JP5774428B2 - Dry etching method and plasma etching apparatus - Google Patents

Description

The present invention relates to a dry etching apparatus for semiconductor elements, and more particularly to a dry etching method and a plasma etching apparatus that can stably maintain a discharge.

  With regard to a technique for pulse-modulating plasma in a dry etching apparatus, for example, Patent Document 1 discloses high-precision etching by controlling the radical density by pulse-modulating plasma while measuring the radical density in the plasma. A way to achieve is described.

  Further, Patent Document 2 discloses that an oxide film on a processing wafer is subjected to dielectric breakdown by controlling the electron temperature in the plasma by synchronizing the on-off of the high frequency bias phase plasma applied to the wafer simultaneously with the pulse modulation of the plasma. A way to prevent this is described. Further, Patent Document 3 describes a method in which plasma is pulse-modulated at 10 to 100 μs and a high frequency bias of 600 KHz or less is applied to the wafer to prevent dielectric breakdown of the oxide film and at the same time achieve high-speed anisotropic etching. Yes.

  Furthermore, Patent Document 4 describes a method of performing high-precision etching by controlling the decomposition of reactive gas by pulse-modulating microwaves that generate plasma and setting the frequency and duty ratio to constant values. . Further, Patent Document 5 describes a method in which a microwave for generating plasma is pulse-modulated at a frequency of 10 KHz or more to control radicals and suppress ion instability to reduce ion temperature.

  Currently, one of dry etching apparatuses used for mass production of semiconductor elements is an ECR (Electron Cyclotron Resonance) type apparatus. This apparatus is characterized in that high-density plasma can be generated by applying a magnetic field to the plasma and setting the magnetic field strength so that the microwave frequency and the electron cyclotron frequency resonate.

JP 09-185999 A JP 09-092645 A Japanese Patent Laid-Open No. 08-181125 Japanese Patent Laid-Open No. 07-094130 Japanese Patent Laid-Open No. 06-267900

  With the recent miniaturization of semiconductor elements, the thickness of the gate oxide film has become 5 nm or less. Therefore, it is necessary to realize controllability of the plasma etching process and a high selection ratio between the gate oxide film and the silicon film.

  In order to cope with these processes, an ECR type dry etching apparatus requires a wider process window than ever before. Regarding microwave power, a high selectivity ratio region exists on the high microwave power side (high density region). However, on the high microwave power side, a cut-off phenomenon occurs as the plasma density increases, and a mode jump occurs in which the distribution of the plasma density in the chamber changes. When this phenomenon occurs, the plasma emission intensity and the peak value of the bias voltage (Vpp voltage) change abruptly, and the distribution of the etching rate within the wafer surface changes greatly with this, so the power before and after the mode jump cannot be used. there were.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a dry etching method and apparatus that realizes expansion of a process region effective for etching, in particular, expansion to a higher density region, that is, a high power side.

The dry etching method and the plasma etching apparatus of the present invention modulate a microwave for generating plasma into a pulse shape, set the microwave power value at the time of turning on higher than the power value at which the cutoff phenomenon occurs, and set the duty ratio. By changing, the average power of the microwave is controlled. Further, the pulse repetition frequency and the duty ratio are controlled so that the pulse OFF time is 50 μs or more.

  By performing pulse modulation on the microwave, a mode jump generated on the high microwave power side can be avoided, and an effective process area for etching can be expanded.

FIG. 1 is a schematic sectional view showing an example of a dry etching apparatus for carrying out the etching method of the present invention. FIG. 2 is a graph showing the selection ratio of silicon / silicon oxide to microwaves. FIG. 3 is a graph showing the emission intensity ratio of O (oxygen) / Br (bromine) to the microwave of the present invention. FIG. 4 is a graph showing the selection ratio of silicon / silicon oxide to the pulsed microwave according to the present invention. FIG. 5 is a process flow diagram of an apparatus that automates the measurement of power at which mode jumps occur.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing an example of an etching apparatus for carrying out the dry etching method of the present invention, which is an ECR type plasma etching apparatus using a microwave and a magnetic field as plasma generating means. This apparatus is provided with a chamber 101 capable of evacuating the inside, a sample stage 103 on which a wafer 102 to be processed is placed, a microwave transmitting window 104 such as quartz provided on the upper surface of the chamber 101, and an upper part thereof. It comprises a waveguide 105, a magnetron 106, a solenoid coil 107 provided around the chamber 101, an electrostatic adsorption power source 108 connected to the sample stage 103, and a high frequency power source 109.

  The wafer 102 is carried into the chamber 101 from the wafer carry-in port 110 and then electrostatically adsorbed to the sample stage 103 by the electrostatic adsorption power source 108. Next, process gas is introduced into the chamber 101. The inside of the chamber 101 is evacuated by a vacuum pump (not shown) and adjusted to a predetermined pressure (for example, 0.1 Pa to 50 Pa). Next, a microwave having a frequency of 2.45 GHz is oscillated from the magnetron 106 and propagated into the chamber 101 through the waveguide 105. The processing gas is excited by the action of the microwave and the magnetic field generated by the solenoid coil 107, and plasma 111 is formed in the space above the wafer 102.

On the other hand, a bias is applied to the sample stage 103 by a high-frequency power source 109, and ions in the plasma 111 are accelerated and incident on the wafer 102 vertically. The wafer 102 is anisotropically etched by the action of radicals and ions from the plasma 111. In addition, a pulse generator 112 is attached to the magnetron 106 so that the microwave can be pulse-modulated. The etching apparatus used in this embodiment is an apparatus for processing a wafer 102 having a diameter of 300 mm. The inner diameter of the chamber 101 is 44.2 cm, and the distance between the wafer 102 and the microwave transmission window 104 is 24.3 cm (space in which plasma is generated). Apparatus with a volume of 37267 cm ³ ).

Next, Table 1 shows an example of conditions for etching the wafer 102 using the apparatus shown in FIG.

  Using the conditions shown in Table 1 (however, the Vpp voltage is constant), the wafer 102 having the entire surface and the silicon oxide wafer 102 having the entire surface were etched, and the selection ratio was determined from the ratio of the amount of each cut. The result is shown in FIG. In FIG. 2, CW represents a continuous discharge and Duty represents a duty ratio of pulse discharge.

  FIG. 3 shows the relationship between the microwave power and the emission intensity ratio of O (oxygen) and Br (bromine). As can be seen from FIG. 2, the selectivity for silicon oxide tends to increase on the high microwave power side. As shown in FIG. 3, this is considered to be caused by suppressing the abrasion of silicon oxide because the emission intensity of O (oxygen), that is, the density of O radicals increases on the high microwave side.

  However, when the microwave power value is further increased, as shown in FIG. 3, in CW (continuous discharge), when the microwave power value is 900 W or more, the light emission intensity suddenly changes, that is, the mode jump phenomenon (at CW) ) 301 occurs. For this reason, the high microwave region cannot be used in continuous discharge.

  Therefore, in the present invention, the duty ratio is controlled by pulsing the microwave and setting the peak power at the time of turning on sufficiently higher than the power value at which the mode jump occurs. It can be seen that when the duty is 65% or less, the emission intensity ratio (FIG. 3) does not change abruptly, that is, mode jump is avoided.

  The reason is estimated as follows. In CW (continuous discharge), the electron density increases with the microwave power value, and the mode changes from the power value that reaches the density at which the vibration of the plasma 111 and the frequency of the electromagnetic wave resonate. On the other hand, in the pulsed microwave, most of free electrons are trapped by atoms and molecules within several μsec when turned off, and most of the plasma 111 becomes anions and cations. For this reason, in the pulse microwave which repeats ON / OFF, the electron density does not increase.

  FIG. 4 shows the selection ratio results obtained by evaluating the high microwave power side using the conditions shown in Table 1. In CW (continuous discharge), the selection ratio decreases (becomes unstable) due to the effect of mode jump when the microwave power value is 900 W or more, but by pulsing the microwave, the high microwave power side is used, A high selectivity can be obtained.

  In general, in pulse discharge, it is known that the electron density is attenuated by one digit or more after 50 μs after power-off. Accordingly, if the discharge is pulsed and the pulse repetition frequency and the duty ratio are set so that the OFF time is 50 μs or more, the mode jump can be sufficiently avoided.

  As described above, in the present invention, the mode modulation generated on the high microwave power side can be avoided and the effective process area for etching can be expanded by pulse-modulating the microwave.

  Next, a method and apparatus for automatically avoiding this mode jump area will be described. As shown in FIG. 3, the mode jump occurs in a high power region where the microwave power is about 900 W or more. However, since the density of the plasma 111 differs depending on the gas pressure and the type of gas, the power at which the mode jump occurs depends on these conditions. Depends on different.

  A method for avoiding this is to first measure the power value at which the mode jump occurs under the conditions to be used in advance. Has a function of automatically pulse-modulating the microwave power. An apparatus having this function can prevent an erroneous operation using the mode jump area by mistake.

  Furthermore, an apparatus for automating the measurement of power that causes a mode jump in advance will be described. FIG. 5 shows a process flow diagram of an apparatus that automates the measurement of power at which mode jumps occur. Normally, etching is performed in units of lots (25 sheets), but before the lots are processed, the dummy wafer processing 501 is performed under the same conditions as those to be processed.

  After that, the lot processing 502, the cleaning 503 of the chamber 101 by the oxygen plasma 111, etc. are followed. The dummy wafer processing 501 includes a microwave power automatic scan measurement 504 that is a step of automatically scanning from a set value of microwave power, for example, from 800 W to 1200 W and measuring the emission intensity of the plasma 111 during this period with a photodiode or the like.

  Next, the personal computer 507 for etching apparatus control performs a mode jump power identification 505 for extracting and storing a region where the emission intensity changes suddenly from this data, and a region where the microwave power is mode jumped when a recipe is input. A function of performing automatic recipe generation 506 that automatically performs pulse modulation in the case of This function allows the operator to perform etching without being bothered by the mode jump region.

The physical quantity measured when the microwave power is scanned is not limited to the light emission intensity, and the same function can be achieved as long as the quantity changes rapidly corresponding to the mode jump such as the peak value (Vpp) of the bias voltage. Further, the absolute value of the microwave power described in the present invention largely varies depending on the size of the chamber 101, that is, the diameter of the wafer 102 to be processed. As a standard, if a value normalized by the volume of the chamber 101 is used, it can be converted into an amount independent of the volume of the chamber 101. For example, in the above embodiment, 900 W corresponds to 0.024 W / cm ³ .

DESCRIPTION OF SYMBOLS 101 Chamber 102 Wafer 103 Sample stand 104 Microwave transmission window 105 Waveguide 106 Magnetron 107 Solenoid coil 108 Electrostatic adsorption power supply 109 High frequency power supply 110 Wafer carry-in 111 Plasma 112 Pulse generator 301 Mode jump phenomenon (at the time of CW)
501 Dummy wafer processing 502 Lot processing 503 Cleaning 504 Microwave power automatic scan measurement 505 Mode jump power identification 506 Automatic recipe generation

Claims (6)

In a dry etching method that etches a wafer using plasma generated by the interaction of a microwave and a magnetic field ,
When plasma is generated by the power in the mode jump region when plasma is generated by continuous discharge,
Modulating the microwave on and off,
The power value of the on period of the on-off modulated microwave is higher than the power value of the mode jump region,
The on-off modulated dry etching method time average value of the power of the microwave is characterized that you control the duty ratio of the on-off keying as the power value of the mode jump region. The dry etching method according to claim 1,
The duty ratio is 65% or less,
The dry etching method, wherein to Rukoto and the off time of the on-off keying 50μs or more. In a dry etching method that etches a wafer using plasma generated by the interaction of a microwave and a magnetic field ,
Scanning the microwave power,
When plasma is generated by continuous discharge based on the rate of change of the emission intensity of plasma during the scan period or the rate of change of the bias voltage applied to the sample stage on which the wafer is placed during the scan period Detect the mode jump area
When generating plasma by the power of the mode jump region,
Modulating the microwave on and off,
The power value of the on period of the on-off modulated microwave is higher than the power value of the mode jump region,
A dry etching method , wherein a duty ratio of the on / off modulation is controlled so that a time average value of the power of the microwave subjected to the on / off modulation becomes a power value of the mode jump region . A processing chamber in which the wafer is plasma-etched, a high-frequency power source for supplying microwave high-frequency power to the processing chamber via a waveguide, and a pulse generator for generating a pulse for on-off modulation of the high-frequency power; In a plasma etching apparatus comprising: a magnetic field generating means for generating a magnetic field for generating plasma by interaction with the microwave in the processing chamber; and a sample table placed on the processing chamber and mounting the wafer .
The control unit further includes on / off modulation of the high-frequency power when the plasma is generated by the power of the mode jump region when the plasma is generated by continuous discharge, and the on-off-modulated high-frequency power is generated. The on-off modulation duty ratio is set so that the power value of the on-time is higher than the power value of the mode jump region, and the time average value of the on-off modulated high-frequency power becomes the power value of the mode jump region. A plasma etching apparatus characterized by controlling . The plasma etching apparatus according to claim 4, wherein
The duty ratio is 65% or less,
The plasma etching apparatus according to claim more and to Rukoto 50μs OFF time of the on-off keying. A processing chamber in which the wafer is plasma-etched, a high-frequency power source for supplying microwave high-frequency power to the processing chamber via a waveguide, and a pulse generator for generating a pulse for on-off modulation of the high-frequency power; In a plasma etching apparatus comprising: a magnetic field generating means for generating a magnetic field for generating plasma by interaction with the microwave in the processing chamber; and a sample table placed on the processing chamber and mounting the wafer .
And a control unit that scans the microwave high-frequency power and changes a plasma emission intensity change rate during the scan period or a change in bias voltage applied to the sample stage during the scan period. The mode jump region when plasma is generated by continuous discharge based on the rate is detected, and when generating plasma by the power of the mode jump region, the high frequency power is on-off modulated, and the on / off modulated high frequency power The on-off modulation duty ratio is set so that the power value of the on-period is higher than the power value of the mode jump region and the time average value of the on / off-modulated high-frequency power becomes the power value of the mode jump region. control to the plasma etching apparatus according to claim Rukoto.

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