JP6449141B2 - Etching processing method and plasma processing apparatus - Google Patents

Description

  The present invention relates to an etching processing method and a plasma processing apparatus.

  In order to perform good etching in the process of etching a substrate with plasma, it has been proposed to control the surface temperature of the substrate by a heater and a refrigerant mechanism provided on a mounting table on which the substrate is mounted. For example, in Patent Document 1, the process temperature indicating the temperature of the surface of the substrate to be held during etching is lower than the plasma heating temperature indicating the temperature at which the substrate reaches thermal equilibrium due to heating from the plasma. The surface temperature of the substrate rises due to heat input. Therefore, it is disclosed that the substrate is cooled by a cooling mechanism so that the surface temperature of the substrate during etching is maintained at the process temperature.

JP-A-10-303185 Japanese Patent No. 3084497 JP-A-8-92765

  However, in Patent Document 1, for example, when the plasma heating temperature is 300 ° C. and the process temperature is 87 ° C., the temperature of the refrigerant is set to about 20 ° C., and the temperature control method for the surface of the substrate in the plasma process at room temperature About. Further, in Patent Document 1, when etching a via hole or a contact hole, the surface temperature of the substrate is changed during etching in order to improve the problem of so-called microloading, in which the etching rate varies depending on the size of the hole. To control.

  However, the plasma treatment under normal temperature and the plasma treatment under a cryogenic environment are different in process characteristics and temperature range to be controlled, so the problems caused by heat input from the plasma may be different. The approach to solving the problem may be different.

  With respect to the above-described problem, in one aspect, an object of the present invention is to promote etching by temperature control at a very low temperature.

  In order to solve the above problem, according to one aspect, the temperature of the surface of the substrate is controlled to be less than −35 ° C., and the first high frequency power output from the first high frequency power source and the second high frequency power source output from the second high frequency power source. A first step of generating plasma from a hydrogen-containing gas and a fluorine-containing gas using high-frequency power, etching the silicon oxide film with the plasma, and stopping the output of the second high-frequency power source, And a second step of performing an etching process, wherein the first step and the second step are repeated a plurality of times.

  According to one aspect, etching can be promoted by temperature control at a very low temperature.

The figure which shows an example of the longitudinal cross-section of the etching processing apparatus which concerns on one Embodiment. The figure which shows an example of the application method and result of LF in the cryogenic etching which concerns on one Embodiment. The figure which shows an example of LF power and heat-transfer gas dependence of the temperature of a wafer. The flowchart which shows an example of the etching processing method which concerns on one Embodiment. The figure which shows an example of the effect of LF off in the cryogenic etching which concerns on one Embodiment. The figure which shows an example of the effect of LF off in the cryogenic etching which concerns on one Embodiment. The figure which shows an example of the temperature transition during the cryogenic etching which concerns on one Embodiment. The figure which shows an example of the effect of the repetition in the cryogenic etching which concerns on one Embodiment. The figure which shows an example of the effect of LF power in the cryogenic etching which concerns on one Embodiment. The figure which shows an example of the relationship between the temperature of the chamber and ER in the cryogenic etching which concerns on one Embodiment. The figure which shows an example of the relationship between LF power and ER in the cryogenic etching which concerns on one Embodiment. The figure which shows an example of a structure of the temperature control part which concerns on one Embodiment. The figure which shows an example of an interference thermometer typically. The figure which shows an example of the temperature control mechanism which concerns on one Embodiment. The figure which shows an example of the relationship between the pressure of the heat transfer gas in the cryogenic temperature which concerns on one Embodiment, and the temperature of the focus ring. The figure which shows an example of the relationship between the intermittent etching which concerns on one Embodiment, and wafer temperature.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In addition, in this specification and drawing, about the substantially same structure, the duplicate description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[Overall configuration of etching apparatus]
First, an etching processing apparatus 1 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows an example of a longitudinal section of an etching processing apparatus 1 according to the present embodiment. The etching processing apparatus 1 according to the present embodiment is an example of a plasma processing apparatus that performs plasma processing on a substrate. In the etching processing apparatus 1 according to the present embodiment, the wafer is plasma-etched. However, the plasma processing apparatus is not limited to this, and desired plasma processing such as film formation and sputtering is performed in the plasma processing apparatus. The etching processing apparatus 1 according to the present embodiment is a parallel plate type plasma processing apparatus (capacitive coupling type plasma processing apparatus) in which a mounting table 20 and a gas shower head 25 are disposed in a chamber 10 so as to face each other. The mounting table 20 also functions as a lower electrode, and the gas shower head 25 also functions as an upper electrode.

  The etching processing apparatus 1 has a cylindrical chamber 10 made of aluminum whose surface is anodized (anodized), for example. The chamber 10 is electrically grounded. The mounting table 20 is installed at the bottom of the chamber 10 and mounts a semiconductor wafer (hereinafter simply referred to as “wafer W”). The wafer W is an example of a substrate. The mounting table 20 is made of, for example, aluminum (Al), titanium (Ti), silicon carbide (SiC), or the like. An electrostatic chuck 106 for electrostatically attracting the wafer is provided on the upper surface of the mounting table 20. The electrostatic chuck 106 has a structure in which a chuck electrode 106a is sandwiched between insulators 106b. A DC voltage source 112 is connected to the chuck electrode 106a, and a DC voltage HV is applied from the DC voltage source 112 to the chuck electrode 106a, whereby the wafer W is attracted to the electrostatic chuck 106 by Coulomb force.

  A focus ring 108 is disposed on the periphery of the electrostatic chuck 106 so as to surround the periphery of the mounting table 20. The focus ring 108 is made of, for example, silicon or quartz. The focus ring 108 functions to improve the in-plane uniformity of etching.

  The mounting table 20 is supported by the support body 104. A coolant channel 104 a is formed inside the support body 104. A refrigerant inlet pipe 104b and a refrigerant outlet pipe 104c are connected to the refrigerant flow path 104a. A cooling medium such as cooling water or brine (hereinafter also referred to as “refrigerant”) output from the chiller 107 circulates through the refrigerant inlet pipe 104b, the refrigerant flow path 104a, and the refrigerant outlet pipe 104c. The mounting table 20 and the electrostatic chuck 106 are removed by the refrigerant and cooled.

  The heat transfer gas supply source 85 supplies a heat transfer gas such as helium gas (He) or argon gas (Ar) to the back surface of the wafer W on the electrostatic chuck 106 through the gas supply line 130. With this configuration, the temperature of the electrostatic chuck 106 is controlled by the coolant circulated through the coolant channel 104a and the heat transfer gas supplied to the back surface of the wafer W. As a result, the wafer can be controlled to a predetermined temperature. The heat transfer gas supply source 85 and the gas supply line 130 are an example of a heat transfer gas supply mechanism that supplies heat transfer gas to the back surface of the wafer W.

  A power supply device 30 that supplies two-frequency superimposed power is connected to the mounting table 20. The power supply device 30 includes a first high-frequency power source 32 that supplies a first high-frequency power (plasma generation high-frequency power) having a first frequency, and a second high-frequency power (for generating a bias voltage) that is lower than the first frequency. And a second high-frequency power source 34 for supplying high-frequency power). The first high frequency power supply 32 is electrically connected to the mounting table 20 via the first matching unit 33. The second high frequency power supply 34 is electrically connected to the mounting table 20 via the second matching unit 35. The first high frequency power supply 32 applies, for example, a first high frequency power of 60 MHz to the mounting table 20. For example, the second high frequency power supply 34 applies second high frequency power of 13.56 MHz to the mounting table 20. In the present embodiment, the first high-frequency power is applied to the mounting table 20, but may be applied to the gas shower head 25.

  The first matching unit 33 matches the load impedance to the internal (or output) impedance of the first high frequency power supply 32. The second matching unit 35 matches the load impedance to the internal (or output) impedance of the second high frequency power supply 34. The first matching unit 33 functions so that the internal impedance of the first high-frequency power source 32 and the load impedance seem to coincide when plasma is generated in the chamber 10. The second matching unit 35 functions so that the internal impedance of the second high-frequency power source 34 and the load impedance seem to coincide when plasma is generated in the chamber 10.

  The gas shower head 25 is attached so as to close the opening of the ceiling portion of the chamber 10 via a shield ring 40 covering the peripheral edge portion thereof. The gas shower head 25 may be electrically grounded as shown in FIG. A predetermined direct current (DC) voltage may be applied to the gas shower head 25 by connecting a variable direct current power source.

  The gas shower head 25 is formed with a gas inlet 45 for introducing gas. Inside the gas shower head 25, there are provided a diffusion chamber 50a at the center portion and a diffusion chamber 50b at the edge portion branched from the gas inlet 45. The gas output from the gas supply source 15 is supplied to the diffusion chambers 50a and 50b through the gas introduction port 45, diffused in the diffusion chambers 50a and 50b, and directed from the multiple gas supply holes 55 toward the mounting table 20. be introduced.

  An exhaust port 60 is formed on the bottom surface of the chamber 10, and the inside of the chamber 10 is exhausted by an exhaust device 65 connected to the exhaust port 60. Thereby, the inside of the chamber 10 can be maintained at a predetermined degree of vacuum. A gate valve G is provided on the side wall of the chamber 10. The gate valve G opens and closes the loading / unloading port when the wafer W is loaded and unloaded from the chamber 10.

  The etching processing apparatus 1 is provided with a control unit 100 that controls the operation of the entire apparatus. The control unit 100 includes a CPU (Central Processing Unit) 105, a ROM (Read Only Memory) 110, and a RAM (Random Access Memory) 115. The CPU 105 executes a desired process such as an etching process, which will be described later, according to various recipes stored in these storage areas. The recipe includes process time, pressure (gas exhaust), high-frequency power and voltage, various gas flow rates, chamber temperature (upper electrode temperature, chamber sidewall temperature, wafer W temperature (electrostatic), which are control information of the apparatus for process conditions. The temperature of the refrigerant output from the chiller 107, and the like. Note that recipes indicating these programs and processing conditions may be stored in a hard disk or a semiconductor memory. Further, the recipe may be set at a predetermined position and read out while being stored in a portable computer-readable storage medium such as a CD-ROM or DVD.

  During the etching process, the opening and closing of the gate valve G is controlled, and the wafer W is loaded into the chamber 10 and placed on the mounting table 20. When the DC voltage HV is applied from the DC voltage source 112 to the chuck electrode 106a, the wafer W is attracted and held by the electrostatic chuck 106 by the Coulomb force.

  Next, an etching gas and high-frequency power are supplied into the chamber 10 to generate plasma. Plasma etching is performed on the wafer W by the generated plasma. After the etching process, a DC voltage HV having a polarity opposite to that at the time of adsorption of the wafer W is applied from the DC voltage source 112 to the chuck electrode 106 a to remove the charge of the wafer W, and the wafer W is peeled off from the electrostatic chuck 106. The opening and closing of the gate valve G is controlled, and the wafer W is unloaded from the chamber 10.

[Etching process]
Next, the etching of the silicon oxide film (SiO ₂ ) in the etching processing apparatus 1 of the present embodiment having such a configuration will be described. As shown in FIG. 2A, a silicon oxide film 6 that is an example of an etching target film is formed on the wafer W, and a mask film 5 is provided on the silicon oxide film 6. As the mask film 5, a polysilicon film, an organic film, an amorphous carbon film, a titanium nitride (TiN) film, or the like can be used.

  In the etching processing method according to the present embodiment, etching is performed in a cryogenic environment where the surface temperature of the wafer W is less than -35 ° C. Thereby, the temperature of the surface of the wafer W can be etched at a higher etching rate as compared with a normal temperature (for example, around 25 ° C. or higher) process. However, in the plasma etching under a cryogenic environment, the etching rate is drastically lowered due to an increase in the temperature of the surface of the wafer W. Therefore, temperature control of the wafer W surface is very important.

FIG. 2A shows an example of the result of etching under the process conditions under the cryogenic environment shown below.
・ Process conditions Temperature (set temperature of chiller 107) -60 ℃
Pressure 60mT (8.00Pa)
First high frequency power HF 2500W
Second high frequency power LF Displayed in FIG. 2 (continuous wave, pulse wave)
Gas type Hydrogen (H ₂ ) / Carbon tetrafluoride (CF ₄ )
Under the above process conditions, the temperature of the surface of the wafer W during the process was monitored. An example of an etching result when a pulse wave of the second high-frequency power LF having 4000 W, 0.3 kHz, and a duty ratio of 50% is applied is shown in the “LF pulse wave” column (leftmost) in FIG. . In this case, the temperature of the surface of the wafer W during etching is −47 ° C., and the etching rate (ER) is 1259 nm / min. At this time, the effective value of the second high-frequency power LF is 2000 W.

  An example of the etching result when a continuous wave of the second high-frequency power LF of 4000 W, 2000 W, and 1000 W is applied in the “LF continuous wave” column of FIG. In the continuous wave of the second high-frequency power LF of 2000 W, the temperature of the wafer W surface during etching is −43 ° C. and the etching rate is 865 nm / min. According to this, when the effective value is the same 2000 W, the etching rate is improved by about 1.5 times by changing the second high frequency power LF from a continuous wave to a pulse wave.

  However, in the continuous wave of the second high-frequency power LF of 4000 W, the temperature (center portion) of the surface of the wafer W during etching is −35 ° C., the etching rate is 310 nm / min, and the etching does not proceed (hereinafter referred to as “etching”). Also called “stop”.) The phenomenon occurred. That is, it can be seen that in plasma etching under a cryogenic environment, there is a region where the temperature of the surface of the wafer W suddenly rises due to heat input from the plasma, and etching stops without progressing.

  In the continuous wave of the second high frequency power LF of 1000 W, the temperature of the surface of the wafer W during etching is −49 ° C., and the etching rate (ER) is 1256 nm / min. Thus, etch stop can be prevented by maintaining the process temperature at an extremely low temperature of less than -35 ° C. In the extremely low temperature region, the heat input from the plasma decreases and the etching rate increases as the second high-frequency power LF is decreased.

  As described above, in the cryogenic process of the present embodiment, as the second high frequency power LF increases, the heat input from the plasma increases, the etching rate decreases, and an etch stop occurs at 4000 W. From this result, it was found that the etching result is completely different in the cryogenic process from the room temperature process in which the etching rate increases as the second high-frequency power LF increases.

  In the result of FIG. 2, when the pulse wave of the second high-frequency power LF is 4000 W, 0.3 kHz, and the duty ratio is 50%, the surface temperature of the wafer W is the same as that when the continuous wave of the second high-frequency power LF is 1000 W. And an etching rate. That is, as shown in FIG. 2B, when a pulse wave of the second high frequency power LF is applied, the second high frequency power LF (effective value) is applied rather than a continuous wave of the second high frequency power LF. In contrast, the temperature of the surface of the wafer W can be lowered. That is, when the second high-frequency power LF is changed to a pulse wave, the temperature of the surface of the wafer W can be controlled to be lower than the heat input from the plasma as compared with the continuous wave, so that the etching can be promoted at a higher etching rate. .

  FIG. 3 shows the relationship between the pressure on the back surface of the wafer W and the temperature on the front surface of the wafer W by controlling the flow rate of the second high-frequency power LF and the heat transfer gas (He gas). The graph shown in FIG. 3A shows the second high-frequency power LF when the pressure on the back surface of the wafer W is changed to 5 Torr (666.6 Pa), 15 Torr (2000 Pa), 25 Torr (3333 Pa), and 40 Torr (5333 Pa). The temperature change of the wafer W surface is shown. The graph shown in FIG. 3B shows the temperature change of the surface of the wafer W with respect to the pressure on the back surface of the wafer W when the second high-frequency power LF is changed to 0 W, 1000 W, 2000 W, and 4000 W. According to this, it is understood that it is difficult to effectively suppress the temperature rise on the front surface of the wafer W only by controlling the pressure on the back surface of the wafer W.

  As described above, in the present embodiment, when etching the silicon oxide film 6 with the surface temperature of the wafer W being controlled at an extremely low temperature, a time for turning off the pulse wave of the second high-frequency power LF is provided, and etching is performed intermittently. An etching method for performing the above process is proposed. This avoids an abrupt temperature rise on the surface of the wafer W and improves the etching rate, thereby eliminating the etch stop and promoting the etching.

An example of the etching method according to this embodiment is shown in the flowchart of FIG. When the etching processing method of FIG. 4 is started, first, the temperature of the wafer surface is controlled to an extremely low temperature of less than −35 ° C. (step S10). Next, a hydrogen-containing gas and a fluorine-containing gas are supplied into the chamber 10 (step S12). For example, hydrogen (H ₂ ) gas and carbon tetrafluoride (CF ₄ ) gas are supplied.

  Next, the first high frequency power HF is output from the first high frequency power supply 32, and the high frequency power for plasma excitation is applied (turned on) to the mounting table 20. Further, the second high frequency power LF is output from the second high frequency power supply 34, and the high frequency power for bias is applied to the mounting table. Thereby, the silicon oxide film 6 is etched (step S14: first step). At this time, the first high-frequency power HF may be a continuous wave or a pulse wave, but the second high-frequency power LF is a pulse wave. The execution time (predetermined time) of the first step is preferably 30 seconds or less.

  Next, after a predetermined time has elapsed, the silicon oxide film 6 is etched with the application of the pulse wave of the second high-frequency power stopped (off) (step S16: second step). The execution time of the second step is preferably 5 seconds or more as will be described later. The pressure in the chamber 10 when performing the second step may be a low pressure state of 10 mT (1.33 Pa) or less.

  As shown in FIG. 4, in the etching processing method according to the present embodiment, the second high frequency power LF is intermittently applied by repeatedly turning on and off the second high frequency power LF. At this time, the time during which the second high-frequency power LF is applied (on time) is “Ton”, and the time during which the second high-frequency power LF is not applied (off time) is Toff. In this case, a pulse wave of the second high frequency power having a frequency of 1 / (Ton + Toff) is applied. The duty ratio is represented by the ratio of the on time Ton to the total time of the on time Ton and the off time Toff, that is, Ton / (Ton + Toff).

  Next, it is determined whether the number of times the second high-frequency power LF is repeatedly turned on / off exceeds a predetermined number (step S18). The predetermined number of times is a predetermined number of times of two or more. When it is determined that the number of repetitions of the second high-frequency power LF does not exceed the predetermined number, the pulse wave of the second high-frequency power is applied again and the silicon oxide film 6 is etched (step S20: first step). The processes in steps S16 to S20 are repeated until the number of repetitions of the second high-frequency power LF exceeds a predetermined number. When it is determined that the number of repetitions of the second high-frequency power LF exceeds the predetermined number, this process ends.

  An example of the etching result by the etching method according to the embodiment is shown in FIG. An example of the etching result according to the comparative example is shown on the left side of FIG. 5, and three examples of the etching result according to the present embodiment are shown on the right side thereof.

The process conditions of the etching according to the comparative example and the etching according to the present embodiment are as follows.
・ Process conditions (comparative example)
Temperature (set temperature of chiller 107) -60 ° C
Pressure 60mT (8.00Pa)
First high frequency power HF 2500W
Second high frequency power LF 4000 W, 0.3 kHz, Duty ratio 50%
Gas type Hydrogen (H ₂ ) / Carbon tetrafluoride (CF ₄ )
ON time 60 sec
Off time None / Process conditions (this embodiment)
Temperature (set temperature of chiller 107) -60 ° C
Pressure 60mT (8.00Pa)
First high frequency power HF 2500W
Second high frequency power LF 4000 W, 0.3 kHz, Duty ratio 50%
Gas type Hydrogen (H ₂ ) / Carbon tetrafluoride (CF ₄ )
ON time (LF) 15 sec (× 4) (repeated 4 times)
Off time (LF) Available (60sec, 30sec, 15sec)
As a result, in the etching method according to the present embodiment, the etching rate was approximately 1.5 times and the selectivity was improved to nearly 1.5 times as compared with the etching of the comparative example. The reason for this is that, according to the etching method according to the present embodiment, by providing the off-time Toff of the second high-frequency power LF periodically during etching, heat input from the plasma is reduced during the off-time Toff, The temperature rise on the surface of the wafer W during the on-time can be suppressed. As a result, the temperature of the surface of the wafer W can be maintained at an extremely low temperature of less than −35 ° C.

  FIG. 6 shows an example of the etching result when the off time Toff of the process condition of the present embodiment is set to 5 sec. Process conditions other than off-time are the same. As a result, when the off time Toff is set to 5 sec, the etching rate and the selection ratio are further improved in the etching method according to the present embodiment, and the etching rate and the selection ratio are approximately 1. compared with the etching of the comparative example. Improved by a factor of 5.

  FIG. 7 shows the temperature of the surface of the wafer W from when the wafer W is loaded into the etching processing apparatus 1 until it is unloaded after etching by the etching processing method of this embodiment. When the first and second high-frequency power is applied while the wafer W is held by the electrostatic chuck 106, plasma is generated and the etching process is started. When the first and second high frequency powers are applied and plasma is generated, the temperature of the surface of the wafer W rapidly increases in 5 seconds due to heat input from the plasma (plasma on), and then the surface of the wafer W is heated. The temperature rises slowly.

  When the application of the second high-frequency power is stopped during the etching, the temperature of the surface of the wafer W rapidly decreases in 5 seconds. This is because the amount of heat input from the plasma is reduced. From this result, the time for turning off the second high-frequency power LF may be 5 seconds or more.

  In addition, based on the etching result shown in FIG. 5, the off time Toff of the second high-frequency power LF may be in the range of 5 sec to 60 sec. However, considering the throughput, the off time Toff of the second high-frequency power LF is preferably a short time. Therefore, the off time Toff of the second high-frequency power LF is preferably 5 s to 30 s, and more preferably 5 s to 10 s.

  In the temperature transition on the surface of the wafer W shown in FIG. 7, the wafer W is unloaded after the second high-frequency power LF is turned off. For this reason, the temperature of the surface of the wafer W after the second high-frequency power LF is turned off is rising. In the example of FIG. 7, the supply of the refrigerant from the chiller 107 is stopped after the second high-frequency power LF is turned off. However, in the etching method according to the present embodiment, the second high-frequency power LF is turned on and off a plurality of times. Further, the supply of the refrigerant from the chiller 107 is not stopped while the second high-frequency power LF is repeatedly turned on and off a plurality of times (that is, during etching). Thereby, the temperature of the surface of the wafer W can be maintained at an extremely low temperature of less than −35 ° C. during etching. Thus, the etching method according to the present embodiment is suitable for a process of increasing the etching rate and deeply etching a thin hole having an aspect ratio of 20 or more, for example.

  In the present embodiment, a time for turning off the pulse wave of the second high-frequency power LF is provided in step S16 of FIG. However, a time for turning off the first high frequency power HF together with the second high frequency power LF in step S16 of FIG. 4 may be provided. Also by this, in the off time of the first high-frequency power HF and the second high-frequency power LF, by reducing the heat input from the plasma, the surface temperature of the wafer W can be maintained at a very low temperature, and the etching rate can be increased. Can enhance and promote etching.

  FIG. 8 shows an example of the etching result when the on-time Ton is changed once in the process conditions in the etching method of this embodiment, and the etching under the process conditions (no off-time) in the comparative example. Shown with results. In the etching of the present embodiment, an example of etching results when the off time Toff is 60 sec and the on time Ton is 30 sec (× 2), 15 sec (× 4), and 5 sec (× 12) is shown. From this result, according to the etching method of the present embodiment, the etching rate and the selection ratio are improved in any case as compared with the etching result of the comparative example, and the etching is especially performed as the number of on / off repetitions is increased. It can be seen that is promoted.

FIG. 9 shows an example of the etching result when the effective value of the second high-frequency power during the on-time Ton in the process condition is changed in the etching method of the present embodiment. ) And the etching result. In this embodiment, the off time is set to 30 sec, the on time Ton is set to 15 sec (× 4), and the second high frequency power at that time is 2000 W (0.3 kHz, Duty 50%), 4000 W (0.3 kHz, Duty 50%), Set to 6000 W (0.3 kHz, Duty 50%). From this result, it can be seen that according to the etching processing method of the present embodiment, the etch stop does not occur in any case and the etching rate and the selection ratio are improved as compared with the etching result of the comparative example. From this result, since the effective value of the second high frequency power of 2000 W (0.3 kHz, Duty 50%) is 1000 W, the effective value of the output of the second high frequency power is 1000 W or more (1.4 W / cm ² per unit area). Or more).

  As described above, according to the etching method according to the present embodiment, the temperature of the surface of the wafer W is lowered and maintained at an extremely low temperature by intermittently providing the time for turning off the second high-frequency power every predetermined time during the etching. can do. Thereby, an etching rate and a selection ratio can be raised. Further, even in the region of the second high-frequency power LF where the etch stop has occurred when the off-time of the second high-frequency power LF is not provided during etching, the off-time of the second high-frequency power LF is provided intermittently to provide a cryogenic temperature. Etching can be promoted below.

(Cooling heat removal)
The chiller 107 constantly circulates a coolant controlled to a very low temperature through the mounting table 20 during etching. Therefore, during etching, the surface of the wafer W is always removed by the refrigerant. At this time, the total cooling heat removal amount (total heat removal amount) is calculated as heat removal amount per unit area × time.

In the etching method according to the present embodiment, the heat removal amount is sufficient if the total heat removal amount is 71.7 kW / m ² × 5 sec or more when the output of the second high-frequency power source LF is stopped. In the calculation of the heat removal amount, the heat removal performance of the chiller 107 is 5000 Ws, and the diameter of the mounting table 20 is 298 mm. That is, the heat removal amount per unit area when the output of the second high-frequency power source LF is stopped may be 71.7 kW / m ² (7.17 W / cm ² ) or less per second. In addition, when the outputs of the first high frequency power supply HF and the second high frequency power supply LF are intermittently stopped, the heat removal amount per unit area in the state where the outputs from the first high frequency power supply HF and the second high frequency power supply LF are stopped is as follows: It may be 71.7 kW / m ² (7.17 W / cm ² ) or less per second.

  As described above, according to the etching processing method of the present embodiment, the surface temperature of the wafer W is made lower than −35 ° C. by applying intermittent high frequency power during etching in a cryogenic environment. Etching rate can be increased and etching can be promoted. Further, according to the etching processing method of the present embodiment, by applying intermittent high frequency power during etching in a cryogenic environment, etching at cryogenic temperature can be performed without causing an etch stop, and the process window can be reduced. Can be wide. Therefore, the etching method of the present embodiment is preferably applied to a case where a hole having an aspect ratio of 20 or more is to be etched deeper or a thinner hole is desired to be etched.

[Temperature control]
In the etching method according to the present embodiment described above, a very high ER can be obtained in a cryogenic environment where the surface temperature of the wafer W is less than -35 ° C. That is, temperature control of the surface of the wafer W is very important. For example, FIG. 10 shows an example of the relationship between the chamber temperature and the ER of the silicon oxide film in the cryogenic etching according to the present embodiment. The etching result shown in FIG. 10 is the result of etching the silicon-containing antireflection film under the following process conditions. The horizontal axis in FIG. 10 represents the process conditions (Case 1 to Case 4) of the wafer W, and the vertical axis represents the etching rate (ER) at the center position of the 300 mm wafer.
・ Process conditions Temperature (set temperature of chiller) -60 ℃
Pressure 60mT (8.00Pa)
First high frequency power HF 2500W
Second high frequency power LF 4000 W Pulse wave duty ratio 50% (effective value 2000 W)
Gas type Hydrogen (H ₂ ) / Carbon tetrafluoride (CF ₄ )
Under the above process conditions, Case 1 and Case 2 in FIG. 10 are cases where the pressure of He gas (heat transfer gas) supplied to the back surface of the wafer W is controlled to 50 T (6666 Pa), and Case 3 and Case 4 in FIG. Is a case where the pressure of He gas is controlled to 80T (10666 Pa). In Case 1 and Case 3 of FIG. 10, the temperature of the top plate constituting the gas shower head 25 is 30 ° C., and the temperature of the side wall of the chamber 10 is 40 ° C. In this case, if the He gas pressure is set to 80 T, the effect of cooling the back surface of the wafer W by He gas can be enhanced compared to setting the He gas pressure to 50 T, and the temperature of the wafer W can be maintained at a very low temperature. As a result, the etching rate can be increased.

  In Case 2 and Case 4 of FIG. 10, the temperature of the top plate constituting the gas shower head 25 is 150 ° C., and the temperature of the side wall of the chamber 10 is 150 ° C. Similarly, in this case, if the He gas pressure is set to 80 T, the effect of cooling the back surface of the wafer W by He gas can be enhanced compared to setting the He gas pressure to 50 T, and the temperature of the wafer W can be made extremely low. As a result, the etching rate can be increased.

  In other words, temperature control of the surface of the wafer W is very important in a cryogenic environment, and it is possible to control the temperature of the surface of the wafer W to be less than −35 ° C. compared to etching in a room temperature environment. It can be seen that the rate is greatly affected.

  In addition to the cooling effect by the heat transfer gas such as He gas, the heat input from the plasma to the wafer W can be controlled by changing the parameters on the heat input side. Also by this, the temperature of the surface of the wafer W can be made extremely low, and the etching rate can be increased.

For example, FIG. 11 shows an example of the relationship between ER power control and ER in the cryogenic etching according to the present embodiment. The etching results shown in FIG. 11 are the results of etching the silicon-containing antireflection film under the following process conditions. The horizontal axis in FIG. 11 represents the process conditions of the wafer W, and the vertical axis represents the etching rate (ER) at the center position of the 300 mm wafer.
・ Process conditions Temperature (set temperature of chiller) -70 ℃
Pressure 60mT (8.00Pa)
First high frequency power HF 2500W
Second high frequency power LF Displayed in FIG. 2 (pulse wave, continuous wave)
Gas type Hydrogen (H ₂ ) / Carbon tetrafluoride (CF ₄ )
On the left side of FIG. 11, the second high frequency power LF is a pulse wave of 4000 W, and the duty ratio is controlled to 50%. Therefore, the effective value of the second high-frequency power LF on the left side of FIG. 11 is 2000 W. On the right side of FIG. 11, the second high-frequency power LF is a continuous wave of 4000 W. Therefore, the effective value of the second high-frequency power LF on the right side of FIG. 11 is 4000 W.

  Referring to each graph, the second high-frequency power LF is turned on / off, the heat input from the plasma is suppressed while the second high-frequency power LF is off, and the etching rate on the left side that can reduce the surface temperature of the wafer W Is much higher than the etching rate on the right side of FIG.

  From the above, the effect of cooling the back surface of the wafer W can be enhanced by controlling the pressure control of the He gas and the on / off of the high-frequency power. Thereby, since the temperature of the surface of the wafer W can be maintained below -35 degreeC, an etching rate can be raised and productivity can be improved.

[Temperature control unit]
Therefore, as shown in FIG. 12, the temperature measurement unit 200 according to the present embodiment measures the temperature of the focus ring 108 of the etching processing apparatus 1 and controls the temperature of the surface of the wafer W in real time from the measurement result. PC 201 for use. The control PC 201 is an example of a monitor mechanism that monitors the surface temperature of the wafer W in real time. At that time, the control PC 201 controls the temperature of the surface of the wafer W from the result of the temperature measurement of the focus ring 108.

  Further, the temperature measuring unit 200 includes a temperature measuring mechanism 205. The temperature measurement mechanism 205 measures the temperature of the focus ring 108. As an example of the temperature measurement mechanism 205, a method for measuring the temperature of the focus ring 108 will be described using the interference thermometer shown in FIG. 13 as an example. However, as long as the temperature measuring mechanism 205 can measure the temperature of the focus ring 108, any known thermometer can be used regardless of the interference thermometer.

  The temperature measurement mechanism 205 includes a spectroscope 202, a light source 203, a circulator 204, and a collimator 207. As shown in FIG. 12, the tip of the optical fiber 206 is embedded in the mounting table 20 so as to be in close contact with the focus ring 108 under the focus ring 108 of the etching processing apparatus 1. The optical fiber 206 is connected to the temperature measurement mechanism 205 via a collimator 207.

  As shown in FIG. 13, the temperature measuring mechanism 205 measures the temperature of the focus ring 108 made of silicon (Si) having a refractive index n. The focus ring 108 as the measurement object has a first main surface corresponding to the back surface of the focus ring 108 and a second main surface facing the first main surface corresponding to the surface of the focus ring 108.

  First, spectrum light having a wavelength λ of 1560 nm is emitted from the light source 203. The light source 203 is a measurement light source having a wavelength that passes through the focus ring 108. The 1560 nm measurement light output from the light source 203 is input to the collimator 207 via the circulator 204, collected, and output from the output end of the optical fiber 206 toward the focus ring 108. The collimator 207 receives the first reflected light A of the measurement light reflected by the first main surface and the second reflected light B of the measurement light that has been transmitted through the focus ring 108 and reflected by the second main surface. To do. The incident first reflected light A and second reflected light B are transmitted to the spectroscope 202 via the circulator 204. Returning to FIG. 12, a control PC 201 is connected to the spectroscope 202. The control PC 201 measures the temperature of the focus ring 108 based on a waveform obtained by Fourier transforming the interference intensity distribution between the first reflected light A and the second reflected light B transferred from the spectroscope 202.

  Thus, in the present embodiment, the temperature of the focus ring 108 is measured using the temperature measurement mechanism 205, and the temperature of the mounting table 20 on which the wafer W is mounted is not directly measured. The reason for this is that when the temperature of the back surface of the mounting table 20 is directly measured, there is a predetermined distance between the mounting table 20 and the wafer W. Therefore, the measured value on the back surface of the mounting table 20 indicates the actual temperature of the front surface of the wafer W. Although not shown, it is difficult to accurately control the temperature of the wafer W. Further, when the temperature is measured on the back surface of the mounting table 20, the wafer W is easily affected by heat input from the plasma generated above the wafer W, or is easily affected by the electrical influence of the electrostatic chuck 106. It is likely to hinder accurate measurement of the temperature of the surface. For the above reason, the temperature measurement unit 200 according to the present embodiment measures the temperature of the focus ring 108 and estimates the temperature of the surface of the wafer W based on the measurement result.

  At that time, the etching apparatus 1 causes the electrostatic chuck 106 to attract the cooling mechanism for cooling the focus ring 108 and the focus ring 108 so that the temperature of the surface of the wafer W can be accurately estimated from the measured temperature of the focus ring 108. And an adsorption mechanism. These mechanisms will be specifically described with reference to FIG.

  FIG. 14A shows an example of a conventional electrostatic chuck 106, a focus ring 108 and the vicinity thereof. In the example of FIG. 14A, an intermediate body 310 is provided between the electrostatic chuck 106 and the focus ring 108 so that the electrostatic chuck 106 and the focus ring 108 are in close contact with the heat transfer sheet 300 interposed therebetween. . As a result, the electrostatic chuck 106 and the focus ring 108 are thermally separated. As a result, in the configuration example shown in FIG. 14A, it is difficult to accurately estimate the temperature of the surface of the wafer W from the measured temperature of the focus ring 108.

  On the other hand, FIG. 14B shows the electrostatic chuck 106, the focus ring 108 and the vicinity thereof in the etching processing apparatus 1 according to the present embodiment. In the etching processing apparatus 1 according to this embodiment, the intermediate body 310 and the heat transfer sheet 300 are not held between the focus ring 108 and the electrostatic chuck 106, and the focus ring 108 and the electrostatic chuck 106 are directly connected to each other. It touches.

  In addition, chuck electrodes 406 a and 406 b are provided inside the electrostatic chuck 106 below the focus ring 108. A DC voltage source 412a is connected to the chuck electrode 406a, and a DC voltage HV-A is applied from the DC voltage source 412a to the chuck electrode 406a. Similarly, a DC voltage source 412b is connected to the chuck electrode 406b, and a DC voltage HV-B is applied from the DC voltage source 412b to the chuck electrode 406b. Thereby, the electrostatic chuck 106 and the focus ring 108 are electrostatically attracted by the Coulomb force.

  Furthermore, the etching processing apparatus 1 according to the present embodiment is provided with a gas supply line 430 for supplying a heat transfer gas such as helium gas (He) or argon gas (Ar) to the back surface of the focus ring 108. . A heat transfer gas supply source 85 shown in FIG. 1 is connected to the gas supply line 430. Thereby, the back surface of the focus ring 108 is cooled by the heat transfer gas in the same manner as the back surface of the wafer W. Further, the back surface of the focus ring 108 is cooled by the refrigerant flow path 104a in the same manner as the back surface of the wafer W.

  According to the etching processing apparatus 1 having such a configuration, since the back surface of the focus ring 108 and the back surface of the wafer W are cooled in the same environment, the focus ring 108 and the mounting table against heat input from plasma during etching. The heat removal performance with 20 can be made the same. Therefore, if the temperature of the focus ring 108 is measured, the surface temperature of the wafer W can be accurately estimated based on the material and structure of the mounting table 20, the structure of the refrigerant flow path 104a, the refrigerant temperature, and the like. Thereby, the temperature of the surface of the wafer W can be monitored in real time by measuring the temperature of the focus ring 108 in real time.

  The mechanism for supplying the refrigerant from the chiller 107 to the refrigerant flow path 104a and the mechanism for supplying the heat transfer gas from the heat transfer gas supply source 85 via the gas supply lines 130 and 430 are the temperatures provided on the mounting table 20. It is an example of a control mechanism. The temperature measurement unit 200 adjusts the temperature of the surface of the wafer W using a temperature control mechanism and on / off control of the high-frequency power RF.

  Specifically, the control PC 201 in FIG. 12 acquires the temperature of the focus ring 108 in real time every predetermined time. Then, the control PC 201 obtains the temperature of the focus ring 108 obtained based on the relationship graph Gh1 between the output of the high-frequency power RF and the temperature of the wafer W that are recorded in advance in a recording unit such as the ROM 110 as shown in FIG. The on / off of the high frequency power RF is controlled in real time from the information. For example, when the temperature indicated by the acquired temperature information is higher than −35 ° C., the control PC 201 determines that the surface temperature of the wafer W is not in an extremely low temperature state, and controls the high frequency power RF to be turned off. A signal for turning off the high-frequency power RF is output to the unit 100. The control unit 100 feedback-controls the high frequency power RF off based on the signal transmitted from the control PC 201.

  Further, for example, if the temperature indicated by the temperature information of the acquired focus ring 108 is less than −35 ° C., the control PC 201 determines that the surface temperature of the wafer W is in an extremely low temperature state, and turns on the high-frequency power RF. Thus, a signal for turning on the high-frequency power RF is output to the control unit 100. The control unit 100 feedback-controls the high-frequency power RF based on the signal transmitted from the control PC 201. In this manner, by applying pulsed high frequency power RF in real time based on the measured temperature of the focus ring 108, the surface temperature of the wafer W can be maintained at an extremely low temperature of less than -35 ° C.

  Note that the control PC 201 may control only on / off of the output of the second high frequency power supply 34 as the high frequency power RF, or may turn on the output of the first high frequency power supply 32 and the output of the second high frequency power supply 34. -You may control OFF in synchronization.

  As described above, the temperature measuring unit 200 stops the output of the second high frequency power supply 34 based on the measured temperature of the focus ring 108 or outputs the outputs of the first high frequency power supply 32 and the second high frequency power supply 34. Stop and perform feedback control so that the temperature of the surface of the wafer W is maintained below -35 ° C. With the feedback function described above, according to the present embodiment, the temperature of the surface of the wafer W can be maintained at an extremely low temperature. In particular, the etching processing apparatus 1 according to the present embodiment has a temperature control mechanism (cooling mechanism and heat transfer mechanism) shown in FIG. 14 below the focus ring 108 in order to control the temperature of the end portion of the wafer W. Thereby, the heat removal performance of the focus ring 108 and the mounting table 20 can be made the same. Therefore, if the temperature of the focus ring 108 is measured, the temperature of the surface of the wafer W can be accurately estimated. Thus, by measuring the temperature of the focus ring 108, feedback control of the high frequency power RF can be performed so that the temperature of the surface of the wafer W is maintained at an extremely low temperature of less than −35 ° C.

  In the present embodiment, feedback control of the pressure of the heat transfer gas is performed so that the temperature of the surface of the wafer W is maintained at an extremely low temperature of less than −35 ° C. by measuring the temperature of the focus ring 108. Can do.

  FIG. 15 shows an example of the relationship between the heat transfer gas and the temperature of the focus ring 108 at a cryogenic temperature according to an embodiment. The horizontal axis of FIG. 15 shows the pressure (FR He BP) of He gas when He gas is supplied to the back surface of the focus ring 108 as heat transfer gas. The vertical axis in FIG. 15 indicates the temperature of the focus ring 108. According to this, it can be seen that in a cryogenic environment, the pressure of the He gas and the temperature of the focus ring 108 have the relationship of the graph shown in FIG.

  FIG. 16 shows an example of the result of feedback control by the control PC 201. According to this, the surface temperature of the wafer W that rises while the high-frequency power RF is turned on is lowered while the high-frequency power RF is turned off by repeatedly turning on and off the high-frequency power RF. Is done. Thereby, the temperature of the surface of the wafer W can be maintained at an extremely low temperature of less than −35 ° C.

  Since the on / off control of the high-frequency power RF and the pressure control of the heat transfer gas are performed in real time according to the temperature measurement of the focus ring 108 during etching, the temperature controllability is high. Therefore, according to the etching processing apparatus 1 according to the present embodiment, by measuring the temperature of the focus ring 108, both the on / off control of the high frequency power RF and the pressure control of the heat transfer gas are autonomously controlled in real time. It is possible. As a result, a high etching rate can be obtained by maintaining the surface temperature of the wafer W at an extremely low temperature of less than −35 ° C., and productivity can be improved.

  The control PC 201 may control at least one of He gas pressure control and high-frequency power RF on / off control. For example, in the control PC 201, the output stop of the first high-frequency power or the second high-frequency power and the pressure control of the heat transfer gas may be performed by autonomous control.

  As mentioned above, although the etching processing method and the plasma processing apparatus were demonstrated by the said embodiment, the etching processing method and plasma processing apparatus concerning this invention are not limited to the said embodiment, A various deformation | transformation is carried out within the scope of the present invention. And improvements are possible. The matters described in the above embodiments can be combined within a consistent range.

For example, in the said embodiment, hydrogen gas was mentioned as an example as hydrogen-containing gas, and carbon tetrafluoride gas was mentioned as an example as fluorine-containing gas, and demonstrated. However, the hydrogen-containing gas is not limited to hydrogen (H ₂ ) gas, but methane (CH ₄ ) gas, fluoromethane (CH ₃ F) gas, difluoromethane (CH ₂ F ₂ ) gas, and trifluoromethane (CHF ₃ ) gas. As long as it contains at least one of the above gases. The fluorine-containing gas is not limited to carbon tetrafluoride (CF ₄ ) gas, but C ₄ F ₆ (hexafluoro1,3 butadiene) gas, C ₄ F ₈ (perfluorocyclobutane) gas, C ₃ F ₈ ( It may be octafluoropropane) gas, NF ₃ (nitrogen trifluoride) gas, or SF ₆ (sulfur hexafluoride) gas.

Further, the step of removing the reaction product generated by the etching may be performed at the off time Toff of the second high frequency power or the off time Toff of the first and second high frequency power. For example, oxygen (O ₂ ) gas may be supplied during the off time Toff, and reaction products attached to the hole opening may be removed by O ₂ plasma generated from the oxygen gas. Alternatively, hydrogen (H ₂ ) gas and carbon tetrafluoride (CF ₄ ) gas may be supplied, etching may be promoted by plasma generated from these mixed gases, and reaction products may be removed.

  The plasma processing apparatus according to the present invention is applicable not only to a capacitively coupled plasma (CCP) apparatus but also to other plasma processing apparatuses. Other plasma processing apparatuses include inductively coupled plasma (ICP), a plasma processing apparatus using a radial line slot antenna, a helicon wave excited plasma (HWP) apparatus, an electron cyclotron resonance plasma ( An ECR (Electron Cyclotron Resonance Plasma) apparatus or the like may be used.

  In this specification, the semiconductor wafer W has been described as an object to be etched, but various substrates used for LCD (Liquid Crystal Display), FPD (Flat Panel Display), etc., photomasks, CD substrates, printed boards, etc. good.

DESCRIPTION OF SYMBOLS 1: Etching processing apparatus 10: Chamber 15: Gas supply source 20: Mounting stand 25: Gas shower head 30: Power supply apparatus 32: 1st high frequency power supply 33: 1st matching device 34: 2nd high frequency power supply 35: 2nd matching 85: Heat transfer gas supply source 106: Electrostatic chuck 107: Chiller 200: Temperature control unit 202: Spectrometer 203: Light source 204: Circulator 205: Temperature measuring mechanism 207: Collimator

Claims (12)

An etching processing method executed in a parallel plate type plasma processing apparatus in which a lower electrode and an upper electrode on which a substrate is placed are arranged to face each other,
The temperature of the surface of the substrate is controlled to be less than −35 ° C., and plasma is generated from the hydrogen-containing gas and the fluorine-containing gas using the first high-frequency power output from the first high-frequency power source and the second high-frequency power output from the second high-frequency power source And a first step of etching the silicon oxide film with plasma,
A second step of stopping the output of the second high frequency power source and etching the silicon oxide film with plasma;
Including
An etching method, wherein the first step and the second step are repeated a plurality of times. Plasma is generated from hydrogen-containing gas and fluorine-containing gas using the first high-frequency power output from the first high-frequency power source and the second high-frequency power output from the second high-frequency power source by controlling the surface temperature of the substrate to less than -35 ° C. A first step of generating and etching the silicon oxide film with plasma;
A second step of stopping the output of the first high-frequency power source and the second high-frequency power source and etching the silicon oxide film with plasma;
Including
An etching method, wherein the first step and the second step are repeated a plurality of times. The hydrogen-containing gas is at least one of hydrogen (H ₂ ) gas, methane (CH ₄ ) gas, fluoromethane (CH ₃ F) gas, difluoromethane (CH ₂ F ₂ ) gas, and trifluoromethane (CHF ₃ ) gas. Including gas,
The etching processing method according to claim 1 or 2. The value of the second high frequency power is 1.4 W / cm ² or more per unit area.
The etching processing method as described in any one of Claims 1-3. A parallel plate type plasma processing apparatus in which a lower electrode and an upper electrode on which a substrate is placed are opposed to each other,
A mounting table for mounting the substrate;
Using the temperature control mechanism provided on the mounting table, a temperature measuring unit that controls the temperature of the surface of the substrate to less than -35 ° C;
A heat transfer gas supply mechanism for supplying a heat transfer gas to the back surface of the substrate;
A first high-frequency power source that outputs first high-frequency power;
A second high frequency power source that outputs a second high frequency power having a frequency lower than the frequency of the first high frequency power;
The temperature measurement unit performs feedback control to stop the output of the second high-frequency power source;
Plasma processing equipment. A mounting table for mounting the substrate;
Using the temperature control mechanism provided on the mounting table, a temperature measuring unit that controls the temperature of the surface of the substrate to less than -35 ° C;
A heat transfer gas supply mechanism for supplying a heat transfer gas to the back surface of the substrate;
A first high-frequency power source that outputs first high-frequency power;
A second high frequency power source that outputs a second high frequency power having a frequency lower than the frequency of the first high frequency power;
The temperature measurement unit performs feedback control to stop the outputs of the first high-frequency power source and the second high-frequency power source;
Plasma processing equipment. Both the first high-frequency power and the second high-frequency power or the second high-frequency power are output by a pulse wave.
The plasma processing apparatus according to claim 5 or 6. The stop of the output of the first high frequency power or the second high frequency power and the pressure control of the heat transfer gas are performed by autonomous control.
The plasma processing apparatus as described in any one of Claims 5-7. Having a monitoring mechanism for monitoring the temperature of the surface of the substrate in real time;
The plasma processing apparatus as described in any one of Claims 5-8. The monitoring mechanism monitors the temperature of the surface of the substrate from the result of temperature measurement of the focus ring,
The plasma processing apparatus according to claim 9. The temperature measuring unit measures the temperature of the surface of the substrate with an interference thermometer;
The plasma processing apparatus according to claim 10. The temperature measurement unit stops the output of the second high-frequency power source or stops the output of the first high-frequency power source and the second high-frequency power source, and the temperature of the surface of the substrate or the focus ring is less than −35 ° C. Feedback control to maintain the state of
The plasma processing apparatus as described in any one of Claims 5-8.

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