ALD device and method

Abstract

As an atomic layer deposition (ALD) method and apparatus, an ALD film such as aluminum oxide is deposited on the surface of a substrate (11) in a reaction chamber (10) by alternately introducing a precursor such as trimethylaluminum or triethylaluminum and water vapor into the reaction chamber (10), and oxygen gas is used as a carrier gas for the water vapor.

Description

Technology Field

[0001] The present invention generally relates to atomic layer deposition (ALD) methods and apparatuses. Background Technology

[0002] This section exemplifies useful background information and is not to be acknowledged that any technology described in this specification represents the prior art.

[0003] In atomic layer deposition (ALD), reactants require specific temperatures for planned chemical reactions to occur. For example, in the thermal Al2O3 deposition process, a very common ALD process in which aluminum oxide is deposited from trimethylaluminum (TMA) and water vapor (H2O), the thermal activation of the deposition process requires an external heat source to heat the substrate surface. However, in certain applications, it would be beneficial if the required deposition temperature could be lowered.

[0004] In certain applications, plasma has been used to provide additional energy to the substrate surface to enable lowered deposition temperatures. However, plasma systems are very complex and not always applicable.

[0005] The object of specific embodiments of the present invention is to provide atomic layer deposition at a reduced temperature or at least provide an alternative solution to the existing technology. A further object of specific embodiments is, in particular, to provide atomic layer deposition of aluminum oxide from trimethylaluminum and water vapor at a reduced temperature. As specified herein, a reduced temperature means a temperature below a typical thermal activation temperature.

[0006] According to a first exemplary aspect of the present invention, an atomic layer deposition (ALD) method is provided, and the method is

[0007] The method includes the step of depositing an ALD film on a substrate surface within a reaction chamber by alternately introducing a precursor and water vapor into the reaction chamber, wherein oxygen gas is used as a carrier gas for the water vapor.

[0008] In certain embodiments, the ALD film is a metal oxide film (the ALD film is a metal oxide). In certain embodiments, the metal oxide is aluminum oxide (Al2O3) or includes it. In certain embodiments, the precursor is trimethylaluminum (TMA) or includes it. In certain embodiments, the precursor is triethylaluminum (TEA) or includes it.

[0009] In certain embodiments, a gas other than oxygen (preferably an inert gas) is used as a carrier gas for the precursor. In certain embodiments, the "precursor" may be denoted as the "first precursor" and water vapor (or water) as the "second precursor".

[0010] In certain embodiments, the use of oxygen gas as a carrier gas will ignite methane released from the substrate surface. Accordingly, in certain embodiments, the method is,

[0011] The method includes the step of obtaining energy for a water vapor reaction on the substrate surface by burning methane released from the substrate surface with the help of the oxygen gas used as a carrier gas. Advantageously, the burning of methane leads to a lower required deposition temperature.

[0012] In certain embodiments, an ALD film, such as a film of aluminum oxide (or metal oxide), is deposited under vacuum.

[0013] In certain embodiments, the oxygen gas is introduced into the headspace of the water vapor precursor container.

[0014] In certain embodiments, the method includes the step of using an inert carrier gas for a precursor. In certain embodiments, the method includes the step of using an inert gas, such as nitrogen, as a carrier gas for trimethylaluminum or triethylaluminum (when depositing aluminum oxide).

[0015] According to a second exemplary aspect of the present invention, an atomic layer deposition (ALD) apparatus is provided, and the apparatus is,

[0016] Reaction chamber;

[0017] A source system connected to the reaction chamber; and

[0018] It includes at least one processor,

[0019] The above-mentioned at least one processor is configured to control a source system to alternately introduce a precursor and water vapor into a reaction chamber using oxygen gas as a carrier gas for water vapor, based on stored instructions.

[0020] In certain embodiments, the ALD device includes the instructions stored in memory.

[0021] In certain embodiments, the source system includes a carrier gas valve in the carrier gas line, and the carrier gas valve allows oxygen gas to be mixed with water vapor upstream of the reaction chamber.

[0022] In certain embodiments, the source system includes an oxygen gas source and a water vapor precursor container. In certain embodiments, the oxygen gas source is connected to the water vapor precursor container through a carrier gas line and a carrier gas valve.

[0023] In certain embodiments, the source system comprises an inert gas source and a trimethylaluminum (or triethylaluminum) precursor container. In certain embodiments, the inert gas source is connected to the trimethylaluminum (or triethylaluminum) precursor container.

[0024] According to a third exemplary aspect of the present invention, when executed by at least one processor, the ALD device is enabled,

[0025] By alternately introducing a precursor and water vapor into the reaction chamber, an ALD film is deposited on the surface of a substrate inside the reaction chamber, and

[0026] A computer program product is provided that enables the use of oxygen gas as a carrier gas for water vapor.

[0027] Different non-binding exemplary aspects and embodiments have been illustrated in the foregoing. The above embodiments are used solely to describe selected aspects or steps that may be utilized in the implementations of the present invention. Some embodiments may be presented by reference only to specific exemplary aspects. It should be understood that corresponding embodiments apply to other exemplary aspects as well. In particular, embodiments described in the context of the first aspect are applicable to each additional aspect, and vice versa. Any suitable combination of embodiments may be formed. Brief explanation of the drawing

[0028] The present invention will now be described only by way of example with reference to the accompanying drawings, and in the drawings, FIG. 1 illustrates a basic cycle for atomic layer deposition (ALD); FIG. 2 illustrates an ALD method according to specific embodiments; FIG. 3 illustrates specific reactions related to specific embodiments; FIG. 4 illustrates a schematic block diagram of an ALD device according to specific embodiments; FIG. 5 illustrates a block diagram of a control system according to specific exemplary embodiments; FIG. 6 illustrates a schematic block diagram of an ALD device according to specific other embodiments. Specific details for implementing the invention

[0029] The basics of the atomic layer deposition (ALD) growth mechanism are known to those skilled in the art. ALD is a specialized chemical vapor deposition method based on the sequential introduction of at least two reactive precursor species into at least one substrate. As shown in FIG. 1, a basic ALD deposition cycle consists of four sequential steps: pulse A, purge A, pulse B, and purge B. Pulse A consists of a first precursor vapor, and pulse B consists of another precursor vapor. An inert gas and vacuum pump are typically used to purge gas reaction byproducts and residual reactant molecules from the reaction space during purge A and purge B. A deposition sequence includes at least one deposition cycle. Deposition cycles are repeated until the deposition sequence produces a thin film or coating of the desired thickness. Deposition cycles may be simpler or more complex. For example, cycles may include three or more reactant vapor pulses separated by purge steps, or certain purge steps may be omitted. Alternatively, in the case of plasma-assisted ALD, e.g., PEALD (plasma-enhanced atomic layer deposition), or photon-assisted ALD, one or more of the deposition steps may be assisted by providing additional energy required for surface reactions through plasma or photon in-feed, respectively. Thus, pulse and purge sequences may differ depending on each specific case. The deposition cycles form a timed deposition sequence controlled by at least one processor. Thin films grown by ALD are dense, pinhole-free, and have a uniform thickness.

[0030] In relation to the substrate processing steps, at least one substrate is generally exposed to time-separated precursor pulses in a reaction vessel (or chamber) to deposit material on substrate surfaces by sequential self-limiting surface reactions. In the context of this application, the term ALD includes all applicable ALD-based technologies and equivalent or closely related technologies, such as, for example, the following ALD subtypes: MLD (Molecular Layer Deposition), plasma-assisted ALD, e.g., PEALD (Plasma Enhanced Atomic Layer Deposition), and photon-assisted or photon-enhanced atomic layer deposition (also known as flash-enhanced ALD or photo-ALD).

[0031] The thermal aluminum oxide (Al2O3) deposition process has played a leading role within the ALD industry. In a very typical Al2O3 deposition process, aluminum oxide is deposited in a reaction chamber from trimethylaluminum (TMA) and water vapor (H2O). The deposition process is activated through thermal activation by heating the substrate with the help of an external heat source. The associated growth mechanism is as follows: During pulse A, trimethylaluminum (Al(CH3)3) vapor is introduced to the OH-terminated substrate surface as a first precursor and reacts with surface-bonded monomethylaluminum or dimethylaluminum to produce methane (CH4) gas as a byproduct. Upon saturation, the substrate surface contains the aforementioned methyl groups. During the subsequent purge A, excess trimethylaluminum and CH4 are removed. During the subsequent pulse B, a ligand exchange process occurs, in which water vapor (H2O) is introduced as a second precursor onto the methylated substrate surface, dissociates on the substrate surface, provides one OH group to a surface Al atom, and provides one hydrogen to a cleaved -CH3 ligand from the substrate surface. This results in the formation of OH-terminated substrate surfaces and the release of CH4 gas as a byproduct. After purging the chamber with an inert gas during pulse B, this deposition cycle is repeated until the desired film thickness is achieved.

[0032] Now, it has been observed that oxygen gas (O2) can be used as a carrier gas for H2O in the aforementioned aluminum oxide deposition process. By using oxygen gas (O2) as a carrier gas for H2O, the ligand exchange reaction occurs in the same manner as previously described, but due to the O2 environment accompanied by H2O pulses, the -CH3 ligand cleavage reaction from the substrate surface can provide sufficient energy or electronic activation to ignite the combustion of the released CH4 gas. When the CH4 gas is combusted, a large amount of thermal energy is released. Thus, the process chemistry provides the thermal energy required for the H2O surface reactions, and the Al2O3 deposition process can be performed at a lower temperature or without an external heat source.

[0033] Accordingly, in a method according to specific embodiments as illustrated in FIG. 2, an inert gas purge (step 22) is performed following a TMA pulse (step 21), and then an H2O pulse (step 23) using O2 as a carrier gas is performed, followed by an inert gas purge (step 24). The entire deposition sequence comprises this deposition cycle, which is repeated a predetermined number of times to achieve a desired film thickness. Preferably, an inert carrier gas, such as nitrogen, is used for the TMA.

[0034] Alternatively, triethylaluminum (TEA) is used as an aluminum-containing precursor instead of TMA.

[0035] In other embodiments, the aluminum oxide deposition process is carried out by alternately introducing TMA (or another aluminum-containing precursor) and O3 (or another oxygen-containing precursor) into a reaction chamber. Preferably, oxygen gas (O2) is also used as a carrier gas for the oxygen-containing precursor in these embodiments (to provide additional energy or assist combustion).

[0036] In additional embodiments, another ALD film is deposited by alternately introducing a precursor and an oxygen-containing precursor, preferably water vapor, into a reaction chamber. In certain of these embodiments, a metal oxide film is deposited from a (metal-containing) precursor and an oxygen-containing precursor (H2O or O3). Also in this case, oxygen gas (O2) is used as a carrier gas for the oxygen-containing precursor (to provide additional energy or assist combustion).

[0037] Figure 3 illustrates the net reaction (reaction [1]) of aluminum oxide deposition from TMA and water vapor. Thus, one molecule of hydrolyzed TMA (along with 3 / 2 molecules of water) produces 1 / 2 molecule of aluminum oxide and 3 molecules of methane. Additionally, 600 kJ of thermal energy is released per mole of TMA. Figure 3 further illustrates the combustion reaction of methane (CH4) (reaction [2]). Thus, one molecule of combusted methane (consuming 2 molecules of oxygen) produces 1 molecule of carbon dioxide (CO2) and 2 molecules of water (H2O). Additionally, 890.7 kJ of thermal energy is released per mole of CH4. Since the mass of one mole of TMA is 72.09 g, it can be concluded that the total amount of thermal energy released when one gram of TMA is hydrolyzed and the resulting CH4 is combusted is 45.4 kJ. This energy release will promote the cleavage reaction of -CH3 during pulse B, contributing to lowering the required process temperature or even eliminating the need to use an external heat source.

[0038] FIG. 4 illustrates a schematic block diagram of an ALD device (or ALD reactor) (100) according to specific embodiments. The device (100) includes a reaction chamber (10) and source systems S1 and S2 connected to the reaction chamber (10). In specific embodiments, the device (100) further includes at least one processor configured to control the operation of the device (100) based on stored commands. In specific embodiments, the at least one processor is included in a control system (50). In specific embodiments, the device (100) includes at least one in-feed line for supplying reactants to the reaction chamber (10). In specific embodiments, the device (100) includes a vacuum pump (30) connected to the reaction chamber by an exhaust line. In specific embodiments, the vacuum pump (30) provides vacuum conditions to the reaction chamber so that ALD deposition occurs on the surface of the substrate (11). In specific embodiments, the reaction chamber (10) is at least partially enclosed by a vacuum chamber (20) which is an outer chamber. In certain embodiments, the heater (15) is located in an intermediate space formed between the wall of the reaction chamber (10) and the wall of the vacuum chamber (20).

[0039] In certain embodiments, the source system comprises an aluminum-containing (or metal-containing) precursor source S1 and an oxygen-containing precursor source S2. In the specific embodiment described above, source S1 is a TMA or TEA source, and source S2 is an H2O source. Alternatively, source S2 is an ozone (O3) source.

[0040] In certain embodiments, the source system includes a first pulsing valve (41) for supplying precursor vapor from source S1 to the reaction chamber (10). Likewise, in certain embodiments, the source system includes a second pulsing valve (42) for supplying precursor vapor (or reactant) from source S2 to the reaction chamber (10). The precursor in-feed to the reaction chamber (10) may occur through separate in-feed lines (as shown in FIG. 4) or along a common in-feed line (as shown in FIG. 6).

[0041] In certain embodiments, the source system includes an oxygen source X2 for oxygen gas to be used as a carrier gas for an oxygen-containing precursor. In certain embodiments, the source system further includes a third pulsing valve (62) downstream of the oxygen source X2 in the first carrier gas line. In certain embodiments, the third pulsing valve (62) is configured to open and close fluid communication between the oxygen source X2 and the oxygen-containing precursor source S2. In certain embodiments, the first carrier gas line enters the headspace of the oxygen-containing precursor source S2, whereby the oxygen gas as the carrier gas is mixed with the oxygen-containing precursor vapor (in these embodiments, the headspace forms a mixing region). In other embodiments, the oxygen gas as the carrier gas is mixed with the oxygen-containing precursor vapor only downstream of the outlet of the oxygen-containing precursor source S2. In these embodiments, the mixing may be performed at a three-leg valve or similar (each valve forms a mixing region).

[0042] In certain embodiments, the source system comprises an inert gas source X1 for an inert gas to be used as a carrier gas for an aluminum-containing (or metal-containing) precursor. In certain embodiments, the source system further comprises a fourth pulsing valve (61) downstream of the inert gas source X1 in a second carrier gas line. In certain embodiments, the fourth pulsing valve (61) is configured to open and close fluid communication between the inert gas source X1 and the aluminum-containing precursor source S1. In certain embodiments, the second carrier gas line enters the headspace of the aluminum-containing precursor source S1, whereby the inert gas as the carrier gas is mixed with the aluminum-containing precursor vapor. In other embodiments, the inert gas as the carrier gas is mixed with the aluminum-containing precursor vapor only downstream of the outlet of the aluminum-containing precursor source S1. In these embodiments, the mixing may be performed at a three-way valve or similar. When the vapor pressure of the aluminum-containing (metal-containing) precursor is sufficiently high, the aluminum-containing (metal-containing) precursor can be supplied to the reaction chamber (10) without using a carrier gas.

[0043] Depending on the implementation, the device may include an additional in-feed line for introducing an inert gas into the reaction chamber (10) to implement the purging steps (or in-feed line(s) for supplying the reactant(s) may be used to introduce the inert gas into the reaction chamber for purging).

[0044] At least one processor (or control system (50)) controls the source system to alternately introduce an aluminum-containing precursor (trimethylaluminum in a specific embodiment) and an oxygen-containing precursor (water vapor in a specific embodiment) into the reaction chamber (10) using oxygen gas as a carrier gas for the oxygen-containing precursor. In practice, at least one processor controls the opening and closing timing cycles of each valve, controls the heating of the heater (15), and controls the vacuum pump (30) so that the intended reactants (in some cases, together with the carrier gas) and the inert gas enter the reaction chamber (10) and are removed from the reaction chamber (10) as intended, and the reaction conditions (temperature and pressure) are maintained as intended. Some of these control connections between at least one processor (or control system (50)) are shown as dashed lines in FIG. 4. In certain embodiments, at least one processor controls the operation of the device (100) based on instructions stored in memory included in the control system (50).

[0045] FIG. 5 illustrates a block diagram of a control system (50) according to certain exemplary embodiments. The control system (50) includes at least one processor (51) configured to control the operation of the device (100) and at least one memory (52) containing a computer program or software (53). The software (53) includes instructions or program code to be executed by the at least one processor (51) to control the device (100). The software (53) may generally include an operating system and different applications. In certain embodiments, the control system (50) is configured as a computerized system using one or more computers.

[0046] At least one memory (52) may form part of the device (100) or may be formed as a detachable module. The control system (50) further includes at least one communication unit (54). The communication unit (54) provides an interface for internal communication of the device (100). In certain embodiments, the control system (50) uses the communication unit (54) to transmit commands or instructions to valves, heater(s), pressure sensor(s), vacuum pump(s), and other control devices (not shown). In certain embodiments, the control system (50) further uses the communication unit (54) to receive data from different parts of the device (100).

[0047] The control system (50) may further include a user interface (56) for cooperating with an operator, for example, for receiving inputs such as process parameters from the operator. In certain embodiments, the user interface (56) is connected to at least one processor (51).

[0048] In relation to the operation of the device (100), at least one processor (51) controls the first pulsing valve (41) to be opened during, for example, an aluminum-containing (or metal-containing) precursor pulse, and the second pulsing valve (42) to be opened during an oxygen-containing precursor pulse. Additionally, at least one processor (51) controls oxygen gas as a carrier gas to flow from an oxygen source X2 to each mixing area as needed and to be mixed with the oxygen-containing precursor.

[0049] FIG. 6 illustrates a schematic block diagram of an ALD device (200) according to certain other embodiments. The ALD device (200) corresponds to the ALD device (100) except that separate in-feed lines to the reaction chamber (10) are replaced with a common in-feed line having a common (inert) carrier gas (and may be supplemented by other features of the device (100)). Sources S1 and S2 are connected to the common in-feed line at respective three-way pulsing valves, in which the first leg provides an inlet for the common carrier gas, the second leg provides an inlet for each precursor (optionally carried with the carrier gas), and the third leg provides an outlet for a mixture of the common carrier gas and each precursor toward the reaction chamber (10). Oxygen gas (O2) is again used as a carrier gas for an oxygen-containing precursor (e.g., H2O). In FIG. 6, source S1 is another precursor source (e.g., a metal-containing or aluminum-containing precursor source), source S2 is an oxygen-containing precursor source, X0 refers to the common (inert) carrier gas, X1 refers to the (inert) carrier gas (if present) for the metal-containing or aluminum-containing precursor (TMA or TEA in certain embodiments), and X2 refers to the oxygen gas as the carrier gas for the oxygen-containing precursor (H2O in certain embodiments).

[0050] Without limiting the scope and interpretation of the claims, specific technical effects of one or more exemplary embodiments disclosed herein are listed below. A technical effect is a reduction in the deposition temperature required in ALD deposition, such as aluminum oxide deposition. An additional technical effect is low-temperature deposition on substrates that cannot withstand higher temperatures. An additional technical effect is the use of more sophisticated chemicals.

[0051] The foregoing description has provided a complete and beneficial description of the best manner currently considered by the inventors to carry out the invention, as non-limiting examples of specific embodiments and embodiments of the invention. However, it will be apparent to those skilled in the art that the invention is not limited to the details of the embodiments presented above and may be embodied in other embodiments using equivalent means without departing from the characteristics of the invention.

[0052] Furthermore, some of the features of the embodiments disclosed above may be advantageously used without corresponding use of other features. Accordingly, the foregoing description should be considered merely illustrative of the principles of the invention and not as limiting. Accordingly, the scope of the invention is limited only by the appended claims.

Claims

Claim 1 An atomic layer deposition (ALD) method, wherein the method comprises the step of depositing an ALD film on a substrate surface within a reaction chamber by alternately introducing a precursor and water vapor into the reaction chamber, wherein oxygen gas is used as a carrier gas for the water vapor. Claim 2 ALD method according to claim 1, wherein the ALD film is a metal oxide film, preferably aluminum oxide. Claim 3 ALD method according to claim 1 or 2, comprising trimethylaluminum or triethylaluminum as the precursor. Claim 4 An ALD method comprising the step of obtaining energy for a water vapor reaction on a substrate surface by burning methane released from a substrate surface with the help of the oxygen gas used as a carrier gas, in any one of claims 1 to 3. Claim 5 ALD method according to any one of claims 1 to 4, wherein the oxygen gas is introduced into the headspace of a water vapor precursor container. Claim 6 An atomic layer deposition (ALD) apparatus comprising: a reaction chamber; a source system connected to the reaction chamber; and at least one processor, wherein the at least one processor is configured to control the source system to alternately introduce a precursor and water vapor into the reaction chamber using oxygen gas as a carrier gas for water vapor based on stored instructions. Claim 7 In paragraph 6, the source system includes a carrier gas valve in the carrier gas line, said carrier gas valve is configured to allow oxygen gas to be mixed with water vapor upstream of the reaction chamber, an ALD device. Claim 8 A computer program product that, when executed by at least one processor, causes an ALD device to deposit an ALD film on a substrate surface within a reaction chamber by alternately introducing a precursor and water vapor into the reaction chamber, and to use oxygen gas as a carrier gas for the water vapor.

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