TW451342B - Induction plasma processing chamber - Google Patents

Abstract

A method and an apparatus of plasma treating a wafer with low capacitive coupling, high induction power density and high uniformity of reactive species were disclosed in this invention. A first embodiment manages a multiturn helical coil to match with an impedance at an RF drive frequency for reducing capacitive coupling. A second embodiment uses a can-like dielectric to prompt plasma species approaching the wafer surface at a low pressure, thus providing higher plasma density and higher etch rate. A third embodiment uses a cap-like dielectric to raise the ceiling above the wafer for improving the plasma generation uniformity in the chamber.

Description

451 342 V. Description of the invention (l) [Field of invention] The present invention mainly describes a multifunctional inductively coupled plasma reactor with a variable dielectric window. The low voltage range of the plasma reactor can reach 1x1 〇-6 Torr to 4x1 0-1 Torr, very suitable for semiconductor etching and chemical deposition process. [Background and past technology] Due to the rapid development of plasma technology, materials that could only be synthesized at high temperatures in the past can gradually be replaced by low temperature technology. Plasma technology is widely used in microelectronics, photo-sensing systems or micro-electromechanical systems. In the semi-conductor front-end process, chemical etching is involved, and it will gradually be replaced by plasma etching. Plasma technology is roughly Divided into two types of traditional plasma and high-density plasma, the two have considerable differences in characteristics. The basic structure of the reactor in the traditional plasma is two electrode plates, each connected to one end of the high-frequency power supply, borrowing the two electrodes. The free electric field in the field is accelerated to collide with the gas molecules to excite the electrons in the gas molecules to generate a plasma. This type of plasma has its limitations in high-resolution etching; its optimal working range is Between 1X1 0-1 Torr and 4 Torr, due to the high working pressure, the probability of collision between particles is large, and the plasma density generated is not high enough, so that the rate and depth of vertical etching, and the ratio to the horizontal Very low. Based on the above-mentioned shortcomings in traditional plasma, there is a demand for high-density electricity sources. Inductively coupled plasma (ICP) is one of the developed forms. Its principle The current flows through a coil, using this page 5 451342 V. Description of the invention (2) Indue tance generated by the coil to induce a magnetic field. This magnetic field can pass through a medium (such as air, vacuum or ferromagnetic core) ) Generate secondary induced current and release energy in the form of plasma. As for how to release energy in a low voltage condition to produce high density and high uniformity plasma, it is the goal that scientists are pursuing.

Jacob et al. First published a high-density plasma reactor in II. S. Pat. No. 3,705,091, in which the plasma was generated in a spiral coil at a radio frequency (RF) operating frequency of 13 MHz; Although this plasma reaction device has a high etching rate, the pollution caused by the cavity wall due to capacitive coupling between the coil and the reaction chamber wall is very serious. In 1990, Ogle in US Patent 4, 948, 458 Another plasma reaction device with a different design was published; the coil was a flat induction coil and placed on a dielectric window. There is a matching network between the coil and the RF generator to protect the RF generator. When the frequency of 100MHz (typically 13.56MHz) is turned on, a parallel circle will be generated above the wafer in the reaction chamber. Like a plasma zone, the applicable pressure range of this plasma reactor is 1x1. 4 Torr to 5 Torr. According to Fob in IKS. Patent 5,619,103, the addition of a dielectric window will help reduce the capacitive coupling effect between the coil and the plasma.

Cuomo in U.S. Patent 5, 622, 635 further combined the above-mentioned techniques to design a plasma reactor containing a conductive shield. Its design is to add a conductive shielding layer between the planar or spiral coil and the dielectric window. This shielding layer is grounded and has a

Page 6 4 5 13 42 V. Description of the invention ⑶ It has the function of directing the induction capacitor away from the plasma / dielectric window interface "In theory, as the number of coil turns increases, the capacitive coupling effect on the coil will be effectively reduced And increase the intensity of the induced magnetic field and enhance the plasma reaction effect. However, as described by Forgotson in Inductively Coupled Plasma for Polymer Etching of 200 mm Wafers (J. Vac. Sci. Technol. B 14 (2), pp '732-737, 1 996), the matching network currently used cannot be used in 13.5 Self-inductance generated by a copper tube spiral coil with a diameter of 24 cm and 3 turns at a frequency of 6M Hz. Therefore, how to match multi-turn (Mul i turn) spiral coils to achieve better plasma generation efficiency is a problem that needs to be overcome urgently. Another problem that must be considered at the beginning of the plasma reactor design It is the uniformity of Li Li. The earliest application of the ICP system is in the field of money engraving. Hua is used in the field of chemical deposition (CVD). The pressure requirements and etching are greatly different; the working pressure range required for CVD is at least higher than that of etching Dozens of times, and the increase of pressure will cause the collision probability of reaction particles such as ions and electrons in the cavity to increase; if the reaction particles have recombinat ion due to collision with each other, non-uniform Density of electrical mass ° Fairbairn in U, S. Patent 5,6 14,055, designed a dome-shaped response top-of-the-line gj, and improved the uniformity of the plasma by increasing the distance between the induction line 圏 and the chip C. How to produce high-density and high-uniformity plasma in a low-voltage environment is a goal pursued by the eyes; how to reduce the capacitive coupling and increase the intensity of the induced magnetic field is a noteworthy direction. Explanation (4) [Objective of the Invention and Problem to be Solved] The object of the present invention is to design a multifunctional inductively coupled plasma reactor with a variable dielectric window, and aim at reducing the coil reactor wall. Capacitive coupling, improvement of the induced magnetic field in the reactor, improvement of the ionic substance flux, promotion of the plasma etching reaction rate, and uniformity of the plasma [Illustration of the diagram] Yuanyi, the plasma reaction of the present invention Analytical diagram of the side of the reactor; which successfully matched multiple turns of a spiral induction coil of large size (30 cm in diameter, 4 圏). Circle 2. The side of the plasma reactor of the present invention is a schematic circle; it contains a unique cylindrical medium The electric window 'is suitable for extremely low-voltage and high-efficiency etching processes. Circle III. The side profile of the plasma reactor of the present invention is illustrated; it contains a unique cap-shaped dielectric window. [Solution to the problem] The following is aimed at reducing capacitive coupling The solutions proposed to improve the induced magnetic field, increase the plasma density and uniformity will be described in detail; of course, the scope and effects of the present invention are not limited. The following embodiment: As described by Forgotson, the matching network used cannot adjust the copper pipe spiral with a diameter of 24 cm and a circle of 3 turns at a frequency of 13.56 MHz. Page 8 451342 V. Description of the invention (5) Loop Spontaneous inductance generated. However, in order to effectively reduce the capacitive coupling effect on the coil and increase the intensity of the induced magnetic field, the present invention successfully uses a self-developed matching system to successfully overcome a 30-cm-diameter, 4-turn spiral inductor at a frequency of 13.56 MHz. The spontaneous inductance of the coil is designed as shown in the inductively coupled plasma reactor of Fig. 1. The vacuum reactor main body 10 of Fig. 1 has stainless steel side walls 12, 18, and a bottom plate. 14. Glass window (viewing window) 20 and flange (flange) 16; flange has a gas inlet port (gas inlet port) 22, the vacuum reaction gas is through the hole 22 to provide β-dielectric A dielectric window 28 spans the central hole of the flange 16 and is hermetically bonded together. The dielectric window may be made of ceramic such as aluminum oxide or quartz. All vacuum components are welded, various gaskets, o-rings, and bolts to form a gas-tight connection to form a reaction chamber. The reaction gas entering through the air inlet 22 is excited to form an electrical apparatus' reactor main Zhao 10 in the reaction chamber, and the pressure range can reach 1x10 · β ~ 4x10_1 Torr through the operation of an external vacuum pump. The energy obtained by the plasma in the cavity is provided by a suitable high-frequency power source, and the magnetic field is induced by the inductance generated by the coil to provide the necessary energy to excite the plasma. The coil 26 of FIG. 1 in the present invention is a spiral coil wound with a diameter of 30 cm by a copper tube with a diameter of 6 cm in section; the coil formed is placed on the upper edge of the dielectric window 28 and is powered by an RF power source 38 A matching network 36 is connected to provide the required power through the output terminal 42; one of the input terminals 40 is guided to ground. A layer of metal frame 24 is provided on the periphery of the induction coil 26 to isolate the exposed electromagnetic generated by the coil.

4 5 1 3 4 2 5 'Explanation of invention (6) ----- wave. The frequency power used by the RF power supply μ μ ς, two + is 13.56MHz. Due to the role of the inductor coil, the system will naturally be poor ^ ^ ^ ^ ^ • The voltage of the tile house is quite high, and its voltage value is often as high as 1. and above, and the resonance caused by the conversion of electromagnetic energy: the high frequency in the system The current can reach more than 50 amps. Therefore, the tolerance of high-frequency power generators and resonance matching systems to high voltage and high current becomes a very important necessary condition. The invention overcomes the coil impedance to make a large size and high number of turns Spiral line 圏 'in order to reduce capacitive coupling. At the same time, the induced magnetic field is related to the sum of the magnetic flux generated by each number of turns of the coil; and the intensity of the induced magnetic field for each number of turns is related to the amount of current supplied . Therefore, 'high-turn induction coils not only reduce the capacitive coupling effect, but also increase the induced magnetic field under the provision of equivalent RF power, and then increase the reaction plasma density in the cavity. In the reaction cavity' ceramic dielectric Immediately below the window 28 is a crystal holder 32 on which a wafer 30 is placed. The crystal holder is connected to the chassis 14 by a support post (support r0 (j) 34; among them, there is a ceramic in the middle of the support post) The insulation layer 52 is to prevent the bias (bi as) provided to the wafer from being dissipated. There is a concentric RF shield 50 around the wafer. The wafer and the bottom of the dielectric window The distance D will affect the processing efficiency of the plasma process: it is designed to have a range of centimeters. The power supply for the wafer bias is a high-frequency rf generator 48; like another RF generator 38, the frequency used is also 13. 5 6MHz. As for other frequency power sources from kHz to MHz, 9 can also be used. For the purpose of low power and high response etching rate, the present invention has designed an inductively coupled plasma reactor as the second one; the dielectric window 28 'Designed with a unique cylindrical structure dielectric layer. In the present invention, the spiral inductor coil is convenient ΗΒΗ »451342 V. Description of the invention (?) Coaxially placed in the cylinder' Reuse this cylindrical dielectric layer 28 'It is placed in the reaction chamber to shorten the distance between the inductor coil and the wafer. Under extremely low-voltage etching conditions, it can achieve an isotropic tropic etching and a high reactive etching rate at a lower output power. Figure 2 Medium, cylindrical dielectric layer 28 'deep into vacuum The distance between the inside of the main body of the reactor 10 is X'X and the range is 0 cm to cm; in the embodiment of the present invention, the preferred range is 0 cm to 5 cm. Compared with the plasma device published by jac〇b 'Deep into the cavity to isolate the dielectric layer 28 between the inductive coil and the cavity wall as shown in Figure 2 of the present invention' 'It has the effect of reducing the capacitive coupling between the coil and the plasma. Because the distance between the coil and the wafer is shortened, so This device is suitable for the etching range of extremely low pressure; the pressure range is from 1xΐ〇-β torr to 1x104 torr, and the preferred operating range is from lxl0-s torr to 1xl0_2 torr. Under this pressure range ' This device can produce high plasma ion density and excellent anisotropic etching rate. In the following discussion ', the etching performance of gallium nitride (GaN) will be taken as an example to show the excellent performance of the device shown in the second aspect of the present invention. In addition, in order to solve the problem of uneven plasma density distribution caused by the collision between the low and medium reaction particles, the present invention designs an inductively coupled plasma reactor as shown in Fig. 3; the dielectric window 28 " is designed into a unique hat shape Structure dielectric layer. As is generally understood, there is a direct relationship between the operating pressure and the mean free path (Cmean-free-path). The mean free path refers to the path traveled by each particle in the system during two consecutive collisions with other particles. Average distance. Because the particle density is directly proportional to the system pressure 'and both are inversely proportional to the mean free path. In other words, the average free path of a gas vessel in a low-pressure system is higher than in a high-pressure system.

Page 11 451342 V. Description of the invention (8) Large, relatively low collision probability of particles. "When an ion is accelerated towards a wafer and an etching reaction is to occur, the lower the collision probability encountered. The etching direction caused by this particle to this wafer will be more vertical; on the contrary, the increase of the working pressure when the reactor is used in the CVD process will increase the probability of collision between the reaction particles; If a combination reaction occurs, an uneven plasma density will be generated in the cavity. In order to solve this plasma distribution problem, one of the solutions is to increase the distance between the inductor coil and the wafer and increase the average free path of particles to improve the uniformity of the plasma. Fairbairn, in U.S. Paten t 5, 614, 055, designed a dome-shaped reactor roof to increase the distance between the inductor and the chip. The present invention designs an inductively-coupled plasma reactor containing a unique hat-shaped dielectric layer as shown in Fig. 3 to improve the uniformity of the plasma. A spiral inductor coil can be conveniently placed coaxially in this unique hat-shape. The dielectric layer is structured, and the electric field β with a uniform plasma density is excited. In FIG. 3, the distance between the cap-shaped dielectric layer 28 and the flange 16 is x, and the preferred range of x is from 0 cm to 10 cm. Compared with the plasma device published by Fairbairn, the reactor of the present invention can adjust the ceiling height by maneuverability and is suitable for different requirements under different operating conditions. [Effect] The inductively coupled plasma reactor with multifunctional variable dielectric window designed by the present invention successfully reduces the capacitive coupling, improves the induction magnetic field, promotes the uniformity of the plasma and the etching reaction rate. Inventions in industry should

Page 12 451342 V. Explanation of the invention (9) The advantage of using etched GaN as an example "First, the GaN wafer 30 is sent to the platform 32 of the second reactor body 10 by a robotic arm, and the coil 26 and The distance D on the wafer surface is 7.5 cm (X is 2.5 cm); the gas in the reactor is evacuated to a pressure of 5x1 0-6 Torr 'by using a vacuum pump, and then the gas and the boronized reaction gas are passed through the air inlet 2 by a gas flow meter. 2Into the reactor body 10, the flow of gas and boron gas is set at 20 standard cubic centimeters (SCCIn) and 10 standard cubic centimeters per minute, respectively. The pressure in the reaction chamber is adjusted to 1x1 〇-2 Torr, RF The power supply is set to 100 Off and the bias voltage is 200 volts. At this time, the reaction gas is excited and presents a unique discharge and luminescence phenomenon of the plasma. After the 2 minute etching process, the GaN wafer (removed by the robot arm, the interpretation results show that there are Excellent anisotropy and still #etch rate; #etch rate can reach 3,500 angstroms per minute. In the etching experiment using the device shown in circle three (^ is 丨?. 5 cm; X is 2.5 cm), RF power 75 ff; 1χ The plasma generated by ΐ_2_2 Torr and Ar gas flow rate of 40 standard cubic centimeters has a peak ion density value of 5 × 10 cm-3 at the lower 6 cm of the dielectric window 28, and its diagonal exceeds 20 cm. The uniformity can reach 15%.

Page 13

Claims (1)

451342 Case No. 88120381 Correction / Addition 6 Amendment _ _ VI. Patent application scope Amend S. Please request I Cao 1. An inductively coupled plasma reactor, including: a reactor body: the display 0. A dielectric window having a planar base and an upright wall integrally formed around the planar base; and a coil for generating an inductively coupled plasma, the coil is placed on the dielectric window On a flat substrate; It. Among them, the free end of the upright wall of the dielectric window is air-tightly bonded to the inverter body, thereby providing a plasma generating area confined between the reactor body and the dielectric, wherein the dielectric window The method of hermetically bonding to the body of the reactor allows the flat base of the dielectric window to protrude beyond the reactor itself or into the body of the reactor β 2. Inductively coupled as in the first patent application The plasma reactor has a cylindrical interface window. 3. The inductively coupled plasma reactor according to item 1 of the patent application scope, wherein the height of the upright wall from the plane base is less than 10 cm. 4. The inductively-coupled plasma reactor according to item 3 of the patent application, wherein the height of the upright wall from the plane base is less than 5 cm. 5. The inductively-coupled plasma reactor according to item 1 of the patent application scope, wherein the reactor body includes a chassis; an upright side wall surrounding the chassis; a flange at the free end of the upright side wall, wherein the method The blue disk extends inwardly from the upright side wall and forms a hole at its center, wherein the dielectric window covers the hole airtightly. \\ α1εη1 «η \ 199911Ο3 \ ΡΑΤΈΝΤ \ η3Π1020Αηιβηά01.ρΐο Page 14 2001.01.11.015 451342 Case No. 88〗 2Π381 Amendment VI. Patent Application Scope 6. Such as the inductive coupling plasma reactor of the first scope of the patent application ' The manner in which the dielectric window is air-tightly coupled to the reactor body allows the planar base of the dielectric window to protrude outside the reactor body. 7. The inductively-coupled plasma reactor according to item 1 of the patent application, wherein the dielectric window is hermetically coupled to the reactor body such that the planar base of the dielectric window projects into the reactor body. . 8. The inductively-coupled plasma reactor according to item 5 of the patent application, wherein the dielectric window covers the hole in a gas-tight manner so that the planar base of the dielectric window protrudes out of the reactor body. 9. The inductively-coupled plasma reactor according to item 5 of the application, wherein the dielectric window covers the hole in a gas-tight manner so that the planar base of the dielectric window extends into the reactor body. 10. The inductively-coupled plasma reactor according to item 1 of the patent application scope, wherein the dielectric window is made of ceramic. 11. Inductively coupled plasma reaction such as the scope of patent application No. 12 \\ Chenlin \ 19991103 \ PATENT \ narll020Amend01.ptc Page 15 2001.01.11.016 451342 _ __ Case No. 88120381_ Year Month Date. Revised-6 、 Patent application scope device, where the line coil is a spiral coil, and The electric window is cylindrical, wherein the spiral coil is coaxial with the dielectric window. 12. A method for improving the flux of ionic substances in an inductively coupled plasma reactor and an inductively coupled plasma generated under a vacuum pressure of from 0.00 to 10.0 millitorr, The bottom plate of the inductively coupled plasma reactor has a fixed height from the top plate. The method includes using a dielectric window as a part of the top plate. The dielectric window has a planar substrate and is integrated around the planar substrate. The upright wall is formed, and the dielectric window is hermetically bonded to the top plate, and the planar base of the dielectric window is protruded into the body of the reactor i in a combined manner. I 13. The method according to item 12 of the patent application range, wherein the inductive consumable plasma is generated using a coil placed on a flat substrate of the dielectric window. 14. The method of claim 13 in which the coil is a spiral coil, and the dielectric window is cylindrical, and wherein the spiral coil is coaxial with the dielectric window. 15. The method of claim 12 in the scope of patent application, wherein the height of the upright wall from the plane base is less than 10 cm. 16. The method of claim 15 in which the upright wall is from WChenl in \ 1999! 103 \ PATENT \ nar 1! 020Amend01 .ptc Page 16 2001.01.11.017 4 5 T 3 4 2 _ Case No. 88120381 _ Year Month Day Amendment__ Sixth, the scope of patent application The height is less than 5 cm. 17. The method of claim 12, wherein the inductively coupled plasma is generated under a vacuum pressure of 0.01 to 10.0 millitorr. 18. —A method for improving the uniformity of the plasma generation of an inductively coupled plasma generated in an inductively coupled plasma reactor and a vacuum pressure higher than 10.0 millitorr 'The inductively coupled plasma The bottom plate of the reactor has a fixed height from its top plate. The method includes using a dielectric window as a part of the top i plate. The dielectric window has a flat substrate and an upright wall integrally formed around the flat substrate. In addition, the dielectric window is hermetically bonded to the top plate, and in a combined manner, the planar base of the dielectric window protrudes out of the reactor body. 19. The method of claim 18, wherein the inductively coupled plasma is generated using a coil placed on a flat substrate of the dielectric window. 20. The method as claimed in claim 19, wherein the coil is a spiral coil 'and the dielectric window is cylindrical, wherein the spiral coil and the dielectric window share a secret. 21. The method of claim 18, wherein the height of the upright wall from the plane base is less than 10 cm. WChenl in \ 19991103 \ PATENT \ narll020Amend01 .ptc page 17 2001 〇1 11 〇18 451342 _; _ case number 88120381_ year month day amendment _ 6, the scope of patent application 22. If the method of applying for the scope of the patent No. 21, where The upright wall is less than 5 cm south from the plane base. 23. The method of claim 18, wherein the inductively coupled plasma is generated under a vacuum pressure between 10 and 100 millitorr. \ \ Chen1i η \ 19991103 \ PATENT \ na r11020Amend01.p t c page 18 2001.01.11.019