Patent Application
20060216548
The present invention generally relates to film deposition, and more particularly to a nanolaminate thin film and method for forming the same using atomic layer deposition.
Atomic layer deposition (ALD), also known as sequential pulsed chemical vapor deposition (SP-CVD), atomic layer epitaxy (ALE) and pulsed nucleation layer (PNL) deposition, has gained acceptance as a technique for depositing thin and continuous layers of metals and Dielectrics with high conformality. In an ALD process, a substrate is alternately dosed with a precursor and one or more reactant gases so that reactions are limited to the surface of a substrate. Thus, gas phase reactions are avoided since the precursor and the reactant gases do not mix in the gas phase. Uniform adsorption of precursors on the wafer surface during the ALD process produces highly conformal layers at both microscopic feature length scales and macroscopic substrate length scales, and achieves a high density of nucleation sites. These attributes result in the deposition of spatially uniform, conformal, dense and continuous thin films.
The high quality films achievable by ALD have resulted in increased interest in ALD for the deposition of conformal barriers, high-k dielectrics, gate dielectrics, tunnel dielectrics and etch stop layers for semiconductor devices. ALD films are also thermally stable and very uniform which makes them attractive for optical applications. Another potential application for ALD is the deposition of oxides (e.g., Al2O3) as a gap layer for thin film heads, such as heads for recording densities of 50 Gb/in2 and beyond which require very thin and conformal gap layers.
As recording densities for hard disk drives continue to increase, the thickness of gap layers required for read heads used in the disk drives decreases. For example, the thickness of the gap layer required for a read head in a hard disk drive having a recording density of approximately 100 Gb/in2 should be significantly below 200 angstroms (Å). The gap layer should also have a high dielectric strength, a low internal stress and a high resistance to resist developer etch. In general, oxide and nitride films, such as Al2O3 and aluminum nitride (AlN), formed by an ALD process have produced high quality gap layers for read head applications. At thicknesses below 200 Å, however, Al2O3 films typically have a lower dielectric strength and are more susceptible to resist developer etch.
In addition, conventionally sputtered gap layers may not be suitable for higher recording densities because they are difficult to reliably scale below 300 Å due to excessive leakage currents. Although ion beam deposited gap layers can be scaled down in thickness to below 300 Å, such layers tend not to be adequately conformal. Further, process integration considerations for thin film heads of 200 Å or less may constrain the maximum deposition temperature to below 200° C.
In accordance with the present invention, the disadvantages and problems associated with fabricating a high quality nanolaminate thin film have been substantially reduced or eliminated. In a particular embodiment, a method is disclosed for forming a nanolaminate thin film of aluminum oxide and silicon dioxide on a substrate surface.
In accordance with one embodiment of the present invention, a method for forming a nanolaminate thin film using ALD includes forming an aluminum oxide layer having a first thickness on at least a portion of a substrate surface by sequentially pulsing a first precursor and a first reactant into an enclosure containing the substrate. A silicon dioxide layer having a second thickness is formed on at least a portion of the aluminum oxide layer by sequentially pulsing a second precursor and a second reactant into the enclosure to form a nanolaminate thin film.
In accordance with another embodiment of the present invention, a method for forming a nanolaminate thin film using ALD includes forming an aluminum oxide layer having a first thickness on at least a portion of a substrate surface by sequentially pulsing trimethylaluminum (TMA) and water into an enclosure containing the substrate. A silicon dioxide layer having a second thickness is formed on at least a portion of the aluminum oxide layer by sequentially pulsing TMA and tris(tert-butoxy)silanol into the enclosure to form a read head gap layer.
In accordance with a further embodiment of the present invention, a thin film includes an ALD-formed aluminum oxide layer having a first thickness and an ALD-formed silicon dioxide layer having a second thickness formed on at least a portion of the aluminum oxide layer. The aluminum oxide layer and the silicon dioxide layer cooperate to form a nanolaminate thin film.
Important technical advantages of certain embodiments of the present invention include nanolaminate films formed using an ALD process that have high dielectric breakdown strengths. For certain applications, such as gap fill layers in read heads included in hard disk drives, the thickness of the film should be below a minimum value and the film should have certain characteristics. Single layer oxide films, such as aluminum oxide (Al2O3), may have lower breakdown fields at thickness below, for example, approximately 200 Å. A nanolaminate of Al2O3 and silicon dioxide (SiO2) having a thickness at or below approximately 200 Å, however, has a higher breakdown field due to the addition of SiO2 to the film and may be used to form high quality gap layers for read heads of high density hard disks.
Another important technical advantage of certain embodiments of the present invention includes nanolaminate films formed using an ALD process that have high resistances to resist developer etch. During fabrication of microelectronic structures, an etch process may be used to remove one or more materials from a surface. In a read head in a hard disk drive, for example, a resist layer may be removed to expose the surface of an underlying oxide material used to form a gap fill layer in the read head. For hard disks having higher recording densities, it may be desirable to have a thin gap layer (e.g., below 200 Å) and, in order to maintain the required thickness of the gap layer, the material should be resistant to resist developer etch. An Al2O3 film formed by an ALD process, however, may not be resistant to the etch process such that the etch process decreases the thickness of the film and degrades other desired properties. In contrast, SiO2 is much more resistant to an etch process and may be used to form a Al2O3/SiO2 nanolaminate such that almost none of the nanolaminate film is removed by the etch process.
A further important technical advantage of certain embodiments of the present invention includes nanolaminate films formed using an ALD process that have lower film stress. In many applications, it may be important for a thin film to have low stress. Single layer Al2O3 films formed using an ALD process may exhibit a high tensile stress, which is undesirable for applications such as gap layers of read heads in hard disk drives. SiO2 films formed using the ALD process, however, typically have a low tensile or compressive stress. Therefore, the film stress of an Al2O3/SiO2 nanolaminate may be controllably reduced by adding SiO2 to decrease the Al2O3 concentration of the film.
All, some, or none of these technical advantages may be present in various embodiments of the present invention. Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
A more complete and thorough understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:
Preferred embodiments of the present invention and their advantages are best understood by reference to
The conceptual groundwork for the present invention involves an atomic layer deposition (ALD) process to create highly conformal thin films. In an ALD process, a precursor and a reactant, such as a reactant gas are sequentially pulsed onto the surface of a substrate contained in a reaction chamber, without mixing the precursor and reactant in the gas phase. Each of the precursor and the reactant reacts with the surface of the substrate to form an atomic layer in such a way that only one layer of a material forms at a time. The introduction of the precursor and/or the reactant into the reaction chamber may be referred to as a doping pulse. In between doping pulses, the reaction chamber may be purged by flowing an inert gas over the substrate. One film that may be formed using an ALD process is aluminum oxide (Al2O3). ALD Al2O3 has been used for gap fill layers of a read head included in a hard disk drive, in particular, as a second read gap over topography composed of a read sensor and hard bias/sensing leads due to the superior deposition conformality and dielectric strength of Al2O3. However, as recording densities continue to increase, the read heads require half read gap thickness below approximately 200 angstroms (Å).
The present invention provides a thin film that may be fabricated at lower thicknesses with higher dielectric strength and higher resistance to resist developer etch. In one embodiment, the film may be a nanolaminate of Al2O3 and silicon dioxide (SiO2). Layers of Al2O3/SiO2 at a thickness of less than approximately 200 Å may have an increased dielectric strength of up to approximate fourteen (14) MV/cm at an Al2O3 composition of less than fifty percent (50%). Additionally, Al2O3/SiO2 nanolaminates have an etch resistance to resist developer that is substantially greater than the etch resistance of a single film of Al2O3. Although other materials, such as tantalum oxide and zirconium oxide, have been used to form nanolaminate films, the Al2O3/SiO2 nanolaminates disclosed below have shown superior qualities for applications that require high dielectric strength, low film stress and high resistance to resist developer etch.
Gas valves 16 may interface with shield assembly 12. During an ALD process, a gas may be introduced into the enclosure from one or more gas reservoirs (not expressly shown) through gas valves 16. In one embodiment, the gas reservoirs may contain a precursor and/or one or more reactants used during a doping pulse. In another embodiment, the gas reservoirs may contain an inert gas that is used as a carrier gas during a doping pulse and/or that is used to remove any remaining reactants from the enclosure during a purge pulse.
During an ALD process, at least one of gas valves 16 may be opened to allow the precursor, reactant and/or inert gas to flow into the enclosure formed by shield assembly 12. The precursor, reactant and inert gas may be removed from the enclosure by opening isolation valves 18 that are interfaced with shield assembly 12 opposite gas valves 16. Isolation valves 18 may further be linked to a mechanical pump (not expressly shown) through a throttle valve (not expressly shown) that facilitates automated process pressure control during an ALD process. During a doping pulse, isolation valves 18 may be opened to allow the mechanical pump to pump the precursor or the reactant and any carrier gas through the enclosure. After the purge pulse is completed, a high speed turbo pump (not expressly shown) coupled to pump inlet 22 may be used to allow vacuum chamber 14 to quickly reach the base pressure. During a purge pulse, isolation valves 18 may be opened to allow the mechanical pump to remove any remaining precursor or reactant from the enclosure. Use of only the mechanical pump during a doping pulse to exhaust the precursor or the reactant and the carrier gas from the enclosure, therefore, may extend the operation duration and life expectancy of the turbo pump.
Substrates on which a thin film may be deposited may be loaded into vacuum chamber 14 from a central wafer handler (not expressly shown) through substrate loader 20. In one embodiment, a substrate placed in vacuum chamber 14 may be a p-type or n-type silicon substrate. In other embodiments, the substrate may be formed from gallium arsenide, an AlTiC ceramic material or any other suitable material that may be used as a substrate on which one or more material layers may be deposited. The one or more layers deposited by ALD system 10 may form films used to fabricate conformal barriers, high-k dielectrics, gate dielectrics, tunnel dielectrics and barrier layers for semiconductor devices. ALD films are also thermally stable and substantially uniform, which makes them attractive for optical applications. Another potential application for ALD is the deposition of oxides as a gap layer for thin film heads, such as heads for recording densities of 50 Gb/in2 and beyond that require very thin and conformal gap layers, or as an isolation layer on an abut junction to insulate a TMR or CPP type read head from hard bias layers. Additionally, ALD thin films may be used to form structures with high aspect ratios, such as MicroElectroMechanical (MEM) structures.
Top hat 40 may include substrate seat 42 for holding a substrate on which a thin film is to be deposited. Substrate seat 42 may have a depth slightly greater than or approximately equal to the thickness of a substrate. In one embodiment, substrate seat 42 may be a recess formed in top hat 40 such that substrate seat 42 is integral to top hat 40. In another embodiment, substrate seat 42 may be mounted on top hat 40 such that substrate seat 42 is separate from top hat 40. Top hat 40 may be mounted on chuck 38 located in vacuum chamber 14. Chuck 38 may function to control the position of substrate seat 42 within vacuum chamber 14 and the position of top hat 40 in relation to shield assembly 12. In one embodiment, chuck 38 includes a heating mechanism with a temperature control and constant backside gas flow to a substrate located in substrate seat 42. The temperature control with constant backside gas flow may ensure fast heating and temperature uniformity across a substrate positioned in substrate seat 42. In another embodiment, chuck 38 includes a RF power application mechanism, which allows in-situ RF plasma processing.
Enclosure 44 may be defined by the position of shield assembly 12 in relation to top hat 40. In one embodiment, enclosure 44 may be formed when top hat 40 is in contact with bottom shield 32 such that enclosure 44 has a volume defined by substrate seat 42 and the thickness of bottom shield 32. When top hat 40 is contacting bottom shield 32 of shield assembly 12, the volume of enclosure 44 may be approximately three (3) to approximately five (5) times the volume of the substrate. Deposition of the thin film on the substrate may occur on the entire substrate surface without edge exclusion but may be confined only to enclosure 44. By minimizing the volume of enclosure 44, a minimum amount of precursor may be efficiently distributed in a minimum amount of time over the entire surface of the substrate. Additionally, surplus reactants and any reaction byproducts may be quickly removed from enclosure 44 to reduce the possibility of unwanted reactions from occurring inside enclosure 44.
In another embodiment, enclosure 44 may have a volume approximately equal to the volume of vacuum chamber 14 when chuck 38 is in the loading position (e.g., chuck 38 is at its lowest position in vacuum chamber 14). In other embodiments, the volume of enclosure 44 may depend on the distance between bottom shield 32 and top hat 40 such that the volume is varied between approximately fifty milliliters (50 ml) when top hat 40 is in close proximity to bottom shield 32 of shield assembly 12 to approximately twenty liters (20 l) when chuck 38 is in the substrate loading position.
Gas lines 37a and 37b (generally referred to as gas lines 37) may be connected to diffuser plate 36. During a purge pulse, gas valves 16 may be open to allow a gas to flow through one or both of gas lines 37a and 37b from gas reservoirs (not expressly shown). The gas then flows through diffuser plate 36 included in a gas injector located between diffuser plate 36 and top shield 30. In one embodiment, gas lines 37 may be formed of stainless steel and have a diameter of approximate one-quarter (¼) inch. Although the illustrated embodiment shows a particular number of gas lines, ALD system 10 may include any number of gas lines and any number of gas reservoirs. For example, a single gas line may be connected to multiple gas reservoirs such that the gas flowing through the gas line is controlled by one or more valves. In another embodiment, a separate gas line may be provided for each gas reservoir.
The thin film may be formed on a substrate by alternately flowing a precursor and one or more reactants combined with an inert gas during a doping pulse and the inert gas during a purge pulse through gas lines 37 and into enclosure 44. For example, the precursor may be introduced into enclosure 44 through gas lines 37 and may be chemisorbed onto the surface of a substrate to form a single, monolayer of film. Enclosure 44 may be purged by flowing a purge gas through gas lines 37 and into enclosure 44 to remove any remaining precursor. After purging, the reactant be introduced into enclosure 44 through gas lines 37 and may combine with the chemisorbed monolayer of precursor to form an atomic layer of the desired thin film. Again, enclosure 44 may be purged to remove any of the remaining reactant. The doping and purge pulses may be repeated until a thin film having the desired thickness is formed on the substrate.
As illustrated, the reactants and/or inert gas may be injected into enclosure 44 from one end of top shield 30 and exhausted at the other end through vertical shield 34. Vertical shield 34 may be coupled to isolation valves 18 (as illustrated in
In one embodiment, ALD system 10 may be used to form an aluminum oxide (Al2O3)/silicon dioxide (SiO2) nanolaminate on a substrate. The Al2O3 layer may be formed by sequentially pulsing a precursor and a reactant into enclosure 44. The precursor may be vapor-phase pulses of an aluminum source chemical and the reactant may be an oxygen source chemical. In a specific embodiment, the aluminum source chemical may be trimethylaluminum (TMA) and the oxygen source chemical may be selected from the group containing water (H2O), ozone (O3) or an oxygen radical (O2). In other embodiments, the aluminum source chemical may be any aluminum compound that is volatile at the source temperature and thermally stable at the substrate temperature and the oxygen source material may be any volatile or gaseous compounds that contain oxygen and are capable of reacting with an adsorbed portion of the selected aluminum source compound on the substrate surface at the deposition conditions such that an Al2O3 thin film is deposited on the substrate surface.
The SiO2 layer may also be formed by sequentially pulsing a precursor and a reactant into enclosure 44. The precursor may be vapor-phase pulses of an aluminum source chemical that produces aluminum to catalyze the growth of a SiO2 film and the reactant may be a silicon source chemical. In a specific embodiment, the aluminum source chemical may be TMA and the silicon source chemical may be tris(tert-butoxy)silanol ([ButO]3SiOH), tris(tert-pentoxy)silanol or tris(iso-propoxy)silanol. In other embodiments, the aluminum source chemical may be any aluminum compound that is volatile at the source temperature and thermally stable at the substrate temperature, which produces aluminum to catalyze the growth of a SiO2 film, and the silicon source chemical may be any volatile alkoxy organosilicon compound that is thermally stable at the deposition temperature.
An inert gas may be used as a carrier gas to convey the precursor and reactant during a doping pulse and as a purge gas to remove any remaining reactants from enclosure 44 during a purge pulse. In one embodiment, the inert gas may be Argon (Ar). In other embodiments, the inert gas may be any suitable inactive gas.
Nanolaminates of [xAl2O3/ySiO2]n may be synthesized by pulsing a TMA precursor and an oxygen based reactant (e.g., H2O) into enclosure 44 to form a layer of Al2O3 and pulsing a TMA precursor and a butoxy silanol reactant into enclosure 44 to form a layer of SiO2. The Al2O3 composition of the nanolaminate film may be adjusted between approximately zero (0) and approximately one-hundred (100) percent by varying x and y. Film thickness may be adjusted by varying the number (n) of Al2O3 and SiO2 cycles.
In one embodiment, alternating layers of Al2O3 and SiO2 may be formed by alternating Al2O3 and SiO2 deposition cycles until an Al2O3/SiO2 nanolaminate having a desired thickness is formed. The deposition process may begin with either a layer of Al2O3 or a layer of SiO2. The thickness of each Al2O3 layer may be approximately the same or each layer may have a different thickness. Additionally, the thickness of each SiO2 layer may be approximately the same or each layer may have a different thickness. The total number of Al2O3 layers and SiO2 layers may depend on the desired thickness for the nanolaminate film. In another embodiment, a layer of SiO2 may be formed over a layer of Al2O3 having a specific thickness by performing one or more Al2O3 deposition cycles before performing a SiO2 deposition cycle. In a further embodiment, the nanolaminate film may have an odd number of material layers formed on a substrate surface where either the Al2O3 layer or the SiO2 layer may be the top layer of the film. If the nanolaminate film includes multiple Al2O3 layers, the thickness of each Al2O3 layer may be approximately the same or each layer may have a different thickness. If the nanolaminate film includes multiple SiO2 layers, the thickness of each SiO2 layer may be approximately the same or each layer may have a different thickness. Again, the total number of material layers may depend on the desired thickness for the nanolaminate film.
The thickness of gap fill layers 56 and 62 may be used to control the linear recording density of a hard disk drive including read head 50. Additionally, gap fill layers 56 and 62 may provide insulation for read sensor 52 and may dissipate heat throughout read head 50. As the recording densities for disk drives increase, the thickness of gap fill layers 56 and 62 should decrease. Additionally, reducing the thickness of gap fill layers 56 and 62 may improve the heat dissipation of read head 50. Although Al2O3 has traditionally been used as a gap fill layer, Al2O3 films may be unable to retain certain properties (e.g., a high dielectric breakdown strength) if the film is less than a certain thickness.
A nanolaminate of Al2O3 and SiO2, however, may be used to form gap layers 56 and 62 having decreased thicknesses because the addition of SiO2 allows the film to maintain certain characteristics as the thickness decreases. In one embodiment, gap layers 56 and 62 may have a thickness of between approximately fifty angstroms (50 Å) and approximately 250 Å. At a thickness of 250 Å, an Al2O3/SiO2 nanolaminate thin film may have a dielectric breakdown field of approximately 13 MV/cm where as a single layer of Al2O3 may have a dielectric breakdown field of approximately 10 MV/cm. Even for a thickness at or below 50 Å, for example, an Al2O3/SiO2 nanolaminate may have a dielectric breakdown field of approximately 11 MV/cm where as a single layer of Al2O3 may only have a dielectric breakdown field of approximately 8 MV/cm. Other properties of an Al2O3/SiO2 nanolaminate thin film are shown in more detail below with respect to
In comparison, a single layer of Al2O3 shows a lower dielectric break down over the range of deposition temperatures as illustrated by
As illustrated in
As illustrated in
Although the present invention has been described with respect to a specific preferred embodiment thereof, various changes and modifications may be suggested to one skilled in the art and it is intended that the present invention encompass such changes and modifications fall within the scope of the appended claims.
