CN1382829A - Method for modifying inner surface of tubular workpiece - Google Patents

Abstract

The invention belongs to the field of plasma material surface modification. The invention provides a method for modifying an enhanced inner surface of a grid, which comprises the steps of forming a three-electrode system by a cathode, a grid electrode and a sample, realizing the uniformity of dosage and the uniform ion implantation by applying radio frequency power and pulse negative high voltage, and realizing the inner surface coating and the inner surface metal ion implantation by introducing particles of a cathode material into radio frequency plasma through cathode sputtering, so that the modification means is richer. The invention improves the stability and accelerating voltage of the plasma by introducing the grid.

Description

A method for modifying the inner surface of a tubular workpiece

The invention belongs to the field of plasma material surface modification.

Plasma source ion implantation (PSII) (document 1, J.R.Conrad, J.L.Radtke, R.A.Dodd, F.J.Worzala, N.C.Tran, J.Appl.Phys.62 (1987) 4591) is a new material surface ion implantation technology, Especially suitable for injecting samples with complex shapes. In this technique, a homogeneous plasma is generated in a large vacuum chamber by a magnetic multipole filament discharge, the sample to be injected is completely immersed in the plasma, and a negative high-voltage pulse is applied to the sample, so that during the pulse , the ions in the plasma will be accelerated and injected into the surface layer of the sample.

PSII technology provides the possibility of implanting ions into the inner surface of the sample, but there are serious problems in directly injecting the inner surface of the tubular sample with PSII technology, that is, the inhomogeneity of the dose and the accelerating electric field. To solve this problem, we once proposed a method based on PSII technology inner surface modification (document 2, M.Sun, S.Z.Yang, Bing Li, J.Vac.Sci.Technol., A14, (1996) 367) , has aroused the interest of domestic and foreign research and engineering technicians (document 3, A.G.Liu, X.F.Wang, B.Y.Tang, P.K.Chu, J.Appl.Phys.84 (1998) 1859.4.T.E.Sheridan, T.K.Kwok, P.K.Chu, Appl . Phys. Lett. 72 (1998) 1826). The main idea of this method is that, as shown in Figure 1, Figure 1A is a three-dimensional schematic diagram of the principle of internal surface modification, Figure 1B is its cross-sectional view, an auxiliary anode 3 is inserted into the inside of the tubular sample 4, and the auxiliary anode is connected to the ground 13 The sample is connected to a negative high voltage pulse power supply 2, so that a uniform electric field will be established between the auxiliary anode and the inner surface of the sample during the negative high voltage pulse. When processing a sample, the sample is placed in a cloud of plasma generated by a filament discharge in a vacuum chamber. Plasma can diffuse into the interior of the tubular sample to form diffuse plasma 1, in which positive ions are accelerated and injected into the inner surface of the sample under the action of an accelerating electric field. In addition, due to the acceleration of electrons by the auxiliary anode, more primary electrons (primary electrons are high-energy electrons emitted by the filament and accelerated by the cathode sheath) enter the sample and strengthen the ionization of the neutral gas, increasing the plasma density. and its uniformity. However, the disadvantage of this method is that since the plasma inside the sample is mainly formed by the diffusion of the plasma outside the sample, there must be a diffusion gradient, and the plasma distribution along the axial direction is not uniform, which leads to the injection dose Inhomogeneity, especially for slender tubes (diameter-to-length ratio less than 0.6), the dose in the middle of the tube is very small; secondly, it is impossible to inject metal ions and deposit films.

The purpose of the present invention is to improve the deficiency of the current internal surface modification method, and propose a grid-enhanced internal surface modification method. The method consists of a cathode, a grid electrode and a sample to form a three-electrode system. By adding radio frequency power between the cathode and the grid electrode to generate a group of radio frequency plasma uniformly distributed in the axial direction, the problem of uniformity of the dose is solved; A pulsed negative high voltage is applied between the sample and the grid electrode to establish a uniform electric field that accelerates positive ions, thereby achieving uniform ion implantation; through RF sputtering of the cathode, ions of metal or other solid substances can be introduced into the RF plasma or Atoms can realize inner surface coating and inner surface metal ion implantation.

The purpose of the present invention is achieved like this:

Fig. 2 is a principle diagram of the core technology of the present invention, wherein Fig. 2A is a schematic perspective view, Fig. 2B is a schematic cross-sectional view, and Fig. 2B also shows the ceramic sleeve 10 outside the sample. The core component of the technology of the present invention is a three-electrode system composed of a columnar cathode 8 , a tubular grid electrode 9 and a tubular sample 4 . The specific steps to achieve are as follows:

(1) As shown in FIG. 2 , insert the cathode 8 and the tubular grid electrode 9 into the sample 4 coaxially, and fix the three electrodes coaxially. The cathode 8 and the grid 9 are connected to the radio frequency power supply 5 outside the vacuum chamber through a sealed coaxial joint; the cathode 8 is connected to the power pole of the radio frequency power supply 5 through a DC blocking capacitor 6, and the grid 9 is connected to the ground electrode and the ground 13 of the radio frequency power supply.

(2) As shown in FIG. 3, the above-mentioned three-electrode system is placed in a vacuum chamber 11, and the vacuum chamber is connected to a vacuum system 12 composed of a diffusion pump and a mechanical pump. The working gas is provided by the argon gas bottle 14 and the nitrogen gas bottle 15, and the air pressure and gas flow can be changed by fine-tuning the needle valve 7. In order to facilitate the micro-analysis of the film layer, single crystal silicon substrates are placed at different positions on the inner surface of the sample, so that by characterizing the surface characteristics of the silicon substrate, some characteristics of the film layer on the inner surface of the sample can be obtained indirectly.

(3) Vacuumize to 10 ^-3 Pa.

(4) Fill the working gas to 0.1～1Pa, output the radio frequency power from the radio frequency power supply 5, and generate a pod of axially uniform steady-state radio frequency plasma between the cathode 8 and the grid 9, and pass the radio frequency sputtering mechanism Cathode material atoms and ions are introduced into the plasma. This plasma can diffuse to the inner surface of the tubular sample through the mesh of the grid, so that diffused plasma 1 is formed between the grid and the inner surface of the sample. The diffused plasma is uniform along the axial direction, which ensures a uniform dose incident on the inner surface of the sample.

(5) The sample 4 is connected to the pulsed negative high-voltage power supply 2. During the negative high-voltage pulse, a uniform radial electric field that accelerates the ions is formed between the grid and the inner surface of the sample, and enters the ion between the grid and the inner surface of the sample. Positive ions will be accelerated into the inner surface of the sample.

(6) When a negative high voltage is applied to the sample, a plasma sheath is formed between the inner surface of the sample and the diffused plasma. In the time scale of the reciprocal of the plasma electron frequency, the electrons near the inner surface of the sample are first repelled by the sample at negative potential and leave the inner surface of the sample to move towards the grid, forming a positive ion sheath; at the time of the reciprocal of the plasma ion frequency Within the scale, ions start to be accelerated to move toward the inner surface of the sample and are injected into the inner surface. At the same time, the space charge decreases due to ion injection, which further causes further repulsion of electrons, making the edge of the sheath move toward the gate 9, and finally ends at The grid forms a stable plasma emitting surface near the grid. In this case, the generation of plasma and the acceleration of ions are limited to two regions, namely the cathode 8 and the grid 9 to generate plasma, and the grid 9 and the inner surface of the sample 4 to extract and accelerate ions. The electrode configuration at this time is similar to a classical ion source composed of a discharge chamber and an extraction system.

(7) The high-voltage pulse ends and the plasma returns to a normal state.

(8) After one hour of treatment, turn off the high voltage power supply and the radio frequency source, stop the high vacuum, and take out the sample.

If the outer surface does not need to be modified, a ceramic sleeve 10 (as shown in FIG. 2B ) can be placed outside the sample.

The measurement of the axial distribution of the plasma near the inner surface of the sample by the Langmuir probe shows that the plasma density along the axial direction is indeed very uniform, and the expected effect is achieved.

The chemical composition of the inner surface of the treated sample was characterized by material surface analysis technology, and the results showed that a metal film layer was deposited on the inner surface of the sample, and the film layer was relatively uniform along the axial direction.

In the present invention, because the radio frequency plasma is excited between the cathode and the grid, the density distribution of the plasma along the axial direction is uniform, the plasma density is high, and the plasma distribution along the axial direction does not change with the change of parameters such as discharge pressure and sample diameter-to-length ratio. , which fundamentally solves the problem of injection dose uniformity. The invention uses the cathode sputtering mechanism to introduce cathode material particles into radio frequency plasma. When the cathode material is metal, metal ion implantation or thin film deposition can be realized, which makes the modification methods more abundant and can comprehensively improve the inner surface performance. Due to the existence of the grid, the dynamically changing sheath edge can be finally fixed near the grid, and the ion generation area is separated from the ion acceleration area. On the one hand, the instability caused by the interference of the negative high voltage pulse on the plasma is greatly reduced. ; On the other hand, the acceleration voltage can be further increased.

Below in conjunction with accompanying drawing and embodiment the present invention is described in detail:

Figure 1 is a schematic diagram of the internal surface modification technology. 1A is a perspective view, and FIG. 1B is a cross-sectional view.

Figure 2 is a schematic diagram of the grid-enhanced inner surface modification technology. 2A is a perspective view, and FIG. 2B is a cross-sectional view.

Figure 3 is a block diagram of the gate-enhanced inner surface technology system.

Figure 4 is the axial distribution of plasma density in the cylinder.

Fig. 5 is the silicon surface film composition at different axial positions measured by electron probe microanalysis technique. Wherein Fig. 5A is a schematic diagram of placing a silicon chip on the inner surface of a cylinder; Fig. 5B is a diagram of the measured surface composition.

Figure 6 is the X-ray photoelectron spectra of Ti2p and N1s. Figure 6A is the X-ray photoelectron spectrum of Ti2p measured at different film depths; Figure 6B is the N1s X-ray photoelectron spectrum, which shows that there is titanium nitride in the film.

Among them: 1. Diffusion plasma; 2. Negative high-voltage pulse power supply; 3. Auxiliary anode; 4. Tubular sample; 5. Radio frequency power supply; 6. Capacitance; 7. Fine-tuning needle valve; 8. Cathode; 10. Ceramic sleeve; 11. Vacuum chamber; 12. Vacuum system; 13. Ground; 14. Argon cylinder; 15. Nitrogen cylinder.

Example 1:

As shown in Figure 3, a horizontal stainless steel with a length of 40 centimeters and a wall thickness of 5 millimeters is made into a vacuum chamber 11, which is provided with several windows for observation and monitoring. An automobile cylinder is used as a tubular sample 4 to be processed, a cylindrical cathode 8 is processed with a titanium rod, and a cylindrical grid 9 is processed with a stainless steel grid. The shaft is inserted so that the cathode, the grid and the cylinder are coaxially fixed. The cathode and the grid are connected to the radio frequency power supply 5 outside the vacuum chamber through a well-designed sealed coaxial joint, wherein the cathode is connected to the power pole of the radio frequency power supply through a DC blocking capacitor 6 , and the grid is connected to the ground 13 . A radio frequency discharge is established between the grid and the cathode to generate a uniform plasma along the axial direction. The negative bias is connected to the injected tubular sample 4 through the sealed window at the top of the vacuum chamber 11 . In order to facilitate various micro-analysis, single crystal silicon is placed as a substrate in different positions on the inner surface of the cylinder along the axial direction, and the effect of inner surface modification can be indirectly characterized through the analysis of the silicon substrate.

Wherein the cathode 8 is processed by 99.9% metal titanium; the grid 9 is processed by a stainless steel grid; the size of the automobile cylinder as a sample is φ120mm (inner diameter)×200mm. The pressure of the working gas nitrogen is maintained at 0.3Pa. The radio frequency power is 10 watts. In order to strengthen the sputtering, a DC voltage is applied to the cathode at the same time. The DC discharge voltage is maintained at 1800 volts, and the discharge current is maintained at 200 mA. A 1000 V DC negative bias was applied to the sample.

The axial distribution of the plasma density in the sample was measured with a Langmuir probe, and Fig. 4 is the axial distribution of the plasma density in the cylinder. In order to facilitate comparison of effects, the results of the other two known methods are also shown in this figure. The vertical axis represents the normalized plasma density, the horizontal axis represents the axial position, and the origin is selected in the middle of the sample. The upper triangle symbol represents the axial distribution of plasma density in the present invention; the dot symbol represents the axial distribution of plasma in the original internal surface modification technology; the circle represents the axial distribution of plasma in a cylinder immersed in plasma. It can be seen from the comparison that the uniformity of the plasma density inside the sample is greatly improved. Because in the previous method, the plasma inside the sample is diffused from the outside of the sample, so the density decreases toward the middle of the tube, where the density is the smallest; while the plasma of the present invention is generated inside, so the internal density is basically uniform, The maximum is in the middle. Due to diffusion losses, the plasma density decreases slightly at both ends of the sample.

In order to confirm that the present invention can indeed realize the metal plasma ion implantation and deposition and the uniformity of the dose, the surface of the treated single crystal silicon sample is analyzed by electron probe microanalysis technology. Figure 5A shows a schematic diagram of silicon wafer placement, and Figure 5B is the composition analysis result, expressed in atomic percentage. It can be seen from the figure that the film contains two components of titanium and nitrogen, and the ratio of titanium to nitrogen is about 2:1, which shows that the present invention realizes the deposition of the metal film, and the axial distribution of the components is basically uniform.

The film valence state was analyzed by X-ray photoelectron spectroscopy, and Fig. 6 is the analysis result. The results illustrate the formation of a titanium nitride phase, while it can be seen that the film has been oxidized.

From the above experiments and analysis, it is proved that the grid-enhanced inner surface modification technology can realize the uniform modification of the inner surface of the tubular sample. In fact, this technology provides a way to modify the inner surface. No matter what shape the sample is, as long as the gate and cathode can be processed to meet the requirements, the inner surface can be modified. The present invention only takes the internal surface modification of tubular samples as an example, and the internal surface modification of other complex shape samples can be solved by the three-electrode configuration idea proposed by the present invention. Therefore, any use of the three-electrode configuration idea proposed by the present invention , should belong to the scope of protection of this patent.

Claims (2)

1. the method for a modifying inner surface of tubular workpiece is characterized in that: may further comprise the steps:

(1) cylindrical cathode and tubulose grid electrode are inserted the tubulose sample interior coaxially, will be coaxial by three electrodes that negative electrode, grid, sample are formed, fixing, negative electrode is connected by the outer radio-frequency power supply of sealing coaxial fitting and vacuum chamber with grid, wherein negative electrode is connected with the radio-frequency power supply power utmost point by stopping condenser, and grid is connected with radio-frequency power supply ground electrode and ground;

(2) above-mentioned three-electrode system is placed vacuum chamber, vacuum chamber is connected with the vacuum system of being made up of diffusion pump and mechanical pump, working gas is provided by argon bottle and nitrogengas cylinder, by the size of fine setting needle-valve change air pressure and airshed, places monocrystal silicon substrate at sample internal surface different positions;

(3) be evacuated to 10 ^-3Pa;

(4) charge into working gas to 0.1～1Pa, by radio-frequency power supply output radio frequency power, between negative electrode and grid, produce a uniform vertically stable state radio-frequency plasma, and cathode material atom and ion are introduced plasma body by radio-frequency sputtering mechanism, this plasma body to the diffusion of tubular specimen internal surface, vertically uniformly spreads plasma body thereby form by grid mesh between grid and sample internal surface;

(5) sample and pulse negative high voltage power source join, and at the negative high voltage impulse duration, form the even radial electric field to acceleration of ions between grid and sample internal surface, enter into positive ion between grid and sample internal surface and are accelerated and are injected into the sample internal surface;

(6) when negative high voltage is added on the sample, form plasma sheath between sample internal surface and diffusion plasma body, in the time scale of plasma electron frequency inverse, near the sample internal surface electronics at first is in the sample repulsion of negative potential and leaves the sample internal surface and move to the grid direction, form a positive ion sheath, in the time scale of plasma ion frequency inverse, ion begins to be accelerated to the sample inner surface movement and is injected into internal surface, reduce owing to the ion implantation space charge that causes simultaneously, and then cause further repulsion to electronics, make the sheath edge move to the grid direction, and finally terminate in grid, near grid, form stable plasma emission face, in this case, the generation of plasma body and acceleration of ions are limited in two zones, and promptly negative electrode and grid produce plasma body, and grid and sample internal surface are drawn and speeding-up ion;

(7) high-voltage pulse finishes, and plasma body recovers standard state;

(8) handle after one hour, close high-voltage power supply and radio frequency source, stop high vacuum, take out sample.

2. by the method for the described modifying inner surface of tubular workpiece of claim 1, it is characterized in that: if do not need the modification outside surface, then can be at sample outside cover one ceramic jacket.

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