Abstract:
Methods for forming anisotropic features for high aspect ratio application in etch process are provided in the present invention. The methods described herein advantageously facilitates profile and dimension control of features with high aspect ratios through a sidewall passivation management scheme. In one embodiment, sidewall passivations are managed by selectively forming an oxidation passivation layer on the sidewall and/or bottom of etched layers. In another embodiment, sidewall passivation is managed by periodically clearing the overburden redeposition layer to preserve an even and uniform passivation layer thereon. The even and uniform passivation allows the features with high aspect ratios to be incrementally etched in a manner that pertains a desired depth and vertical profile of critical dimension in both high and low feature density regions on the substrate without generating defects and/or overetching the underneath layers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is related to U.S. patent application Ser. No. ______, filed ______, 2006 entitled “Etch Methods to Form Anisotropic Features for High Aspect Ratio Applications” by Leucke, et al. (Attorney Docket No. APPM/010666/ETCH/CONE/PJS), which is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention generally relates to methods for forming anisotropic features for high aspect ratio applications. More specifically, the present invention generally relates to methods of forming anisotropic features for high aspect ratio applications by an etch process in semiconductor manufacture.  
         [0004]     2. Description of the Related Art  
         [0005]     Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large-scale integration (ULSI) of semiconductor devices. However, as the limits of circuit technology are pushed, the shrinking dimensions of interconnects in VLSI and ULSI technology have placed additional demands on processing capabilities. Reliable formation of gate pattern is important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.  
         [0006]     As the feature sizes have become smaller, the aspect ratio, or the ratio between the depth of the feature and the width of the feature has steadily increased, such that manufacturing processes are being required to etch materials into features having aspect ratios of from about 50:1 to about 100:1 or even greater. Traditionally, features having aspect ratios of about 10:1 or so were produced by anisotropic etching the dielectric layers to a predetermined depth and width. However, when forming higher aspect ratio features, anisotropic etching using conventional sidewall passivation techniques, has become increasingly harder to obtain, thereby resulting in the features having uniform spacing and/or having double or multiple sloped profiles, thus losing the critical dimensions of the features.  
         [0007]     Moreover, redeposition or build-up of passivation layers generated during the etching process on the top or sidewall of the features may block the opening defined in a mask. As the mask opening and/or opening of the etching features are narrowed or sealed by the accumulated redeposition layer, the reactive etchants are blocked from penetrating into the opening, thereby limiting the aspect ratio that may be obtained. As such, failure to sufficiently etch the features results in inability to obtain the desired aspect ratio of the features.  
         [0008]     Another problem in etching features with high aspect ratio is the occurrence of a microloading effect, which is a measure of the variation in etch dimensions between regions of high and low feature density. The low feature density regions (e.g., isolated regions) receive more reactive etchants per surface area compared to the high feature density regions (e.g., dense regions) due to larger total openings of the surface areas, thereby resulting in a higher etching rate. The sidewall passivation generated from the etch by-products exhibited the similar pattern density dependence where more passivation is formed for the isolated features due to more by-products being generated in the region. The difference in reactants and the passivation per surface area between these two regions increase as feature density difference increase. As shown in  FIG. 8A , due to different etch rates and by-products formation in high and low feature density regions, it is often observed that while the low feature density regions  802  have been etched and defined in a certain desired and controlled vertical dimension, the high feature density regions  804  are bowed and/or undercut  806  by the lateral attacking due to the insufficient sidewall passivation. In other processes, the low feature density regions  808  are described being etched at a faster rate with more passivation than the high feature density regions  810 , as shown in  FIG. 8B , resulting in a tapered top portion  812  on the sidewall of the etched layer  814 . Therefore, insufficient sidewall protection associated with the different etch rates in high and low feature density regions with high aspect ratios often results in inability to hold critical dimension of the etch features and poor patterned transfer.  
         [0009]     Yet another challenge associated with etching features with high aspect ratios is controlling the etch rate in feature formed through multiple layers and having different feature density. Here, each layer may etch at a different rate depending on feature density. As shown in  FIG. 9 , faster etch rates in the low feature density regions  902  often results in selectively overetching a layer  904  disposed below the upper etched layer  906 , while slower etch rates in the dense feature regions  908  prevents a portion of the layer  910  from being completely etched. As the features move toward even higher aspect ratios, maintaining efficient etching rate over the low and high feature density regions without either underetching the upper layers or overetching into the lower layers has become increasingly difficult to control. The failure to form the features or patterns on the substrate as designed may result in unwanted defects, and further adversely affect subsequent process steps, ultimately degrading or disabling the performance of the final integrated circuit structure.  
         [0010]     Therefore, there is a need in the art for improved methods to etch features with high aspect ratios.  
       SUMMARY OF THE INVENTION  
       [0011]     Methods for forming anisotropic features for high aspect ratio application in etch process are provided in the present invention. The methods described herein advantageously facilitates profile and dimension control of features with high aspect ratios through a sidewall passivation management scheme. In one embodiment, sidewall passivations are managed by selectively forming an oxidation passivation layer on the sidewall and/or bottom of etched layers. In another embodiment, sidewall passivation is managed by periodically clearing the overburden redeposition layer to preserve an even and uniform passivation layer thereon. The even and uniform passivation allows the features with high aspect ratios to be incrementally etched in a manner that pertains a desired depth and vertical profile of critical dimension in both high and low feature density regions on the substrate without generating defects and/or overetching the underneath layers.  
         [0012]     In one embodiment, the method includes placing a substrate having a layer disposed thereon in an etch chamber, etching the layer through an opening formed in a mask layer using a first gas mixture to define a first portion of a feature, clearing the opening by in-situ etching a redeposition layer formed during etching using a second gas mixture, and etching the layer through the cleared opening.  
         [0013]     In another embodiment, the method includes placing a substrate having a layer disposed thereon in an etch chamber, etching at least a portion of the layer on the substrate, forming an oxidation layer on the etched layer, and etching the exposed portion of the etched layer unprotected by the oxidation layer in the etch chamber.  
         [0014]     In yet another embodiment, the method includes placing a substrate having a film stack comprising a first layer and a second layer in an etch chamber, etching the film stack to expose the first and the second layer in the etch chamber, forming an oxidation layer on the first layer, and etching the second layer in the etch chamber.  
         [0015]     In yet another embodiment, the method includes placing a substrate having a film stack comprising a first layer and a second layer in an etch chamber, etching the film stack in the etch chamber to expose the first layer and the second layer using a first gas mixture, etching a redeposition layer formed during etching using a second gas mixture, forming an oxidation layer on the first layer by exposing the substrate to an oxygen gas containing environment, and etching the second layer unprotected by the oxidation layer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0017]      FIG. 1  is a schematic diagram of a plasma processing apparatus used in performing the etching processed according to one embodiment of the invention;  
         [0018]      FIG. 2  is a process flow diagram illustrating a method incorporating one embodiment of the invention;  
         [0019]      FIGS. 3A-3E  are diagrams illustrating a cross-sectional view of a portion of a composite structure having a dense region and an isolated region;  
         [0020]      FIGS. 4A-4G  are diagrams illustrating a cross-sectional view of a portion of a composite structure having a layer containing at least a high-k material;  
         [0021]      FIGS. 5A-5E  are diagrams illustrating a cross-sectional view of a portion of a substrate having a shallow trench isolation (STI) structure;  
         [0022]      FIG. 6  is a process flow diagram illustrating a method incorporating another embodiment of the invention;  
         [0023]      FIGS. 7A-7D  are diagrams illustrating a cross-sectional view of a portion of a substrate having a high aspect ratio structure to be formed;  
         [0024]      FIG. 8A-8B  are illustrating cross-sectional views of embodiments of prior arts of features with high aspect ratios being etched with poor dimensional control; and  
         [0025]      FIG. 9  is illustrating cross-sectional view of one embodiment of prior arts of features with high aspect ratios in multiple layers. 
     
    
       [0026]     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.  
         [0027]     It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
       DETAILED DESCRIPTION  
       [0028]     The invention generally relates to methods for forming anisotropic features for high aspect ratio application by etch process. In one embodiment, the method includes plasma etching redeposition material deposited on the top and/or sidewall of features with high aspect ratios. In another embodiment, the method includes forming a protective oxidation layer on a portion of an etched region on a substrate surface. The etching process may be performed in one or more chambers integrated in a cluster tool.  
         [0029]     The etch process described herein may be performed in any plasma etch chamber, for example, a HART etch reactor, a HART TS etch reactor, a Decoupled Plasma Source (DPS), DPS-II, or DPS Plus, or DPS DT etch reactor of a CENTURA® etch system, all of which are available from Applied Materials, Inc. of Santa Clara, Calif. Plasma etch chambers from other manufacturers may also be utilized. The DPS reactor uses a 13.56 MHz inductive plasma source to generate and sustain a high density plasma and a 13.56 MHz source bias power to bias a wafer. The decoupled nature of the plasma and bias sources allows independent control of ion energy and ion density. The DPS reactor provides a wide process window over changes in source and bias power, pressure, and etchant gas chemistries and uses an endpoint system to determine an end of the processing.  
         [0030]      FIG. 1  depicts a schematic diagram of one embodiment of an etch process chamber  100 . The chamber  100  includes a conductive chamber wall  130  that supports a dielectric dome-shaped ceiling (referred hereinafter as the dome  120 ). Other chambers may have other types of ceilings (e.g., a flat ceiling). The wall  130  is connected to an electrical ground  134 .  
         [0031]     At least one inductive coil antenna segment  112  is coupled to a radio-frequency (RF) source  118  through a matching network  119 . The antenna segment  112  is positioned exterior to a dome  120  and is utilized to maintain a plasma formed from process gases within the chamber. In one embodiment, the source RF power applied to the inductive coil antenna  112  is in a range between about 0 Watts to about 2500 Watts at a frequency between about 50 kHz and about 13.56 MHz. In another embodiment, the source RF power applied to the inductive coil antenna  112  is in a range between about 200 Watts to about 800 Watts, such as at about 400 Watts.  
         [0032]     The process chamber  100  also includes a substrate support pedestal  116  (biasing element) that is coupled to a second (biasing) RF source  122  that is generally capable of producing an RF signal to generate a bias power about 1500 Watts or less (e.g., no bias power) at a frequency of approximately 13.56 MHz. The biasing source  122  is coupled to the substrate support pedestal  116  through a matching network  123 . The bias power applied to the substrate support pedestal  116  may be DC or RF.  
         [0033]     In operation, a substrate  114  is placed on the substrate support pedestal  1146  and is retained thereon by conventional techniques, such as electrostatic chucking or mechanical clamping of the substrate  114 . Gaseous components are supplied from a gas panel  138  to the process chamber  100  through entry ports  126  to form a gaseous mixture  150 . A plasma, formed from the mixture  150 , is maintained in the process chamber  100  by applying RF power from the RF sources  118  and  122 , respectively, to the antenna  112  and the substrate support pedestal  116 . The pressure within the interior of the etch chamber  100  is controlled using a throttle valve  127  situated between the chamber  100  and a vacuum pump  136 . The temperature at the surface of the chamber walls  130  is controlled using liquid-containing conduits (not shown) that are located in the walls  130  of the chamber  100 .  
         [0034]     The temperature of the substrate  114  is controlled by stabilizing the temperature of the support pedestal  116  and flowing a heat transfer gas from source  148  via conduit  149  to channels formed by the back of the substrate  114  and grooves (not shown) on the pedestal surface. Helium gas may be used as the heat transfer gas to facilitate heat transfer between the substrate support pedestal  116  and the substrate  114 . During the etch process, the substrate  114  is heated by a resistive heater  125  disposed within the substrate support pedestal  116  to a steady state temperature via a DC power source  124 . Helium disposed between the pedestal  116  and substrate  114  facilitates uniform heating of the substrate  114 . Using thermal control of both the dome  120  and the substrate support pedestal  116 , the substrate  114  is maintained at a temperature of between about 100 degrees Celsius and about 500 degrees Celsius.  
         [0035]     Those skilled in the art will understand that other forms of etch chambers may be used to practice the invention. For example, chambers with remote plasma sources, microwave plasma chambers, electron cyclotron resonance (ECR) plasma chambers, and the like may be utilized to practice the invention.  
         [0036]     A controller  140 , including a central processing unit (CPU)  144 , a memory  142 , and support circuits  146  for the CPU  144  is coupled to the various components of the DPS etch process chamber  100  to facilitate control of the etch process. To facilitate control of the chamber as described above, the CPU  144  may be one of any form of general purpose computer processor that can be used in an industrial setting for controlling various chambers and subprocessors. The memory  142  is coupled to the CPU  144 . The memory  142 , or computer-readable medium, may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits  146  are coupled to the CPU  144  for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. An etching process, such as described herein, is generally stored in the memory  142  as a software routine. The software routine may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by the CPU  144 .  
         [0037]      FIG. 2  is a flow diagram of one embodiment of an etch process  200  that may be practiced in the chamber  100  or other suitable processing chamber.  FIGS. 3A-3D  are schematic cross-sectional views of a portion of a composite substrate corresponding to various stages of the process  200 . Although the process  200  is illustrated for forming a gate structure in  FIGS. 3A-3D , the process  200  may be beneficially utilized to etch other structures.  
         [0038]     The process  200  begins at step  200  by transferring (i.e., providing) a substrate  114  to an etch process chamber. In the embodiment depicted in  FIG. 3A , the substrate  114  has a film stack  300  suitable for fabricating a gate structure. The substrate  114  may be any one of semiconductor substrates, silicon wafers, glass substrates and the like. The layers that comprise the film stack  300  may be formed using one or more suitable conventional deposition techniques, such as atomic layer deposition (ALD), physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), and the like. The film stack  300  may be deposited using the respective processing modules of CENTURA®, PRODUCER®, ENDURA® and other semiconductor wafer processing systems available from Applied Materials, Inc. of Santa Clara, Calif., among other module manufacturers. In one embodiment, the film stack  300  includes a gate electrode layer  314  and a gate dielectric layer  302 . At least a portion of the gate electrode layer  314  is exposed for etching. In the embodiment shown in  FIG. 3 , portions  318 ,  320  of the gate electrode layer  314  are exposed through one or more openings in a patterned mask  308 .  
         [0039]     In one embodiment, the gate electrode layer  314  may comprise a stack of a metal material  306  on top of a polysilicon material  304 . The metal material  306  may be selected from a group of tungsten (W), tungsten nitride (WN), tungsten silicide (WSi), tungsten polysilicon (W/poly), tungsten alloy, tantalum (Ta), tantalum nitride (TaN), tantalum silicon nitride (TaSiN), titanium nitride (TiN), alone or the combination thereof.  
         [0040]     In the exemplary embodiment of the  FIG. 3A , the mask  308  may be a hard mask, photoresist mask or a combination thereof. The mask  308  may be used as an etch mask to form opening portions in dense regions  320  and in isolated regions  318  for etching both the gate electrode layer  314 , and the gate dielectric layer  302  into predetermined features.  
         [0041]     At step  204 , a first gas mixture is supplied to the etch chamber to etch the substrate  114  placed therein. During etching, the layer  306  on the substrate  114  is etched and removed from the portions  318 ,  320 , as shown in  FIG. 3B , leaving the trench defined by the mask  308 . After reaching an endpoint, at least a portion of the layer  306  has been removed on the substrate. The endpoint may be determined by any suitable method. For example, the endpoint may be determined by monitoring optical emissions, expiration of a predefined time period or by another indicator for determining that the layer to be etched has been sufficiently removed.  
         [0042]     The first gas mixture may include any gas suitable for etching a metal containing gate electrode layer. In one embodiment, the first gas mixture may include, but not limited to, an oxygen gas accompanying with at least one of nitrogen gas (N 2 ), chlorine gas (Cl 2 ), nitrogen trifluoride (NF 3 ), sulfur hexafluoride gas (SF 6 ), carbon and fluorine containing gas, such as CF 4 , CHF 3 , C 4 F 8  or among others, argon (Ar), helium (He), and the like.  
         [0043]     Several process parameters are regulated while the first gas mixture supplied into the etch chamber. In one embodiment, the chamber pressure in the presence of the first gas mixture is regulated. In one exemplary embodiment, a process pressure in the etch chamber is regulated between about 2 mTorr to about 100 mTorr, for example, at about 10 mTorr. RF source power may be applied to maintain a plasma formed from the first process gas. For example, a power of about 100 Watts to about 1500 Watts may be applied to an inductively coupled antenna source to maintain a plasma inside the etch chamber. The first gas mixture may be flowed into the chamber at a rate between about 50 sccm to about 1000 sccm. A substrate temperature is maintained between about 30 degrees Celsius to about 500 degrees Celsius.  
         [0044]     During etching, the by-products, such as silicon and carbon containing elements, formed during the etching of unmasked areas within the etch chamber may condense and accumulate on the sidewall or top of the mask layer  308  and etched layer  306 , thereby forming a redeposition layer  324 , as shown in  FIG. 3B . As the redeposition layer  324  grows, the opening portion  320  of the trench may be closed or narrowed, thereby disrupting the etching process. As such, an optional step  205  of supplying a cleaning gas into the etch chamber to etch the redeposition layer  324  accumulated on the top or sidewall of the mask layer  308  and etched layer  306 . The cleaning gas removes the redeposition layer  324 , thereby reopening the patterned mask predefined thereof.  
         [0045]     The cleaning gas may include a fluorine-containing gas. In one embodiment, the cleaning gas comprises nitrogen trifluoride (NF 3 ), sulfur hexafluoride gas (SF 6 ), tetrafluoromethane gas (CF 4 ). In another embodiment, the cleaning gas comprises carbon and fluorine containing gas includes CHF 3 , C 4 F 8 , and the like. A carrier gas, such as argon (Ar), helium (He), and the like, may also be utilized to supply into the etch chamber during cleaning.  
         [0046]     Referring back to  FIG. 3B , the portions  320  in the dense regions  310  receive fewer etching species per surface area compared to the portions  318  in the isolated regions  312  due to larger total openings of the surface areas. The difference in reactant per surface area between these two regions increase as pattern density difference increases, thereby increasing the undesired microloading effect. The microloading effect is prevalent while etching substrates with high aspect ratios or densely packed features formed thereon. A relatively high amount of etching species is accumulated on the portions  318  in isolated regions  312 , thereby resulting in a higher etching rate and, as such, the portions  318  exposed in the isolated regions  312  are etched at a much faster rate than dense regions  310 . After the substrate has been etched for a predetermined period, the portions  318  of the layer in the isolated regions  312  have been removed while the portions  320  of the layer in the dense regions  310  still remain at least a portion to be etched due to the different etching rate occurred thereto.  
         [0047]     At step  206 , an oxidation layer  322  may be deposited on the substrate  114 , as shown in  FIG. 3C . In one embodiment, a second gas or gas mixture is supplied to the etch chamber that includes an oxygen-containing gas. The oxygen-containing gas reacts with the portions  318  of the exposed underlying layer  304 , e.g., a polysilicon layer to form the oxidation layer  322 , such as SiO 2 . The oxidation layer  322  formed thereon serves as a passivation layer to protect the underlying layer  304  from being attacked while removing the remaining portion of the layer  306  in the dense regions  310  defined by the mask layer  308 . The portions  320  of the gate electrode layer  306  in dense regions  310  are less unlikely to form the oxidation layer as with the portions  318  exposed on the underlying polysilicon layer  304 , due to the inactive characteristic of the material and insufficient contact with the oxygen species, thereby selectively oxidizing a portion of the substrate surface. As such, the oxidation layer  322  is substantially formed selectively on the portion  318  where the underlying layer  304  has been exposed and leaves the to-be-etched portions  320  of the layer  306  unprotected and available for further etching to remove the remaining portion  320  of the layer  306 .  
         [0048]     The oxidation layer described herein may be formed in various methods. In one embodiment, the oxidation layer may be formed in situ by supplying at least an oxygen-containing gas, e.g., O 2 , N 2 O, NO, CO, CO 2 , and the like, into the etch chamber to react with the polysilicon surface. In another embodiment, the polysilicon layer  304  may be exposed to an environment containing at least oxygen gas or an oxygen-containing gas (i.e., transferring the substrate to a buffer chamber or transferring chamber) to form an oxidation layer thereon. In yet another embodiment, the substrate may be transferred to another process chamber or another tool providing at least oxygen gas or an oxygen-containing gases to form an oxidation layer on the surface of the substrate.  
         [0049]     Several process parameters are regulated while the oxygen-containing gas supplied into the etch chamber. In one embodiment, the chamber pressure in the presence of the oxygen-containing gas inside the etch chamber is regulated. In one exemplary embodiment, a pressure of the oxygen-containing gas in the etch chamber is regulated between about 2 mTorr to about 150 mTorr, for example, between about 10 mTorr to about 100 mTorr. RF source power may be applied to maintain a plasma formed the second gas to oxidize at least a portion of the layer  304  on the substrate. For example, a power of about 200 Watts to about 1500 Watts may be applied to an inductively coupled antenna source to maintain a plasma inside the etch chamber. The oxygen-containing gas may be flowed at a rate between about 50 sccm to about 2000 sccm.  
         [0050]     At step  208 , a third gas mixture is supplied to the process chamber to further etch the remaining portion  320  of the layer  306  inside the process chamber, as shown in  FIG. 3D . In one embodiment, the etch process may be terminated when the remaining portion  320  of the layer  306  in the dense regions  310  has been removed. In another embodiment, the etch process may be terminated by overetching into a portion  316  (shown in phantom) of the underlying layer  304 . In yet another embodiment, the etching process may be terminated after the exposed plan surface of the underlying layer  304  has been removed and the patterned feature of the mask  308  has been successfully transferred to the film stack  300 , as shown in  FIG. 3E . In an optional embodiment, the steps  205 ,  206 ,  208  may be performed repeatedly, as indicated by loop  210  illustrated in  FIG. 2 , to incrementally remove the portions  320  of the layer  306  in the dense regions  310  until the portions  320  have been entirely removed, thereby exposing the gate dielectric layer  302 .  
         [0051]     The third gas mixture may be any suitable gas mixture for etching the remaining portion of the layer on the substrate. In one embodiment, the third gas mixture may be the same as the first gas mixture in the step  202  described above. In another embodiment, the third has mixture may be any suitable gas used for etching a silicon layer. In yet another embodiment, the third gas mixture may be selected from a group consisting of gas, such as Cl 2 , HCl, HBr, CF 4 , CHF 3 , NF 3 , SF 6 , O 2 , N 2 , He or Ar among others.  
         [0052]     Furthermore, the process parameters may be regulated while the third gas mixture supplied into the etch chamber. In one embodiment, a process pressure in the etch chamber is regulated between about 2 mTorr to about 100 mTorr, for example, at about 4 mTorr. RF source power may be applied to maintain a plasma formed from the first process gas to etch at least a portion of the layer  304  on the substrate. For example, a power of about 150 Watts to about 1500 Watts may be applied to an inductively coupled antenna source to maintain a plasma inside the etch chamber. The third gas mixture may be flowed at a rate between about 50 sccm to about 1000 sccm. A substrate temperature is maintained within a temperature range of about 20 degrees Celsius to about 80 degrees Celsius.  
         [0053]     The method for etching a substrate described herein may be utilized to etch a substrate with different film layers and structures. In another exemplary embodiment, illustrated in  FIGS. 4A-4G , a substrate is etched by using the another embodiment of the method  200  of  FIG. 2 .  FIGS. 4A-4G  are schematic cross-sectional views of a portion of a composite substrate corresponding to the process  200  for etching a composite substrate. Although the process  200  is illustrated for forming a gate structure in  FIGS. 4A-4G , the process  200  may be beneficially utilized to etch other structures.  
         [0054]     The method  200  begins at step  202  where a substrate is provided and transferred to an etch process chamber. The substrate  114 , as shown in  FIG. 4A , contains a layer containing a high-k dielectric layer disposed thereon. In one embodiment, the substrate  114  includes a film stack  410 , within which a structure, e.g., a gate, is to be formed thereon. The film stack  410  includes at least one or more layers  404 ,  406  sandwiching a high dielectric constant material layer  402  (high-k materials have dielectric constants greater than 4.0). The film stack  410  may be disposed on a dielectric layer  414 , e.g., a gate dielectric layer or directly on the substrate  114 . A mask  408 , e.g., a hard mask, photoresist mask, or the combination thereof, may be used as an etch mask exposing portions  412  of the film stack  410  for etching features thereon. The substrate  114  may be any semiconductor substrates, silicon wafers, glass substrates and the like. It is contemplated that the sandwiched dielectric layer  402  may be any suitable dielectric layers utilized to form a structure on a substrate. Suitable examples of dielectric layers include, but not limited to, an oxide layer, a nitrogen layer, a composite of oxide and nitrogen layer, at least one or more oxide layers sandwiching a nitrogen layer, and among others.  
         [0055]     In the embodiment depicted in  FIG. 4 , the high-k material layer  402  may include materials having dielectric constant greater than 4.0, examples of which include hafnium dioxide (HfO 2 ), zirconium dioxide (ZrO 2 ), hafnium silicon oxide (HfSiO 2 ), zirconium silicon oxide (ZrSiO 2 ), tantalum dioxide (TaO 2 ), aluminum oxide, aluminum doped hafnium dioxide, bismuth strontium titanium (BST), and platinum zirconium titanium (PZT), among others.  
         [0056]     A layer  406  above the high-K material layer  402  may include one or more layers. In one embodiment, the layer  406  includes a metal material for the gate electrode, including tungsten (W), tungsten silicide (WSi), tungsten polysilicon (W/poly), tungsten alloy, tantalum (Ta), tantalum nitride (TaN), tantalum silicon nitride (TaSiN), and titanium nitride (TiN), among others. Alternatively, the layer  406  may also be or include a polysilicon layer. The layer  404 , e.g., a polysilicon layer or an oxide layer, is optionally disposed under the high-k material layer  402  if desired for the structure being fabricated from the stack  410 .  
         [0057]     At step  204 , a first gas mixture is supplied to the etch chamber to etch the film stack  410 , as shown in  FIG. 4B . In step  204 , the portions  412  of the layer  406  is etched through openings defined by the mask  408  to form a trench in the stack  410 .  
         [0058]     In one embodiment, the first gas mixture includes a halogen-containing gas and does not include an oxygen-containing gas. The halogen-containing gas may be a chlorine containing gas, including, but not limited to, at least one of chlorine gas (Cl 2 ), boron chloride (BCl 3 ), and hydrogen chloride (HCl), among others. Alternatively, both chlorine gas (Cl 2 ) and boron chloride (BCl 3 ) can be included in the first gas mixture. The type of halogen gas (e.g., Cl 2 , BCl 3  or both) is selected to efficiently remove the metal (e.g., hafnium, zirconium, etc.) from the layer  406 .  
         [0059]     In another embodiment, the first gas mixture used in step  204  may further include a reducing agent with or without oxygen-containing gas. Suitable reducing agents include, but are not limited to, hydrocarbon gases, such as carbon monoxide (CO), oxygen gas (O 2 ), methane (CH 4 ), ethane (C 2 H 6 ), ethylene (C 2 H 4 ), and combinations thereof, among others. In one alternative embodiment, the hydrocarbon (e.g., methane) is selected to serve as a polymerizing gas that combines with by-products produced during the etch process. The methane is used to suppress etching of silicon material, such that a high etch selectivity for high-K dielectric materials (e.g., HfO 2  or HfSiO 2 ) to silicon materials is obtained. Additionally, the first gas mixture may further include one or more additional gases, such as helium (He), argon (Ar), nitrogen (N 2 ), among others.  
         [0060]     Process parameters may be regulated while the first gas mixture is supplied to the etch chamber. In one embodiment, the chamber pressure in the presence of the first gas mixture inside the etch chamber is regulated between about 2 mTorr to about 100 mTorr, for example, at about 10 mTorr. A substrate bias power may be applied to the substrate support pedestal at a power between about 0 and about 800 Watts. RF source power may be applied to maintain a plasma formed from the first process gas to etch at least a portion of the layer  406 . For example, a power of about 0 Watts to about 3000 Watts may be applied to an inductively coupled antenna source to maintain the plasma inside the etch chamber. A substrate temperature is maintained within a temperature range of about 30 degrees Celsius to about 500 degrees Celsius.  
         [0061]     At an optional step  205 , a cleaning gas may be supplied to etch a redeposition layer  426  deposited during the etching step  204 . The redeposition layer  426  may be formed during etching of unmasked releasing by-products, such as silicon and carbon containing elements, within the etch chamber. The by-products may condense and accumulate on the sidewall or top of the mask layer  408  and etched layer  406 , thereby forming a redeposition layer  426 , as shown in  FIG. 4B . As the redeposition layer  426  grows, the opening portion  412  of the trench may be narrowed and/or sealed, thereby disrupting the termination of the trench etching process. As such, a cleaning gas may be supplied into the etch chamber to etch the redeposition layer  426  to remove the polymer accumulation, thereby reopening the patterned mask to allow etching to continue without adverse effects to critical dimensions and/or trench sidewall profile/angle.  
         [0062]     The cleaning gas may include a fluorine-containing gas. In one embodiment, the cleaning gas comprises at least one fluorine-containing gas, such as nitrogen trifluoride (NF 3 ), sulfur hexafluoride gas (SF 6 ), tetrafluoromethane gas (CF 4 ) and the like. In another embodiment, the cleaning gas comprises carbon and fluorine containing gas includes CHF 3 , C 4 F 8 , and the like. An inserting gas, such as argon (Ar), helium (He), and the like, may additionally be provided in the cleaning gas.  
         [0063]     In conventional processes, insufficient sidewall passivation of the etched layer with high aspect ratio may be observed during the etching process. Without enough sidewall passivation, lateral as well as vertical etching may occur concurrently, resulting in large changes in the predetermined dimensions of a feature or eroding the corners of a feature, e.g., rounded corners, as a result of an etching process. Such changes are referred to as critical dimension (CD) bias.  
         [0064]     To prevent CD bias, an oxidation layer  418  is deposited at step  206 . The oxidation layer  418  may be applied by supplying a second gas mixture having an oxygen-containing gas into the etch chamber to form the oxidation layer  418  on sidewalls  422  of the etched layer  406  on the substrate, as shown in  FIG. 4C . In one embodiment, the exposed sidewall  422  of the layer  406  reacts with the oxygen gas supplied into the process chamber to form the oxidation layer  418  as a SiO 2  layer. The oxidation layer  418  serves as a passivation layer to protect the sidewall  422  of the layer  406  from lateral attack in following etching steps.  
         [0065]     The oxidation layer  418  may be formed in various methods. In one embodiment, the oxidation layer  418  may be formed in-situ by supplying at least an oxygen-containing gas, e.g., O 2 , N 2 O, NO, CO and CO 2 , among others, into the etch chamber to react with the substrate. In another embodiment, the etched layer  406  may be exposed to an environment containing an oxygen gas and/or oxygen-containing gas to form an oxidation layer thereon. In yet another embodiment, the oxidation layer is formed during transfer between tools by exposure to atmospheric conditions outside the vacuum environment of the tool by transferring the substrate to a buffer chamber or transferring chamber.  
         [0066]     At step  208 , a third gas mixture is supplied into the process chamber to etch the high-k material layer  402 , as shown in  FIG. 4D . In one embodiment, a portion of the layer  406  remaining after step  204  is etched along with the layer  402 . The etching process at step  208  is substantially vertical. In one embodiment, the etching process at step  208  may be ended while the high-k material  402  has been entirely removed. In another embodiment, the etching process may include overetching the substrate to remove a portion  424  of the underlying layer  404  disposed below the high-k material layer  402 .  
         [0067]     The redeposition layer  426  may be redeposited during the subsequent etching process of step  208 , and the oxidation layer  418  may be consumed during the etching process. As such, the steps  205 ,  206 ,  208  may optionally be performed cyclically to incrementally etch the layer  402 . Incremental etching with repetitive removal of redeposition layers  426  and deposition of oxidation layers  418  improves trench verticality and enhances mask to trench CD transfer by reopening the patterned mask and maintaining an oxidation layer during the feature etching of the layer  402 .  
         [0068]     In an alternative embodiment, a second oxidation layer  420  may be applied to the sidewall  422  of the etched layers  406 ,  402  after the first oxidation layer  418  is consumed by providing the second gas mixture into the etch chamber again to further prevent the layer from lateral etching during the subsequent etching process, as shown in  FIG. 4E .  
         [0069]     Subsequent the optional deposition of the second oxidation layer  420 , a third gas mixture may be supplied into the process chamber to etch the layer  404 , as shown in  FIG. 4F . The third gas mixture gas may be any suitable gas used to remove the layer  404 . In one embodiment, the third gas mixture may be the same as the first gas mixture in step  204 . In another embodiment, the third gas mixture may be selected from a group consisting of HBr, Cl 2 , HCl, CF 4 , CHF 3 , NF 3 , SF 6 , N 2 , O 2 , He, Ar and among others.  
         [0070]     Process parameters may be regulated during etching of the layer  404 . for example, a process pressure in the etch chamber is regulated between about 2 mTorr to about 100 mTorr, such as at about 20 mTorr. RF source power may be applied to maintain a plasma formed from the first process gas. For example, a power of about 100 Watts to about 800 Watts may be applied to an inductively coupled antenna source to maintain the plasma inside the etch chamber. The third gas mixture may be flowed into the chamber at a rate between about 50 sccm to about 1000 sccm. A substrate temperature is maintained within a temperature range of about 20 degrees Celsius to about 500 degrees Celsius.  
         [0071]     The mask layer  408  may be removed after the film stack  410  has been etched, as shown in  FIG. 4G . In an alternative embodiment, the steps  205 ,  206 ,  208  may be performed repeatedly to incrementally etch the layer  404  while reopening the patterned mask and maintaining an oxidation layer protecting the sidewalls of the etched feature, as indicated by loop  210 , illustrated in  FIG. 2 .  
         [0072]     The method described above may be utilized to etch substrates having different film layers and/or to form different structures. In yet another exemplary embodiment, illustrated in  FIGS. 5A-5E , a substrate  114  is etched by using the another embodiment of the method  200  of  FIG. 2 .  
         [0073]      FIGS. 5A-5E  are schematic cross-sectional views of a portion of a substrate corresponding to the process  200  for etching a shadow trench isolation (STI) structure. Although the process  200  is illustrated for forming an STI structure in  FIGS. 5A-5E , the process  200  may be beneficially utilized to etch other structures.  
         [0074]     The method  200  begins at step  202  where a substrate is transferred to an etch process chamber. The substrate  114 , as shown in  FIG. 5A , contains a layer  500  disposed thereon. In one embodiment, the layer  500  is suitable to fabricate the STI structure. The layer  500  may be a silicon film, e.g., blanket bare silicon film. In embodiments wherein the layer  500  is not present, processes described as performed on the layer  500  may alternatively be on the substrate  114 . The substrate  114  may be any semiconductor substrates, such as silicon wafers, glass substrates and the like.  
         [0075]     A mask  502  may be a hard mask, photoresist mask, or a combination thereof. The mask  502 , used as an etch mask, having openings exposing portions  504  of the layer  500 . The substrate  114 , with or without the layer  500 , may be etched through the openings to remove material from the exposed portions  504  to form features.  
         [0076]     At step  204 , a first gas mixture is supplied to the etch chamber to etch the layer  500 . In step  204 , the portion  504  of the layer  500  is etched, as shown in  FIG. 5B , through openings defined by the mask  502  to form a trench in the film layer  500 .  
         [0077]     In one embodiment, the first gas mixture includes a halogen-containing gas. The halogen-containing gas may be a bromine containing gas, including, but not limited to, at least one hydrogen bromide (HBr), bromine gas (Br 2 ), and the like, and may be accompanied by at least one fluorine-containing gas. In one embodiment, the first gas mixture includes bromine gas (Br 2 ) and nitrogen trifluoride (NF 3 ). In another embodiment, the first gas mixture used in step  204  may further include a silicon containing gas. A suitable silicon containing gas may be tetrafluorosilane (SiF 4 ) gas.  
         [0078]     Process parameters may be regulated during step  204 . In one embodiment, the chamber pressure in the presence of the first gas mixture inside the etch chamber is regulated between about 2 mTorr to about 100 mTorr, for example, at about 10 mTorr. A substrate bias power may be applied to the substrate support pedestal at a power between about 0 and about 300 Watts. RF source power may be applied to maintain a plasma formed from the first process gas to etch at least a portion of the layer  406 . For example, a power of about 200 Watts to about 3000 Watts may be applied to an inductively coupled antenna source to maintain the plasma inside the etch chamber. A substrate temperature is maintained within a temperature range of about 30 degrees Celsius to about 500 degrees Celsius.  
         [0079]     At an optional step  205 , redeposition layer  506  (shown in  FIG. 5B ), deposited during the etching step  204 , may be removed by providing a cleaning gas to the chamber. The cleaning gas etches the redeposition layer  506  accumulated on the top or sidewall of the mask  502  and the etched layer  500  to reopen the patterned mask.  
         [0080]     The cleaning gas used herein may include at least a fluorine-containing gas. In one embodiment, the cleaning gas comprises at least fluorine-containing gas, such as nitrogen trifluoride (NF 3 ), sulfur hexafluoride gas (SF 6 ), tetrafluoromethane gas (CF 4 ) and the like. In another embodiment, the cleaning gas comprises carbon and fluorine containing gas includes CHF 3 , C 4 F 8 , and the like. The cleaning gas may include an inserting gas, such as argon (Ar), helium (He), and the like.  
         [0081]     As stated above, insufficient sidewall passivation of the etched layer with high aspect ratio may be observed during the etching process. To provide sufficient protection of the sidewall, an oxidation layer  508  is deposited at step  206 . The oxidation layer  508  may be applied by supplying a second gas mixture having an oxygen-containing gas into the etch chamber to form the oxidation layer  508  on sidewalls  510  of the etched layer  500  on the substrate, as shown in  FIG. 5C . In one embodiment, the exposed sidewall  510  of the layer  500  reacts with the oxygen gas supplied into the process chamber to form the oxidation layer  508  as a SiO 2  layer. The oxidation layer  508  serves as a passivation layer to protect the sidewall  510  of the layer  500  from lateral attack in following etching steps.  
         [0082]     The oxidation layer  508  may be formed in various methods. In one embodiment, the oxidation layer  508  may be formed in-situ by supplying at least an oxygen-containing gas, such as O 2 , N 2 O, NO, CO and CO 2 , among others, into the etch chamber to react with the substrate. In another embodiment, the etched layer  500  may be exposed to an environment containing at least an oxygen gas and/or oxygen-containing gas (i.e., by transferring the substrate to a buffer chamber or transferring chamber) to form an oxidation layer thereon. In yet another embodiment, the oxidation layer is formed during transfer between tools by exposure to atmospheric conditions outside the vacuum environment of the tool.  
         [0083]     At step  208 , a third gas mixture is supplied into the process chamber to etch the remaining portion  504  of the etched layer  500  unprotected by the mask  502 , as shown in  FIG. 5D . The etching process is substantially vertical. The third gas mixture gas may be any suitable gas used to remove the layer  500 . In one embodiment, the third gas mixture may be the same as the first gas mixture in step  204 . In one embodiment, the etching process at step  208  may be ended while the layer  500  has been entirely removed.  
         [0084]     The redeposition layer  506  may be redeposited during the subsequent etching process of step  208 , and the oxidation layer  508  may be consumed during the etching process. As such, the steps  205 ,  206 ,  208  may optionally be performed cyclically to incrementally etch the layer  500 , as indicated by loop  210  illustrated in  FIG. 2 . Incremental etching with repetitive removal of redeposition layers  506  and/or deposition of oxidation layers  508  improves trench verticality by reopening the patterned mask and maintaining an oxidation layer during the etch feature in the layer  500  while promoting accurate CD transfer. The mask layer may be removed after the layer  500  has been etched into a desired feature, as shown in  FIG. 5E .  
         [0085]     The third gas mixture gas may be any suitable gas used to remove the layer  500 . In one embodiment, the third gas mixture may be the same as the first gas mixture in step  204 .  
         [0086]      FIG. 6  is a flow diagram of another embodiment of an etch process  600 .  FIGS. 7A-7D  are schematic cross-sectional views of a portion of a substrate corresponding to the process  600  for etching a substrate with high aspect ratio. Although the process  600  is illustrated for forming a high aspect ratio structure in  FIGS. 7A-7D , the process  600  may be beneficially utilized to etch other structures.  
         [0087]     The process  600  begins at step  602  by transferring a substrate  114  to an etch process chamber. In one embodiment depicted in  FIG. 7A , the substrate  114  has a layer  700  suitable for fabricating a high aspect ratio structure. The layer  700  may be any material, such as a dielectric material, a silicon material, metals, metal nitrides, metal alloys, and other conductive materials. The substrate  114  may be any one of semiconductor substrates, silicon wafers, glass substrates and the like. The layers that comprise the layer  700  may be formed using a suitable conventional deposition technique, such as atomic layer deposition (ALD), physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), and the like.  
         [0088]     A mask  702 , e.g., a hard mask, photoresist mask, or the combination thereof, may be used as an etch mask exposing portions  704  of the layer  700 . The exposed portions  704  of the layer  700  may be etched through openings in the mask  702  to form features, such as high aspect ratio trenches.  
         [0089]     At step  604 , a first gas mixture is supplied to the etch chamber to etch the layer  700 , as shown in  FIG. 7B . In step  604 , a portion  704  of the layer  700  is etched through openings defined by the mask  702  to form a trench in the film layer  700 .  
         [0090]     At step  606 , a cleaning gas may be utilized to etch a redeposition layer  706  generated during the etching step  604 . The mask layer  702  or the etched layer  700 , when attacked during step  604 , release reactants, such as silicon and carbon containing elements, within the etch chamber. The reactants may condense and accumulate on the sidewall and/or top of the mask layer  702  and etched layer  700 , thereby forming the redeposition layer  706 , as shown in  FIG. 7B . As the redeposition layer  706  accumulates, the opening portion  704  of the trench may be narrowed and/or closed, thereby disrupting the etching process. As such, a cleaning gas is supplied into the etch chamber to etch the polymer redeposition layer  706  to reopen the patterned mask.  
         [0091]     The cleaning gas may include at least one fluorine-containing gas. In one embodiment, the cleaning gas comprises at least fluorine-containing gas, such as nitrogen trifluoride (NF 3 ), sulfur hexafluoride gas (SF 6 ), tetrafluoromethane gas (CF 4 ) and the like. In another embodiment, the cleaning gas comprises carbon and fluorine containing gas includes CHF 3 , C 4 F 8 , and the like. An inserting gas, such as argon (Ar), helium (He), and the like, may be contained in the cleaning gas.  
         [0092]     At step  608 , a second gas mixture is supplied into the process chamber to etch the remaining portion  704  of the etched layer  700  unprotected by the mask  702 , as shown in  FIG. 7C . The etching process is substantially vertical. The second gas mixture gas may be any suitable gas used to remove the layer  700 . In one embodiment, the second gas mixture may be the same as the first gas mixture in step  604 . In one embodiment, the etching process at step  608  may be ended while the layer  700  has been entirely removed.  
         [0093]     The redeposition layer  706  may be redeposited during the subsequent etching process of step  608 . As such, the steps  606 ,  608  may optionally be performed repeatedly to cyclically etch the layer  700 , as indicated by loop  610  illustrated in  FIG. 6 . Incremental etching with repetitive removal of the redeposition layer  706  improves verticality while etching high aspect ratio by reopening the patterned mask during the etch feature in the layer  700  while providing accurate CD transfer. The mask layer  702  may be alternatively removed after the layer  700  has been etched into a desired feature, as shown in  FIG. 7D .  
         [0094]     Thus, the present application provides an improved method for etching a substrate. The method advantageously facilitates profile and dimension control while etching by selectively forming a protective oxidation layer and/or removing the redeposition layer generated during etching.  
         [0095]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.