Patent Application
20050255714
1. Field of the Invention
Embodiments of the invention generally relate to methods for depositing materials containing silicon (Si) and nitrogen (N), and more particularly, embodiments of the invention relate to chemical vapor deposition techniques for thermally depositing SiN materials.
2. Description of the Related Art
Thermal chemical vapor deposition (CVD) of silicon-containing films, such as silicon nitride, is a state of the art, front end process used during semiconductor device manufacturing. For example, in a thermal CVD process for depositing silicon nitride, thermal energy is utilized for breaking one or more feedstock chemicals, which includes a silicon precursor, to make a thin film of a silicon nitride on a substrate surface. Conventional thermal CVD of SiN-containing materials is typically performed in a batch furnace or in a single wafer deposition chamber operating at elevated processing temperatures. As device geometries shrink to enable faster integrated circuits, the thermal budget for deposited films must be reduced in order to obtain avoid device damage, satisfactory processing results, good production yield and robust device performance. Although some CVD processes for SiN-containing materials having deposition temperatures less than 650 degrees Celsius have been proposed, no thermal-only (i.e., no plasma or photon assisted processes) have exhibited production worthiness suitable for large scale utilization in semiconductor device fabrication.
Thus, there is a need for a method of depositing SiN-containing materials, such as silicon nitride and silicon oxynitride, at a temperature less than about 650 degrees Celsius.
Embodiments of the invention generally provide a method for depositing a film containing silicon (Si) and nitrogen (N). In one embodiment, a method for depositing a SiN-containing layer on a substrate includes heating a substrate disposed in a processing chamber to a temperature less than about 650 degrees Celsius, flowing a nitrogen-containing gas into the processing chamber, flowing a silicon-containing gas into the processing chamber, and depositing a SiN-containing layer on a substrate. The silicon-containing gas is at least one of a gas identified as NR2—Si(R′2)—Si(R′2)—NR2 (amino(di)silanes), R3—Si—N═N═N (silyl azides), R′3—Si—NR—NR2 (silyl hydrazines) or 1,3,4,5,7,8-hexamethytetrasiliazane, wherein R and R′ comprise at least one functional group selected from the group of a halogen, an organic group having one or more double bonds, an organic group having one or more triple bonds, an aliphatic alkyl group, a cyclical alkyl group, an aromatic group, an organosilicon group, an alkyamino group, or a cyclic group containing N or Si.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical 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.
FIGS. 3A-B are cross sectional views of a MOSFET transistor having a silicon nitride layer at least partially deposited according to the method of
To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. It is contemplated that some elements of one embodiment may be beneficially incorporated in other embodiments.
Embodiments of the invention provide a method for depositing a silicon-containing layer, such as silicon nitride and the like, on a substrate utilizing temperatures less than about 650 degrees Celsius. Although the invention is described with reference to a single wafer thermal-chemical vapor deposition (processing) chamber 100 illustrated in
Besides thermal-CVD, other useful processes to deposit silicon nitride materials include pulsed-CVD and atomic layer deposition (ALD). During a pulsed-CVD process, reagents, such as a silicon precursor and a reactant, are co-flowed and pulsed into the process chamber. During an ALD process, reagents, such as a silicon precursor and a reactant, are individually and sequentially pulsed into the process chamber. Plasma enhanced deposition techniques may be used during either ALD or CVD processes. SiN-containing materials may be deposited to a single substrate or a batch of substrates during the deposition processes described herein.
In the embodiment of
A substrate support pedestal 124 is disposed in the internal volume 104 of the chamber body 102 and supports the substrate 122 during processing. The substrate support pedestal 124 includes a heater 120 configured to regulate the temperature of the substrate 122 and/or heat the interior volume 104 of the processing chamber 100. In the embodiment depicted in
A pedestal lift assembly 130 is coupled to the substrate support pedestal 124 and is configured to control the elevation of the pedestal 124 between an elevated processing position (as shown in
The gas panel 136 is coupled to the processing chamber 100 and is configured to provide process and other gases to the internal volume 124 of the chamber body. In the embodiment depicted in
A showerhead 144 is coupled to the chamber body 102 to enhance the uniform distribution of gases provided by the gas panel 136 into the internal volume 104 of the processing chamber 100. The showerhead 144 includes a perforated region 154. The holes formed in the perforated region 154 are configured in size, geometry, number and distribution as to provide a predefined flow distribution of gases passing through the showerhead 144 to the substrate 122.
Lift pins 114 (of which one is shown in
The pumping system 138 is coupled to a pumping port 126 formed in the chamber body 102. The pumping system 138 generally includes a throttle valve and one or more pumps arranged to control the pressure within the internal volume 104 of the processing chamber 100. Gases flowing from the internal volume 104 to the pumping port 126 may be routed through a pumping ring 142 to enhance gas flow uniformity across the surface of the substrate 122. One pumping ring which may be adapted to benefit from the invention is described in U.S. patent Ser. No. 10/911,208, filed Oct. 4, 2004, which is hereby incorporated by reference in its entirety.
The controller 146 is coupled to the various components of the processing chamber 100 to facilitate control of a silicon nitride deposition process as described below. The controller 146 generally includes a central processing unit (CPU) 150, a memory 148, and support circuits 152. The CPU 150 may be one of any form of computer processor that can be used in an industrial setting for controlling various chambers and sub processors. The memory 148, or computer readable medium, may be one or more of readily available memory, such as random access memories (RAM), read-only memory (ROM), floppy disk, hard drive, flash memory, or any other form of digital storage, local or remote. The support circuits 152 are coupled to the CPU 150 for supporting the processor in a conventional manner. These support circuits 152 include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. A process, for example, a silicon-containing material deposition process 200 described below, is generally stored in the memory 148, typically 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 150. Although the deposition process of the present invention is described as being implemented as a software routine, some of the method steps that are disclosed therein may be performed in hardware as well as by the software controller. As such, the invention may be implemented in software as executed upon a system computer, in hardware as an application specific integrated circuit or other type of hardware implementation, or a combination of software and hardware.
At step 204, the substrate 122 is heated to a temperature less than about 650 degrees Celsius. In one embodiment, the substrate 122 is heated by applying power from the power source 116 to the resistive heating element (i.e., the heater 120) to heat the substrate 122 to a temperature between about 400 and about 650 degrees Celsius, and in yet another embodiment, the substrate 122 is heated to less than about 600 degrees Celsius.
At step 206, a flow of nitrogen-containing gas from the gas panel 136 is provided to the interior volume of the processing chamber 100 through the showerhead 144. The nitrogen-containing gas is generally provided from the gas panel 136 to the inlet 104.
Examples of suitable nitrogen-containing gases include, but are not limited to ammonia (NH3), hydrazine N2H4), hydrogen azide HN3, and combinations thereof. The nitrogen-containing gas ideally contains a nitrogen-nitrogen single bond (i.e., N—N single bond) for decomposition of the nitrogen source gas at low temperatures. Additionally, when a Si-source gas and a nitrogen-containing gas are used in the process gas mix, some amount of a nitrogen source gas may be included in the gas mix for additional control over the composition of the deposited layer during deposition. In one embodiment, the nitrogen-containing gas is NH3.
At step 208, a flow of Si-source gas is provided to the interior volume 104 of the chamber body 102 through the showerhead 144 from the gas panel 136. Although one gas line 140 is shown disposed between the gas panel 136 and the inlet port 134, it is contemplated that the Si-source gas and the nitrogen-containing gas are provided to the processing chamber 100 in separate gas lines. It is also contemplated that the gas lines may be temperature controlled. It is further also contemplated that the nitrogen-containing gas in step 206 together with Si-source gas in step 208 can be introduced to inlet port 134 simultaneously, or in either step 206 or step 208, or step 206 can be ahead of step 208, and vice versa. Furthermore, step 206 and step 208 can be programmed in such way the chemical dosing time can be designed to ensure atomic layer coverage and enough purge between each step with desirable inert gases such as argon.
Si-source gases that can be used to produce a silicon nitride layer by thermal chemical vapor deposition at sufficiently high deposition rates at a low temperatures include compounds having one or more Si—N bonds or Si—Cl bonds, such as bis-tertbutylaminosilane (BTBAS) or hexachlorodisilane (HCD or Si2Cl6). While Cl is discussed herein, other halogens such as Fi, I, and others, can substitute Cl. Further inclusion of Si—Si bonds, N—N bonds, N═N bonds, a mixture of Si—N and Si—Cl bonds, or combinations thereof, in the precursor is may be beneficial in certain embodiments.
Combination of a Si—Cl functional group (bond) and a Si—N functional group (bond) has been observed to improved step coverage and microloading especially for the ever decreasing temperatures at suitable deposition rates. The number of Si—Cl groups can be varied relative to the number of Si—N groups. The Si—Cl and S—N bonds appear to have different effects on layer properties and deposition properties, and the ratio of Si—N to and S—Cl bonds can be used to balance layer properties and deposition properties.
Compounds having preferred bond structures described above have the generic structures:
In the above generic structures, R and R′ comprise one or more functional groups selected from the group of a halogen, an organic group having one or more double bonds, an organic group having one or more triple bonds, an aliphatic alkyl group, a cyclical alkyl group, an aromatic group, an organosilicon group, an alkyamino group, or a cyclic group containing N or Si, and combinations thereof.
Examples of suitable functional groups include chloro (Cl−), methyl (—CH3), ethyl (—CH2CH3), isopropyl, trimethylsilyl, pyrrolidine, and combinations thereof. Examples of suitable compounds include:
It is believed that silicon source gas (precursor) or the silicon and nitrogen source gas (precursor) having a silicon to silicon single bond (i.e., Si—Si single bond) enables the molecule to decompose or disassociate at reduced temperatures, such as about 550° C. or less.
Other examples of suitable Si-source gases include silyl azides R3—SiN3 and silyl hydrazine class of precursors R3SiNR—NR2, linear and cyclic with any combination of R groups. The R groups may be H or any organic functional group such as methyl, ethyl, propyl, butyl, and the like (CXHY). The R groups attached to Si can optionally be another amino group NH2 or NR2. One benefit of using this Si-source gas is that silicon and nitrogen are simultaneously delivered while avoiding the presence of chlorine to yield films with good step coverage and minimal pattern dependence (so-called pattern loading) without the undesirable ammonium chloride particle formation problematic to other conventions Si—N film precursors.
It is noted that an N—N bond also exists in hydrogen azide, hydrazine, and methyl hydrazine, and CVD deposition of SiN-containing films performed. However, addition of a separate Si-source is required for these latter precursors, and low temperature silicon sources such as disilane show poor step coverage and high pattern loading while hexachlorodisilane (HCD) is plagued with ammonium chloride particle issues. Noting that aminosilanes, such as BTBAS, show minimal pattern loading and good step coverage with no ammonium chloride concerns, the delivery of the intact Si—N unit appears to be a requisite. However, aminosilanes generally require processing temperatures well in excess 600 degrees Celsius to have acceptable deposition rates. The solution to meet all the requirements is to utilize a precursor that contains both of the critical features—the weak N—N bond and the aminosilane functionality Si—N— for low temperature decomposition.
Examples of specific silyl azides include trimethylsilylazide (available commercially from United Chemical Technologies, located in Bristol, Pa.) and tris-dimethylamino-silyl azide. Examples of specific silylhydrazines include (CH3)2HSiNH—N)CH3)2.
As the Si-source gas and the nitrogen-containing gas are combined in the substrate processing chamber 100, a silicon-containing material, such as a silicon nitride (Si3N4) film, is formed on the heated substrate 122. Despite the delivery of nitrogen from the Si-containing gas to the reaction zone within the interior volume, the Si-containing gas is mixed with the nitrogen-containing gas since the incorporation efficiencies for Si and N into the deposited SiN-containing film have different kinetic barriers. The deposited silicon-containing material exhibit good film qualities such as reflective index and wet etch rate, and deposition rates greater than 5 Å/min. In one embodiment, the silicon-containing film is deposited at a rate from about 10 Å/min to about 500 Å/min and is deposited to a thickness from about 10 Å to about 1,000 Å. The silicon-containing film formed as described above exhibits low hydrogen content and includes a small amount of carbon doping, which enhances boron retention in PMOS devices. In embodiments where a halogen-free Si-source gas is utilized, improved wet etch rate may be realized.
Stoichiometric silicon nitride films made utilizing the method 200 generally contain less than about 30 percent carbon (C) through potentially still greater than about 10 percent hydrogen (H) depending on temperature and choice of the R groups. Films deposited using the method 200 are additionally suitable for further post-processing treatments to lower the percent hydrogen, if desired. For example, hydrogen radicals may be introduced into the chamber utilized to reduce the hydrogen content of the deposited SiN-containing film. Hydrogen radicals may be produced using a remote plasma source, hot wire catalytic decomposition or other suitable method, One post-processing treatment is described in the previously incorporated U.S. patent application Ser. No. 10/741,417, filed Dec. 19, 2003 by S. Wang et al. Post-processing of films deposited using the method 200 may be optionally performed on any of the embodiments described herein.
A carrier gas may be provided at step 206 and/or step 208 to control the partial pressure of the nitrogen gas and/or the Si-source containing gas from a few mTorr to a few hundred Torr, and to control the total process pressure from about 1 Torr to about 760 Torr in single wafer chambers. In another embodiment, pressure in the processing chamber is between about 10 and 350 Torr. The carrier gas may be provided to control the partial pressure of the Si-source gas and/or the nitrogen and carbon containing gas from about 100 mTorr to about 1 Torr pressure in batch processing systems. Examples of suitable carrier gases include N2, Ar and He, among others.
Optionally, an oxygen precursor may be added to the deposition method 200, typically at step 204 and/or step 206, to form silicon oxide or silicon oxynitride. Oxygen precursors that may be used in the deposition processes described herein include atomic oxygen, oxygen (O2), ozone (O3), H2O, H2O2, organic peroxides, alcohols, N2O, NO, NO2, N2O5, derivatives thereof and combinations thereof. It is contemplated that use of carrier gases and/or oxygen precursors may be optionally performed on any of the embodiments described herein.
In another embodiment of the method 200, the Si-containing gas is an aminochlorodisilane class of precursors having a formula (R2N)x—Si(CL)3-x—Si(Cl)3-x—(NR2)x, wherein x is 1 or 2, and the R group may be any combination of organic alkyl groups such as methyl, ethyl, isopropyl, and the like. The Si-containing gas of this type is unique that it contains an N—Si—Si—N chain with the Si—Si bond being weak enough to permit facile thermal delivery of a Si—N unit for deposition of a Si—N containing film with deposition rates in excess of 40 Å/min and low activation energy.
The Si-containing gas, such as aminochlorodisilane class of precursors, is unique in that nitrogen is simultaneously delivered while still providing some necessary chlorine to yield films with good step coverage and minimal pattern dependence. The reduced chlorine in the precursor translates to substantial reduction in the undesirable ammonium chloride particle formation compared to other conventional SiN precursors.
Si-containing gas of the aminochlorodisilane class of precursors delivers lower carbon content into the deposited SiN film compared to alkylchlorodisilanes Rx—Si(Cl)3-x—Si(Cl)3-x—Rx, when no direct Si—C bond exists. The Si bonds are instead bonded in the form of the more important Si—N. While the N's, in turn, are bonded to C's, the N—C bond is weaker than the Si—C bond.
Two embodiments of a method 200 performed using aminochlorodisilanes as the Si-containing gas is described as follows. In a first embodiment performed in the processing chamber 100 described above, the method 200 includes heating the substrate 122 at step 202 to a temperature between about 400 and about 650 degrees Celsius, for example less than about 600 degrees Celsius. In another embodiment, the substrate is heated to less than about 500 degrees Celsius. A Si-source gas, for example, an aminochlorodisilane, is provided to the processing chamber 100 at step 204 at a rate between about 0.2 to about 1.0 grams/minute (g/m). In another example, the Si-source gas is provided at about 0.5 g/m. The spacing between the pedestal and showerhead is generally set to between about 500 to about 1000 mils. A nitrogen-containing gas, for example, NH3, is provided to the processing chamber 100 at step 206 and combines with the Si-containing gas. The nitrogen-containing gas is delivered at a rate about 10 times greater than the rate of the Si-containing gas. For example, a ratio of NH3 to Si-containing gas is in the range of about 1:100 to about 100:1. The chamber pressure is generally maintained in the range of about 10 to about 300 Torr, for example, between about 50 to about 100 Torr. Performance of this embodiment of the method 200 generally results in a SiN deposition rate of between about 60 to about 200 Å/min, for example, about 100 Å/min.
In a second embodiment of the method 200 suitable for depositing a SiN-containing film in a batch furnace, the method 200 includes heating the substrate 122 at step 202 to a temperature between about 400 and about 650 degrees Celsius, for example less than about 600 degrees Celsius. In another example, the substrate 122 is heated to less than about 500 degrees Celsius. The nitrogen-containing gas, such as NH3, is provided to the processing chamber 100 at step 206 and combines with the Si-containing gas. The nitrogen-containing gas is delivered at a rate about 10 times less than the rate of the Si-containing gas, which is generally dependent on the furnace tube volume. For example, a ratio of NH3 to Si-containing gas is in the range of about 5:1 to about 1:1. The furnace pressure is generally maintained in the range of about 0.1 to about 2.0 Torr, for example, between about 0.4 to about 1.0 Torr. Performance of this embodiment of the method 200 generally results in a SiN deposition rate of between about 5 to about 20 Å/min, for example, about 12 Å/min.
In another example of using other Si-containing gases to perform the method 200, a Si-containing gas comprised of 1,3,4,5,7,8-hexamethytetrasiliazane may be utilized to deposit a SiN-containing film. The 1,3,4,5,7,8-hexamethytetrasiliazane precursor is unique in that it contains alternating N—Si bond in a chain with each Si atom not fully terminated with a methyl group, thus leaving active Si—H bonds as well as two basic N—H groups that can react with Si—H (for example, other two N's are N-methyl groups). This structure permits the facile thermal delivery of Si—N units for deposition of a SiN-containing film with fast deposition rates in excess of about 40 Å/min with low activation energy.
In the above embodiments and examples, while Si-containing gas is described as being introduced first followed by N-containing gas, it should be appreciated that the sequence of introduction of the Si-containing gas and N-containing can be reversed for certain applications.
1,3,4,5,7,8-hexamethytetrasiliazane precursor falls in the general class of compounds called silazanes, which also have an alternating N—Si chain. Silazanes are commonly used in the manufacture of SiN ceramic components via high temperature pyrolysis (e.g., at temperatures in excess of 1000 degrees Celsius). Pyrolysis of silazanes at lower temperatures generally leaves at least about 20 percent carbon in the ceramic material (and typically about 50 percent in the by-product). Thus, silazanes are better known in the CVD community for the deposition of SixCyNz films either at thermally high temperatures or using plasma enhancement.
Two unique aspects of this invention are the choice of 1,3,4,5,7,8-hexamethytetrasiliazane as the Si-containing gas and the addition of large amounts of NH3. This combination results in both low carbon content for films deposited at high rates despite the low temperatures, e.g., at temperatures less than about 600 degrees Celsius. The compound 1,3,4,5,7,8 hexamethyltetrasilazane is unique in the silazane class in that each Si is not fully terminated with a methyl group, thus leaving active Si—H bonds as well as two basic nitrogens N—H that can react with Si—H (other two N's are N-methyl). Furthermore, lower C to Si/N ratios are present in this compound compared to the more common silazanes. The compound 1,3,4,5,7,8 hexamethyltetrasilazane is available commercially from United Chemical Technologies, located in Bristol, Pa.
SiN-containing materials are deposited utilizing the method 200 described above are used throughout electronic features/devices due to several physical properties. SiN-containing materials are electric insulators, as well as barrier materials. The barrier properties inhibit ion diffusion between dissimilar materials or elements when silicon-containing material is placed therebetween, such as a gate material and an electrode or between a low dielectric constant porous materials and copper. Therefore, SiN-containing materials may be used in barrier layers, protective layers, off-set layers, spacer layers and capping layers. Another physical property of silicon nitride materials is a high degree of hardness. In some applications, SiN-containing materials may be used as a protective coating for various optical devices as well as tools. Yet another physical property of silicon-containing material such as silicon nitride is etch selectivity to silicon oxide, i.e., silicon nitride can be used as etch stop layer under a silicon oxide dielectric layer to accurately control etch depth without over etching or under etching. Yet another physical property of silicon-nitrogen-containing materials contains carbon and hydrogen and carbon and hydrogen concentration can be used to tune film stress such as high tensile stress for desirable application.
In some embodiments, silicon nitride materials may be deposited as various layers in MOSFET and bipolar transistors as depicted in FIGS. 3A-B and 4. For example,
In another embodiment,
Thus, a method for depositing a silicon-containing layer, such as silicon nitride, has been provided. The method described above is suitable for device fabrication having small critical dimensions requiring low thermal budgets due to the use of deposition temperatures less than about 650 degrees Celsius, which advantageously facilitates robust circuit fabrication using sub 90 nm technology. Although the foregoing embodiments were described using temperatures below 650 degrees Celsius, it is contemplated that for some applications of the invention, the substrate and its circuits are resilient to higher temperatures. As such, the forgoing embodiments may find application in processes that use temperatures in excess of 650 degrees Celsius.
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.
This application is a continuation-in-part of U.S. patent application Ser. No. 10/741,417, filed Dec. 19, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 10/327,467, filed Dec. 20, 2002 that claims benefit of U.S. Provisional Patent Application Ser. No. 60/435,813, filed Dec. 20, 2002, all of which are herein incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 60435813 | Dec 2002 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10741417 | Dec 2003 | US |
| Child | 11152501 | Jun 2005 | US |
| Parent | 10327467 | Dec 2002 | US |
| Child | 10741417 | Dec 2003 | US |
