Method and apparatus for processing surface of substrate

Abstract

To further improve the quality of the interface between a substrate and a thin film grown by ALD on a compound semiconductor, to improve the quality of the compound semiconductor-ALD interface, to further simplify the required apparatus and reduce its quantity, and to reduce the amount of electricity and chemicals used, in ALD growth technology.SOLUTION: Aspects of disclosed embodiments relate to surface treatment of a substrate for growing high-quality thin film layers using atomic layer deposition (ALD), by first preparing the substrate surface and then generating an improved interface layer on the substrate surface prior to ALD growth. These processes are achieved within a single processing apparatus.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Aspects of the disclosed embodiments relate to processes and apparatus for manufacturing semiconductor devices. In particular, aspects of the disclosed embodiments relate to methods for producing the highest quality interface between a substrate and a thin film grown by ALD on a semiconductor substrate, particularly a compound semiconductor substrate, by first preparing the substrate and then creating an improved interfacial layer prior to ALD growth, wherein these processes are performed within the same processing chamber / processing reactor apparatus. [Background technology]

[0002] A compound semiconductor substrate is a semiconductor substrate, wafer, or epitaxially fabricated structure containing compound semiconductor materials. Compound semiconductors are classified according to the family of their constituent elements in the periodic table. Generally, these compounds can be classified as binary, ternary, or quaternary alloys, depending on the number of different atomic components that make up the semiconductor crystal. Examples include GaAs, GaN, SiC, AlGaN, and InAlGaP. In this context, the substrate is considered to present a structural pattern on one of its surfaces that defines an electronic device, such as a transistor, microLED, vertical cavity surface-emitting laser (VCSEL), photodetector, or diode.

[0003] Atomic layer deposition (ALD) is a technique for producing conformal, uniform inorganic thin films of materials with atomic layer precision. The technique involves half-cycle reactions in which precursor gases are repeatedly purged into the reaction chamber and onto the substrate. The reactions are self-terminating; that is, only one layer of the desired material is deposited on the target surface during one reaction cycle. When other reactants are introduced to the surface, they react with the previous precursor reactant and remove by-products / unreacted reactants. Thus, films ideally grow one atomic layer per half-cycle, making ALD a highly controlled thin film production method.

[0004] Amorphous native oxides are oxides of the substrate material that naturally form on the surface of semiconductors whenever the semiconductor is exposed to an oxygen source, such as air. These oxides are characterized by structural disorder, partially filled dangling bonds, and dimer-type and compound semiconductor oxide bonds, and therefore a high density of defects and associated states in the semiconductor bandgap. These defects result in detrimental properties such as Fermi level pinning, high surface recombination velocity, and leakage current, among others, and generally lead to poor electrical properties that are detrimental to semiconductor device performance.

[0005] Oxides with long-range order / highly ordered native oxides / ordered native oxides / long-range ordered native oxides are crystalline oxides with long-range order, where the surface atoms have similar or different translational symmetry compared to the compound semiconductor substrate (whereas amorphous oxides consist of irregularly shaped structures and have only short-range order). Highly ordered native oxides of a material are oxides that form on the surface of a material when exposed to some oxygen source and exhibit long-range order or crystalline alignment.

[0006] Compound semiconductors are known to undergo severe oxidation upon exposure to any oxygen source, such as air, and the native oxides formed are amorphous and therefore exhibit high levels of surface defects. It is important to remove these poor quality oxides prior to thin film growth.

[0007] Producing highly ordered native oxides, i.e., oxides with long-range order, that are crystalline and exhibit very low levels of surface defect states, can help improve the quality of interfaces between materials and, therefore, the quality of thin films grown on compound semiconductor materials.

[0008] In the semiconductor industry, substrates are subjected to multiple complex processes to produce all of the functional layers that provide the desired properties of the final chips fabricated from those substrates.

[0009] Many of these processes consist of depositing and growing functional layers or coatings by several thin film deposition techniques, such as chemical vapor deposition (CVD) or atomic layer deposition (ALD). Thin film deposition methods are used to produce conformal barriers, high-k dielectrics, gate dielectrics, tunnel dielectrics, and etch stop layers for semiconductor devices. ALD films are particularly attractive for optoelectronic, power electronic, and radio frequency applications because they are thermally stable and highly uniform.

[0010] To achieve the necessary high quality functionality, the surface of the substrate needs to be treated prior to thin film growth to remove contaminants and other defects resulting from poor quality amorphous native oxide.

[0011] It is well known that compound semiconductors, in particular, tend to oxidize aggressively, resulting in the immediate formation of an amorphous native oxide layer characterized by a high level of defect-state density, or surface defects, that hinder the performance of semiconductor devices. A surface preparation step is typically performed to remove these defects by processes such as the removal of the amorphous native oxide, e.g., dry or wet etching techniques. After the cleaning step, an interface deposition step may be applied, in which an interface material is created or deposited that will serve as a base for thin film growth. For example, this layer may be a few monolayers of AlN grown prior to the deposition of Al2O3.

[0012] All these processing steps are typically performed in different equipment. When transferring highly sensitive substrates from one process to another, there is a high risk of re-oxidation of the clean substrate surface or the appearance of contamination from the ambient atmosphere. For this reason, a common approach is to transfer the substrate from one equipment / processing chamber to the other through some kind of vacuum or inert gas transfer line. Furthermore, it is known in the art that unless the transfer is performed in an ultra-high vacuum (UHV) environment, some degree of oxidation of compound semiconductor substrates will always occur.

[0013] In existing methods for providing a functional layer on a substrate surface, all process steps, i.e., surface preparation, interface step, and step for providing the functional material layer, are performed in separate equipment, and at least two different processing chambers / equipment are required to perform all three steps.

[0014] After the substrate is prepared, it must be transferred to a thin film growth apparatus, during which time the substrate is exposed to oxygen.

[0015] To overcome these challenges, the industry uses cluster tools, in which all the required processing equipment is interconnected via some kind of transport mechanism that is kept under vacuum conditions to minimize exposure to oxygen. This results in very large and complex systems, making the production process slow and not efficient enough in terms of quality and productivity. Also, as explained earlier, the presence of oxygen during each processing step is more or less unavoidable, and native amorphous oxides still form on the surface of the compound semiconductor. (Figures 1 and 2 are examples of cluster tools.)

[0016] Regarding the ALD process itself, there are known techniques for improving the quality of the interface between the compound semiconductor and the dielectric film grown thereon. These techniques involve the use of multiple steps (such as cleaning, deposition of an interface layer or multiple layers), but all of these techniques always require the use of a cluster tool with at least two different processing chambers.

[0017] Additionally, particularly when growing thin films on compound semiconductors by ALD processes, the inventors have demonstrated that the oxygen levels present in the apparatus (at very low base pressure levels) or contained in either the precursors or the oxidizer react readily with the clean substrate surface, producing a suboptimal interface of amorphous native oxide between the compound semiconductor and the ALD-grown dielectric layer (Figure 4A). This is a critical issue for devices such as transistors, where the quality of the interface between different materials in the semiconductor stack directly impacts the performance of the final product.

[0018] ALD growth techniques are also known to be particularly time consuming and have a significant carbon footprint. ALD processes use chemical reactions of gaseous reactants in a vacuum chamber to obtain a coating with defined properties on the surface of a substrate, requiring significant amounts of chemicals, generating excessive by-products, and requiring significant amounts of electricity.

[0019] There is a need to further improve the quality of the interface between the substrate and the thin film grown by ALD on the compound semiconductor, as well as to improve the quality of the compound semiconductor-ALD interface, further simplify and reduce the amount of equipment required, and reduce the amount of electricity and chemicals used.

[0020] A known passivation method for compound semiconductor materials consists in generating long-range ordered oxide structures on the surface of the substrate (Laukkanen et al., Method for treating a substrate and a substrate, U.S. Patent No. 9,269,763). These long-range ordered oxide structures have proven to be stable and protective against further exposure to atmospheric atmospheres. In addition, the inventors have demonstrated how these structures can help generate a high-quality interface between the compound semiconductor and the ALD-grown layer (Figure 4B).

[0021] One advantage of using oxides with long-range order prior to thin-film growth is that they reduce the amount of atomic-level defects at the interface, so the amount of leakage current through the stack (ALD-grown insulator / dielectric material - passivation layer - compound semiconductor) is lower than the level obtained without the passivation layer. This means that the minimum thickness required for the isolation material to achieve similar performance can be reduced. This helps reduce the thickness of the thin films required to be grown by ALD, thus reducing the amount of chemicals used, electricity, waste generation, etc.

[0022] Currently, this combination of passivation processes with ALD is also performed by using separate equipment or by using equipment combined into clusters with different processing conditions. Summary of the Invention

[0023] Aspects of the disclosed embodiments are based on the idea of ​​providing a method and apparatus for producing the highest quality interface between a thin film grown by ALD and a compound semiconductor substrate by implementing an improved process that includes preparation and surface passivation steps prior to ALD growth, with the novelty that all three process steps occur within the same processing chamber. The surface passivation step selected for this method consists in producing a long-range ordered oxide layer on the surface of the substrate prior to thin film growth by ALD.

[0024] This process can be applied, for example, to form a gate dielectric stack in an AlGaN / GaN metal-insulator-semiconductor high-electron-mobility-transistor (MIS-HEMT) to improve the interface between the transistor channel material and the dielectric layer. This improved dielectric / compound semiconductor interface can result in better transistor performance, lower leakage current through the gate dielectric, and ultimately, as demonstrated by the present inventors, a reduction in the overall film thickness required to maintain a given level of leakage current (Marjukka Tuominen et al., Oxidation-Induced Changes in the ALD-Al2O3 / InAs(100) Interface and Control of the Changes for Device Processing (ACS Publications, December 3, 2018)). Furthermore, implementing such a good-quality interface can significantly improve the performance of enhancement-mode AlGaN / GaN HEMTs in RF and power electronics applications. In addition, such implementation leads to a more sustainable ALD process, since the amount of chemicals and electricity used to fabricate the chip can be reduced while maintaining similar or better electrical properties.

[0025] According to a first aspect, the above and further aspects and advantages are achieved by a method for processing a surface of a substrate. In one embodiment, the method is carried out in an apparatus having a single processing chamber, and all processing steps occur in the single processing chamber, the method comprising the following processing steps: a) a preparation step, b) a surface passivation step, and c) an ALD growth step, where the preparation step comprises treating the surface of the substrate to reduce contaminants, carbon, hydrocarbons, water, and / or amorphous native oxide from the surface of the substrate, the surface passivation step comprises an oxidation process to produce an oxide having high quality long-range order on the surface of the substrate, and the ALD growth step comprises growing a thin film by atomic layer deposition, and all of the processing steps occur in the single processing chamber.

[0026] In a possible implementation, the method further includes adjusting process conditions between each processing step, such that at least the substrate temperature, processing chamber pressure, and processing chamber wall temperature are adjusted to levels required by each processing step.

[0027] In a possible implementation, the preparation step further includes at least one or more of the following: a dry etching process to remove amorphous native oxide, annealing the substrate in a vacuum to remove adsorbed water and volatile atomic species from the surface of the substrate, and a surface stoichiometry modification step to obtain specific concentrations of elements at the surface of the substrate.

[0028] In a possible implementation, the preparation step includes annealing the substrate in a vacuum to remove adsorbed water and volatile atomic species from the surface of the substrate.

[0029] In a possible implementation, the surface stoichiometry modification step consists in depositing metal components to modify the substrate stoichiometry to have a higher concentration of elements, achieving an oxide with long-range order in a surface passivation step.

[0030] In a possible implementation, deposition of the metal component is performed by introducing a chemical metal precursor into the processing chamber.

[0031] In a possible implementation, the deposition of the metal component is performed by physical vapor deposition.

[0032] In a possible implementation, the stoichiometric modification step comprises only an annealing step of the substrate in at least high vacuum conditions.

[0033] In possible implementations, the method further includes using an inert gas curtain around the ALD reactive gas and precursor to prevent excess ALD reactive gas and precursor from reaching the walls of the single processing chamber.

[0034] In a possible implementation, the substrate includes a compound semiconductor material.

[0035] According to a second aspect, the above aspects and advantages, as well as further aspects and advantages, are provided by an apparatus for processing a surface of a substrate. In one embodiment, the apparatus includes a load lock, a processing chamber, and a transfer mechanism for transferring substrates from the load lock to and from the processing chamber, the load lock including at least a substrate holding mechanism, a door, and a pumping system for providing a vacuum and regulating the pressure of the load lock, the load lock being separated from the processing chamber by a gate valve configured to isolate pressure conditions between the load lock and the processing chamber, the processing chamber including a substrate holding mechanism, a substrate heating element, a pumping system for providing a vacuum, regulating the pressure of the processing chamber, and providing an exhaust system for gases and precursors during the processing step, a chamber wall temperature adjustment system, a gas delivery system, and a precursor delivery system, and the processing chamber is configured to achieve ultra-high vacuum conditions.

[0036] In a possible implementation, the apparatus is configured to adjust conditions to meet the requirements of each of the processing steps for processing the surface of the substrate.

[0037] In a possible implementation, the load lock further includes a substrate heating system.

[0038] In a possible implementation, the processing chamber has a double-walled structure or built-in fluid channels through which heating or cooling fluids are circulated to regulate the temperature of the chamber walls.

[0039] In a possible implementation, the processing chamber further includes a plasma source.

[0040] In a possible implementation, the processing chamber further includes an internal enclosure and a movable / retractable substrate holder and heater assembly that can be moved toward or retracted into the internal enclosure during the thin film growth process, and the apparatus further includes a movable shielding element that can isolate the internal enclosure from the heating source when the substrate holder and heater assembly is retracted to prevent excessive heating during the passivation process.

[0041] In a possible implementation, the precursor delivery system and gas manifold delivery system are arranged such that an inert gas curtain is provided around the precursor gas focused onto the substrate to prevent the precursor gas from reaching the walls of the processing chamber.

[0042] In possible implementations, ultra-high vacuum conditions include pressure conditions in the range of less than 5e-9 mbar. [Brief explanation of the drawings]

[0043] [Figure 1] 1 is a diagram of a prior art system in which multiple processing chambers are interconnected by modular tracks for transporting specimens, i.e., substrates (e.g., compound semiconductor substrates), from one chamber to another. Source: U.S. Pat. No. 8,859,441 (B2) [Figure 2] 1 is a diagram of a prior art system with multiple processing reactors connected to a transfer chamber. Source: Finnish Patent No. 129628(B) / US Patent Application Publication No. 2022 / 0356561(A1) [Figure 3] FIG. 1 is a diagram of a conventional atomic layer deposition reactor. [Figure 4A] High-resolution transmission electron microscope (HRTEM) image of the amorphous native oxide interface between a compound semiconductor and a thin film layer. Credit: R&D / Comptek Solutions [Figure 4B] High-resolution transmission electron microscope (HRTEM) image of an oxide interface layer with long-range order between a compound semiconductor and a thin film layer. Credit: R&D / Comptek Solutions [Figure 5] FIG. 1 is an exemplary process flow diagram of a novel process in accordance with aspects of the disclosed embodiment; [Figure 6] FIG. 1 is a schematic diagram of a tool for implementing the entire process in a single processing chamber. [Figure 7] 1 is a schematic diagram of a processing chamber with the basic components required to perform a complete process. [Figure 8] 1 is a schematic diagram of a processing chamber with a wall temperature control solution. [Figure 9] FIG. 1 is a schematic diagram of an approach to avoid condensation of ALD precursors on the walls of the process chamber by using an inert gas curtain around the precursor gas. [Figure 10] FIG. 1 is a schematic diagram of a processing chamber having an inner enclosure used to create a smaller processing environment during ALD growth and a movable / retractable substrate holder mechanism for moving the substrate closer to or further away from the inner enclosure. DETAILED DESCRIPTION OF THE INVENTION

[0044] A known passivation method for compound semiconductor materials consists in generating long-range-ordered oxide structures on the surface of the substrate. These structures have proven stable and protect the substrate against further exposure to atmospheric conditions. Furthermore, we have demonstrated how these structures can help generate high-quality interfaces between compound semiconductors and thin-film layers grown, for example, by ALD. Figure 4A shows a cross-section of a semiconductor stack with a thin film of Al2O3 (402) grown by ALD on a compound semiconductor material, in this case GaAs (400). Although the ALD growth was performed after cleaning the GaAs (400) surface, oxygen present in the equipment as well as oxygen from the ALD process itself oxidized the substrate material, forming an amorphous native oxide layer (401). In Figure 4B, we show the generation of a long-range-ordered oxide (403) on the same material, GaAs (400). This long-range ordered oxide exhibits a high degree of crystallinity and uniform thickness, creating a sharp interface between the substrate and the subsequent Al2O3 layer (402) grown on top of it.

[0045] The use of these long-range ordered oxides prior to thin-film growth reduces the amount of atomic-level defects at the interface, and the amount of leakage current through the stack (ALD-grown insulator / dielectric material - passivation layer - compound semiconductor) is lower than that obtained without the passivation layer. This means that the minimum thickness required for the insulator material to achieve similar performance can be reduced. This helps reduce the amount of ALD growth and therefore the amount of chemicals, electricity, waste generation, etc.

[0046] Aspects of the disclosed embodiment provide a solution consisting of an improved method for growing thin films by ALD with higher quality by combining three processes, and an apparatus in which these three processes are performed within a single processing chamber (101).

[0047] Processing step 1: Preparation of substrate (108) The surface of the substrate is prepared to obtain certain properties required to enable a subsequent second step, which may include, for example, removal of amorphous native oxide and contaminants by plasma treatment (dry etching process), thermal annealing under UHV conditions, etc., and / or modification of the substrate surface to obtain certain properties such as the desired stoichiometry and surface reconstruction.

[0048] Processing step 2: Passivation of the substrate surface by creating a long-range ordered oxide structure. A substrate surface passivation layer is produced, which is characterized by the formation of a high-quality long-range ordered oxide structure through the production of a highly ordered oxide of the substrate.

[0049] Process step 3: Thin film growth by ALD The thin film is grown on the passivation layer by atomic layer deposition (ALD). The ALD process may be, for example, thermal ALD, UV-assisted ALD, or plasma-enhanced ALD.

[0050] While process steps 1 and 3 have previously occurred in a single process chamber, such as a plasma-enhanced ALD reactor, process steps 2 and 3 have not been combined into a single process chamber because the processing conditions for each of these steps are significantly different. Passivation processes may require high substrate temperatures (e.g., 500°C to 1000°C) to operate on, for example, GaN or SiC substrates, compared to substrate temperatures (e.g., 100°C to 350°C) typically implemented during ALD growth.

[0051] The vacuum levels required for each process step are also quite different: the creation of oxide structures with long-range order may require up to ultra-high vacuum (UHV)-based pressure conditions (<5e-9 mbar) in the process chamber, while ALD typically only requires medium vacuum conditions (1e-3 mbar).

[0052] The temperature requirements of the processing chamber walls are also different for both processes.

[0053] Typically, ALD processes are performed at moderate temperatures (<350°C). The temperature range over which layer-by-layer growth is achieved depends on the specific ALD process and is referred to as the "ALD temperature window." Temperatures outside this window generally result in poor growth rates and non-ALD deposition due to effects such as slow reaction rates or precursor condensation (at low temperatures) and precursor thermal decomposition or rapid desorption (at high temperatures). This means that during ALD processes, to ensure high-quality thin film growth, the temperature throughout the chamber should be as uniform as possible, and the chamber walls may need to be heated, for example, to 150°C-200°C, to prevent precursor condensation on the chamber walls.

[0054] In contrast to the passivation process, the ideal situation is to keep the temperature of the chamber walls as low as possible to prevent outgassing of contaminants from the chamber walls. Typically, UHV conditions and high temperatures promote outgassing or outgassing of materials such as gas / water present on the chamber walls, which can adversely affect the passivation process, for example, as follows: If outgassing is too high, it becomes difficult to reach the base pressure required to obtain oxides with long-range order on the surface. Contaminants released from the wall may be deposited on the substrate.

[0055] One aspect to be considered in processing chamber design is how to minimize deposition or growth of precursors on the chamber walls.

[0056] Aspects of the disclosed embodiments provide an apparatus design that can implement the entire process, i.e., substrate surface preparation + surface passivation + ALD growth, without the need to transfer the substrate (108) between different processing chambers, maintaining the lowest contamination / oxidation levels on the substrate and obtaining the highest quality interface, resulting in the highest quality thin film. In addition, the amount and size of equipment required is also reduced, as all process steps can be performed within a single processing chamber (101) and no transfer mechanisms between different pieces of equipment are required. This represents a significant cost savings for manufacturers.

[0057] During the surface preparation step, the substrate surface is prepared to accommodate the interfacial layer, which can include several sub-processes, such as removing amorphous native oxide and / or removing contaminants such as carbon that are known to interfere with the formation of subsequent processes. This can be done, for example, by a dry etching process using atomic hydrogen generated by a radio frequency (RF) plasma or pyrolysis device.

[0058] Additional surface preparation subprocesses may be applied to modify the surface stoichiometry, resulting in certain surface reconstructions and compositions that may be beneficial for subsequent passivation steps. By modifying the stoichiometry of the substrate surface, it is possible to obtain compositions that exhibit higher concentrations of certain elements from Group III or Group V of the Periodic Table of Elements. This may be done by adding or removing some of these elements. The concentrations of these elements determine which types of long-range ordered oxides can be obtained, as well as the process parameters required to obtain them.

[0059] In one embodiment, this may be done by thermal annealing at least under high vacuum (HV) conditions, where the most volatile species can be evaporated from the surface. For example, in GaAs compounds, As and As oxides evaporate at lower temperatures than Ga, and therefore a certain Ga-rich surface stoichiometry and surface reconstruction can be obtained.

[0060] In another embodiment, the surface preparation step comprises a metal deposition step, where several metal elements, e.g., Sn, In, Ga, are deposited on the surface in order to functionalize and modify the surface stoichiometry and surface crystal reconstruction, obtain a more favorable surface structure for certain compound semiconductors, and act as a starting surface for subsequent passivation steps.

[0061] In one embodiment, metal deposition may be performed by an evaporation process, for example, using an effusion cell or an E-beam evaporator. In another embodiment, metals may be deposited by introducing metal precursors into the processing chamber, which react and deposit on the substrate surface, similar to a metal organic chemical vapor deposition (MOCVD) or ALD process.

[0062] In the passivation process, an interfacial layer (passivation layer) is formed on the surface of the substrate 108. The interfacial layer is composed of a combination of native oxides of the forming compounds on the substrate surface and native oxides that exhibit a long-range ordered structure.

[0063] The crystalline native oxides of these compound semiconductors are known to provide a stable passivation effect on the compound semiconductor surface. These long-range ordered oxides can be obtained, for example, by exposing the surface to a certain amount of oxidizing agent under certain pressure and temperature conditions specific to the particular compound semiconductor. The actual processing conditions depend on the reactivity of the oxidizing agent, the oxidizing agent exposure measured by Langmuir, and the reactivity of the substrate surface, which is determined by the preparation process (stoichiometry, reconstitution) and the substrate temperature. In addition, the chamber (101) must be designed to ensure that a base pressure at ultra-high vacuum (UHV) levels can be achieved to enable the passivation process.

[0064] In one embodiment, the oxidizer may be molecular oxygen. In another embodiment, the oxidizer may be atomic oxygen generated by a plasma. In another embodiment, the oxidizer may be, for example, ozone, HO, HO, CO, CO, NO, NO, etc.

[0065] Thin film growth is achieved by atomic layer deposition, a well-known and widely used process. In one embodiment, ALD growth is performed by a thermal ALD process. In another embodiment, ALD growth is performed by a plasma-enhanced ALD process. In another embodiment, ALD growth occurs by UV-assisted ALD.

[0066] The detailed process is at least as follows (Figure 5: Flowchart). 501. Insert substrate (108) into load lock (102): Load a sample (e.g., compound semiconductor substrate) (108) into the loading chamber or load lock (102). 502. Pump down the load lock (102) to match the vacuum level of the processing chamber (101): The loading chamber / load lock (102) is pumped down to the required vacuum level using the pumping system (106). 503. Gate valve (103) between chambers is opened: The gate valve (103) between the load lock (102) and the processing chamber (101) which is at the required vacuum level is opened. 504. Transferring the substrate (108) from the load lock (102) to the processing chamber (101): The substrate (108) is transferred to the processing chamber (101) via the transfer mechanism (107), and the substrate (108) is mounted on the substrate holding mechanism (116). Then, the transfer mechanism (107) is retracted. 505. Gate valve (103) closes 506. The substrate (108) is heated using the heating element (109) in the substrate holding mechanism (116) according to the required processing temperature until it reaches the preparation process temperature. 507. Adjust the pressure and wall temperature of the processing chamber (101) to the preparation process requirements: the required chamber pressure level is achieved by the pumping system (105), and the chamber wall temperature is regulated via the cooling / heating mechanisms (114, 115, 117). 508. Preparation step: The substrate surface is modified by different processes to obtain certain properties. At least a high temperature annealing step is carried out under at least high vacuum conditions. 509. Adjust the temperature of the substrate (108) for the passivation process. The temperature of the substrate (108) is set to a target temperature suitable for the upcoming passivation process. 510. The pressure in the processing chamber (101) and the temperature of the walls of the processing chamber (101) are adjusted to the temperature required for the passivation process. 511. Passivation Step: Creation of Long-Range Ordered Oxide Structure. The passivation process is performed to create a high-quality, long-range ordered oxide on the surface of the substrate (108). This is achieved by controlling the exposure of the oxidant, determined by the Langmuir coefficient, the sticking coefficient of the oxidant to the substrate (108), etc. This ordered native oxide constitutes the interfacial layer. The oxidant is introduced into the processing chamber (101), for example, via a leak valve (113) or a gas manifold line (111). 512. Decrease the temperature of the substrate (108) to the ALD growth requirements: The substrate (108) temperature is adapted to the ALD growth process. 513. Adjust the pressure and wall temperature of the processing chamber (101) for the ALD growth process. 514.ALD growth 515. The pressure in the processing chamber (101) and the load lock (102) is regulated to a similar level by the corresponding pumping systems (105, 106). 516. Gate valve (103) opens 517. Transfer the substrate (108) from the processing chamber (101) to the load lock (102). 518. Gate valve (103) closes 519. The load lock (102) is vented to reach atmospheric pressure. 520. Remove the sample (108) from the load lock (102)

[0067] Detailed process: The sample (108), i.e., a substrate, e.g., a compound semiconductor, is introduced into the loading chamber or load lock (102) through a door, e.g., a rapid entry door, and placed on a sample holding mechanism. This holding mechanism may be designed to hold one or more samples so that the load lock (102) does not have to be opened too frequently. Once the sample(s) (108) are introduced and the door is closed, the pressure in the loading chamber (102) is reduced to reach the required vacuum conditions. This is accomplished by a pumping system (106), which may include, e.g., pumps, valves, pressure gauges, and gas lines.

[0068] The loading chamber (102) may also include a heating mechanism, e.g., an IR lamp, that raises the temperature of the sample (108) while under high vacuum to a temperature high enough to evaporate any moisture or water present in the sample (108). This process is known as vacuum annealing and / or degassing. Such a process may, for example, help reduce the processing time required to achieve an adequate vacuum level in the processing chamber (101).

[0069] Once the vacuum level in the load lock (102) reaches the required vacuum level present in the processing chamber (101), the gate valve (103) between the chambers is opened.

[0070] The transfer mechanism (107) retrieves one specimen (108) from the holding mechanism in the load lock (102) and transfers it to the holding mechanism (116) in the processing chamber (101).

[0071] Thereafter, the transfer mechanism (107) is retracted to the outside of the processing chamber (101), and the gate valve (103) is closed.

[0072] The temperature of the sample (108) is then altered, for example, by a heating element (109) located within the holding mechanism (116) to reach the desired temperature for applying the preparation step.

[0073] The pressure in the processing chamber (101) is also regulated by a pumping system (105) to reach or maintain the required vacuum level specific to each preparation process sub-step. The pumping system (105) connected to the processing chamber (101) may include, for example, a turbomolecular pump (105A) to reach high vacuum levels, gate valves, gas lines, valves, and additional pumps (105B) to enable purging of gases or excess precursors used during the ALD process.

[0074] The preparation process can consist of different sub-processes, such as the use of a remote plasma containing, for example, argon, hydrogen, or nitrogen, provided to a plasma source (110) via a gas delivery system (111), which may include different types of valves and flow control mechanisms, such as mass flow controllers. While the sample (108) is maintained at a certain temperature, a plasma is generated via the radio frequency plasma source (110). This sub-process may remove amorphous native oxide from the substrate (108). The use of plasma may also help preferentially remove certain compounds or materials from the surface to achieve a specific stoichiometry that will be useful in subsequent passivation processes.

[0075] Another preparation sub-step may consist, for example, in the deposition or growth of certain metal elements on the substrate surface using chemical precursors (e.g., trimethylgallium Ga(CH3)3, trimethylindium In(CH3)3) at certain temperature and pressure levels. The precursors may be injected via a dedicated precursor injection line (112). For those skilled in the art, this is a well-known setup used, for example, in ALD reactors or metalorganic chemical vapor deposition (MOCVD) apparatus.

[0076] Metal deposition may also be performed by well-known physical vapor deposition processes such as effusion cell, pulsed laser deposition, sputter deposition, thermal evaporation, or electron beam evaporator.

[0077] Another approach to modifying the stoichiometry may be to perform high-temperature annealing under at least high-vacuum conditions. The temperature of the substrate (108) is adjusted via heater elements (109). During this process, due to the different vaporization temperature limits of the constituent elements of compound semiconductors, it is possible to modify the surface composition of the material by forcing the vaporization of some elements.

[0078] During each sub-step of the preparation process, the vacuum and temperature conditions of the chamber (101) and the temperature of the sample (108) are adjusted and controlled. The wall temperature of the processing chamber (101) is controlled by some cooling / heating mechanism (104).

[0079] After the preparation step, the pressure and chamber wall temperature are readjusted to the required levels to proceed with the passivation step.

[0080] The passivation process is achieved by controlling the amount of oxidant exposure to the process chamber (101) and the substrate (108) while maintaining the substrate temperature at the required level. The oxidant exposure, defined by the Langmuir (L) method, is determined by the oxidant reactivity and the substrate surface reactivity toward the oxidant. In one embodiment, the oxidant exposure can be established, for example, through the injection of molecular oxygen gas into the process reactor (101). In another embodiment, the oxidant can be atomic oxygen generated by a radio frequency plasma source (110). In yet another embodiment, the oxidant can be hydrogen peroxide (HO) vapor, carbon monoxide (CO), carbon dioxide (CO), nitric oxide (NO), or nitrogen dioxide (NO). The oxidant administration can be achieved, for example, through a leak valve (113) or a mass flow controller (MFC). Controlling the temperature and oxidant exposure of the sample substrate (108) can produce oxides with long-range order on the sample surface. This can be monitored, for example, by using a reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED) ellipsometer, or reflectance anisotropy spectroscopy (RAS) instrument installed within the processing chamber (101). These techniques are used to characterize the surface structure, orientation, and roughness of crystalline materials. It is known in the art that different materials require different process parameters, and such processes may require an initial chamber base pressure at ultra-high vacuum levels.

[0081] Once the passivation layer is formed, the temperature of the substrate (108) is reduced to the level required to proceed with ALD growth, as determined by the target material being grown and the precursors being used. Simultaneously, the wall temperature of the process chamber (101) is increased to the level required to prevent precursor condensation on the chamber walls and non-ALD growth. The vacuum level is also adjusted to the required level typically used in ALD growth. This can be achieved, for example, by introducing an inert gas (e.g., N2, Ar) into the process chamber (101).

[0082] In one embodiment, the pressure in the processing chamber (101) is adjusted to match the conditions required by ALD growth such that when in the UHV region, the valve to the pump is closed and the first ALD precursor pulse is introduced into the chamber (101) (still in the UHV range).

[0083] ALD growth is performed by using precursor injection lines (112) and other necessary components mounted on the processing chamber (101), such as a plasma source (110) or an inert gas line manifold (111). The components required to perform ALD growth are well known in the industry. A simple schematic is shown in Figure 3.

[0084] After ALD growth is performed, the pressure in the processing chamber (101) is adjusted to match the pressure in the load lock (102). Once they are equal, the gate valve (103) is opened and the sample (108) is transferred by the transfer mechanism (107) to the holding mechanism in the load lock (102).

[0085] The gate valve (103) is then closed and the pressure in the load lock (102) is adjusted to reach atmospheric pressure via some venting mechanism, for example a pumping system (106) including a nitrogen line and a leak valve.

[0086] Once the pressure matches atmospheric pressure, the load lock (102) can be opened and the sample (108) can be removed.

[0087] These three processes are carried out in a single processing chamber (101) designed to operate under ultra-high vacuum (UHV) conditions and equipped with the components necessary to perform the three processing steps. To achieve UHV pressure levels, the processing chamber must be designed using components and connections designed to do so, such as the use of standard conflat flanges and conflat gaskets, the connection of components to the processing chamber, and the use of valves, gate valves, and / or other components designed and constructed with appropriate sealing and gasketing to operate under UHV pressure levels. The components, gaskets, and flanges used to achieve UHV pressure levels are well known in the industry.

[0088] The processing chamber (101) is connected to a load lock (102) and separated by a gate valve (103). A transfer mechanism (107) is provided to move the substrate (108) from the load lock (102) to the processing chamber (101) and vice versa while maintaining the required vacuum conditions (Figure 7).

[0089] Both the processing chamber (101) and the load lock (102) have their own pumping units / systems (105, 106) that are used to achieve the required vacuum levels within the processing chamber (101) and the load lock chamber (102).

[0090] The load lock (102) should include at least the following: 1. A substrate holding mechanism that can hold a single substrate (108) or multiple substrates, for example a cassette mechanism for holding multiple substrates. 2. A pumping unit (106) for varying and achieving the required vacuum level, which may include turbomolecular pumps, vent valves, gate valves, and other pressure regulation mechanisms. 3. A door for introducing the sample (108) into the load lock (102).

[0091] In another embodiment, the load lock (102) may also include a sample heating system, e.g., IR lamps, to heat the sample (108) after loading, such that an initial degassing / annealing process removes absorbed water, etc., before transferring the substrate to the processing chamber (101). This will help achieve the required vacuum level more quickly.

[0092] The processing chamber (101) includes at least: 1. A substrate fixture (116) into which the substrate (108) is transferred from the load lock (102) via the transfer mechanism (107). 2. A substrate heating element (109) that changes the substrate temperature according to process requirements. 3. A substrate temperature measuring element, such as a thermocouple, pyrometer, or band edge thermometer. 4. A pumping system (105) for achieving the required vacuum level (105A) and for evacuating residual gases and precursors during the ALD growth process. (105B) 5. A chamber wall temperature control system (104) that varies the chamber wall temperature to the level required for a particular process step. 6. A gas delivery system (111) for providing different types of gases for all process steps. This system may include, for example, regulating valves, mass flow controllers, etc. to ensure accurate dosing of such gases. 7. A precursor / chemical delivery system (112) for providing the chemicals required during the preparation and ALD growth processes.

[0093] In one embodiment, the processing chamber (101) also includes an RF plasma source (110) or pyrolysis device, for example, to perform preparation steps such as native oxide removal, to generate oxygen plasma during passivation steps, or to enable plasma-enhanced ALD growth.

[0094] In yet other embodiments, the processing chamber (101) may include a LEED system, RHEED, ellipsometer, or reflectance anisotropy spectroscopy (RAS) instrument to monitor surface crystalline quality.

[0095] The substrate (108) temperature measurement element may be, for example, a thermocouple. In another embodiment, substrate temperature measurement may be performed using an IR thermal camera mounted outside the processing chamber (101) and focused on the substrate (108) through a window in the chamber. In another embodiment, the temperature of the substrate (108) may be determined using an optical spectrometer, band edge thermometer, or pyrometer.

[0096] The processing chamber (101) is designed so that the wall temperature can be altered during processing, either by cooling or heating. In one embodiment, this is done by using a double-walled processing chamber (101) in which a cooling / heating liquid can be circulated, the liquid being delivered by a heating / cooling device (104), and the temperature of the chamber wall can be measured by some temperature measuring element (120), for example a thermocouple.

[0097] In another embodiment, the wall temperature control system is created by combining different cooling and heating systems. For example, cooling of the chamber is performed by circulating a cooling fluid (114, 115) through a double wall or through fluid channels constructed in the chamber walls. Heating of the chamber is performed via separate heating elements placed in the walls of the processing chamber (101). These may be, for example, heating tapes or heating jackets (117) covering a sufficient wall surface of the chamber to achieve the required wall temperature distribution. Both solutions are well known in the art.

[0098] The pumping system (105) of the processing chamber (101) may include several pumps, such as a turbomolecular pump (105A), a cryopump, an ion getter pump, a diffusion pump, a titanium sublimation pump for achieving ultra-high vacuum conditions, gate valves (105C, 105D) for isolating the pumps during certain process steps, and an additional pump (105B) for evacuating residual gases during the ALD process.

[0099] In one embodiment, the design of the processing chamber (101) may include the use of certain techniques to prevent excess contamination (material growth, precursor condensation) on the walls during the ALD process. For example, a known technique is to use an inert gas curtain (902) around the ALD reactive gases and precursors (903) to prevent their excess from reaching the chamber walls and direct them toward a pumping / exhaust unit (904). This can be achieved, for example, using a gas distribution head (901) that circulates inert gas supplied by a gas delivery system (905) to an exterior region, while precursors supplied by a precursor delivery system (906) and using some carrier gas, e.g., Ar, are introduced through the interior region of the head (901). The pressure and volume of the inert gas curtain are selected to create a barrier to prevent the expansion of precursors and chemicals through it ( FIG. 9 ).

[0100] In another embodiment (FIG. 10), the processing chamber (101) includes an inner protection / enclosure (1000) that forms a smaller enclosure around the substrate (108) when the ALD process is performed, protecting the walls of the main processing chamber (101) from precursor condensation or growth. The substrate holder (116) and substrate heater (109) assembly may be mounted on a linear shift mechanism (1005) so that the assembly can be moved toward the enclosure (1000). The precursor delivery system (112) may have two individual inlets with corresponding valves, one (1003A) providing precursor inside the enclosure and the other (1003B) providing precursor outside the enclosure toward the substrate (108) when in the retracted position. The plasma source (110) may also have two distinct plasma inlet regions (1004), one directing the plasma toward the inside of the enclosure and the other directing the plasma toward other regions of the processing chamber (101). When the ongoing process is not ALD growth, the substrate holder (116) may be in a retracted position, resulting in some distance between the substrate (108) and the enclosure (1000), and a moving shielding element (1001) may protect the enclosure (1000) from the heat source / hot substrate (108, 109). This moving shielding element (1001) prevents heating of the interior surface of the enclosure (1000), and therefore prevents contaminated walls from outgassing the enclosure.

Claims

1. 1. A method for processing a surface of a substrate, the method being carried out in an apparatus having a single processing chamber in which all processing steps occur, the method comprising the following processing steps: a) a preparation step; b) a surface passivation step; and c) an ALD growth step; the preparing step includes treating a surface of the substrate to reduce contaminants, carbon, hydrocarbons, water, and / or amorphous native oxides from the surface of the substrate; the surface passivation step comprises an oxidation process to produce a high quality long range ordered oxide on the surface of the substrate; the ALD growing step includes growing a thin film by atomic layer deposition; A method for processing a surface of a substrate, wherein all of the processing steps occur within the single processing chamber.

2. 10. The method of claim 1, further comprising adjusting process conditions between each processing step, wherein at least the substrate temperature, the processing chamber pressure, and the processing chamber wall temperature are adjusted to levels required by each processing step.

3. The preparation step includes the following steps: a dry etching process to remove the amorphous native oxide; annealing the substrate in a vacuum to remove adsorbed water and volatile atomic species from the surface of the substrate; and 4. The method of claim 1, further comprising at least one of the following steps: surface stoichiometry modification to obtain specific concentrations of elements at the surface of the substrate.

4. The method of claim 1 , wherein the preparing step comprises annealing the substrate in a vacuum to remove adsorbed water and volatile atomic species from the surface of the substrate.

5. 4. The method of claim 3, wherein the surface stoichiometry modification step consists in depositing metal components to modify the stoichiometry to have higher concentrations of elements, thereby achieving an oxide with long-range ordering in the surface passivation step.

6. The method of claim 5 , wherein the deposition of the metal component is performed by introducing a chemical metal precursor into the processing chamber.

7. The method of claim 5 , wherein the deposition of the metal component is performed by physical vapor deposition.

8. The method of claim 3 , wherein the stoichiometric modification step comprises at least the step of annealing the substrate in high vacuum conditions.

9. 10. The method of claim 1, further comprising using an inert gas curtain around the ALD reactive gases and precursors to prevent excess of the ALD reactive gases and precursors from reaching walls of the single processing chamber.

10. The method of claim 1 , wherein the substrate comprises a compound semiconductor material.

11. An apparatus for processing a surface of a substrate, the apparatus comprising: a load lock; a processing chamber; and a transfer mechanism for transferring the substrate from the load lock to and from the processing chamber; the load lock including at least a substrate holding mechanism, a door, and a pumping system for providing vacuum and regulating pressure in the load lock; the load lock is separated from the processing chamber by a gate valve configured to isolate pressure conditions between the load lock and the processing chamber; The processing chamber comprises: a substrate holding mechanism, a substrate heating element, a pumping system for providing a vacuum and regulating the pressure of said processing chamber and for providing an exhaust system for gases and precursors during processing steps, a chamber wall temperature adjustment system, a gas delivery system, and a precursor delivery system; The processing chamber is configured to achieve ultra-high vacuum conditions, and the apparatus is configured to adjust the conditions to meet the requirements of each of the processing steps for processing the surface of the substrate.

12. The apparatus of claim 11 , wherein the load lock further comprises a substrate heating system.

13. 12. The apparatus of claim 11, wherein the processing chamber has a double-walled structure or built-in fluid channels through which heating or cooling fluids are circulated to regulate the temperature of the chamber walls.

14. The apparatus of claim 11 , wherein the processing chamber further comprises a plasma source.

15. the processing chamber further comprising an inner enclosure and a movable / retractable substrate holder and heater assembly that can be moved toward or retracted into the inner enclosure during a thin film deposition process; 12. The apparatus of claim 11, further comprising a moving shielding element capable of isolating the inner enclosure from a heat source when the substrate holder and the heater assembly are retracted to prevent excessive heating during a passivation process.

16. 12. The apparatus of claim 11 , wherein the precursor delivery system and gas manifold delivery system are arranged such that an inert gas curtain is provided around the precursor gas focused onto the substrate to prevent the precursor gas from reaching walls of the processing chamber.

17. The apparatus of claim 11, wherein the ultra-high vacuum conditions include pressure conditions in the range of less than 5e-9 mbar.

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