the second macro etch period 306 may be different etching the first material 202A as compared to etching the second material 202B.

The frequency of the macro etch cycles 302 is generally in a single to hundreds of Hz range. For example, the frequency of the macro etch cycles 302 may be, but is not limited to, about 5 Hz to about 100 Hz. The frequency of the macro etch cycle 302 may be constant or change over the entire duration 310 for etching of the feature 224. For example, the frequency of the macro etch cycle 302 may be higher during portions of the waveform 320 closer to T₀ than portions of the waveform 320 closer to TE. It has been demonstrated that using lower frequency macro etch cycles 302 at deeper depths D improves verticality of the sidewalls 222 of the etched feature 224 by allowing more time for by-product removal from the etch chamber between active etching of the target materials 202. Alternatively, the frequency of the macro etch cycle 302 may be higher or lower at different portions of the duration 310 of the etch method 100.

As illustrated in FIG. 3, the DC power is predominantly not applied to the electrode of the substrate support during the second macro etch period 306.

Referring back to the first macro etch period 304, the first macro etch period 304 includes times in which DC power is applied to the electrode disposed in the substrate support that supports the substrate within the plasma etch chamber. Etch if the target material 202 generally occurs when DC power is applied to the electrode, but not when the DC power to the electrode is off. The DC power is cyclically applied to the electrode during the first macro etch period 304, as further described below with reference to FIG. 4.

FIG. 4 is one example of a bias power timing diagram further detailing one macro etch cycle 302. In FIG. 4, the vertical axis is representative of DC power applied to the electrode disposed in the substrate support, while the horizontal axis is representative of time. Each macro etch cycle 302 (one of which is shown in FIG. 4) includes a single first macro etch period 304 and a single second macro etch period 306. Each first macro etch period 304 includes a plurality of micro etch cycles 402. Each micro etch cycle 402 includes a first micro etch period 404 and a second micro etch period 406.

As described above, the first macro etch period 304 is generally is used to etch the portion 208 of the target material 202 of the substrate 200 that is exposed through the opening 206 in of the patterned mask 204. To enable etching during each first macro etch period 304, bias power is provided to the electrode of the substrate support during each of the first macro etch periods 404. As the first micro etch periods 404 are milliseconds in duration, bias power is applied to the electrode of the substrate support for many first micro etch periods 404 that comprise each first macro etch period 304 to effectively etch the target material 202.

The frequency of bias power on periods (e.g., DC power pulses) of the micro etch cycle 402 is generally in single to hundreds of kHz range. For example, the frequency of the micro etch cycles 402 may be, but is not limited to, about 25 kHz to about 600 kHz, for example 25 kHz to about 500 kHz. The frequency of the micro etch cycles 402 may be constant or change over the duration of the macro etch cycle 302, and/or may be constant or change over the duration 310 of the etching of the feature 224. For example, the frequency of the micro etch cycles 402 may be higher during portions of the waveform 320 closer to T₀ than portions of the waveform 320 closer to TE. It has been demonstrated that using lower frequency micro etch cycles 402 at deeper depths D improves verticality of the sidewalls 222 of the etched feature 224 by allowing more time for by-products to escape high aspect ratio features 224 between active etching of the target materials 202 during each first micro etch period 404. Alternatively, the frequency of the micro etch cycle 402 may be higher or lower at different portions of the duration 310 of the etch method 100 to suit other needs.

During the micro etch cycle 402, the voltage waveform 320 includes a first micro etch period 404 and a second micro etch period 406. The first micro etch period 404 corresponds to a bias power on period while the second micro etch period 406 corresponds to a bias power off period. During the bias power on period of the first micro etch period 404, DC power is applied to the electrode disposed in the substrate support. During the bias power off period of the second micro etch period 406, DC power is predominately not applied to the electrode disposed in the substrate support, where predominately not applying DC power is defined as not applying DC power from a DC power source coupled to the electrode between zero and 10 percent of the duration of the bias power off period. In one example, essentially no DC power is applied to the electrode disposed in the substrate support for the entire duration of the bias power off period.

Thus with DC power applied to the electrode during the first micro etch period 404, the portion 208 of the target material 202 of the substrate 200 that is exposed through the opening 206 is effectively etched as the bias power directs etchants from the plasma into the feature 224 being etched in the target material 202. Similarly, with DC power predominantly not applied to the electrode during the second micro etch period 406, the target material 202 of the substrate 200 is not etched, thus allowing etch by-products to exit the etched feature 224. Advantageously as the second micro etch period 406 (i.e., bias power off) allows the etch by-products to be substantially removed from feature 224, the DC power applied in next first micro etch period 404 allows etchants to be directed vertically to the bottom 220 of the etched feature 224 with reduced probability of collision with by-products in feature 224. The reduction in by-products collision results in the bottom 220 of the feature being vertically etch with little etching of the sidewalls 222 of the feature 224. The reduced etching of the sidewalls 222 of the feature 224 beneficially results in a high degree of verticality of the sidewalls 222.

Similar to the second macro etch period 306, DC power is predominately not applied to the electrode disposed in the substrate support during the second micro etch period 406. DC power is predominately not applied from a DC power source to the electrode when DC power is not applied between zero and 90 percent of the duration of the second micro etch period 406. In one example, essentially no DC power is applied to the electrode disposed in the substrate support for the entire duration of the second micro etch period 406.

Providing sufficient time for the by-products to be removed from the feature 224 enhances the ability to achieve very vertical sidewalls 222. As such, the first micro etch period 404 has a duration that is generally less than a duration of the second micro etch period 406. In one example, the first micro etch period 404 has a duration that is generally less than 45 percent of the duration of the micro etch cycle 402, for example less than 30 percent. In another example, the first micro etch period 404 has a duration that is generally about 10 to about 45 percent of the duration of the micro etch cycle 402, for example less than 10 to about 15 percent. In another example, the BPON period of one of the micro etch cycles is less than 45% of the BPOFF period. In yet another example, the BPON period of one of the micro etch cycles is between about 10% and about 45% of the BPOFF period. Additionally, as the time needed to clear the feature 224 of etch by-products may be different at different micro etch cycles 402 within the same first macro etch period 304, or between different first macro etch periods 304, the ratio of the duration of the first micro etch period 404 to the second micro etch period 406 may decrease, increase or be constant over the course of the duration 310 of the etch method 100, particularly decreasing closer to the endpoint at time (TE). Alternatively, the ratio of the duration of the first micro etch period 404 to the duration of the second micro etch period 406 may be different etching the first material 202A as compared to etching the second material 202B. In addition or as an alternative to adjusting the duration ratio between first micro etch period 404 to the second micro etch period 406, the power applied to the bias electrode used to etch the feature 224 in the target material 202 may be different at different micro etch cycles 402 within the same first macro etch period 304, or between different first macro etch periods 304. For example, the power used during different micro etch cycles 402 may decrease, increase, or be modulated within the same first macro etch period 304 and/or within different first macro etch periods 304 over the duration 310 of the etch method 100. As an example, the power applied to the bias electrode during a first micro etch period 404 used to etch the first material 202A may be different than the power during a first micro etch period 404 used to etch the second material 202B.

FIG. 5 is a schematic cross-sectional view of an exemplary plasma etch chamber 510 configured to practice the methods described above, such as the method 100 and the like. In some embodiments, the plasma etch chamber 510 is configured for plasma-assisted etching processes, such as a reactive ion etch (RIE) plasma processing. The plasma etch chamber 510 can also be used in other plasma-assisted processes, such as plasma-enhanced deposition processes (for example, plasma-enhanced chemical vapor deposition (PECVD) processes, plasma-enhanced physical vapor deposition (PEPVD) processes, plasma-enhanced atomic layer deposition (PEALD) processes, plasma treatment processing, plasma-based ion implant processing, or plasma doping (PLAD) processing. In one configuration, as shown in FIG. 5, the plasma etch chamber 510 is configured to form a capacitively coupled plasma (CCP). However, in some embodiments, a plasma may alternately be generated by an inductively coupled source disposed over the processing region of the plasma etch chamber 510. In this configuration, a coil may be placed on top of a ceramic lid (vacuum boundary) of the plasma etch chamber 510. It is also contemplated that the method 100 described above may be practiced in other types of plasma etch chambers.

The plasma etch chamber 510 includes a chamber body 513, a substrate support assembly 536, a gas panel 582, a DC power system 583, an RF power system 589, and a system controller 526. The chamber body 513 includes a chamber lid 523, one or more sidewalls 522, and a chamber base 524. The chamber lid 523, one or more sidewalls 522, and the chamber base 524 collectively define the processing volume 529. A substrate 503 is loaded into, and removed from, the processing volume 529 through an opening (not shown) in one of the sidewalls 522. The substrate 503 is the same as the substrate 200 described above. The opening is sealed with a slit valve (not shown) during plasma processing of the substrate 503.

A gas panel 582, which is coupled to the processing volume 529 of the plasma etch chamber 510, includes a processing gas panel 519 and a gas inlet 528 disposed through the chamber lid 523. The gas inlet 528 is configured to deliver one or more processing gases to the processing volume 529 from the plurality of processing gas panel 519. Exemplary processing gases have been described above.

The plasma etch chamber 510 further includes an upper electrode (e.g., a chamber lid 523) and a lower electrode (e.g., a substrate support assembly 536) disposed in a processing volume 529. The upper electrode and lower electrode are positioned to face each other. As seen in FIG. 5, in one embodiment, a radio frequency (RF) source is electrically coupled to the lower electrode. The RF source is configured to deliver an RF signal to ignite and maintain a plasma (e.g., the plasma 501) between the upper and lower electrodes. In some alternative configurations, the RF source can also be electrically coupled to the upper electrode. For example, the RF source can be electrically coupled to the chamber lid. In another example, the RF source could also be electrically coupled to the support base 507.

The substrate support assembly 536 includes a substrate support 505, a substrate support base 507, an insulator plate 511, a ground plate 512, a plurality of lift pins 586, and a bias electrode 504. Each of the lift pins 586 are disposed through a through hole 585 formed in the substrate support assembly 536 and are used to facilitate the transfer of a substrate 503 to and from a substrate support surface 505A of the substrate support 505. The substrate support 505 is formed of a dielectric material. The dielectric material can include a bulk sintered ceramic material, a corrosion-resistant metal oxide (for example, aluminum oxide (Al₂O₃), titanium oxide (TiO), yttrium oxide (Y₂O₃), a metal nitride material (for example, aluminum nitride (AlN), titanium nitride (TiN)), mixtures thereof, or combinations thereof.

The substrate support base 507 is formed of a conductive material. The substrate support base 507 is electrically isolated from the chamber base 524 by the insulator plate 511, and the ground plate 512 interposed between the insulator plate 511 and the chamber base 524. In some embodiments, the substrate support base 507 is configured to regulate the temperature of both the substrate support 505, and the substrate 503 disposed on the substrate support 505 during substrate processing. In some embodiments, the substrate support base 507 includes one or more cooling channels (not shown) disposed therein that are fluidly coupled to, and in fluid communication with, a coolant source (not shown), such as a refrigerant source or substrate source having a relatively high electrical resistance. In other embodiments, the substrate support 505 includes a heater (not shown) to heat the substrate support 505 and substrate 503 disposed on the substrate support 505.

A bias electrode 504 is embedded in the dielectric material or otherwise coupled to the substrate support 505. Typically, the bias electrode 504 is formed of one or more electrically conductive parts. The electrically conductive parts typically include meshes, foils, plates, or combinations thereof. The bias electrode 504 may function as a chucking pole (i.e., electrostatic chucking electrode) that is used to secure (e.g., electrostatically chuck) the substrate 503 to the substrate support surface 505A of the substrate support 505. In general, a parallel plate like structure is formed by the bias electrode 504 and a layer of the dielectric material that is disposed between the bias electrode 504 and the substrate support surface 505A. The layer of dielectric material may be aluminum nitride (AlN), aluminum oxide (Al₂O₃), or other suitable material.

The bias electrode 504 is electrically coupled to a clamping network, which provides a chucking voltage thereto. The clamping network includes a DC voltage supply 573 (e.g., a high voltage DC supply) that is coupled to a filter 578A of the filter 578 that is disposed between the DC voltage supply 573 and bias electrode 504. In one example, the filter 578A is a low-pass filter that is configured to block RF frequency and pulsed voltage (PV) waveform signals (e.g., the waveform 320) provided by other biasing components found within the plasma etch chamber 510 from reaching the DC voltage supply 573 during plasma processing. In one configuration, the static DC voltage is between about −5000V and about 5000V, and is delivered using an electrical conductor (such as a coaxial power delivery line 560). In some embodiments, the bias electrode 504 can also bias the substrate 503 with respect to the plasma 501 using one or more of the pulsed-voltage biasing schemes described in further detail below.

In some configurations, the substrate support assembly 536, further includes an edge control electrode 515. The edge control electrode 515 is positioned below the edge ring 514 and surrounds the bias electrode 504 and/or is disposed a distance from a center of the bias electrode 504. In general, for a plasma etch chamber 510 that is configured to process circular substrates, the edge control electrode 515 is annular in shape, is made from a conductive material, and is configured to surround at least a portion of the bias electrode 504. As seen in FIG. 5, one or both of the bias electrode 504 and the edge control electrode 515 is positioned within a region of the substrate support 505, and is biased with the waveform 320 by use of a pulsed voltage (PV) waveform generator 575. In one configuration, the edge control electrode 515 is biased by use of a PV waveform generator that is different from the PV waveform generator 575 used to bias electrode 504. In another configuration, the edge control electrode 515 is biased by splitting part of the signal provided from the PV waveform generator 575 to the bias electrode 504.

The DC power system 583 includes the DC voltage supply 573, the pulsed voltage (PV) waveform generator 575, and a current source 577. The RF power system 589 includes a radio frequency (RF) waveform generator 571, match 572, and a filter 574. As previously mentioned, the DC voltage supply 573 provides a constant chucking voltage, while the RF waveform generator 571 delivers an RF signal to the processing region, and the PV waveform generator 575 establishes a PV waveform (such as the waveform 320) at the bias electrode 504. Applying a sufficient amount of RF power to an electrode, such as the substrate support base 507, cause the plasma 501 to be formed in the processing volume 529 of the plasma etch chamber 510.

In some embodiments, the power system 583 further includes a filter assembly 578 to electrically isolate one or more of the components contained within the power system 583. As shown in FIG. 5, a power delivery line 563 electrically connects the output of the RF waveform generator 571 to an impedance matching circuit 572, an RF filter 574 and substrate support base 507. Power delivery line 560 electrically connects the output of the voltage supply 573 to a filter assembly 578. Power delivery line 561 electrically connects the output of the PV waveform generator 575 to the filter assembly 578. Power delivery line 562 connects the output of the current source 577 to the filter assembly 578. In some embodiments, the current source 577 is selectively coupled to the bias electrode 504 by use of a switch (not shown) disposed in the delivery line 562, so as to allow the current source 577 to deliver a desired current to the bias electrode 504 during one or more stages (e.g., ion current stage) of the voltage waveform generated by the PV waveform generator 575. As seen in FIG. 5, the filter assembly 578, which can include multiple separate filtering components (i.e., discrete filters 578A-178C) that are each electrically coupled to the output node via power delivery line 564.

The system controller 526, also referred to herein as a processing chamber controller, includes a central processing unit (CPU) 533, a memory 534, and support circuits 535. The system controller 526 is used to control the process sequence (e.g., the method 100) used to etch the substrate 503. The CPU is a general-purpose computer processor configured for use in an industrial setting for controlling the processing chamber and sub-processors related thereto. The memory 534 described herein, which is generally non-volatile memory, can include random access memory, read-only memory, hard disk drive, or other suitable forms of digital storage, local or remote, and can be used to story computer readable instructions for enabling the method 100 to be performed by the plasma etch chamber 510. The support circuits 535 are conventionally coupled to the CPU 533 and comprises cache, clock circuits, input/output subsystems, power supplies, and the like, and combinations thereof. Software instructions (program) and data can be coded and stored within the memory 534 for instructing a processor within the CPU 533. A software program (or computer instructions) readable by CPU 533 in the system controller 526 determines which tasks are performable by the components in the plasma etch chamber 510, such as performing the method 100 to etch the substrate 200 in the manner described above.

Typically, the program, which is readable by the CPU 533 in the system controller 526 includes code, which, when executed by the CPU 533, performs tasks relating to the plasma processing method 100 described herein. The program may include instructions that are used to control the various hardware and electrical components within the plasma etch chamber 510 to perform the various process tasks and various process sequences used to implement the methods described herein. As such, in operation the plasma etch chamber 510 performs the method 100 to each the substrate 200 in a manner that produces excellent verticality of the sidewalls 222 of the etched feature 224.

In one example of the etch method 100 performed in the exemplary plasma etch chamber 510, a substrate 200 disposed on a substrate supporting surface of substrate support 505 to a plasma disposed within the etch chamber 510. The substrate includes a target layer to be etched. In one example, the target layer is a dielectric material, such an oxide or nitride. A voltage waveform to an electrode (e.g., the bias electrode 504) disposed in the substrate support 505 while the substrate is exposed to the plasma during a plurality of macro etch cycles. The plasma is formed from a processing gas suitable for etching the target layer as described above. For example when etching a dielectric target material, such as an oxide material or nitride material processing gas one or both of CxFz and CxHyFz, wherein x, y and z are integers.

In the presence of the plasma in the chamber above the substrate, the target material is etched using a waveform having plurality of macro etch cycles, wherein each macro etch period includes a plurality of micro etch cycles. Each micro etch cycle has a bias power on period and a bias power off period, where a duration of the bias power on period is less than a duration of the bias power off period. The macro etch cycles are repeated until an endpoint is reached. Once the endpoint is reached, the plasma is extinguished, the flow of processing gases into the chamber is halted, and the etched substrate is removed from the plasma etch chamber.

Thus, methods and apparatus for etching a substrate in a plasma etch chamber have been disclosed that reduce tilting of the vertical sidewalls of the etched features compared to conventional techniques. The novel etch method leverages a waveform used to apply bias power to an electrode of a substrate support utilized to support the substrate during etching in both macro and micro regimes. In the macro regime, a plurality of macro etch cycles are utilized to etch the substrate. The waveform includes periods where the bias power is essentially stopped during a portion of each macro etch cycle to allow etch by-products to be exhausted from the plasma etch chamber. By periodically clearing the etch by-products from the chamber, etchants may more effectively be delivered to the feature being etched with a vertical trajectory. In the micro regime of the waveform, a plurality of micro etch cycles are utilized during a portion of each macro etch cycle. Each micro etch cycle includes a first period in which the bias power is on and a second period in which the bias power is essentially stopped. The duration of the second period is greater than a duration of the first period to provide time for etch by-products to exit the feature being etched (such as a hole, a trench, or the like). By periodically clearing the etch by-products from the etched feature, etchants may more effectively be delivered to the bottom of the etched feature with a vertical trajectory. The reduced number of collisions between etchants and the etch by-products enables the etchants maintain a substantially vertical trajectory all the way to the bottom of the etched feature, thus beneficially resulting in a reduced etching of the sidewalls and consequently, excellent verticality of the sidewalls of the etched feature. The enhanced verticality is particularly desirable when forming high aspect ratio features by etching.

While the forgoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A method for etching a substrate in a plasma etch chamber, the method comprising: exposing the substrate disposed on a substrate supporting surface of a substrate support to a plasma within the processing chamber; andapplying a voltage waveform to an electrode disposed in the substrate support while the substrate is exposed to the plasma during a plurality of macro etch cycles, each macro etch cycle including a first macro etch period and a second macro etch period, the macro etch period comprises a plurality of micro etch cycles, each micro etch cycle having a bias power on (BPON) period and a bias power off (BPOFF) period, a duration of the BPON period being less than a duration of the BPOFF period, and bias power predominantly not applied to the electrode during the second macro etch period.

2. The method of claim 1, wherein the BPON period of one of the micro etch cycles is less than 45% of the BPOFF period.

3. The method of claim 1, wherein the BPON period of one of the micro etch cycles is between about 10% and about 45% of the BPOFF period.

4. The method of claim 1, wherein the plurality of macro etch cycles includes a first macro etch cycle occurring prior to a second macro etch cycle, and wherein a BPON period of one of the micro etch cycles of the first macro etch cycle is greater than a BPON period of one of the micro etch cycles of the second macro etch cycle.

5. The method of claim 1, wherein a frequency of the macro etch cycles of the plurality of macro etch cycles decreases as the substrate is etched.

6. The method of claim 1, wherein the frequency of the macro etch cycles is between about 2 to about 100 Hz.

7. The method of claim 1, wherein a frequency of the micro etch cycles is between about 25 to about 500 KHz.

8. The method of claim 7, wherein the frequency of the macro etch cycles is between about 2 to about 100 Hz.

9. The method of claim 1, wherein each micro etch cycle is at least an order of magnitude less than the macro etch cycle.

10. The method of claim 1 further comprising: forming the plasma from a processing gas comprising carbon and at least one halogen.

11. The method of claim 10, wherein a dielectric material is removed from the substrate during the BPON period.

12. The method of claim 11, wherein the dielectric material is an oxide material, nitride material, or a stack of oxide and nitride layer pairs.

13. The method of claim 11, wherein the dielectric material includes at least one oxide layer and at least one nitride layer.

14. The method of claim 11, wherein the processing gas one or both of CxFz and CxHyFz, wherein x, y and z are integers.

15. A method for etching a substrate in a plasma etch chamber, the method comprising: forming a plasma from a processing gas containing carbon and at least one halogen;exposing a dielectric layer disposed on the substrate to the plasma within the plasma etch chamber; andapplying bias power to an electrode disposed in a substrate support supporting the substrate within the plasma etch chamber while exposed to the plasma during a plurality of macro etch cycles until an end point is reached, each macro etch cycle including a first macro etch period and a second macro etch period, the macro etch period comprises a plurality of micro etch cycles, each micro etch cycle having a bias power on (BPON) period and a bias power off (BPOFF) period, a duration of the BPON period being less than a duration of the BPOFF period, bias power predominantly not applied to the electrode during the second macro etch period, wherein in at least macro etch cycle:the BPON period is at least two orders of magnitude shorter in duration than the first macro etch period; andthe BPOFF period is at least two orders of magnitude shorter in duration than the second macro etch period.

16. The method of claim 15, wherein the BPON period of one of the micro etch cycles is less than 45% of the BPOFF period.

17. The method of claim 15, wherein the BPON period of one of the micro etch cycles is between about 10% and about 45% of the BPOFF period.

18. The method of claim 15, wherein the plurality of macro etch cycles includes a first macro etch cycle occurring prior to a second macro etch cycle, and wherein a BPON period of one of the micro etch cycles of the first macro etch cycle is greater than a BPON period of one of the micro etch cycles of the second macro etch cycle.

19. The method of claim 15, wherein a frequency of the macro etch cycles of the plurality of macro etch cycles decreases as the substrate is etched.

20. A plasma etch chamber comprising a chamber body having an interior volume; a substrate support disposed in the interior volume of the chamber body, the substrate support configured to retain a substrate thereon during processing, the substrate support having an electrode;a bias power control system coupled to the electrode;a gas panel configured to provide a processing gas to the interior volume; anda controller configured to: maintain a plasma within the processing chamber formed from the processing gas; andapply a voltage waveform to the electrode while the substrate disposed on the substrate support is exposed to the plasma during a plurality of macro etch cycles, each macro etch cycle including a first macro etch period and a second macro etch period, the macro etch period comprises a plurality of micro etch cycles, each micro etch cycle having a bias power on (BPON) period and a bias power off (BPOFF) period, a duration of the BPON period being less than a duration of the BPOFF period, and bias power is predominantly not applied to the electrode during the second macro etch period.