text: Patent US6790723 - Semiconductor device and method of manufacturing the same - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsHexachlorodisilane (Si2Cl6) is used as a Si raw material for forming a silicon nitride film that can be widely different in the etching rate from a silicon oxide film. The silicon nitride film is formed by an LPCVD method....http://www.google.com/patents/US6790723?utm_source=gb-gplus-sharePatent US6790723 - Semiconductor device and method of manufacturing the sameAdvanced Patent SearchPublication numberUS6790723 B2Publication typeGrantApplication numberUS 09/984,404Publication dateSep 14, 2004Filing dateOct 30, 2001Priority dateJan 8, 1999Fee statusPaidAlso published asUS6333547, US7060555, US7098115, US7129132, US20020024119, US20040259386, US20040266176, US20040266177Publication number09984404, 984404, US 6790723 B2, US 6790723B2, US-B2-6790723, US6790723 B2, US6790723B2InventorsMasayuki Tanaka, Shigehiko Saida, Yoshitaka TsunashimaOriginal AssigneeKabushiki Kaisha ToshibaExport CitationBiBTeX, EndNote, RefManPatent Citations (3), Non-Patent Citations (1), Referenced by (21), Classifications (42), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetSemiconductor device and method of manufacturing the same
  US 6790723 B2Abstract
  preparing a semiconductor substrate; and forming a silicon nitride insulation film on said semiconductor substrate by a low pressure chemical vapor deposition method using a compound having a Si—Si bond and a Si—Cl bond as a Si raw material. 2. A method of manufacturing a semiconductor device according to claim 1, wherein said silicon nitride film is formed to cover the surfaces of said semiconductor substrate and a gate electrode formed on the semiconductor substrate, and said method further comprises the steps of:
  forming an interlayer insulating film on said silicon nitride film; and forming a through-hole extending through a portion of said interlayer insulating film and silicon nitride film to reach the surface of the semiconductor substrate. 3. A method of manufacturing a semiconductor device according to claim 2, wherein the raw material of said silicon nitride film is represented by a general formula SinCl2n+2−xHx, where n is an integer not smaller than 2, and x is an integer not larger than 2n+1.
  4. A method of manufacturing a semiconductor device according to claim 1, wherein the said silicon nitride film is formed to a thickness of 10 nm or more.
  This is a division of application Ser. No. 09/478,369, filed Jan. 6, 2000 now U.S. Pat. No. 6,333,547, which is incorporated herein by reference.
  In the next step, a treatment with a dilute hydrofluoric acid is carried out for removing the native oxide film in the contact portion. What should be noted is that the etching rate of the DCS-SiN film formed at 780� C. by using dichlorosilane (DCS) as a raw material is 0.2 nm/min when etched with a dilute hydrofluoric acid ({fraction (1/200)}) in contrast to about 1 nm/min for the native oxide film. Since the etching rate of the DCS-SiN film is low, the native oxide film fails to be removed in the etching step with the dilute hydrofluoric acid.
  On the other hand, a high processing speed is required for a logic device, making it necessary to decrease the so-called "RC delay time", i.e., to decrease the capacitance between adjacent wirings and the wiring resistance. For decreasing the wiring resistance, use of copper for forming the metal wiring is being studied. For using a copper wiring, a barrier layer is required for preventing oxidation of the copper wiring and for preventing diffusion of copper within the copper wiring. Use of a SiN layer is now under study as one of the barrier layers.
  In a semiconductor device, the aspect ratio of the device element separating trench and the concave portion between gate electrodes tends to be increased in accordance with miniaturization of the device element. With increase in the aspect ratio, it gradually becomes difficult to bury an insulating film such as a silicon oxide film within the trench without forming a so-called "void".
  According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the step of forming a silicon nitride film having a chlorine concentration of at least 4�1020 cm−3 by an LPCVD method using a compound having a Si—Si bond and a Si—Cl bond as a Si raw material.
  (4) The silicon nitride film having a chlorine concentration of at least 4�1020 cm−3 is formed by an LPCVD method using a compound having a Si—Si bond and a Si—Cl bond as a Si raw material. Specifically, the Si raw material is represented by SinCl2n+2, where n is 2 or more, or SinCl2n−2Hx, where n is 2 or more, and x is 2n+2 or less. Particularly, it is desirable to use Si2Cl6 as the Si raw material. Also, NH3 is used as the nitrogen source.
  It has been found as a result of the research conducted by the present inventors that, if a compound having a Si—Si bond and a Si—Cl bond such as Si2Cl6 is used as the Si raw material in the LPCVD method for forming a silicon nitride film, it is possible to form a silicon nitride film exhibiting a selectivity ratio relative to a silicon oxide film in respect of the polishing and etching. Also, the step coverage remains unchanged because the LPCVD method satisfactory in step coverage is employed in the method of the present invention.
  Concerning the LPCVD method for forming a silicon nitride film, it has been found that, if a compound having a Si—Si bond and a Si—Cl bond such as Si2Cl6 is used as the Si raw material, it is possible to form a silicon nitride film exhibiting a sufficiently large etching selectivity relative to a silicon oxide film.
  (4) The silicon nitride film is formed by an LPCVD method using a compound having a Si—Si bond and a Si—Cl bond as a raw material gas.
  (5) The compound used in the LPCVD method is represented by SinCl2n+2 or SinCl2n+−xHx, where n is an integer of 2 or more, and x is an integer smaller than 2n+2. A typical example of the particular compound is hexachlorodisilane.
  The chlorine concentration of the HCD-SiN film higher than that of the DCS-SiN film is considered to be brought about by mainly two factors given below. First of all, the film-forming rate of the HCD-SiN film is higher than that of the DCS-SiN film. Naturally, the HCD-SiN film can be formed in a shorter time than the DCS-SiN film under the same film-forming conditions including the temperature, with the result that the amount of chlorine lost from the film during the film formation is suppressed. The difference in the film-forming rate between the HCD-SiN film and the DCS-SiN film is considered to be brought about because the dissociation of the Si—Si bond is advantageous for the film formation.
  When it comes to the bond energy, the Si—Cl bond has a bond energy of 4.16 eV, which is the highest bond energy among the bonds conceivable in the case of using the HCD+NH3 system. If the same number of chlorine atoms are supposed to be attached to the surfaces of the DCS-SiN film and the HCD-SiN film in the film forming step, the Si—Cl bonds that are unlikely to be cut away are included in a larger amount in the HCD-SiN film having a higher film-forming rate.
  As apparent from the graph of FIG. 3, the permittivity of the HCD-SiN film was lower than the permittivity (=7.8) of the ordinary silicon nitride film (Si3N4) under the film-forming temperature not higher than 700� C. For example, the permittivity of the HCD-SiN film formed at 450� C., which is denoted by the black square ▪, is smaller by 20 to 30% than that of P-CVD-SiN film denoted by dotted lines in the graph. Also, the permittivity of the HCD-SiN film formed at 450� C., which is denoted by the black square ▪, is small, i.e., 5.4, compared with that (7.3) of the HCD-SiN films formed at 550� C. to 700� C. under the ammonia flow rate R of 100 sccm and a pressure of 0.5 Torr, which are denoted by white circles ◯. Further, the white squares □ represent HCD-SiN films formed under the ammonia flow rate 100 and a pressure of 1.4 Torr. Also, the permittivity of the HCD-SiN film under the film-forming temperature not higher than 450� C. was very low, i.e., not larger than 6, which is smaller than the permittivity (=about 7) of a plasma-silicon nitride film (p-SiN). Since the permittivity is small, the wiring capacitance can be markedly decreased, which is highly advantageous in the case where the HCD-SiN film is used as an insulating film in a so-called "multi-layered wiring" portion. Also, in this experiment, the samples used in the film formation under 600� C. or more were different from the samples used in the film formation under 450� C. or less. However, similar results were obtained in the case of using the same samples. Incidentally, a nitrogen gas was not allowed to flow during formation of the HCD-SiN films shown in FIG. 3. However, an appreciable difference in the permittivity of the HCD-SiN film is not recognized even if the film is formed under the nitrogen gas stream.
  FIG. 4 is a graph showing the relationship between the chlorine concentration in the silicon nitride film and the polishing rate. As apparent from the graph, the polishing rate is increased in proportion to the chlorine concentration. The reason for the particular phenomenon is considered to reside in that a large number of chlorine ions having a large radius of ion are contained in the network consisting of Si—N so as to disturb the network. In other words, a high chlorine concentration permits forming a silicon nitride film of a low density, leading to a high polishing rate by CMP.
  FIG. 6 is a graph showing the relationship among the RIE selectivity ratio of the TEOS oxide film to the HCD-SiN film, i.e., etching rate of TEOS oxide film/etching rate of HCD-SiN film, the film-forming temperature and the ammonia flow rate R. The RIE selectivity ratio of the TEOS oxide film to the DCS-SiN film formed at 700� C. is also shown in the graph of FIG. 6. Line indicated in the figure shows the RIE rate of DCS-SiN formed at 700� C., the black circles  the graph represent HCD-SiN films formed under a pressure of 0.5 Torr, an ammonia/HCD flow rate ratio R of 100, and temperatures of 600� C., 650� C. and 700� C. As shown in the graph, the etching selectivity ratio was found to be about 7 in each of these cases. On the other hand, the blacks square ▪ and black triangle ▴ in the graph represent HCD-SiN films formed under a pressure of 1.4 Torr and ammonia/HCD flow rate ratios R of 50 and 20, respectively. In each of these cases, the selectivity ratio was found to be about 6, though these films were formed at a low temperature of 450� C. As apparent from the graph, RIE permits obtaining a selectivity ratio substantially equal to that of DCS-SiN film regardless of the ammonia flow rate R and the film-forming temperature.
  Further, in the first embodiment, Si2Cl6 is used as the Si raw material. In the case of forming a silicon nitride film having a high chlorine concentration, the similar effect can be obtained by using a chloride having at least one Si—Si bond such as Si3Cl8 and Si4Cl10 and a Si raw material such as SinCl2n+2, where n is not smaller than 2.
  The bonding state of silicon atoms within the silicon nitride films formed by changing the film-forming temperatures in the method of the second embodiment of the present invention was examined by the surface analysis by X-ray photoelectron spectroscopy (XPS). FIG. 8 shows the results. As apparent from FIG. 8, a silicon nitride film having Si—N bonds can be formed in the second embodiment of the present invention even if the film-forming temperature is changed.
  The distance of Si—Si bond is 0.225 nm, which is longer than the distance of Si—N bond of 0.157 nm. Therefore, if a silicon nitride film having an excess silicon is formed, the network consisting of Si—N bonds is considered to be greatly disturbed. In other words, the silicon nitride film having an excess silicon has a lower density and, thus, the polishing rate is increased when polished by CMP. Also, the chlorine concentration in the film is increased, as shown in FIG. 2.
  Further, in the second embodiment, Si2Cl6 is used as the Si raw material. In the case of forming a silicon nitride film having a high chlorine concentration and an excess silicon, the similar effect can be obtained by using a chloride having at least one Si—Si bond such as Si3Cl8 and Si4Cl10 and a Si raw material such as SinCl2n+2, where n is not smaller than 2.
  Further, an interlayer insulating film 132 is formed on the entire surface in a thickness of All about 350 nm by an LPCVD method using TEOS series raw material, as shown in FIG. 11F, followed by polishing the interlayer insulating film 132 by a CMP method to flatten the surface. In this step, the HCD-SiN film 125 acts as a CMP stopper.
  The low permittivity is deeply related to the low density. Specifically, the permittivity and the density are considered to meet the Clausius-Mossotti formula given on page 542 of "Solid State Physics (Saunders College Inc. (1976), by Ashcroft Mermin", i.e.,
  As shown in the graph, the hydrogen was found to be decreased by the heat treatment from about 1.5�105 CPS to about 4�102 CPS, i.e., decreased to less than {fraction (1/100)} of the value before the heat treatment. On the other hand, a significant difference was not recognized between the chlorine concentration before the heat treatment and that after the heat treatment.
  FIGS. 17a and 17B are cross sectional views collectively showing a method of manufacturing a semiconductor device according to a fifth embodiment of the present invention. These drawings show cross sections in a direction perpendicular to the Cu wiring included in the semiconductor device.
  FIG. 18 is a graph showing the results of a so-called "BT test" (bias-temperature stress test), in which the application time (stress time, minutes) is plotted on the abscissa, and the leakage current is plotted on the ordinate. Specifically, FIG. 18 shows the change with time in the leakage current, covering the case where any of a P-SiN film having a thickness of 50 nm, an HCD-SiN film having a thickness of 10 nm and an HCD-SiN film having a thickness of 50 nm is formed on a silicon substrate, followed by forming a Cu film on the SiN film, and a voltage of 1 MV/cm was applied between the silicon substrate and the Cu film at 100� C. so as to measure the change with time in the leakage current (amperes).
  The term "breakdown" implies the point where the leakage current is rapidly changed. FIG. 18 shows that the breakdown occurs in about 13 minutes in the P-SiN film having a thickness of 50 nm, in about 1,000 minutes in the HCD-SiN film having a thickness of 10 nm, and in 5,000 minutes or more in the HCD-SiN film having a thickness of 50 nm.
  Then, a silicon nitride film 411 acting as a cap insulating film is formed in a thickness of 200 nm by an LPCVD method excellent in controllability and covering properties, as shown in FIG. 25B. The silicon nitride film 411 is required to be homogeneous and uniform. In addition, the silicon nitride film 411 must be formed not to leave a clearance in the trench 407. Therefore, a film-forming method exhibiting good covering properties such as an LPCVD method is employed for forming the silicon-nitride film 411.
  The parasitic capacitance is generated between, for example, the gate electrodes 402-404 and the metal wiring 410. In the present invention, the thin silicon nitride film 411 having a permittivity lower than that of the conventional silicon nitride film is formed between the gate electrode and the metal wiring, making it possible to sufficiently decrease the parasitic capacitance.
  Since it is possible to decrease the parasitic capacitance, to diminish the capacitor area and to decrease the distances between the adjacent wirings and between the adjacent gate electrodes, the chip size can be finally made smaller. Also, since a so-called "RC delay resistance" is diminished, the device characteristics can be improved.
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