JP5583076B2 - Plasma processing equipment - Google Patents

Description

  The present invention relates to a plasma processing apparatus and a substrate processing method.

  In order to form an impurity implantation layer on a substrate surface in a semiconductor manufacturing process, an ion implantation technique is generally used. Efforts are being made to bring the impurity profile closer to the ideal in order to enhance the performance of the manufactured device. As one of such approaches, it has been proposed to use a plasma doping technique in addition to an ion implantation technique. For example, Patent Document 1 describes that after plasma doping, helium plasma post-treatment is performed.

JP 2005-277220 A

  One of exemplary purposes of an embodiment of the present invention is to provide a plasma processing apparatus and a substrate processing method excellent in practical use for injecting impurities into a substrate from a surface layer containing impurities.

  A plasma processing apparatus according to an aspect of the present invention is a plasma processing apparatus for injecting impurities from a surface layer containing impurities into a substrate according to a required profile, the plasma processing conditions including a bias voltage for plasma processing, and the plasma A plasma processing time depending on processing conditions is set from the required profile, a substrate holder for holding the substrate to give a set bias voltage, a set plasma processing time, and plasma to act on the substrate And a plasma source for generating plasma. The required profile includes an impurity element to be implanted, a depth of implantation from the substrate surface where the impurity concentration is equal to the reference value, a depth equal to the first reference concentration, and a depth equal to the second reference concentration. A steepness that is a difference. The setting unit executes a first setting process for setting the bias voltage based on the implantation depth and a second setting process for setting the plasma processing time based on the impurity element and the steepness.

  Another embodiment of the present invention is also a plasma processing apparatus. This apparatus includes a plasma processing parameter setting unit for plasma processing for injecting impurities to a required implantation depth from the surface layer of the substrate containing impurities. The plasma processing parameters include a main parameter that determines the depth from the substrate surface at which the impurity concentration becomes equal to the reference value by the plasma processing, and a sub parameter that has a saturation range that saturates the impurity concentration to the reference value. The setting unit sets the main parameter from a required injection depth, and sets the sub parameter in the saturation range.

  Yet another embodiment of the present invention is also a plasma processing apparatus. This apparatus includes a setting unit that sets a bias voltage for plasma processing for injecting impurities from the surface layer of the substrate containing impurities to a required implantation depth. The setting unit sets a bias voltage from a required implantation depth based on a relationship between an implantation depth common to different types of impurity elements and a bias voltage.

  Yet another embodiment of the present invention is also a plasma processing apparatus. This apparatus includes a setting unit that sets the plasma processing time of the substrate for the plasma processing for injecting the impurity with the steepness required from the surface layer of the substrate including the impurity. The setting unit sets the plasma processing time from the required steepness based on the relationship between the steepness of the impurity element to be implanted and the plasma processing time.

  Yet another embodiment of the present invention is a substrate processing method. This method includes a first step of forming a surface layer containing impurities on a substrate, and a step of applying a bias voltage to the substrate to inject the impurities to a required implantation depth and processing the surface layer with plasma containing helium. 2 steps. The second step includes a first setting process for setting a bias voltage from a required implantation depth and a second setting process for setting a plasma processing time from a required steepness.

  Yet another embodiment of the present invention is also a substrate processing method. The method includes a first step of forming a surface layer containing impurities on a substrate, and a second step of treating the surface layer with a plasma containing helium and hydrogen to inject the impurities to a required implantation depth. .

  Yet another embodiment of the present invention is also a substrate processing method. This method includes a first step of forming an impurity layer on the surface of the substrate, and a second step of treating the impurity layer with a plasma containing helium to inject impurities into the substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the plasma processing apparatus and substrate processing method which are excellent in practicality for inject | pouring an impurity from the surface layer containing an impurity to a board | substrate are provided.

It is a figure for demonstrating notionally the mechanism of the injection | pouring of the impurity element in the plasma processing which concerns on one Embodiment of this invention. It is a figure for demonstrating notionally the mechanism of the injection | pouring of the impurity element in the plasma processing which concerns on one Embodiment of this invention. It is a figure which shows typically the structure of the plasma processing apparatus which concerns on one Embodiment of this invention. It is a graph showing the relationship between the bias electric power and bias voltage in the plasma processing apparatus which concerns on one Embodiment of this invention. It is a figure showing typically the substrate processing system concerning one embodiment of the present invention. It is a graph which shows the analysis result by the secondary ion mass spectrometry which concerns on one Embodiment of this invention. It is a graph which shows the analysis result by the secondary ion mass spectrometry which concerns on one Embodiment of this invention. It is a graph which shows the analysis result by the secondary ion mass spectrometry which concerns on one Embodiment of this invention. It is a flowchart for demonstrating the setting process of the plasma processing condition which concerns on one Embodiment of this invention. It is a figure which shows an example of the table for the 1st setting process which concerns on one Embodiment of this invention. It is a figure which shows an example of the table for the 2nd setting process which concerns on one Embodiment of this invention.

  One embodiment of the present invention is an impurity implantation method including a two-step process. The first stage is a process for forming a surface layer containing impurities on the substrate. The impurity surface layer is formed shallower than the finally required implantation depth. Examples of processes that can be used for this pretreatment include ion implantation, plasma doping, and film formation. The second stage is plasma processing for injecting impurities from the impurity surface layer to the required depth. The impurity element is pushed in from the surface layer of the substrate in the depth direction by plasma of an inert gas such as helium. Hereinafter, this plasma treatment may be referred to as “plasma injection”.

  In order to further improve the performance of a manufactured device, it is important to bring the concentration profile of the impurity element in the depth direction closer to an ideal one. A so-called box-type profile having good steepness at a desired depth is considered preferable.

  Prior to the plasma processing, plasma processing conditions are set. However, in general, each of a plurality of parameters included in the processing conditions can affect the impurity profile. It takes a lot of trial and error to adjust the parameters and obtain the optimum conditions. An efficient procedure for adjusting each of the multiple parameters is not clear. It would be desirable to provide a practical technique for obtaining optimal processing conditions from a given request profile.

  The present inventor has found that it is possible to optimally set the plasma processing conditions by a relatively simple procedure from the consideration of the mechanism of the plasma injection processing and the experimental results. According to this method, it is possible to set processing conditions in a sequential procedure from a given profile.

In one embodiment, the plurality of parameters included in the plasma processing conditions are classified into a main parameter, a sub parameter, and other ancillary parameters. The main parameter is a parameter that determines the depth Xj from the substrate surface at which the impurity concentration or the dose is equal to a reference value (for example, 5 × 10 ¹⁸ atoms / cm ³ ) by the plasma treatment. The main parameter has a relatively large influence on the impurity implantation depth. The attached parameters are parameters that have a relatively small or almost no influence on the injection depth.

  The secondary parameter is an intermediate positioning parameter. The secondary parameters have a range that has a relatively large effect on the implantation depth and a range that has a relatively small or almost no effect. For example, when the value of the sub parameter is small, the implantation depth increases as the value increases, and when the value increases further, the increment of the implantation depth decreases. That is, the impurity concentration at the depth Xj corresponding to a certain value of the main parameter is saturated when the value of the subparameter increases. The secondary parameter has a saturation range that saturates the impurity concentration to the reference value. It can be evaluated that the injection depth does not substantially change even if the subparameter is changed in the saturation range.

  The depth of implantation by plasma implantation is related to the bias voltage applied to the substrate in order to attract ions in the plasma to the substrate. The implantation depth is controlled by the bias voltage. As will be described later with reference to the drawings, this relationship is a common relationship that does not depend on the type of impurity element to be implanted in the case of “plasma implantation” using inert gas ions.

  Thus, the main parameter is, for example, a parameter representing a bias voltage applied to the substrate for plasma injection. Since the bias voltage can be rephrased as the implantation energy of ions in the plasma, it can be said that the main parameter is a parameter representing the implantation energy of plasma into the substrate. Further, the sub parameter is, for example, a parameter indicating a plasma processing time for plasma injection. Even if the plasma processing is continued beyond a certain time (that is, the saturation time), the implantation depth Xj corresponding to the set bias voltage is maintained.

  The main parameters are set directly from the required implantation depth using a common relationship to the impurity elements. The main parameters are set first to achieve the required depth, and then the remaining parameters are set. Preferably, the subparameters are selected from the saturation range so that the remaining parameter settings have little effect on the implantation depth. Thus, a procedure is provided for sequentially setting the plasma processing conditions that provide the required implantation depth.

  Sub-parameters or other ancillary parameters may be set to control other items of the request profile, such as steepness. In this way, the plasma processing condition setting process is subdivided into one item of the required profile, for example, a main parameter setting for controlling the implantation depth, and another item, for example, a sub parameter setting for controlling the steepness. Can be Compared to optimizing a large number of parameters while considering two items at the same time, it is expected that an efficient optimum condition can be set by setting a small number of parameters related to each item.

  Therefore, in one embodiment, the setting unit of the plasma processing apparatus individually executes a first setting process for setting a main parameter and a second setting process for setting a sub parameter. In the first setting process, the main parameter may be set to a value that realizes the required implantation depth. In the first setting process, the main parameter may be set using the relationship between the implantation depth common to different impurity elements and the main parameter. In the second setting process, the sub parameter may be set to a value that realizes the required steepness. In the second setting process, the sub parameter may be set using the relationship between the steepness and the sub parameter for the impurity element to be implanted. In the second setting process, the value of the sub parameter may be selected from the saturation range.

  FIG. 1 and FIG. 2 are diagrams for conceptually explaining an impurity element implantation mechanism in plasma processing according to an embodiment of the present invention. FIG. 1 shows a substrate 102 having an impurity surface layer 100. FIG. 2 shows the substrate 102 during the plasma implantation process.

  A substrate processing method according to an embodiment of the present invention includes a first step of forming a layer including impurity atoms 101 on the substrate surface 103, and a second step of implanting impurity atoms 101 deeper than the layer. Including. The processing conditions of the second step are set so as to obtain a required impurity concentration profile in the depth direction. The first step is a pretreatment for preparing an impurity supply source on the substrate 102. The substrate 102 obtained by the first step is shown in FIG.

  As shown in FIG. 1, the impurity surface layer 100 includes a large number of impurity atoms 101. The impurity atom 101 is, for example, boron (boron) B, phosphorus P, or arsenic As. The material constituting the substrate 102 is, for example, silicon Si. The pretreatment for forming the impurity surface layer 100 on the substrate 102 is, for example, ion implantation or plasma doping. The pretreatment may be a film forming process such as CVD (chemical vapor deposition) or PVD (physical vapor deposition).

  The impurity surface layer 100 includes an upper deposition film 104 and a lower initial implantation layer 106. The boundary between the deposited film 104 and the initial injection layer 106 is the original substrate surface (that is, the substrate surface before the pretreatment) 103. The deposited film 104 is formed from impurity atoms 101 deposited on the substrate surface 103 by pretreatment. The initial injection layer 106 is formed by implanting impurity atoms 101 into a very shallow region of the substrate 102 by pretreatment. The initial injection layer 106 may include atoms (not shown) of the substrate material. The deposited film 104 may also include substrate atoms that are repelled from the substrate 102 by the collision of the impurity atoms 101.

The initial implantation layer 106 has an initial implantation depth 108. The initial implantation depth 108 is shallower than the required depth 110 that is ultimately required for the substrate 102. The required depth 110 is shown in FIG. Both the initial implantation depth 108 and the required depth 110 are depths from the substrate surface 103 at which the impurity concentration becomes equal to a reference value (for example, 5 × 10 ¹⁸ atoms / cm ³ ). The initial implantation depth 108 is, for example, a depth of less than about 5 nm or less than about 10 nm. The required depth 110 is, for example, a depth of about 5 nm to 10 nm, or a depth of about 10 nm to 15 nm. The initial implantation depth 108 is determined by the energy of impurity ions flying to the substrate surface 103.

  Therefore, the energy of the impurity ions flying to the substrate surface 103 in the first step may be smaller than the energy required for implantation to the required depth 110. For example, in order to implant impurities to the required depth 110 by typical low energy ion implantation, an implantation energy of about 500 eV is required. On the other hand, when ion implantation is used for the pretreatment, an implantation energy of about 200 eV is sufficient. For this reason, it is possible to reduce the influence of the pretreatment on the substrate surface 103 such as surface roughness. Further, since the obtained concentration profile is mainly determined by the processing conditions of the next plasma injection, the strictness is not required for setting the processing conditions of the preprocessing. That is, the preprocessing has a wide process window.

  The plasma implantation shown in FIG. 2 is a process in which an inert gas plasma 112 acts on the substrate 102. A bias voltage is applied to the substrate 102 to promote the arrival and entry of the inert gas ions 114 to the substrate 102. Implanted energy having a magnitude corresponding to the bias voltage is applied to the inert gas ions 114.

  The implantation energy of the inert gas ions 114 determines the entry position that becomes the limit in the depth direction of the substrate 102. The inert gas ions 114 can reach a depth position corresponding to the implantation energy. The plasma processing conditions including the bias voltage are set so that the maximum reachable depth of the inert gas ions 114 is the required depth 110.

  The impurity surface layer 100 of the substrate 102 is irradiated with a large amount of inert gas ions 114 from the plasma 112. The impurity atoms 101 in the impurity surface layer 100 are pushed deeper by the incoming inert gas ions 114. Due to the pushing action of the inert gas ions 114, the impurity surface layer 100 extends in the depth direction beyond the initial implantation depth 108.

  Since the maximum reachable depth of the inert gas ions 114 is equal to the required depth 110, the pushing action to the impurity atoms 101 is limited to a depth range from the substrate surface 103 to the required depth 110. Therefore, the arrival position of the pushed-in impurity atoms 101 remains at the required depth 110 at the maximum. Impurity atoms 101 are not implanted beyond the required depth 110. Since the reaching depth is determined by the inert gas ions 114 (implantation energy), it is considered that the reaching depth does not depend on the type of the impurity element.

  Thus, on the premise that a sufficient plasma 112 is applied (for example, on the premise of a sufficient plasma processing time), the impurity atoms 101 are pushed into the required depth 110 by the inert gas ions 114. The bias voltage in this case can be realized with a voltage lower than that of the same depth by normal ion implantation. An impurity profile having an implantation depth Xj required for a desired impurity element can be realized on the surface of the substrate 102.

  Further, as described above, the pushing action to the impurity atoms 101 remains in the depth range up to the required depth 110. By continuing the plasma treatment, an effect of accumulating the impurity atoms 101 in a very thin depth range with the required depth 110 as the lower boundary occurs. Therefore, the impurity concentration gradient in the depth range, that is, the impurity concentration decrease amount with respect to the depth increment can be reduced. That is, it is possible to realize a profile having excellent steepness near the required depth 110.

  The type of inert gas used is preferably selected in consideration of the action of pushing into the impurity atoms 101 and the surface roughness of the substrate surface 103. If the atomic weight or molecular weight of the inert gas is small, the pushing action may be insufficient. On the other hand, when the atomic weight or molecular weight of the inert gas is large, there is a possibility that the surface roughness that becomes apparent when the annealing process, which is a subsequent process of the present process, is performed becomes large. A practically preferable inert gas selected in consideration of these is helium. In this case, the plasma 112 contains only helium.

  Hydrogen may be mixed into the inert gas plasma 112. The hydrogen crystal recovery action described later has the effect of reducing the surface roughness of the substrate surface 103. Therefore, in this case, an inert gas (for example, argon) having an atomic weight larger than that of helium can also be employed.

  FIG. 3 is a diagram schematically showing the configuration of the plasma processing apparatus 10 according to an embodiment of the present invention. The plasma processing apparatus 10 is an apparatus for providing a plasma injection process according to an embodiment of the present invention. The plasma processing apparatus 10 may be configured to provide a plasma doping process that is an example of a pre-process of the plasma injection process together with the plasma injection process or instead of the plasma injection process.

  The plasma processing apparatus 10 includes a chamber 12, a gas supply unit 14, a plasma source 16, and a substrate holder 18. The plasma processing apparatus 10 includes a control unit 11 for controlling these components and other elements. The control unit 11 includes a setting unit 13 for performing a setting process for setting plasma processing conditions.

  As will be described later, the setting unit 13 performs an operation for setting the plasma processing parameters from the required parameters using a table or a relational expression prepared in advance. Such a table or relational expression is stored in a memory (not shown) attached to the control unit 11. The setting unit 13 may perform setting calculation of the plasma processing parameter using other information as necessary in addition to the request parameter.

  The chamber 12 is a vacuum container for providing a vacuum environment inside. The chamber 12 is provided with a vacuum pump 20 for evacuating the inside. The vacuum pump 20 is, for example, a turbo molecular pump. The vacuum pump 20 is connected to the chamber 12 via a vacuum valve 22. The vacuum valve 22 is a variable conductance valve, for example, and is attached to the suction port of the turbo molecular pump. A roughing pump (not shown) is provided after the turbo molecular pump. Chamber 12 is connected to ground.

  The vacuum pump 20 and the vacuum valve 22 constitute an automatic pressure adjustment system (APC) for controlling the inside of the chamber 12 to a desired degree of vacuum. The automatic pressure regulation system includes a pressure sensor (not shown) for measuring the pressure in the chamber 12 and a pressure controller (not shown) for controlling the vacuum valve 22 (and the vacuum pump 20) based on the pressure measurement. ). With the automatic pressure regulation system, the vacuum environment in the chamber 12 is maintained within a process gas pressure range that is preferred for plasma doping processes, for example.

  The gas supply unit 14 is provided to supply process gas to the chamber 12. The gas supply unit 14 includes a single or a plurality of gas sources, and a piping system for connecting the gas sources to the chamber 12 and introducing gas into the chamber 12. This piping system may include a mass flow controller for controlling the flow rate of gas supplied to the chamber 12. When the gas supply unit 14 has a single gas source, a process gas in which a plurality of types of gases are mixed in advance at a desired ratio may be stored in the gas source.

  In the illustrated embodiment, the gas supply unit 14 includes an impurity gas source 24 and a carrier gas source 28. The gas supply unit 14 includes a first mass flow controller 26 for controlling the flow rate of the impurity gas supplied from the impurity gas source 24 and a second mass flow for controlling the flow rate of the carrier gas supplied from the carrier gas source 28. And a controller 30.

The impurity gas is a source gas containing a desired impurity to be added to the substrate W or a gas obtained by diluting the source gas with a dilution gas. The source gas is selected according to the desired impurity. Impurity elements are contained in the molecules of the source gas. When the impurity implanted into the substrate W is, for example, boron (B), phosphorus (P), or arsenic (As), the source gas is, for example, B ₂ H ₆ , PH ₃ , AsH ₃ or the like. In one embodiment, the impurity may be at least one of boron, phosphorus, arsenic, gallium, germanium, and carbon.

A diluent gas for diluting the source gas is, for example, any one of hydrogen, argon, helium, neon, and xenon. Or several types may be used together as dilution gas among these. The dilution gas may be used as an assist gas for improving the ignitability of the source gas plasma. In one embodiment, when B ₂ H ₆ gas is used as the source gas, it is diluted to 20% or less with hydrogen gas in order to avoid boron powdering in the gas source. The carrier gas supplied from the carrier gas source 28 is, for example, any one of hydrogen, argon, helium, neon, and xenon, like the dilution gas. Moreover, multiple types may be used together as carrier gas among these.

  In the case of providing the plasma doping process, the gas supply unit 14 controls the flow rate of the impurity gas by the first mass flow controller 26 and controls the flow rate of the carrier gas by the second mass flow controller 30. Then, the mixed gas is supplied to the chamber 12. On the other hand, in the case of providing the plasma injection process according to an embodiment of the present invention, the gas flow rate is controlled by the second mass flow controller 30 to supply a gas containing no impurities at a desired flow rate.

  The plasma source 16 generates plasma in the gas supplied from the gas supply unit 14 to the chamber 12. The plasma source 16 is disposed outside the chamber 12 in contact therewith. In one embodiment, the plasma source 16 is a plasma generation type plasma source called ICP (inductively coupled plasma). The plasma source 16 includes a high frequency power source 32, a plasma generating coil 34, and an insulator 36. The high frequency power supply 32 is, for example, an AC power supply of 13.56 MHz, and supplies power to the plasma generating coil 34. The plasma generating coil 34 is attached to one surface (upper surface in the illustrated example) facing the substrate holder 18 of the chamber 12. An insulator 36 that is a flange made of a dielectric material is provided on one surface of the chamber 12 to which the coil 34 is attached.

  The substrate holder 18 is provided inside the chamber 12 in order to hold the substrate W to be subjected to plasma processing. The substrate W is a semiconductor substrate, for example, a substrate mainly made of silicon. The substrate holder 18 may include, for example, an electrostatic chuck or other fixing means for holding the substrate W. In one embodiment, the substrate holder 18 has a substrate contact portion whose temperature is controlled, and the substrate W is placed on the substrate contact portion and fixed by electrostatic attraction. Thus, the substrate W is managed at a substrate temperature preferable for plasma processing.

  In addition, a bias power source 38 is connected to the substrate holder 18. The bias power supply 38 gives the substrate W a potential (ie, bias voltage) for attracting ions in the plasma toward the substrate W held by the substrate holder 18. The bias power source 38 is a DC power source, a pulse power source, or an AC power source. In the illustrated embodiment, the bias power source 38 is an AC power source. In this case, an AC power source having a lower frequency (for example, 1 MHz or less) than the high frequency power source 32 for generating plasma is used. Therefore, hereinafter, the bias power supply 38 may be referred to as a low frequency power supply.

  In the case of the plasma implantation process, the impurity atoms in the surface layer of the substrate W are implanted by being pushed into a deeper position by ions in the plasma. In the case of the plasma doping process, impurity ions are implanted into the surface layer of the substrate W from the plasma. In one embodiment, the plasma processing pre-treatment may be performed using the plasma processing apparatus 10 and the plasma implantation process may be subsequently performed using the plasma processing apparatus 10.

  The substrate W that has been subjected to the plasma treatment may be subjected to a heat treatment as a subsequent step. This heat treatment is a process for recovering crystal defects generated in the substrate W by the plasma treatment and electrically activating the implanted impurities. The heat treatment is, for example, rapid thermal annealing (RTA, laser annealing, flash lamp annealing, etc.), and is performed by an annealing apparatus (not shown).

  FIG. 4 is a graph showing the relationship between the bias power and the bias voltage in the plasma processing apparatus 10 according to an embodiment of the present invention. The horizontal axis of FIG. 4 represents the power LF supplied from the bias power supply 38 that is an AC power supply. The vertical axis represents the bias voltage applied to the substrate W by the power LF.

  Since the inert gas ions in the plasma are positive ions, the ions are accelerated toward the substrate when the substrate becomes a negative electrode. Since the bias power supply 38 is an AC power supply, the half value of the peak-to-peak voltage Vpp corresponds to the maximum value of the bias voltage. No voltage exceeding this voltage is applied.

  FIG. 4 shows a measurement value represented by the symbol ◆ and a linear relationship obtained from these measurement values. For example, when the power LF is 135 W, 300 W, 500 W, and 800 W, it can be read that the bias voltages corresponding to the power LF are about 125 V, about 250 V, about 380 V, and about 590 V, respectively.

  Implanting impurities by typical low energy ion implantation to the required implantation depth requires, for example, an implantation energy of about 500 eV, that is, about 500 V in terms of voltage. Therefore, as can be seen from FIG. 4, when the bias power LF for plasma processing is set to a range of about 600 W or less, impurities are implanted with an implantation energy lower than typical low energy ion implantation.

  For example, as shown in FIG. 6, implantation to the same depth level as in a typical method of implanting impurities only by ion implantation processing is realized with a bias power LF of about 600 W or less. Thus, the ability to implant impurities with relatively low implantation energy is one advantage of the plasma implantation process according to one embodiment of the present invention. Impurities can be efficiently implanted with low implantation energy. If the implantation energy is low, the surface roughness of the substrate can be reduced.

  In addition, since impurities can be implanted at a low voltage, it is possible to suppress charge-up in a device pattern on a substrate to be manufactured. This is expected to improve device manufacturing yield.

  FIG. 5 is a diagram schematically showing a substrate processing system 200 according to an embodiment of the present invention. The substrate processing system 200 includes a preprocessing apparatus 202 and a plasma processing apparatus 204. The substrate processing system 200 may include a transfer device 206 for transferring an object to be processed from the pretreatment device 202 to the plasma processing device 204.

  The pretreatment device 202 is a device for performing pretreatment for forming a layer containing impurities on the surface of an object. As described above, the pretreatment is, for example, ion implantation, plasma doping, or film formation. Therefore, the pretreatment apparatus 202 is, for example, an ion implantation apparatus, a plasma processing apparatus, or a film formation apparatus. The pretreatment device 202 may be a known low energy ion implantation device.

  The pretreatment device 202 may be the plasma treatment device 10 described above (see FIG. 3). That is, the substrate processing system 200 may include the plasma processing apparatus 10 dedicated to preprocessing and another plasma processing apparatus 204 for plasma injection processing.

  The substrate processing system 200 may include a post-processing device (not shown) for post-processing. The post-treatment apparatus is, for example, a heat treatment apparatus for heat treatment, such as an annealing apparatus. The substrate processing system 200 may further include a transfer device (not shown) for transferring an object to be processed from the plasma processing apparatus 204 to the post-processing apparatus.

  FIG. 6 is a graph showing an analysis result by secondary ion mass spectrometry (SIMS) according to an embodiment of the present invention. The vertical axis in FIG. 6 indicates the impurity concentration, and the horizontal axis indicates the depth from the substrate surface. FIG. 6 shows SIMS analysis results for four samples AD. The SIMS analysis result represents the impurity concentration profile in the depth direction of the sample.

  Sample A is only pretreated and not plasma-injected. Samples B to D were pre-treated under the same processing conditions as Sample A, and were subjected to plasma injection treatment under different bias powers.

The pretreatment common to the samples A to D is ion implantation of very low energy boron. Until the pretreatment stage, the samples A to D are prepared by a normal ion implantation process. The ion implantation treatment conditions are an implantation energy of 200 eV and a dose of 1 × 10 ¹⁵ atoms / cm ² . The plasma processing conditions common to the samples B to D are a power output for plasma generation of 1500 W, a helium gas flow rate of 300 sccm, a gas pressure of 0.8 Pa, and a processing time of 1 minute. The bias powers of Samples B to D are 300 W, 500 W, and 800 W, respectively.

As can be seen from FIG. 6, it can be seen that boron is implanted deeper than the state after the pretreatment (sample A) by performing the plasma implantation process (samples B to D). Further, as the bias power in the plasma processing is larger, boron is implanted deeper. Specifically, the depth Xj from the substrate surface at which the boron concentration decreases to the reference value 5 × 10 ¹⁸ atoms / cm ³ is about 8 nm for sample A, about 10 nm for sample B, about 11 nm for sample C, D is about 13 nm.

  Therefore, the bias power greatly affects the implantation depth in the plasma implantation process. It can be seen that the depth of impurity implantation can be controlled by setting the bias power.

It can also be seen that the ion implantation shows a relatively gradual decrease in concentration gradient (that is, inferior in steepness), whereas the present plasma implantation process tends to be superior in steepness. Here, for example, the steepness is defined as a depth difference from a depth from the substrate surface where the impurity element concentration becomes the first reference concentration to a depth where the concentration decreases to the second reference concentration. The smaller the depth difference, the better the steepness. The first reference concentration is, for example, 5 × 10 ¹⁹ atoms / cm ³ , and the second reference concentration is, for example, 5 × 10 ¹⁸ atoms / cm ³ . As shown in FIG. 6, compared with the sample A, for example, the samples B and C are superior in steepness.

  FIG. 7 is a graph showing an analysis result by secondary ion mass spectrometry (SIMS) according to an embodiment of the present invention. The vertical axis in FIG. 7 indicates the impurity concentration, and the horizontal axis indicates the depth from the substrate surface. FIG. 7 shows SIMS analysis results for six samples B1 to B3 and P1 to P3. In Samples B1 to B3, the implanted impurity element is boron, and Samples P1 to P3 are phosphorus. All samples are pre-treated for ion implantation and plasma-implanted.

The ion implantation processing conditions for the samples B1 to B3 are an implantation energy of 200 eV and a dose of 1 × 10 ¹⁵ atoms / cm ² . The ion implantation processing conditions for the samples P1 to P3 are an implantation energy of 500 eV and a dose of 1 × 10 ¹⁵ atoms / cm ² . In the ion implantation process, since phosphorus is generally less likely to be implanted into the substrate than boron, the implantation energy into the samples P1 to P3 is increased, but this is not essential. The samples P1 to P3 may have the same implantation energy, for example, 200 eV.

  The plasma processing conditions are common to the samples B1 to B3 and P1 to P3 except for the bias power. Specifically, the power output for plasma generation is 1500 W, the helium gas flow rate is 300 sccm, the gas pressure is 0.8 Pa, and the processing time is 1 minute. The bias powers of the samples B1 to B3 are 300 W, 500 W, and 800 W, respectively. Similarly, the bias powers of the samples P1 to P3 are 300 W, 500 W, and 800 W, respectively.

As shown in FIG. 7, the depth Xj at which the impurity concentration decreases to the reference value of 5 × 10 ¹⁸ atoms / cm ³ is approximately equal to 9.5 nm for the samples B1 and P1. Similarly, it can be read that Samples B2 and P2 are approximately equal to approximately 11.5 nm, and Samples B3 and P3 are approximately equal to approximately 12.5 nm. The same implantation depth can be realized with the same bias power regardless of the impurity ion species to be implanted. There is no need to change the implantation energy for each impurity element as in the ion implantation process.

  Therefore, according to one embodiment of the present invention, impurities can be implanted to a desired implantation depth using a common set bias power without depending on the type of impurity element to be implanted. The setting process can be simplified. Further, it is also preferable in that ion species that are relatively difficult to implant by a normal ion implantation process can be implanted with relatively low energy.

  On the other hand, the steepness is different between boron and phosphorus under common plasma processing conditions. For example, in sample B1 and sample P1, boron (sample B1) has better steepness than phosphorus (sample P1). As will be described later with reference to FIG. 8, it is considered that the steepness can be improved by extending the plasma processing time.

  Note that an amorphous layer is formed on the surface of the substrate by the action of the plasma treatment. The thickness of the amorphous layer when the bias power is 300 W is shown in FIG. This is a value measured with an ellipsometer and is about 16.5 nm. In the case of 500 W, the depth becomes about 24 nm, and in the case of 800 W, the depth becomes about 32 nm. As described above, since the impurity implantation depth is about 10 nm, it is sufficiently shallower than the interface between the amorphous layer and the crystal layer of the substrate. Therefore, it can be concluded that the amorphous layer and its interface are not involved in controlling the impurity profile by the plasma implantation process. In addition, since the amorphous interface is deeper than the impurity implantation depth, it can be considered to function effectively as a stopper in the heat treatment in the subsequent process.

  FIG. 8 is a graph showing an analysis result by secondary ion mass spectrometry (SIMS) according to an embodiment of the present invention. The vertical axis in FIG. 8 indicates the impurity concentration, and the horizontal axis indicates the depth from the substrate surface. FIG. 8 shows SIMS analysis results for four samples W to Z. In any sample, boron is implanted into the substrate by plasma doping. The plasma processing conditions are a bias power of 135 W, a helium flow rate of 270 sccm, a flow rate of B2H6 diluted to 5% with helium at 30 sccm, and a gas pressure of 0.9 Pa. Samples W to Z have different plasma processing times. The processing times of the samples W to Z are 5 seconds, 15 seconds, 30 seconds, and 60 seconds, respectively.

As can be seen from FIG. 8, the implantation depth increases as the processing time increases until the plasma processing time increases to 30 seconds (samples W, X, Y). However, it has not increased since then. The sample Y having a processing time of 30 seconds and the sample Z having a processing time of 60 seconds have substantially the same injection depth. The depth Xj at which the impurity concentration is reduced to the reference value 5 × 10 ¹⁸ atoms / cm ³ is equal between the sample Y and the sample Z. Therefore, in this case, the saturation time is about 30 seconds.

  Until the saturation time elapses, the implantation depth increases as the plasma processing time increases. However, after the saturation time, the implantation depth at the saturation point is maintained even if the plasma treatment is continued. On the other hand, the sample Z is somewhat better than the sample Y with respect to the steepness. Therefore, by making the plasma processing time longer than the saturation time, the steepness of the profile can be adjusted while maintaining the implantation depth at a value determined from the bias power. FIG. 8 shows the experimental results of plasma doping, but the controllability of such depth and steepness is the same for the plasma implantation process.

  FIG. 9 is a flowchart for explaining plasma processing condition setting processing according to an embodiment of the present invention. In one embodiment, the plasma processing apparatus 10 includes a setting unit 13 for setting plasma processing conditions, and the setting unit 13 executes this setting process (see FIG. 3). The setting process is executed prior to the plasma injection process. The setting unit 13 sets plasma processing conditions from the input data and outputs them as necessary.

  This setting process includes a first setting process (S12) and a second setting process (S14). The setting unit 13 individually executes the first setting process and the second setting process. The setting unit 13 may execute the setting process in the order of the first setting process and the second setting process, or may execute these two processes individually in parallel. You may perform in order of a 2nd setting process and a 1st setting process. The plasma processing parameters are set without depending on the processing conditions of the preprocessing. FIG. 10 shows an example of a table for the first setting process. FIG. 11 shows an example of a table for the second setting process.

  As shown in FIG. 9, the setting unit 13 first receives input of information required for the setting process (S10). This input data includes a required profile which is a concentration profile in the depth direction of impurities to be realized in the substrate. The input data is supplied to the setting unit 13 by an operator's input to an input unit associated with the plasma processing apparatus 10 or the control unit 11 or by communication with another control device.

  The request profile includes a plurality of request parameters. The required profile includes, for example, a parameter representing an impurity element to be implanted, a parameter representing an implantation depth from the substrate surface where the impurity concentration is equal to a reference value, a depth equal to the first reference concentration, and a second reference concentration. And a parameter representing a steepness that is a depth difference from a depth equal to. Moreover, the plasma processing conditions include a plurality of plasma processing parameters. The plasma processing parameters include, for example, a parameter representing a bias voltage or bias power and a parameter representing a plasma processing time. The plasma processing parameter may include a parameter representing a gas flow rate or a gas pressure supplied for plasma generation.

  The setting unit 13 performs a first setting process for setting the bias voltage from the required implantation depth (S12). In the first setting process, a plasma processing parameter representing a bias voltage is set from a request parameter representing the implantation depth based on the relationship between the implantation depth and the bias voltage.

  The relationship between the implantation depth and the bias voltage is, for example, a table shown in FIG. This first table is common to different types of impurity elements, for example, at least common to boron and phosphorus. A different relationship or table may be used for each impurity element.

  The first table includes a correspondence relationship between a plurality of sets of implantation depths and bias voltages. Such relationships can be determined experimentally or empirically. The first table is stored in advance in the setting unit 13 or an associated memory. The first table may represent the relationship between the implantation depth and the bias power LF. In the illustrated example, the first table includes three sets of correspondences, and the corresponding depths Xj when the bias power LF is 300 W, 500 W, and 800 W are 9.8 nm, 12 nm, and 13 nm, respectively. .

  The setting unit 13 selects a bias voltage corresponding to the input implantation depth from the first table. When the input value of the required implantation depth is in the first table, the setting unit 13 selects the corresponding bias voltage. When the input value of the required implantation depth is not in the first table, the setting unit 13 obtains the corresponding bias voltage by interpolation calculation. For example, the bias voltage may be obtained by linear interpolation from two values close to the input value of the implantation depth.

  Instead of the table, a relational expression between the implantation depth and the bias voltage or the bias power may be used. In that case, the setting unit 13 may store at least a coefficient of the relational expression in advance. The setting unit 13 may calculate the bias voltage from the implantation depth based on the relational expression between the implantation depth and the bias voltage. For example, when the relationship between the implantation depth D and the bias voltage V can be expressed by a linear expression V = a · D + b, the setting unit 13 uses the coefficients a and b stored in advance. The bias voltage V may be calculated from the depth D.

  The setting unit 13 performs a second setting process for setting the plasma processing time based on the required steepness (S14). The setting unit 13 sets a plasma processing parameter that represents a plasma processing time from a required parameter that represents an impurity element and a required parameter that represents steepness. The relationship between the steepness and the plasma processing time is preferably prepared for each type of impurity element to be implanted.

  The setting unit 13 sets the plasma processing time using, for example, the second table shown in FIG. The second table includes a set of required impurity elements and steepness and corresponding plasma processing parameters. The second table includes at least a plasma processing time as a plasma processing parameter. Similar to the first table, these relationships can be determined experimentally or empirically.

  The setting unit 13 selects a plasma processing time corresponding to the input impurity element and steepness from the second table. When the required impurity element and the input value of the steepness are in the second table, the setting unit 13 selects the corresponding plasma processing time. When the required input value is not in the second table, the setting unit 13 obtains the corresponding plasma processing time by, for example, interpolation calculation.

  The plasma processing time is preferably set to be equal to or longer than the saturation time for saturating the impurity concentration to the reference value under the plasma processing conditions. Thereby, impurities can be implanted to a desired implantation depth Xj with good uniformity. The second table shown in FIG. 11 may give a plurality of plasma processing parameter candidates for the same required parameter. The setting unit 13 may select a plasma processing parameter from a plurality of candidates on the condition that the plasma processing time is equal to or longer than the saturation time. When the plasma processing time is set to be less than the saturation time, the setting unit 13 may appropriately correct other plasma processing parameters including the bias voltage.

  The second table may include a parameter representing the bias power LF as shown. When the first setting process has already been performed and the parameter representing the bias power LF has been set, the setting unit 13 selects from the second table the plasma processing time corresponding to the input value of the required parameter and the set bias power LF. May be. When the first setting process is not completed, the setting unit 13 may select the plasma processing time and the bias power LF corresponding to the input value of the request parameter. In this case, in order to guarantee the required implantation depth, the setting unit 13 may execute a correction process for correcting the selected bias power LF. The first setting process may be omitted.

  The second table may further include additional plasma processing parameters such as gas flow rates. The setting unit 13 may set these attached parameters in the second setting process. Alternatively, the first table may include attached parameters, and the setting unit 13 may set the attached parameters in the first setting process. The setting unit 13 may execute a third setting process for setting the attached parameter. The attached parameter may be preset with one or more values as candidates. The setting unit 13 may select an appropriate attached parameter according to the set value of the plasma processing parameter in the first setting process and the second setting process.

  The setting unit 13 outputs the set plasma processing conditions to the output unit or display unit associated with the plasma processing apparatus 10 or the control unit 11 (S16). Thus, the setting process according to the embodiment of the present invention ends. The control unit 11 executes the plasma injection process using the set plasma processing conditions.

  In the plasma processing apparatus 10 having the above configuration (see FIG. 3), the operation when implanting impurities into the substrate will be described. The operator sets the processing conditions for the plasma injection process. For this purpose, an impurity profile to be formed on the substrate is determined, and the required profile is input to the plasma processing apparatus 10 through input means attached to the plasma processing apparatus 10. The plasma processing apparatus 10 executes the processing condition setting process including the first setting process and the second setting process described above, and obtains the plasma processing condition from the request profile.

  In addition, the operator prepares a substrate on which the above-described pretreatment has been performed as a preparation stage for the plasma injection process. In the plasma processing, first, the chamber 12 is evacuated to a desired degree of vacuum by the vacuum pump 20 and the substrate W to be processed is carried into the chamber 12. The substrate W is held by the substrate holder 18. An inert gas is supplied from the gas supply unit 14 to the chamber at a desired flow rate and pressure. Alternatively, the process gas mixed at a desired flow rate ratio by the gas supply unit 14 is supplied to the chamber 12. At this time, the degree of vacuum is continuously adjusted by the automatic pressure control system. A magnetic field is generated by energizing the plasma generating coil 34 from the high frequency power supply 32. The magnetic field passes through the insulator 36 and enters the chamber 12 to generate a plasma of a process gas (for example, helium gas).

  A bias power source 38 is used to generate a potential on the substrate W held on the substrate holder 18. The control unit 11 controls the bias power supply 38 so as to generate the bias voltage or bias power set by the setting unit 13. As a result, ions existing in the plasma are accelerated toward the substrate W, and ions fly and enter the surface layer region of the substrate W. Power supply from the high frequency power supply 32 and the bias power supply 38 is stopped when a predetermined termination condition is satisfied. Gas supply is also stopped. For example, the plasma processing is ended when the plasma processing time set by the setting unit 13 has elapsed. The processed substrate W is unloaded from the chamber 12.

  In addition, the impurity profile by the plasma implantation process performed may be measured, and the 1st table and the 2nd table may be updated from a measurement result. For example, the correspondence between the request parameter indicated by the measurement result and the plasma processing parameter may be added to the first table and the second table.

  As described above, according to an embodiment of the present invention, a two-step impurity implantation method including a pretreatment and a plasma implantation treatment is provided. By appropriately setting the conditions for the post-process plasma implantation process, it is possible to realize a desired impurity profile without depending on the pretreatment process conditions. Regardless of the type of impurity element to be implanted, the implantation depth can be controlled uniformly by setting the plasma implantation energy or bias to the substrate. A desired steepness can be obtained by setting the plasma processing time. Since the bias and the processing time can be set independently, the processing conditions can be easily set.

  The present invention has been described based on the embodiments. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiment, and various design changes are possible, various modifications are possible, and such modifications are within the scope of the present invention. By the way.

  The plasma for the plasma implantation process may include hydrogen. By mixing an appropriate amount of hydrogen into the plasma, the bombardment effect due to the collision particles and thus the uneven density of the amorphous layer can be reduced, and good uniformity, reproducibility, and steepness can be obtained after annealing.

  By mixing a suitable amount of hydrogen into the plasma, the self-healing action of the crystal on the substrate surface against ion collision from the plasma is enhanced. That is, hydrogen radicalized or ionized by plasma enters a bond between substrate atoms (for example, silicon) destroyed by helium bombardment, and a bond is instantaneously generated between silicon and hydrogen. The bond strength of this bond is weak and eventually it is destroyed by helium bombardment. However, the presence of this silicon-hydrogen bond requires more energy to destroy the crystal than when no hydrogen is mixed. For this reason, at the same energy, the degree of crystal breakdown becomes relatively weak. Therefore, the uneven distribution of density in the substrate surface amorphous layer caused by the plasma irradiation is reduced, and the growth of defects during the activation process in the subsequent process is suppressed.

  One aspect for determining the preferred hydrogen gas concentration is to consider the balance between the crystal recovery action by hydrogen gas and the bombardment effect by inert gas, and the preferred range of hydrogen gas concentration can be determined experimentally. It is. For example, the flow rate ratio of hydrogen gas is less than 20%, or less than 10%, preferably 3% to 5%, or less than 4%.

  Further, the first step and the second step are not necessarily performed separately. The second step may be started before the first step is finished. In the case where the pretreatment is performed by plasma doping treatment, plasma containing impurities to be implanted may be generated, and the plasma implantation treatment may be performed under the plasma. The plasma may be generated from a process gas obtained by diluting a compound containing an impurity to be injected with helium gas. As described above, hydrogen may be further mixed. In this case, the subparameter may include the impurity gas flow rate instead of or in addition to the plasma processing time.

  DESCRIPTION OF SYMBOLS 10 Plasma processing apparatus, 11 Control part, 12 Chamber, 13 Setting part, 14 Gas supply part, 16 Plasma source.

Claims (5)

A plasma processing apparatus for injecting impurities into a substrate according to a required profile from a surface layer containing impurities,
A setting unit for setting a plasma processing condition including a bias voltage for the plasma processing, and a plasma processing time according to the plasma processing condition from the request profile;
A substrate holder for holding the substrate to provide a set bias voltage;
A plasma source for generating plasma to cause the plasma to act on the substrate for a set plasma processing time;
The required profile includes an impurity element to be implanted, a depth of implantation from the substrate surface where the impurity concentration is equal to the reference value, a depth equal to the first reference concentration, and a depth equal to the second reference concentration. A steepness that is a difference, and
The setting unit executes a first setting process for setting the bias voltage from the implantation depth and a second setting process for setting the plasma processing time from the impurity element and the steepness. A plasma processing apparatus.   The setting unit has a relationship between the implantation depth and the bias voltage in advance, and the relationship is common to different types of impurity elements, and the first setting process is performed based on the relationship. The plasma processing apparatus according to claim 1, wherein the bias voltage is set from a depth.   The setting unit has a relationship between the steepness and the plasma processing time in advance for each type of impurity element, and the plasma processing time is used to saturate the impurity concentration to the reference value under the plasma processing conditions. 3. The plasma processing apparatus according to claim 1, wherein the second setting process sets the plasma processing time from the steepness based on the relationship.   4. The plasma processing apparatus according to claim 1, wherein a depth at which an impurity concentration is equal to the reference value is shallower than the implantation depth in the surface layer containing the impurities. 5. A gas supply unit for supplying helium gas or a mixed gas of helium and hydrogen;
5. The plasma processing apparatus according to claim 1, wherein the plasma source generates helium plasma or helium and hydrogen plasma.

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