Etching method

Abstract

Provided is an etching technology which provides high uniformity in the etching amount and has an improved yield of etching processing. This etching method for etching a film layer to be processed which contains titanium carbide and is disposed on a surface of a wafer comprises: a step for supplying a surface of the film layer with reactive particles that contain fluorine and oxygen but do not contain hydrogen, thereby forming a reaction layer on the surface of the film layer; and a step for heating the film layer to detach the reaction layer.

Description

Etching Method

[0001] The present disclosure relates to a method for etching a film layer containing a metal carbide, such as a titanium carbide film, using plasma.

[0002] Driven by the widespread use of mobile devices such as smartphones, semiconductor devices are becoming increasingly highly integrated. In the field of semiconductor devices for storage, three-dimensional (3D) NAND flash memory, in which memory cells are stacked in multiple layers in three dimensions, is being mass-produced. In addition, in the field of semiconductor devices for logic, fin-type field-effect transistors (FETs), which have a fine three-dimensional structure, have become the mainstream transistor structure. Currently, stacked nanowire FETs are approaching the practical application stage, aiming to further improve integration.

[0003] As device structures become more three-dimensional and feature sizes become smaller, the need for etching techniques that combine isotropy with high-level atomic-level feature size control is increasing in device manufacturing processes (semiconductor device manufacturing methods). Conventionally, such isotropic etching techniques have been widely used, including etching of silicon dioxide using a mixed aqueous solution of hydrofluoric acid and ammonium fluoride, etching of silicon nitride using hot phosphoric acid, and wet etching. However, these conventional wet etching techniques using such chemical solutions have a problem: as patterns become smaller, pattern collapse due to the surface tension of the rinse solution becomes apparent.

[0004] For example, when using high-aspect-ratio silicon patterns, it has been reported that the critical value of the pattern spacing at which the pattern begins to collapse due to surface tension when the rinse solution dries increases in proportion to the square of the aspect ratio. For this reason, there has been a strong demand for the development of a process method for isotropically etching various films without using chemical solutions.

[0005] On the other hand, metal carbide films such as titanium carbide and titanium aluminum carbide are widely used as work function metals in the above semiconductor devices. Therefore, a titanium carbide etching technology that combines isotropy, high dimensional controllability at the atomic layer level, and high selectivity is required for the manufacturing process of next-generation semiconductor devices.

[0006] A conventional technique for etching a titanium carbide film using plasma without using a chemical solution is proposed, for example, in Japanese Patent Laid-Open Publication No. 01-223733 (Patent Document 1).

[0007] Patent Document 1 discloses a method for etching and removing a titanium carbide film using CF ４ / O ２ The technique for etching using plasma is disclosed.

[0008] Japanese Patent Application Publication No. 01-223733

[0009] The conventional technology disclosed in Patent Document 1 has had problems due to insufficient consideration of the following points.

[0010] That is, although the technology of Patent Document 1 discloses a technique for etching titanium carbide, it does not take into consideration the conditions for isotropically etching a film to be processed that has been deposited on a pattern, such as in the fabrication process of work function metals. In particular, when conformal etching at the atomic layer level is required in a fine three-dimensional structure, such as in the fabrication process of work function metals for finFETs and stacked nanowire FETs, the etching rate differs between the top and bottom of the pattern, and the resulting vertical variation in the film thickness of the processed film after etching is not taken into consideration. For this reason, the technology of Patent Document 1 has a problem in that a large variation in the amount of etching of the film layer to be processed occurs in the vertical (depth) direction of the pattern formed in the film structure, which reduces the yield of the etching process (etching step) for semiconductor devices.

[0011] Furthermore, in the technology of Patent Document 1, the etching of the titanium carbide film progresses continuously in response to an increase in etching time. In such a continuous etching process, the amount of etching is adjusted by detecting and adjusting the time after the start of the etching process. This type of adjustment of the amount of etching based on the etching process time makes it difficult to accurately adjust the extremely fine amount of etching required in the manufacturing process of next-generation and later fine semiconductor devices, for example, etching with an etching depth (width) at the atomic layer level, which may result in a loss of precision and a loss of yield in the etching process.

[0012] As described above, in the continuous plasma etching technique of Patent Document 1, the etching amount is non-uniform due to the distribution of radicals, and the uniformity of the etching amount in the wafer in-plane direction and the pattern depth direction is low, and the etching amount must be controlled by the plasma processing time. For this reason, the continuous plasma etching technique of Patent Document 1 is likely to have limited applicability in next-generation and future device manufacturing processes that require high dimensional control at the atomic layer level.

[0013] An object of the present disclosure is to provide an etching technique that provides highly uniform etching amounts and improves the yield of etching processing.

[0014] Other objects and novel features of the present disclosure will become apparent from the description of this specification and the accompanying drawings.

[0015] A brief summary of representative aspects of this disclosure is as follows.

[0016] An etching technique according to one embodiment of the present disclosure is an etching method for etching a film layer to be processed, which contains metal carbides and is arranged on the surface of a wafer, and includes a step of supplying reactive particles containing fluorine and oxygen but not hydrogen to the surface of the film layer to form a reaction layer containing metal-fluorine bonds on the surface of the film layer, and a step of heating the film layer to detach the reaction layer.

[0017] The effects obtained by the representative aspects of the present disclosure can be briefly explained as follows.

[0018] The etching technique disclosed herein can improve the uniformity of the etching amount and the yield of the etching process. For example, when etching a titanium carbide film as a film layer containing metal carbide to be processed, it is possible to provide an isotropic atomic layer etching technique that achieves high uniformity of the etching amount in the wafer in-plane direction and the pattern depth direction, and high dimensional controllability at the atomic layer level.

[0019] FIG. 1 is a longitudinal cross-sectional view schematically illustrating the configuration of a plasma processing apparatus according to an embodiment of the present disclosure. FIG. 2 is a flowchart illustrating an outline of the flow of an etching process for a titanium carbide-containing film pre-formed on a wafer, performed by the plasma processing apparatus according to an embodiment of the present disclosure. FIG. 3 is a time chart illustrating the changes over time of multiple parameters included in the process conditions during wafer processing according to the embodiment shown in FIG. 1. FIG. 4 is a cross-sectional view schematically illustrating the changes in the structure of a film containing titanium carbide during wafer processing according to the embodiment shown in FIG. 3. FIG. 5 is a diagram illustrating the analysis results of a wafer surface according to the embodiment shown in FIG. 1. FIG. 6 is a diagram illustrating the reaction time dependence of the amount of surface reaction layer generated according to the embodiment shown in FIG. 1. FIG. 7 is a diagram illustrating the heating temperature dependence of the amount of remaining surface reaction layer according to the embodiment shown in FIG. 1. FIG. 8 is a graph illustrating the relationship between the number of cycles and the amount of etching in the etching process performed by the plasma processing apparatus according to the embodiment shown in FIG. 1. FIG. 9 is a graph illustrating the relationship between the number of cycles and the amount of etching in the etching process performed by the plasma processing apparatus according to the embodiment shown in FIG. 1, showing the results when the wafer temperature is changed. 10 is a longitudinal cross-sectional view schematically showing a change in a fine, high-aspect-ratio film structure formed on a sample on a substrate such as a semiconductor wafer to be processed when the film structure is subjected to plasma etching according to the technique of the present disclosure. FIG. 11 is a longitudinal cross-sectional view schematically showing a change in a fine, high-aspect-ratio film structure formed on a sample on a substrate such as a semiconductor wafer to be processed when the film structure is subjected to plasma etching according to a conventional technique.

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the same components are designated by the same reference numerals, and repeated description may be omitted. In addition, the drawings may be more schematic than the actual embodiment to clarify the description, but they are merely examples and do not limit the interpretation of the present disclosure.

[0021] In a process for forming a work function metal in a manufacturing process of a semiconductor device, for example, a finFET, a technology is considered to be required for isotropic etching of a titanium carbide film formed on a fine fin structure with a high aspect ratio, with high precision at the atomic layer level. Therefore, the present inventors have studied, as an example, a case where a structure such as that shown in FIG. 11 is subjected to etching using plasma by a conventional technology.

[0022] 11 is a longitudinal cross-sectional view showing a change in a film structure when a predetermined structure having a plurality of fin structures adjacent to each other on the left and right sides is subjected to plasma etching by a conventional technique, and (a) to (c) of this Figure show three stages of the shape of the film structure that change as a result of the etching process.

[0023] Fig. 11(a) is a diagram showing a film structure in a state before plasma etching has started. The film structure is a film structure in which a titanium carbide film 903 to be processed and a mask 904 to protect the titanium carbide film 903 in the portion not to be processed are formed on the surface of a fin structure 902 formed on an underlying structure 901. Fig. 11(b) is a diagram showing a state in which etching of the titanium carbide film 903 has progressed. In Fig. 11(b), tetrafluoromethane (CF ４ ) and oxygen (O ２ ) gas (hereinafter referred to as CF ４ / O ２A plasma is formed using a fluorine-containing gas (hereinafter referred to as a gas). Then, reactive species 905 containing fluorine in the plasma are supplied into grooves 911 of the film structure and reacted with the surface of the titanium carbide film 903 while the wafer temperature is maintained at room temperature. This results in the formation of reaction products 906 containing titanium fluoride, which are removed upward, and the etching of the titanium carbide film 903 has progressed. FIG. 11( c ) is a diagram showing the state after the etching of the titanium carbide film 903 using the plasma has stopped. In this example, the fin structure 902 is made of silicon and is formed in advance on the base structure 901, and its surface is coated with hafnium oxide or titanium nitride (not shown).

[0024] The present inventors' investigations have revealed the following. Specifically, as shown in FIG. 11B , an attempt was made to uniformly etch only the titanium carbide film 903 inside a high-aspect-ratio trench 911, whose sidewalls were made up of a structure in which the surface of a fin structure 902 was covered with a titanium carbide film 903. However, because a low wafer temperature that would suppress the volatilization of the reaction product 906 was not used, a surface reaction layer was not retained on the surface of the titanium carbide film 903. It was confirmed that etching proceeded continuously due to continuous desorption caused by the volatilization of the reaction product 906. Meanwhile, reactive species 905 supplied from the plasma formed above the sample penetrated into the trench 911 from above and were consumed by the titanium carbide film 903 formed near the opening at the top of the trench 911. Therefore, the amount of reactive species 905 reaching the titanium carbide film 903 in the lower portion 9111 of the trench 911 (the bottom of the trench 911) was reduced. 11(c), the distribution of the amount of etching of the titanium carbide film 903 becomes non-uniform in the vertical direction of the trench 911, and as a result, the amount of etching of the titanium carbide film 903 becomes large near the opening of the upper part 9112 of the trench 911 and small near the lower part 9111 of the trench 911. As a result, when etching the titanium carbide film 903 using conventional technology, the non-uniform distribution of the amount of etching of the titanium carbide film 903 occurs, which may reduce the yield of sample processing or semiconductor device manufacturing.

[0025] As described above, with conventional plasma-based etching techniques, the amount of etching of the titanium carbide film 903 is non-uniform due to the distribution of radicals, resulting in low uniformity in the amount of etching of the titanium carbide film 903 in the wafer in-plane direction and in the pattern depth direction, and the amount of etching of the titanium carbide film 903 must be controlled by the plasma treatment time. For this reason, it is believed that the application of conventional continuous plasma etching techniques will be limited in next-generation and future device manufacturing processes that require high dimensional control at the atomic layer level.

[0026] The present inventors have attempted to etch titanium carbide films using plasmas of various gases. As a result, they have discovered the following (1) to (3): (1) By supplying plasma of a gas containing fluorine and oxygen but not hydrogen to a titanium carbide film, a surface reaction layer composed mainly of titanium-fluorine (Ti-F) bonds is formed on the surface of the film. (2) The amount of this surface reaction layer produced is self-saturating (self-limiting). (3) The surface reaction layer can be removed by heating.

[0027] The present disclosure was made based on these new findings ((1)-(3)). The method for etching a titanium carbide film (a film layer to be treated) specifically includes the following steps: 1) etching a titanium carbide film with tetrafluoromethane (CF ４ ) and oxygen (O ２ ), and supplying reactive particles containing fluorine and oxygen but not hydrogen from the plasma to the surface of the titanium carbide film to be etched, to form a surface reaction layer on the surface of the titanium carbide film (also referred to as a surface reaction layer formation step); and second step) subsequently, a step of removing the surface reaction layer by heating (or a step of detaching the surface reaction layer by heating) (also referred to as a surface reaction layer removal step).

[0028] These two steps (first step and second step) are treated as a single cycle, and this cycle is repeated multiple times to achieve a desired amount of etching of the titanium carbide film.

[0029] With the above-described configuration, the surface reaction layer formation process and the surface reaction layer removal process are self-saturating, thereby suppressing non-uniformity in the amount of etching in the in-plane direction of the wafer and in the depth direction of the pattern of film structures such as trenches or holes. Furthermore, the thickness of the titanium carbide film removed in one cycle can be adjusted with high precision at the atomic layer level, and the amount of etching obtained by repeating the cycle can be adjusted by the number of repeated cycles, thereby improving the dimensional precision of semiconductor devices formed by etching the laminated titanium carbide film.

[0030] 10A to 10C are longitudinal cross-sectional views schematically illustrating changes in a fine, high-aspect-ratio film structure formed on a sample on a substrate such as a semiconductor wafer to be processed when the film structure is subjected to plasma etching according to the technique of the present disclosure. (a) to (c) of FIG. 10 show three stages of the shape of the film structure that change as a result of the etching process.

[0031] 10(a) is a diagram showing a film structure in which a titanium carbide film 903 to be processed and a mask 904 to protect the titanium carbide film 903 in the portion not to be processed are formed on the surface of a fin structure 902 formed on an underlying structure 901, and the film structure is in a state where plasma etching has not yet started. FIG. 10(b) shows a film structure in which tetrafluoromethane (CF ４ ) and oxygen (O ２ ), and reactive particles containing fluorine and oxygen but not hydrogen are supplied from the plasma to the surface of the titanium carbide film 903 to be etched that is not covered by the mask 904, forming a surface reaction layer on the surface of the titanium carbide film 903 to be etched. Next, this surface reaction layer is removed (desorbed) by heating. That is, a step of forming a surface reaction layer (first step) and a step of desorbing the surface reaction layer by heating (second step) are performed. These two steps (first step and second step) are then considered as a single cycle, and this cycle is repeated multiple times to achieve the desired amount of etching of the titanium carbide film.

[0032] 10(c), the titanium carbide film 903 to be etched, which is not covered by the mask 904, can be selectively etched away. Furthermore, the gas of the present disclosure does not contain hydrogen, and therefore does not etch nitride films such as titanium nitride. With the gas of the present disclosure, titanium nitride oxide is formed on the surface of the titanium nitride, and etching stops.

[0033] In contrast, for example, trifluoromethane (CHF ３ ) and oxygen (O ２ When a mixed gas of titanium nitride and titanium carbide is used, a surface reaction layer of ammonium titanium fluoride or the like is formed on the surface of the titanium nitride, and this surface reaction layer of ammonium titanium fluoride or the like volatilizes during the heating step, resulting in etching of the titanium nitride. However, in this case, there is a problem that the method cannot be applied to processes that selectively etch titanium carbide relative to titanium nitride, such as the fabrication process of work function metals. For a more detailed explanation of Figures 10(a)-(c), please refer to the explanation of Figures 4(a)-(c) below.

[0034] In the following examples, the term atomic layer etching refers to an etching process that involves repeating a set of steps (steps 1 and 2), each of which includes a self-saturating surface reaction layer formation step (step 1) and a self-saturating surface reaction layer removal step (step 2). In this example, "atomic layer" etching is not limited to atomic layer etching in the narrow sense, in which the etching volume per cycle is equivalent to the thickness of a layer composed of a single atom of the material that makes up the target film. Even if the etching volume per cycle is on the order of nanometers or larger, the process is referred to as atomic layer etching if each step tends to be self-saturating, i.e., self-limiting, with respect to processing time, etc. Terms such as "digital etching," "self-limiting cycle etching," "atomic level etching," and "layer-by-layer etching" can also be used to refer to equivalent processes.

[0035] Hereinafter, the present disclosure will be described with reference to the accompanying drawings.

[0036] Examples of the present disclosure will be described below with reference to FIGS. 1 to 9. In the examples, the following etching techniques are described: First, tetrafluoromethane (CF ４ ) and oxygen (O ２ The first step is to form a surface reaction layer on the surface of the titanium carbide film to be treated using plasma generated from a mixed gas of nitrogen (N) and argon (Ar). The second step is then to remove the surface reaction layer by heating the wafer with an infrared lamp. This results in isotropic atomic layer etching of the titanium carbide film to be treated, which has been formed in advance on a semiconductor wafer such as silicon.

[0037] FIG. 1 is a vertical cross-sectional view schematically illustrating the configuration of a plasma processing apparatus according to an embodiment of the present disclosure.

[0038] The processing chamber 1 is composed of a base chamber 11, in which a wafer stage 4 (hereinafter referred to as stage 4) is installed for placing a wafer 2 (hereinafter referred to as wafer 2), which is a sample to be processed. The plasma source uses an ICP (Inductively Coupled Plasma) discharge method, and above the processing chamber 1, a plasma source equipped with a quartz chamber 12, an ICP coil 34, and a high-frequency power supply 20 is installed. Here, the ICP coil 34 is installed outside the quartz chamber 12.

[0039] A high-frequency power supply 20 for generating plasma is connected to the ICP coil 34 via a matching box 22. The frequency of the high-frequency power is in the frequency band of several tens of megahertz, such as 13.56 MHz. A top plate 6 is installed on the top plate 6, and a gas dispersion plate 17 is installed below the shower plate 5. The processing gas is introduced into the processing chamber 1 from the outer periphery of the gas dispersion plate 17.

[0040] The flow rate of the process gas supplied is adjusted by the mass flow controllers 50 installed for each gas type in the mass flow controller control unit 51. In FIG. ４ ), oxygen (O ２), and argon (Ar) are supplied to the processing chamber 1 as processing gases, and mass flow controllers 50-2, 50-3, 50-4, and 50-6 are provided corresponding to these gases, respectively. The gases to be supplied are not limited to these. The mass flow controller control unit 51 also includes a mass flow controller 50-7 that adjusts the flow rate of He gas supplied between the rear surface of the wafer 2 and the upper surface of the dielectric film of the stage 4 on which the wafer is placed, as will be described later.

[0041] The lower part of the processing chamber 1 is connected to an exhaust means 15 via a vacuum exhaust pipe 16 in order to reduce the pressure inside the processing chamber 1. The exhaust means 15 is composed of, for example, a turbomolecular pump, a mechanical booster pump, or a dry pump. A pressure adjusting means 14 is installed upstream of the exhaust means 15. The pressure adjusting means 14 adjusts the flow rate of the internal gas and plasma 10 particles exhausted from the processing chamber 1 by the operation of the exhaust means 15 by increasing or decreasing the flow path cross-sectional area, which is the cross-sectional area on a plane perpendicular to the axial direction of the vacuum exhaust pipe 16. The pressure adjusting means 14 is composed of a plurality of plate-like flaps arranged with an axis transverse to the flow path and rotating about the axis, and a plate member moving within the flow path transverse to the axial direction, in order to adjust the pressure inside the processing chamber 1 and the discharge region 3.

[0042] An infrared lamp unit for heating the wafer 2 is installed between the stage 4 and the quartz chamber 12 constituting the ICP plasma source. The infrared lamp unit mainly includes an infrared lamp 62, a reflector 63 for reflecting infrared light, and a light-transmitting window 74. A circular (ring-shaped) lamp is used as the infrared lamp 62. Note that the light emitted from the infrared lamp 62 is assumed to be primarily light in the visible to infrared range. Here, such light is referred to as infrared light. In the configuration shown in FIG. 1, three infrared lamps 62-1, 62-2, and 62-3 are installed as the infrared lamps 62, but two, four, or more lamps may be installed. A reflector 63 is installed above the infrared lamp 62 to reflect the infrared light downward.

[0043] An infrared lamp power supply 64 is connected to the infrared lamp 62, and a high frequency cut filter 25 is installed midway between the power supply and the infrared lamp to prevent noise from the high frequency power for plasma generation generated by the high frequency power supply 20 from entering the infrared lamp power supply 64. The infrared lamp power supply 64 is also provided with a function that enables the power supplied to the infrared lamps 62-1, 62-2, and 62-3 to be controlled independently of one another, making it possible to adjust the radial distribution of the amount of heat applied to the wafer 2.

[0044] A gas flow path 75 is formed in the center of the infrared lamp unit to allow gas supplied from the mass flow controller 50 into the quartz chamber 12 to flow toward the processing chamber 1. A slit plate (ion shielding plate) 78 with multiple holes is installed in this gas flow path 75 to shield ions and electrons generated in the plasma generated inside the quartz chamber 12 and to transmit only neutral gases and neutral radicals to irradiate the wafer 2.

[0045] A coolant flow path 39 for cooling the stage 4 is formed inside the stage 4, and the coolant is circulated and supplied by a chiller 38. Furthermore, to fix the wafer 2 to the stage 4 by electrostatic attraction, electrostatic attraction electrodes 30, which are plate-shaped electrodes, are embedded in the stage 4, and DC (Direct Current) power supplies 31 for electrostatic attraction are connected to each of them.

[0046] In order to efficiently cool the wafer 2, He gas can be supplied between the stage 4 and the backside of the wafer 2 placed on the stage 4. In addition, the wafer-mounting surface of the stage 4 is coated with a resin such as polyimide to prevent scratches on the backside of the wafer 2 even when heating or cooling is performed while the wafer 2 is electrostatically attracted by activating the electrostatic attraction electrode 30. A thermocouple 70 for measuring the temperature of the stage 4 is installed inside the stage 4, and this thermocouple 70 is connected to a thermocouple thermometer 71.

[0047] In addition, optical fibers 92-1 and 92-2 for measuring the temperature of the wafer 2 are installed at three locations: near the center of the wafer 2 placed on the stage 4 (also referred to as the wafer center), near the middle in the radial direction of the wafer 2 (also referred to as the wafer middle), and near the outer periphery of the wafer 2 (also referred to as the wafer outer periphery). The optical fiber 92-1 guides infrared light from an external infrared light source 93 to the back surface of the wafer 2 and irradiates the back surface of the wafer 2. On the other hand, the optical fiber 92-2 collects IR light that has passed through and reflected from the wafer 2 out of the infrared light irradiated by the optical fiber 92-1, and transmits it to a spectroscope 96.

[0048] The external infrared light generated by the external infrared light source 93 is transmitted to an optical path switch 94 for turning the optical path on and off, and then branched into multiple beams by an optical distributor 95 (three beams in the case of FIG. 1), and irradiated onto the respective positions on the backside of the wafer 2 via three optical fibers 92-1.

[0049] The infrared light absorbed and reflected by the wafer 2 is transmitted to a spectrometer 96 via optical fiber 92-2, and a detector 97 obtains data on the wavelength dependency of the spectral intensity. The obtained data on the wavelength dependency of the spectral intensity is then sent to the calculation unit 41 of the control unit 40, which calculates the absorption wavelength and uses this as a reference to determine the temperature of the wafer 2. An optical multiplexer 98 is also installed midway along the optical fiber 92-2, which allows switching between the measurement points of the light to be spectroscopically measured - the wafer center, wafer middle, or wafer periphery. This allows the calculation unit 41 to determine the temperatures of the wafer center, wafer middle, and wafer periphery.

[0050] In FIG. 1, reference numeral 60 denotes a container that covers the quartz chamber 12 , and 81 denotes an O-ring for vacuum sealing between the stage 4 and the bottom surface of the base chamber 11 .

[0051] The control unit 40 controls the on / off of the high frequency power supply from the high frequency power source 20 to the ICP coil 34. It also controls the mass flow controller control unit 51 to adjust the type and flow rate of gas supplied from each mass flow controller 50 to the inside of the quartz chamber 12. In this state, the control unit 40 further operates the exhaust means 15 and controls the pressure adjustment means 14 to adjust the inside of the processing chamber 1 to a desired pressure.

[0052] Furthermore, the control unit 40 operates the DC power supply 31 for electrostatic attraction to electrostatically attract the wafer 2 to the stage 4, and operates the mass flow controller 50-7, which supplies He gas between the wafer 2 and the stage 4. The control unit 40 then controls the infrared lamp power supply 64 and the chiller 38 so that the temperature of the wafer 2 falls within a predetermined temperature range. The control unit 40 then controls the infrared lamp power supply 64 and the chiller 38 so that the temperature of the wafer 2 falls within a predetermined temperature range, based on the temperature inside the stage 4 measured by the thermocouple thermometer 71 and the temperature distribution information of the wafer 2 calculated by the calculation unit 41 based on the spectral intensity information measured by the detector 97 near the center, the radial middle portion, and the periphery of the wafer 2. A suitable temperature range is −40°C to 0°C. A typical temperature is −20°C. Here, if the wafer temperature is −40°C or lower, the temperature cycle performed in the etching process takes longer to lower the wafer temperature to that temperature, which increases the time required for the etching process, resulting in an undesirable decrease in throughput, i.e., the number of wafers processed per unit time. On the other hand, if the wafer temperature becomes 0° C. or higher, the titanium fluoride contained in the surface reaction layer generated during plasma processing will volatilize, causing the problem that self-saturation of the reaction cannot be achieved.

[0053] The flow of processing the wafer 2 performed in the plasma processing apparatus 100 of this embodiment will be described with reference to Fig. 2. Fig. 2 is a flowchart showing an outline of the flow of etching a film containing titanium carbide pre-formed on a wafer, performed by the plasma processing apparatus according to the embodiment of the present disclosure.

[0054] In FIG. 2, before processing of the wafer 2 is started, the wafer 2, on whose surface a film structure including a film layer to be processed, including a titanium carbide film, is pre-arranged, is placed on the stage 4 in the processing chamber 1, and is held on the stage 4 by electrostatic force generated when direct current power is supplied from the DC power source 31 to the electrostatic adsorption electrode 30.

[0055] After the start of the process, in step S201, a gas containing fluorine and oxygen but not containing hydrogen is introduced into the process chamber 1. Here, the gas containing fluorine and oxygen but not containing hydrogen is tetrafluoromethane (CF ４ ) / oxygen (O ２ ) and nitrogen trifluoride (NF ３ ) / oxygen (O ２ ) can be used. These gases can also be used in place of argon (Ar) or nitrogen (N ２ ) or the like may be used. The wafer temperature in this step S201 is kept constant by the temperature control function of the stage 4 on which the wafer 2 is placed. ３ ) and nitrogen (N ２ ) is used, nitrogen (N ２ ) mass flow controllers 50-1, 50-8, and nitrogen trifluoride (NF ３ ) is used.

[0056] Next, in step S202, plasma 10 is generated inside discharge region 3 using the above gas, and reactive particles (also called reactive particles) such as radicals (active species) of fluorine (F) etc. are generated by activating atoms or molecules of the gas containing fluorine and oxygen but not hydrogen in plasma 10.

[0057] In step S203, reactive particles are supplied to the surface of the wafer 2 through the gas flow path 75 and the through-holes in the slit plate 78, and adhere to the surface of the film layer containing the titanium carbide film. The reactive particles react with the material of the surface of the film layer to which they adhere, forming a surface reaction layer with a thickness determined by the conditions for generating the plasma 10 and the processing conditions such as the temperature of the stage 4. At this time, the surface reaction layer formed on the surface of the film layer containing the titanium carbide film contains at least titanium-fluorine (Ti—F) bonds.

[0058] Then, in step S204, after the control unit 40 confirms that a surface reaction layer of a predetermined thickness has been formed using a film thickness detector (not shown) or by confirming the passage of a predetermined time, the pressure adjusting means 14 increases the flow path cross-sectional area of ​​the vacuum exhaust pipe 16 to increase the exhaust rate and greatly reduce the pressure inside the processing chamber 1. Then, the gas containing fluorine and oxygen but not containing hydrogen that was supplied into the processing chamber 1 is quickly exhausted. This completes the processing for forming the surface reaction layer. At this time, an inert gas such as Ar may be supplied into the processing chamber 1 to replace the gas containing fluorine and oxygen but not containing hydrogen inside the processing chamber 1, thereby promoting the exhaust of the gas containing fluorine and oxygen but not containing hydrogen.

[0059] Next, in step S205, the infrared lamp 62 is turned on, and the surface of the wafer 2 is heated in a vacuum state by the light (infrared light) emitted from the infrared lamp 62. The irradiation time of the infrared light at this time is, for example, 20 seconds, and the maximum temperature reached on the surface of the wafer 2 at this time is, for example, 120° C. The pressure in the processing chamber 1 during heating is, for example, 1×10 －３ The temperature of the wafer 2 is set to Pa. At this time, the temperature of the wafer 2 rises at a rate of, for example, about 7°C / sec as the irradiation time of the infrared lamp increases, and this temperature rise causes the surface reaction layer to volatilize from the surface and be removed (desorbed) from the surface of the film layer. After the temperature detection mechanism (92-97, 41) confirms that the temperature of the wafer 2 has risen to a predetermined temperature, or after the control unit 40 confirms that a predetermined time has passed, the infrared lamp 62 is turned off.

[0060] Examples of volatile reaction products include titanium fluoride (TiF ４ ) and carbon dioxide (CO２ These reaction product particles desorbed from the wafer 2 are exhausted from the inside of the processing chamber 1 to the outside of the processing chamber 1 by the exhaust operation of the inside of the processing chamber 1 by the operation of the pressure adjusting means 14 or the exhaust means 15 or the flow of particles moving inside the processing chamber 1 caused by this. Subsequently, in step S206, the gas containing the reaction products is exhausted from the inside of the processing chamber 1 to the outside of the processing chamber 1.

[0061] One cycle, which is a set of steps S201 to S206, is completed. The surface reaction layer formed on the surface of the titanium carbide film by the reaction with plasma is removed (desorbed) during this cycle, and the titanium carbide film is removed by the thickness of the surface reaction layer, resulting in a thinner titanium carbide film. This change in film thickness is the etching amount per cycle.

[0062] Thereafter, the control unit 40 receives an output from a film thickness detector (not shown) and determines from the results obtained therefrom whether the desired etching amount has been reached, or whether the termination conditions, including the number of cycles performed that have been determined from prior tests to result in the desired etching amount, have been met (step S207). If it is determined that the conditions are met (S207: Yes), the etching process for the film layer containing the titanium carbide film is terminated. If it is determined that the conditions are not met (S207: No), the process returns to step S201 and the cycle (S201-S206) is performed again. Thus, in this embodiment, the cycle (S201-S206) is repeated until the desired etching amount is reached.

[0063] Hereinafter, etching of a film layer including a titanium carbide film on a wafer 2 using the plasma processing apparatus 100 of this embodiment will be described using CF4 as a gas for forming a reactive layer. ４ / O ２ The sequence of operations when using / Ar will be described with reference to Figures 3 and 4. Figure 3 is a time chart showing the changes over time of multiple parameters included in the processing conditions during wafer processing in the embodiment shown in Figure 1. In Figure 3, the parameters shown from top to bottom are gas supply flow rate, high-frequency power supply power, infrared lamp power, electrostatic adsorption, and wafer surface temperature.

[0064] Fig. 4 is a cross-sectional view showing a schematic overview of changes in a film structure including a film layer including a titanium carbide film during processing of a wafer according to the embodiment shown in Fig. 3. In particular, Fig. 4 shows a schematic view of the structure and changes near the surface of the titanium carbide film 402 in a film structure in which the titanium carbide film 402 is laminated and arranged in contact with an undercoat film 401 of the wafer 2.

[0065] First, at time t0 during processing shown in FIG. 3 , in response to a command signal from the control unit 40, a wafer 2 having a pre-formed film structure including an underlayer 401 and a titanium carbide film 402 to be etched, as shown in FIG. 4A , is loaded into the processing chamber 1 through a transfer port (not shown) provided in the processing chamber 1 and placed on the stage 4. Power is then supplied from the DC power supply 31 to the electrostatic adsorption electrode 30, and the wafer 2 is electrostatically adsorbed and held on the dielectric film on the stage 4. Furthermore, in response to the command signal from the control unit 40, the He gas-compatible mass flow controller 50-7 of the mass flow controller control unit 51 adjusts the flow rate of the He gas for wafer cooling supplied to the gap between the backside of the wafer 2 and the stage 4, and the pressure of the He gas in the gap is adjusted to a value within a predetermined range. As a result, heat transfer between the stage 4 and the wafer 2 is promoted, and the surface temperature of the wafer 2 is raised to a value T1 close to the temperature of the stage 4, through which a coolant previously adjusted to a predetermined temperature by the chiller 38 is supplied to the coolant flow path 39 and circulated. In this embodiment, the surface temperature T1 of the wafer 2 is set to, for example, -20°C.

[0066] Next, at time t1 shown in FIG. 3, the CF of the mass flow controller 50 is turned on in response to a command signal from the control unit 40. ４ Mass flow controller 50-3 or 50-6 for ２ The flow rates of the Ar and Ar gases are adjusted by the mass flow controller 50-2 for Ar and the mass flow controller 50-4 for Ar, respectively. As a result, a mixed gas containing these multiple types of substance gases is supplied as a processing gas at a flow rate within a predetermined range into the processing chamber 1. At the same time, the aperture of the pressure adjusting means 14 is adjusted to set the pressure inside the processing chamber 1 and the discharge region 3 inside the quartz chamber 12 to a value within a desired range.

[0067] 3, high frequency power of a predetermined value W is supplied from high frequency power supply 20 to ICP coil 34 in response to a command signal from control unit 40, plasma discharge is initiated in discharge region 3 inside quartz chamber 12, and plasma 10 is generated inside quartz chamber 12. At this time, no power is supplied to infrared lamp 62 so that the temperature of wafer 2 while plasma 10 is being generated is maintained at the same temperature as before plasma 10 was generated.

[0068] In this state, CF ４ / O ２ At least a portion of the Ar gas particles are excited, dissociated, or ionized in the plasma 10, forming charged particles such as ions or reactive particles such as activated species. The reactive particles such as activated species formed in the discharge region 3 and neutral gas pass through slits or through-holes formed in the slit plate 78, are introduced into the processing chamber 1, and are supplied to the surface of the wafer 2. As shown in FIG. 4( b), activated species 403 including fluorine radicals (F) and the like are adsorbed onto the surface of the titanium carbide film 402 of the wafer 2, interacting with the material of the titanium carbide film 402 to form a surface reaction layer 404. In other words, reactive particles 403 containing fluorine and oxygen but not hydrogen are supplied to the surface of the titanium carbide film 402, forming a surface reaction layer 404 on the surface of the titanium carbide film 402.

[0069] This surface reaction layer 404 is a reaction product containing Ti—F bonds as its main component, and is characterized by peaks in the binding energy of titanium 2p near 462±2 eV (2p 3 / 2) and near 467±2 eV (2p 1 / 2) when measured by X-ray photoelectron spectroscopy using aluminum Kα radiation. Figure 5 shows a photoelectron spectrum obtained by analyzing the surface of the titanium carbide film 402 on which the surface reaction layer 404 has been formed by X-ray photoelectron spectroscopy using aluminum Kα radiation. Peaks attributable to the surface reaction layer 404, indicating the presence of Ti—F bonds, are observed near 462±2 eV and 467±2 eV in binding energies (eV). The composition of this surface reaction layer depends on the composition of the gas used and the reaction time, and may be a mixture of various bonding states of carbon, fluorine, and titanium, such as simple fluorine, carbon fluoride, or titanium fluoride, or may contain titanium carbide oxide or carbon oxide. Note that the bond energy values ​​shown here are values ​​calibrated assuming that the position of the carbon 1s peak due to surface contamination carbon observed on the surface of the initial sample is 284.5 eV.

[0070] FIG. 6 is a graph showing the dependence of the titanium 2p peak intensity due to the surface reaction layer 404 on plasma processing time. The plasma processing time indicates the elapsed time from the start of the supply of high-frequency power. As shown in FIG. 6, the intensity of the titanium 2p peak due to the surface reaction layer 404 increased with the passage of plasma processing time, tended to saturate, and became almost constant after the plasma processing time exceeded 60 seconds. Thus, the self-saturating nature of the amount of reaction product generated is similar to the natural oxidation phenomenon of metal and silicon surfaces. Because the formation of the surface reaction layer is self-saturating, the amount of surface reaction layer 404 generated per cycle can be made constant by performing plasma processing for a time longer than the time required for saturation. In this embodiment, it took 60 seconds for the amount of surface reaction layer 404 generated to saturate. However, the time required for saturation varies depending on equipment parameters such as the distance between the plasma source (12, 34) and the wafer 2 and the substrate temperature.

[0071] 3, in response to a command signal from the control unit 40, the output of high frequency power from the high frequency power supply 20 is stopped and the supply of the processing gas to the discharge region 3 is stopped. This causes the plasma 10 in the discharge region 3 to disappear. In addition, between time t3 and time t4, the processing gas and particles such as reactive particles in the processing chamber 1 are exhausted to the outside of the processing chamber 1 via the vacuum exhaust pipe 16 and exhaust means 15, the opening of which is adjusted by the pressure adjustment means 14.

[0072] At time t4, the infrared lamp 62 is turned on in response to a command signal from the control unit 40, and the surface of the wafer 2 is vacuum-heated by the light (infrared light) 405 emitted from the infrared lamp 62, as shown in FIG. 4C. At this time, the pressure in the processing chamber 1 is, for example, 1×10 －３ The irradiation time of the infrared lamp 62 was set to, for example, 20 seconds at a temperature of 50°C. The maximum temperature reached on the surface of the wafer 2 was, for example, 120°C. This process is a reaction in which the surface reaction layer 404 is decomposed into a reaction product 406 containing titanium fluoride, which is then volatilized or desorbed. This desorption reaction is more advantageous at higher temperatures and lower pressures. The present inventors have found that in order to cause this desorption reaction, the temperature of the surface of the wafer 2 must be 50°C or higher, and that the pressure in the processing chamber 1 is preferably 10 Pa or lower.

[0073] In this embodiment, the maximum temperature of the surface of the wafer 2 is set to 120° C., and the degree of vacuum in the processing chamber 1 is set to 1×10 －３ However, the maximum temperature may be set to an appropriate value within a temperature range of 50° C. or higher. A typical temperature range is 50 to 150° C., and a typical pressure range in the processing chamber 1 during heating is 1×10 －５ The pressure is 10 Pa or less. A heating temperature of 150° C. increases the time required for heating, which reduces the throughput, which is the number of wafers that can be processed per unit time. Therefore, the heating temperature for the wafer is preferably 150° C. or less.

[0074] FIG. 7 shows a vacuum level of 1×10 －４1 is a graph showing the change in the titanium 2p peak intensity due to the surface reaction layer 404 versus heating temperature when the surface reaction layer 404 is removed by vacuum heating at 100°C. As a result, it can be seen that the intensity of the titanium 2p peak, which indicates the remaining amount of the surface reaction layer 404, decreases with increasing heating temperature, and the surface reaction layer 404 is significantly reduced at a heating temperature of 50°C and completely disappears at a heating temperature of 100°C. As a result, it can be said that the preferable temperature range for heating is between 50°C and 150°C. In other words, the wafer temperature in the step (second step) of desorbing the surface reaction layer 404 is preferably between 50°C and 150°C. If the heating temperature is below 50°C, there is a problem that the surface reaction layer 404 is not sufficiently volatilized, resulting in residual residue. Furthermore, if the heating temperature is above 150°C, the temperature range for heating and cooling becomes wider, and the time required for heating and cooling becomes longer, which undesirably reduces the throughput of wafer processing. In this heating step, only the surface reaction layer 404 formed on the surface of the wafer 2 is decomposed and volatilized, and the unreacted titanium carbide film 402 present below the surface reaction layer 404 remains unchanged, so that only the surface reaction layer 404 can be removed. Therefore, in addition to the step of forming the surface reaction layer 404, the step of removing the surface reaction layer 404 is also self-saturating.

[0075] During this heating step, the wafer 2 remains mounted on the wafer stage 4, but the supply of helium gas, which is used to increase the thermal conductivity of the backside of the wafer 2, is stopped so that the temperature of the front side of the wafer 2 can be increased quickly. In this embodiment, the wafer 2 is processed while still mounted on the wafer stage 4. However, the wafer 2 may be irradiated with infrared light while not in thermal contact with the wafer stage 4, using lift pins (not shown). After the heating time required to remove the surface reaction layer 404 has elapsed, the infrared lamp 62 is turned off, and the residual gas in the processing chamber 1 is exhausted to the outside of the processing chamber 1 using the exhaust means 15. Thereafter, the supply of helium gas is resumed to increase the thermal conductivity between the wafer 2 and the wafer stage 4, and the wafer temperature is cooled to −20° C. by the chiller 38, completing the first cycle of processing.

[0076] 3, infrared lamp 62 is turned off in response to a command signal from control unit 40. Gas containing reaction product particles and the like in processing chamber 1 is exhausted to the outside of processing chamber 1 via vacuum exhaust piping 16, the opening of which is adjusted by pressure adjustment means 14, and exhaust means 15. Furthermore, after time t5, as explained in FIG. 2, it is determined whether the amount of etching or the remaining film thickness of titanium carbide film 402 on wafer 2 has reached a desired value (corresponding to step S207), and depending on the determination result, the next cycle (S201-S206) is started or the process of wafer 2 is terminated.

[0077] When the next cycle is to be started, at any time t6 after time t5, the CF is operated in response to a command signal from the control unit 40 in the same manner as the operation from time t1. ４ / O ２ 4(c) 。 When the processing of the wafer 2 is completed, the supply of He gas to the gap between the rear surface of the wafer 2 and the upper surface of the stage 4 is stopped at time t6, and the valve 52 is opened to exhaust He gas from the gap, making the pressure in the gap approximately the same as the pressure in the processing chamber 1. The process of releasing the electrostatic adsorption of the wafer 2, including removing static electricity, is performed. This completes the etching process of the titanium carbide film 402.

[0078] In this example, when an etching depth of 6 nm was required, the above cycle was repeated five times to complete the etching. FIG. 8 is a graph showing the relationship between the number of cycles and the etching depth in the etching process performed by the plasma processing apparatus 100 according to this example shown in FIG. 1 , and shows the results for the target films titanium carbide and titanium nitride. The pressure was 50 Pa. In FIG. 8, the horizontal axis represents the number of cycles, and the vertical axis represents the etching depth (etching depth) detected using in-situ ellipsometry after each cycle and before the start of the next cycle.

[0079] As shown in FIG. 8 , in this example, the etching amount changes almost linearly with increasing number of cycles. From FIG. 8 , it can be seen that the etching amount per cycle of the titanium carbide film in this example was, for example, 1.2 nm / cycle. Furthermore, in this example, etching of titanium nitride did not proceed, and titanium carbide was selectively etched relative to titanium nitride. Therefore, when a target film layer containing titanium carbide and another film layer containing titanium nitride are disposed on the surface of the wafer 2, etching of titanium nitride in the other film layer does not proceed, and titanium carbide in the target film layer can be selectively etched relative to titanium nitride. This is due to the fact that the gas disclosed herein does not contain hydrogen. In the plasma processing process, because the gas contains fluorine and oxygen but does not contain hydrogen, a surface reaction layer such as titanium ammonium fluoride is not formed on the surface of the titanium nitride, and etching of the titanium nitride does not proceed.

[0080] FIG. 9 is a graph showing the relationship between the number of cycles and the amount of etching in an etching process performed by the plasma processing apparatus 100 according to the present embodiment shown in FIG. 1 , and illustrates the results when the wafer temperature was varied between −20°C, 0°C, and 20°C. The pressure was 50 Pa. The plasma exposure time was also varied between 60 seconds, 90 seconds, and 120 seconds. As shown in FIG. 9 , when the wafer temperature was as low as −20°C, the amount of etching per cycle did not change even when the plasma exposure time was changed, indicating that the amount of etching exhibited self-saturation with respect to the plasma exposure time. On the other hand, when the wafer temperature was relatively high, such as 0°C or 20°C, the amount of etching per cycle increased with increasing plasma exposure time, and no self-saturation with respect to the amount of etching exhibited with respect to the plasma exposure time was observed. This is because, when the wafer temperature was 0°C or higher, the volatilization of reaction products such as titanium fluoride proceeded during plasma exposure. From these results, it was found that the wafer temperature range suitable for the process disclosed herein is between −40°C and 0°C. That is, the wafer temperature in the step of forming the surface reaction layer 404 is preferably in the range of -40°C to 0°C. The reason why the lower limit of the wafer temperature is -40°C is that if the wafer temperature is set to -40°C or lower, the temperature range for heating and cooling will widen, the time required for the process will increase, and the throughput of wafer processing will decrease, which is undesirable. The appropriate pressure range for the plasma irradiation step is 0.1 Pa to 1000 Pa, and more specifically, the high effectiveness of the present disclosure has been confirmed in the range of 1 Pa to 100 Pa.

[0081] As described above, in this embodiment, both the process (first process) for forming the surface reaction layer 404 and the process (second process) for removing the surface reaction layer 404 have the property of completing in a self-saturating manner. For this reason, in this embodiment, when etching a wafer 2 on which a film structure having a circuit pattern is pre-formed, the etching amount of the surface of the titanium carbide film 402 after one cycle is completed has reduced variations in the in-plane direction and depth direction of the wafer 2, and can be made more uniform.

[0082] Because the self-saturation property is utilized, even if the density of reactive particles such as radicals supplied to the wafer 2 varies depending on the horizontal or depth direction of the upper surface of the wafer 2, the etching amount is prevented from becoming excessively large or insufficient, thereby reducing variation in the etching amount. Furthermore, the total etching amount can be adjusted by increasing or decreasing the number of repetitions of one cycle (the first and second steps) including the first and second steps. The etching amount in this embodiment is the etching amount per cycle multiplied by the number of repetitions or the sum of the number of repetitions. As a result, this embodiment can improve the controllability of dimensions after etching and the processing yield compared to conventional continuous plasma processing.

[0083] As described above, according to this embodiment, it is possible to provide an isotropic atomic layer etching technique that etches a titanium carbide film with high uniformity in the wafer in-plane direction and the pattern depth direction, and with high processing dimension controllability at the atomic layer level.

[0084] Although the present embodiment describes a titanium carbide film as an example of a film layer containing metal carbide to be treated, the present disclosure is also applicable to titanium carbide films containing oxygen, nitrogen, or both oxygen and nitrogen as other constituents. Specifically, the present disclosure is applicable not only to TiC films but also to films of TiCO, TiCN, TiCNO, and the like.

[0085] 1, the infrared lamps 62 are disposed outside the vacuum vessel above the processing chamber 1 on the outer periphery of the quartz chamber 12 surrounding the discharge region 3, but they may also be disposed inside the quartz chamber 12 or the vacuum vessel. The above example has been described in detail to clearly explain the present disclosure, and is not necessarily limited to an example having all of the described configurations.

[0086] 1: Processing chamber, 2: Wafer, 3: Discharge area, 4: Stage, 5: Shower plate, 6: Top plate, 10: Plasma, 11: Base chamber, 12: Quartz chamber, 14: Pressure adjustment means, 15: Exhaust means, 16: Vacuum exhaust piping, 17: Gas dispersion plate, 20: High frequency power supply, 22: Matching box, 25: High frequency cut filter, 30: Electrostatic adsorption electrode, 31: DC power supply, 34: ICP coil, 38: Chiller, 39: Coolant flow path, 40: Control unit, 41: Calculation unit, 50: Mass flow controller, 51: Mass flow controller control unit, 52: Valve, 60: Container, 62: Infrared lamp , 63: reflector, 64: power supply for infrared lamp, 70: thermocouple, 71: thermocouple thermometer, 74: light-transmitting window, 75: gas flow path, 78: slit plate, 81: O-ring, 92: optical fiber, 93: external infrared light source, 94: optical path switch, 95: optical distributor, 96: spectroscope, 97: detector, 98: optical multiplexer, 100: plasma processing apparatus, 401: base film, 402: titanium carbide film, 403: activated species, 404: surface reaction layer, 406: reaction products, 901: base structure, 902: fin structure, 903: titanium carbide film, 904: mask, 905: reactive species, 906: reaction products.

Claims

1. An etching method for etching a film layer containing titanium carbide that is placed on the surface of a wafer, the method comprising the steps of: supplying reactive particles that contain fluorine and oxygen but do not contain hydrogen to the surface of the film layer to form a reaction layer on the surface of the film layer; and heating the film layer to remove the reaction layer.

2. An etching method according to claim 1, characterized in that the reactive particles containing fluorine and oxygen but not hydrogen are formed from a gas composed of tetrafluoromethane and oxygen.

3. An etching method according to claim 1, characterized in that when the film layer to be processed containing titanium carbide and another film layer containing titanium nitride are placed on the surface of the wafer, the other film layer containing titanium nitride is not etched.

4. The etching method according to claim 1, wherein the amount of the reaction layer produced is self-saturating.

5. An etching method according to claim 1, characterized in that the step of forming the reaction layer and the step of removing the reaction layer are treated as a single cycle, and the cycle is repeated a plurality of times.

6. The etching method according to claim 1, wherein the wafer temperature in the step of forming the reaction layer is in the range of -40°C to 0°C.

7. The etching method according to claim 1, wherein the wafer temperature in the step of removing the reaction layer is in the range of 50°C to 150°C.

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