JP5918886B2 - Plasma processing method - Google Patents

Description

  The present invention relates to a plasma etching method for forming a silicon trench in microwave plasma etching.

As background art of this technical field, in JP 2007-103876 A (Patent Document 1), a gas containing H is added to a mixed gas composed of SF ₆ , O ₂ , and SiF _{4 with} respect to a silicon substrate. It is described that trench etching can be realized with no etching or roughening on the side wall surface of the trench by forming a silicon trench with mixed gas plasma.

  Japanese Patent Application Laid-Open No. 2007-129260 (Patent Document 2) discloses that a silicon substrate is etched at a very high etching rate by performing separate and alternately continuous etching and polymerization processes in anisotropic etching of silicon. It is described that deep etching can be performed.

JP 2007-103876 A JP 2007-129260 A

  In the prior art described in Patent Document 1, there is a disclosure that silicon trench etching with an aspect ratio of about 5 can be realized at high speed by, for example, a microwave plasma etching apparatus. However, in the above prior art, the etching rate may decrease even if the pressure is increased in order to further improve the etching rate, and even if a higher microwave power is applied, the transition region of the discharge state may be reduced. The problem that discharge may become unstable due to the existence and may not be used has not been considered.

  On the other hand, the prior art described in Patent Document 2 discloses that the silicon substrate can be deeply etched at a very high etching rate by repeatedly performing the etching and polymerization steps. However, in the above prior art, for example, in order to solve the above-mentioned problems, the generation of foreign matters and the decrease in reproducibility of etching characteristics occur due to the continuous deposition of the polymer film in the processing chamber by the polymerization process. It was necessary to perform single wafer cleaning, and the problem of reduced throughput was not considered.

  An object of the present invention is to provide a plasma etching method with high productivity by realizing high-speed etching of silicon trenches or holes by microwave plasma etching.

  In order to solve the above problems, a plasma etching method according to the present invention includes a processing chamber capable of reducing the pressure inside thereof, a gas supply means for supplying a processing gas into the processing chamber, and a plasma by supplying a microwave into the processing chamber. A microwave supply means for generating a microwave, a microwave rotation generator for rotating the polarization plane of the microwave and supplying it to the processing chamber, and introducing the microwave into the processing chamber via the microwave rotation generator A microwave introduction section, a sample placement electrode provided in the processing chamber for placing a sample, a high frequency power source for applying high frequency power to the sample placement electrode, and a gas supplied by the gas supply means are exhausted A plasma etching method for forming a silicon trench in a silicon substrate or an SOI substrate using a plasma processing apparatus including an exhaust means for performing fluorine etching, including fluorine Using the scan and oxygen gas, a process pressure 60Pa or less, said to the power of the microwave 1000~5000W rotate the polarization plane of the microwave and performing an etching process.

  According to the present invention, it is possible to provide a plasma etching method capable of reducing the etching time and improving the throughput without deteriorating the shape of the silicon trench.

FIG. 1 is a view showing a microwave plasma etching apparatus of the present invention. FIG. 2 is a diagram showing the trench shape of the substrate to be processed. FIG. 3 is a diagram showing the trench shape of the substrate to be processed. FIG. 4 is a diagram showing the trench shape of the substrate to be processed. FIG. 5 is a diagram showing the trench shape of the substrate to be processed. FIG. 6 is a diagram showing the trench shape of the substrate to be processed. FIG. 7 is a diagram showing the processing pressure dependence of the silicon etching rate when the silicon deep trench trench is etched. FIG. 8 is a diagram showing the processing pressure dependence of the in-plane uniformity of the silicon etching rate. FIG. 9 is a diagram showing the processing pressure dependence of the taper angle of the silicon trench. FIG. 10 is a diagram showing the microwave output dependency of the discharge stability. FIG. 11 is a diagram showing the processing pressure dependence of the silicon etching rate when silicon etching is performed. FIG. 12 is a diagram illustrating the microwave output dependency of the taper angle of the silicon trench when the deep silicon trench is etched. FIG. 13 is a diagram showing the microwave output dependency and duty ratio dependency obtained in the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a microwave plasma etching apparatus using a microwave and a magnetic field as means for forming plasma used in Embodiment 1 of the present invention.

  In this apparatus, an etching gas is supplied to the etching chamber 101 from a gas introduction means 107 through a transmission window 108 made of, for example, quartz having a porous structure. Further, the microwave oscillated by the microwave generator 102 passes through the matching unit 103 and the waveguide 104, passes through the microwave rotation generator 105 provided in the middle of the waveguide 104, and passes through the microwave introduction window 106. Microwaves are transported to the etching chamber 101 to turn the etching gas into plasma.

  A solenoid coil 109 for generating a magnetic field for high-efficiency discharge is arranged around the etching processing chamber 101 to generate a magnetic field of 0.0875 Tesla and generate high-density plasma using electron cyclotron resonance. A sample stage 110 is provided in the etching processing chamber 101, and a substrate 111 to be processed is placed thereon, and etching is performed by gas plasma generated by microwaves. A high frequency power source 112 is connected to the sample stage 110 on which the substrate to be processed 111 is installed, and a high frequency bias of 400 kHz to 13.56 MHz can be applied.

  The high frequency power source 112 includes a pulse generator (not shown), and can selectively apply time-modulated intermittent high frequency power or continuous high frequency power to the sample stage 110. . An electrostatic adsorption force is generated on the surface of the sample stage 110 by applying a DC voltage from the electrostatic adsorption power source 113, and the substrate 111 to be processed is adsorbed to the sample stage 110 by the electrostatic chuck.

Further, a groove is formed on the front surface of the sample stage 110, and He, Ar, O _2, etc. from the cooling gas supply port 114 to a flow path (not shown) formed between the back surface of the fixed substrate 111 to be processed. The cooling gas is supplied so that the inside of the flow path can be maintained at a predetermined pressure. The temperature rise of the surface of the substrate 111 to be processed is transferred to the surface of the sample stage 110 by gas heat transfer in the flow path and heat conduction from the contact surface, and is maintained at a constant temperature. In order to cool the substrate to be processed 111 to a low temperature of 0 ° C. or lower, a refrigerant whose temperature is controlled to a specified low temperature by the chiller unit 115 is circulated in the refrigerant circulation channel embedded in the sample table 110.

  An insulating cover (not shown) made of ceramic or quartz is disposed around the substrate to be processed 111. Note that the etching gas introduced into the etching chamber 101 is exhausted out of the etching chamber 101 by an exhaust pump 116 and an exhaust pipe (not shown) during the etching process.

Next, a specific example of the deep silicon trench etching method including the groove in the first embodiment will be described. Here, an example in a process mainly using a mixed gas plasma of SF ₆ , O ₂ , and SiF ₄ using the above-described plasma etching apparatus will be described.

Moreover, the detailed structure of the to-be-processed substrate 202 and the state after an etching are shown in FIGS. As shown in FIG. 2, the substrate 202 to be processed is a silicon substrate patterned with a mask material 201 made of SiO ₂ or the like. After this substrate 202 to be processed is placed on the sample stage 110 using a transfer means (not shown), SF ₆ , O ₂ , and SiF ₄ are adjusted to flow rates of 600, 80, and 400 ml / min, respectively. The pressure is supplied to the etching processing chamber 101, and the processing pressure is adjusted to 5 Pa with an adjusting valve (not shown).

After that, plasma is generated by applying a microwave output of 3000 W, and by applying a bias output of 225 W to the sample stage 110, etching proceeds from the trench opening 203 as shown in FIG. 3, and a deep groove trench is formed. The Table 1 shows typical processing conditions.

In the above etching process, SF ₆ , O ₂ , and SiF ₄ gas introduced into the etching chamber 101 dissociate into Si, S, F, and O ions and radicals, respectively, and react with the surface of the substrate 202 to be processed. At the same time, SiF and SiO are generated.

On the other hand, at the same time as the etching in the trench opening 203 progresses, moderate SiO is formed as a side wall protective film, suppressing isotropic etching due to F radicals and enabling anisotropic / high-speed etching. In the above description, the inclusion of SiF ₄ as a mixed gas is essential. However, the present invention can be achieved even with SF ₆ and O ₂ gas if moderate SiO is formed as a sidewall protective film.

  Next, the effect of the microwave rotation generator 105 used in the present invention will be described.

  FIG. 7 is a diagram showing the processing pressure dependence of the silicon etching rate when etching a silicon deep groove trench. Similarly, FIG. 8 is a diagram showing the processing pressure dependence of in-plane uniformity of the silicon etching rate, and FIG. 9 is a diagram showing the processing pressure dependence of the taper angle of the trench. Here, as shown in FIG. 3, the taper angle is represented by an angle formed by a horizontal line drawn from the bottom of the silicon trench and a side wall surface of the silicon trench.

  When the microwave output is relatively small, in FIG. 7, as in the case of the microwave output of 600 W, the silicon etching rate increases with the pressure until the processing pressure is 2.5 Pa, but at a pressure higher than 5 Pa, the etching rate is increased. As shown in FIG. 9, the taper angle of the silicon trench decreases. At this time, the etching shape has an abnormal shape such as rough surface or rolling.

  As described above, the etching rate decreases even when the pressure is increased at a relatively small microwave output. The higher the pressure is, the shorter the period during which electrons are accelerated by the microwave due to the increased probability of collision of electrons. As a result, it is considered that the density of ions necessary for the progress of etching, that is, the plasma density is decreased.

  Therefore, if the silicon etch rate is to be increased at higher pressures, the plasma density must be increased. For this reason, it is necessary to apply a higher microwave output. At this time, however, the problem was discharge stability.

  FIG. 10 is a diagram showing the dependence of discharge stability on the microwave output. As shown in FIG. 10, in the conventional apparatus that does not include the microwave rotation generator 105, discharge instability occurred when the microwave output was approximately 1000 W or more.

  One of the causes of this discharge instability is that the discharge state changes in the microwave output before and after the plasma density obtained by electron cyclotron resonance becomes a number that becomes the plasma cutoff frequency. It is mentioned that discharge state transition, that is, abnormal discharge occurs in a microwave output capable of obtaining a plasma density close to the number.

  On the other hand, as shown in FIG. 1, when the microwave rotation generator 105 is provided, the discharge instability is hardly seen as shown in FIG. As one of the reasons why the discharge is stabilized by the microwave rotation generator 105, when the microwave rotates, the valley of the standing wave passes through a locally high region of the plasma density that causes abnormal discharge, so that the plasma This is thought to be due to the density being averaged.

  Thus, when a relatively large microwave output can be applied, the silicon etching rate is 5 Pa even if the processing pressure is increased from 5 Pa to 10 Pa in FIG. 7, as in the case where the microwave output is 3000 W. It continued to increase to 1.4 times that of. However, the uniformity deteriorated at a pressure of 7.5 Pa or more as shown in FIGS. Further, the taper angle is decreased.

  Even in this case, since the etching rate does not decrease even when the pressure is increased, it is considered that there is room for optimization in a higher pressure region.

  FIG. 11 is a graph showing the processing pressure dependence of the silicon etching rate when silicon etching is performed on a sample having a relatively small pattern aperture ratio in the sample and a pattern size of 100 μm square or more. As shown in FIG. 11, when the microwave output is 1000 W, the silicon etching rate is increased by increasing the processing pressure, but when it exceeds 30 Pa, the silicon etching rate is decreased.

  This is considered because the plasma density decreases as the pressure increases, as described in the first embodiment.

  Therefore, if the silicon etch rate is to be increased at higher pressures, the plasma density must be increased. For this reason, it is necessary to apply a higher microwave output.

  Based on this, when silicon etching is performed with the microwave output increased to 3000 W, the silicon etching rate continues to increase to 60 Pa as shown in FIG. For this reason, the processing pressure range of a present Example is 60 Pa or less.

  By applying a higher microwave output, it is considered that a high etching rate, a desired shape, and in-plane uniformity can be secured, but it is desirable to use in a microwave output range of 1000 W to 5000 W.

  As described above, since the microwave rotation generator 105 is equipped, a high microwave output can be applied, so that an etching rate higher than the conventional one can be obtained.

Next, a second embodiment of the present invention will be described. Here, an example of a process mainly using a mixed gas plasma of SF ₆ , O ₂ and SiF ₄ using the same apparatus as the plasma etching apparatus described in the first embodiment will be described with reference to FIG.

  FIG. 12 is a diagram illustrating the microwave output dependency of the taper angle of the silicon trench when the deep silicon trench is etched. As the microwave power was increased from 1900 W to 3000 W, the taper angle decreased from 90.4 ° to 89.5 °. This indicates that the deposition property increases, that is, the formation of the sidewall protective film increases as the microwave output increases. Therefore, it is considered that the use of this makes it easier to improve the selection ratio and form a sidewall protective film necessary for preventing bowing.

  As shown in FIG. 4, when deeper etching is performed (generally with an aspect ratio of 5 or more), side wall protection becomes insufficient as the etching proceeds in the depth direction, a bowing shape is generated, and the trench width is reduced at the bottom of the silicon trench. There may be a problem that the taper shape becomes narrower. In this example, in order to reduce such bowing and taper shape, as an example, a method of changing the duty ratio of the time modulation of the bias power applied to the sample (on time with respect to one cycle of the repetition frequency), This will be described with reference to FIG.

  FIG. 13 shows a taper angle of the silicon trench when the duty ratio of the time modulation of the bias power applied to the sample is changed. When the duty ratio is relatively small, such as 20%, the amount of deposit during the period when the power is off is large, so the taper angle of the silicon trench is small. On the other hand, when the duty ratio is relatively large at 40%, the amount of deposit during the period in which the power is off is reduced, so that the taper angle of the silicon trench is increased.

  A method for forming a silicon trench by combining these will be described with reference to FIGS. First, FIG. 5 shows a case where the duty ratio is 20%. Next, FIG. 6 shows a case where processing is continuously performed with a duty ratio of 40%. In this way, a more vertical silicon trench shape can be obtained by combining the condition that the taper angle of the silicon trench is increased and the condition that the taper is reduced in order to suppress bowing.

  Furthermore, by dividing the period for forming the silicon trench into a plurality of parts and changing the duty ratio of each step, the groove width can be changed over the entire region in the depth direction, and a more vertical or uniform taper angle. The silicon trench shape can be obtained.

  The process conditions shown in Table 1 are typical etching conditions used in the magnetic field microwave plasma etching apparatus of FIG. The process conditions shown here are conditions optimized in the present invention, and are different from other etching apparatuses such as a helicon wave etching apparatus, an inductively coupled etching apparatus, a capacitive coupling etching apparatus, and a magnetic field RIE apparatus. The optimum values of process parameters are somewhat different. In the present embodiment, the method for forming a deep silicon trench has been described. However, the present embodiment is not limited to the formation of a silicon trench, and can also be applied to the formation of a hole.

  However, the method for controlling the etching shape in trench etching is not limited to this apparatus, and can be applied to other etching apparatuses. If the person is involved in the etching process, the other apparatus can be adjusted and adapted to the optimum conditions based on the process conditions presented here.

DESCRIPTION OF SYMBOLS 101 Etching chamber 102 Microwave generator 103 Matching device 104 Waveguide 105 Microwave rotation generator 106 Microwave introduction window 107 Gas introduction means 108 Transmission window 109 Solenoid coil 110 Sample stand 111 Substrate 112 High frequency power supply 113 Electrostatic Adsorption power supply 114 Cooling gas supply port 115 Chiller unit 116 Exhaust pump 201 Mask material 202 Substrate 203 Trench opening

Claims (1)

In a plasma etching method for forming a silicon trench in a silicon substrate or SOI substrate using plasma ,
Using a mixed gas of SF ₆ gas, SiF ₄ gas and oxygen gas, the silicon trench is formed while intermittently time-modulated high frequency power is supplied to a sample stage on which the silicon substrate or the SOI substrate is placed. ,
A plasma etching method, wherein the duty ratio of the time modulation is increased as the depth of the formed silicon trench increases .

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