US20070099428A1

US20070099428A1 - Plasma for patterning advanced gate stacks

Info

Publication number: US20070099428A1
Application number: US11/544,351
Authority: US
Inventors: Denis Shamiryan; Vasile Paraschiv; Marc Demand; Werner Boullart
Original assignee: Interuniversitair Microelektronica Centrum vzw IMEC
Current assignee: Interuniversitair Microelektronica Centrum vzw IMEC
Priority date: 2005-10-28
Filing date: 2006-10-05
Publication date: 2007-05-03
Also published as: JP5328094B2; EP1780779A3; EP1780780A3; EP1780780A2; EP1780779A2; JP2007123903A; US20070099403A1; US7598184B2

Abstract

A plasma composition and its use in a method for the dry etching of a stack of at least one material chemically too reactive towards the use of a Cl-based plasma are provided. Small amounts of nitrogen (5% up to 10%) can be added to a BCl₃comprising plasma and used in an anisotropical dry etching method whereby a passivation film is deposited onto the vertical sidewalls of stack etched for protecting the vertical sidewalls from lateral attack such that straight profiles can be obtained.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S. provisional application Ser. No. 60/731,608, filed Oct. 28, 2005, and U.S. provisional application Ser. No. 60/839,897, filed Aug. 23, 2006, the disclosures of which are hereby expressly incorporated by reference in their entirety and are hereby expressly made a portion of this application.

FIELD OF THE INVENTION

A method of dry etching of advanced gate stacks is provided which can be used to etch metal gate comprising stacks and pure germanium comprising stacks. An etch plasma composition is also provided for dry etching of metal gate comprising stacks and pure germanium comprising stacks, thereby preserving the vertical profile of the gate stack after patterning.

BACKGROUND OF THE INVENTION

As the critical dimensions in CMOS manufacturing shrink for the 90 nm technology node and beyond, conventional (poly) silicon gates are being replaced by metal gates (meaning pure metals, metal alloys or metal nitrides, etc) and SiO₂as a gate dielectric is replaced by materials with higher dielectric constant (so called “high-k dielectrics). The key challenge is to adapt the conventional gate etch process flow to the metal gate stack. Etching this metal gate stack now requires a process that defines the metal gate profile without affecting the gate critical dimension (CD) and stops on thin gate oxide without pitting or punch through.
Etching of metal gates has been studied addressing metal gate and gate oxide surface roughness, CD control, etch selectivity, and low damage etching but none of them succeeded in preserving the vertical profile of the gate stack after patterning.
One of the promising chemistry for patterning of advanced gate stacks (metal gate etch or high-k removal) is BCl₃. The main advantage of this plasma is that it can etch both metal gates and high-k dielectric with reasonable selectivity to the Si substrate. However, there are number of gate stack materials that are incompatible with BCl₃plasma as they are too reactive. As a result, BCl₃produces some undesirable lateral etch that compromises the gate profiles. Two particular examples are Ge gates and TaN metal gates. If a pure BCl₃plasma is applied during the patterning of the gate stacks containing Ge or TaN a profile distortion caused by lateral etch is observed.

SUMMARY OF THE INVENTION

A dry-etch plasma composition for preserving the vertical profile of a structure comprising a stack of layers during anisotropical dry-etch patterning is provided.
Said plasma composition is further characterized such that during the dry-etch patterning of said stack a water-soluble film, which is removable against the structure, is deposited onto the sidewalls of said stack such that lateral attack of said patterned stack is avoided.
Preferably, the plasma composition of preferred embodiments is characterized as a plasma comprising a boron-halogen compound and nitrogen and wherein the ratio of the boron-halogen compound to nitrogen is from 19:1 up to 9:1. More preferred, the plasma composition of the preferred embodiments is characterized as a plasma composition wherein said plasma comprises a boron-halogen compound, nitrogen and optionally an inert compound. Most preferred said boron-halogen compound is BCl₃.
Preferably, the plasma composition of the preferred embodiments is characterized as a plasma comprising (or consisting of) a boron-halogen compound and 5 up to 10% nitrogen (of the total plasma composition).
More preferably, the plasma composition comprises (or consists of) a boron-halogen compound and less than 10% nitrogen (of the total plasma composition). More particularly, said boron-halogen compound is BCl₃.
Most preferred, said plasma is (i.e. consists of) a BCl₃plasma further comprising (or to which is added) from 5% to 10% nitrogen (based on the total plasma composition).
In a preferred embodiment, the stack of layers to be patterned is a metal gate comprising stack.
More preferred, said metal gate comprising stack comprises at least one TaN layer or combinations of a TaN layer and a TiN layer (referred to as TaN/TiN metal gates) wherein said TaN layer is too sensitive to a (pure) BCl₃plasma. Or in other words the stack of layers to be patterned is a stack wherein at least one layer of said stack of layers is a TaN layer.
In another preferred embodiment, at least one layer of said stack of layers to be patterned is a germanium comprising layer.
Said germanium layer can be situated upon a layer to be patterned by the plasma composition. Said germanium layer can be a pure Ge layer.
Preferably, the plasma of the preferred embodiments (during patterning) has a substrate bias which is different from zero.
Preferably, the plasma of the preferred embodiments (during patterning) has a plasma power of from 100 W up to 1200 W. More preferred said plasma power is about 450 W.
Preferably, the plasma of the preferred embodiments (during patterning) has a pressure in the plasma chamber of minimum 0.666 Pa (5 mT) and maximum 10.665 Pa (80 mT). More preferred said pressure is 0.666 Pa (5 mT).
Preferably, the plasma of the preferred embodiments (during patterning) has a temperature below 100° C. and most preferred said plasma temperature during dry-etch patterning is about 60° C.
An anisotropical dry etching method is also provided using the plasma composition of the preferred embodiments as described above for patterning a stack of layers to create a vertical structure wherein lateral attack during patterning of said stack is avoided.
Preferably said method comprises the steps of first applying a dry-etch step using the plasma composition of the preferred embodiments wherein during the etching a protective and water-soluble film is deposited onto the vertical sidewalls of said structure such that the vertical profile of said structure is preserved and lateral attack is avoided. In a next step said water-soluble film is removed from said structure.
Said water-soluble film is preferably removed using a wet removal process using water.
Use is provided of a plasma comprising (or consisting of) BCl₃, to which nitrogen is added to reach 5% to 10% of the total volume of the resulting plasma composition, for etching a (suitable) stack of layer (i.e. comprising at least one layer etchable by said BCl₃component) and simultaneously passivating (or protecting) the sidewalls of said stack of layers from lateral etch.
A method is also provided for etching (or patterning) a (suitable) stack of layers while/and simultaneously passivating (or protecting) the sidewalls of said stack of layers comprising the step of providing a plasma comprising (or consisting of) BCl₃, to which nitrogen is added to reach 5% to 10% of the total volume of the resulting plasma composition.
Said use or said method is particularly useful for (patterning) a stack of layers wherein at least one layer is germanium, or at least one layer is TaN.
Said passivating (or protecting) effect results from the formation and deposition of a film (or layer) which contains boron and nitrogen (and further compounds such as oxygen) on the sidewalls of said stack of layers. Said film obtainable by a method of the preferred embodiments is also provided.
Said use or said method can be carried out in the framework of CMOS manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

All drawings are intended to illustrate some aspects and embodiments of the present invention. Not all alternatives and options are shown and therefore the invention is not limited to the content of the given drawings.
FIG. 1 shows FTIR (Fourier Transform Infrared Spectroscopy) spectra of films deposited from BCl₃/N₂plasma mixture (70% BCl₃) at 275° C. and 60° C.
FIG. 2 shows a Ge gate profile after the gate patterning and before the high-k removal.
FIG. 3 shows a Ge gate profile after high-k removal by pure BCl₃plasma for 10 seconds (FIG. 3A) and BCl₃/N₂(10% N₂) plasma for 20 seconds (FIG. 3B)
FIG. 4 shows a TaN gate profile after etching in pure BCl₃plasma (FIG. 4A), an arrow indicates the lateral attack of TaN. FIG. 4B shows a TaN gate profile after etching in BCl₃/N₂(5% N₂) plasma.
FIG. 5 shows a TaN gate profile after etching in BCl₃/N₂plasma (FIG. 5A) and a TaN gate profile after etching in BCl₃/O₂plasma (FIG. 5B).
FIG. 6 illustrates the deposition rate of a BxNy film using a BCl₃/N₂plasma (Pressure=1,333 Pa (10 mT)).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures herein are to be considered illustrative rather than restrictive.
In the context of the preferred embodiments, the term “critical dimension” (CD) as used herein is a broad term, and is to be given its ordinary and customary meaning to a person of ordinary skill in the art (and is not to be limited to a special or customized meaning), and refers without limitation to the smallest dimensions of geometrical features (e.g. width of gate electrode) which can be formed during semiconductor device manufacturing. In the context of the preferred embodiments the term “bias” as used herein is a broad term, and is to be given its ordinary and customary meaning to a person of ordinary skill in the art (and is not to be limited to a special or customized meaning), and refers without limitation to the voltage applied to the substrate during patterning in a dry etch chamber.
The term “selectivity” as used herein is a broad term, and is to be given its ordinary and customary meaning to a person of ordinary skill in the art (and is not to be limited to a special or customized meaning), and refers without limitation to the etch rate of a selected material towards another material. The material to be etched away should have a much higher etch rate than the other materials.
The term “ratio” as used herein is a broad term, and is to be given its ordinary and customary meaning to a person of ordinary skill in the art (and is not to be limited to a special or customized meaning), and refers without limitation to an expression of an amount of a first compound to a second compound, e.g. a ratio of 9:1 means e.g. 9 sccm (standard centimeter cube per minute) of the first compound and 1 sccm of the second compound.
Use of plasma composition according to the preferred embodiments surprisingly results in the deposition of a BxNy film during the etching of a structure wherein the deposition is performed in a plasma etch chamber (e.g., Versys 2300 etch chamber from LAM®) at low temperatures (e.g. 60° C.), which was never reported before (BN deposition is usually performed at temperatures of 390° C.-650° C.). The BxNy film is deposited at a rate as high as 10 nm/min to more than 100 nm/min depending on the pressure, plasma power, gas flows, and plasma composition (more specifically the BCl₃to N₂ratio). Said deposited BxNy-like film, in contrast to a pure BN film, was found to be easily decomposing by temperature (the film thickness decreases at temperatures above 100° C.) and soluble in water at room temperatures.
The preferred embodiments are further related to the patterning of a stack of layers, more specifically to the dry etching of a stack of layers.
Said patterning is making use of a plasma etch compound wherein at least one of the layers is too sensitive to said etch compound. By adding an extra component to the plasma it is possible to deposit a protective layer onto the stack of layers such that said stack is protected for e.g. sidewall damage. Said protective layer is deposited during the patterning (dry etching). Furthermore said protective layer is sacrificial and hence easy removable.
The “sacrificial” layer, also referred to as “protective” layer or “passivation” layer refers to the BxNy like film resulting from the addition of nitrogen in the boron-halogen plasma, also referred to as BxNy film or as to boron nitride like film, which is deposited during etching. Said BxNy film is used as a “protective” or “passivating” film during patterning/etching of a structure, said BxNy film is also referred to as a sacrificial layer because said layer is removed after patterning is completed. Due the unstable character of the BxNy film and water soluble character said BxNy film can be easily removed by e.g. a water rinse.
The term “BxNy” film refers to a film comprising mainly boron and nitrogen which is further characterized as a water-soluble film. The BxNy film of the preferred embodiments is water soluble, in contrast to a pure BN which is insoluble in water. The BxNy film contains hexagonal boron nitride, but is very unlikely to be a stoichiometric BN. The BxNy film is therefore referred to as BxNy wherein the integers x and y indicate that the ratio of nitrogen and boron in the film is not fixed due to the presence of other compounds (impurities) in the film such as water, oxygen and/or ammonia which are possibly absorbed from the plasma and/or atmosphere after dry-etching.
More specifically, the preferred embodiments relate to the patterning of metal gate stacks or germanium gate stacks, more specifically it relates to the dry etching of said gate stacks such as TaN comprising metal gate stacks and to the dry etching of Ge comprising stacks (or in other words a stack comprising e.g. a pure Ge layer).
The methods and compositions of preferred embodiments can solve or minimize the problem of lateral etch and profile attack during the patterning of advanced gate stacks such as metal gate stacks and germanium stacks by adding small amounts of nitrogen to a boron-halogen plasma such as BCl₃plasma in order to improve gate profile control. The mixture of BCl₃/N₂plasma results in a deposition of BxNy-like film that inhibits the lateral etch but does not inhibit vertical etch as the formed BxNy-like film is destroyed by ion bombardment.
A plasma composition is provided for patterning metal gate stacks and/or germanium stacks wherein during the patterning of said stack a protective and water-soluble film is deposited such that the vertical profile of the stack is preserved and lateral attack of said stack is avoided.
More specifically a plasma composition is provided for patterning a stack of layers wherein at least one layer of said stack is sensitive to one of the etch compounds.
The plasma composition is preferably a Boron-halogen comprising plasma with small additions of nitrogen.
The Boron-halogen compound is preferably BCl₃and said small additions of nitrogen are such that the ratio of the boron-halogen compound to nitrogen is from 19:1 up to 9:1.
Optionally an inert compound can be added to the plasma comprising boron-halogen and nitrogen. Said inert compound can be e.g. argon or helium (He) and these compounds can be added to the plasma in concentrations up to 50% of the total plasma composition. It is further known that addition of inert compounds (meaning that these compounds do not react with the substrate to be etched such that volatile compounds are formed) can improve the dissociation rate in the plasma and hence improve the etch rate and more specifically in case of the invention improve the formation (deposition) of a BxNy film. In that case the inert compound can be seen as a catalyst.
For the patterning of metal gates comprising TaN, such as TaN metal gates and metal gates comprising layers of TaN and TiN (TaN/TiN metal gates) the ratio of the boron-halogen compound to nitrogen is below 9:1 (having more boron-halogen), more preferred said ratio of the boron-halogen compound to nitrogen is below 11:1 and most preferred said ratio of the boron-halogen compound to nitrogen is 19:1.
For the patterning of metal gates comprising TaN, such as TaN metal gates and metal gates comprising combinations of TaN and TiN layers (TaN/TiN metal gates) the ratio of BCl₃to nitrogen is below 9:1, more preferred said ratio of BCl₃to nitrogen is below 11:1 and most preferred said ratio of BCl₃to nitrogen is 19:1.
For the patterning of germanium comprising stacks wherein germanium is at least one of the layers of the stack and said germanium layer needs to be protected to avoid lateral attack during patterning of a layer situated under said germanium layer, the ratio of the boron-halogen compound to nitrogen is higher than 19:1. More preferred said ratio of the boron-halogen compound to nitrogen is higher than 11:1 and most preferred the ratio of the boron-halogen compound to nitrogen is 9:1.
For the patterning of germanium comprising stacks wherein germanium is at least one of the layers of the stack said germanium layer needs to be protected to avoid lateral attack during patterning of a layer situated under said germanium layer, the ratio of BCl₃to nitrogen is higher than 19:1. More preferred said ratio of BCl₃to nitrogen is higher than 11:1 and most preferred the ratio of BCl₃to nitrogen is 9:1.
In a preferred embodiment, the plasma composition is preferably a plasma comprising (or consisting of) a Boron-halogen compound and nitrogen, or in other words small additions of nitrogen in a boron-halogen plasma.
Preferably, the plasma comprises (or consists of) a boron-halogen compound and 5% up to 10% nitrogen (of the total plasma composition).
More preferred, the plasma composition comprises (or consists of) a boron-halogen compound and less than 10% nitrogen (of the total plasma composition) and most preferred said boron-halogen is BCl₃.
For the patterning of germanium comprising stacks wherein said germanium layer needs to be protected to avoid lateral attack during patterning of a layer situated under said germanium layer, the amount of N₂to the total BCl₃/N₂plasma composition is higher than 5%, more preferred said amount of N₂is higher than 8% N₂to the total BCl₃/N₂plasma composition and most preferred said amount of N₂is 10% to the total BCl₃/N₂plasma composition.
For the patterning of metal gates such as TaN and/or combinations of TaN and TiN (TaN/TiN metal gates) the amount of N₂to the total BCl₃/N₂plasma composition is lower than 10%, more preferred said amount of N₂is lower than 8% N₂to the total BCl₃/N₂plasma composition and most preferred said amount of N₂is 5% to the total BCl₃/N₂plasma composition.
Preferably the plasma of the preferred embodiments (during patterning) has a substrate bias which is different from zero.
Preferably the plasma of the preferred embodiments (during patterning) has a plasma power is from 100 W up to 1200 W. More preferred said plasma power is about 450 W.
Preferably the plasma of the preferred embodiments (during patterning) has a pressure in the plasma chamber of minimum 0.666 Pa (5 mT) and maximum 10.665 Pa (80 mT). More preferred said pressure is 0.666 Pa (5 mT).
Preferably the plasma of the preferred embodiments (during patterning) has a temperature below 100° C. and most preferred said plasma temperature during dry-etch patterning is about 60° C. A boron-nitrogen (B_xN_yor BN) film deposited at higher temperatures is equal to a higher quality film containing less (or no) impurities which is more difficult or even not possible to remove.
A method is provided for the dry etching of non-Si comprising gate stacks, said non-Si comprising gate stacks are preferably metal gate comprising gate stacks such as TaN comprising gate stacks and preferably metal gate stacks comprising a (pure) germanium layer.
More specifically the dry-etching method of the preferred embodiments uses a plasma composition wherein at least one layer of said stack is too sensitive to one of the etch compounds.
Said dry etching method is characterized in that the vertical profile of said gate stack is preserved after etching. The method of the preferred embodiments solves or minimizes the problem of negatively sloped gate profiles after dry etching by depositing a sacrificial layer during the etching. Said sacrificial layer serves as a passivating layer during dry etching such that the vertical profile or CD of the gate stack is preserved.
The dry-etching method of the preferred embodiments solves or minimizes the problem of lateral etch and profile attack during the patterning of advanced gate stacks such as metal gate stacks and germanium comprising stacks by adding small amounts of nitrogen to a boron-halogen plasma such as BCl₃plasma in order to improve gate profile control. The mixture of BCl₃/N₂plasma results in a deposition of BxNy-like film that inhibits the lateral etch but does not inhibit vertical etch as the formed BxNy-like film is destroyed by ion bombardment.
Preferably the method of the preferred embodiments comprises the steps of first applying a dry-etch step using the plasma composition of the preferred embodiments whereby during the etching a protective and water-soluble film is deposited onto the vertical sidewalls of said structure such that the vertical profile of said structure is preserved and lateral attack is avoided. In a next step said water-soluble film is removed from said structure.
Said water-soluble film is preferably removed using a wet removal process, most preferred said wet removal is using water.
The dry-etching method of the preferred embodiments uses a boron-halogen comprising plasma with small additions of nitrogen.
The Boron-halogen compound is preferably BCl₃and said small additions of nitrogen are such that the ratio of the boron-halogen compound to nitrogen is from 19:1 up to 9:1.
Optionally an inert compound can be added to the plasma comprising boron-halogen and nitrogen. Said inert compound can be e.g. argon or helium (He) and these compounds can be added to the plasma in concentrations up to 50% of the total plasma composition.
In a method of the preferred embodiments for patterning metal gates such as TaN metal gates and metal gates comprising combinations of TaN and TiN (TaN/TiN metal gates), the ratio of the boron-halogen compound to nitrogen is preferably below 9:1. More preferably, said ratio of the boron-halogen compound to nitrogen is below 11:1 and most preferred said ratio of the boron-halogen compound to nitrogen is 19:1.
In particular, said boron-halogen compound is BCl₃.
In a method of the preferred embodiments for patterning germanium comprising stacks, wherein said germanium layer is a layer of the stack which needs to be protected to avoid lateral attack during patterning of a layer situated under said germanium layer, the ratio of the boron-halogen compound to nitrogen is preferably higher than 19:1. More preferred said ratio of the boron-halogen compound to nitrogen is higher than 11:1 and most preferred the ratio of the boron-halogen compound to nitrogen is 9:1.
In particular, said boron-halogen compound is BCl₃.
In a preferred embodiment, the plasma composition used in a method of the preferred embodiments is a plasma comprising (or consisting of) a Boron-halogen compound and nitrogen, or in other words small additions of nitrogen in a boron-halogen plasma.
Preferably, the plasma comprises (or consists of) a boron-halogen compound and 5% up to 10% nitrogen (of the total plasma composition).
More preferred, the plasma composition comprises (or consists of) a boron-halogen compound and less than 10% nitrogen (of the total plasma composition) and most preferred said boron-halogen is BCl₃.
In a method of the preferred embodiments for patterning germanium comprising stacks wherein said germanium layer needs to be protected to avoid lateral attack during patterning of a layer situated under said germanium layer, the amount of N₂to the total BCl₃/N₂plasma composition is higher than 5%, more preferred said amount of N₂is higher than 8% N₂to the total BCl₃/N₂plasma composition and most preferred said amount of N₂is 10% to the total BCl₃/N₂plasma composition.
In a method of the preferred embodiments for patterning metal gates such as TaN and/or combinations of TaN and TiN (TaN/TiN metal gates), the amount of N₂to the total BCl₃/N₂plasma composition is lower than 10%, more preferred said amount of N₂is lower than 8% N₂to the total BCl₃/N₂plasma composition and most preferred said amount of N₂is 5% to the total BCl₃/N₂plasma composition.
Preferably the plasma used in a method of the preferred embodiments (during patterning) has a substrate bias which is different from zero.
Preferably, said plasma has a plasma power of 100 W up to 1200 W. More preferred said plasma power is about 450 W.
Preferably, said plasma has a pressure in the plasma chamber of minimum 0.666 Pa (5 mT) and maximum 10.665 Pa (80 mT). More preferred said pressure is 0.666 Pa (5 mT).
Preferably, said plasma has a temperature below 100° C. and more preferred said plasma temperature during dry-etch patterning is about 60° C.
Indeed, a boron-nitrogen (B_xN_yor BN) film deposited at higher temperatures is equal to a higher quality film containing less (or no) impurities, which is more difficult or even not possible to remove.
In relation to the drawings the preferred embodiments can also be described as follows in the text below.
A method is provided for the dry etching of non-Si comprising gate stacks, said non-Si comprising gate stacks are preferably metal gate comprising gate stacks such as TaN comprising gate stacks and preferably pure germanium comprising metal stacks. Said dry etching method is characterized in that the vertical profile of said gate stack is preserved after etching. The method of the preferred embodiments solves the problem of negatively sloped gate profiles after dry etching by depositing a sacrificial layer during the etching. Said sacrificial layer serves as a passivating layer during dry etching such that the vertical profile or CD of the gate stack is preserved.
A composition is provided of a plasma used to etch materials that are too sensitive to Cl-based plasmas. If those materials are etched with pure Cl-based plasmas such as BCl₃plasmas, the etch profiles are distorted because these materials are etched in the lateral direction as well. Examples of said materials are metal gate comprising gate stacks such as TaN comprising gate stacks and pure germanium comprising metal stacks. The plasma of the preferred embodiments solves or minimizes the problem of damage caused by Cl-based plasmas, more specifically this is achieved by adding small amounts of nitrogen to the Cl-based plasma. For the patterning of metal gate comprising gate stacks such as TaN comprising gate stacks and pure germanium comprising metal stacks said Cl compound is preferably BCl₃. The amount of nitrogen added to the plasma is preferably from 5% up to 10%. The addition of nitrogen to a Cl-based plasma such as BCl₃preserves the vertical profile through the formation of a passivating B_xN_y-like layer on the vertical surfaces.
A Cl-based plasma with small additions of nitrogen for the patterning of non-Si based stacks is also provided. Said patterning is further characterized as a patterning which avoids lateral etching and preserves the vertical profile. Said stacks are preferably metal gate comprising gate stacks such as TaN comprising gate stacks and preferably pure germanium comprising metal stacks. For patterning TaN comprising gate stacks and pure Germanium comprising gate stacks, said Cl compound is BCl₃.

EXAMPLES

The method of the preferred embodiments as well as the plasma and its use can be applied to any material that can be etched by Cl-based plasma but is too chemically reactive and has significant lateral etch component. Said lateral etch can be blocked by a BxNy-like passivation film deposited onto the vertical sidewalls while at the meanwhile the vertical etch is not significantly affected.
The BCl₃/N₂plasma was applied for patterning of two different stacks as described in Example 1 and 2: pure Ge gates and TaN metal gates in the TiN/TaN gate stack. In both cases, the lateral attack of the gate material was prevented by addition of small amount of N₂(5%-10%) to the BCl₃plasma. Furthermore the plasma settings were optimized and illustrated in Example 3. The deposited (passivation) BxNy-like layer of the preferred embodiments is characterized by FTIR and illustrated in Example 4.

Example 1

Application of BCl₃/N₂Plasma for TaN Gate Profile Control

The BCl₃/N₂plasma was used to etch TaN metal gates, in the example presented here said TaN metal gate is present in a TiN/TaN gate stack where 15 nm TaN is in the contact with the gate dielectric and 70 nm TiN covers the TaN or in other words 70 nm TiN is situated on top of said 15 nm TaN.
The most critical step is TaN etching after TiN patterning. BCl₃plasma is used here for the TaN patterning as it is selective to the Si substrate and can be used as high-k removal as well.
If TaN is etched with pure BCl₃plasma, then a notch (lateral attack) is observed in the TaN layer.
FIG. 4A shows the gate profile after etching in pure BCl₃, an arrow indicates the lateral attack of TaN.
The addition of 5% of N₂to the BCl₃plasma resulted in a straight TaN profile without the lateral attack of the TaN layer.
The effect of N₂addition is illustrated in FIG. 4B. A B_xN_ycomprising passivation layer will be deposited onto the vertical sidewalls of the stack during patterning, said B_xN_ycomprising passivation layer will protect the TaN during patterning and avoid lateral attack.
The deposition of a B_xN_ycomprising layer onto the horizontal surfaces will be negligible due to a continuous ion bombardment in the vertical direction (in other words the B_xN_ycomprising layer will be removed immediately after deposition onto horizontal surfaces).
This means that the deposition of the BxNy like film inhibits the lateral etch but does not inhibit vertical etch as the formed BxNy-like film is destroyed by ion bombardment.
A straight TaN profile can also be obtained by using a BCl₃/O₂plasma mixture, as shown in FIG. 5B. However, the presence of O₂in the etching plasma will have a detrimental effect on the high-k dielectric and, therefore, is preferably avoided.
After patterning of the TaN comprising gate stack, the B_xN_ycomprising passivation layer can be removed by a wet treatment e.g. a removal in water.

Example 2

Application of BCl₃/N₂Plasma for Pure Ge Gate Profile Control

The BCl₃/N₂plasma was used to pattern pure Ge gates having a high-k dielectric underneath (in the presented case the high-k dielectric is HfO₂). The high-k dielectric must be removed selectively to the underlying Si substrate.
The Ge gate profile just after patterning and before high-k removal as shown in FIG. 2 is straight.
The conventional way of HfO₂removal is etching in BCl₃plasma. If high-k is removed by such plasma, the Ge gate suffers from profile distortion while addition of 10% N₂to the BCl₃plasma preserves the profile even if the removal time is doubled as shown in FIG. 3.
FIG. 3A shows the Ge gate profile after high-k removal by a pure BCl₃plasma for 10 seconds and FIG. 3B shows the Ge gate profile after high-k removal by a BCl₃/N₂(10% N₂) plasma for 20 seconds. No lateral attack of the Ge profile is seen in FIG. 3B.
It can be concluded that addition of small amounts of N₂(in the presented case 10% N₂was added) to the BCl₃plasma during high-k removal preserves the shape of the Ge gate. This is due to the deposition of a BxNy-like passivation film on the gate (vertical) sidewalls. Said BxNy-like passivation film is a sacrificial layer which can be removed afterwards by wet treatment.

Example 3

Plasma Parameters Used to Deposit a BxNy Passivation Film

The plasma parameters used for the deposition of a BxNy passivation film during TaN metal gate patterning as presented in Example 1 using a plasma of a preferred embodiment are as follows: pressure 0.666 Pa (5 mT), plasma power 450 W, flow BCl₃95 sccm (standard centimeter cube per minute), flow N ₂5 sccm, and substrate bias 55V.
The plasma parameters used for the deposition of a BxNy passivation film during high-k removal in a Ge gate stacks as presented in Example 2 are as follows: pressure 0.666 Pa (5 mT), plasma power 450 W, substrate bias 30V, BCl₃90 sccm, N₂10 sccm.

Example 4

Characterization of the Deposited BxNy Layer

Using the plasma composition (BCl₃/N₂) and method of the preferred embodiments resulted in the deposition of a BxNy layer. Said BxNy film was characterized by Fourier Transmission Infra-Red spectrometry (FTIR) and X-ray Photoelectron Spectroscopy (XPS). It was found that a plasma mixture of BCl₃and N₂resulted in the deposition of a BxNy film onto a (flat) wafer surface if no bias was applied to the substrate (to avoid ion bombardment). Said BxNy film was deposited in an etch chamber (LAM Versys 2300) at 60° C. and 275° C. at a rate as high as 300 nm/min depending on the pressure, plasma power, gas flows and BCl₃to N₂ratio.
The FTIR spectra of the BxNy films deposited at 60° C. and 275° C. (for comparison) are shown in FIG. 1. A strong peak at about 1400 cm⁻¹is attributed to a hexagonal boron nitride (h-BN). This peak dominate the spectrum of the film deposited at 275° C. but the spectrum of the film deposited at 60° C. contains number of other peaks and, therefore, that film is not pure BN.
The XPS analysis of the surface of the film deposited at 60° C. showed primarily boron (about 36%), nitrogen (about 20%) and oxygen (about 36%). Some carbon (about 7%) is attributed to the contamination from the atmosphere. The amount of chlorine did not exceed 1%. As the deposition plasma contains no O₂, the significant amount of oxygen in the film is a sign of the film oxidation during the atmosphere exposure.
The deposited BxNy-like film was found to be easily decomposing by temperature (the film thickness decreases at temperatures above 100° C.) and soluble in water at room temperatures. These properties make cleaning of any deposited inhibitor layer easy: the water rinse is enough to clean any BxNy-like film that is left after the gate patterning.
It can be concluded that by mixing BCl₃and N₂in a plasma etch chamber it is possible to deposit a BxNy-like film that contains almost no Cl₂. The film is relatively unstable and can be easily removed by a water rinse, as it is soluble in water.
All references cited herein are incorporated herein by reference in their entirety. To the extent publications and patents or patent applications incorporated by reference contradict the disclosure contained in the specification, the specification is intended to supersede and/or take precedence over any such contradictory material.
The term “comprising” as used herein is synonymous with “including,” “containing,” or “characterized by,” and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps.
All numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.
The above description provides several methods and materials of the present invention. This invention is susceptible to modifications in the methods and materials, as well as alterations in the fabrication methods and equipment. Such modifications will become apparent to those skilled in the art from a consideration of this disclosure or practice of the invention disclosed herein. Consequently, it is not intended that this invention be limited to the specific embodiments disclosed herein, but that it cover all modifications and alternatives coming within the true scope and spirit of the invention as embodied in the attached claims.

Claims

1. A dry-etch plasma composition for preserving a vertical profile of a structure comprising a stack of layers, wherein a removable water-soluble film is deposited onto the sidewalls of the stack from the plasma composition during dry-etch patterning of the stack, such that lateral attack of the patterned stack is avoided.

2. The plasma composition of claim 1, wherein the plasma comprises a boron-halogen compound and nitrogen.

3. The plasma composition of claim 2, further comprising an inert compound.

4. The plasma composition of claim 2, wherein a ratio of the boron-halogen compound to nitrogen is from 19:1 to 9:1.

5. The plasma composition of claim 2, wherein the boron-halogen compound is BCl₃.

6. The plasma composition of claim 1, wherein the stack of layers is a metal gate-comprising stack.

7. The plasma composition of claim 6, wherein the metal gate-comprising stack comprises TaN or TaN/TiN.

8. The plasma composition of claim 6, wherein at least one layer of the stack of layers is a germanium-comprising layer.

9. The plasma composition of claim 8, wherein the germanium layer is situated upon a layer to be patterned by the plasma composition.

10. The plasma composition of claim 1, wherein the substrate bias is different from zero.

11. The plasma composition of claim 1, wherein the plasma power is from 100 W to 1200 W.

12. The plasma composition of claim 11, wherein the plasma power is about 450 W.

13. The plasma composition of claim 1, wherein the pressure in the plasma chamber is from 0.666 Pa to 10.665 Pa.

14. The plasma composition of claim 1, wherein the pressure in the plasma chamber is 0.666 Pa.

15. The plasma composition of claim 1, wherein a temperature of the plasma during patterning is below 100° C.

16. The plasma composition of claim 1, wherein a temperature of the plasma during patterning is about 60° C.

17. The plasma composition of claim 1, wherein the plasma consists of a boron-halogen compound and nitrogen, and wherein from 5% to 10% of the total plasma composition is nitrogen.

18. The plasma composition of claim 1, wherein the plasma consists of a boron-halogen compound and nitrogen, and wherein less than 10% of the total plasma composition is nitrogen.

19. The plasma composition of claim 1, wherein the plasma consists of a boron-halogen compound and nitrogen, and wherein less than 8% of the total plasma composition is nitrogen.

20. The plasma composition of claim 1, wherein the plasma is a BCl₃plasma wherein 5% of the total plasma composition is nitrogen.

21. An anisotropical dry etching method for patterning a stack of layers to create a vertical structure, the method comprising the steps of:

patterning a stack of layers to create a vertical structure by dry etching using a plasma composition comprising a boron-halogen compound and nitrogen, wherein a protective and water-soluble film is deposited from the plasma onto vertical sidewalls of the structure during dry etching, such that a vertical profile of the structure is preserved and lateral attack is avoided during dry etching; and

removing the film from the structure.

22. The method of claim 21, wherein the film is removed by a wet removal process using water.

23. The method of claim 21, wherein a ratio of boron-halogen compound to nitrogen is from 19:1 to 9:1.

24. The method of claim 21, wherein the boron-halogen compound is BCl₃.

25. The method of claim 21, wherein the plasma further comprises an inert compound.

26. The method of claim 21, wherein the stack of layers is a metal gate-comprising stack.

27. The method of claim 26, wherein the metal gate-comprising stack comprises TaN or TaN/TiN.

28. The method of claim 26, wherein at least one layer of the stack of layers comprises germanium.

29. The method of claim 28 wherein the germanium-comprising layer is situated upon a layer to be patterned by the plasma composition.

30. The method of claim 21, wherein a substrate bias during patterning is different from zero.

31. The method of claim 21, wherein a plasma power during patterning is from 100 W to 1200 W.

32. The method of claim 21, wherein a plasma power during patterning is about 450 W.

33. The method of claim 21, wherein a pressure in the plasma chamber during patterning is from 0.666 Pa to 10.665 Pa.

34. The method of claim 21, wherein a pressure in the plasma chamber during patterning is 0.666 Pa.

35. The method of claim 21, wherein the temperature of the plasma during patterning is below 100° C.

36. The method of claim 21, wherein the temperature of the plasma during patterning is about 60° C.

37. The method of claim 21, wherein the plasma consists of a boron-halogen compound and nitrogen, and wherein from 5% to 10% of the total plasma composition is nitrogen.

38. The method of claim 21, wherein the plasma consists of a boron-halogen compound and nitrogen, and wherein less than 10% of the total plasma composition is nitrogen.

39. The method of a claim 21, wherein the plasma consists of a boron-halogen compound and nitrogen, and wherein less than 8% of the total plasma composition is nitrogen.

40. The method of claim 21, wherein the plasma is a BCl₃plasma wherein 5% of the total plasma composition is nitrogen.