JP4890025B2 - Etching method and recording medium - Google Patents

Description

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

For example, in a semiconductor device manufacturing process, a method of dry etching a silicon oxide film existing on the surface of a semiconductor wafer (hereinafter referred to as “wafer”) without using plasma is known (Patent Documents 1, 2, and 5). 3). In such a dry etching method, the inside of the chamber in which the wafer is housed is brought to a low pressure state close to a vacuum state, and the temperature of the wafer is adjusted to a predetermined temperature, while hydrogen fluoride gas (HF) and ammonia gas (NH ₃ ) are contained in the chamber. A modification process in which a mixed gas containing gas is supplied to alter the silicon oxide film to produce a reaction product, and a heating process in which the reaction product is heated to vaporize (sublimate) the surface of the silicon oxide film. The silicon oxide film is etched by changing to a reaction product and then removing it by heating.

  By the way, there are various types of silicon oxide films with different causes and film formation methods. For example, natural oxide films that are naturally generated on silicon by leaving the wafer in the atmosphere, and chemical processing. There are chemical oxide films, CVD oxide films (thermal oxide films, BPSG, etc.) formed by CVD reaction using a CVD (Chemical Vapor Deposition) apparatus. Among these silicon oxide films, the reaction of the mixed gas selectively and actively takes place in the alteration process of the etching method is a natural oxide film, a chemical oxide film, etc., even if the same silicon oxide film is used. However, it is not actively applied to CVD-based oxide films. That is, the above dry etching method has a high etching selectivity with respect to a natural oxide film or a chemical oxide film, and can efficiently remove only the natural oxide film or the chemical oxide film while suppressing the etching of other structures. it can. Therefore, this dry etching method is suitable for a process of removing a natural oxide film or a chemical oxide film adhering to the wafer, for example, as a pretreatment before performing a film forming process on the wafer.

  On the other hand, as a method for etching a CVD oxide film, wet etching using a chemical solution, plasma etching using reactive gas plasma, and the like are performed.

US Patent Application Publication No. 2004/0182417 US Patent Application Publication No. 2004/0184792 JP 2005-39185 A

  However, in the wet etching of a CVD oxide film, there is a problem that other films formed on the wafer are likely to be adversely affected by the chemical solution. In addition, plasma etching has a problem in that electrical damage (charge-up damage) caused by plasma occurs on the wafer. Therefore, it is desired to develop a new method for etching a CVD-based oxide film. For example, it is conceivable to apply a plasmaless dry etching method comprising the above-described alteration process and heating process. However, in the dry etching method, the reaction rate with respect to the CVD oxide film in the alteration process is slow, so that the alteration process takes a long time and the efficiency is poor. Further, the alteration of the oxide film (generation of the reaction product) has a property that when it progresses to a certain depth from the surface of the oxide film, it enters a saturation state (Saturation) and does not progress further. That is, there is a limit to the etching amount that can be etched by one alteration process and heating process. Therefore, in order to obtain the etching amount required for the CVD oxide film, it is necessary to repeat the alteration process and the heating process a plurality of times, which is very inefficient.

  The present invention has been made in view of the above points, and an object thereof is to provide an etching method capable of efficiently dry-etching various types of silicon oxide films.

In order to solve the above problems, according to the present invention, there is provided a method for etching a silicon oxide film made of a BPSG film, wherein a mixed gas containing hydrogen fluoride gas and ammonia gas is supplied to the surface of the silicon oxide film. , A chemical modification reaction between the silicon oxide film and the mixed gas, a modification process for modifying the silicon oxide film to generate a reaction product, and a heating process for heating and removing the reaction product, An etching method characterized in that, in the alteration step, a partial pressure of the hydrogen fluoride gas in the mixed gas is set to 15 mTorr or more , and a temperature range of the silicon oxide film is set to 35 ° C. or more and 100 ° C. or less. Provided.
According to another aspect of the present invention, there is provided a method for etching a BPSG film on a wafer surface on which a BPSG film and a CVD-based silicon oxide film formed using a bias high-density plasma CVD method are formed. , A denatured step of supplying a mixed gas containing hydrogen fluoride gas and ammonia gas, causing a chemical reaction between the BPSG film and the mixed gas, and modifying the BPSG film to generate a reaction product, and the reaction product In the alteration step, the partial pressure of the ammonia gas in the mixed gas is made smaller than the partial pressure of the hydrogen fluoride gas , and the temperature range of the BPSG film An etching method is provided in which the temperature is 35 ° C. or higher and 100 ° C. or lower .

Here, the process of generating a reaction product by modifying the silicon oxide film (BPSG film) present on the surface of the substrate is, for example, a COR (Chemical Oxide Removal) process (chemical oxide removal process). In the COR process, a gas containing a halogen element and a basic gas are supplied to a substrate as a processing gas, whereby a silicon oxide film on the substrate and a gas molecule of the processing gas are chemically reacted to generate a reaction product. is there. The gas containing a halogen element is, for example, hydrogen fluoride gas (HF), and the basic gas is, for example, ammonia gas (NH ₃ ). In this case, mainly ammonium fluorosilicate ((NH ₄ ) ₂ SiF ₆ ) And water (H ₂ O). The process for removing the reaction product by heating is, for example, a PHT (Post Heat Treatment) process. The PHT process is a process in which the wafer after the COR process is heated to vaporize (sublimate) a reaction product such as ammonium fluorosilicate.

  The etching amount of the reaction product may be 30 nanometers or more.

  Furthermore, according to the present invention, there is provided a recording medium on which a program that can be executed by a control computer of a processing system is recorded, and the program is executed by the control computer, whereby the processing system includes There is provided a recording medium characterized by performing any one of the etching methods.

  According to the present invention, the silicon oxide film can be efficiently dry etched. Since plasma is not used, there is no fear of causing charge-up damage due to plasma on a wafer or the like. There is no worry of adversely affecting other parts other than the etching target.

Hereinafter, preferred embodiments of the present invention will be described. First, the structure of a wafer that is a substrate processed by the etching method according to the present embodiment will be described. FIG. 1 is a schematic cross-sectional view of a wafer W in the process of forming a DRAM (Dynamic Random Access Memory) as a semiconductor device, and shows a part of the surface (device formation surface) of the wafer W. The wafer W is, for example, a thin silicon wafer formed in a substantially disk shape, and a BPSG (Boron-Doped Phospho Silicate Glass) film, which is an insulating film, is formed on the surface of the Si (silicon) layer. Yes. BPSG is a silicon oxide film (silicon dioxide (SiO ₂ )) containing boron (B) and phosphorus (P). The BPSG film is a CVD silicon oxide film formed on the surface of the wafer W by a thermal CVD method in a CVD (Chemical Vapor Deposition) apparatus or the like.

  Two gate portions G each having a gate electrode are provided side by side on the upper surface of the BPSG film. Each gate portion G includes a gate electrode, a hard mask (HM) layer, and a side wall (side wall). The gate electrode is, for example, a Poly-Si (polycrystalline silicon) layer, and is formed side by side on the upper surface of the BPSG film. For example, a WSi (tungsten silicide) layer is formed on the upper surface of each Poly-Si layer. The HM layer is made of an insulator such as SiN (silicon nitride), and is formed on the upper surface of each WSi layer. The side wall portion is an insulator such as a SiN film, and is formed so as to cover both sides of each Poly-Si layer, WSi layer, and HM layer. The lower end portion of the SiN film is formed up to a position in contact with the upper surface of the BPSG film.

Further, an HDP-SiO ₂ film (silicon oxide film), for example, is formed above the BPSG film so as to cover the entire BPSG film and the two gate portions G. This HDP-SiO ₂ film is a CVD-based silicon oxide film (plasma CVD oxide film) formed by using a bias high-density plasma CVD method (HDP-CVD method), and is used as an interlayer insulating film. Note that the HDP-SiO ₂ film and the BPSG film are both CVD-based oxide films, but the HDP-SiO ₂ film has a higher density and is harder than the BPSG film. A film is not yet formed on the surface of the HDP-SiO ₂ film, and is exposed.

In the HDP-SiO ₂ film, a contact hole H is formed between two gate portions G (between SiN films formed on each gate portion G). The contact hole H is formed so as to penetrate from the surface of the HDP-SiO ₂ film to the surface of the BPSG film. On the inner side of the contact hole H, a part of the upper surface of the HM layer of each gate portion G and the SiN film provided so as to face each other are exposed, and at the bottom of the contact hole H, , The surface of the BPSG film is exposed. The contact hole H is formed by selectively (anisotropically) etching the HDP-SiO ₂ film with respect to the SiN film and the HM layer of the gate portion G by, for example, plasma etching or the like.

  Next, a processing system for etching the BPSG film exposed at the bottom of the contact hole H on the wafer W will be described. The processing system 1 shown in FIG. 2 includes a load / unload unit 2 for loading / unloading the wafer W into / from the processing system 1, two load lock chambers 3 provided adjacent to the load / unload unit 2, and each load lock chamber 3. COR (Chemical Oxide Removal) processing as an alteration process provided adjacent to each PHT processing apparatus 4 and each PHT processing apparatus 4 for performing a PHT (Post Heat Treatment) process as a heating process. A COR processing device 5 that performs the process and a control computer 8 that gives control commands to each part of the processing system 1 are provided. The PHT processing device 4 and the COR processing device 5 respectively connected to each load lock chamber 3 are arranged in a straight line in this order from the load lock chamber 3 side.

  The loading / unloading unit 2 has a transfer chamber 12 in which a first wafer transfer mechanism 11 for transferring a wafer W having a substantially disk shape, for example, is provided. The wafer transfer mechanism 11 has two transfer arms 11a and 11b that hold the wafer W substantially horizontally. On the side of the transfer chamber 12, for example, three mounting tables 13 are provided on which carriers 13 a that can accommodate a plurality of wafers W are arranged. In addition, an orienter 14 is installed for rotating and aligning the wafer W by optically determining the amount of eccentricity.

  In the loading / unloading unit 2, the wafer W is held by the transfer arms 11 a and 11 b, and is transferred to a desired position by being rotated and linearly moved and moved up and down in a substantially horizontal plane by driving the wafer transfer device 11. . The transfer arms 11 a and 11 b are moved forward and backward with respect to the carrier 13 a, the orienter 14, and the load lock chamber 3 on the mounting table 10, so that they can be carried in and out.

  Each load lock chamber 3 is connected to the transfer chamber 12 with a gate valve 16 provided between the load lock chamber 3 and the transfer chamber 12. In each load lock chamber 3, a second wafer transfer mechanism 17 for transferring the wafer W is provided. The wafer transfer mechanism 17 has a transfer arm 17a that holds the wafer W substantially horizontally. Further, the load lock chamber 3 can be evacuated.

  In the load lock chamber 3, the wafer W is held by the transfer arm 17 a, and is transferred by being rotated and moved in a substantially horizontal plane and moved up and down by driving the wafer transfer mechanism 17. Then, the transfer arm 17a is moved back and forth with respect to the PHT processing apparatus 4 connected in series to each load lock chamber 3, whereby the wafer W is carried into and out of the PHT processing apparatus 4. Further, the wafer W is carried into and out of the COR processing apparatus 5 by moving the transfer arm 17a forward and backward with respect to the COR processing apparatus 5 via each PHT processing apparatus 4.

  The PHT processing apparatus 4 includes a sealed processing chamber (processing space) 21 in which the wafer W is stored. Although not shown, a loading / unloading port for loading / unloading the wafer W into / from the processing chamber 21 is provided, and a gate valve 22 for opening / closing the loading / unloading port is provided. The processing chamber 21 is connected to the load lock chamber 3 with a gate valve 22 provided between the processing chamber 21 and the load lock chamber 3.

As shown in FIG. 3, a mounting table 23 is provided in the processing chamber 21 of the PHT processing apparatus 4 for mounting the wafer W substantially horizontally. Furthermore, a supply mechanism 26 having a supply path 25 for supplying an inert gas such as nitrogen gas (N ₂ ) to the process chamber 21 by heating, and an exhaust mechanism 28 having an exhaust path 27 for exhausting the process chamber 21 are provided. Is provided. The supply path 25 is connected to a nitrogen gas supply source 30. The supply passage 25 is provided with a flow rate adjusting valve 31 that can open and close the supply passage 25 and adjust the supply flow rate of nitrogen gas. The exhaust passage 27 is provided with an open / close valve 32 and an exhaust pump 33 for forced exhaust.

  The operation of each part of the PHT processing device 4 such as the gate valve 22, the flow rate adjustment valve 31, the on-off valve 32, and the exhaust pump 33 is controlled by a control command of the control computer 8. That is, the supply of nitrogen gas by the supply mechanism 26 and the exhaust by the exhaust mechanism 28 are controlled by the control computer 8.

  As shown in FIG. 4, the COR processing apparatus 5 includes a chamber 40 having a sealed structure, and the inside of the chamber 40 is a processing chamber (processing space) 41 in which the wafer W is stored. Inside the chamber 40, a mounting table 42 for mounting the wafer W in a substantially horizontal state is provided. Further, the COR processing apparatus 5 is provided with a supply mechanism 43 that supplies gas to the processing chamber 41 and an exhaust mechanism 44 that exhausts the inside of the processing chamber 41.

  A loading / unloading port 53 for loading / unloading the wafer W into / from the processing chamber 41 is provided on the side wall of the chamber 40, and a gate valve 54 for opening / closing the loading / unloading port 53 is provided. The processing chamber 41 is connected to the processing chamber 21 with a gate valve 54 provided between the processing chamber 41 and the processing chamber 21 of the PHT processing apparatus 4. A shower head 52 having a plurality of discharge ports for discharging process gas is provided on the ceiling of the chamber 40.

  The mounting table 42 has a substantially circular shape in plan view, and is fixed to the bottom of the chamber 40. A temperature controller 55 that adjusts the temperature of the mounting table 42 is provided inside the mounting table 42. The temperature controller 55 is provided with a pipe line through which, for example, a temperature adjusting liquid (for example, water) is circulated, and heat exchange is performed with the liquid flowing in the pipe line so that the temperature of the upper surface of the mounting table 42 is increased. Further, the temperature of the wafer W is adjusted by exchanging heat between the mounting table 42 and the wafer W on the mounting table 42. The temperature controller 55 is not limited to this, and may be, for example, an electric heater that heats the mounting table 42 and the wafer W using resistance heat.

The supply mechanism 43 includes the above-described shower head 52, a hydrogen fluoride gas supply path 61 that supplies hydrogen fluoride gas (HF) to the processing chamber 41, and an ammonia gas supply path that supplies ammonia gas (NH ₃ ) to the processing chamber 41. 62, an argon gas supply path 63 for supplying argon gas (Ar) as an inert gas to the processing chamber 41, and a nitrogen gas supply path 64 for supplying nitrogen gas (N ₂ ) as an inert gas to the processing chamber 41. . The hydrogen fluoride gas supply path 61, the ammonia gas supply path 62, the argon gas supply path 63, and the nitrogen gas supply path 64 are connected to the shower head 52, and the treatment chamber 41 is fluorinated via the shower head 52. Hydrogen gas, ammonia gas, argon gas, and nitrogen gas are discharged so as to be diffused.

  The hydrogen fluoride gas supply path 61 is connected to a hydrogen fluoride gas supply source 71. The hydrogen fluoride gas supply path 61 is provided with a flow rate adjusting valve 72 capable of opening / closing the hydrogen fluoride gas supply path 61 and adjusting the supply flow rate of the hydrogen fluoride gas. The ammonia gas supply path 62 is connected to an ammonia gas supply source 73. The ammonia gas supply path 62 is provided with a flow rate adjusting valve 74 capable of opening / closing the ammonia gas supply path 62 and adjusting the supply flow rate of the ammonia gas. The argon gas supply path 63 is connected to an argon gas supply source 75. Further, the argon gas supply path 63 is provided with a flow rate adjusting valve 76 capable of opening / closing the argon gas supply path 63 and adjusting the supply flow rate of the argon gas. The nitrogen gas supply path 64 is connected to a nitrogen gas supply source 77. The nitrogen gas supply path 64 is provided with a flow rate adjusting valve 78 that can open and close the nitrogen gas supply path 64 and adjust the supply flow rate of the nitrogen gas.

  The exhaust mechanism 44 includes an exhaust passage 85 in which an open / close valve 82 and an exhaust pump 83 for performing forced exhaust are interposed. An end opening of the exhaust path 85 is opened at the bottom of the chamber 40.

  The operation of each part such as the gate valve 54, the temperature controller 55, the flow rate adjusting valves 72, 74, 76, 78, the on-off valve 72, the exhaust pump 83, etc. It has come to be. That is, supply of hydrogen fluoride gas, ammonia gas, argon gas, nitrogen gas by the supply mechanism 43, exhaust by the exhaust mechanism 44, temperature adjustment by the temperature controller 55, and the like are controlled by the control computer 8.

  Each functional element of the processing system 1 is connected to a control computer 8 that automatically controls the operation of the entire processing system 1 via signal lines. Here, the functional elements include, for example, the wafer transfer mechanism 11, the wafer transfer mechanism 17, the gate valve 22 of the PHT processing device 4, the flow rate adjusting valve 31, the exhaust pump 33, the gate valve 54 of the COR processing device 5, and the temperature control. This means all elements that operate to realize predetermined process conditions, such as the vessel 55, the flow rate adjusting valves 72, 74, 76, 78, the on-off valve 72, the exhaust pump 83, and the like. The control computer 8 is typically a general-purpose computer that can realize any function depending on the software to be executed.

  As shown in FIG. 2, the control computer 8 includes a calculation unit 8a having a CPU (central processing unit), an input / output unit 8b connected to the calculation unit 8a, and control software inserted into the input / output unit 8b. And a stored recording medium 8c. The recording medium 8c stores control software (program) that is executed by the control computer 8 to cause the processing system 1 to perform a predetermined substrate processing method to be described later. By executing the control software, the control computer 8 realizes various process conditions (for example, pressure in the processing chamber 41) defined for each functional element of the processing system 1 by a predetermined process recipe. To control. That is, as will be described in detail later, a control command for realizing an etching method in which the COR processing step in the COR processing device 5 and the PHT processing step in the PHT processing device 4 are performed in this order is given.

  The recording medium 8c may be fixedly provided in the control computer 8, or may be detachably attached to a reading device (not shown) provided in the control computer 8 and readable by the reading device. In the most typical embodiment, the recording medium 8 c is a hard disk drive in which control software is installed by a service person of the manufacturer of the processing system 1. In another embodiment, the recording medium 8c is a removable disk such as a CD-ROM or DVD-ROM in which control software is written. Such a removable disk is read by an optical reading device (not shown) provided in the control computer 8. Further, the recording medium 8c may be in any format of RAM (random access memory) or ROM (read only memory). Further, the recording medium 8c may be a cassette type ROM. In short, any medium known in the technical field of computers can be used as the recording medium 8c. In a factory where a plurality of processing systems 1 are arranged, control software may be stored in a management computer that comprehensively controls the control computer 8 of each processing system 1. In this case, each processing system 1 is operated by a management computer via a communication line and executes a predetermined process.

Next, a wafer W processing method in the processing system 1 configured as described above will be described. First, as shown in FIG. 1, the wafer W in which the contact hole H is formed in the HDP-SiO ₂ film is accommodated in the carrier 13 a and transferred to the processing system 1.

  In the processing system 1, as shown in FIG. 2, a carrier 13 a storing a plurality of wafers W is placed on the mounting table 13, and one wafer W is taken out from the carrier 13 a by the wafer transport mechanism 11. , Are loaded into the load lock chamber 3. When the wafer W is loaded into the load lock chamber 3, the load lock chamber 3 is sealed and decompressed. Thereafter, the gate valves 22 and 54 are opened, and the load lock chamber 3 is communicated with the processing chamber 21 of the PHT processing apparatus 4 and the processing chamber 41 of the COR processing apparatus 5 that are respectively decompressed with respect to the atmospheric pressure. The wafer W is unloaded from the load lock chamber 3 by the wafer transfer mechanism 17 and is moved straight so as to pass through the loading / unloading port (not shown) of the processing chamber 21, the processing chamber 21, and the loading / unloading port 53 in this order. It is carried into the chamber 41.

  In the processing chamber 41, the wafer W is transferred from the transfer arm 17 a of the wafer transfer mechanism 17 to the mounting table 42 with the device formation surface as the upper surface. When the wafer W is loaded, the transfer arm 17a is withdrawn from the processing chamber 41, the loading / unloading port 53 is closed, and the processing chamber 41 is sealed. Then, the COR processing process is started.

  After the processing chamber 41 is sealed, ammonia gas, argon gas, and nitrogen gas are supplied to the processing chamber 41 from an ammonia gas supply path 62, an argon gas supply path 63, and a nitrogen gas supply path 64, respectively. Further, the pressure in the processing chamber 41 is set to a lower pressure than the atmospheric pressure. Further, the temperature of the wafer W on the mounting table 42 is adjusted to a predetermined target value (for example, about 35 ° C.) by the temperature controller 55.

  Thereafter, hydrogen fluoride gas is supplied from the hydrogen fluoride gas supply path 61 to the processing chamber 41. Here, since ammonia gas is supplied to the processing chamber 41 in advance, by supplying hydrogen fluoride gas, the atmosphere of the processing chamber 41 is a processing atmosphere composed of a mixed gas containing hydrogen fluoride gas and ammonia gas. To be. Thus, the COR process is performed on the wafer W by supplying the mixed gas to the surface of the wafer W in the processing chamber 41.

  Due to the low-pressure processing atmosphere in the processing chamber 41, the BPSG film existing at the bottom of the contact hole H on the surface of the wafer W chemically reacts with the molecules of hydrogen fluoride gas and ammonia gas in the mixed gas. It is transformed into a product (see FIG. 5). As the reaction product, ammonium fluorosilicate, moisture and the like are generated. Since this chemical reaction proceeds isotropically, the chemical reaction proceeds from the bottom of the contact hole H to the upper surface of the Si layer, and also proceeds from directly below the contact hole H to the lateral direction above the Si layer.

  During the COR process, by adjusting the supply flow rate of each process gas, the supply flow rate of the inert gas, the exhaust flow rate, etc., the mixed gas (processing atmosphere) is reduced to a constant pressure (for example, about 80 mTorr (about 80 mTorr)). So that the pressure is maintained at about 10.7 Pa). Further, the partial pressure of hydrogen fluoride gas in the mixed gas may be adjusted to be about 15 mTorr (about 2.00 Pa) or more. As described above, the temperature of the wafer W, that is, the temperature of the portion where the chemical reaction is performed in the BPSG film (the temperature of the portion where the BPSG film and the mixed gas are in contact) is, for example, a constant temperature of about 35 ° C. or more. May be maintained. Thereby, a chemical reaction is accelerated | stimulated, the production | generation speed | rate of a reaction product is raised, and the layer of a reaction product can be formed rapidly. Further, the depth at which the chemical reaction is saturated (the distance from the surface of the BPSG film to the position where the chemical reaction stops) can be made sufficiently deep. That is, until the reaction product layer reaches the upper surface of the Si layer, the chemical reaction is sufficiently performed without stopping. Note that the sublimation point of ammonium fluorosilicate in the reaction product is about 100 ° C., and if the temperature of the wafer W is 100 ° C. or higher, the reaction product may not be generated satisfactorily. Therefore, it is preferable that the temperature of the wafer W is about 100 ° C. or less.

  The depth at which the chemical reaction becomes saturated depends on the type of silicon oxide film (BPSG film in this embodiment) that is the object to be altered, the temperature of the silicon oxide film (or the mixed gas in contact with the silicon oxide film). Temperature) and the partial pressure of the hydrogen fluoride gas in the mixed gas. That is, by adjusting the temperature of the silicon oxide film and the partial pressure of the hydrogen fluoride gas according to the type of silicon oxide film, the depth at which the chemical reaction becomes saturated, the amount of reaction products generated, etc. Thus, the etching amount after the PHT process, which will be described in detail later, can be controlled. In the case of a BPSG film, the depth at which the chemical reaction becomes saturated, that is, the etching amount can be about 30 nm (nanometers) or more.

  In the conventional COR process, the temperature of the wafer W is set to about 30 ° C. or less. In addition, even if the partial pressure of hydrogen fluoride gas in the mixed gas is increased, the chemical reaction has progressed only to a certain depth, so the etching amount is considered to be limited. The amount of etching that can be reliably etched is, for example, about 30 nm or less for a BPSG film. On the other hand, in this embodiment, the temperature of the wafer W is set to 35 ° C. or higher, which is higher than the conventional temperature, and the partial pressure of the hydrogen fluoride gas in the mixed gas is increased to about 15 mTorr or higher. Thus, the depth at which the chemical reaction becomes saturated can be increased, and a sufficient etching amount can be applied even with a single COR process.

By the way, in the COR process, the HDP-SiO ₂ film formed above the BPSG film can also be chemically reacted with the mixed gas, so that the HDP-SiO ₂ film may be altered. In order to suppress the alteration of the HDP-SiO ₂ film, the partial pressure of ammonia gas in the mixed gas is preferably made smaller than the partial pressure of hydrogen fluoride gas. That is, the ammonia gas supply flow rate is preferably smaller than the hydrogen fluoride gas supply flow rate. By doing so, it is possible to prevent the chemical reaction from proceeding in the HDP-SiO ₂ film while the chemical reaction is actively proceeding in the BPSG film. That is, it is possible to selectively and efficiently alter only the BPSG film while suppressing alteration of the HDP-SiO ₂ film or the like. Therefore, damage to the HDP-SiO ₂ film can be prevented. Thus, by adjusting the partial pressure of the ammonia gas in the mixed gas, the BPSG film and the HDP-SiO ₂ film, that is, the same silicon oxide film, but having different densities, compositions, film forming methods, etc. In the meantime, the reaction rate of the chemical reaction, the amount of reaction products generated, and the like can be made different from each other. Consequently, the etching amounts after the PHT process described in detail later can be made different from each other. The chemical reaction when the partial pressure of ammonia gas is smaller than the partial pressure of hydrogen fluoride gas is not a reaction rate-determining method in which the production rate of the reaction product is determined by the chemical reaction between the BPSG film and the mixed gas. It is considered that the supply rate-controlled reaction is determined in which the generation rate of the reaction product is determined by the supply flow rate of the hydrogen gas.

  When the reaction product layer is sufficiently formed and the COR process is completed, the process chamber 41 is forcibly evacuated and depressurized. Thereby, hydrogen fluoride gas and ammonia gas are forcibly discharged from the processing chamber 41. When the forced exhaust of the processing chamber 41 is completed, the loading / unloading port 53 is opened, and the wafer W is unloaded from the processing chamber 41 by the wafer transfer mechanism 17 and loaded into the processing chamber 21 of the PHT processing apparatus 4. As described above, the COR processing step is completed.

In the PHT processing apparatus 4, the wafer W is placed in the processing chamber 21 with the surface as the upper surface. When the wafer W is loaded, the transfer arm 17a is withdrawn from the processing chamber 21, the processing chamber 21 is sealed, and the PHT processing step is started. In the PHT process, while the processing chamber 21 is evacuated, a high-temperature heating gas is supplied into the processing chamber 21 to raise the temperature of the processing chamber 21. As a result, the reaction product generated by the COR process is heated and vaporized, and is discharged from below the contact hole H to the outside of the HDP-SiO ₂ film (outside the wafer W) through the contact hole H. . That is, as shown in FIG. 6, by removing the reaction product from the BPSG film, a space H ′ communicating with the bottom of the contact hole H is formed above the Si layer, and a new surface of the BPSG film is formed. Is exposed. In this way, the reaction product is removed by performing the PHT process after the COR process, and the BPSG film can be isotropically dry-etched.

Thus, by performing the PHT process after the COR process, the BPSG film can be etched to a predetermined depth. In the above-described COR process, the HDP-SiO ₂ film, which is a silicon oxide film, undergoes a slight chemical reaction with the mixed gas, so that the surface of the HDP-SiO ₂ film is altered and a small amount of reaction occurs. Although the product is generated, as described above, the BPSG film and the HDP-SiO ₂ film have different amounts of reaction products, and the depth at which the reaction product is generated in the HDP-SiO ₂ film. This is very small compared to the depth at which reaction products are generated in the BPSG film. Therefore, the depth at which the reaction product is removed from the HDP-SiO ₂ film by the PHT treatment, that is, the etching amount can be suppressed to an extremely small amount as compared with the etching amount of the BPSG film. As described above, by adjusting the partial pressure of the ammonia gas in the mixed gas to be smaller than the partial pressure of the hydrogen fluoride gas in the COR processing, the etching amount of each silicon oxide film after the PHT processing can be adjusted. . That is, the etching selectivity can be adjusted. In this embodiment, the etching selectivity of the BPSG film can be made higher than other structures such as the HDP-SiO ₂ film.

  When the PHT process is completed, the supply of the heated gas is stopped, and the loading / unloading port of the PHT processing apparatus 4 is opened. Thereafter, the wafer W is unloaded from the processing chamber 21 by the wafer transfer mechanism 17 and returned to the load lock chamber 3. Thus, the PHT processing process in the PHT processing device 4 is completed.

  After the wafer W is returned to the load lock chamber 3 and the load lock chamber 3 is sealed, the load lock chamber 3 and the transfer chamber 12 are communicated with each other. Then, the wafer transport mechanism 11 unloads the wafer W from the load lock chamber 3 and returns it to the carrier 13 a on the mounting table 13. As described above, a series of etching steps in the processing system 1 is completed.

The wafer W after the etching process is completed in the processing system 1 is carried into a film forming apparatus such as a CVD apparatus in another processing system, and a film forming process such as a CVD method is performed on the wafer W. Is called. In such a film formation process, film formation is performed so as to fill the contact hole H and the space H ′ as shown in FIG. Thereby, the capacitor C is formed in the contact hole H and the space H ′. The capacitor C is formed so as to penetrate the HDP-SiO ₂ film and the BPSG film between the gate portions G, and the lower end portion of the capacitor C is connected to the upper surface of the Si layer in the space H ′.

  According to this processing system 1, the BPSG film can be efficiently dry etched without using plasma. Therefore, there is no fear of adversely affecting other structures (films, layers, etc.) other than the BPSG film formed on the wafer, such as charge-up damage caused by plasma. Also, by adjusting the partial pressure of hydrogen fluoride gas and the temperature of the BPSG film, the speed of the chemical reaction to the BPSG film in the COR processing process can be improved, and the chemical reaction is saturated in the COR processing process. Can be deep enough. Accordingly, the throughput of the COR processing step can be improved and the etching amount of the BPSG film can be improved. A sufficient etching amount can be obtained at one time without repeating the COR processing step and the PHT processing step a plurality of times.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to such examples. It is obvious for those skilled in the art that various changes and modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  The type of gas supplied to the processing chamber 41 in addition to the hydrogen fluoride gas and ammonia gas is not limited to the combinations shown in the above embodiments. For example, the inert gas supplied to the processing chamber 41 may be only argon gas. The inert gas may be any other inert gas, for example, helium gas (He) or xenon gas (Xe), or argon gas, nitrogen gas, helium gas, or xenon gas. Of these, a mixture of two or more gases may be used.

  The structure of the processing system 1 is not limited to that shown in the above embodiment. For example, in addition to the COR processing apparatus and the PHT processing apparatus, a processing system including a film forming apparatus may be used. For example, as in the processing system 90 shown in FIG. 8, a common transfer chamber 92 having a wafer transfer mechanism 91 is connected to the transfer chamber 12 via a load lock chamber 93, and around the common transfer chamber 92, A COR processing apparatus 95 and a PHT processing apparatus 96, for example, a film forming apparatus 97 such as a CVD apparatus may be provided. In the processing system 90, the wafer W is transferred into and out of the load lock chamber 92, the COR processing device 95, the PHT processing device 96, and the film forming device 97 by the wafer transfer mechanism 91. The common transfer chamber 92 can be evacuated. That is, by making the common transfer chamber 92 in a vacuum state, the wafer W unloaded from the PHT processing apparatus 96 can be loaded into the film forming apparatus 97 without being brought into contact with oxygen in the atmosphere. Therefore, it is possible to prevent the natural oxide film from adhering to the wafer W after the PHT process, and film formation (capacitor C formation) can be suitably performed.

  In the above embodiment, the silicon wafer W, which is a semiconductor wafer, is exemplified as the substrate having the silicon oxide film. However, the substrate is not limited to this, and other types, for example, glass for LCD substrates, CD substrates, A printed board, a ceramic board, etc. may be sufficient.

  Further, the structure of the substrate processed in the processing system 1 is not limited to that described in the above embodiment. Further, the etching performed in the processing system 1 is not limited to the etching performed on the bottom of the contact hole H before the formation of the capacitor C as shown in the embodiment, and the present invention is not limited to various parts. The etching method can be applied.

The silicon oxide film to be etched in the processing system 1 is not limited to the BPSG film, and may be another type of silicon oxide film such as an HDP-SiO ₂ film. Also in this case, the reaction product is saturated by adjusting the temperature of the silicon oxide film in the COR processing step and the partial pressure of the hydrogen fluoride gas in the mixed gas according to the type of the silicon oxide film. Depth, etching amount, etc. can be controlled. In particular, it is possible to increase the depth at which the reaction product is saturated and to improve the etching amount, compared to the etching method performed in the conventional natural oxide film and chemical oxide film.

  In addition, regarding the CVD-based oxide film formed on the substrate, the type of the CVD method used for forming the CVD-based oxide film is not particularly limited. For example, a thermal CVD method, an atmospheric pressure CVD method, a low pressure CVD method, a plasma CVD method, or the like may be used.

  Furthermore, the present invention relates to silicon oxide films such as silicon oxide films other than CVD oxide films, such as natural oxide films, chemical oxide films generated by chemical treatment in resist removal processes, thermal oxide films formed by thermal oxidation, and the like. It can also be applied to film etching. Even in such a silicon oxide film other than the CVD oxide film, the etching amount can be increased or decreased by adjusting the partial pressure of the hydrogen fluoride gas and the temperature of the silicon oxide film in the COR process.

  For example, after processing in the previous processing step (resist removal step or the like) and before the next processing step (film formation step) is performed, the wafer W is left for a long time, and a natural oxide film is formed on the wafer W. Even if it is formed thick, the natural oxide film can be sufficiently removed by performing the natural oxide film removing step by the etching method according to the present invention immediately before performing the next processing step. Therefore, it is possible to extend the waiting time until the natural oxide film removal process or the next processing process is performed after the previous processing process is completed. Therefore, the management time (Q-time) can be given a degree of freedom.

  If a natural oxide film and another silicon oxide film (BPSG) such as an interlayer insulating film are mixed on the wafer W and it is desired to remove only the natural oxide film, the temperature of the wafer W is lowered in the COR process. Alternatively, the partial pressure of hydrogen fluoride gas in the mixed gas should be adjusted low. For example, the temperature of the wafer W may be about 30 ° C. or less, and the partial pressure of the hydrogen fluoride gas in the mixed gas may be about 15 mTorr or less. As a result, the natural oxide film can be efficiently altered while suppressing the alteration of other silicon oxide films such as an interlayer insulating film. That is, the natural oxide film can be efficiently removed while suppressing damage to other structures.

As a structure in which a natural oxide film and other types of silicon oxide films are mixed on a wafer, for example, there is a structure as shown in FIG. In FIG. 9, a Si layer is formed on the surface of a wafer W ′, and two gate portions G ′ having gate electrodes are provided side by side on the upper surface. Each gate portion G ′ includes a gate electrode, a hard mask (HM) layer, and a side wall (side wall). That is, two SiO ₂ films, which are gate oxide films, are formed on the upper surface of the Si layer, a Poly-Si layer as a gate electrode is formed on the upper surface of each SiO ₂ film, and an upper surface of each Poly-Si layer is formed. , SiN layers are respectively formed. Side wall portions made of an insulator are formed on both side surfaces of each SiO ₂ film, Poly-Si layer, and SiN layer. Further, a BPSG film as an interlayer insulating film is formed so as to cover these two gate portions G ′, and a PE-SiO ₂ film is formed on the upper surface of the BPSG film. The PE-SiO ₂ film is a CVD-based silicon oxide film formed by using a plasma enhanced CVD (PECVD) method. A contact hole H is formed between the two gate portions G ′ (between the side wall portions) so as to penetrate the PE-SiO ₂ film and the BPSG film. The Si layer is exposed at the bottom of the contact hole H, and a natural oxide film is formed on the Si layer. That is, in this structure, three types of silicon oxide films, that is, a natural oxide film, a BPSG film, and a PE-SiO ₂ film are mixed. Even when the natural oxide film is removed from such a wafer W ′, the temperature of the wafer W ′ and the partial pressure of the hydrogen fluoride gas in the mixed gas are appropriately adjusted, so that the BPSG film and the PE-SiO ₂ film can be removed. The natural oxide film can be selectively removed while suppressing damage (CD shift). In addition, if the temperature of the wafer W ′ and the partial pressure of hydrogen fluoride gas in the mixed gas are adjusted according to the thickness of the natural oxide film, even a natural oxide film that has been formed for a long period of time can be reliably Can be removed. In the capacitor formation (film formation process) performed after removing the natural oxide film on the wafer W ′, the natural oxide film is removed from the Si layer exposed at the bottom of the contact hole H. , The lower end of the capacitor can be securely connected to the Si layer.

(Experiment 1)
The present inventors conducted an experiment 1 for examining conditions in the COR processing step when etching a silicon oxide film. The object to be etched was a thermal oxide film (SiO ₂ ) formed by a thermal oxidation method. Then, the relationship between the partial pressure of the hydrogen fluoride gas and the etching amount when the temperature of the wafer W was 25 ° C., 30 ° C., 35 ° C., and 40 ° C. was measured. The partial pressure of hydrogen fluoride gas was changed between 5 mTorr (about 0.67 Pa) and 35 mTorr (about 4.67 Pa). The result is shown in the graph of FIG. As shown in FIG. 10, when the temperature of the wafer W was 25 ° C., the etching amount was the largest when the partial pressure of the hydrogen fluoride gas was about 10 mTorr (about 1.33 Pa). The etching amount at that time was about 35 nm. As a result, the etching amount decreased as the partial pressure of hydrogen fluoride gas was lowered below about 10 mTorr, and the etching amount decreased as the partial pressure was increased. When the temperature of the wafer W was 30 ° C., the etching amount was the largest when the partial pressure of the hydrogen fluoride gas was about 30 mTorr (about 4.00 Pa), and the etching amount at that time was about It was about 40 nm. When the temperature of the wafer W was 35 ° C., the etching amount increased as the partial pressure of the hydrogen fluoride gas was increased. Although the etching amount is small compared with the case where the temperature of the wafer W is 25 ° C. and 30 ° C. until the partial pressure of the hydrogen fluoride gas is about 20 mTorr (about 2.67 Pa), the partial pressure of the hydrogen fluoride gas is small. When the pressure was about 25 mTorr (about 3.33 Pa) or more, the etching amount was larger than when the temperature of the wafer W was 25 ° C. and 30 ° C. The etching amount was the largest when the partial pressure of the hydrogen fluoride gas was about 35 mTorr, and the etching amount at that time was about 50 nm. Even when the temperature of the wafer W was 40 ° C., the etching amount increased as the partial pressure of the hydrogen fluoride gas was increased, as in the case of 35 ° C. When the partial pressure of hydrogen fluoride gas is about 30 mTorr, the etching amount is small compared to the case where the temperature of the wafer W is 25 ° C. and 30 ° C., but when the partial pressure of hydrogen fluoride gas is about 30 mTorr or more, The etching amount was larger than when the temperature of the wafer W was 25 ° C. and 30 ° C. The etching amount was the largest when the partial pressure of the hydrogen fluoride gas was about 35 mTorr, and the etching amount at that time was about 40 nm. From the above results, it was found that an etching amount of about 35 nm or more can be obtained.

(Experiment 2)
The present inventors conducted an experiment 2 for examining conditions in the COR processing step when etching a silicon oxide film. The object to be etched was a plasma CVD oxide film (SiO ₂ ) formed by the plasma CVD method. Then, the relationship between the partial pressure of the hydrogen fluoride gas and the etching amount when the temperature of the wafer W was 25 ° C., 30 ° C., 35 ° C., and 40 ° C. was measured. The partial pressure of hydrogen fluoride gas was changed between 5 mTorr and 35 mTorr. The result is shown in the graph of FIG. As shown in FIG. 11, when the temperature of the wafer W was 25 ° C., the etching amount was the largest when the partial pressure of hydrogen fluoride gas was about 20 mTorr, and the etching amount at that time was about It was about 30 nm. As a result, the etching amount decreased as the partial pressure of the hydrogen fluoride gas was lowered below about 20 mTorr, and the etching amount decreased as the partial pressure was increased. When the temperature of the wafer W was 30 ° C., the etching amount was the largest when the partial pressure of the hydrogen fluoride gas was about 30 mTorr, and the etching amount at that time was about 35 nm. When the temperature of the wafer W was 35 ° C., the etching amount increased as the partial pressure of the hydrogen fluoride gas was increased. When the partial pressure of hydrogen fluoride gas is up to about 25 mTorr, the etching amount is smaller than when the temperature of the wafer W is 25 ° C. or 30 ° C., but when the partial pressure of hydrogen fluoride gas is about 30 mTorr or more, The etching amount was larger than when the temperature of the wafer W was 25 ° C. and 30 ° C. The etching amount was the largest when the partial pressure of hydrogen fluoride gas was about 35 mTorr, and the etching amount at that time was about 40 nm or more. Even when the temperature of the wafer W was 40 ° C., the etching amount increased as the partial pressure of the hydrogen fluoride gas was increased, as in the case of 35 ° C. The etching amount was the largest when the partial pressure of hydrogen fluoride gas was about 35 mTorr.

(Experiment 3)
The present inventors conducted Experiment 3 for comparing etching amounts for various materials when the partial pressure of hydrogen fluoride gas and the partial pressure of ammonia gas in the mixed gas in the COR treatment were changed. The objects to be etched were four types: Poly-Si, SiN, plasma CVD oxide film, and thermal oxide film. As a mixed gas, a gas obtained by mixing three kinds of hydrogen fluoride gas, ammonia gas, and argon gas was used. Each object was subjected to COR processing under the following four conditions A, B, C, and D (see FIG. 12), and then subjected to PHT processing. And the removal amount of the reaction product after a PHT process, ie, the etching amount, was measured. Furthermore, the average value and standard deviation of the etching amount were calculated.
(Condition A)
The pressure of the entire mixed gas (Press) was 40 mTorr (about 5.33 Pa), and the partial pressure of hydrogen fluoride gas and the partial pressure of ammonia gas were 18 mTorr (about 2.40 Pa), respectively. That is, the partial pressure of hydrogen fluoride gas and the partial pressure of ammonia gas were set to the same value.
(Condition B)
The total pressure of the mixed gas was 80 mTorr (about 10.7 Pa), the partial pressure of hydrogen fluoride gas was 26.7 mTorr (about 3.56 Pa), and the partial pressure of ammonia gas was 15.2 mTorr (about 2.03 Pa). . That is, the partial pressure of ammonia gas was made lower than that of hydrogen fluoride gas.
(Condition C)
The total pressure of the mixed gas was 80 mTorr, and the partial pressure of hydrogen fluoride gas and the partial pressure of ammonia gas were 26.7 mTorr, respectively. That is, the partial pressure of the hydrogen fluoride gas is increased by decreasing the partial pressure of the argon gas and increasing the partial pressure of the ammonia gas while keeping the pressure of the entire mixed gas and the partial pressure of the hydrogen fluoride gas the same as the condition B. And the partial pressure of ammonia gas were set to the same value.
(Condition D)
The pressure of the entire mixed gas was 80 mTorr, the partial pressure of hydrogen fluoride gas was 32.9 mTorr (about 4.39 Pa), and the partial pressure of ammonia gas was 18.8 mTorr (about 2.51 Pa). That is, the partial pressure of argon gas is reduced from condition B, the partial pressure of hydrogen fluoride gas and the partial pressure of ammonia gas are increased from condition B, respectively, and the partial pressure of ammonia gas is changed to the partial pressure of hydrogen fluoride gas. Made smaller.

  The conditions of Experiment 3 above are shown in the table of FIG. 12, and the results of Experiment 3 are shown in the table of FIG. 12 and the graph of FIG. As shown in FIG. 13, in any of the conditions A to D, the plasma CVD oxide film and the thermal oxide film can be obtained with an etching amount larger than that of Poly-Si and SiN. It was confirmed that a high etching selectivity was obtained for the oxide film. The etching amounts of Poly-Si and SiN are almost the same under any of the conditions A to D, but the etching amounts of the plasma CVD oxide film and the thermal oxide film are more in the conditions B, C, and D than in the condition A. There were many. Conditions C and D have a relatively large etching amount of the plasma CVD oxide film, and Conditions B and D have a relatively large etching amount of the thermal oxide film. The ratio of the etching amount of the plasma CVD oxide film to the etching amount of the thermal oxide film was the smallest in the condition B, and the ratio of the etching amount of the plasma CVD oxide film to the etching amount of the thermal oxide film was the largest. Was condition C. From the above results, in a wafer in which a plasma CVD oxide film and a thermal oxide film coexist, when it is desired to selectively etch only the thermal oxide film while preventing the etching of the plasma CVD oxide film, the state of the mixed gas in the COR process Is considered to be preferable to be in the condition B, that is, in a state where the partial pressure of ammonia gas is smaller than the partial pressure of hydrogen fluoride gas.

  The present invention can be applied to an etching method and a recording medium.

It is the schematic longitudinal cross-sectional view which showed the structure of the surface of the wafer before etching a BPSG film | membrane. It is a schematic plan view of a processing system. It is explanatory drawing which showed the structure of the PHT processing apparatus. It is explanatory drawing which showed the structure of the COR processing apparatus. It is the schematic longitudinal cross-sectional view which showed the state of the wafer after COR processing. It is the schematic longitudinal cross-sectional view which showed the state of the wafer after PHT process. It is the schematic longitudinal cross-sectional view which showed the state of the wafer after the film-forming process. It is a schematic plan view of the processing system concerning another embodiment. It is the schematic longitudinal cross-sectional view which showed the structure of the surface of the wafer concerning another embodiment. 6 is a graph showing an experimental result of Experiment 1. 6 is a graph showing an experimental result of Experiment 2. 6 is a table showing experimental conditions and experimental results of Experiment 3. 10 is a graph showing an experimental result of Experiment 3.

Explanation of symbols

W wafer 1 processing system 4 PHT processing apparatus 5 COR processing apparatus 8 control computer 40 chamber 41 processing chamber 61 hydrogen fluoride gas supply path 62 ammonia gas supply path 85 exhaust path

Claims (4)

A method of etching a silicon oxide film made of a BPSG film,
A mixed gas containing hydrogen fluoride gas and ammonia gas is supplied to the surface of the silicon oxide film, the silicon oxide film and the mixed gas are chemically reacted, and the silicon oxide film is altered to generate a reaction product. Alteration process
Heating to remove the reaction product by heating,
In the alteration step, the partial pressure of the hydrogen fluoride gas in the mixed gas is set to 15 mTorr or more , and the temperature range of the silicon oxide film is set to 35 ° C. or more and 100 ° C. or less . A method of etching a BPSG film on a wafer surface on which a BPSG film and a CVD type silicon oxide film formed using a bias high density plasma CVD method are formed,
A denatured step of supplying a mixed gas containing hydrogen fluoride gas and ammonia gas to the wafer surface, chemically reacting the BPSG film with the mixed gas, denatured the BPSG film, and generating a reaction product;
Heating to remove the reaction product by heating,
In the alteration step, the partial pressure of the ammonia gas in the mixed gas is made smaller than the partial pressure of the hydrogen fluoride gas , and the temperature range of the BPSG film is 35 ° C. or more and 100 ° C. or less. Etching method. The etching method according to claim 1, wherein an etching amount of the reaction product is 30 nanometers or more. A recording medium on which a program that can be executed by a control computer of a processing system is recorded,
  A recording medium, wherein the program is executed by the control computer to cause the processing system to perform the etching method according to claim 1.

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