Low-temperature plasma processing equipment

Abstract

To provide a low-temperature plasma processor which can stably control the temperature of a processing target substrate without affecting original plasma processing.SOLUTION: A low-temperature plasma processor 1 according to the present invention includes: a cooling unit (a cooling flow passage 118) using liquid nitrogen, provided in the inside or in the lower part of a lower electrode 11 on which a processing target object W is placed; a gas passage space (a heating flow passage 117) between the cooling unit and the upper surface of the lower electrode 11, the gas passage space allowing passage of gas; and a heating unit 151 for supplying heated gas into the gas passage space.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a plasma processing apparatus for performing processes such as etching and film formation on the surface of a semiconductor substrate or the like using plasma.

Background Art

[0002] With the miniaturization of semiconductors, the requirements for higher performance in etching rate (processing speed), aspect ratio (degree of anisotropy), and selectivity with respect to a mask in etching using plasma have been continuously increasing. In response to such requirements, as a method for increasing the etching rate of silicon carbide (SiC), silicon (Si), silicon nitride (SiN), etc., improving the selectivity with respect to a mask, and forming a protective film on the side walls of the trenches (grooves) to be formed to achieve high aspect ratio anisotropic etching, cryogenic etching (cryo-etching) is known.

[0003] When performing cryogenic etching using plasma, a method of cooling the lower electrode on which the substrate to be processed is placed with liquid nitrogen is generally used. However, since the etching rate, aspect ratio, etc. vary depending on the temperature of the substrate to be processed in addition to the plasma conditions, it is necessary to control the temperature in order to perform stable processing.

[0004] In the plasma processing apparatuses described in Patent Document 1 and Patent Document 2, a heater is provided between a cooling dam filled with liquid nitrogen (LN2) and the substrate to be processed, and the temperature of the sub-susceptor on which the substrate to be processed is placed is detected, and the power to the heater is feedback-controlled.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] In configurations using heaters, as described in Patent Documents 1 and 2, a mechanism is needed to prevent the high-frequency waves used for plasma generation from flowing through the heater's wiring and control system. Conversely, current to the heater and changes in that current may affect the plasma processing, and measures to prevent this are also necessary.

[0007] This invention was made to solve the problems of the prior art, and its objective is to provide a low-temperature plasma processing apparatus that can stably control the temperature of the substrate to be processed without affecting the original plasma processing. [Means for solving the problem]

[0008] The low-temperature plasma processing apparatus according to the present invention, which was developed to solve the above problems, A cooling unit using liquid nitrogen is provided inside or below the lower electrode on which the substrate to be processed is placed, A gas flow space through which gas can flow is provided between the cooling section and the upper surface of the lower electrode, A heating unit that supplies heated gas to the aforementioned gas flow space and It is characterized by having the following features.

[0009] The low-temperature plasma processing apparatus according to the present invention may be of either inductively coupled or capacitively coupled type.

[0010] The cooling unit may be a storage type (storage type liquid nitrogen cooling unit) that stores liquid nitrogen, or a flow type (flow type liquid nitrogen cooling unit) that circulates liquid nitrogen.

[0011] In both the storage type and the flow type, the gas flow space can be formed by creating a cavity inside the lower electrode and forming it on the upper surface of a plate-shaped member that separates the cavity vertically. In the storage type, a storage section for storing liquid nitrogen is provided below the plate-shaped member, and in the flow type, a flow passage for circulating liquid nitrogen is provided on the lower surface of the plate-shaped member.

[0012] The temperature of the gas supplied by the heating unit to the gas flow space should preferably be between 40°C and 300°C. Furthermore, the gas can be nitrogen gas, air, argon gas, or helium gas. It is desirable that the heating unit be configured to allow arbitrary control of the temperature of the substrate to be processed by changing the temperature and / or flow rate (or both) of the gas supplied to the gas flow space. [Effects of the Invention]

[0013] In the low-temperature plasma processing apparatus according to the present invention, a gas flow space is provided between the cooling unit and the substrate to be processed, which is placed on the lower electrode. By circulating gas through this gas flow space and appropriately setting the temperature of the gas, the temperature of the substrate to be processed can be appropriately controlled in conjunction with the cooling by liquid nitrogen in the cooling unit. Furthermore, in the low-temperature plasma processing apparatus according to the present invention, there is no electrical influence on the plasma processing of the substrate, enabling stable plasma processing and temperature control. [Brief explanation of the drawing]

[0014] [Figure 1] A schematic diagram of one embodiment of a low-temperature plasma processing apparatus according to the present invention. [Figure 2] A cross-sectional view of the lower electrode of the low-temperature plasma processing apparatus of the above embodiment, and a schematic diagram of the cooling section and heating section. [Figure 3] A diagram showing the heating flow path pattern on the upper surface of the separator member within the lower electrode. [Figure 4] A diagram showing the cooling channel pattern on the lower surface of the separator member within the lower electrode. [Figure 5] Plan view of the wafer for temperature measurement used when performing various temperature measurement tests with the low-temperature plasma device. [Figure 6] Graph showing the temperature change during cooling of the lower electrode. (a) is a graph of the temperature change of the lower electrode and five measurement points on the wafer for temperature measurement after starting to flow liquid nitrogen through the cooling channel. (b) is a table showing the temperatures of the five measurement points on the wafer for temperature measurement after the temperature has become substantially stable. [Figure 7] Graph representing the temperature change of the lower electrode when control is performed so that the temperature of the lower electrode becomes -150 °C. (a) is a graph when heating nitrogen gas is flowed through the heating channel, and (b) is a graph when no gas is flowed through the heating channel. [Figure 8] Graph showing the temperature change of the lower electrode from -100 °C to room temperature. (a) is a graph when heated nitrogen is circulated through the heating channel, and (b) is a graph when no gas is circulated. [Figure 9] Schematic configuration diagram of an example of the storage-type cooling unit according to an embodiment of the present invention. (a) is a cross-sectional view, and (b) is a longitudinal sectional view. [Figure 10] Schematic configuration diagram of an example of a conventional storage-type cooling unit. (a) is a cross-sectional view, and (b) is a longitudinal sectional view. [Figure 11] Graph showing the relationship between the time from when liquid nitrogen is injected into the storage part of the lower electrode adopting the storage-type cooling unit and the temperature of the wafer for temperature measurement placed on the lower electrode. [Figure 12] Graph showing the result of examining the followability of the temperature of the lower electrode when the set temperature of the lower electrode is gradually lowered from 0 °C to -150 °C.

Mode for Carrying Out the Invention

[0015] In order to confirm the effects of the present invention, the results of various tests performed using a commercially available low-temperature plasma processing device equipped with the lower electrode according to the present invention will be described.

[0016] First, we will describe the inductively coupled low-temperature reactive ion etching apparatus (product name: RIE-800iPLN, manufactured by Samco Co., Ltd.), which is the low-temperature plasma processing apparatus used in the test. Figure 1 is a schematic diagram of the low-temperature plasma processing apparatus 1. The low-temperature plasma processing apparatus 1 has a processing chamber 10 for performing plasma etching, and a lower electrode 11 is provided at the bottom of the chamber on which the substrate (hereinafter referred to as the workpiece) W, which is the object to be processed, is placed. The lower electrode 11 is equipped with an electrostatic adsorption mechanism or a mechanical chuck mechanism (not shown) for fixing the workpiece W during plasma processing, and a temperature control mechanism for cooling the workpiece W to below room temperature and controlling it to a predetermined temperature below room temperature (described later). The lower electrode 11 is also equipped with a high-frequency power supply 101 for drawing ions from the plasma into the workpiece W.

[0017] The side wall of the processing chamber 10 is provided with a gas inlet 12 for introducing etching gas and a gas exhaust port 13 for exhausting the inside of the processing chamber 10. A gas supply unit 121 for supplying plasma gas and a flow rate control unit (MFC) 122 for adjusting the flow rate are connected to the gas inlet 12, and a vacuum pump 131 is connected to the gas exhaust port 13.

[0018] At the top of the processing chamber 10, a spiral-shaped high-frequency coil 141, which serves as the upper electrode, is provided via a dielectric window 14. High-frequency power for plasma generation of the plasma gas is supplied to the high-frequency coil 141 from a high-frequency power supply 142.

[0019] The low-temperature plasma processing apparatus 1 is equipped with a control unit 15, which is configured as a computer. The operator performs various processes using the low-temperature plasma processing apparatus 1 through the control unit 15. In order to perform predetermined plasma processing on the workpiece W, the control unit 15 appropriately operates the vacuum pump 131, flow rate control unit 122, high-frequency power supply 142, etc., based on conditions specified by the operator and preset conditions, and also controls each part of the temperature control mechanism provided in the lower electrode 11 to control the temperature of the workpiece W during processing.

[0020] The detailed structure of the lower electrode 11 is shown in Figure 2. The lower electrode 11 consists of a base portion 111 having a cavity on the lower side of the upper surface on which the workpiece W is placed, a separator member 112 housed in the cavity, an internal partition wall 113 for sealing the separator member 112 within the cavity, and a lower partition wall 115 for forming a vacuum space 114 below the internal partition wall 113. A shallow recess 116 is provided on the upper surface of the base portion 111, i.e., the surface in contact with the workpiece W. During processing, helium gas is introduced and sealed in this recess to improve heat transfer between the base portion 111, i.e., the lower electrode 11, and the workpiece W. The vacuum space 114 is provided to prevent condensation on the lower electrode 11 due to liquid nitrogen.

[0021] The separator member 112 airtightly and liquid-tightly separates the cavity formed by the base portion 111 and the internal partition wall 113 vertically. The upper surface of the separator member 112 is in close contact with the lower surface of the base portion 111, and the lower surface of the separator member 112 is in close contact with the upper surface of the internal partition wall 113. A heating channel 117 having a pattern as shown in Figure 3 is formed on the upper surface of the separator member 112, and a cooling channel 118 having a pattern as shown in Figure 4 is formed on the lower surface of the separator member 112. Nitrogen gas (G-N2) is supplied to the heating channel 117 on the upper surface from the heating control unit 151, and liquid nitrogen (L-N2, -196°C) is supplied to the cooling channel 118 on the lower surface from the liquid nitrogen supply unit 152. The liquid nitrogen supply unit 152 and the cooling channel 118 constitute the cooling unit of the present invention. In the heating control unit 151, the nitrogen gas (G-N2) is heated by the heater 153, and its temperature is controlled.

[0022] The lower partition wall 115 is provided with a suction port 119 for evacuating the vacuum space 114 below the inner partition wall 113. A turbomolecular pump is preferably used as the pump for evacuating the vacuum space 114. Furthermore, a sealing material usable down to -60°C is preferably used as a seal to maintain an airtight pressure difference between the vacuum space 114 and other parts such as the processing chamber 10. Examples of such sealing materials include ethylene propylene diene rubber (EPDM) and indium.

[0023] When performing low-temperature etching on a workpiece W using the lower electrode 11 having such a structure, the control unit 15 operates as follows. First, liquid nitrogen is supplied from the liquid nitrogen supply unit 152 to the cooling channel 118 through piping equipped with a valve 162, and heated nitrogen gas is supplied from the heating control unit 151 to the heating channel 117. Then, by pulse-controlling the opening and closing and degree of the valve 162, the amount and / or timing of the liquid nitrogen supplied to the cooling channel 118 is adjusted to control the temperature of the workpiece W during plasma processing, and the temperature of the nitrogen gas supplied to the heating channel 117 is controlled by the heater 153 to improve the temperature controllability of the workpiece W. The heated nitrogen gas is also used to rapidly raise the temperature when raising the temperature from a low temperature. According to the present invention, the temperature of the workpiece W can be uniformly controlled to a low temperature during plasma processing, and this control can also be performed quickly.

[0024] To confirm the effectiveness of this control, various temperature measurement tests were conducted using a temperature measurement wafer W0. As shown in Figure 5, the temperature measurement wafer W0 is a silicon wafer with a diameter of 200 mm (8 inches), and thermocouple temperature sensors were fixed to the center and four sides of its upper surface at a total of five points p1 to p5.

[0025] First, the temperature uniformity during cooling of the lower electrode 11 was investigated. Figure 6(a) is a graph showing the temperatures of the lower electrode 11 (point p0 in Figure 5) and five measurement points (points p1 to p5) on the temperature measurement wafer W0 placed on top of it, measured by the temperature measurement unit 154, when the lower electrode 11 was cooled by flowing liquid nitrogen (-196°C) through the cooling channel 118 of the lower electrode 11, which is at room temperature, without flowing gas through the heating channel 117.

[0026] The temperature measurement wafer W0 was cooled to approximately -170°C in about 1500 seconds after liquid nitrogen was started flowing through the cooling channel 118, and then stabilized at that temperature. The solid lines in Figure 6(a) almost overlap, indicating that the temperature control (rate of temperature decrease) at the measurement points (p1 to p5) was uniform. The temperatures at the five measurement points (p1 to p5) at 2000 seconds after the temperature had stabilized are shown in the table in Figure 6(b). The temperature range Δ at the five points on the surface of the temperature measurement wafer W0 was 1.2°C or less, confirming that good temperature uniformity was achieved. At this time, the temperature of the lower electrode 11 (p0) was -179.5°C.

[0027] Next, the temperature stability when the temperature of the lower electrode 11 was controlled was investigated. Based on the detected temperature at measurement point p0 of the lower electrode 11, the heater 153 of the heating control unit 151 was controlled using PID, and the temperature of each point p1 to p5 of the temperature measurement wafer W0 was measured over time by the temperature measurement unit 154. The results are shown in Figure 7. Figure 7 is a graph showing the change over time of the average temperature of each point p1 to p5 of the temperature measurement wafer W0 when the temperature at measurement point p0 of the lower electrode 11 is controlled using PID so that it is -150°C. (a) is a graph when heated nitrogen gas is flowed through the heating channel 117, and (b) is a graph when the temperature is controlled by changing only the flow rate of liquid nitrogen to the cooling channel 118 without flowing gas through the heating channel 117. When heated nitrogen gas is not flowed through the heating channel 117 (b), the temperature of wafer W0 fluctuates within a range of -155 °C to -140 °C (Δ=15 °C), whereas when heated nitrogen gas is flowed (a), it stays within a range of -153 °C to -147 °C (Δ=6 °C).

[0028] When removing the workpiece W from the processing chamber 10 after low-temperature plasma treatment, it is necessary to return the lower electrode 11 to room temperature to avoid condensation. Even at this stage, the lower electrode 11 can be returned to room temperature in a short time by flowing heated nitrogen gas through the heating channel 117. Figure 8 shows the results of investigating this effect, illustrating the time course of the temperature at measurement point p0 as the lower electrode 11 returns from -100 °C to room temperature. (a) shows the case where heated nitrogen gas heated to approximately 100 °C is flowed through the heating channel 117, and (b) shows the case where heated nitrogen gas is not flowed. When heated nitrogen gas was flowed, the lower electrode 11 reached +12 °C in approximately 120 mins, but when heated nitrogen gas was not flowed, it took more than 800 mins to reach +12 °C.

[0029] In the above embodiment, the cooling unit was of the type in which liquid nitrogen was circulated through a cooling channel 118 provided on the lower surface of the separator member 112 (circulation type), but it may also be of the type in which liquid nitrogen is stored (storage type). An example of the structure of a storage type cooling unit 155 is shown in Figure 9. In this type of storage type cooling unit 155, a storage section 156 for storing liquid nitrogen (L-N2) is provided, and the liquid nitrogen is stored in it leaving space at the top. A number of heat transfer rods (heat transfer members) 157 are provided so as to protrude downward from the ceiling of the storage section 156, with a length sufficient to be immersed in the stored liquid nitrogen.

[0030] In conventional storage-type cooling units, the heat transfer members protruding from the ceiling of the storage unit were in the form of plate-shaped fins, as shown in Figure 10. As a result, gaseous nitrogen (G-N2) vaporized from various parts of the liquid nitrogen (L-N2) had to travel a long path before being discharged from the gaseous nitrogen outlet, which resulted in the problem of low exhaust conductance (ease of exhaust). Low exhaust conductance increases the pressure in the upper space of the liquid nitrogen (gasic nitrogen storage space), leading to a large pressure drop at the lower electrode and potentially causing damage to the welded joints of the storage unit 156, which is designed to be thin for optimal heat transfer efficiency.

[0031] In contrast, the rod-shaped heat transfer member 157 shown in Figure 9 has a large exhaust conductance of vaporized nitrogen, allowing liquid nitrogen to be supplied without increasing the pressure of gaseous nitrogen, and thus the liquid nitrogen level can be raised more quickly. As a result, the coldness of the liquid nitrogen can be effectively transferred to the lower electrode 11 and the workpiece W. In terms of heat transfer, it is preferable that the rod and the ceiling of the storage section 156 are an integrated structure. Furthermore, in this rod shape, the heat capacity of the part in contact with the liquid nitrogen is small, which suppresses film boiling on the surface of the heat transfer member 157 and allows for efficient cooling with liquid nitrogen.

[0032] In Figure 9, the heat transfer rod has a triangular cross-section, but it can be in various shapes such as square or circular. Furthermore, the heat transfer efficiency between the liquid nitrogen and the workpiece W can be adjusted by increasing or decreasing the number of heat transfer members 157. In the conventional fin configuration shown in Figure 10, increasing the number of heat transfer members (fins) worsens the exhaust conductance, making it difficult to simply increase or decrease their number. Moreover, by making the tip of the heat transfer member 157, i.e., the part immersed in liquid nitrogen, narrower, the heat transfer area can be increased while its heat capacity can be reduced, suppressing film boiling on the surface and improving cooling efficiency. It is desirable that the cross-sectional area of ​​the heat transfer member 157 be 30% or more of the total cross-sectional area of ​​the liquid nitrogen storage section 156.

[0033] In the configuration shown in Figure 9, a flow path 158 for circulating heated nitrogen gas is formed at the top of the storage-type cooling unit 155. Similar to the above embodiment, the temperature of the workpiece W can be controlled to a low temperature by circulating heated nitrogen gas from the heating control unit 151 through this flow path 158. Furthermore, in the storage unit 156, the temperature of the workpiece W can also be controlled by adjusting the amount of liquid nitrogen supplied to it and changing the liquid nitrogen level in the storage unit 156.

[0034] A test was conducted to confirm the cooling effect of the lower electrode 11 employing the storage-type cooling unit 155 shown in Figure 9. Figure 11 plots the relationship between the time from the moment liquid nitrogen (L-N2, -196°C) is injected into the storage unit 156 with the temperature measurement wafer W0 (Figure 5) placed on the lower electrode 11 of this embodiment, and the temperatures of five measurement points p1 to p5 on the temperature measurement wafer W0. Compared with Figure 6, it can be seen that the initial cooling after the start of cooling is rapid, and the temperature reached by the temperature measurement wafer W0 is -190.3°C, indicating that a greater cooling effect is obtained. Therefore, by combining the heating unit of the present invention with this embodiment, it becomes possible to control plasma processing over a wider range of low temperatures.

[0035] Therefore, the temperature control characteristics of the lower electrode 11 employing the storage-type cooling unit 155 of this embodiment and the heating unit of the present invention were investigated. Figure 12 shows the results of investigating the temperature tracking ability of the lower electrode 11 when the heating control unit 151 is controlled by the temperature of the measurement point p0 of the lower electrode 11 and the set temperature of p0 is gradually lowered from 0 °C to -150 °C. Although some overshoot was observed immediately after a rapid change in the set temperature, it was confirmed that the temperature of the lower electrode 11 approached the set temperature in about 10 min (600 sec) at each stage, and sufficient controllability was ensured.

[0036] In the embodiments described above, the cooling section is described as being formed inside the lower electrode. However, the cooling section may also be provided separately from the lower electrode, below the lower electrode, to ensure good heat transfer with the lower electrode. [Explanation of Symbols]

[0037] 10… Processing Room 11…Lower electrode 111...Base section 112... Separator component 113…Internal bulkhead 114...Vacuum space 115…Lower bulkhead 116... Helium gas recess 117…Heating channel 118…Cooling channel 119...Vacuum suction port 12...Gas inlet 121...Gas Supply Department 122…Flow Control Unit 13…Gas exhaust port 131... Vacuum pump 14… Dielectric window 141… High-frequency coil 142...High frequency power supply 15…Control Unit 151… Heating control unit 152…Liquid nitrogen supply unit 153… Heater 154...Temperature measurement section 155, 160... Storage-type cooling unit 156... Storage section 157… Heat transfer components 158…Heating channel 161... Pressure chamber 162... Valve

Claims

1. A cooling unit using liquid nitrogen is provided inside or below the lower electrode on which the object to be processed is placed, A gas flow space through which gas can flow is provided between the upper surface of the lower electrode and the cooling section, A heating unit that supplies heated gas to the aforementioned gas flow space and A low-temperature plasma processing apparatus characterized by having the following features.

2. The low-temperature plasma processing apparatus according to claim 1, wherein the cooling unit is a storage-type liquid nitrogen cooling unit comprising a storage unit for storing liquid nitrogen at the bottom and a heat transfer member that protrudes downward from the upper wall and is immersed in the liquid nitrogen to transfer heat to the lower electrode.

3. The low-temperature plasma processing apparatus according to claim 2, wherein the heat transfer member comprises a plurality of columnar members.

4. The low-temperature plasma processing apparatus according to claim 1, wherein the cooling unit is a flow-through type liquid nitrogen cooling unit having a channel through which liquid nitrogen flows.

5. The low-temperature plasma processing apparatus according to claim 4, comprising a separator member which vertically separates a cavity provided inside or below the lower electrode, the upper surface of which is provided with the gas flow space and the lower surface of which is provided with a flow path for the liquid nitrogen.

6. The low-temperature plasma processing apparatus according to claim 1, wherein the temperature of the gas supplied by the heating unit to the gas flow space is 40°C or higher and 300°C or lower.

7. The low-temperature plasma processing apparatus according to claim 1, wherein the gas supplied by the heating unit is nitrogen gas.

8. The low-temperature plasma processing apparatus according to claim 1, wherein the heating unit can change the temperature or flow rate of the supplied gas.

9. The low-temperature plasma processing apparatus according to claim 1, further comprising a vacuum suction unit for vacuum suction of the heat insulating space provided below the cooling unit.

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