A preferred etching machine and process for precisely controlling the etching of silicon wafer material

Abstract

The application discloses a preferential etching machine and process for precisely controlling a silicon wafer material etching process, and relates to the technical field of semiconductor production.The preferential etching machine and process for precisely controlling a silicon wafer material etching process can precisely control various parameters of the etching process, including etching rate, temperature, pressure and the like, so that the material etching process is optimized; the rotating mechanism is arranged, the rotating disc can drive multiple silicon wafer loading assemblies to rotate, the etching liquid in the etching cylinder can be stirred in the rotating process, the etching liquid at different positions can be mixed, and the etching liquid concentration at different positions is kept in a relatively stable state; secondly, the etching liquid can enter the inside of the loading box through the through holes on the surface of the loading box, the flowability of the etching liquid is improved, the etching liquid around the silicon wafer is prevented from being in a stationary state, the etching liquid concentration is prevented from being unevenly distributed, and the etching degree of the silicon wafer surface is prevented from being inconsistent.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, specifically to a selective etching machine and process for precisely controlling the etching process of silicon wafer materials. Background Technology

[0002] In many industrial applications, the corrosion process of materials has a significant impact on product performance and lifespan. For example, in fields such as oil and gas extraction, the chemical industry, and marine engineering, the corrosion resistance of materials is a key performance indicator. In the semiconductor industry, corrosion is a crucial step in the process of manufacturing silicon wafers, and precise processing of silicon wafers can be achieved by controlling the corrosion rate and depth.

[0003] Currently, during the etching process of silicon wafers, the wafers to be treated are in a static state in the acid etching bath. The corrosion products adhere to the surface of the wafer, isolating it from the etching solution. This reduces the etching rate and can easily lead to local thickness differences or pits during the etching process, thus affecting the quality and performance of the wafer. Secondly, the etching solution around the wafer reacts with it faster, while the acid concentration further away from the wafer is higher due to the slower reaction rate with the reactants. This can easily lead to different reaction rates on different parts of the wafer, thus affecting the desired etching effect.

[0004] Therefore, this invention proposes a preferred etching machine and process for precisely controlling the etching process of silicon wafers to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a selective etching machine and process for precisely controlling the etching process of silicon wafers. It solves the problems of current etching methods where silicon wafers are statically placed in an acid etching bath, which easily leads to etching products adhering to the silicon wafer surface, reducing the etching rate, and causing localized thickness differences or pits during etching, thus affecting the quality and performance of the silicon wafer. Furthermore, the different concentrations of the etching solution at different locations on the silicon wafer can easily lead to variations in reaction rates at different locations, thus affecting the etching effect.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a selective etching machine for precisely controlling the etching process of silicon wafers, comprising a support base, an etching cylinder for storing etching solution fixedly mounted on the top of the support base, a sealing cap for preventing etching solution leakage mounted on the top of the etching cylinder via a hinge, a liquid injection mechanism for replenishing etching solution into the etching cylinder on one side of the outer wall of the support base, a temperature control mechanism for controlling the temperature of the etching solution inside the etching cylinder, and a rotating mechanism for driving the silicon wafer to rotate inside the etching cylinder, with multiple silicon wafer loading assemblies for loading silicon wafers mounted on the top of the rotating mechanism, a control box for controlling the operation of the etching solution replenishment mechanism, the temperature control mechanism, and the rotating mechanism fixedly mounted on one side of the top of the support base, and a pressure sensor for monitoring the internal pressure of the etching cylinder fixedly mounted on the front of the etching cylinder.

[0007] Furthermore, the liquid injection mechanism includes a level gauge fixedly connected to the outer wall of the corrosion cylinder for monitoring the level of the corrosion liquid and a storage tank fixedly connected to the outer wall of the support for storing replenishing the corrosion liquid. A liquid pump is fixedly connected to the top of the storage tank. A suction pipe for drawing the corrosion liquid is fixedly connected to the input end of the liquid pump, which is located inside the storage tank, and a delivery pipe for conveying the corrosion liquid to the corrosion cylinder is fixedly connected to the output end of the liquid pump.

[0008] Furthermore, the temperature control mechanism includes a temperature sensor fixedly connected to the outer wall of the corrosion cylinder for detecting the temperature of the corrosion liquid and a heating plate fixedly connected to the inner wall of the corrosion cylinder for heating the corrosion liquid. The heating plate is connected to an external heating controller via wires, and the controller is used to control the heating temperature of the corrosion liquid.

[0009] Furthermore, the rotating mechanism includes a motor fixedly connected inside the bearing seat and a turntable rotatably connected inside the corrosion cylinder. The output shaft of the motor rotatably passes through the bearing seat and is fixedly connected to the bottom of the turntable. Multiple limiting plates are evenly fixedly arranged on the top of the turntable. A gear ring is fixedly connected to the inner wall of the corrosion cylinder above the turntable.

[0010] Furthermore, the silicon wafer loading assembly includes a loading box slidably disposed inside four adjacent sealing covers and partitions uniformly fixedly connected inside the loading box. Multiple through holes for the passage of etching liquid are uniformly opened on the outer wall of the loading box, and an elongated through groove is opened at the bottom of the loading box. A fluid actuation component for driving the flow of etching liquid inside the loading box is disposed inside the elongated through groove.

[0011] Furthermore, the fluid actuation component includes a main pipe fixedly connected inside the elongated channel. Multiple branch pipes are uniformly fixedly arranged on the outer wall of the main pipe inside the loading box. One end of the main pipe is fixedly connected to a tapered pipe that communicates with the main pipe. Multiple elongated holes for the passage of corrosive liquid are uniformly opened on the outer surface of the tapered pipe. An impeller is rotatably connected inside the tapered pipe via a rotating shaft. One end of the rotating shaft rotatably passes through the tapered pipe and is fixedly connected to a gear that meshes with a gear ring.

[0012] Furthermore, the surface of the turntable is uniformly provided with multiple filter holes for impurities in the corrosion liquid to pass through, and a drain port for discharging corrosion waste liquid is fixedly connected to one side of the outer wall of the corrosion cylinder.

[0013] This invention also discloses an etching process for a selective etching machine used to precisely control the etching process of silicon wafer materials. The selective etching machine for precisely controlling the etching process of silicon wafer materials specifically includes the following steps:

[0014] Step 1: Place the material to be etched into the silicon wafer loading assembly of the machine, and then place the silicon wafer loading assembly containing the material to be etched into the etching cylinder;

[0015] Step 2: Set the required temperature and other relevant parameters;

[0016] Step 3: Start the machine. The rotating mechanism drives the silicon wafer loading assembly to rotate, so that the material to be etched comes into uniform contact with the etchant.

[0017] Step 4: The temperature control mechanism will heat the corrosive liquid according to the set temperature;

[0018] Step 5: The liquid injection mechanism will inject corrosive liquid into the container corrosion cylinder at the set rate. At the same time, the control box will adjust the rotation speed of the rotating mechanism and the set temperature of the temperature control mechanism according to the detected temperature and pressure signals of the corrosive liquid.

[0019] Step 6: After the corrosion process is completed, the rotating mechanism will automatically stop working, and the temperature control mechanism and liquid injection mechanism will record and output all data during the corrosion process.

[0020] Beneficial effects

[0021] This invention provides a preferred etching machine and process for precisely controlling the etching process of silicon wafers. Compared with the prior art, it has the following advantages:

[0022] 1. A selective etching machine and process for precisely controlling the etching process of silicon wafers. An etching cylinder for storing etching solution is fixedly mounted on the top of a support base. A sealing cap for preventing etching solution leakage is hinged to the top of the etching cylinder. A liquid injection mechanism for replenishing etching solution into the etching cylinder is located on one side of the outer wall of the support base. A temperature control mechanism for controlling the temperature of the etching solution is located inside the etching cylinder. A rotating mechanism for driving the silicon wafer material is also located inside the etching cylinder. Multiple silicon wafer loading assemblies for loading silicon wafer material are located on the top of the rotating mechanism. A control box for controlling the operation of the etching solution replenishment mechanism, temperature control mechanism, and rotating mechanism is fixedly mounted on one side of the top of the support base. A pressure sensor for monitoring the internal pressure is fixedly mounted on the front of the etching cylinder. This method solves the problems of current etching methods where silicon wafers are statically placed in an acid etching bath, which easily leads to etching products adhering to the silicon wafer surface, reducing the etching rate, and easily causing local thickness differences or pits during the etching process, thus affecting the quality and performance of the silicon wafer; and the problem that the concentration of etching solution varies at different locations on the silicon wafer, easily leading to differences in the reaction rate of the silicon wafer at different locations, thus affecting the etching effect.

[0023] 2. A selective etching machine and process for precisely controlling the etching process of silicon wafers can precisely control various parameters of the etching process, including etching rate, temperature, and pressure, thereby optimizing the material etching process. Secondly, by rotating the container and replenishing the etching liquid, the contact between the material to be etched and the etching liquid is made more uniform, thereby improving the etching effect and efficiency. Furthermore, various parameters during the etching process are detected and recorded in real time, which facilitates subsequent data analysis and optimization. The high degree of automation reduces the cost and error of manual operation. In addition, the selective etching machine of this invention has a simple structure, is easy to operate, safe and reliable, and is suitable for various application scenarios that require precise control of the material etching process.

[0024] 3. A selective etching machine and process for precisely controlling the etching process of silicon wafers. By setting up a rotating mechanism, multiple silicon wafer loading components can be rotated using a turntable. During the rotation, the etching solution in the etching cylinder can be agitated, achieving the purpose of mixing the etching solution at different locations and ensuring that the concentration of the etching solution at different locations is in a relatively stable state. Secondly, the etching solution can enter the interior of the loading box through the through holes on the surface of the loading box, accelerating the flow of the etching solution and preventing the etching solution around the silicon wafer from being in a stagnant state, which would lead to uneven distribution of the etching solution concentration and inconsistent etching degree on the silicon wafer surface.

[0025] 4. A selective etching machine and process for precisely controlling the etching process of silicon wafers. During the rotation of the silicon wafer loading assembly, the impeller can be driven to rotate by the meshing of gears and gear rings, thereby drawing the etching liquid into the main pipe and promoting the upward flow of the etching liquid at the bottom of the loading box. The flow of the etching liquid can be accelerated from both the side and the bottom, so that the etching liquid can wash away the etching products on the surface of the silicon wafer, which is conducive to promoting the smooth progress of etching and improving the etching quality of silicon wafers. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0027] Figure 2 This is a schematic diagram of the first three-dimensional structure for opening the sealing cover of the present invention;

[0028] Figure 3 This is a schematic diagram of the second three-dimensional structure for opening the sealing cover of the present invention;

[0029] Figure 4 This is a schematic diagram of the corrosion cross-sectional structure of the present invention;

[0030] Figure 5 This is a schematic diagram of the exploded state structure of the silicon wafer loading assembly of the present invention;

[0031] Figure 6 For the present invention Figure 3 A magnified structural diagram of part A in the diagram.

[0032] In the diagram: 1. Support base; 2. Etching cylinder; 3. Sealing cover; 4. Level gauge; 5. Storage tank; 6. Infusion pipe; 7. Pump; 8. Temperature sensor; 9. Heating plate; 10. Control box; 11. Motor; 12. Turntable; 13. Limiting plate; 14. Gear ring; 15. Silicon wafer loading assembly; 151. Loading box; 152. Partition plate; 153. Through hole; 154. Long through groove; 155. Main pipe; 156. Branch pipe; 157. Tapered pipe; 158. Impeller; 159. Gear; 16. Pressure sensor. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] like Figures 1-6 This invention provides two technical solutions: a selective etching machine for precisely controlling the etching process of silicon wafer materials, specifically including the following embodiments:

[0035] Example 1: A selective etching machine for precisely controlling the etching process of silicon wafers includes a support base 1. An etching cylinder 2 for storing etching liquid is fixedly installed on the top of the support base 1. A sealing cover 3 for preventing etching liquid leakage is rotatably installed on the top of the etching cylinder 2 via a hinge. A liquid injection mechanism for replenishing etching liquid into the etching cylinder 2 is provided on one side of the outer wall of the support base 1. A temperature control mechanism for controlling the temperature of the etching liquid is provided inside the etching cylinder 2. A rotating mechanism for driving the silicon wafer material to rotate is also provided inside the etching cylinder 2. Multiple silicon wafer loading assemblies 15 for loading silicon wafer material are provided on the top of the rotating mechanism. A control box 10 for controlling the operation of the etching liquid replenishment mechanism, the temperature control mechanism, and the rotating mechanism is fixedly installed on one side of the top of the support base 1. A pressure sensor 16 for monitoring its internal pressure is fixedly installed on the front of the etching cylinder 2. The liquid injection mechanism includes a level gauge 4 fixedly connected to the outer wall of the corrosion cylinder 2 for monitoring the level of the corrosive liquid, and a storage tank 5 fixedly connected to the outer wall of the support 1 for storing replenishing the corrosive liquid. A liquid pump 7 is fixedly connected to the top of the storage tank 5. A suction pipe for drawing corrosive liquid is fixedly connected to the input end of the liquid pump 7, located inside the storage tank 5, and a delivery pipe 6 for supplying corrosive liquid to the corrosion cylinder 2 is fixedly connected to the output end of the liquid pump 7. The temperature control mechanism includes a temperature sensor 8 fixedly connected to the outer wall of the corrosion cylinder 2 for detecting the temperature of the corrosive liquid, and a heating plate 9 fixedly connected to the inner wall of the corrosion cylinder 2 for heating the corrosive liquid. The heating plate 9 is connected to an external heating controller via wires, and the controller is used to control the heating temperature of the corrosive liquid. The rotating mechanism includes a motor 11 fixedly connected inside the bearing 1 and a turntable 12 rotatably connected inside the corrosion cylinder 2. The output shaft of the motor 11 rotates through the bearing 1 and is fixedly connected to the bottom of the turntable 12. Multiple limiting plates 13 are evenly fixedly arranged on the top of the turntable 12. A gear ring 14 is fixedly connected to the inner wall of the corrosion cylinder 2 above the turntable 12. Multiple filter holes are evenly opened on the surface of the turntable 12 for impurities in the corrosion liquid to pass through. A drain port for discharging corrosion waste liquid is fixedly connected to one side of the outer wall of the corrosion cylinder 2.

[0036] Example 2: The main difference between this example and the first technical solution is that: the selective etching machine used to precisely control the etching process of silicon wafer materials includes a silicon wafer loading assembly 15 comprising a loading box 151 slidably disposed inside four adjacent sealing covers 3 and a partition 152 uniformly fixedly connected inside the loading box 151. Multiple through holes 153 for the passage of etching liquid are uniformly opened on the outer wall of the loading box 151, and a long through groove 154 is opened at the bottom of the loading box 151. A fluid actuation component for driving the flow of etching liquid inside the loading box 151 is provided inside the long through groove 154. The fluid actuation assembly includes a main pipe 155 fixedly connected inside the elongated channel 154. Multiple branch pipes 156 are uniformly fixedly arranged on the outer wall of the main pipe 155 inside the loading box 151. One end of the main pipe 155 is fixedly connected to a tapered pipe 157 that communicates with the main pipe 155. Multiple elongated holes for the passage of corrosive liquid are uniformly opened on the outer surface of the tapered pipe 157. An impeller 158 is rotatably connected inside the tapered pipe 157 via a rotating shaft. One end of the rotating shaft rotatably passes through the tapered pipe 157 and is fixedly connected to a gear 159 that meshes with the gear ring 14.

[0037] This invention also discloses an etching process for a selective etching machine used to precisely control the etching process of silicon wafer materials. The selective etching machine for precisely controlling the etching process of silicon wafer materials specifically includes the following steps:

[0038] Step 1: Place the material to be etched into the silicon wafer loading assembly 15 of the machine, and place the silicon wafer loading assembly 15 containing the material to be etched into the etching cylinder 2. The specific process is as follows: Place the silicon wafer to be etched into the two adjacent partitions 152 in the loading box 151 in sequence, hold both ends of the loading box 151, place the loading box 151 inside the four adjacent limiting plates 13, and keep the gear 159 and the gear ring 14 in a meshing connection state.

[0039] Step 2: Set the required temperature and other relevant parameters. The specific process is as follows: Set the temperature and rotation speed of the turntable 12 through the controller and control box 10.

[0040] Step 3: Start the machine. The rotating mechanism drives the silicon wafer loading assembly 15 to rotate, so that the material to be etched comes into uniform contact with the etchant. The specific process is as follows: the motor 11 drives the turntable 12 to rotate at a low and uniform speed. The turntable 12 drives multiple silicon wafer loading assemblies 15 to rotate inside the etching cylinder 2. The etchant enters the interior of the loading box 151 through the through hole 153 on the surface of the loading box 151. The etchant and the material to be etched undergo a chemical reaction. At the same time, when the gear 159 rotates relative to the gear ring 14, the gear 159 itself is driven by the gear ring 14 and rotates on its own. When the impeller 158 rotates, it draws the external etchant into the main pipe 155 and sprays it out from the bottom of the loading box 151 through the branch pipe 156, thereby achieving the purpose of multi-directional flow of the etchant.

[0041] Step 4: The temperature control mechanism will heat the corrosive liquid according to the set temperature. The specific process is as follows: Based on the temperature of the corrosive liquid detected by the temperature sensor 8, the heating plate 9 will be started to heat the corrosive liquid in the corrosion cylinder 2. The controller will control the specific heating value of the heating plate 9 until the heating plate 9 heats the corrosive liquid to a certain temperature and then stops heating. The temperature of the corrosive liquid will always be kept dynamically within a certain range of the set value. During this period, the heating plate 9 will continuously heat the corrosive liquid to ensure the stability of the temperature of the corrosive liquid.

[0042] Step 5: The liquid injection mechanism will inject corrosive liquid into the corrosion cylinder 2 of the container according to the set rate. At the same time, the control box 10 will adjust the rotation speed of the rotating mechanism and the set temperature of the temperature control mechanism according to the detected temperature and pressure signals of the corrosive liquid. When the level gauge 4 detects that the amount of corrosive liquid in the corrosion cylinder 2 is less than the initial set value, the liquid pump 7 will be started to draw the corrosive liquid replenishment liquid in the storage tank 5 and input it into the corrosion cylinder 2 through the delivery pipe 6 until the amount of corrosive liquid in the corrosion cylinder 2 reaches the initial set value.

[0043] Step 6: After the corrosion process is completed, the rotating mechanism will automatically stop working, and the temperature control mechanism and liquid injection mechanism will record and output all data during the corrosion process.

[0044] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A selective etching machine for precisely controlling the etching process of silicon wafers, comprising a support (1), characterized in that: The top of the support (1) is fixedly provided with an etching cylinder (2) for storing etching liquid. The top of the etching cylinder (2) is provided with a sealing cover (3) for preventing the etching liquid from leaking through a hinge. A liquid injection mechanism for replenishing the etching liquid into the etching cylinder (2) is provided on one side of the outer wall of the support (1). A temperature control mechanism for controlling the temperature of the etching liquid is provided inside the etching cylinder (2). A rotating mechanism for driving the silicon wafer material to rotate is also provided inside the etching cylinder (2). Multiple silicon wafer loading assemblies (15) for loading silicon wafer material are provided on the top of the rotating mechanism. A control box (10) for controlling the operation of the etching liquid replenishment mechanism, the temperature control mechanism, and the rotating mechanism is fixedly provided on one side of the top of the support (1). A pressure sensor (16) for monitoring the internal pressure of the etching cylinder (2) is fixedly provided on the front. The rotating mechanism includes a motor (11) fixedly connected inside the bearing seat (1) and a turntable (12) rotatably connected inside the corrosion cylinder (2). The output shaft of the motor (11) rotates through the bearing seat (1) and is fixedly connected to the bottom of the turntable (12). Multiple limiting plates (13) are evenly fixedly arranged on the top of the turntable (12). A gear ring (14) is fixedly connected on the inner wall of the corrosion cylinder (2) above the turntable (12). The silicon wafer loading assembly (15) includes a loading box (151) slidably disposed inside four adjacent sealing covers (3) and a partition (152) uniformly fixedly connected inside the loading box (151). The outer wall of the loading box (151) is uniformly provided with a plurality of through holes (153) for the passage of etching liquid, and the bottom of the loading box (151) is provided with a long through groove (154). The long through groove (154) is provided with a fluid actuation component for driving the flow of etching liquid inside the loading box (151). The fluid actuation assembly includes a main pipe (155) fixedly connected inside the elongated through-slot (154). The main pipe (155) has multiple branch pipes (156) uniformly fixedly arranged on the outer wall inside the loading box (151). One end of the main pipe (155) is fixedly connected to a tapered pipe (157) that communicates with the main pipe (155). The outer surface of the tapered pipe (157) is uniformly provided with multiple elongated holes for the passage of corrosive liquid. An impeller (158) is rotatably connected inside the tapered pipe (157) via a rotating shaft. One end of the rotating shaft rotates through the tapered pipe (157) and is fixedly connected to a gear (159) that meshes with the gear ring (14).

2. The selective etching machine for precisely controlling the etching process of silicon wafers according to claim 1, characterized in that: The liquid injection mechanism includes a level gauge (4) fixedly connected to the outer wall of the corrosion cylinder (2) for monitoring the level of the corrosion liquid and a storage tank (5) fixedly connected to the outer wall of the support (1) for storing the replenishment liquid of the corrosion liquid. A liquid pump (7) is fixedly connected to the top of the storage tank (5). A suction pipe for drawing the corrosion liquid is fixedly connected to the input end of the liquid pump (7) and located inside the storage tank (5). A delivery pipe (6) for delivering the corrosion liquid to the corrosion cylinder (2) is fixedly connected to the output end of the liquid pump (7).

3. The preferred etching machine for precisely controlling the etching process of silicon wafers according to claim 1, characterized in that: The temperature control mechanism includes a temperature sensor (8) fixedly connected to the outer wall of the corrosion cylinder (2) for detecting the temperature of the corrosion liquid and a heating plate (9) fixedly connected to the inner wall of the corrosion cylinder (2) for heating the corrosion liquid. The heating plate (9) is connected to an external heating controller via wires, and the controller is used to control the heating temperature of the corrosion liquid.

4. The preferred etching machine for precisely controlling the etching process of silicon wafers according to claim 1, characterized in that: The turntable (12) has multiple filter holes evenly distributed on its surface for impurities in the corrosion liquid to pass through. The corrosion cylinder (2) has a drain port fixedly connected to one side of its outer wall for discharging waste corrosion liquid.

5. An etching process for a selective etching machine used to precisely control the etching process of silicon wafers, characterized in that: The preferred etching machine for precisely controlling the etching process of silicon wafer materials as described in any one of claims 1-4 specifically includes the following steps: Step 1: Place the material to be etched into the silicon wafer loading assembly (15) of the machine, and place the silicon wafer loading assembly (15) containing the material to be etched into the etching cylinder (2); Step 2: Set the required temperature and other relevant parameters; Step 3: Start the machine. The rotating mechanism drives the silicon wafer loading assembly (15) to rotate, so that the material to be etched comes into uniform contact with the etchant. Step 4: The temperature control mechanism will heat the corrosive liquid according to the set temperature; Step 5: The liquid injection mechanism will inject corrosive liquid into the container corrosion cylinder (2) at the set rate. At the same time, the control box (10) will adjust the rotation speed of the rotating mechanism and the set temperature of the temperature control mechanism according to the detected temperature and pressure signals of the corrosive liquid. Step 6: After the corrosion process is completed, the rotating mechanism will automatically stop working, and the temperature control mechanism and liquid injection mechanism will record and output all data during the corrosion process.

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