ALD apparatus and method

Abstract

An atomic layer deposition, ALD, method and apparatus, wherein an ALD film, such as aluminum oxide, is deposited onto a substrate (11) surface 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

[0001] ALD APPARATUS AND METHOD

[0002] FIELD

[0003] The present invention generally relates to atomic layer depositions, ALD, methods and apparatuses.

[0004] BACKGROUND

[0005] This section illustrates useful background information without admission of any technique described herein representative of the state of the art.

[0006] In atomic layer deposition, ALD, reactants need a certain temperature so that planned chemical reactions will occur. For example, in a very common ALD process, the thermal AI2O3 deposition process, in which aluminum oxide is deposited from trimethylaluminum, TMA, and water vapor, H2O, thermal activation of the deposition process requires an external heat source that heats a substrate surface. However, in certain applications, it would be beneficial if the required deposition temperature could be reduced.

[0007] In certain applications, plasma has been used to provide the substrate surface with additional energy to enable reduced deposition temperatures. However, plasma systems are very complex and are not always applicable.

[0008] SUMMARY

[0009] It is an object of certain embodiments of the invention to provide atomic layer deposition at a reduced temperature or at least to provide an alternative solution to existing technology. It is a further object of certain embodiments to provide, in particular, atomic layer deposition of aluminum oxide from trimethylaluminum and water vapor at a reduced temperature. By a reduced temperature herein is meant a temperature below a typical thermal activation temperature.

[0010] According to a first example aspect of the invention there is provided an atomic layer deposition, ALD, method, comprising: depositing an ALD film onto a substrate surface in 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.

[0011] In certain embodiments, the ALD film is a metal oxide film (the ALD film is of metal oxide). In certain embodiments, the metal oxide is or comprises aluminum oxide, AI2O3. In certain embodiments, the precursor is or comprises trimethylaluminum, TMA. In certain embodiments, the precursor is or comprises triethylaluminum, TEA.

[0012] In certain embodiments, a gas other than oxygen (preferably an inert gas) is used as a carrier gas for the precursor. In certain embodiments, said “precursor” may be denoted as a “first precursor” and water vapor (or water) as a “second precursor”.

[0013] In certain embodiments, the use of oxygen gas as carrier gas will ignite methane released from the substrate surface. Accordingly, in certain embodiments, the method comprises: obtaining energy for a reaction of water vapor on the substrate surface by combusting, with the aid of said oxygen gas used as a carrier gas, methane released from the substrate surface. Advantageously, combusting methane leads into a lower required deposition temperature.

[0014] In certain embodiments, the ALD film, such as a film of aluminum oxide (or metal oxide) is deposited under vacuum.

[0015] In certain embodiments, said oxygen gas flows into a headspace of a water vapor precursor container.

[0016] In certain embodiments, the method comprises using an inert carrier gas for the precursor. In certain embodiments, the method comprises using an inert gas, such as nitrogen, as a carrier gas for trimethylaluminum or for triethylaluminum (when depositing aluminum oxide).

[0017] According to a second example aspect of the invention there is provided an atomic layer deposition, ALD, apparatus, comprising: a reaction chamber; a source system connected to the reaction chamber; and at least one processor, wherein said at least one processor is configured, based on stored instructions, to control the source system so as to alternately introduce a precursor and water vapor into the reaction chamber, with oxygen gas as carrier gas for the water vapor.

[0018] In certain embodiments, the ALD apparatus comprises said stored instructions in a memory.

[0019] In certain embodiments, the source system comprises a carrier gas valve in a carrier gas line allowing oxygen gas to mix with the water vapor upstream of the reaction chamber.

[0020] In certain embodiments, the source system comprises an oxygen gas source and a water vapor precursor container. In certain embodiments, the oxygen gas source is connected through the carrier gas line and carrier gas valve with the water vapor precursor container.

[0021] In certain embodiments, the source system comprises an inert gas source and a trimethylaluminum (or a triethylaluminum) precursor container. In certain embodiments, the inert gas source is connected with the trimethylaluminum (or a triethylaluminum) precursor container.

[0022] According to a third example aspect of the invention there is provided a computer program product which when run by at least one processor causes an ALD apparatus to: deposit an ALD film onto a substrate surface in a reaction chamber by alternately introducing a precursor and water vapor into the reaction chamber, and use oxygen gas as a carrier gas for the water vapor.

[0023] Different non-binding example aspects and embodiments have been illustrated in the foregoing. The above embodiments are used merely to explain selected aspects or steps that may be utilized in implementations of the present invention. Some embodiments may be presented only with reference to certain example aspects. It should be appreciated that corresponding embodiments apply to other example aspects as well. In particular, the embodiments described in the context of the first aspect are applicable to each further aspect, and vice versa. Any appropriate combinations of the embodiments may be formed.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0026] Fig. 1 shows a basic cycle for atomic layer deposition, ALD;

[0027] Fig. 2 shows an ALD method in accordance with certain embodiments;

[0028] Fig. 3 shows certain reactions in connection with certain embodiments;

[0029] Fig. 4 shows a schematic block diagram of an ALD apparatus in accordance with certain embodiments;

[0030] Fig. 5 shows a block diagram of a control system in accordance with certain example embodiments; and

[0031] Fig. 6 shows a schematic block diagram of an ALD apparatus in accordance with certain other embodiments. DETAILED DESCRIPTION

[0032] The basics of an atomic layer deposition, ALD, growth mechanism are known to a skilled person. ALD is a special chemical deposition method based on sequential introduction of at least two reactive precursor species to at least one substrate. A basic ALD deposition cycle, as shown in Fig. 1 , 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 of another precursor vapor. Inactive gas and a vacuum pump are typically used for purging gaseous reaction by-products and the residual reactant molecules from the reaction space during purge A and purge B. A deposition sequence comprises at least one deposition cycle. Deposition cycles are repeated until the deposition sequence has produced a thin film or coating of desired thickness. Deposition cycles can also be either simpler or more complex. For example, the cycles can include three or more reactant vapor pulses separated by purging steps, or certain purge steps can be omitted. Or, as for plasma-assisted ALD, for example PEALD (plasma-enhanced atomic layer deposition), or for photon- assisted ALD, one or more of the deposition steps can be assisted by providing required additional energy for surface reactions through plasma or photon in-feed, respectively. Accordingly, the pulse and purge sequence may be different depending on each particular case. The deposition cycles form a timed deposition sequence that is controlled by at least one processor. Thin films grown by ALD are dense, pinhole free and have uniform thickness.

[0033] As for substrate processing steps, the at least one substrate is typically exposed to temporally separated precursor pulses in a reaction vessel (or chamber) to deposit material on the substrate surfaces by sequential self-limiting surface reactions. In the context of this application, the term ALD comprises all applicable ALD based techniques and any equivalent or closely related technologies, such as, for example the following ALD sub-types: MLD (Molecular Layer Deposition), plasma-assisted ALD, for example PEALD (Plasma Enhanced Atomic Layer Deposition) and photon- assisted or photon-enhanced Atomic Layer Deposition (known also as flash enhanced ALD or photo-ALD). The thermal aluminum oxide, AI2O3, deposition process has been a driver within the ALD industry. In a very typical AI2O3 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 a substrate with the aid of an external heat source. The associated growth mechanism is as follows: during pulse A, trimethylaluminum AI(CHs)3 vapor is introduced as a first precursor to an OH-terminated substrate surface where it reacts to produce surface-bound monomethylaluminum or dimethylaluminum, and methane CH4 gas as a by-product. Upon saturation, the substrate surface comprises the preceding 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 H2O vapor is introduced as a second precursor to the methylated substrate surface where it dissociates on the substrate surface, donating one OH- group for a surface Al-atom and one hydrogen for a -CH3 ligand cleaved from the substrate surface. This results in formation of an OH-terminated substrate surface and release of CH4 gas as the by-product. After purging the chamber during purge B with inert gas, this deposition cycle is repeated until a desired film thickness is achieved.

[0034] Now, it has been observed that oxygen gas O2 may be used as a carrier gas for H2O in the preceding aluminum oxide depositing process. By using oxygen gas O2 as the carrier gas for H2O, the ligand exchange reaction occurs in the same way as described in the preceding, but because of the O2 environment with the H2O pulse, the -CH3 ligand cleavage reaction from the substrate surface can provide enough energy or electronic activation so that it ignites combustion of the CH4 gas once released. When the CH4 gas is combusted, a large amount of thermal energy is released. The process chemistry therefore carries the thermal energy needed for the H2O surface reactions and the AI2O3 deposition process can be performed at lower temperatures or without an external heat source.

[0035] Accordingly, in a method according to certain embodiments as shown in Fig. 2, a TMA pulse (step 21 ) is followed by an inert gas purge (step 22), which is followed by an H2O pulse using O2 as carrier gas (step 23) followed by an inert gas purge (step 24). A whole deposition sequence comprises this deposition cycle repeated for a predetermined number of times to achieve a desired film thickness. Preferably, an inert carrier gas, such as nitrogen, is used for TMA.

[0036] Alternatively, triethylaluminum, TEA, is used as the aluminum-containing precursor instead of TMA.

[0037] In other embodiments, the aluminum oxide deposition process is performed by alternately introducing TMA (or another aluminum-containing precursor) and O3 (or another oxygen-containing precursor) into the reaction chamber. Preferably, oxygen gas O2 is used as a carrier gas for the oxygen-containing precursor also in these embodiments (to provide additional energy or to assist in combustion).

[0038] In further embodiments, another ALD film is deposited by alternately introducing a precursor and an oxygen-containing precursor, preferably water vapor, into the reaction chamber. In certain such embodiments, a metal oxide film is deposited from a (metal-containing) precursor and an oxygen containing precursor (H2O or O3). Also therein, oxygen gas O2 is used as a carrier gas for the oxygen-containing precursor (to provide additional energy or to assist in combustion).

[0039] Fig. 3 shows the net reaction of aluminum oxide deposition from TMA and water vapor (reaction [1]). Accordingly, one molecule of TMA hydrolyzed (with 3 / 2 molecules of water) computationally produces half a molecule of aluminum oxide and three molecules of methane. Further, thermal energy of 600 kJ per one mole of TMA is released. Fig. 3 further shows the combustion reaction of methane CH4 (reaction [2]). Accordingly, one molecule of methane combusted (consuming 2 molecules of oxygen) computationally produces one molecule of carbon dioxide CO2 and two molecules of water H2O. Further, thermal energy of 890,7 kJ per one mole of CH4 is released. Since the mass of one mole of TMA is 72,09 g it can be concluded that in total when one gram of TMA is hydrolyzed and resulting CH4 is combusted the thermal energy release is 45,4 kJ. This energy release will facilitate the cleavage reaction of -CH3 during pulse B leading to reduced required process temperature or even to the omission of the need to use an external heat source. Fig. 4 shows a schematic block diagram of an ALD apparatus (orALD reactor) 100 in accordance with certain embodiments. The apparatus 100 comprises a reaction chamber 10, and a source system, Si and S2, connected to the reaction chamber 10. In certain embodiments, the apparatus 100 further comprises at least one processor configured to control the operation of the apparatus 100 based on stored instructions. In certain embodiments, said at least one processor is comprised by a control system 50. In certain embodiments, the apparatus 100 comprises at least one in-feed line for feeding reactants into the reaction chamber 10. In certain embodiments, the apparatus 100 comprises a vacuum pump 30 connected to the reaction chamber by an exhaust line. In certain embodiments, the vacuum pump 30 provides the reaction chamber with vacuum conditions for ALD deposition to occur onto a surface of a substrate 11. In certain embodiments, the reaction chamber 10 is at least partially surrounded by an outer chamber, a vacuum chamber 20. In certain embodiments, a heater 15 is positioned within an intermediate space formed in between a wall of the reaction chamber 10 and a wall of the vacuum chamber 20.

[0040] In certain embodiments, the source system comprises an aluminum-containing (or metal-containing) precursor source Si, and an oxygen-containing precursor source S2. In a specific embodiment as described in the preceding, the source Si is a TMA or TEA source and the source S2 is an H2O source. Alternatively, the source S2 is an ozone O3 source.

[0041] In certain embodiments, the source system comprises a first pulsing valve 41 for feeding precursor vapor from the source Si into the reaction chamber 10. Similarly, in certain embodiments, the source system comprises a second pulsing valve 42 for feeding precursor vapor (or reactant) from the source S2 into the reaction chamber 10. The precursor in-feed into the reaction chamber 10 may occur via separate in- feed lines (as shown in Fig. 4) or along a common in-feed line (as shown in Fig. 6).

[0042] In certain embodiments, the source system comprises an oxygen source X2 for oxygen gas to be used as a carrier gas for the oxygen-containing precursor. In certain embodiments, the source system further comprises downstream of the oxygen source X2 in a first carrier gas line a third pulsing valve 62. In certain embodiments, the third pulsing valve 62 is configured to open and close a fluid communication between the oxygen source X2 and the oxygen-containing precursor source S2. In certain embodiments, the first carrier gas line enters a headspace of the oxygen-containing precursor source S2, wherein the oxygen gas as carrier gas mixes with oxygen-containing precursor vapor (the headspace forming a mixing region in these embodiments). In other embodiments, the oxygen gas as carrier gas mixes with oxygen-containing precursor vapor only downstream of an outlet from the oxygen-containing precursor source S2. In such embodiments, said mixing may be performed in a three-leg valve or similar (the respective valve forming the mixing region).

[0043] In certain embodiments, the source system comprises an inert gas source Xi for inert gas to be used as a carrier gas for the aluminum-containing (or metalcontaining) precursor. In certain embodiments, the source system further comprises downstream of the inert gas source Xi in a second carrier gas line a fourth pulsing valve 61 . In certain embodiments, the fourth pulsing valve 61 is configured to open and close a fluid communication between the inert gas source Xi and the aluminum- containing precursor source Si. In certain embodiments, the second carrier gas line enters a headspace of the aluminum-containing precursor source Si, wherein the inert gas as carrier gas mixes with aluminum-containing precursor vapor. In other embodiments, the inert gas, as carrier gas, mixes with aluminum-containing precursor vapor only downstream of an outlet from the aluminum-containing precursor source Si. In such embodiments, said mixing may be performed in a three-leg valve or similar. In the event of high enough vapor pressure of the aluminum-containing (metal-containing) precursor, the aluminum-containing (metalcontaining) precursor may be fed into the reaction chamber 10 without using a carrier gas.

[0044] Depending on the implementation, the apparatus may comprise a further in-feed line to introduce inert gas into the reaction chamber 10 for implementing the purge phases (or the in-feed line(s) for feeding reactant(s) may be used to introduce inert gas into the reaction chamber for purging). The at least one processor (or the control system 50) controls the source system so as to alternately introduce the aluminum-containing precursor (trimethylaluminum in the specific embodiment) and oxygen-containing precursor (water vapor in the specific embodiment) into the reaction chamber 10, with oxygen gas as carrier gas for the oxygen-containing precursor. In practice, the at least one processor controls the open and close timing cycles of the respective valves, controls the heating of the heater 15, and controls the vacuum pump 30 such that intended reactants (with carrier gas, as the case may be) and inert gas enter the reaction chamber 10 and are removed from the reaction chamber 10 as intended and that the reaction conditions (temperature and pressure) are as intended. Some such control connections between the at least one processor (or the control system 50) have been shown in Fig. 4 by dashed lines. In certain embodiments, the at least one processor controls the operation of the apparatus 100 based on instructions stored on a memory comprised by the control system 50.

[0045] Fig. 5 shows a block diagram of the control system 50 in accordance with certain example embodiments. The control system 50 comprises at least one processor 51 configured to control the operation of the apparatus 100 and at least one memory 52 comprising a computer program or software 53. The software 53 includes instructions or a program code to be executed by the at least one processor 51 to control the apparatus 100. The software 53 may typically comprise an operating system and different applications. In certain embodiments, the control system 50 is configured as a computerized system, which uses one or more computers.

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

[0047] The control system 50 may further comprise a user interface 56 to co-operate with an operator, for example, to receive input such as process parameters from the operator. In certain embodiments, the user interface 56 is connected to the at least one processor 51 .

[0048] As to the operation of the apparatus 100, the at least one processor 51 controls e.g. that the first pulsing valve 41 is open during the aluminum-containing (or metalcontaining) precursor pulse, and the second pulsing valve 42 is open during the oxygen-containing precursor pulse. Further, the at least one processor 51 controls that oxygen gas as carrier gas flows from the oxygen source X2 to the respective mixing region to mix with said oxygen-containing precursor once needed.

[0049] Fig. 6 shows a schematic block diagram of an ALD apparatus 200 in accordance with certain other embodiments. The ALD apparatus 200 otherwise corresponds to the ALD apparatus 100 (and can be complemented also with other features of apparatus 100) except that the separate in-feed lines into the reaction chamber 10 have been replaced by a common in-feed line having a common (inert) carrier gas. The sources Si and S2 connect with said common in-feed line at respective three- leg pulsing valves in which a first leg provides an inlet for the common carrier gas, a second leg is provides an inlet for a respective precursor (optionally carried with a carrier gas), and a third leg provides an outlet of the mixture of the common carrier gas and the respective precursor towards the reaction chamber 10. Oxygen gas O2 is, again, used as a carrier gas for the oxygen-containing precursor (e.g., H2O). In Fig. 6, the source Si is another precursor source (such as a metal-containing or an aluminum-containing precursor source), the source S2 is an oxygen-containing precursor source, Xo refers to said common (inert) carrier gas, Xi refers to the (inert) carrier gas (if any) for the metal-containing or aluminum-containing precursor (TMA or TEA in a specific embodiment), and X2 refers to the oxygen gas as carrier gas for the oxygen-containing precursor (H2O in a specific embodiment).

[0050] Without limiting the scope and interpretation of the patent claims, certain technical effects of one or more of the example embodiments disclosed herein are listed in the following. A technical effect is a reduction in required deposition temperature in ALD deposition, such as aluminum oxide deposition. A further technical effect is deposition at low temperature on substrates that are unable to withstand higher temperatures. A further technical effect is a more sophisticated chemical usage.

[0051] The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments of the invention a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented above, but that it can be implemented in other embodiments using equivalent means without deviating from the characteristics of the invention.

[0052] Furthermore, some of the features of the above-disclosed embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

Claims1 . An atomic layer deposition, ALD, method, comprising: depositing an ALD film onto a substrate surface in 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.

2. The ALD method of claim 1 , wherein the ALD film is a metal oxide film, preferably of aluminum oxide.

3. The ALD method of claim 1 or 2, comprising trimethylaluminum or triethylaluminum as said precursor.

4. The ALD method of any preceding claim, comprising: obtaining energy for a reaction of water vapor on the substrate surface by combusting, with the aid of said oxygen gas used as the carrier gas, methane released from the substrate surface.

5. The ALD method of any preceding claim, wherein said oxygen gas flows into a headspace of a water vapor precursor container.

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 said at least one processor is configured, based on stored instructions, to control the source system so as to alternately introduce a precursor and water vapor into the reaction chamber, with oxygen gas as carrier gas for the water vapor.

7. The ALD apparatus of claim 6, wherein the source system comprises a carrier gas valve in a carrier gas line allowing oxygen gas to mix with the water vapor upstream of the reaction chamber.

8. A computer program product which when run by at least one processor causes an ALD apparatus to: deposit an ALD film onto a substrate surface in a reaction chamber by alternately introducing a precursor and water vapor into the reaction chamber, and use oxygen gas as a carrier gas for the water vapor.

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