JP5804978B2 - Plasma etching method and computer recording medium - Google Patents

Description

  The present invention relates to a plasma etching method and a computer recording medium.

  Conventionally, in a manufacturing process of a semiconductor device, a plasma etching method is used in which etching is performed by applying plasma to a substrate (for example, a semiconductor wafer) disposed in a processing chamber. For example, this plasma etching method is used when a contact hole is formed in a silicon dioxide film in a manufacturing process of a semiconductor device. The contact hole is required to have a high aspect ratio contact (HARC), which suppresses the occurrence of bowing and keeps the side wall shape vertical. It is becoming difficult to form contact holes.

  In such a plasma etching method, etching is performed during a period in which a protective film is formed by applying plasma under a gas condition having high deposition properties and a period in which etching is performed by applying plasma under gas conditions having low deposition properties. There is known a technique of performing a multi-step etching by switching in the middle of the process (for example, see Patent Document 1).

JP 2006-278436 A

  As described above, a contact hole with a high aspect ratio is required in the manufacturing process of a semiconductor device, and by plasma etching, the occurrence of bowing is suppressed and the side wall shape is kept vertical while maintaining a high aspect ratio. It is difficult to form a contact hole.

  The present invention has been made in response to such a conventional situation, and a plasma etching method and computer recording capable of forming a high aspect ratio contact hole while suppressing the occurrence of bowing and maintaining a vertical sidewall shape. The purpose is to provide a medium.

  One aspect of the plasma etching method of the present invention is a plasma etching method in which holes are formed in a silicon oxide film through a mask layer by plasma of a processing gas containing carbon (C) and fluorine (F). (C) and fluorine (F) ratio (C / F) is a first value by plasma etching using a processing gas containing a first processing gas, the remaining amount of the mask layer, and the bowing CD of the hole The remaining amount of the mask layer using a preparation gas for obtaining the remaining amount of the mask layer corresponding to the changing point at which the amount of change in the Boeing CD increases, and a processing gas containing the first processing gas Comprising: a first plasma etching step for performing plasma etching until the change point becomes a point before the change point; and a second plasma etching step for performing after the first plasma etching step. In the second plasma etching step, at least a period of performing plasma etching using a processing gas containing a second processing gas having a smaller ratio (C / F) of carbon (C) to fluorine (F) than the first value. It is characterized by including.

  ADVANTAGE OF THE INVENTION According to this invention, the plasma etching method and computer recording medium which can suppress the generation | occurrence | production of a bow and can form a contact hole of a high aspect ratio, maintaining a side wall shape perpendicular | vertical can be provided.

The figure which shows typically schematic structure of the plasma etching apparatus used for one Embodiment of this invention. The figure which shows typically the structure of the semiconductor wafer used for the plasma etching method which concerns on one Embodiment of this invention. The flowchart which shows the process of the plasma etching method which concerns on one Embodiment of this invention. A graph showing the relationship between the Boeing CD and the remaining amount of mask. The figure for demonstrating the relationship between the increase amount of Boeing CD, and a mask residual amount. The figure which shows the result of having investigated the etching gas seed | species and the state of a deposit. The graph which shows the relationship between the Boeing CD and mask remaining amount in an Example. An electron micrograph showing the state of a cross section of a semiconductor wafer. The graph which shows the relationship between mask top CD and etching time. The figure which shows typically the structure of the semiconductor wafer used for the plasma etching method which concerns on other embodiment of this invention. A graph showing the relationship between the Boeing CD and the remaining amount of mask. A graph showing the relationship between the Boeing CD and the etching depth. The graph which shows the change of the flow volume of etching gas. The figure which shows typically the change of the side wall shape in a hall | hole.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a plasma etching apparatus used in this embodiment. First, the configuration of the plasma etching apparatus will be described.

  The plasma etching apparatus has a processing chamber 1 that is airtight and electrically grounded. The processing chamber 1 has a cylindrical shape, and is made of, for example, aluminum having an anodized film formed on the surface thereof. In the processing chamber 1, a mounting table 2 that horizontally supports a semiconductor wafer W as a substrate to be processed is provided.

  The mounting table 2 has a base 2a made of a conductive metal, such as aluminum, and has a function as a lower electrode. The mounting table 2 is supported by a conductor support 4 via an insulating plate 3. A focus ring 5 made of, for example, single crystal silicon is provided on the outer periphery above the mounting table 2. Further, a cylindrical inner wall member 3 a made of, for example, quartz is provided so as to surround the periphery of the mounting table 2 and the support table 4.

  A first high frequency power source 10a is connected to the base material 2a of the mounting table 2 via a first matching unit 11a, and a second high frequency power source 10b is connected via a second matching unit 11b. Yes. The first high frequency power supply 10a is for generating plasma, and high frequency power of a predetermined frequency (27 MHz or more, for example, 40 MHz) is supplied from the first high frequency power supply 10a to the base material 2a of the mounting table 2. It has become. The second high-frequency power source 10b is for ion attraction (bias), and the second high-frequency power source 10b has a predetermined frequency (13.56 MHz or less, for example, 3.5 MHz or lower) than that of the first high-frequency power source 10a. 2 MHz) is supplied to the base material 2 a of the mounting table 2. On the other hand, a shower head 16 having a function as an upper electrode is provided above the mounting table 2 so as to face the mounting table 2 in parallel. The shower head 16 and the mounting table 2 have a pair of electrodes ( Upper electrode and lower electrode).

  An electrostatic chuck 6 for electrostatically attracting the semiconductor wafer W is provided on the upper surface of the mounting table 2. The electrostatic chuck 6 is configured by interposing an electrode 6a between insulators 6b, and a DC power source 12 is connected to the electrode 6a. The semiconductor wafer W is configured to be electrostatically attracted by the Coulomb force when a DC voltage is applied to the electrode 6a from the DC power source 12.

  A refrigerant channel 2b is formed inside the support base 4, and a refrigerant inlet pipe 2c and a refrigerant outlet pipe 2d are connected to the refrigerant channel 2b. The support 4 and the mounting table 2 can be controlled to a predetermined temperature by circulating an appropriate refrigerant such as cooling water in the refrigerant flow path 2b. Further, a backside gas supply pipe 30 for supplying cold transfer gas such as helium gas (backside gas such as He gas) to the back side of the semiconductor wafer W is provided so as to penetrate the mounting table 2 and the like. The backside gas supply pipe 30 is connected to a backside gas supply source (not shown). With these configurations, the semiconductor wafer W attracted and held on the upper surface of the mounting table 2 by the electrostatic chuck 6 can be controlled to a predetermined temperature.

  The shower head 16 described above is provided on the top wall portion of the processing chamber 1. The shower head 16 includes a main body portion 16 a and an upper top plate (shower plate) 16 b forming an electrode plate, and is supported on the upper portion of the processing chamber 1 via an insulating member 45. The main body portion 16a is made of a conductive material, for example, aluminum whose surface is anodized, and is configured such that the upper top plate 16b can be detachably supported at the lower portion thereof.

  Gas diffusion chambers 16c and 16d are provided inside the main body portion 16a, and a large number of gas flow holes 16e are formed at the bottom of the main body portion 16a so as to be positioned below the gas diffusion chambers 16c and 16d. Has been. The gas diffusion chamber is divided into a plurality of parts, for example, a gas diffusion chamber 16c provided in the central part and a gas diffusion chamber 16d provided in the peripheral part, and the central part and the peripheral part are independently provided. The supply state of the processing gas can be changed.

  The upper top plate 16b is provided with a gas introduction hole 16f so as to penetrate the upper top plate 16b in the thickness direction so as to overlap the gas flow hole 16e. With such a configuration, the processing gas supplied to the gas diffusion chambers 16c and 16d is dispersed and supplied into the processing chamber 1 through the gas flow holes 16e and the gas introduction holes 16f. ing. The main body 16a and the like are provided with a pipe (not shown) for circulating the refrigerant so that the temperature of the shower head 16 can be controlled to a desired temperature during the plasma etching process.

  In the main body 16a, two gas inlets 16g and 16h for introducing the processing gas into the gas diffusion chambers 16c and 16d are formed. Gas supply pipes 15a and 15b are connected to the gas inlets 16g and 16h, and a processing gas supply source 15 for supplying a processing gas for etching is connected to the other ends of the gas supply pipes 15a and 15b. Has been. The gas supply pipe 15a is provided with a mass flow controller (MFC) 15c and an on-off valve V1 in order from the upstream side. The gas supply pipe 15b is provided with a mass flow controller (MFC) 15d and an on-off valve V2 in order from the upstream side.

  Then, a processing gas for plasma etching is supplied from the processing gas supply source 15 to the gas diffusion chambers 16c and 16d via the gas supply pipes 15a and 15b, and the gas flow holes 16e are supplied from the gas diffusion chambers 16c and 16d. In addition, they are dispersed and supplied into the processing chamber 1 through the gas introduction holes 16f.

  A variable DC power source 52 is electrically connected to the shower head 16 as the upper electrode through a low-pass filter (LPF) 51. The variable DC power supply 52 can be turned on / off by an on / off switch 53. The current / voltage of the variable DC power supply 52 and the on / off of the on / off switch 53 are controlled by a control unit 60 described later. As will be described later, when a high frequency is applied from the first high frequency power supply 10a and the second high frequency power supply 10b to the mounting table 2 to generate plasma in the processing space, the control unit 60 turns on as necessary. The off switch 53 is turned on, and a predetermined DC voltage is applied to the shower head 16 as the upper electrode.

  A cylindrical grounding conductor 1 a is provided so as to extend upward from the side wall of the processing chamber 1 above the height position of the shower head 16. The cylindrical ground conductor 1a has a top wall at the top.

  An exhaust port 71 is formed at the bottom of the processing chamber 1, and an exhaust device 73 is connected to the exhaust port 71 via an exhaust pipe 72. The exhaust device 73 has a vacuum pump, and the inside of the processing chamber 1 can be depressurized to a predetermined degree of vacuum by operating the vacuum pump. On the other hand, a loading / unloading port 74 for the semiconductor wafer W is provided on the side wall of the processing chamber 1, and a gate valve 75 for opening and closing the loading / unloading port 74 is provided at the loading / unloading port 74.

  In the figure, reference numerals 76 and 77 denote depot shields that are detachable. The deposition shield 76 is provided along the inner wall surface of the processing chamber 1, and has a role of preventing etching by-products (deposition) from adhering to the processing chamber 1. A conductive member (GND block) 79 connected to the ground in a DC manner is provided at substantially the same height as the semiconductor wafer W of the deposition shield 76, thereby preventing abnormal discharge.

  The operation of the plasma etching apparatus having the above configuration is comprehensively controlled by the control unit 60. The control unit 60 includes a process controller 61 that includes a CPU and controls each unit of the plasma etching apparatus, a user interface 62, and a storage unit 63.

  The user interface 62 includes a keyboard that allows a process manager to input commands in order to manage the plasma etching apparatus, a display that visualizes and displays the operating status of the plasma etching apparatus, and the like.

  The storage unit 63 stores a recipe in which a control program (software) for realizing various processes executed by the plasma etching apparatus under the control of the process controller 61 and processing condition data are stored. Then, if necessary, an arbitrary recipe is called from the storage unit 63 by an instruction from the user interface 62 and executed by the process controller 61, so that a desired process in the plasma etching apparatus is performed under the control of the process controller 61. Processing is performed. Also, recipes such as control programs and processing condition data may be stored in a computer-readable computer recording medium (for example, hard disk, CD, flexible disk, semiconductor memory, etc.), or It is also possible to transmit the data from other devices as needed via a dedicated line and use it online.

  Next, a procedure for plasma etching the silicon dioxide layer and the like formed on the semiconductor wafer W by the plasma etching apparatus having the above configuration will be described. First, the gate valve 75 is opened, and the semiconductor wafer W is loaded into the processing chamber 1 from the loading / unloading port 74 via a load lock chamber (not shown) by a transfer robot (not shown) and mounted on the mounting table 2. Thereafter, the transfer robot is retracted out of the processing chamber 1 and the gate valve 75 is closed. Then, the inside of the processing chamber 1 is exhausted through the exhaust port 71 by the vacuum pump of the exhaust device 73.

  After the inside of the processing chamber 1 reaches a predetermined degree of vacuum, a predetermined processing gas (etching gas) is introduced from the processing gas supply source 15 into the processing chamber 1 and the inside of the processing chamber 1 is maintained at a predetermined pressure. . At this time, the supply state of the processing gas from the processing gas supply source 15 can be made different between the central portion and the peripheral portion, and the supply amount from the central portion and the peripheral portion of the entire processing gas supply amount. The ratio with the supply amount from the section can be controlled to a desired value.

  In this state, high-frequency power having a frequency of, for example, 40 MHz is supplied from the first high-frequency power source 10a to the base material 2a of the mounting table 2. Further, from the second high frequency power supply 10b, high frequency power (for bias) having a frequency of, for example, 3.2 MHz is supplied to the base material 2a of the mounting table 2 for ion attraction. At this time, a predetermined DC voltage is applied from the DC power source 12 to the electrode 6a of the electrostatic chuck 6, and the semiconductor wafer W is attracted to the electrostatic chuck 6 by Coulomb force.

  As described above, an electric field is formed between the shower head 16 as the upper electrode and the mounting table 2 as the lower electrode by applying high-frequency power to the mounting table 2 as the lower electrode. Due to this electric field, a discharge is generated in the processing space where the semiconductor wafer W exists, and the silicon dioxide layer and the like formed on the semiconductor wafer W are etched by the plasma of the processing gas formed thereby.

  Further, as described above, a direct current voltage can be applied to the shower head 16 during the plasma processing, and therefore the following effects are obtained. That is, depending on the process, a plasma having a high electron density and low ion energy may be required. If a DC voltage is used in such a case, the ion energy injected into the semiconductor wafer W is suppressed, the plasma electron density is increased, and the etching rate of the film to be etched of the semiconductor wafer W is increased. The sputter rate to the film serving as a mask provided on the upper part of the etching target is lowered, and the selectivity is improved.

  When the etching process described above is completed, the supply of high-frequency power, the supply of DC voltage, and the supply of processing gas are stopped, and the semiconductor wafer W is unloaded from the processing chamber 1 by a procedure reverse to the procedure described above. .

  Next, the plasma etching method according to an embodiment of the present invention will be described in the case where a high aspect ratio contact hole is formed. FIG. 2 schematically shows a cross-sectional configuration of a semiconductor wafer W to be plasma etched. FIG. 3 is a flowchart showing the steps of the plasma etching method according to one embodiment of the present invention.

As shown in FIG. 2, a silicon dioxide (SiO ₂ ) layer 201 (thickness 2500 nm) is formed on a semiconductor wafer W as a substrate to be processed. A carbon layer 202 (thickness 900 nm) is formed on the silicon dioxide (SiO ₂ ) layer 201, and an SiON layer 203 and an antireflection layer (BARC) 204 are formed on the carbon layer 202. Yes. On the antireflection layer (204), a photoresist layer 205 is formed which is patterned into a predetermined shape and has a plurality of (only one is shown in FIG. 2) hole-shaped openings 206.

  In this embodiment, the antireflection layer 204, the SiON layer 203, and the carbon layer 202 are plasma etched using the photoresist layer 205 as a mask. Then, using the carbon layer 202 as a mask, the silicon dioxide layer 201 is plasma-etched to form a high aspect ratio hole 201a.

In the plasma etching of the silicon dioxide layer 201, a processing gas containing carbon (C) and fluorine (F), for example, C ₄ F ₆ gas, C ₄ F ₈ gas, C ₃ F ₈ gas, or the like is used. In the plasma etching process of the silicon dioxide layer 201, as shown in the flowchart of FIG. 3, a preparatory process is first performed to determine the remaining amount of mask at a change point (bending point) described later (process 301 shown in FIG. 3). Thereafter, a first plasma etching step (step 302 shown in FIG. 3) and a second plasma etching step (step 304 shown in FIG. 3) performed after the first plasma etching step are performed.

In the first plasma etching step, a processing gas containing a first processing gas having a first ratio of carbon (C) to fluorine (F) (C / F) is used, and in the second plasma etching step, carbon is used. A processing gas containing a second processing gas in which the ratio (C / F) of (C) to fluorine (F) is smaller than the first value is used. For example, C ₄ F ₆ gas (C / F = 2/3) or C ₄ F ₈ gas (C / F = 1/2) is used as the first processing gas. On the other hand, as the second processing gas, for example, C ₃ F ₈ gas (C / F = 3/8) or the like is used.

In the preparation step, the correlation between the remaining amount of the mask layer (the remaining amount of the mask) and the boeing CD of the hole is examined by plasma etching using the process gas including the first process gas, and the change amount of the bowing CD is determined. The remaining mask amount corresponding to the increasing change point (bending point) is obtained (step 301 shown in FIG. 3). For example, C ₄ F ₆ gas is used as the first processing gas, and the preparation process is performed in a gas system of C ₄ F ₆ gas / Ar / O ₂ . In this case, for example, as shown in the graph of FIG. 4 where the vertical axis represents the bowing CD (nm) and the horizontal axis represents the remaining mask amount (nm), the remaining mask amount is equal to or less than a certain value (in the example of FIG. Then, the amount of change in the Boeing CD increases. The value of the remaining amount of mask at this time becomes a change point (bending point).

  As described above, in the relationship between the remaining amount of the mask and the amount of change in the Boeing CD, it is assumed that there is a remaining amount of the mask that is a changing point at which the amount of change in the Boeing CD increases. . That is, as shown in FIG. 5A, when the remaining amount of the mask is large, it collides with the vicinity of the entrance of the mask (carbon layer 202) (the overhanging portion deposited so that the depot overhangs the mask side wall) and obliquely. The ions whose traveling direction is bent collide with the side wall portion of the mask (carbon layer 202). However, as shown in FIG. 5B, when the remaining amount of the mask is reduced, ions bent obliquely in the vicinity of the entrance of the mask (carbon layer 202) are in the holes 201a of the silicon dioxide layer 201. Etching is performed by colliding with the side wall, and bowing occurs in the hole 201a. With such a mechanism, when the remaining amount of the mask falls below a certain value, the bowing amount increases rapidly.

  For this reason, when the remaining amount of the mask layer corresponding to the change point (bending point) at which the change amount of the bowing CD obtained in the above preparation step increases (step 303 shown in FIG. 3), the first plasma etching is performed. The step (step 302 shown in FIG. 3) is switched to the second plasma etching step (step 304 shown in FIG. 3). The above change point (bending point) varies depending on the opening diameter (mask top CD) of the upper end of the initial mask (photoresist layer 205), and when the opening diameter of the upper end of the initial mask is larger than 50 nm. When the opening diameter at the upper end of the initial mask is smaller than 50 nm, it is smaller than 400 nm. The range of the remaining amount of the mask layer serving as such a change point (bending point) varies depending on various process conditions, the mask CD, and the mask material, but is in the range of about 100 to 500 nm. Preferably it is the range of about 100-400 nm, Furthermore, it is the range of about 200-400 nm.

In the first plasma etching step (step 302 shown in FIG. 3), the first processing gas having a relatively high carbon (C) to fluorine (F) ratio (C / F) as compared to the second processing gas was used. Plasma etching is performed. For example, plasma etching is performed using a gas system of C ₄ F ₆ gas / Ar / O ₂ or the like. The first processing gas having a high ratio of carbon (C) to fluorine (F) (C / F) is a so-called deposition gas, and can etch silicon dioxide at a high selectivity with respect to carbon.

In the second plasma etching step (step 304 shown in FIG. 3), a second processing gas having a relatively small ratio of carbon (C) to fluorine (F) (C / F) as compared to the first processing gas was used. A period for performing plasma etching is included. The plasma etching using the second processing gas uses, for example, a C ₃ F ₈ gas / Ar / O ₂ gas system. The second processing gas having a low ratio of carbon (C) to fluorine (F) (C / F) is a gas having a small amount of deposit, and the selectivity of silicon dioxide to carbon is low.

  For this reason, in the second plasma etching step (step 304 shown in FIG. 3), the period for performing the 2-1 plasma etching step using the second processing gas (step 305 shown in FIG. 3) and the first processing gas are used. The period of performing the 2-2 plasma etching step (step 306 shown in FIG. 3) may be alternately repeated a plurality of times in a short time (eg, about 10 seconds) until the etching is completed (shown in FIG. 3). Step 307). As a result, a necessary selection ratio can be secured while suppressing an increase in the Boeing CD.

FIG. 6 schematically shows the results of examining the difference in the state of the deposit when using C ₄ F ₆ gas and when using C ₃ F ₈ gas. As shown in FIG. 6 (a), when C ₄ F ₆ gas is used, there is a tendency to deposit a lot near the entrance of the hole. As the flow rate of C ₄ F ₆ gas increases, the depot moves to the inside of the hole. Many overhangs. On the other hand, as shown in FIG. 6B, when C ₃ F ₈ gas is used, the deposit near the entrance of the hole is small, and the amount of protrusion to the inside of the hole is small. In other words, etching is performed under conditions that facilitate deposition, and bowing can be suppressed by performing etching under conditions with less deposition when reaching a change point (bending point) between the deposition of the deposition and the remaining amount of the mask.

  As an example, first, an etching apparatus having the structure shown in FIG. 1 was used, and a preparation process was performed on the semiconductor wafer W having the structure shown in FIG. 2 under the following conditions.

Pressure: 3.99 Pa (30 mTorr)
Processing gas: C ₄ F ₆ / Ar / O ₂ = 50/600/47 sccm
High frequency power (high frequency / low frequency): 1700W / 4500W
DC voltage: -300V
Gas flow ratio in the center: 50%
Helium gas pressure (center / periphery): 2.0 kPa / 5.32 kPa (15 Torr / 40 Torr)
Temperature (upper / side wall / lower): 150/150/10 ° C.

  FIG. 7 is a graph in which the vertical axis represents the bowing CD (nm) and the horizontal axis represents the remaining mask amount (nm), and the relationship between the bowing CD and the remaining mask amount in the above preparation process is shown. As indicated by the solid line B shown in FIG. 6, in this preparation step, the amount of increase in the bowing CD increased when the remaining amount of the mask was less than about 420 nm. Therefore, it was found that the vicinity of the mask remaining amount of 420 nm is the changing point (bending point). In this case, the initial opening diameter of the photoresist layer 205 is 53 nm, whereas the final bowing CD is 68 nm. An electron micrograph in this case is shown in FIG.

  From the result of the above preparation process, plasma etching was performed as the first plasma etching process under the same processing conditions as the above preparation process until the remaining amount of the mask reached 420 nm. In this case, the etching time was about 8 minutes. Thereafter, as a second plasma etching step, plasma etching was performed under the following conditions.

(Step 2-1)
Pressure: 3.99 Pa (30 mTorr)
Process _{gas: C 3 F 8 / Ar /} O 2 = 60/600 / 10sccm
High frequency power (high frequency / low frequency): 1700W / 4500W
DC voltage: -300V
Gas flow ratio in the center: 50%
Helium gas pressure (center / periphery): 2.0 kPa / 5.32 kPa (15 Torr / 40 Torr)
Temperature (upper / side wall / lower): 150/150/10 ° C.
Time: 10 seconds (2-2 process)
Pressure: 3.99 Pa (30 mTorr)
Processing gas: C ₄ F ₆ / Ar / O ₂ = 50/600/47 sccm
High frequency power (high frequency / low frequency): 1700W / 4500W
DC voltage: -300V
Gas flow ratio in the center: 50%
Helium gas pressure (center / periphery): 2.0 kPa / 5.32 kPa (15 Torr / 40 Torr)
Temperature (upper / side wall / lower): 150/150/10 ° C.
Time: 10 seconds

  The above-described 2-1 step and 2-2 step were alternately repeated a plurality of times to carry out the second plasma etching step. As a result, as shown by the dotted line A in the graph of FIG. 7, the increase amount of the bowing CD after the changing point (bending point) near the remaining mask amount of 420 nm could be suppressed. An electron micrograph in this case is shown in FIG. In this example, the initial opening diameter of the photoresist layer 205 was 53 nm, whereas the final bowing CD was 58 nm.

  Further, as shown in the electron micrograph of FIG. 8A, according to this example, compared with the case shown in FIG. 8B in the preparation process, the opening diameter of the upper end portion of the carbon layer 202 which is a mask layer. The (mask top CD) could be maintained in a large state. In addition, the result of having investigated the relationship between etching time and mask top CD using another sample is shown in FIG. As shown in the graph of FIG. 9, the mask top CD is gradually reduced in the first plasma etching step, but the mask top CD is gradually increased in the second plasma etching step. Therefore, the mask top CD is larger at the end of the second plasma etching process than at the end of the first plasma etching process.

  In the above embodiment and examples, the case where the silicon dioxide layer 201 is plasma-etched using the carbon layer 202 as a mask to form the high-aspect-ratio hole 201a has been described. However, the present invention is not limited to the semiconductor wafer W having such a configuration, but can also be applied to the formation of a high aspect ratio hole in the semiconductor wafer W having another structure. For example, as shown in FIG. 10, a structure in which a silicon dioxide layer 402 formed under the polysilicon layer 401, a silicon nitride film 403, and a silicon dioxide layer 404 is laminated using the polysilicon layer 401 as a mask. The same can be applied to the case where the hole 405 having a high aspect ratio is formed in the semiconductor wafer W.

  When the high aspect ratio hole 405 is formed in the semiconductor wafer W having the above structure, bowing occurs in the upper silicon dioxide layer 402, and the incident is deeper depending on the direction in which ions generated on the overhanging portion of the inner wall of the mask collide. When tilted, the upper side of the lower silicon dioxide layer 404 is etched and bowing occurs. However, bowing becomes more prominent in the upper silicon dioxide layer 402.

  The graph of FIG. 11 shows the results of measuring the relationship between the bowing CD of the upper silicon dioxide layer 402 and the remaining mask amount with the vertical axis as the bowing CD (nm) and the horizontal axis as the remaining mask amount (nm). . Also in this case, as in the case shown in FIG. 7, when the remaining amount of the mask decreases from a certain value (about 220 to 230 nm), the increase amount of the bowing CD increases. Therefore, it was found that the vicinity of the mask remaining amount of 220 to 230 nm is the changing point (bending point). Then, before and after the change point (bending point), switching from the first plasma etching step to the second plasma etching step is necessary while suppressing an increase in the bowing CD as in the above-described embodiments and examples. A selection ratio can be ensured.

  The change point (bending point) varies depending on various process conditions, mask CD, and mask material, but the remaining range of the mask layer is in the range of about 100 to 500 nm. Preferably it is the range of about 150-300 nm, Furthermore, it is the range of about 200-250 nm.

  Note that the remaining amount of the mask and the etching depth depend on the selection ratio (etching rate of the etching layer (oxide film) / etching rate of the mask) and the remaining amount of the mask decreases as the etching depth increases. is there. Therefore, as shown in the graph of FIG. 12 in which the vertical axis represents the bowing CD (nm) and the horizontal axis represents the etching depth, the bowing CD (nm) can be considered in relation to the etching depth. In this case, when the etching depth reaches a predetermined depth of about 1500 to 1600 nm, a changing point (bending point) where the amount of increase in the bowing CD increases appears.

  In the above embodiment, as shown in FIG. 3, the second plasma etching step is performed during the period of performing the 2-1 plasma etching step using the second processing gas (step 305 shown in FIG. 3). Description will be given of a case where a period of performing a 2-2 plasma etching process using a process gas (process 306 shown in FIG. 3) is alternately repeated a plurality of times in a short time (for example, about 10 seconds) until etching is completed. However, although the etching gas is alternately switched in this way, the gas component of the etching gas may be gradually switched.

For example, as shown in the graph of FIG. 13, in the first plasma etching process, as an etching gas,
_{C 4 F 8 / C 4 F} 6 / Ar / O 2 = 0/80/400 / 77sccm
In the second plasma etching step, C ₄ F ₈ is gradually increased, C ₄ F ₆ is gradually decreased, and O ₂ is also slightly decreased.
C ₄ F ₈ / C ₄ F ₆ / Ar / O ₂ = 100/0/400/50 sccm
And As described above, even if the gas components of the etching gas are gradually switched, the same effects as those of the above-described embodiments and examples can be obtained.

FIG. 14 shows the change in the shape of the sidewall in the hole 405 when the semiconductor wafer W having the structure shown in FIG. 10 is plasma etched to form the high aspect ratio hole 405 by SEM at each etching depth. The result of extracting the contour is shown. FIG. 14A shows a case where plasma etching is performed under the following conditions using one kind of etching gas from the beginning to the end.
Pressure: 2.66 Pa (20 mTorr)
Process _{gas: C 4 F 8 / C 4} F 6 / Ar / O 2 = 40/40/400 / 48sccm
High frequency power (high frequency / low frequency): 1700W / 6600W
DC voltage: -150 to -900V
Gas flow ratio in the center: 50%
Helium gas pressure (center / periphery): 2.0 kPa / 5.32 kPa (15 Torr / 40 Torr)
Temperature (upper / side wall / lower): 150/150/40 ° C

FIG. 14B shows the case where the plasma etching is performed by switching from the first plasma etching process to the second plasma etching process at the change point, and the plasma etching is performed under the following conditions.
(First plasma etching process)
Pressure: 2.66 Pa (20 mTorr)
Process _{gas: C 4 F 6 / Ar /} O 2 = 80/400 / 77sccm
High frequency power (high frequency / low frequency): 1700W / 6600W
DC voltage: -150 to -900V
Gas flow ratio in the center: 50%
Helium gas pressure (center / periphery): 2.0 kPa / 5.32 kPa (15 Torr / 40 Torr)
Temperature (upper / side wall / lower): 150/150/40 ° C
(Second plasma etching process)
Pressure: 2.66 Pa (20 mTorr)
Processing gas:
(initial)
C ₄ F ₆ / C ₄ F ₈ / Ar / O ₂ = 40/40/400/50 sccm
C ₄ F ₈ is gradually increased, C ₄ F ₆ is gradually decreased, and O ₂ is also slightly decreased.
(Last)
_{C 4 F 6 / C 4 F} 8 / Ar / O 2 = 0/80/400 / 35sccm
It was.
High frequency power (high frequency / low frequency): 1700W / 6600W
DC voltage: -150 to -900V
Gas flow ratio in the center: 50%
Helium gas pressure (center / periphery): 2.0 kPa / 5.32 kPa (15 Torr / 40 Torr)
Temperature (upper / side wall / lower): 150/150/40 ° C

  FIG. 14A shows the contours of the sidewalls when the etching depth is 1511 nm, 1592 nm, 1639 nm, and 1757 nm and overetching (two points). FIG. 14B shows the etching depth of 1395 nm, The outlines of the side walls at the time of over-etching (2 points) are shown at 1596 nm, 1741 nm, and 1883 nm. From FIG. 14, compared with the case of FIG. 14A in which the etching gas is not switched, the direction of FIG. 14B in which the etching gas is switched in the first plasma etching process and the second plasma etching process. However, it can be seen that bowing of the upper silicon dioxide layer 402 is particularly suppressed.

  As described above, according to the present embodiment and examples, it is possible to suppress the occurrence of bowing and form a contact hole with a high aspect ratio while maintaining the side wall shape vertical. In addition, this invention is not limited to said embodiment and Example, Various deformation | transformation are possible.

  W ... Semiconductor wafer, 201 ... Silicon dioxide layer, 202 ... Carbon layer, 203 ... SiON layer, 204 ... Antireflection layer, 205 ... Photoresist layer, 206 ... Opening.

Claims (11)

A plasma etching method for forming holes in a silicon oxide film through a mask layer by plasma of a processing gas containing carbon (C) and fluorine (F),
The remaining amount of the mask layer and the bowing of the holes are performed by plasma etching using a processing gas containing a first processing gas having a first ratio of carbon (C) to fluorine (F) (C / F). A step of examining the correlation with the CD and determining the remaining amount of the mask layer corresponding to the changing point at which the amount of change in the Boeing CD increases;
A first plasma etching step of performing plasma etching using a processing gas containing the first processing gas until the remaining amount of the mask layer reaches the change point;
A second plasma etching step performed after the first plasma etching step;
Comprising
In the second plasma etching step, at least a period of performing plasma etching using a processing gas containing a second processing gas having a smaller ratio (C / F) of carbon (C) to fluorine (F) than the first value. A plasma etching method comprising: The plasma etching method according to claim 1,
In the second plasma etching step, a period for performing plasma etching using the second processing gas and a period for performing plasma etching using the first processing gas are alternately repeated a plurality of times. Plasma etching method. The plasma etching method according to claim 1 or 2,
The plasma processing method, wherein the first processing gas is a C ₄ F ₆ gas and the second processing gas is a C ₃ F ₈ gas. The plasma etching method according to any one of claims 1 to 3,
The plasma etching method, wherein the mask layer includes a carbon layer. The plasma etching method according to claim 1,
In the second plasma etching step, the flow rate of the second processing gas is gradually increased. A plasma etching method according to claim 5,
The plasma etching method, wherein the mask layer includes a polysilicon layer. A plasma etching method according to claim 5 or 6,
The plasma processing method, wherein the first processing gas is C ₄ F ₆ gas and the second processing gas is C ₄ F ₈ gas. The plasma etching method according to any one of claims 1 to 7,
In the first plasma etching step, an opening size of the mask layer is smaller than an initial size,
In the second plasma etching step, the opening size of the mask layer is larger than the opening size of the mask layer at the end of the first plasma etching step. A plasma etching method according to any one of claims 1 to 8,
The remaining amount of the mask layer corresponding to the change point is larger than 400 nm when the initial opening dimension of the mask layer is larger than 50 nm, and is 400 nm when the initial opening dimension of the mask layer is smaller than 50 nm. A plasma etching method characterized by being smaller. A processing chamber for accommodating a substrate to be processed;
A processing gas supply mechanism for supplying a processing gas into the processing chamber;
A computer recording medium on which a control program for controlling a plasma etching apparatus having a plasma generation mechanism for generating plasma of the processing gas is recorded,
The computer control medium controls the plasma etching apparatus so that the plasma etching method according to any one of claims 1 to 9 is executed. A plasma etching method according to any one of claims 1 to 9,
The plasma etching method, wherein the remaining amount of the mask layer corresponding to the change point is 100 to 500 nm.

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