Apparatus and method for etching semiconductor wafer

Abstract: A semiconductor wafer etching apparatus capable of anisotropically etching a large-diameter semiconductor wafer with high accuracy without causing the semiconductor wafer to be charged. The semiconductor wafer etching apparatus has a fast atom beam source (4) for generating an electrically neutral fast atom beam of gas atoms or molecules to etch a semiconductor wafer by using the fast atom beam.

Description: The present invention relates to a semiconductor wafer etching apparatus and method, more particularly, to an apparatus for etching a semiconductor wafer by a fast atom beam. Semiconductor devices are decreasing in size year by year. Nowadays, LSIs of high integration, e.g., 16 Mega (M) to 64 M bit memories, are being produced. In the process of producing these semiconductor devices, etching apparatuses are used to etch thin films formed by sputtering, CVD, etc. into desired circuit patterns. Such etching apparatuses are demanded to be capable of effecting finer etching at higher reaction rate and with improved selectivity and also compatible with wafers having large diameters. Conventional etching apparatuses of the type described above have heretofore been arranged to etch specimens, e.g., semiconductor wafers, chemically and physically by using charged particles such as those in a plasma or ions. Therefore, the conventional etching apparatuses have disadvantages as stated below: I. With the etching process that employs a plasma, anisotropic etching cannot be effected because it is impossible to control the direction of incidence of charged particles or active species impinging on the substrate surface. II. When an insulating film such as SiO₂ is etched by using ions, for example, the semiconductor substrate itself may be charged with electricity. There is therefore likelihood that the etching will not proceed, or dielectric breakdown of the insulating film will occur due to the charged substrate. III. When etching is carried out by using an ion beam, the beam is likely to diverge by the repulsion between ions, so that it is difficult to hold the required etching accuracy. IV. Charged particles are readily affected by a magnetic field or the condition of the atmosphere because of their electrical properties. Therefore, it is difficult to etch semiconductor wafers having large diameters by using charged particles. In addition, the conventional etching apparatuses of the type described above suffer from the disadvantage that the semiconductor wafer surface may be contaminated by impurities generated from the apparatus or impurities in the atmosphere before or after or during the etching operation. An apparatus and method for etching semiconductor wafers by a neutral beam of reactive fast atoms is described in the article by Kuwano and Shimokawa in J. Vac. Sci. Technol. B6(5), Sept/Oct 1988, pages 1565-1569. It is an object of the present invention to provide a semiconductor wafer etching apparatus capable of anisotropic etching and also capable of etching a large-diameter semiconductor wafer with high accuracy without causing the semiconductor wafer to be charged. The present invention provides a semiconductor wafer etching apparatus by using an electrically neutral fast atom or molecule beam having means whereby a gas, e.g., fluorine, chlorine, bromine, etc., is adsorbed on a semiconductor wafer at a low temperature, thereby keeping the semiconductor wafer clean, and moreover increasing the reaction rate and the selectivity by utilization of the interaction between the adsorbed atoms and the fast atom beam. According to the present invention, a semiconductor wafer etching apparatus comprises a cooling means for cooling a semiconductor wafer located in nitrogen gas or a halogen gas so that said semiconductor wafer absorb said gas and is covered with atoms of said gas, a fast atom beam source for generating an electrically neutral fast atom beam of gas atoms or molecules, and reaction means for etching said semiconductor wafer covered with atoms of said gas using said fast atom beam. The apparatus also comprises process gas supply means for supplying process gas to said fast atom beam source and a beam shutter means for cutting off said atom beam when said atom beam is unstable. The cooling means comprises a preliminary chamber having first gate means for carrying said semiconductor wafer therethrough to or from said preliminary chamber, cooling system, vacuum means for evacuating said preliminary chamber and gas supply means for supplying said preliminary chamber with nitrogen gas or a halogen gas. The reaction means comprises a main reaction chamber having second gate means for carrying said semiconductor wafer therethrough to or from said main reaction chamber, vacuum means for evacuating said main reaction chamber, stage means for lifting and rotating said semiconductor wafer during applying said fast atom beam to it, and heat means for heating said semiconductor wafer during applying said fast atom beam to it. The present invention also provides a method for etching a semiconductor wafer comprises the steps of carrying a semiconductor wafer from a first cassette loader into a preliminary chamber, cooling said semiconductor wafer and having said semiconductor wafer absorb nitrogen gas or a halogen gas in said preliminary chamber so that said semiconductor wafer is covered with atoms of said gas, carrying said semiconductor wafer from said preliminary chamber into a main reaction chamber, introducing a process gas into a fast atom beam source and applying a high voltage to said fast atom beam source so that an electrically neutral fast atom beam of gas atoms or molecules is generated, applying said fast atom beam to said semiconductor wafer in said reaction chamber so that etching is performing on said semiconductor wafer, carrying said etched semiconductor wafer from said reaction chamber into a second cassette loader. The method further comprises the step of cooling said etched semiconductor wafer and having it absorb nitrogen gas or a halogen gas so that it is covered with atoms of said gas, before carrying said etched semiconductor wafer into a second cassette loader. Preferably the process gas comprises an element selected from fluorine, chlorine, oxygen, bromine, and hydrogen, or a compound of these elements. The main feature of the present invention resides in that a gas, e.g., fluorine, chlorine, bromine, etc., is introduced in a preliminary chamber so as to be adsorbed on a semiconductor wafer at a low temperature, and this semiconductor wafer is etched by irradiation with a fast atom beam of an element, e.g., fluorine, chlorine, oxygen, bromine, hydrogen, etc., and a compound of these elements in a main reaction chamber, and that after the completion of the etching process, a gas, e.g., fluorine, is adsorbed on the semiconductor wafer again to keep it clean. The present invention differs from the prior art in that the preliminary chamber, which has been employed merely for isolating the main reaction chamber from the atmosphere in the prior art, is employed for adsorption of a gas, e.g., fluorine, chlorine, bromine, etc., on the semiconductor wafer at a low temperature in addition to the isolating purpose, and that an electrically neutral fast atom beam is employed for the etching process instead of ions or a plasma, and the interaction between the fast atom beam and the adsorbed atoms is utilized, and further that after the completion of the etching process, a gas, e.g., fluorine, is adsorbed on the semiconductor wafer again to keep it clean. Fig. 1 shows a semiconductor wafer etching apparatus according to one embodiment of the present invention. Fig. 2 shows the flow of gases in the semiconductor wafer etching apparatus according to one embodiment of the present invention. Fig. 3 shows an analyzing system in the semiconductor wafer etching apparatus according to one embodiment of the present invention. Fig. 1 shows a semiconductor wafer etching apparatus according to one embodiment of the present invention. Reference numeral 1 denotes a main reaction chamber, 2 and 3 preliminary chambers, and 4 a fast atom beam source. Reference numeral 5 denotes a cassette loader, 6 a cassette unloader, 7 and 8 transfer arms, 9 a loader arm, 10 an unloader arm, and 11 a wafer rotating and lifting stage. These elements constitute a transfer system for transferring a semiconductor wafer. Reference numerals 12, 13, 14 and 15 denote rectilinear mechanisms. These mechanisms drive the cassette loader 5 and the cassette unloader 6 to transfer a semiconductor wafer. Fig. 2 shows the flow of gases in the semiconductor wafer etching apparatus. Fig. 2(A) is a front view of the etching apparatus, and Fig. 2(B) is a side view thereof. The evacuation system will first be explained. A main process pump 16 and a roughing vacuum pump 17 are used to evacuate the main reaction chamber 1 and the fast atom beam source 4. A roughing vacuum pump 18 is used to evacuate the preliminary chambers 2 and 3. A main process pump 19 and a roughing vacuum pump 20 are provided for the purpose of mass spectrometric analysis. Gate valves 21, 22, 23 and 24 are used to separate the vacuum chamber from each other. Valves 25, 26, 27, 28, 29, 30, 31 and 32 are used to isolate the pump evacuation systems from each other. A valve 33, a mass flow controller 34 and vacuum gauges 35, 36 and 37 are used to introduce a process gas comprising an element, e.g., fluorine, chlorine, oxygen, bromine, hydrogen, etc. and a compound of these elements, and to control the pressure. Valves 38 and 39 and vacuum gauges 40 and 41 are used to introduce nitrogen gas or a gas, e.g., fluorine, chlorine, bromine, etc., into the preliminary chambers 2 and 3 and to measure the pressure. Fig. 3 shows the analyzing system of the main reaction chamber for etching a semiconductor wafer. Fig. 3(A) is a front view of the etching apparatus, and Fig. 3(B) is a side view thereof. A high-voltage supply current lead-in terminal 42 is used to produce an electric discharge in a discharge space provided in the fast atom beam source 4. Infrared lamps 43 and 44 are used to heat a semiconductor wafer as a specimen. A photoelectric sensor 45 and a reflector 46 are provided to stop the rotation of the stage at a predetermined position. A beam shutter 47 is used to cut off the fast atom beam from the fast atom beam source 4. A mass spectrometer 48 is used to make an analysis in the main reaction chamber 1. The operation of the semiconductor wafer etching apparatus according to the present invention will be explained below with reference to Figs. 1, 2 and 3. With the gate valves 21, 22, 23 and 24 closed, the main reaction chamber 1 is first roughly evacuated by using the roughing vacuum pump 17 and then evacuated to a high-vacuum region by using the main process pump 16. At the same time, the preliminary chambers 2 and 3 are also evacuated to the region of 10⁻³ Torr by using the roughing vacuum pump 18. After the completion of the evacuation, nitrogen gas is introduced by opening the valve 38 with the valve 25 closed. When the pressure becomes near the atmospheric pressure, the gate valve 23 is opened. An arm is associated with the rectilinear mechanism 14 and takes out a semiconductor wafer from the cassette loader 5 which moves vertically on the rectilinear mechanism 12. The loader arm 9 moves up to receive the semiconductor wafer and then moves down to carry it into the preliminary chamber 2. Then, the valve 23 and the valve 38 are closed and the valve 25 is opened, and the preliminary chamber 2 is evacuated to the region of 10⁻³ Torr. After that, the valve 25 is closed and the valve 38 is opened, thus fluorine, chlorine bromine etc., is introduced in the preliminary chamber. The preliminary chamber 2 is provided with a semiconductor wafer cooling means, for example, liquid nitrogen cooling system which is provided in a stage where the semiconductor wafer is placed, thereby cooling the semiconductor wafer to a low temperature. By using this cooling means, atoms of the introduced gas, e.g., fluorine, chlorine, bromine, etc., are adsorbed on the semiconductor wafer at low temperature. Then, the transfer arm 7 receives the semiconductor wafer, and the valve 25 is opened to evacuate the preliminary chamber 2 to the region of 10⁻³ Torr. After the completion of the evacuation, the gate valve 21 opens, and the transfer arm 7 carries the semiconductor wafer into the main reaction chamber 1 and transfers it to the wafer rotating and lifting stage 11. After the transfer arm 7 has returned to the preliminary chamber 2, the gate valve 21 is closed to initiate etching by a fast atom beam. First, the valve 33 is opened to introduce a process gas comprising an element, e.g., fluorine, chlorine, oxygen, bromine, hydrogen, etc., and a compound of these elements into the fast atom beam source 4 with the flow rate being controlled by the mass flow controller 34. It should be noted that the vacuum gauge 35 is used to measure the pressure in the fast atom beam source 4, while the vacuum gauges 36 and 37 are used to measure the pressure in the main reaction chamber 1. Next, a high voltage is applied to electrodes placed in the discharge space of the fast atom beam source 4 through the high-voltage supply current lead-in terminal 42 to generate an electrically neutral fast atom beam of gas atoms or molecules. At this time, the beam shutter 47 is disposed in front of the fast atom beam source 4 to cut off the beam. When the fast atom beam has become stable, the wafer rotating and lifting stage 11 raises the semiconductor wafer as a specimen to a predetermined position. Then, the beam shutter 47 is withdrawn to apply the fast atom beam to the semiconductor wafer. At the same time, the semiconductor wafer is heated by the infrared lamps 43 and 44, and the stage 11 is continuously rotated. In this way, etching is performed. In addition, reaction products formed in the main reaction chamber 1 are measured by using the mass spectrometer 48. It should be noted that the details of the fast atom beam source 4 are disclosed, for example, in Japanese Patent Application No. 3-261231 (1991). Upon completion of the etching, the beam shutter 47 is advanced to cut off the fast atom beam. The stage 11 is stopped from rotating at a predetermined position by using the photoelectric sensor 45 and the reflector 46. At this time, the gate valve 22 opens, and the transfer arm 8 receives the semiconductor wafer which has undergone the etching process. The transfer arm 8 carries the semiconductor wafer to the center of the preliminary chamber 3 and transfers it to the stage of the unloader arm 10. Then, the gate valve 22 and the valve 30 are closed, while the valve 39 is opened to introduce a gas, e.g., fluorine, chlorine, bromine, etc., thereby adsorbing atoms of fluorine, chlorine, bromine, etc. on the semiconductor wafer at a low temperature. The stage where the semiconductor wafer is placed is provided with a cooling means, for example, liquid nitrogen cooling system, to cool the semiconductor wafer. Then, the valve 39 is closed and the valve 30 is opened, and the preliminary chamber 3 is evacuated to the region of 10⁻³ Torr. After that, the valve 30 is closed and the valve 39 is opened, thus nitrogen gas is introduced into the preliminary chamber 3. When the pressure becomes near the atmospheric pressure, the gate valve 24 is opened. Then, the unloader arm 10 moves up and transfers the semiconductor wafer to an arm that is associated with the rectilinear mechanism 15. The semiconductor wafer is then loaded into the cassette loader 6, which moves up and down by the operation of the rectilinear mechanism 13. Thus, the whole process of etching is completed. The above-described operations are automatically carried out under control of a computer that is provided on a control panel. As has been described above, the etching apparatus of the present invention has a fast atom beam source and a semiconductor wafer cooling means. Consequently, there is no contact with the atmosphere during a series of steps in the semiconductor wafer etching process, and there is no possibility of the semiconductor wafer being contaminated by impurities. In addition, since the semiconductor wafer surface is covered with atoms of fluorine, chlorine, bromine, etc., a clean and fine etching process can be realized. Further, the automation allows a rise in the etch rate and an increase in the number of substrates which can be etched. Since the present invention employs an electrically neutral fast atom beam, it is possible to solve serious problems presently existing in the semiconductor manufacturing process, i.e., charge-up, problems of none vertical etching in the semiconductor wafer in case of using charged particles of which beam diverges by the repulsion between ions, and damage to the substrate by ions. Accordingly, it is possible to realize finer etching with high accuracy, which has heretofore been impossible to attain because of the above-described problems. In addition, another problem attendant on the prior art, that is, the demanded improvement in the reaction rate and selectivity, can be solved by selecting an element for the fast atom beam and atoms to be adsorbed in conformity to the substrate and thin film to be etched. With the above-described contrivance, the present invention can also cope with large-diameter wafers appearing with the increase in the integration density, i.e., 16 M to 64 M bit memories.

Claims: A semiconductor wafer etching apparatus comprising; a cooling means for cooling a semiconductor wafer located in nitrogen gas or a halogen gas so that said semiconductor wafer absorb said gas and is covered with atoms of said gas, a fast atom beam source (4) for generating an electrically neutral fast atom beam of gas atoms or molecules, and reaction means (1) for etching said semiconductor wafer covered with atoms of said gas using said fast atom beam. A semiconductor wafer etching apparatus of Claim 1 further comprising process gas supply means (33) for supplying process gas to said fast atom beam source and a beam shutter (47) means for cutting off said atom beam when said atom beam is unstable. A semiconductor wafer etching apparatus of Claim 1 wherein said cooling means comprises a preliminary chamber (2,3) having first gate means for carrying said semiconductor wafer therethrough to or from said preliminary chamber, cooling system, vacuum means (18) for evacuating said preliminary chamber and gas supply means (38) for supplying said preliminary chamber with nitrogen gas or a halogen gas. A semiconductor wafer etching apparatus of Claim 1 wherein said reaction means comprises a main reaction chamber having second gate means for carrying said semiconductor wafer therethrough to or from said main reaction chamber, vacuum means (16) for evacuating said main reaction chamber, stage means (11) for lifting and rotating said semiconductor wafer during applying said fast atom beam to it, and heat means for heating said semiconductor wafer during applying said fast atom beam to it. A method for etching a semiconductor wafer comprising the steps of; carrying a semiconductor wafer from a first cassette loader (5) into a preliminary chamber (2), cooling said semiconductor wafer and having said semiconductor wafer absorb nitrogen gas or a halogen gas in said preliminary chamber so that said semiconductor wafer is covered with atoms of said gas, carrying said semiconductor wafer from said preliminary chamber into a main reaction chamber (1), introducing a process gas into a fast atom beam source (4) and applying a high voltage to said fast atom beam source so that an electrically neutral fast atom beam of gas atoms or molecules is generated, applying said fast atom beam to said semiconductor wafer in said reaction chamber so that etching is performing on said semiconductor wafer, carrying said etched semiconductor wafer from said reaction chamber into a second cassette loader (6). A method of Claim 5 further comprising the step of cooling said etched semiconductor wafer and having it absorb nitrogen gas or a halogen gas so that it is covered with atoms of said gas, before carrying said etched semiconductor wafer into a second cassette loader. A method of Claim 5, wherein said process gas comprises an element selected from fluorine, chlorine, oxygen, bromine, and hydrogen, or a compound of these elements.

Inventors: HATADA YOSHIO, NISHIMURA TATSUYA, SUZUKI HIDENAO, HATADA, YOSHIO, NISHIMURA, TATSUYA, SUZUKI, HIDENAO
Applicants: EBARA CORP, EBARA CORPORATION
Application year: 1993
Main classification: H01J37
IPC codes: H01J37, H01L21