An ion source device with adjustable plasma density

Abstract

The present invention discloses an ion source device with adjustable plasma density, comprising a discharge chamber, a spiral coil and an ion source chamber coaxially arranged from the inside to the outside; a metal foil is arranged on the outer wall of the discharge chamber, and the metal foil can shield the inner edge magnetic field strength of the discharge chamber, neutralize the high plasma density caused by the skin effect, and make the plasma density in the discharge chamber uniform. The width W of the metal foil ranges from 1 to 20 mm, and the thickness T of the metal foil ranges from 0.1 mm to t, where t is the skin depth; the thickness T and surface area of ​​the metal foil are selected according to the difference between the edge plasma density and the central area plasma density in the discharge chamber. The present invention adds a Faraday structure outside the discharge chamber, distributes power to the Faraday structure, and adjusts the plasma density according to different working conditions, thereby effectively improving the etching uniformity.

Description

Technical Field

[0001] The invention relates to the field of ion beam etching, in particular to an ion source device with adjustable plasma density. Background Art

[0002] Ion beam etching can be used to etch various metals (Ni, Cu, Au, Al, Pb, Pt, Ti, etc.) and their alloys, as well as non-metals, oxides, nitrides, carbides, semiconductors, polymers, ceramics, infrared and superconducting materials. In principle, the principle of glow discharge is used to decompose argon gas into argon ions, which are accelerated by the anode electric field to physically bombard the sample surface to achieve the effect of etching. The etching process is to fill the Ar gas into the ion source discharge chamber and ionize it to form a plasma, and then the grid draws out and accelerates the ions in a beam shape. The ion beam with a certain energy enters the studio and shoots at the solid surface to bombard the atoms on the solid surface, causing the atoms of the material to sputter and achieve the purpose of etching. It is pure physical etching. Since the ions are not generated by glow discharge, but by an independent ion source that emits inert gas ions and enters the vacuum chamber where the sample is placed after being accelerated by the electric field, the vacuum degree of the ion beam source and the sample chamber can reach their respective optimal states, and the purity of the film is very high.

[0003] An ion source is a device that ionizes neutral atoms or molecules and extracts ion beams from them. The quality of the ion source directly affects the etching performance. Existing ion sources mainly include Kaufman ion sources, radio frequency ion sources, ECR ion sources, and End Hall ion sources. Among them, radio frequency ion sources are widely used in ion beam etching, material surface modification, and thin film processing due to their advantages of high density, no pollution, easy maintenance, and long life. The working principle is: when a certain radio frequency current flows into the radio frequency coil placed on the dielectric window, an induced radio frequency electric field is induced in the discharge chamber. The induced electric field accelerates the movement of electrons, causing them to collide and ionize with neutral gas molecules continuously, thereby coupling the radio frequency energy in the induction coil to the ionized gas to maintain plasma discharge. Most of the ions generated by radio frequency discharge are drawn out through the grid system to form an ion beam. Radio frequency ion sources have the characteristics of non-polar discharge, long-term stable operation, large uniform area, precise control of ion beam density, and low pollution, and are widely used in the process of ion beam etching.

[0004] In the existing ion source, when the coil is powered on during use, the plasma density is highest in its skin layer, and the plasma density gradually decays in the area outside the skin layer. Under low pressure conditions, the plasma density in the discharge chamber is mostly parabolic. As the current increases, the edge skin effect is enhanced, and the plasma density distribution in the discharge chamber generally presents a saddle-shaped distribution. The plasma density center and edge of the discharge chamber are unevenly distributed. Figure 1 and Figure 2The existing method is to solve this problem by opening holes of different specifications on the screen grid, but it can only improve certain working conditions and cannot be adjusted for multiple working conditions, which affects the etching uniformity. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an ion source device with adjustable plasma density in view of the deficiencies of the above-mentioned prior art. The ion source device with adjustable plasma density increases a Faraday structure outside the discharge chamber and distributes power to the Faraday structure, thereby adjusting the plasma density according to different working conditions, thereby effectively improving the etching uniformity.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] An ion source device with adjustable plasma density comprises a discharge chamber, a spiral coil and an ion source chamber which are coaxially arranged in sequence from the inside to the outside; a metal foil is arranged on the outer wall of the discharge chamber, and the metal foil can shield the magnetic field strength at the inner edge of the discharge chamber, neutralize the high plasma density caused by the skin effect, and make the plasma density in the discharge chamber evenly distributed.

[0008] The width W of the metal foil ranges from 1 to 20 mm, and the thickness T of the metal foil ranges from 0.1 mm to t, where t is the skin depth of the spiral coil. The thickness T and surface area of ​​the metal foil are selected according to the difference between the edge plasma density and the central area plasma density in the discharge chamber.

[0009] When the edge plasma density is higher than that of the central area by more than 3%, the thickness T or surface area of ​​the metal foil should be increased to increase the shielding effectiveness of the metal foil and reduce the edge plasma density; when the edge plasma density is higher than the plasma density of the central area by 3% or less, the thickness or surface area of ​​the metal foil should be reduced to reduce the shielding effectiveness and avoid the plasma density in the edge area being lower than that in the central area.

[0010] The metal foil is annular and arranged axially on the outer wall of the discharge chamber.

[0011] The metal foil is in the shape of a strip and is spirally wound on the outer wall of the discharge chamber.

[0012] The metal foil is in the form of vertical strips and is arranged circumferentially on the outer wall of the discharge chamber.

[0013] The metal foil is made of aluminum, gold or copper and has a Faraday shielding effect, shielding against voltage.

[0014] A Grid component is arranged at the tail end of the discharge chamber; the Grid component comprises a screen grid and an acceleration grid arranged in sequence from the inside to the outside, the screen grid is used to focus the plasma in the discharge chamber to form an ion beam; the acceleration grid is used to accelerate the formed ion beam.

[0015] The grid assembly also includes a deceleration grid arranged outside the acceleration grid. The screen grid and the acceleration grid are respectively connected to a filtered DC power supply, and the deceleration grid is grounded to reduce the divergence of the ion beam.

[0016] The spiral coil is connected to a radio frequency power supply through a radio frequency matcher.

[0017] The present invention has the following beneficial effects:

[0018] 1. The metal foil forms a Faraday structure outside the discharge chamber. By distributing power to the Faraday structure, the plasma density is adjusted according to different working conditions, thereby effectively improving the etching uniformity.

[0019] 2. The metal foil can shield the magnetic field strength at the inner edge of the discharge chamber, neutralize the high plasma density caused by the skin effect, and make the plasma density in the discharge chamber uniform.

[0020] 3. The thickness T and surface area of ​​the metal foil can be selected according to the difference between the edge plasma density and the central area plasma density in the discharge chamber.

[0021] 4. The material of the metal foil is conductors such as aluminum, gold, and copper, so it can achieve a good Faraday shielding effect and form a shielding effect on the voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram showing the distribution of plasma density in a discharge chamber in the prior art is shown.

[0023] Figure 2 The diagram shows the distribution of ion beam current density in the reaction chamber under high energy conditions and low energy conditions in the prior art.

[0024] Figure 3 The schematic diagram shows the structure of an ion source device with adjustable plasma density according to the present invention.

[0025] Figure 4 A schematic diagram showing the layout of the metal foil on the outer wall of the discharge chamber when the metal foil is in a ring shape.

[0026] Figure 5 A schematic diagram showing the layout of the metal foil on the outer wall of the discharge chamber when the metal foil is in the first spiral shape.

[0027] Figure 6 A schematic diagram showing the layout of the metal foil on the outer wall of the discharge chamber when the metal foil is in the second spiral shape.

[0028] Figure 7 The figure shows the layout of the metal foil in the form of vertical strips on the outer wall of the discharge chamber.

[0029] Among them are:

[0030] 10. ion source chamber; 20. discharge chamber; 21. discharge chamber support;

[0031] 30. Helical coil; 31. Helical coil fixed;

[0032] 40. RF power supply; 41. RF matching device; 42. RF column; 43. RF column;

[0033] 50. Metal foil;

[0034] 60.Grid component;

[0035] 61. Screen grid; 611. DC power supply; 612. Filter; 613. RF column;

[0036] 62. Acceleration grid; 621. DC power supply; 622. Filter; 623. RF column;

[0037] 63. Speed ​​reduction fence;

[0038] 70. Air intake duct. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific preferred embodiments.

[0040] In the description of the present invention, it should be understood that the terms "left side", "right side", "upper part", "lower part" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second" and the like do not indicate the importance of the components, and therefore cannot be understood as limiting the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution, and do not limit the scope of protection of the present invention.

[0041] like Figure 3 As shown, an ion source device with adjustable plasma density includes a discharge chamber 20, a spiral coil 30 and an ion source chamber 10 which are coaxially arranged in sequence from the inside to the outside.

[0042] A plurality of spiral coil fixings 31 are circumferentially distributed on the inner wall of the ion source chamber 10, and the spiral coil 30 is placed on the spiral coil fixings 31. The positive end of the spiral coil is connected to a radio frequency matcher 41 through a radio frequency column 42 provided on the ion source chamber, and the radio frequency matcher is connected to a radio frequency power supply 40.

[0043] The configuration of the RF matcher 41 enables the load impedance to match the impedance of the RF power source 40 , thereby reducing the reflected power and ensuring that the transmission power reaches the maximum.

[0044] The discharge chamber 20 is mounted on the ion source chamber 10 via a discharge chamber support 21 .

[0045] An air inlet pipe 70 is provided at the front end of the discharge chamber for introducing plasma gases such as Ar and O2 into the discharge chamber.

[0046] A Grid assembly 60 is disposed at the rear end of the discharge chamber; the Grid assembly 60 may be selected to have two grids or three grids.

[0047] When the Grid assembly 60 has two grids, it includes a screen grid 61 and an acceleration grid 62 which are sequentially arranged from the inside to the outside.

[0048] The screen grid 61 is connected to the filter 612 and the DC power supply 611 in sequence through the radio frequency column 613 arranged on the ion source chamber. The screen grid 61 can focus the plasma to form an ion beam.

[0049] The acceleration grid 62 is connected to the filter 622 and the DC power supply 621 in sequence through the radio frequency column 623 arranged on the ion source cavity, and the acceleration grid 62 accelerates the ion beam.

[0050] When the grid assembly 60 is a three-grid assembly, the three-grid assembly is a two-grid assembly with a deceleration grid 64 added thereto, and the deceleration grid 63 is arranged outside the acceleration grid, which can effectively reduce the divergence of the ion beam. Among them, the screen grid is negatively charged, the acceleration grid is positively charged, and the deceleration grid is grounded.

[0051] A metal foil 50 is preferably attached to the outer wall surface of the discharge chamber. The material of the metal foil is preferably a conductor such as aluminum, gold or copper, which has a Faraday shielding effect and shields the voltage.

[0052] The above-mentioned metal foil may be in the following forms:

[0053] (1) Annular distribution along the axial direction: Figure 4 As shown, the metal foil is annular and arranged axially on the outer wall of the discharge chamber, and its axial distribution can be uniform or uneven.

[0054] (2) Spiral distribution, preferably including the following two embodiments.

[0055] The first embodiment: Figure 5 As shown, the metal foil is in the shape of a strip and is a whole long strip, which is spirally wound on the outer wall of the discharge chamber, and the winding spacing can be uniform or uneven.

[0056] The first embodiment: Figure 6 As shown, the metal foil is in the shape of a strip, and is composed of multiple metal foil strips of different lengths, which are spirally wound on the outer wall of the discharge chamber, and the winding interval can be uniform or uneven.

[0057] (3) Vertical stripes are distributed along the circumference: Figure 7 As shown, the metal foil is a vertical strip, which is arranged on the outer wall of the discharge chamber along the circumferential direction, and the circumferential distribution can be uniform or uneven. Figure 7 The middle is evenly distributed.

[0058] When etching is required, the DC power supplies 611, 621 and the RF power supply 40 are started. When the RF power is added to the spiral coil 30 through the matcher, an RF current flows through the spiral coil 30, thereby generating an RF magnetic flux and inducing an RF electric field along the axial direction of the discharge chamber 20; Ar, O2 and other plasma gases enter the discharge chamber through the air inlet pipe 70, and under the action of the spiral coil, the gas in the discharge chamber is ionized, and the electrons in the discharge chamber are accelerated by the electric field to generate dense plasma. After the plasma in the discharge chamber is drawn out through the Grid component 60, it bombards the target material in the form of an ion beam to etch the wafer.

[0059] During the etching process, as the electrostatic field increases, an obvious skin effect will occur. At the same time, the charged particles in the plasma move under the action of the electric field force or produce pressure and temperature changes through gas discharge, and at the same time exert controllable disturbances on the flow field in the discharge chamber. Multiple factors such as the uneven distribution of the flow field and the accumulation of charges cause the edge plasma density to be high.

[0060] In the present invention, by providing a metal foil 50 outside the discharge chamber 20, the edge magnetic field strength in the discharge chamber can be effectively shielded, and the high plasma density caused by the skin effect can be neutralized, so that the plasma density in the discharge chamber is evenly distributed.

[0061] The width W of the metal foil is preferably in the range of 1 to 20 mm, and the thickness T of the metal foil is preferably in the range of 0.1 mm to t, where t is the skin depth of the spiral coil.

[0062] According to the difference between the edge plasma density and the central plasma density in the discharge chamber, the thickness T and surface area of ​​the metal foil are selected. Specifically, when the edge plasma density is more than 3% higher than that in the central area, the thickness T or surface area of ​​the metal foil should be increased to increase the shielding effectiveness of the metal foil and reduce the edge plasma density; when the edge plasma density is 3% or less higher than the central plasma density, the thickness or surface area of ​​the metal foil should be reduced to reduce the shielding effectiveness and avoid the edge plasma density being lower than the central plasma density.

[0063] In addition, the metal foil forms a Faraday structure outside the discharge chamber. By distributing power to the Faraday structure, the plasma density is adjusted according to different working conditions, thereby effectively improving the etching uniformity.

[0064] The preferred embodiments of the present invention are described in detail above; however, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. An ion source device with adjustable plasma density, comprising a discharge chamber, a spiral coil and an ion source chamber coaxially arranged from inside to outside; characterized in that: A metal foil is arranged on the outer wall of the discharge chamber, which can shield the magnetic field strength at the inner edge of the discharge chamber, neutralize the high plasma density caused by the skin effect, and make the plasma density in the discharge chamber uniform; The metal foil is in a ring or strip shape; when the metal foil is in a ring shape, it is evenly or unevenly arranged along the axial direction on the outer wall surface of the discharge cavity; when the metal foil is in a strip shape, it is spirally wound on the outer wall surface of the discharge cavity; The thickness T of the metal foil ranges from 0.1 mm to t, where t is the skin depth of the spiral coil. The thickness T and surface area of ​​the metal foil are selected according to the difference between the edge plasma density and the central area plasma density in the discharge chamber.

2. The ion source device with adjustable plasma density according to claim 1, characterized in that: When the edge plasma density is greater than 3% of that in the central area, the thickness T or surface area of ​​the metal foil should be increased to increase the shielding effectiveness of the metal foil and reduce the edge plasma density. When the edge plasma density does not exceed 3% of the plasma density in the central area, the thickness or surface area of ​​the metal foil should be reduced to reduce the shielding effectiveness and avoid the plasma density in the edge area being lower than that in the central area.

3. The ion source device with adjustable plasma density according to claim 1, characterized in that: The metal foil is made of aluminum, gold or copper and has a Faraday shielding effect, shielding against voltage.

4. The ion source device with adjustable plasma density according to claim 1, characterized in that: The width W of the metal foil ranges from 1 to 20 mm.

5. The ion source device with adjustable plasma density according to claim 1, characterized in that: A Grid assembly is arranged at the tail end of the discharge chamber; the Grid assembly includes a screen grid and an acceleration grid arranged in sequence from the inside to the outside, and the screen grid is used to focus the plasma in the discharge chamber to form an ion beam; The accelerating grid is used to accelerate the formed ion beam.

6. The ion source device with adjustable plasma density according to claim 5, characterized in that: The grid assembly also includes a deceleration grid arranged outside the acceleration grid; wherein the screen grid and the acceleration grid are respectively connected to a filtered DC power supply, and the deceleration grid is grounded to reduce ion beam divergence.

7. The ion source device with adjustable plasma density according to claim 1, characterized in that: The spiral coil is connected to a radio frequency power supply through a radio frequency matcher.

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