JP2005026552A - Plasma treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma treatment method capable of obtaining a desired size of an etching shape without the inclination and deformation of a resist. <P>SOLUTION: There are provided a flow rate controller for controlling a flow rate of a refrigerant to cool a lower electrode 23 and a heater mounted inside the lower electrode 23 for heating a wafer 24. Before the starting of discharge, the wafer is heated by the heater 30, and the flow rate of a refrigerant is changed for every step to control a wafer temperature during the etching to be constant. Hereby, the thermal contraction of a deposit film 43 is prevented and no stress is generated on the resist 42, so that the resist 42 is prevented from inclining during the etching and a film 41 to be etched can be etched symmetrically. This ensures an improvement in dimensional accuracy and further ensures the maintenance of a high yield. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wafer temperature control means of a plasma processing method.
[0002]
[Prior art]
In recent years, with the miniaturization of semiconductor devices, the resist pattern has become thinner and the resist material has become weaker, so that the plasma resistance has been reduced. For this reason, in the dry etching process, there is a problem that the resist is deformed in plasma and affects the etching shape, which causes a decrease in yield. This is particularly noticeable in devices of 90 nm and after.
[0003]
Hereinafter, an example of a conventional plasma processing method will be described with reference to the drawings.
[0004]
FIG. 4 is a sectional view of an apparatus (dry etching apparatus) used in a conventional plasma processing method.
[0005]
FIG. 5 is a flowchart of a process cross-sectional view of a wafer to be processed using a conventional plasma processing method.
[0006]
FIG. 6 is a graph showing changes in wafer temperature with time in a conventional plasma processing method.
[0007]
In FIG. 4, 1 is a dry etch chamber, 2 is an upper electrode installed at the upper part of the dry etch chamber 1, and 3 is a lower electrode installed at the lower part of the dry etch chamber 1 and has an electrostatic adsorption function. 4 is a wafer placed on the lower electrode 3, 5 is a groove in the lower electrode 3 for flowing a coolant for controlling the temperature of the lower electrode 3, and 6 is a temperature of the coolant for controlling the temperature of the lower electrode 3. A chiller for keeping constant, 7 is a feed-side piping for sending refrigerant from the chiller 6 to the groove 5 in the lower electrode 3, and 8 is a return side for returning the refrigerant from the groove 5 in the lower electrode 3 to the chiller 6. It is piping.
[0008]
In FIG. 5, 11 is a base film such as polysilicon, 12 is an etching target film such as an oxide film grown on the base film, 13 is a resist patterned on the etching target film 12, and 14 is an anisotropic shape. Therefore, it is a deposition film deposited on the side surface of the film to be etched 12 and the side surface of the resist 13.
[0009]
A conventional plasma processing method configured as described above will be described with reference to FIGS. 4, 5, and 6.
[0010]
FIG. 5A shows the pattern shape of the resist 13 before etching. Next, etching is performed in two steps. In the first step, as shown in FIG. 5B, the etching target film 12 is etched to have a desired dimension. Specifically, gas, for example, CF ₄ is introduced at 100 ml / min and O ₂ is introduced at 20 ml / min in the dry etching chamber 1, and the pressure is maintained at 4 Pa. For example, a high frequency of 13.56 MHz is applied to the lower electrode 3 at 500 W. Then, the first step is started.
[0011]
At this time, in order to protect the sidewall, a deposition film 14 formed by gas polymerization is deposited on the sidewall of the film 12 to be etched and the sidewall of the resist 13. The amount of the deposition film 14 is generally different between the outer side wall and the center side wall of the wafer 4 due to the etching gas flow and the like. Further, the etching progresses, and the end point is detected by the change in the emission spectrum.
[0012]
At this time, as shown in FIG. 5C, the film to be etched remains partially due to non-uniformity in the etching wafer surface.
[0013]
As shown in FIG. 6, at the start of the first step, the temperature of the wafer 4 is the temperature of the refrigerant (60 ° C.). Therefore, as shown in FIG. 5C, the deposited film 14 deposited at the start of the first step is thermally contracted, but the amount of contraction is different on the outer peripheral side and the center side of the wafer 4, and stress is generated. The resist 13 is inclined and the film to be etched is etched asymmetrically using the resist 13 as a mask.
[0014]
Next, as shown in FIG. 5D, in the second step, the remaining film 12 to be etched is etched without etching the base film 11 as much as possible. Specifically, CHF ₃ is introduced into the dry etching chamber 1 at 70 ml / min, O ₂ at 15 ml / min, the pressure is kept at 4 Pa, and a high frequency, for example, 800 W is applied.
[0015]
As shown in FIG. 6, in the second step, since the high-frequency power is higher than in the first step, the amount of heat from the plasma is received, so that the temperature of the wafer 4 rises from the first step.
[0016]
Therefore, as shown in FIG. 5D, the deposition film 14 is further thermally contracted, receives stress, and the resist 13 is inclined, so that the etching target film 12 is processed into a skirt shape (footing).
[0017]
Finally, the high frequency is stopped, the second step is finished, and the etching is finished.
[0018]
[Patent Document 1]
Japanese Patent Laid-Open No. 07-130830
[Problems to be solved by the invention]
In the conventional technique, during the etching, different amounts of deposition films are attached to the resist sidewalls.
[0020]
In other words, the deposition film is thermally contracted by receiving the amount of heat from the plasma and the wafer temperature is increased. However, since the deposition film amount is not equal, the generated stress is different on the left and right, the resist is tilted, and the etched film is etched. The shape becomes a taper shape or a trailing shape, a desired shape cannot be obtained, and the size becomes larger than the standard, which causes a decrease in yield.
[0021]
SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a plasma processing method capable of etching without tilting a resist and obtaining a desired shape and size.
[0022]
[Means for Solving the Problems]
The plasma processing method according to the present invention is a plasma processing method for keeping the temperature of a wafer constant during plasma processing, and includes a step of circulating a coolant in the lower electrode and a step of heating the wafer in the lower electrode by a heater. It is characterized by this.
[0023]
In the plasma processing method of the present invention, the step of circulating the refrigerant in the lower electrode is more preferably performed in the first step and the second step.
[0024]
In the plasma processing method of the present invention, it is more preferable that the step of circulating the refrigerant in the lower electrode in the second step has a higher refrigerant flow rate than the step of circulating the refrigerant in the lower electrode in the first step.
[0025]
In the plasma processing method of the present invention, it is more preferable that the step of heating the lower electrode with a heater is performed before plasma generation and between the first step and the second step.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a plasma processing method according to an embodiment of the present invention will be described with reference to the drawings.
[0027]
(Embodiment)
FIG. 1 is a cross-sectional view of equipment (dry etching apparatus) used in the plasma processing method in the present embodiment.
[0028]
FIG. 2 is a flow of a process cross-sectional view of a wafer processed using the plasma processing method of the present embodiment.
[0029]
FIG. 3 is a graph showing changes in wafer temperature with time in the plasma processing method of the present embodiment. 3A shows the wafer temperature during the plasma processing, and FIG. 3B shows the state of the heater and the refrigerant flow rate during the plasma processing.
[0030]
In FIG. 1, 21 is a dry etch chamber, 22 is an upper electrode installed above the dry etch chamber 21, and 23 is a lower electrode installed below the dry etch chamber 21 and has an electrostatic adsorption function. 24 is a wafer placed on the lower electrode 23, 25 is a groove in the lower electrode 23 for flowing a coolant for controlling the temperature of the lower electrode 23, and 26 is a temperature of the coolant for controlling the temperature of the lower electrode 23. A chiller for keeping constant, 27 is a feed-side piping for sending refrigerant from the chiller 26 to the groove 25 in the lower electrode 23, and 28 is a return side for returning the refrigerant from the groove 25 in the lower electrode 23 to the chiller 26. A pipe 29 is provided in the middle of the feed-side pipe 27, and a flow controller for controlling the flow rate of the refrigerant, 30 is a heater attached in the lower electrode 23 to heat the wafer 24, and 31 is the temperature of the wafer 24. It is a temperature sensor for measuring.
[0031]
In FIG. 2, reference numeral 40 denotes a base film such as polysilicon, 41 denotes a film to be etched such as an oxide film grown on the base film, 42 denotes a resist patterned on the film to be etched 41, and 43 denotes an anisotropic shape. Therefore, it is a deposition film deposited on the side surface of the film to be etched 41 and the side surface of the resist.
[0032]
The plasma processing method of the present invention configured as described above will be described with reference to FIGS.
[0033]
FIG. 2A shows the pattern shape of the resist 42 before etching.
[0034]
Next, etching is performed in two steps. As shown in FIG. 2B, in the first step, the film to be etched 41 is etched so as to have a desired dimension, and the end point is detected by the change in the emission spectrum. At this time, the etching target film remains partially due to non-uniformity of the etched wafer surface.
[0035]
Next, as shown in FIG. 2C, in the second step, the remaining etching target film 41 is etched without etching the base film 40 as much as possible. First, the temperature of the wafer 24 is measured by the temperature sensor 31 and heated by the heater 30 so as to be 100 ° C., for example.
[0036]
As shown in FIG. 3, 10 seconds after the start of etching, that is, at the start of the first step, gas is introduced into the dry etching chamber 21, for example, CF ₄ at 100 ml / min and O ₂ at 20 ml / min, and the pressure is kept at 4 Pa. For example, a high frequency of 13.56 MHz is applied to the lower electrode 23 at 500 W.
[0037]
Next, 50 seconds after the start of etching, that is, at the end of the first step, since the amount of heat is received from the plasma generated simultaneously with the application of the high frequency, the temperature of the wafer 24 tends to rise, so the heater is turned off and the coolant flow rate is increased. The temperature of the wafer 24 is controlled to 100 ° C. ± 10 ° C. The high frequency is stopped when the film to be etched 41 is removed by the end point detection device.
[0038]
Since the amount of heat from the plasma disappears when the high frequency is stopped, the temperature of the wafer 24 tends to decrease. Therefore, the flow rate of the coolant is decreased, the heater is turned on, and the wafer temperature is controlled to be maintained at 100 ° C. ± 10 ° C.
[0039]
Next, as shown in FIG. 3, 60 seconds after the start of etching, that is, at the start of the second step, CHF ₃ is introduced into the dry etching chamber 21 at 70 ml / min, O ₂ is introduced at 15 ml / min, and the pressure is kept at 4 Pa. A high frequency of 800 W, for example, is applied.
[0040]
Since the amount of heat is received from the plasma generated simultaneously with the application of the high frequency, the temperature of the wafer 24 tends to rise. Therefore, the heater is turned off, the coolant flow rate is increased, and the temperature of the wafer 24 is controlled to 100 ° C. ± 10 ° C.
[0041]
At this time, since the high frequency is higher in power than the first step, more heat is received from the plasma. Therefore, the refrigerant flow rate is increased compared to the first step. Finally, the high frequency is stopped, the second step is finished, and the etching is finished.
[0042]
A deposition film 43 formed by gas polymerization is deposited on the side wall of the film to be etched 41 and the side wall of the resist 42 in FIG. The deposition amount of the deposition film 43 is generally different between the outer peripheral side wall and the central side wall of the wafer 24.
[0043]
However, since the wafer temperature is kept constant throughout the etching, the deposition film 43 is not thermally contracted, and no stress is generated in the resist 42. Therefore, the resist 42 is not inclined during the etching, and the film 41 to be etched is Etch symmetrically.
[0044]
As described above, according to the present embodiment, the flow rate controller for controlling the flow rate of the refrigerant for cooling the lower electrode 23 and the heater attached in the lower electrode 23 for heating the wafer 24 are provided. The wafer is heated by the heater 30 before the start, and the coolant flow rate is changed for each step so that the wafer temperature is controlled to be constant throughout the etching, so that the deposition film 43 is not thermally contracted and no stress is generated in the resist 42. Therefore, the resist 42 does not incline during etching, and the film to be etched 41 can be etched symmetrically, dimensional accuracy can be improved, and high yield can be maintained.
[0045]
【The invention's effect】
As described above, according to the present invention, in the plasma processing apparatus, the flow rate controller for controlling the flow rate of the refrigerant for cooling the lower electrode and the heater attached in the lower electrode for heating the wafer are provided. The wafer is heated with a heater before the start of discharge, and the flow rate of the refrigerant is changed at each step so that the wafer temperature is controlled to be constant throughout the etching. Since no stress is generated, the resist does not incline during etching, and the film to be etched can be etched symmetrically and the dimensional accuracy can be improved, so that a high yield can be maintained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an apparatus used in a plasma processing method according to an embodiment of the present invention. FIG. 2 is a flowchart showing a process cross-sectional view of a wafer according to the embodiment of the present invention. FIG. 4 is a cross-sectional view of an apparatus used for a plasma processing method in a conventional example. FIG. 5 is a flow chart of a process cross-sectional view of a wafer in a conventional example. FIG. Graph showing changes in time [Explanation of symbols]
21 dry etch chamber 22 upper electrode 23 lower electrode 24 wafer 25 groove 26 chiller 27 feed side pipe 28 return side pipe 29 flow rate controller 30 heater 31 temperature sensor 40 base film 41 etched film 42 resist 43 deposit film

Claims (4)

In the plasma processing method of keeping the wafer temperature constant during plasma processing,
A plasma processing method comprising a step of circulating a refrigerant in a lower electrode and a step of heating the lower electrode with a heater. The plasma processing method according to claim 1,
The plasma processing method according to claim 1, wherein the step of circulating the refrigerant in the lower electrode is performed in a first step and a second step. The plasma processing method according to claim 2, wherein
The plasma processing method, wherein the step of circulating the refrigerant in the lower electrode in the second step has a larger refrigerant flow rate than the step of circulating the refrigerant in the lower electrode in the first step. The plasma processing method according to claim 1,
The plasma processing method is characterized in that the step of heating the lower electrode with a heater is performed before plasma generation and between the first step and the second step.

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