Method for producing thin films that minimize the increase in defects at interfaces during high temperature oxidation process

Abstract

To provide a method for forming a thin film that minimizes an increase in a defect at an interface when a high-temperature oxidation step is performed.SOLUTION: A method for forming a thin film that minimizes an increase in a defect at an interface during a high-temperature oxidation step of a SiC substrate includes the steps of depositing a first thin film 300 by applying a radical gas onto a SiC substrate using either an ALD method or a radical oxidation method using radicals, forming an oxide film 200 by performing the high-temperature oxidation step on the first thin film, and annealing the oxide film with at least one of NO and N2O.SELECTED DRAWING: Figure 3b

Description

[Technical field]

[0001] The present invention relates to a method for producing a thin film, and more particularly to a method for minimizing the increase in defects at the interface when a high temperature oxidation process is performed. [Background technology]

[0002] Power semiconductors are usually used as switching elements for power conversion. In recent years, the reliability of electrical characteristics of Si (Silicon)-based power semiconductor elements is reaching its limit, and active research is being conducted on SiC (Silicon Carbide) semiconductor elements, a power element material that can operate under extreme conditions such as high voltage, low resistance, high frequency, and high temperature, overcoming the limitations of Si. At that time, one of the factors that affect power semiconductor elements is the interface trap density at the interface between the silicon substrate and the gate oxide film.

[0003] When a gate oxide film is formed by high-temperature oxidation of SiC (Silicon Carbide), carbon (C) that falls off from the SiC (Silicon Carbide) bonds either maintains incomplete bonds around the interface where the oxide film is formed, or forms carbon-carbon (C-C) bonds with high binding energy.

[0004] This situation causes distortion of the flat band voltage and a decrease in carrier mobility, resulting in limitations in the application of the device in high voltage and high current fields, and even when used within the range of electrical capacity, device reliability is affected by malfunctions due to errors in the logic circuits.

[0005] FIG. 1 shows the conventional gate oxide film formation process and atomic bonding formula.

[0006] Referring to FIG. 1, in the case of the conventional high-temperature oxidation technique, the SiC substrate 100 is simply oxidized at high temperature, and then annealed to form an oxide film 200. This is because the SiC on the SiC substrate 100 is oxidized to O 2 By bonding with SiO 2 In this case, the oxide film 200 is formed by the above-mentioned oxidation. At the interface between the SiC substrate 100 and the oxide film 200, unreacted, unbonded or unemitted carbon (C) remains as a by-product during the oxidation process, and the excess carbon (C) is again formed into carbon (C) clusters such as carbon-carbon (CC).

[0007] Specifically, SiC and O 2 When bonded with SiO 2 and carbon (C) can be produced (this may be the main reaction of high-temperature oxidation). In addition, 2SiC and 3O 2 By bonding with 2SiO 2 and 2CO are produced, and SiC and O 2 Further bonding with SiO and CO is produced, but CO and SiO are evaporated as gas, resulting in carbon (C) remaining on the interface as a by-product.

[0008] At that time, carbon (C) remaining on the interface as a by-product is again formed into carbon (C) clusters such as carbon-carbon (CC), which causes defects at the interface, such as flat band voltage distortion and reduced carrier mobility, thereby reducing the reliability of SiC high voltage and high current devices. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention is intended to solve the above-mentioned problems of the prior art, and aims to realize a process that can minimize the increase in defects at the interface during a high-temperature oxidation process for forming a thin film.

[0010] Another object is to reduce defects at the interface by lowering the specific gravity of carbon (C) remaining at the interface of the thin film during high-temperature oxidation.

[0011] However, the technical objectives to be achieved by this embodiment are not limited to the above-mentioned technical objectives, and other technical objectives may exist. [Means for solving the problem]

[0012] As a technical means for achieving the above-mentioned technical object, a thin film formation method for minimizing an increase in defects at an interface during a high-temperature oxidation process of a SiC substrate may include the steps of: (a) forming a first thin film on a SiC substrate using a radical gas; (b) forming an oxide film by performing a high-temperature oxidation process on the first thin film; and (c) performing annealing on the oxide film.

[0013] In addition, in the step (a), the first thin film may be formed by either an ALD method using radicals or a radical oxidation method.

[0014] The first thin film is SiO 2 The insulating layer may be made of

[0015] In addition, SiO 2 During the process of forming the insulating layer, carbon-carbon (cc), carbon (C), etc. of the SiC substrate generated as a by-product may at least partially combine with radical gas and be vaporized.

[0016] In addition, when the ALD method using radicals is performed, the C in the SiC substrate is converted to CO through the chemical reactions in steps (a) and (b). 2 , CH, and CO can be vaporized.

[0017] In addition, when the radical oxidation method is performed, the C in the SiC substrate is converted to CO through the chemical reactions in steps (a) and (b). 2 , CO, and CHx.

[0018] In addition, the annealing in step (c) is carried out using NO or N 2 O may be performed.

[0019] Additionally, the processes corresponding to steps (a) to (c) may be carried out at a process temperature between 500 and 750°C.

[0020] Additionally, the processes corresponding to steps (a) to (c) may be performed at a process pressure of less than 5 Torr.

[0021] Also, steps (a) to (c) may be included in a process of forming a gate oxide film in a process of forming a semiconductor device. Effect of the Invention

[0022] According to an embodiment of the present invention, the increase in interface defects during high temperature oxidation to produce a thin film can be minimized.

[0023] By lowering the specific gravity of carbon (C) remaining at the interface of the thin film during the high-temperature oxidation process, it is possible to reduce defects at the interface. This prevents a decrease in the carrier mobility of the thin film and improves the reliability of SiC high-voltage devices.

[0024] Additionally, the process presented in this invention allows thin films to be produced at lower temperatures and pressures than conventional processes. [Brief description of the drawings]

[0025] [Figure 1] 1 is a diagram showing a conventional gate oxide film formation process and an atomic bonding formula. [Diagram 2]4 is a flow chart illustrating an operation of a thin film formation process for minimizing an increase in defects at an interface during a high-temperature oxidation process of a SiC substrate according to an embodiment of the present invention. [Figure 3a] 1 is a schematic diagram showing the shape of a thin film formed by a conventional high-temperature oxidation process of a SiC substrate. [Figure 3b] 1 is a schematic diagram showing the shape of a thin film produced by a process for minimizing an increase in defects at an interface during a high-temperature oxidation process of a SiC substrate according to an embodiment of the present invention. [Figure 4a] 1 is a cross-sectional view of a thin film formed on a SiC substrate produced by a conventional process. [Figure 4b-4c] 1 is a cross-sectional view of a thin film formed on a SiC substrate according to an embodiment of the present invention. [Diagram 5] 4 is a graph showing the degree of formation of SiO2 and a transition layer (SiOxCy) according to an embodiment of the present invention. [Figure 6] 1 is a first graph showing a relationship between a voltage and a charge trap density for each process according to an embodiment of the present invention. [Figure 7] 11 is a second graph and table showing a relationship between a process voltage and an interface trap density (Dit) according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. In the drawings, in order to clearly explain the present invention, parts that are not related to the description are omitted, and similar parts are designated by similar reference numerals throughout the specification.

[0027] Throughout the specification, when a part is said to be "connected" to another part, this includes not only when it is "directly connected" to another part, but also when it is "electrically connected" to another part via another element in between. Furthermore, when a part is said to "include" a certain component, this does not mean that it excludes the other component, but that it may further include the other component, unless otherwise specified.

[0028] The following examples are detailed descriptions to aid in understanding the present invention, and are not intended to limit the scope of the present invention. Therefore, inventions that perform the same function as the present invention and have the same scope should also fall within the scope of the present invention.

[0029] The term "thin film" or "deposition" as defined in the following specification of the present invention may refer to a process of thinly coating an oxide or metal on the surface of a wafer (substrate) by alternately adsorbing and replacing molecules in a semiconductor manufacturing process. Therefore, each process described in the following specification may be performed by a radical generation unit or deposition device, and the thin film or deposition may be realized by a technique such as atomic layer deposition (ALD) or chemical vapor deposition (CVD).

[0030] FIG. 2 is a flow chart illustrating a thin film formation process that minimizes an increase in defects at an interface during a high-temperature oxidation process of a SiC substrate according to an embodiment of the present invention.

[0031] Referring to FIG. 2, radicals are applied onto a SiC substrate 100 to form a first thin film 300 (S110).

[0032] A first thin film 300 may be formed on the SiC substrate 100 shown in FIG. 3b by a preceding process of step (S110). Here, the first thin film 300 is a SiO 2 The insulating layer may be made of

[0033] In this case, the process of applying the radicals may selectively employ either an ALD method using radicals or a radical oxidation method.

[0034] Next, a high temperature oxidation process is performed on the first thin film 300 to form an oxide film 200 (S120).

[0035] Through the chemical reaction in step (S120), SiO 2 At least a portion of carbon (C) of the SiC substrate 100 that is generated as a by-product during the process of forming the insulating layer may combine with radical gas and be vaporized.

[0036] In addition, the conventional high temperature oxidation and annealing process requires a process temperature of 1100-1400° C. and a process pressure of 600-750 Torr as process conditions. However, when the process proposed in this specification is applied, the oxide film 200 can be formed only at a process temperature of 500-750° C. and a process pressure of less than 5 Torr.

[0037] Finally, gas annealing is performed on the oxide film 200 (S130).

[0038] As shown in FIG. 3, the oxide film 200 is formed on the thin film 300 by the finishing process of step S130. Here, the annealing is performed by using NO or N 2 O may be performed.

[0039] In this case, as an optional embodiment, when the ALD method using radicals is performed in step S110, carbon (C) of the SiC substrate 100 is converted to CO through chemical reactions in steps S120 to S130. 2 , CH, and CO can be vaporized.

[0040] In another alternative embodiment, when a radical oxidation method is performed in step S110, C of the SiC substrate 100 is converted to CO through the chemical reactions in steps S120 to S130. 2, CO and CHx can be vaporized.

[0041] To explain this in detail using chemical formulas, the conventional process performs only two steps of high-temperature oxidation and annealing on the SiC substrate 100. As a result, the following three chemical reactions can occur on the SiC substrate 100: [Chemical formula 1]:SiC+O 2 =SiO 2 +C (solid) [Chemical formula 2]:2SiC+3O 2 =2SiO 2 +2CO [Chemical formula 3]:SiC+O 2 =SiO+CO

[0042] At this time, the main reaction of the high temperature oxidation method corresponds to [Chemical formula 1], and among the by-products formed as a result of the chemical reaction, SiO and CO are vaporized and do not remain on the substrate, but a large amount of carbon (C) generated by [Chemical formula 1] remains on the interface in a solid state.

[0043] In contrast, the process presented in this specification performs a three-step process of forming a first thin film 300 using radicals on a SiC substrate 100, followed by high-temperature oxidation and annealing, whereby five additional chemical reactions can take place, including the three reactions performed in the conventional process. [Chemical formula 4]:SiC+4OH=SiO 2 +CO 2 +2H 2 [Chemical formula 5]:2SiC+6OH=2SiO 2 +2CO+3H 2 [Chemical formula 6]:SiC+HO 2 =SiO 2 +CH [Chemical formula 7]:2SiC+6O+4H→2SiO 2 +CO 2 +CH 4 [Chemical formula 8]Si Precursor+2OH=SiO 2+by-product(g)

[0044] The above [Chemical formula 4] to [Chemical formula 8] may be chemical reactions that occur while forming the first thin film 300 using radical gas before the high temperature oxidation process. Here, CO, CO 2 , CH and CH 4 is a by-product generated by reacting with carbon (C) remaining on the interface when vaporized into a gas, so the amount of solid carbon (C) remaining on the interface can be minimized compared to conventional processes.

[0045] Here, [Chemical Formula 4], [Chemical Formula 5], and [Chemical Formula 8] may correspond to the main reactions occurring in the process of the ALD method using radical oxidation or radicals at the interface. As a result, the process presented herein can lead to the chemical reactions corresponding to [Chemical Formula 4] to [Chemical Formula 8], and has the advantage that by-products can be easily removed even in a low pressure process.

[0046] Meanwhile, while only the SiC substrate 100 and oxide film 200 are shown in Fig. 3a, in reality, a layer may be generated by carbon (C) remaining on the interface. Also, in the case of Fig. 3b showing the process presented in this specification, it is shown that the first thin film 300 remains, but a transition layer (SiOxCy) remains due to the carbon (C) that has not reacted after the elements constituting the layer have evaporated through the high-temperature oxidation and annealing process. The actual cross sections of each thin film can be seen in Figs. 4a to 4c described below.

[0047] FIG. 4a is a cross-section of a thin film formed on a SiC substrate produced by a conventional process, and FIGS. 4b and 4c are diagrams showing cross-sections of a thin film formed on a SiC substrate 100 according to one embodiment of the present invention.

[0048] Figure 4a is a cross-section of a thin film produced by a conventional process, and Figures 4b and 4c can be thin films produced by the processes presented herein, where Figure 4b is the result of applying a radical oxidation process, and Figure 4c can be a process of an ALD method using radicals.

[0049] 4a to 4c, the thickness of the generated transition layer (SiOxCy) is different, but it can be seen that the thickness of the transition layer (SiOxCy) is the thickest in the photograph shown in FIG. 4a. In other words, it can be seen that a thick transition layer (SiOxCy) is formed when only high-temperature oxidation is performed on the SiC substrate 100.

[0050] Also, as shown in FIGS. 4b and 4c, it can be seen that the first thin film 300 formed in step S110 is removed by the radical oxidation or ALD process using radicals.

[0051] FIG. 5 is a graph showing the degree of formation of a transition layer (SiOxCy) according to an embodiment of the present invention.

[0052] Referring to the graph shown in FIG. 5, the red line in the graph may correspond to a conventional oxidation process, the green line may correspond to a process in which radical oxidation and high-temperature oxidation are performed together, and the blue line may correspond to a process in which radical ALD and high-temperature oxidation are performed together.

[0053] Referring to the graph of FIG. 5, it can be seen that when the radical oxidation or radical ALD process is performed before the high temperature oxidation, the intermediate state bonding of the transition layer (SiOxCy) is less than when only the high temperature oxidation is performed.

[0054] FIG. 6 is a first graph showing a relationship between a voltage and a charge trap density for each process according to an embodiment of the present invention.

[0055] Graphs (a) and (b) of FIG. 6 are graphs corresponding to conventional processes, and graphs (c) through (f) of FIG. 6 may be graphs corresponding to processes presented throughout this specification.

[0056] Before describing the graph shown in FIG. 6, it will be noted that the charge trap density at the interface can be one of the factors that affect the characteristics of a semiconductor device.

[0057] Usually, in the process of growing the gate oxide film 200, which is a process of producing a semiconductor device, Si atoms in SiC react with O (oxygen atoms) to form SiO 2 During the formation of the oxide film 200, unreacted carbon (C) atoms remain between the oxide film 200 and the SiC substrate 100, and the excess carbon re-forms clusters, forming interface states and defects. These defects act as a cause of flat band voltage distortion and a decrease in carrier mobility, resulting in device reliability problems.

[0058] As a method for measuring the charge trap density at the interface between the oxide film 200 and the SiC substrate 100, the current is measured while changing the frequency of the applied voltage, and a capacitance-voltage curve (cv curve) is calculated.

[0059] Referring again to FIG. 6, the X-axis of the graph represents voltage (V) and the Y-axis represents capacitance (Cap Den; F / cm 2 ), and the three lines on the graph represent frequency (in this case, the red line represents 1 MHz, the yellow line represents 10 kHz, and the blue line represents 1 kHz).

[0060] Graph (a) corresponding to the conventional process shows that the difference in capacitance value versus voltage increases as the frequency increases when only high-temperature oxidation is applied to the SiC substrate 100. Also, graph (b) shows that the difference is not completely narrowed even when high-temperature oxidation and NO gas annealing are applied to the SiC substrate 100.

[0061] Graphs (c) and (e) corresponding to the processes presented throughout this specification correspond to processes in which radical oxidation and high-temperature oxidation, and ALD using radicals and high-temperature oxidation alone are applied, respectively. As shown in graphs (c) and (e), the difference in capacitance value depending on frequency is improved compared to the process in which only high-temperature oxidation is applied to the SiC substrate 100, but the difference in capacitance value depending on frequency is improved compared to the process in which only high-temperature oxidation is applied to the SiC substrate 100. 2 It can be seen that without the annealing process of O, there is a difference in capacitance value versus voltage as the frequency increases.

[0062] However, as shown in graphs (d) and (f), NO or N 2 When annealing in O gas was performed, it was confirmed that there was almost no difference in the capacitance value versus voltage, regardless of frequency.

[0063] That is, in the conventional process, the charge trap density increases as the difference in capacitance due to the change in frequency of the applied voltage increases, but the process presented herein has a difference in that the charge trap density decreases.

[0064] FIG. 7 is a second graph and table showing the relationship of interface trap density by process according to an embodiment of the present invention.

[0065] Before explaining the second graph and table, the interface defect density D it(Interface Trap Density) refers to the interface defect density calculated by the High-Low Method based on the capacitance-voltage curve (cv curve) measurement of the first graph described above.

[0066] At this time, the interface defect density D it (Interface Trap Density) is calculated by calculating the capacitance value for each frequency in the measured capacitance-voltage curve (cv curve) of FIG. 6 described above using the following [Equation 1], and subtracting the high frequency capacitance value from the low frequency capacitance value.

[0067] [Formula 1] JPEG0007653176000001.jpg8170

[0068] The second graph shown in FIG. 7(a) has the voltage on the X axis and the interface defect density D on the Y axis. it (Interface Trap Density) and each line segment of the graph may correspond to a conventional process and a process presented herein.

[0069] At this time, referring to FIG. 7(a), the interface defect density D it It can be seen that the value of (Interface Trap Density) decreases as the temperature increases, but the slope of the line segment in which only high-temperature oxidation (gray solid line) is performed is the highest. In other words, when only the high-temperature oxidation process is performed, the voltage vs. interface defect density D it It can be seen that the change in (Interface Trap Density) is the largest.

[0070] However, the slopes of the lines in which the process proposed in this specification was applied (red dotted line, blue dotted line) are low, indicating that the change in charge trap density due to voltage is low. The interface defect density D itIt can be seen that (Interface Trap Density) is low.

[0071] This can be seen in Figure 7(b). The interface defect density D it (Interface Trap Density). In this case, the second step (2.66e11cm -2 eV -1 ) and the fourth step (2.85e11cm -2 eV -1 ) and the first step (3.81e11cm -2 eV -1 ) and the 6th step (2.87e12cm -2 eV -1 ) lower interface defect density D it (Interface Trap Density) value.

[0072] That is, before performing high-temperature oxidation on the SiC substrate 100, a radical oxidation or ALD process using radicals is performed in advance, and when high-temperature oxidation and annealing are performed after the formation of the first thin film 300, the interface defect density D it (Interface Trap Density) value can be improved.

[0073] The above description of the present invention is for illustrative purposes only, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting. For example, each component described as a single type may be implemented in a distributed form, and similarly, each component described as a distributed type may be implemented in a combined form.

[0074] The scope of the present invention is indicated by the claims set forth below rather than by the above detailed description, and all modifications and variations derived from the meaning and scope of the claims, as well as their equivalent concepts, should be interpreted as being included within the scope of the present invention. [Explanation of symbols]

[0075] 100 SiC substrate 200 Oxide film 300 First Thin Film

Claims

1. A method for forming a thin film that minimizes an increase in defects at an interface between a SiC substrate and an oxide film during a high-temperature oxidation process of the SiC substrate, comprising: (a) applying a radical gas onto a SiC substrate to deposit a first thin film; (b) performing a high temperature oxidation process on the first thin film to form an oxide film; (c) performing an annealing step on the oxide film, The step (a) performed before the high temperature oxidation step and the annealing step is The method includes a step of performing an ALD method using OH radicals or an oxidation method using OH radicals when depositing the first thin film, and the first thin film is SiO ２ In the step (a), the radical gas composed of OH radicals reacts with at least a portion of the carbon of the SiC substrate to generate a by-product that is vaporized; The processes corresponding to steps (a) to (c) are a method for forming a thin film that minimizes an increase in defects at the interface between a SiC substrate and an oxide film during a high-temperature oxidation process of a SiC substrate, which is carried out at a process temperature of 500 to 750° C. and a process pressure of less than 5 Torr.

2. When the ALD method using the OH radical is performed, Through the chemical reactions in steps (a) and (b), the C in the SiC substrate is converted into CO ２ 2. The method for forming a thin film that minimizes an increase in defects at an interface between a SiC substrate and an oxide film during a high-temperature oxidation process of the SiC substrate as set forth in claim 1, wherein the oxide film is vaporized in any one of the following forms: CH, CO, and / or SiO.

3. When the oxidation method using OH radicals is performed, Through the chemical reactions in steps (a) and (b), the C in the SiC substrate is converted into CO ２ 2. The method for forming a thin film that minimizes an increase in defects at an interface during a high-temperature oxidation process of a SiC substrate as set forth in claim 1, wherein the SiC substrate is vaporized in any one of the following forms: CO, CHx, and Cr.

4. The step (c) comprises: The annealing may be performed using NO or N ２ 2. The method for forming a thin film that minimizes an increase in defects at an interface between a SiC substrate and an oxide film during a high-temperature oxidation process of the SiC substrate according to claim 1, wherein the high-temperature oxidation process is performed using at least one of a SiC substrate, a SiC substrate, a silicon substrate, and an oxide film.

5. 2. The method of claim 1, wherein steps (a) to (c) are included in a process of forming a gate oxide film in a process of forming a semiconductor device.

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