JP2719332B2 - Plasma processing method - Google Patents

Description

The present invention relates to a plasma processing method for a substrate, and more particularly to a plasma processing method suitable for anisotropic dry etching with less side etching. (Conventional technology) Efficiently performing high-precision etching on semiconductor substrates is an essential technology for VLSI manufacturing, and various new technologies related to anisotropic etching with little undercut have been developed and studied. In particular, for a method or apparatus for cooling a substrate to be etched on a sample stage, see Japanese Patent Application No.
No. 11945 and Japanese Patent Application No. 61-260738 have been filed as prior art. (Problems to be Solved by the Invention) Among the above-mentioned prior arts, the former uses a heat pipe as a cooling mechanism to cool the substrate to a temperature of minus several tens degrees Celsius or less, and to control surface reaction to prevent side etching. However, there is a problem that the temperature controllable range is −196 to 160 ° C. and the control range is narrow. In the latter, as a means for solving the former problem, cooling of the sample stage is controlled by using a heater in combination with a heat pipe. The present invention utilizes the above-mentioned prior application technology and further increases the heat absorption capacity between the sample stage and the substrate, thereby efficiently absorbing the heat generated at the time of etching. Suitable for anisotropic dry etching with little side etching, with a sample cooling mechanism that can improve the accuracy of the set temperature in parallel with the expansion of the temperature range in order to set the optimum temperature for the material and etching gas. It is an object of the present invention to provide a plasma processing method. (Means for Solving the Problems) The above object is achieved by disposing a heater on a sample stage on a cooling vessel by introducing a liquefied gas and controlling the liquid level of the liquefied gas by placing the heater in a vacuum chamber. This is achieved by providing means for adjusting the temperature and reducing the contact thermal resistance between the sample stage and the substrate. Further, the low-temperature control means of the sample stage may be provided with a low-temperature gas introduction or a Peltier device. That is, the present invention provides a base on which a base is placed, means for heating the base by heating the base, a radiator fin connected to the base, and for releasing heat of the base, and a radiator fin Liquefied gas for radiating heat from the radiating fins, a liquefied gas container containing the liquefied gas, and means for supplying the liquefied gas into the liquefied gas container from outside the liquefied gas container. Using a device that has
The liquefied gas is replenished into the liquefied gas container by the liquefied gas container, and the liquid surface level of the liquefied gas in the liquefied gas container is adjusted to control the contact area with the radiation fins. And heating the sample stage by the sample stage heating means to adjust and hold the substrate at a predetermined temperature and expose the substrate to plasma for etching. In the following examples, an object to be processed, which is described as a substrate, refers to a portion serving as a basis for forming each semiconductor region, that is, a base. (Operation) The heat generated by the etching is
By controlling the liquid level of the liquefied gas in the cooling vessel, for example, -150
When controlling the temperature of the substrate to a relatively low temperature range of ℃,
When the liquid level of the liquefied gas is raised, and when the temperature of the substrate is controlled in a relatively high temperature range of 0 ° C., the liquid level of the liquefied gas is lowered. The means for reducing the contact thermal resistance between the sample stage and the substrate increases the heat absorption capacity of the sample stage, and enables temperature control over a wide range. When a low-temperature gas is used, the current control of the heater and the flow rate of the low-temperature gas are performed, and in the case of a Peltier element, the substrate is changed from 0 to -180 Temperature control is selectively performed in the range of ° C. (Example) Hereinafter, an example of the present invention will be described with reference to the drawings. <First Embodiment> FIG. 1 is a view showing one embodiment of a plasma processing method according to the present invention. A liquefied gas container 4 provided in a vacuum chamber 1 is provided with a large number of fins having good heat conductivity. And a supply pipe 8 through a supply hose 10 from a supply unit 9 provided separately.
The liquefied gas 12 is introduced into the liquefied gas container 4 via the liquefied gas container 4, and the liquefied gas 12 is automatically replenished into the liquefied gas container 4 by the signal of the liquid level sensor 11 so as to control the liquid level. The liquefied gas container 4 itself is associated with a flange 6 movable in the directions of arrows 5u and 5d. A heater 13 is provided in the sample table 2, and the temperature of the substrate 3 is monitored by a thermocouple 14 while maintaining a thermal balance between the liquefied gas 12 and the heater 13. Control power. The flange 6 associated with the sample stage 2 is connected to the vacuum chamber 1 via a bellows 16 and moves in the direction of the arrow 5u during etching so that the substrate 6 is attached to the fixing ring 17 as shown in FIG. 3 is strongly pressed, the contact area between the substrate 3 and the sample stage 2 is increased, and the contact thermal resistance is reduced, so that the heat conduction effect is increased, and the ability of the liquefied gas to cool the substrate 3 is increased. The etching is performed by applying a high-frequency voltage between the sample stage 2 and the upper electrode 18. A sample introduction chamber 20 is provided on a side surface of the vacuum chamber 1 via a valve 19, so that the substrate 3 can be exchanged without opening the vacuum chamber 1 to the atmosphere. Second Embodiment FIG. 3 shows a second embodiment of the present invention. The figure shows the sample stage 2
The thermal contact between the substrate 3 and the sample stage 2 is increased (the contact thermal resistance is reduced) by interposing the soft thin plate 21 between the substrate and the substrate 3, whereby the temperature of the substrate can be precisely controlled. It is possible to control. As the soft thin plate material, Teflon, silicon rubber, or the like, which does not adversely affect foreign matter during etching, is preferable. The holding ring 17 is fixed to the vacuum chamber 1 via a spring 22 and is configured so that the pressing force can be adjusted by a moving distance for pressing the liquefied gas container 4 in the direction of arrow 5u. <Third Embodiment> FIG. 4 shows a third embodiment of the present invention. This is sample table 2
The sample mounting surface is formed in an arc shape convex upward, and the substrate 3 is arranged on the soft thin plate 21 with the soft thin plate 21 interposed therebetween. The liquefied gas container 4 is moved in the direction of arrow 5u, and the fixing ring 17 and the outer peripheral edge of the substrate 3 come into contact with each other and are pressed. As a result, the thermal contact between the substrate 3 and the sample stage 2 increases (the contact thermal resistance decreases), and the heat generated during etching efficiently moves to the direction of the liquefied gas to control the temperature of the substrate 3 with high accuracy. be able to. <Fourth Embodiment> FIG. 5 shows a fourth embodiment of the present invention. This embodiment is particularly for keeping the substrate 3 at a low temperature, so that the liquid surface of the liquefied gas occupies a higher position than the back surface 24 of the sample table so that the sample table back surface 24 is always in contact with the liquefied gas 4. It is composed. As a result, the etching heat is easily reduced to the liquefied gas 12.
And the substrate 3 can be kept at a low temperature. <Fifth Embodiment> FIG. 6 is a view showing an embodiment using a low-temperature gas according to the present invention, in which a substrate 3 is placed on a sample table 2 placed in a vacuum vessel 1 and cooling is provided below the substrate 3. A block 34 is provided. A large number of fins 35 are arranged in the cooling block 34, and the low-temperature gas introduced through the pipe 36 takes heat from the substrate 3. Cooling gas (for example, dry nitrogen gas) is stored in a cylinder 37 and passes through a pipe 38 to a cooling block.
Introduced in 37. The gas passes through a container 40 containing the liquefied gas 39, where the gas at room temperature is cooled to a low temperature. A high-frequency voltage is applied between the upper electrode 18 in the vacuum chamber 1 and the sample table 2 to perform etching. When the temperature of the substrate 3 rises due to the heat generated at this time, the measurement signal is measured by the thermocouple 14, the temperature controller 15 receives the measurement signal, and the low-temperature gas flow valve 45 is opened to increase the flow of the low-temperature gas. The cooling capacity of the block 34 is increased to maintain the temperature of the substrate 3 at a low temperature. FIG. 7 shows the sample stage 2 of FIG. 6 in which a heater 13 is incorporated. The temperature of the sample stage 2 is controlled by keeping the flow rate of the cooling gas constant and changing the current value of the heater 13. Is what you do. <Sixth Embodiment> FIG. 8 shows a sixth embodiment of the present invention. Cooling block
A flow path 50 of a cooling gas (for example, freon) sent from the refrigerator 55 is formed in the pipe 34, where heat exchange with heat generated at the time of etching is performed. The temperature of the substrate 3 is detected by a thermocouple 14, and a signal from the thermocouple 14 is used to keep the temperature of the substrate 3 constant even when heat is input.
It is configured to perform 55 controls. The cooling gas returns to the refrigerator 55 after heat exchange in the cooling block 34 and is cooled. Seventh Embodiment FIG. 9 shows an embodiment using the Peltier device of the present invention. A Peltier element 51 is provided below the sample table 2. The Peltier element 51 is selectively driven by changing a current value for driving the Peltier element 51 so as to make the heat absorbing capability variable and to reverse the direction of the applied current. Both heating and cooling operations can be performed. The Peltier element is controlled by the controller 52 so that the temperature of the substrate 3 becomes constant. The temperature of the substrate 3 is measured by the thermocouple 14, and a fan 53 is provided below the Peltier element 51 for the purpose of dissipating the heat absorbed from the substrate 3 to the atmosphere, and is configured to blow air in the direction of arrow 5u. ing. Results of controlling the temperature of the substrate using this example
Control was possible with an accuracy of ± 3 ° C in the range of 20 to -120 ° C. In particular, even if the substrate 3 had a heat input of 50 watts at the time of etching, the overshoot value was only around 5 ° C.
It was possible to control to the original set temperature in 10 seconds. When etching was performed using a Si wafer for the substrate,
~ -120 ° C was found to be the optimal temperature. Compiling the experiments of the inventors according to the above embodiments,
The temperature of the substrate can be controlled with an accuracy of ± 3 ° C. in a range of 30 to −150 ° C., and the temperature of the substrate 3 is controlled in a relatively high temperature range of −50 ° C. or higher, and the liquefied gas By lowering the surface, the input power of the heater was 100 W, and the consumption of liquid nitrogen used as liquefied gas was as small as 30 cm ³ / min.
Also, when plasma etching was performed on the Si wafer used in these examples, good etching could be performed between -80 and -120 ° C, and it was determined that this temperature region was optimal for the low-temperature etching of silicon. Was. In summary, the present invention is a plasma processing method characterized by having a means for increasing or decreasing the thermal resistance by controlling the liquid level of the liquefied gas and reducing the contact thermal resistance between the substrate and the sample stage. (Effect of the Invention) By controlling the liquid level of the liquefied gas, placing the container in a vacuum chamber, and applying a mechanical load to the outer edge of the substrate to be etched, and bringing the substrate into close contact with the sample table, High-precision temperature control with a small amount of liquefied gas and heater power, no side etching, etching in the depth direction is possible, and it has a remarkable effect on reducing the manufacturing cost and improving the reliability of the substrate to be etched. did.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 show an embodiment of the plasma processing method according to the present invention, and FIGS. 3 to 9 show other embodiments of the present invention. DESCRIPTION OF SYMBOLS 1 ... Vacuum chamber, 2 ... Sample stand 3 ... Substrate, 4 ... Liquefied gas container 7 ... Fin, 11 ... Liquid level sensor 12 ... Liquefied gas, 13 ... Heater 14 ... Thermocouple, 15 …… Temperature controller 16 …… Bellows, 17 …… Fixing ring 21 …… Soft thin plate, 22 …… Spring 34 …… Cooling block, 37 …… Cylinder 51 …… Peltier element, 52 …… Controller

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Kiichiro Mukai               1-280 Higashi Koigabo, Kokubunji-shi               Central Research Laboratory, Hitachi, Ltd. (72) Inventor Takahiro Oguro               502 Kandachicho, Tsuchiura-shi Hitachi, Ltd.               Inside the factory machinery laboratory (72) Inventor Shigekazu Kieda               502 Kandachicho, Tsuchiura-shi Hitachi, Ltd.               Inside the factory machinery laboratory                (56) References JP-A-61-103530 (JP, A)                 JP-A-61-76674 (JP, A)                 JP-A-51-123944 (JP, A)

Claims (1)

(57) [Claims] A base on which the base is placed; a unit for heating the base by heating the base; a radiator fin connected to the base to release heat of the base; and immersing the radiator fin, Using a device having a liquefied gas that releases heat from the radiation fins, a liquefied gas container that stores the liquefied gas, and a unit that replenishes the liquefied gas into the liquefied gas container from outside the liquefied gas container, The liquefied gas is replenished into the liquefied gas container by means for replenishing the liquefied gas, the liquid surface height of the liquefied gas in the liquefied gas container is adjusted, and the sample table is controlled by controlling the contact area with the radiation fins. Cooling and heating the sample stage by the sample stage heating unit adjusts and holds the substrate at a predetermined temperature, and exposes the substrate to plasma for etching. Plasma processing method. 2. 2. The plasma processing method according to claim 1, wherein the predetermined temperature is 30 ° C. or lower and −150 ° C. or higher. 3. 2. The plasma processing method according to claim 1, wherein said predetermined temperature is not higher than -80C and not lower than -120C. 4. 4. The plasma processing method according to claim 1, wherein said substrate is a silicon substrate.