JP2011211135A - Plasma processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of machining a silicon film containing nitrogen on a polysilicon gate sidewall of 3-dimensional transistor structure into a desired shape, while suppressing scraping of a silicon substrate.SOLUTION: A method of plasma etching the silicon film containing nitrogen on the 3-dimensional transistor structure includes a first step of etching by gas having a high deposit properties, and a second step of removing the deposite component. By alternating the first step and the second step, the silicon film containing nitrogen 34 is left only on a side wall of a polysilicon gate electrode 31, and etching processing is carried out so as to suppress the scraping of the silicon substrate 33.

Description

  The present invention relates to a plasma processing method, and more particularly to a plasma etching method for a poly-silicon gate electrode having a three-dimensional transistor structure and a nitrogen-containing silicon film on a silicon substrate.

  With the miniaturization of semiconductors, the short-channel effect between the source and the drain due to the reduction in the gate length cannot be ignored in the conventional transistor structure, and a three-dimensional transistor structure in which source and drain electrodes called Fin are provided on the side wall of the gate electrode is used. It came to be able to.

  In a general three-dimensional transistor, with the nitrogen-containing silicon film remaining on the side wall of the Poly silicon gate electrode, ion implantation is performed on the Fin portion intersecting the gate electrode to form a source and drain electrode. At this time, when the nitrogen-containing silicon film remains in the Fin portion, there arises a problem that it is difficult to limit the ion implantation direction or to perform uniform ion implantation. In addition, when excessive etching is performed to reduce the nitrogen-containing silicon film residue in the Fin portion, the silicon substrate between the gate electrodes and the Fin itself made of silicon are consumed, and the desired transistor performance cannot be obtained. There is also.

In this process, in order to form a nitrogen-containing silicon film on the side wall of the gate electrode, a nitrogen-containing silicon film previously formed uniformly around the gate electrode and on the Fin is formed in a desired height and thickness only on the side wall portion of the gate electrode. The nitrogen-containing silicon film around Fin is removed. Furthermore, it is also a processing method that suppresses the exhaustion of the Fin itself using the silicon substrate and silicon during this process. Conventionally, various methods have been proposed for highly selective processing of a silicon substrate and a nitrogen-containing silicon-containing film. For example, Patent Document 1 discloses that the processing rate of silicon and a silicon-containing film is changed by changing the content of a processing gas containing a fluorine-based reaction component and a H ₂ O or OH group-containing compound during the processing of the film to be processed. A method characterized by obtaining high selectivity is disclosed.

JP 2009-246331 A

  However, in the above prior art, consideration is insufficient for the case where the film to be processed is formed on a characteristic structure. For high-precision processing of the nitrogen-containing silicon film on the side wall of the Poly silicon gate electrode, adjustment of the etching rate of the nitrogen-containing silicon film in the peripheral part of the gate electrode and the Fin part and control of the high selectivity between the nitrogen-containing silicon film and the silicon substrate Is required.

At this time, a mixed gas plasma containing oxygen and a gas having a high carbon ratio with respect to fluorine, such as CH ₂ F ₂ and CH ₃ F, should be used to suppress silicon scraping when processing the nitrogen-containing silicon film. However, in this case, due to a decrease in the amount of fluorine in the plasma, a polymer containing carbon is deposited on the surface of the nitrogen-containing silicon film, which is a film to be processed, and etching of the nitrogen-containing silicon film tends to be hindered. When the oxygen flow rate is increased to suppress the polymer, the etching of the nitrogen-containing silicon film proceeds, the amount of silicon scraping increases, and the selectivity decreases. For these reasons, when an oxygen flow rate that can suppress the amount of silicon scraping is selected while etching of the nitrogen-containing silicon film proceeds, the polymer adheres unevenly to the surface of the nitrogen-containing silicon film, and a sidewall rough residue is likely to occur. A similar phenomenon occurs when a gas such as N ₂ , NO, or NO ₂ is used instead of oxygen. When a highly selective discharge is performed with a nitrogen-containing silicon film and silicon as described in Patent Document 1 for the purpose of polymer removal, the surface of the nitrogen-containing silicon film is oxidized, and the nitrogen-containing silicon film and the highly selective film It may become a residue due to the alteration. Furthermore, in a structure such as a three-dimensional transistor, the etching rate varies depending on the pattern difference in the deposition state of carbon-containing polymer between narrow openings with a high aspect ratio such as between the opening and the gate electrode on the poly silicon gate electrode. Since they are not necessarily the same, phenomena such as silicon scraping and residue as described above tend to occur remarkably depending on the structure. For the main measure, it is common to divide the film to be processed into a plurality of steps and change the oxygen flow rate or the like for each step, but it is difficult to adjust the difference between patterns. One of the factors is the deposition of a polymer containing excessive carbon on the film to be processed due to the interruption of the discharge between the steps, and the adhesion of other gases that hinder the etching.

  The present invention relates to a plasma etching method for plasma etching a nitrogen-containing silicon film on a three-dimensional transistor structure, wherein the plasma etching method includes a first step of etching with a gas having a high deposition property and a second step of removing a deposition component. The plasma etching method is characterized in that the first step and the second step are alternately repeated.

  According to the present invention, the side wall of the Poly silicon gate electrode and the Fin pattern can be formed in a desired shape without a residue of the nitrogen-containing silicon film, and scraping of the silicon substrate can be suppressed.

Sectional drawing explaining the structure of the process chamber in this invention. The figure explaining the process flow in a present Example. View for explaining the relationship of the etching rate of the N ₂ flow rate and the nitrogen-containing silicon film in this embodiment. The figure explaining the example of a process in a present Example. The figure explaining the model of the correlation of the processing time of the 1st step in this example, polymer deposition amount, and side wall roughening and residue generation of a nitrogen content silicon film. The figure explaining the model of the improvement example of the processing time of the 1st step in this example, polymer deposition amount, and side wall roughening and residue generation of a nitrogen content silicon film. The figure explaining the correlation model of the process time of a 1st step, and the remaining film thickness of the nitrogen-containing silicon film. The figure explaining the correlation model of processing time of the 1st step, and ESC current.

  The present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross section of the plasma processing apparatus used in the present invention. The plasma processing apparatus includes a vacuum processing chamber 1, a lower electrode 2 provided in the vacuum processing chamber and having a wafer placement surface for holding a wafer 3, and a portion that is provided facing the lower electrode and is in contact with plasma is electrically conductive. An upper electrode 9 made of a conductive material, a high-frequency power source for the upper and lower electrodes, a magnetic field forming means, a processing gas supply system, and the like. A focus ring 4 is provided at the periphery of the wafer placement surface of the lower electrode 2. The magnetic field forming means includes a yoke 5 and a coil 6. The processing gas supply means has a gas supply system 10 and a gas dispersion plate 8. The vacuum processing chamber 1 is connected to a vacuum pump that evacuates the vacuum processing chamber. The high frequency power supply unit includes an antenna 7, a first high frequency power supply 11, a first matching device 12, a second high frequency power supply 13, a second matching device 14, a filter circuit 15, a third high frequency power supply 16, 3 matching unit 17, antenna outer peripheral ring 18, antenna lid portion 21, filter circuit 22, and filter circuit 25. In addition, an electrostatic chuck power source 24 is connected to the lower electrode 2 via a filter circuit 23. Since the lower electrode 2 is movable, a lower electrode upper cover 27 and a lower electrode lower cover 28 are provided as protective covers. The side wall of the vacuum processing chamber 1 in contact with the plasma has an inner and outer double wall structure, the outer wall of the side wall is made of a metal material such as aluminum, and the inner wall of the side wall is made of a plasma-resistant protective film. . The wafer 3 is set on the lower electrode 2 through the gate valve 29 and the process valve 26.

  In the apparatus configured as described above, after the pressure inside the vacuum processing chamber 1 is reduced, an etching gas is introduced into the vacuum processing chamber by the gas supply system 10 and adjusted to a desired pressure. A magnetic field is formed between the lower electrode 2 and the upper electrode 9 in the vacuum processing chamber 1 by the coil 6 and the yoke 5 of the magnetic field forming means. Then, for example, high frequency power having a frequency of 200 MHz oscillated by the first high frequency power supply 11 of the high frequency power supply unit is introduced into the vacuum processing chamber 1 via the antenna 7 and the antenna outer ring 18. The electric field generated by the high-frequency power introduced into the processing chamber 1 generates high-density plasma in the processing chamber by interaction with a magnetic field formed in the processing chamber. In particular, when the magnetic field intensity that causes electron cyclotron resonance (for example, about 70 G when the frequency of the high-frequency power source for plasma generation is 200 MHz) is formed between the lower electrode 2 and the upper electrode 9 in the processing chamber, the density is efficiently increased. Plasma can be generated.

  In the apparatus of this configuration, plasma is mainly generated by the first high frequency power source 11 of 200 MHz, the plasma composition or plasma distribution is controlled by the third high frequency power source 16, and ions in the plasma are incident on the wafer by the second high frequency power source 13. Energy is controlled.

  In addition, the electrostatic chuck power supply 24 applies a DC voltage of several hundred volts to electrostatically attract the wafer to the wafer installation surface. As shown in FIG. 1, the gate valve 29 and the process valve 26 are opened by transfer, the wafer 3 is placed on the wafer placement surface of the lower electrode 2, and plasma is generated as described above. 9, high frequency power is supplied from the second high frequency power supply 13 to the lower electrode 2, and the wafer 3 is etched. A quartz window 51 is disposed on the upper electrode 9, and an optical fiber 52 and a spectroscope 50 are sequentially interposed. Information obtained by the spectroscope is stored in a recording medium of a control PC provided in the etching apparatus. The plasma light incident through the quartz window 51 during the etching process is analyzed by the spectroscope 50, the light in the wavelength region peculiar to the material on the wafer surface film is analyzed by the control PC, the remaining film thickness of the film is calculated, and the etching process is performed. Can be controlled. The filter circuit 23 can monitor the ESC current flowing from the plasma through the wafer during the etching process.

<Example 1>
This will be described below with reference to FIGS. This example is a processing example of a nitrogen-containing silicon film on a three-dimensional transistor structure in which source and drain electrodes called Fins are provided on the side walls of a gate electrode. As shown in FIG. 2A, the three-dimensional transistor structure before processing has a nitrogen-containing silicon film 34 shown in FIG. 2A on a pattern composed of a Poly silicon gate electrode 31 and Fin 32 on a silicon substrate 33. Has been. In a processing method having two or more processing steps, as a first step, a step having a high deposition ratio with high selectivity to silicon with respect to etching of a nitrogen-containing silicon film, and as a second step, a deposition with a high selectivity with silicon is deposited. By repeating the steps capable of removing the object, the nitrogen-containing silicon film 34 is left only on the side wall of the poly silicon gate electrode 31 as shown in FIG. Etching is performed.

  The state before the etching process shown in FIG. 2 (1) is the film thickness of the Poly silicon gate electrode 31: 120 nm, the film thickness of the Fin 32: 40 nm, the space between the Poly silicon gate electrodes is 60 nm, the nitrogen-containing silicon film 34 is 15 nm, The film is formed uniformly. A wafer 3 which is a substrate to be processed after film formation is placed on the lower electrode 2.

In the etching of the nitrogen-containing silicon film 34 shown in FIG. 2 (3), as a first step, for example, the processing pressure is 1 Pa, the power 600 W of the first high frequency power supply 11, the power 800 W of the third high frequency power supply 16, and the power of the second high frequency power supply 13. The nitrogen-containing silicon film 34 is etched by a mixed gas plasma of 80 W, CH ₃ F (10 SCCM) N ₂ (200 SCCM). The etching amount in the first step is set to an etching amount equivalent to five times the film thickness of the nitrogen-containing silicon film 34. In this embodiment, CH ₃ F gas is used, but CH ₂ F ₂ gas or CHF ₃ gas may be used instead. Also, rare gases Ar and Xe may be added to a mixed gas of CH ₃ F gas and N ₂ gas. As the second step, for example, the processing pressure is 4 Pa, the power of the first high frequency power supply 11 is 800 W, the power of the third high frequency power supply 16 is 0 W, the power of the second high frequency power supply 13 is 0 W, and the nitrogen-containing silicon film 34 is plasma by NH ₃ (500 SCCM). Remove the deposits. Also, the etching amount in the second step is made equal to the etching amount in the first step. As a gas used in the second step, N ₂ gas can be used in addition to NH ₃ gas. These first step and second step are sequentially repeated n times. In this case, the sum of the etching amounts of the n first steps is set to an etching amount equivalent to five times the film thickness of the nitrogen-containing silicon film 34. Further, the sum of the etching amounts of n times of the second step is made equal to the sum of the etching amounts of n times of the first step. The flow rate of N ₂ gas with respect to CH ₃ F gas in the first step was selected as a flow rate that can reduce the etching rate difference between patterns depending on the three-dimensional transistor structure as shown in FIG. This is to prevent over-etching locally on the silicon substrate or the like by making the etching amount between patterns constant. Over-etching is additional etching for preventing the above-described pattern difference or etching residue of the nitrogen-containing silicon film 34 in the stepped portion.

  In the three-dimensional transistor structure in which the nitrogen-containing silicon film 34 is formed in FIGS. 4A, 4B, and 4C, etching is performed in the first step until the etching process of the nitrogen-containing silicon film 34 is completed. A case where the second step is performed will be shown. FIG. 4A shows the shape after processing, and the result of viewing the AA ′ section from the (⇒) direction is the result of FIG. 4B, and the result of viewing the BB ′ section from the (→) direction is the result of FIG. c). In this case, the side wall roughness of the nitrogen-containing silicon film 34 on the side surface of the Poly silicon gate electrode 31 became significant as shown in FIG. 4C that the nitrogen-containing silicon film 34 on the side surface of the Poly silicon gate electrode 31 is significantly roughened on the side walls of the vertical stripes. Further, a residue 35 of the nitrogen-containing silicon film was generated at the portion where the poly silicon gate electrode and Fin intersected.

  In the above, the etching process of the nitrogen-containing silicon film 34 is performed once for each of the first step and the second step. However, the first step and the second step are sequentially repeated twice, and the etching amount for two times of the first step is obtained. Is equivalent to five times the film thickness of the nitrogen-containing silicon film 34. In addition, the etching amount for the second step twice was set equal to the etching amount for the first step twice. As a result, the side wall roughness of the nitrogen-containing silicon film 34 and the reduction of the residue 35 of the nitrogen-containing silicon film, which were noticeable when the first step and the second step were performed once, were observed. Similarly, by reducing the amount of processing once in the first step and repeating the processing alternately with the second step, the side wall roughness of the nitrogen-containing silicon film 34 and the residue 35 of the nitrogen-containing silicon film are further reduced. As a result. This phenomenon will be described with reference to the model diagrams of FIGS. As shown in FIG. 5, when the deposition amount of the polymer that is deposited on the nitrogen-containing silicon film 34 during the first step process and inhibits etching tends to increase, the nitrogen-containing silicon film 34 exceeds a certain threshold value. Since the side wall is roughened and the residue 35 of the nitrogen-containing silicon film is generated, the first step is temporarily stopped before the threshold is exceeded as shown in FIG. 6, and the polymer deposition is returned to the initial state in the second step. It was judged that both could be improved.

  Further, by reducing the residue 35 of the nitrogen-containing silicon film, it becomes possible to reduce the overetching amount for removing the residue, and the overetching amount of the silicon exposed portion in the pattern can be similarly reduced. This also confirmed that the amount of silicon scraping could be suppressed.

<Example 2>
In the first embodiment, the etching process of the nitrogen-containing silicon film 34 is performed a plurality of times for which the first step and the second step are set in advance, but the remaining amount in the vacuum processing chamber 1 depends on the number of etching processes in the vacuum processing chamber 1. Since the adhesion state of the gas and the deposit on the side wall of the vacuum processing chamber 1 changes, the etching process tends to become unstable only by controlling the same processing time repeatedly. Therefore, the processing time of the first step is calculated by the means for calculating the remaining film thickness of the nitrogen-containing silicon film 34 by analyzing the light in the wavelength region specific to the substance of the nitrogen-containing silicon film 34 which is the wafer surface coating with a control personal computer. It is desirable to manage and the etching process can be made more stable. The remaining film thickness of the nitrogen-containing silicon film 34 is calculated by sequentially measuring and analyzing the plasma emission by optical analysis means. At this time, the calculated value of the remaining film thickness of the nitrogen-containing silicon film 34 as shown in FIG. 7 was compared with the correlation model of the plasma emission and the remaining film thickness prepared in advance, and significantly deviated from the correlation model. In this case (in this example, it is defined as> ± 10% with respect to the correlation model value), it is judged that the progress of etching of the nitrogen-containing silicon film 34 is hindered by the deposit, and the process is switched to the second step for a certain time The deposit was removed. Thereafter, similarly, the timing for switching to the second step is determined by comparing the analysis result of the plasma emission in the first step and the correlation model of the remaining film thickness, and the nitrogen-containing silicon is determined by repeating these first and second steps. Etching is continued until the remaining film thickness of the monitor portion of the film 34 is exhausted. As a result, both the silicon scraping and the reduction of the residue 35 of the nitrogen-containing silicon film can be achieved.

<Example 3>
Next, in the second embodiment, a method of determining the switching timing to the second step based on the comparison between the plasma emission analysis result in the first step and the correlation model of the remaining film thickness is used. A method of determining the switching timing to the first step and the second step with the ESC current flowing in will be described with reference to FIG. The value of the ESC current varies depending on the state of deposit attachment that inhibits etching of the surface of the nitrogen-containing silicon film 34 that is the film to be processed. In this example, the change in the ESC current was monitored, and when the preset threshold value was exceeded, the second step was switched to remove deposits. Thereafter, the first step and the second step were repeated again, and etching was performed until the nitrogen-containing silicon film 34 was in a desired state. As a result, both the silicon scraping and the reduction of the residue 35 of the nitrogen-containing silicon film can be achieved.

  The present invention is a process condition optimized for a test sample of a semiconductor device, and a processing method of a nitrogen-containing silicon film on a three-dimensional transistor structure is not limited to the condition of the present invention.

  The present invention describes a method for processing a nitrogen-containing silicon film on a three-dimensional transistor structure. However, the present invention is not limited thereto, and a hole or a groove is processed in a semiconductor device manufacturing process. In the process comprising a film, the method of the present invention can be applied, and can be applied to, for example, an etch back process or a hard mask processing process.

  Although the present invention uses a plasma etching apparatus using electron cyclotron resonance (ECR), it can be applied regardless of the plasma generation method. For example, the helicon wave etching apparatus, inductively coupled etching apparatus, capacitance The same effect can be obtained even if it is carried out by a combined etching apparatus or the like.

DESCRIPTION OF SYMBOLS 1 Vacuum processing chamber 2 Lower electrode 3 Wafer 4 Focus ring 5 Yoke 6 Coil 7 Antenna 8 Gas dispersion plate 9 Upper electrode 10 Gas supply system 11 First high frequency power source 12 First matching device 13 Second high frequency power source 14 Second matching device 15 , 22, 23, 25 Filter circuit 16 Third high frequency power supply 17 Third matching unit 18 Antenna outer ring 21 Antenna lid 24 Electrostatic chuck power supply 26 Process valve 27 Lower electrode upper cover 28 Lower electrode lower cover 29 Gate valve 31 Poly silicon Gate electrode 32 Fin
33 Silicon substrate 34 Nitrogen-containing silicon film 35 Nitrogen-containing silicon film residue 50 Spectroscope 51 Quartz window 52 Optical fiber

Claims (3)

In a plasma etching method for plasma etching a nitrogen-containing silicon film on a three-dimensional transistor structure,
The plasma etching method includes a first step of etching with a highly depositable gas;
A plasma etching method comprising: a second step of removing a deposition component, wherein the first step and the second step are alternately repeated. The plasma etching method according to claim 1,
A plasma etching method using a mixed gas of CHxFy gas, N ₂ gas, and Ar or Xe as the gas in the first step. The plasma etching method according to claim 1,
A plasma etching method using at least one of NH ₃ gas and nitrogen gas as the gas in the second step.

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