CN101847570B - Selective etching and formation of xenon difluoride - Google Patents

Abstract

This invention relates to the selective etching and formation of xenon difluoride. In particular, it is related to the use of silicon dioxide, silicon nitride, nickel, aluminum, TiNi alloy, photoresist, phosphosilicate glass, borophosphosilicate glass, polyimide, gold, copper, platinum, Chromium, Aluminum Oxide, Silicon Carbide and their mixtures Process for the selective removal of materials such as silicon, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, tantalum, niobium, boron, phosphorus, germanium, arsenic and their mixtures. This process is relevant for important applications such as cleaning or etching processes for semiconductor deposition chambers and semiconductor tools, devices in microelectromechanical systems (MEMS), and ion implantation systems. The present invention also provides a process for forming _XeF2 by reacting Xe _with a fluorinated chemical selected from the group consisting of _F2 , _NF3 , _C2F6 , _{CF4 , C3F8} , SF _6. F atom-containing plasmas and mixtures thereof generated from an upstream plasma generator.

Description

Selective Etching and Formation of Xenon Difluoride

Cross References to Related Applications

This application is a continuation-in-part of U.S. Patent Application Serial No. 11/285,056, filed November 22, 2005, entitled "SELECTIVE ETCHING OFTITANIUM NITRIDE WITH XENON DIFLUORIDE."

technical field

This invention relates to the selective etching and formation of xenon difluoride.

Background technique

Various deposition techniques have been developed in the electronics industry in which selected materials are deposited on a target substrate to fabricate electronic components such as semiconductors. One deposition process is chemical vapor deposition (CVD), in which gaseous reactants are introduced into a heated process chamber to obtain a film deposited on a desired substrate. A subtype of CVD is known as plasma enhanced CVD (PECVD), in which a plasma is established in a CVD process chamber.

In general, all deposition methods result in accumulation of film and particulate material on surfaces other than the target substrate, ie, deposition material also accumulates on walls, tool surfaces, susceptors and other equipment used in the deposition process. Any material, film, etc. that collects on walls, tool surfaces, bases, and other equipment is considered a contaminant and can lead to defects in electronic product components.

It is generally accepted that deposition chambers, tools and equipment must be cleaned periodically to remove unwanted contaminating deposition materials. A generally preferred method _of cleaning deposition chambers, _tools and equipment involves the use of perfluorinated compounds (PFCs) such as _C2F6 , _CF4 , _C3F8 , _SF6 and _NF3 as etchant cleaners. During these cleaning operations, chemically active fluorine species normally carried by the process gas convert unwanted polluting residues into volatile products. The volatile products are then purged out of the reactor by the process gas.

Ion implantation is used in integrated circuit fabrication to introduce precisely controlled amounts of dopant impurities into semiconductor wafers and is an important process in microelectronics/semiconductor production. In an ideal situation, all the feedstock molecules would be ionized and extracted, but in practice a certain amount of feedstock decomposition occurs, which results in the surface in the area of the ion source, or the components of the ion implantation tool, such as low voltage insulators and high voltage components deposition and contamination on the Known contaminating residues are silicon, boron, phosphorus, germanium or arsenic. What would be an important advancement in the field of ion implantation is the provision of an in-situ cleaning process for the efficient and selective removal of unwanted debris deposited throughout the implanter during implantation, particularly in the ion source region. This cleaning in place enhances worker safety and facilitates stable, continuous operation of the injection equipment. Introducing a gas phase reactive halide composition such as _XeF2 , _NF3 , _F2 , XeF6, _{SF6 , C2F6 ,} IFs or IF7 to the contaminated component for a sufficient time and under sufficient conditions to Debris is at least partially removed from the component and is done in such a way that the debris is selectively removed with respect to the material from which the component of the ion implanter is constructed.

In Micro Electro Mechanical Systems (MEMS), a mixture of a sacrificial layer (often with amorphous silicon) and a protective layer is formed, thereby forming the device structural layers. Selective removal of this sacrificial material is a critical step for the structure release etching process, where microns of sacrificial material need to be removed isotropically without damaging other structures. It is understood that the etch process is a selective etch process that does not etch the protective layer. Typical sacrificial materials used in MEMS are: silicon, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, tantalum, niobium. The curved protection material is nickel, aluminum, photoresist, silicon oxide, silicon nitride.

For efficient removal of the sacrificial material, release etching uses an etchant gas that enables spontaneous chemical etching of the sacrificial layer, preferably an isotropic etch that removes the sacrificial layer. Because xenon difluoride has a strong isotropic etching effect, xenon difluoride (XeF ₂ ) is used as an etchant for the lateral etching process.

However, xenon difluoride is expensive and a difficult material to handle. Xenon difluoride is unstable in contact with air, light, or water vapor (humidity). All xenon fluoride must be protected from moisture, light and air to avoid the formation of xenon trioxide and hydrogen fluoride. Xenon trioxide is a dangerous explosive colorless, non-volatile solid. Hydrogen fluoride is not only dangerous but also reduces etching efficiency.

Furthermore, xenon difluoride is a solid with a low vapor pressure, which makes it difficult to transport xenon difluoride to the processing chamber.

The following references exemplify methods used in film deposition in semiconductor production, as well as cleaning of deposition chambers, tools, and equipment, and etching of substrates, etching of sacrificial layers in MEMS, and in the fabrication of microelectronic devices. Cleaning of the ion source area in ion implantation systems:

US 5,421,957 discloses a process for cryogenic cleaning of cold-walled CVD chambers. The process takes place in situ under moisture-free conditions. Cleaning of films of various materials such as epitaxial silicon, polycrystalline silicon, silicon nitride, silicon oxide and refractory metals, titanium, tungsten and their silicides using etchant gases such as nitrogen trifluoride, chlorine trifluoride, sulfur hexafluoride and carbon tetrafluoride to achieve.

US 6,051,052 discloses anisotropic etching of conductor materials in an ion-enhanced plasma _using fluorine compounds such as _NF3 and _C2F6 as etchant. The etchant consists of a fluorine-containing chemical and a noble gas selected from He, Ar, Xe and Kr. The test substrate includes an integrated circuit attached to the substrate. In one embodiment, a titanium layer is formed on the insulating layer and in contact with a tungsten plug. Then, an aluminum-copper alloy layer was formed over the titanium layer, and a titanium nitride layer was formed thereon.

US 2003/0047691 discloses the use of electron beam processing to etch or deposit material or to repair defects in lithography masks. In one embodiment, xenon difluoride is activated by electron beams to etch tungsten and tantalum nitride.

GB 2,183,204A discloses the use of _NF3 for in-situ cleaning of CVD deposition hardware, boats, tubes and quartz vessels, and semiconductor wafers. NF ₃ is introduced into the heated reactor above 350° C. for a sufficient time to remove silicon nitride, polysilicon, titanium silicide, tungsten silicide, refractory metals, and silicides.

Holt, JR etc., Comparison of the Interactions of XeF ₂ and F ₂ withSi(100)(2X1), J.Phys.Chem.B 2002,106,8399-8406 disclosed that XeF ₂ and Si(100)( 2X1) and a comparison with _F2 is provided. _XeF2 was found to react rapidly and isotropically with Si at room temperature.

Chang, FI, Gas-Phase Silicon Micromachining With Xenon Difluoride, SPIE Vol.2641/117-127 discloses the use of _XeF as a gas-phase, room-temperature, isotropic silicon etchant, and points out that it is useful for many microelectromechanical systems. Materials such as aluminum, photoresist, and silicon dioxide are highly selective. It also states on page 119 that _XeF2 has greater than 1000:1 selectivity to silicon dioxide as well as copper, gold, titanium-nickel alloys and acrylic when patterned on silicon substrates.

Isaac, WC et al., Gas Phase Pulse Etching of Silicon For MEMS With Xenon Difluoride, 1999 IEEE, 1637-1642 disclose the use of _XeF2 as an isotropic gas phase etchant for silicon. _XeF2 has been reported to be highly selective to many metals, dielectrics and polymers in integrated circuit fabrication. The author also states on page 1637 that _XeF2 does not etch aluminum, chromium, titanium nitride, tungsten, silicon dioxide, and silicon carbide. Significant etching was also observed for molybdenum:silicon; and titanium:silicon, respectively.

Winters et al., The Etching of Silicon With XeF ₂ Vapor, Appl. Phys. Lett. ₃₄ (1) January 1, 1979, 70-73 discloses F atoms and _CF3 groups to etch solid silicon to produce volatile _SiF4 species. This paper resorts to utilizing XeF ₂ to etch silicon at 300K at 1.4×10 ⁻² Torr. Other experiments have shown that _XeF2 also rapidly etches molybdenum, titanium and perhaps tungsten. Etching of SiO ₂ , Si ₃ N ₄ and SiC is not efficient with XeF ₂ but is effective in the presence of electron or ion bombardment. Therefore, the authors conclude that the etching of these materials requires not only F atoms but also radiation or high temperature.

Both US 6870654 and US 7078293 disclose structure release etching processes which avoid the difficulties caused by the use of xenon difluoride by using etchant having fluorine or chlorine groups instead of xenon difluoride. However, the etching effect is not as effective as when xenon difluoride is used. Therefore, US 6870654 and US 7078293 disclose special structures for facilitating the structure release etching process so that processing times etc. are comparable to those of xenon difluoride.

US 20060086376 discloses the use of _XeF2 to clean debris (silicon, boron, phosphorous, germanium or arsenic) from components of an ion implanter in the manufacture of microelectronic devices.

Specifically, US 20060086376 relates to the in situ removal of residues from vacuum chambers and components contained therein by contacting said vacuum chambers and/or components with a gas-phase reactive halide composition such as _XeF for a sufficient time and at The conditions are sufficient to at least partially remove the debris from the component, and in such a manner that the debris is selectively removed with respect to the material from which the component of the ion implanter is constructed.

An industrial goal is to find new etchants that can be used to remove difficult-to-remove titanium nitride (TiN) films from silicon dioxide ( _SiO2 ) and silicon nitride (SiN) coated surfaces. Such surfaces are found in semiconductor deposition chambers, especially quartz chambers and walls of quartz vessels, semiconductor tools and equipment. Many conventional fluorine-based etchants that attack TiN films also attack _SiO2 and SiN surfaces and are therefore unacceptable for use in removing TiN deposition products from semiconductor deposition chambers and equipment.

Another industrial objective is to provide methods for the selective removal of silicon from silicon dioxide (quartz) surfaces such as those commonly found in semiconductor deposition chambers and semiconductor tools and devices in MEMS.

Yet another industry object is to provide a method for on site production or formation of xenon difluoride as desired to reduce the cost of ownership.

Contents of the invention

The present invention relates to an improved process for the selective removal of nitrogen from silicon dioxide (quartz) surfaces such as those commonly found in semiconductor deposition chambers and semiconductor tools, and silicon nitride (SiN) surfaces commonly found in semiconductor tool components and the like Titanium oxide (TiN) films and deposition products. In the basic process of removing undesired constituents that contaminate a surface, an etchant is brought into contact with the undesired constituents at a contact zone and converts the undesired constituents into volatile species. The volatile species are then removed from the contact zone. An improvement in the basic process for removing undesired TiN deposition material from the surface selected from SiO ₂ and SiN in the contact region consists in using xenon difluoride (XeF ₂ ) as etchant. Conditions are controlled so that the surface selected from _SiO2 and SiN is not converted into volatile components.

Significant advantages for selectively etching TiN films and deposition materials that are difficult to remove from semiconductor deposition chambers (sometimes called reaction chambers), tool parts and equipment, etc. include:

Ability to selectively remove TiN films from quartz, i.e. SiO ₂ , and SiN coated surfaces found in cleaning of deposition chambers;

The ability to remove TiN films from quartz surfaces at moderate temperatures; and

The ability to activate a perfluorinated etchant in a remote plasma to remove TiN films from _SiO2 and SiN surfaces without the undesirable effects normally caused by attack of fluorine atoms in a remote plasma.

The present invention also discloses a process for selectively etching a first material relative to a second material, comprising:

providing a structure comprising a first material and a second material in the chamber;

providing an etchant gas comprising xenon (Xe), an inert gas, and a fluorine-containing chemical to the chamber;

contacting the structure with the etchant gas and selectively converting the first material to a volatile species; and

removing the volatile species from the chamber;

Wherein, the first material is selected from silicon, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, tantalum, niobium, boron, phosphorus, germanium, arsenic and mixtures thereof; and the second material is selected from silicon dioxide , silicon nitride, nickel, aluminum, TiNi alloy, photoresist, phosphosilicate glass, borophosphosilicate glass, polyimide, gold, copper, platinum, chromium, alumina, silicon carbide and their mixture.

The invention also discloses a process for forming xenon difluoride in a chamber comprising:

Providing the chamber with _a fluorine-containing chemical selected from the group consisting of _NF3 , _C2F6 , _CF4 , _C3F8 , _{SF6 ,} F atom-containing plasma generated from an upstream plasma generator, and mixtures thereof ;and

Xenon difluoride is formed by reacting xenon with the fluorine-containing chemical in the chamber.

Description of drawings

Figure 1 is a graph of the etch rate of a silicon substrate as a function of the concentration of Xe compared to Ar in a NF ₃ remote plasma, showing the effect of Xe addition on Si etching at various Xe/(Xe+Ar) ratios .

Figure 2 is a graph of the etch rate of _SiO2 as a function of the concentration of Xe compared to Ar in the _NF3 remote plasma, showing the effect of Xe addition on _SiO2 etching at various Xe/(Xe+Ar) ratios .

Figure 3 is a graph comparing the etch selectivity of silicon versus silicon dioxide as a function of Xe versus Ar concentration in a NF ₃ remote plasma, showing Xe addition at various Xe/(Xe+Ar) ratios Effect on Si/ _SiO2 selectivity.

Figure 4 is a graph of Fourier transform infrared spectroscopy (FTIR) spectra from Ar/NF ₃ and Xe/NF ₃ in a remote plasma of NF ₃ , showing the FTIP spectra from Ar/NF ₃ and Xe/NF ₃ .

Figure 5 is a Fourier Transform Infrared Spectroscopy (FTIR) spectrum from Xe/NF ₃ in a remote plasma of NF ₃ , showing the FTIP spectrum from Xe/NF ₃ .

Figure 6 is a graph of XeF ₂ and XeF ₄ Fourier Transform Infrared Spectroscopy (FTIR) peak heights as a function of Xe/(Xe+Ar) in the NF ₃ remote plasma, giving the XeF ₂ and XeF ₄ FTIR peak heights VSXe /(Xe+Ar).

Figure 7 is a graph of XeF ₂ and XeF ₄ Fourier Transform Infrared Spectroscopy (FTIR) peak heights as a function of the Xe/NF ₃ flow ratio in the NF ₃ remote plasma, giving the XeF ₂ and XeF ₄ FTIR peak heights vs Xe /NF ₃ Flow Ratio.

Figure 8 is a graph of XeF ₂ Fourier transform infrared spectroscopy (FTIR) peak heights and silicon relative to silicon dioxide etch selectivity as a function of Xe/(Xe+Ar) in a NF ₃ remote plasma, giving the XeF ₂ FTIR peak height vs etch selectivity.

Figure 9 is a graph of the etch rate of TiN as a function of temperature and Xe versus Ar concentration in the NF ₃ remote plasma, showing the effect of Xe addition on TiN etch at various substrate temperatures.

Figure 10 is a graph of the etch rate of silicon dioxide as a function of temperature and the concentration of Xe compared to Ar in the _NF3 remote plasma, showing the effect of Xe addition on _SiO2 etching at various substrate temperatures.

Figure 11 is a graph comparing the etch selectivity of TiN relative to SiO2 as a function of Xe relative to Ar concentration in a NF ₃ remote plasma, showing the effect of Xe addition on TiN/SiO ₂ at various substrate temperatures. Selective effects.

Detailed ways

The deposition of titanium nitride (TiN) is commonly practiced in the electronics industry in the manufacture of integrated circuits, electrical components, and the like. During the deposition process, some TiN is deposited on surfaces other than the target substrate surface, such as walls and surfaces within the deposition chamber. _XeF2 has been found to be effective as a selective etchant for TiN-contaminated silicon dioxide ( _SiO2 ) and silicon nitride (SiN) surfaces. Based on this discovery, one can use xenon difluoride (XeF ₂ ) as an etchant to remove unwanted TiN films and deposition material contamination of surfaces such as those found on surfaces coated or lined with silicon dioxide (quartz ) or those in semiconductor reactors or deposition chambers, tools, equipment, components and chips of silicon nitride.

When removing unwanted TiN residues from _SiO2 and SiN surfaces such as those in deposition chambers, in the contact zone there is a large amount of energy used to convert TiN to volatile _TiF4 and then remove this volatile species from the contact zone. The XeF ₂ is brought into contact with the surface under conditions. Often, _XeF2 is added together with inert gases such as _N2 , Ar, and He, among others.

In carrying out the process of removing the TiN deposited material from the SiN and _SiO2 surfaces, the _XeF2 can be pre-formed before being introduced into the contact area, or for the purposes of the present invention and as defined herein, the _XeF2 can be formed by two methods.

In one embodiment where _XeF2 is formed in situ, xenon (Xe) is added to the fluorine-containing chemical and loaded into a remote plasma generator. There, Xe reacts with F atoms present in the resulting remote plasma to form _XeF2 .

In another embodiment, a variation of the in-situ embodiment, the fluorine-containing chemical is added to the remote plasma generator, and then the Xe and F atom-containing remote plasma is added downstream of the remote plasma generator chamber. There, Xe reacts with F atoms to form _XeF2 in the chamber. The chamber may be any type of chamber such as, but not limited to, processing chambers, deposition chambers, cleaning chambers, reactors, and plasma generators.

Exemplary of the fluorinated chemicals used to form XeF ₂ include F ₂ , NF ₃ , perfluorocarbons such as C ₂ F ₆ , CF ₄ , C ₃ F ₈ , sulfur derivatives such as SF ₆ , and upstream plasma generated A remote plasma containing F atoms from a bulk generator. In a preferred embodiment, _NF3 is used as the fluorine-containing chemical used to form _XeF2 .

The fluorochemicals can be generated in situ. For example, a halogen generator is used to generate _F2 on-site and then introduce this _F2 into the process. This would be a possible means of mitigating the hazards associated with fluorine handling.

A wide range of Xe to fluorine-containing chemical ratios can be used in the in situ process of forming _XeF2 . The molar ratio of Xe to fluorine-containing chemical depends on the amount of _XeF2 formed compared to the concentration of F atoms in the remote plasma.

Without being bound by theory, it is believed that the remote plasma acts as a source for excitation and dissociation of the fluorine-containing chemical introduced as the fluorine source. The fluorine radicals then react with Xe present in the section immediately after the plasma generating section. In addition to the energy used to excite the fluorine-containing species and Xe, the path length of this segment is also considered to be an important parameter in balancing the preference for _XeF2 and the reduction of _XeF4 .

Furthermore, it is believed that if Xe is introduced into the space immediately after the plasma excitation section, this can lead to a further reduction in XeF ₄ formation since Xe has not been excited yet. Xenon is well known to have an extremely low metastable energy state. The formation of this metastable state can lead to additional collision reactions between _XeF2 molecules formed within this segment. These collisions can cause dissociation of _XeF2 into XeF and F groups. These species can then lead to further reactions with other _XeF2 molecules to form _XeF4 . Therefore, by introducing Xe after plasma excitation, a Xe metastable state is not formed. Therefore the formation of XeF ₄ will be reduced. This is disclosed in a second embodiment, a variation of the in situ embodiment, in which Xe is added to the remote plasma containing F atoms generated upstream of the plasma generator.

The preferred molar ratio of Xe to fluorochemical is 1:10 to 10:1. Optionally, an inert gas such as argon may be included in the remote plasma generation of XeF ₂ as a means of adjusting the selectivity of etching TiN versus SiO ₂ , SiN or Si versus SiO ₂ and SiN.

Suitable pressures for removing TiN from _SiO2 and SiN surfaces are 0.5 to 50 Torr, preferably 1 to 10 Torr. The temperature at which selective etching of TiN films from silicon dioxide surfaces (quartz) and SiN surfaces is achieved depends primarily on the method by which the process is carried out. Thus, this means that if the _XeF2 is pre-formed and added directly to the contact zone, the temperature should be raised to at least 100°C, eg 100 to 800°C, preferably 150 to 500°C. The pressure for _XeF2 should be at least 0.1 Torr, eg 0.1 to 20 Torr, preferably 0.2 to 10 Torr. Contrary to prior art processes where the etch rate (Si etch) decreases with increasing temperature, here the etch rate increases with increasing temperature. It is believed that this temperature increase increases the rate of TiN etching since _TiF4 is volatile and easily removed from _SiO2 and SiN surfaces under these conditions. The lower temperature makes TiF ₄ species remain near the surface of SiO ₂ and SiN, hindering the attack of XeF ₂ .

In the in situ process of forming _XeF2 , cleaning or etching is performed in the presence of a remote plasma. The temperature may be from ambient to 500°C in the presence of a remote plasma, preferably from ambient to 300°C.

The disclosed process for forming _XeF2 provides a significant advance over the in-situ cleaning process. Because, not only do they provide a process for making _XeF2 at low cost, they also provide efficient selective removal of unwanted residues without major downtime, thereby reducing maintenance costs. Additionally, the disclosed process uses high vapor pressure gases rather than low vapor pressure solids. This improves productivity due to higher gas flow and thus allows higher etch rates.

A further benefit stemming from the use of the disclosed process for forming _XeF2 is the provision in addition to _XeF2 of some free fluorine radicals that may help facilitate the removal of residues that may not react when only in contact with _XeF2 . This is beneficial for all selective cleaning/etching applications such as cleaning of components and semiconductor tools coated with _SiO2 with some unwanted residue deposited thereon; etching of sacrificial layers in MEMS, and in Debris cleaning in the ion source region of ion implantation systems used in the fabrication of microelectronic devices.

The following examples are provided to illustrate various embodiments of the invention without intending to limit the scope thereof.

Example 1

Efficacy of _XeF2 in the etching of deposited materials at various temperatures and pressures

In this example, using XeF ₂ as an etchant, the etching rates for TiN, SiO ₂ and SiN were measured at various temperatures and pressures. Test samples were prepared from silicon wafers coated with thin films of TiN, _SiO2 and SiN. The etch rate is calculated from the change in film thickness between the initial film thickness and the film thickness after timed exposure to etching or processing conditions.

To perform the etching, large volumes of _XeF gas were introduced from gas cylinders into the reactor chamber via a never-used remote plasma generator. The pressure of the _XeF2 gas in the reactor chamber was kept constant by shutting off the gas flow from the cylinder once the desired pressure was reached.

The test specimens were placed on the surface of a pedestal heater used to maintain different substrate temperatures. The results are shown in Table I below.

Table I

Etching rates for various materials using _XeF2

Material Temperature (°C) Pressure (Torr) Etching rate (nm/min) TiN 25 1 0 TiN 100 1 0 TiN 150 1 8 TiN 200 1 13 TiN 300 0.5 20 SiO ₂ 300 0.5 0 SiN 100 1 0 SiN 150 1 0 SiN 300 1 0

The above results indicate that under the pressure of 0.5 to 1 Torr, _XeF2 is effective in etching TiN films at elevated temperatures from 150 to 300 °C, but ineffective at room temperature of 25 °C. Surprisingly, _XeF2 did not etch _SiO2 or SiN surfaces at either of the temperatures and pressures employed, but did etch TiN films at these temperatures. Since XeF ₂ could not etch SiO ₂ and SiN surfaces, but did etch TiN films at these elevated temperatures, it was concluded that XeF ₂ could be used as a reagent to selectively etch TiN films and particles from SiO ₂ and SiN surfaces.

Example 2

Selective etching of silicon relative to _SiO2

In this example, a MKS Astron remote plasma generator was mounted on top of the reactor chamber. The distance between the outlet of the Astron generator and the sample specimen was approximately six inches. Turn on the remote plasma generator, but turn off the pedestal heater in the reactor chamber. The chamber was kept at room temperature. Etch rates were measured for both Si and _SiO2 substrates using remote plasma.

The process gas for the remote plasma was _NF3 and it was mixed with various amounts of the second gas stream. The second gas stream includes Xe, argon (Ar), or combinations thereof. The total gas flow rate to the reactor chamber was fixed at 400 seem and the NF ₃ flow rate was fixed at 80 seem. While maintaining the total flow rate of the second gas stream at 320 sccm, the ratio of the Xe flow rate to the total flow rate of the second gas stream (Xe/(Ar+Xe)) was at 0 (Ar only as the additional process gas) and 1 (only Xe as the additional process gas). The results of Si substrate etching are shown in Table 1, and the results of SiO ₂ substrate etching are shown in Table 2.

As shown in Figure 1, Xe added to the process gas NF ₃ increases the Si etch rate. Surprisingly, adding Xe to the remote plasma generator together with NF ₃ produces a plasma that enhances Si etching.

Figure 2 shows that the addition of Xe to the _NF3 /Argon plasma suppresses the _SiO2 substrate etch rate, which is surprising. F atoms present in remote plasmas usually attack _SiO2 -based substrates.

Along with the analysis of FIG. 1 , it is speculated that the addition of Xe to the plasma resulted in enhanced etching of Si substrates but, as noted in Example 1, reduced or inhibited etching of _SiO substrates.

Figure 3 is provided to compare the effect of adding Xe to the _NF3 process gas on the etch selectivity of Si versus _Si02 . As can be seen by comparing the results in Figures 1 and 2, Figure 3 shows that the etch selectivity of Si relative to _SiO increases with increasing amount of Xe in the process gas. In particular, the selectivity increases from 30 to 250 (>8-fold) as Xe increases from 0% to 100% in the gas stream.

The curved sacrificial materials in MEMS are: silicon, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, tantalum, niobium. The protective material of curved type is nickel, aluminum, photoresist, silicon oxide, silicon nitride.

Example 3

Selective etching of molybdenum (Mo) relative to _SiO2

A large cylindrical SS etch chamber 2.5 m long and 25 cm in diameter was used to determine the etch rate of another common sacrificial material in MEMS applications: molybdenum (Mo). A remote plasma was generated using a water-cooled MKS Astron AX76706 slpm unit. The plasma source was connected to the chamber by a 10 cm long delivery tube with an internal diameter of 4 cm. The sample was placed 2 feet from the load/unload end of the tube.

Mo etch rate = 1.1 microns/min at 2.75 Torr, NF ₃ flow 275 sccm and Xe or Ar flow 600 sccm. The etch rate of SiO ₂ was 82 nm/min for the NF ₃ /Ar gas mixture and 26 nm/min for the NF ₃ /Xe mixture. Therefore, the selectivity of the Xe/NF ₃ mixture is at least 3 times that of the Ar/NF ₃ mixture. Note that the Mo etch rate is limited by the surface oxide. The etch rate of Mo can be increased to >2.7 microns/minute with surface preparation treatments to destroy its native oxide.

Example 4

In situ formation of XeF ₂ via the reaction of Xe and NF ₃

In this embodiment, the steps of Embodiment 2 are followed. An Applied Materials P5000 DxZ2 PECVD chamber equipped with a 6 slpm MKS Astron eX remote plasma generator was used for Fourier transform infrared spectroscopy (FTIR) studies. FTIR measurements were performed downstream of the chamber pump at ambient pressure. A chamber with a path length of 5.6 m at 150°C was used. The instrument resolution is 2em ^-1 .

Figure 4 shows the FTIR spectrum collected under the same conditions as in Example 2: a pressure of 4 Torr, a total gas flow of 400 sccm, a NF flow of ₈₀ sccm, a total flow of Xe and Ar of 320 sccm. A clear and prominent peak was observed in the range of 500-600 cm ^-1 in the Xe/NF ₃ spectrum, while the Ar/NF ₃ spectrum showed no peak in this region. Two main fronts at 551.5cm ^-1 and 570.3cm ^-1 were identified as XeF ₂ peaks. The control spectrum from the XeF ₃ manufacturer shows peaks at 550.8 and 566.4 cm ⁻¹ .

Figure 5 shows that three distinct peaks were observed at 551, 570 and ⁵⁹⁰ cm in the presence of Xe and NF ₃ . XeF ₂ was identified by peaks at 551, 567 cm ⁻¹ , while XeF ₄ was detected at 580, 590 cm ⁻¹ . Thus the peak at 567 cm ^-1 is a combination of the 567 and 580 cm ^-1 peaks. So both XeF ₂ and XeF ₄ are formed in the Xe/NF ₃ mixture. No evidence of XeF ₆ or XeOF ₄ formation was found from the FTIR spectra.

Table II shows several conditions where the pressure was varied from 0.5 to 5 Torr, the Xe flow rate was varied from 200-1000 sccm, and the NF ₃ flow rate was varied from 50 to 500 sccm. In all cases, a XeF ₂ peak was detected. Peaks are recorded here.

Table II

Pressure (Torr) 0.5 4 5 2.75 5 2 NF ₃ (sccm) 50 80 200 275 50 500 Xe(sccm) 200 320 500 600 1000 1000 Peak (530.1cm ^-1 ) 0.06 0.07 0.16 0.22 0.09 0.33 Peak (570.3cm ^-1 ) 1.01 1.18 1.35 1.35 1.36 1.42 Peak (590cm ^-1 ) 0.43 0.43 1.63 1.42 0.18 1.58 Peak (603.1cm ^-1 ) 0.07 0.07 0.44 0.27 0.04 0.31

The peaks tend to saturate under some conditions, so the leading edge of the XeF ₂ peak at 520.1 cm ⁻¹ and the trailing edge of the XeF ₄ peak at 603.1 cm ⁻¹ were also analyzed. The XeF ₂ /XeF ₄ ratio is defined as the ratio of the peak height values at 530 cm ⁻¹ and 603 cm ⁻¹ .

The experimental results using response surface regression are summarized in Table III below.

Table III

Peak height 530.1 551.5 592 603.1 Ratio 603.1/530.1 meaning Frontier XeF ₂ signal XeF ₂ max XeF ₄ max trailing edge XeF ₄ signal XeF ₂ /XeF ₄ Xe weak middle weak weak Enhanced (strong up) NF ₃ powerful powerful powerful powerful strong down P weak middle powerful powerful strong down

Please note: the flux of Xe > the flux of NF ₃ in all conditions here, so NF ₃ is the stronger factor. Higher NF ₃ flux increases both the XeF ₂ and XeF ₄ peaks, with Xe having a weak effect on the peaks (due to the presence of excess Xe). Pressure has a weak effect on the XeF ₂ peak and a strong effect on the XeF ₄ peak. Astron working pressures are typically 1-10 Torr.

Therefore, pressure is a key parameter controlling the formation of _XeF4 . XeF ₄ can be hydrolyzed to produce XeO ₃ , which is an explosive and shock-sensitive compound. Under the current experimental conditions, the XeF ₂ /XeF ₄ ratio can be maximized under high Xe, low NF ₃ and low pressure conditions. For example, the flow rate of Xe is 1000 sccm, the flow rate of NF ₃ is 50 sccm, and the pressure is 0.5 Torr.

Figure 6 shows the XeF ₂ FTIR peak height and the XeF ₄ FTIR peak height as a function of Xe/(Xe+Ar). The unit of peak height is arbitrary. As the fraction of Xe flow increases, the fraction of XeF ₂ produced increases and the fraction of XeF ₄ decreases. A high Xe flux is desired to maximize the formation of _XeF2 relative to _XeF4 . Figure 7 shows the ratio of _XeF2 / _XeF4 FTIR peak heights as a function of the Xe/ _NF3 flow rate ratio. Clearly, a high ratio of Xe/NF ₃ is desired to maximize the formation of XeF ₂ relative to XeF ₄ .

Figure 8 shows the _XeF2 FTIR peak height (right Y-axis) and the etch selectivity of Si/ _SiO2 (left Y-axis) as a function of Xe/(Xe+Ar). The etch selectivity of Si/ _SiO2 is clearly related to the in situ formation of _XeF2 .

The use of plasma excitation to make _XeF2 can also be used to produce _XeF2 for use as an etchant in processes not directly related to where it is made. The data show that conditions exist that significantly favor the production of XeF ₂ and minimize the production of XeF ₄ . Due to the explosive nature of XeF ₄ if it subsequently reacts to form XeO ₃ , it is highly desirable to minimize XeF ₄ production. Since _XeF2 is formed in the reaction zone after the plasma generator, it can be removed from that zone by using cryogenic trapping to condense the material on cold surfaces. The solid _XeF2 can then be extracted from the process chamber and refilled into transfer cylinders for use in the etch process. Since excess xenon is introduced to reduce _XeF4 formation, it is very helpful to utilize xenon recovery or recycle xenon into the process to ensure productive use of all xenon required for _XeF2 production.

Example 5

Effects of Remote Plasma and Temperature on Etching Rates of TiN and _SiO2

In this example, except that both the remote plasma generator and susceptor heater were turned on to allow the remote plasma to be used at various substrate temperatures to determine etch rates for both TiN and _SiO2 , along the lines of The steps of embodiment 2.

In the first set of experiments, the etch rates of TiN and _SiO2 were measured using a mixture of _NF3 and Xe as the process gas. The flow rate of Xe was fixed at 320 sccm. The temperature varies between 100°C and 150°C. The results of these experiments are shown in Figs 9 and 10 as square dots for TiN and _SiO2 , respectively.

In a second set of experiments, the etch rates of TiN and _SiO2 were measured using a mixture of _NF3 and argon (Ar) as the process gas. The flow rate of Ar was fixed at 320 sccm. The temperature varies between 100°C and 150°C. The results of these experiments are shown in Figs 4 and 5 as diamond points for TiN and _SiO2 , respectively.

As shown in Figure 9, the addition of Xe to the process gas increases the TiN etch rate at temperatures generally above 130°C. Figure 10 shows that addition of Xe to NF ₃ suppresses the SiO ₂ etch rate at all temperatures studied compared to Ar addition to NF ₃ . The effect of Xe addition to the process gas on etch selectivity can be seen by comparing the results in FIGS. 9 and 10 .

Figure 11 shows the etch selectivity of TiN versus _SiO2 , and the graph shows that when Xe versus Ar is added to the _NF3 process gas, the TiN selectivity begins to increase at temperatures above about 110°C and rises above 120°C. increase rapidly at °C.

In summary, Example 1 shows that _XeF2 is a selective etchant for TiN films relative to silicon dioxide and silicon nitride substrates when the etching is performed at elevated temperatures.

Examples 2 and 3 show that adding Xe to the _NF3 process gas in the remote plasma generator (or reactor or chamber) can increase _the Si or the etch selectivity of Mo over _SiO2 .

Example 4 shows that when xenon and a fluorine-containing gas such as NF ₃ are introduced into the plasma generator (or reactor or chamber), the in situ formation of XeF ₂ is observed. Combining xenon with a fluorine-containing gas such as NF ₃ without using XeF ₂ directly in the cleaning process has economic advantages (ie, lower cost of ownership). A further benefit derived from using this disclosed process for forming _XeF is that they _provide , in addition to _XeF , some free fluorine radicals that help facilitate the removal of Not a reactive residue.

_Example 5 shows that the addition of Xe to the _NF3 process gas in the remote plasma can increase the etch selectivity of TiN relative to _SiO2 at high (elevated) temperatures compared to the etch selectivity when only NF3 is used as the process gas etch selectivity. The increased selectivity of TiN over _SiO2 is important in quartz tube furnace applications and is important for components and semiconductor tools coated with _SiO2 with TiN deposited thereon. The method can facilitate cleaning of the deposition reactor between deposition cycles by connecting a remote downstream plasma unit to the process reactor and feeding process gases. Combining xenon with a fluorine-containing gas such as NF ₃ without using XeF ₂ for the cleaning process has economic advantages (ie, lower cost of ownership).

The cleaning process described in the examples can also be used in off-line process reactors for the sole purpose of cleaning process reactor components before they are reused. Here, a remote downstream plasma reactor would be connected to an off-line process reactor where the components (elements from the deposition reactor) are placed. Xenon and a fluorine-containing gas such as _NF3 are then introduced into this remote downstream unit before the process gas is fed into the chamber containing the parts to be cleaned.

The increased selectivity of Si, Mo or TiN over _SiO , and the disclosed process of forming _XeF are important in many applications: such as cleaning coated SiO with unwanted Si, Mo or TiN deposition thereon ₂ components and semiconductor tools; etching of sacrificial layers in MEMS; and residue cleaning in the ion source region of ion implantation systems used in microelectronic device fabrication.

The application can be extended from Si ₃ N ₄ , Al, Al ₂ O ₃ , Au, Ga, Ni, Pt, Cu, Cr, TiNi alloy, SiC, photoresist, phosphosilicate glass, borophosphorous Silicate glass, polyimide, gold, copper, platinum, chromium, aluminum oxide, silicon carbide and their combinations, cleaning other unwanted materials such as: tungsten, titanium, zirconium, hafnium, vanadium, tantalum, niobium, Boron, phosphorus, germanium, arsenic and mixtures.

Claims (18)

1. A process for selectively etching a first material relative to a second material, comprising: providing a structure comprising a first material and a second material in the chamber; providing an etchant gas comprising xenon (Xe), an inert gas, and a fluorine-containing chemical to the chamber; contacting the structure with the etchant gas and selectively converting the first material to a volatile species; and removing the volatile species from the chamber; Wherein, the first material is selected from silicon, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, tantalum, niobium, boron, phosphorus, germanium, arsenic and mixtures thereof; and the second material is selected from silicon dioxide , silicon nitride, nickel, aluminum, TiNi alloy, photoresist, phosphosilicate glass, borophosphosilicate glass, polyimide, gold, copper, platinum, chromium, alumina, silicon carbide and their mixture. 2. The process of claim 1, wherein the fluorine containing chemical is _selected from the group consisting of _F2 , _NF3 , _C2F6 , _{CF4 , C3F8} , _SF6 , F containing Atomic plasmas and their mixtures. 3. The process of claim 1, wherein the fluorine-containing chemical is an F atom-containing plasma generated from an upstream plasma generator. 4. The process of claim 1, wherein the inert gas is selected from the group consisting of Xe, Ar, He and mixtures thereof. 5. The process of claim 1, wherein the chamber contains a remote plasma generator. 6. The process of claim 1, wherein the temperature in the chamber is from ambient to 500°C. 7. The process of claim 1, wherein the pressure in the chamber is from 0.1 to 10 Torr. 8. The process of claim 1, wherein the molar ratio of Xe to fluorochemical is from 1:10 to 10:1. 9. The process of claim 1, wherein the structure is a semiconductor device or a semiconductor processing chamber. 10. The process of claim 1, wherein the structure is a microelectromechanical device. 11. The process of claim 1, wherein the structure is an ion implanter tool in an ion implantation system. 12. A process for selectively etching silicon, molybdenum or silicon and molybdenum relative to silicon dioxide, silicon nitride or silicon dioxide and silicon nitride, comprising: providing a structure containing silicon, molybdenum, or silicon and molybdenum, and silicon dioxide, silicon nitride, or silicon dioxide and silicon nitride in the chamber; providing an etchant gas comprising xenon (Xe), an inert gas, and a fluorine-containing chemical to the chamber; contacting the structure with the etchant gas and selectively converting the silicon, molybdenum, or silicon and molybdenum into volatile species; and The volatile species are removed from the chamber. 13. The process of claim 12, wherein the fluorine-containing chemical is selected from the group consisting _{of F2, NF3, C2F6, CF4, C3F8 , SF6 , F - containing atoms} generated from an upstream plasma generator plasmas and their mixtures. 14. The process of claim 12, wherein the fluorine-containing chemical is an F atom-containing plasma generated from an upstream plasma generator. 15. The process of claim 12, wherein the inert gas is selected from the group consisting of Xe, Ar, He and mixtures thereof. 16. The process of claim 12, wherein the chamber contains a remote plasma generator. 17. The process of claim 12, wherein the structure is a semiconductor device or a semiconductor processing chamber. 18. The process of claim 12, wherein the structure is an ion implanter tool in an ion implantation system.

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