JP2011138956A - Method of manufacturing silicon semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a silicon semiconductor substrate of which a surface layer part of a silicon substrate is formed of a silicon oxide layer and a single crystalline silicon carbide layer. <P>SOLUTION: The following steps are carried out sequentially: a step of (1) preparing the silicon semiconductor substrate of which the surface layer part is formed of an embedded silicon oxide film layer and a surface silicon oxide film layer, and (2) implanting carbon ions in a silicon layer between the embedded oxide film layer and the oxide film layer in the silicon substrate to form a carbon-containing layer with silicon and carbon mixed; a step of (3) removing a surface oxide film layer; a step of (4) heat-treating the silicon substrate and turning the carbon-containing layer into a silicon carbide film layer; and a step of (5) removing the oxide film formed on a surface of the silicon substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for manufacturing a silicon semiconductor substrate suitable for manufacturing power devices and optoelectronic devices. More specifically, the present invention relates to a silicon semiconductor substrate in which a surface layer portion of a silicon substrate includes a silicon oxide layer and a single crystal silicon carbide layer. It relates to manufacturing technology.

  Silicon carbide has a high Schottky barrier, a high breakdown field strength, and a high heat transfer property, and thus is suitable as a material for power devices. Silicon carbide has a lattice constant close to that of a nitride compound semiconductor, which is a typical semiconductor material for optoelectronics, and allows nitride compound semiconductors to be epitaxially grown with low defects. Suitable for Therefore, technology development for manufacturing a semiconductor having a single crystal silicon carbide layer on a surface layer portion of a silicon substrate has been conventionally performed (Non-patent Document 1).

  However, in these methods, a step of finally exposing the carbon-containing layer by etching is necessary, and the surface roughness of the single crystal silicon carbide layer on the surface layer portion of the obtained silicon substrate is about 2 nm (RMS in a 10 μm × 10 μm region). : Hereinafter referred to as RMS). Therefore, in order to reduce the surface roughness required for epitaxial growth to 0.5 nm (RMS) or less, a step of smoothing the exposed single crystal silicon carbide layer by CMP is required.

  However, the mechanical hardness of the silicon carbide layer is remarkably high, and it is difficult to obtain a sufficient effect by CMP processing using a normal abrasive, and therefore, a very special abrasive such as colloidal silica particles is used. (Patent Document 1).

JP 2006-528423

J. et al. K. N. LIndner, A.M. Fronwiser, B.H. Rauschenbach and B.M. Stritzker, Fall Meeting of the Materials Research Society, Boston, USA (1994), Mater. Res. Syn. Proc, Vol. 354 (1995), 171

  An object of the present invention is to provide a technique for manufacturing a silicon semiconductor substrate having a single-crystal silicon carbide layer with a small surface roughness as a surface layer, without performing planarization by the CMP process essential in the conventional method. .

  The present inventor starts with a silicon substrate (also abbreviated as SOI) that is capped with an oxide film and has a buried oxide film, and combines the carbon ion implantation process, the annealing process, and the oxide film removal process. The present invention has been completed.

  That is, the method of the present invention is a method for manufacturing a silicon semiconductor substrate, in which the surface layer portion of the silicon substrate includes a silicon oxide layer and a single crystal silicon carbide layer, wherein the following steps are sequentially performed: 1) A silicon semiconductor substrate whose surface layer portion is composed of a buried silicon oxide film layer and a surface silicon oxide film layer is prepared, and (2) carbon is formed between the buried oxide film layer and the oxide film layer in the silicon substrate. Implanting ions to form a carbon-containing layer in which silicon and carbon are mixed; (3) removing the surface oxide film layer; and (4) heat-treating the silicon substrate to form the carbon-containing layer. Forming a silicon carbide film layer, and (5) removing an oxide film formed on the surface of the silicon substrate.

  Further, in the present invention, the carbon-containing layer side carbon atom concentration at the interface between the surface silicon oxide film and the carbon-containing layer between the surface silicon oxide film and the buried oxide film is 15 atom% or more, and the carbon-containing layer has The ion implantation conditions are adjusted so that the maximum value of the carbon atom concentration is 55 atom% or less.

  Further, according to the present invention, the carbon atom concentration on the carbon-containing layer side at the interface between the carbon-containing layer between the surface silicon oxide film and the buried oxide film and the buried oxide film is 15 atom% or more, and the carbon in the carbon-containing layer is The ion implantation conditions are adjusted so that the maximum value of the atomic concentration is 55 atom% or less.

Further, in the present invention, when the thickness between the surface silicon oxide film and the buried oxide film is set to tsoi, the peak of the carbon atom concentration of the carbon-containing layer is not less than tsoi × 1/4 from the lower part of the surface silicon oxide film. The position is adjusted to tsoi × 3/4 or less.
Furthermore, the present invention is characterized in that the carbon ions are implanted while the silicon substrate is heated to a temperature of 400 ° C. or higher and 1000 ° C. or lower.
Furthermore, the present invention is characterized in that the silicon substrate is manufactured by a Czochralski method or a float zone method.

  By using the method of the present invention, the roughness at the boundary between the exposed surface of the silicon carbide layer and the buried oxide film layer becomes extremely small. In particular, the exposed surface of the silicon carbide layer has sufficient flatness (about 0.2 RMS) without being subjected to CMP treatment.

It is a figure which shows the specific process of this invention. It is a figure which represents typically the silicon semiconductor substrate processed at each process in the present invention.

  Hereinafter, specific embodiments for carrying out the present invention will be described with reference to FIGS. 1 and 2.

  In the method of manufacturing a silicon semiconductor substrate according to the present invention, in which the surface layer portion of the silicon substrate includes a silicon oxide layer and a single crystal silicon carbide layer, the following steps are sequentially performed.

  Here, the silicon semiconductor substrate 50 manufactured by the method of the present invention has the following characteristics. (I) The surface layer portion includes the buried oxide film 3 and the exposed silicon carbide layer 5. (Ii) Both the boundary between the buried oxide film 3 and the silicon carbide layer 5 and the surface of the silicon carbide layer 5 have high flatness (0.5 nm (RMS) or less). Therefore, the silicon semiconductor substrate 50 manufactured by the method of the present invention can be used in the same manner as a single crystal silicon carbide surface layer silicon semiconductor substrate subjected to a conventionally known CMP process as it is or by performing a slight CMP process. Specifically, it is used for forming an epitaxial layer such as GaN on the surface layer of a single crystal silicon carbide (reference reference Japanese Patent Publication No. 9-508751), or for bonding to a polysilicon carbide wafer to produce a composite wafer. Use (reference literature JP 2009-117533) is mentioned.

  The first step (S1) of the present invention is a step of preparing a silicon semiconductor substrate 10 whose surface layer portion is composed of a buried silicon oxide film layer and a surface silicon oxide film layer. Here, the silicon semiconductor substrate 10 has a buried oxide film layer 3 on the silicon substrate 1 and an oxide film layer 4 on the surface of the silicon substrate (hereinafter also referred to as a cap layer). The thickness of the buried oxide film layer 3 and the silicon embedding depth are not particularly limited, and can be appropriately selected according to the thickness and depth of the target semiconductor substrate 50 in the conventionally known so-called SOI substrate technology. Further, the thickness of the surface oxide film layer 4 is not particularly limited, and a range in which the effect of the processing in the subsequent second and third steps can be sufficiently obtained can be selected. Further, the silicon layer 2 between the oxide film 3 and the oxide film 4 becomes the carbon ion-containing layer 5 in a later step, but the thickness is not particularly limited, and a thickness in accordance with the purpose is appropriately selected. Is possible. In the method of the present invention, specifically, the thickness of the surface oxide film layer 4 is selected from a value in the range of about 250 nm to 550 nm when, for example, 100 to 200 keV is used as the implantation energy of carbon ions. Further, the thickness of the buried oxide film layer 3 can be selected from about 50 nm to 2 μm. The thickness of the silicon layer 2 between these oxide films is preferably about 100 to 150 nm. A method for manufacturing the silicon semiconductor substrate 10 having such a structure used in the present invention is not particularly limited. For example, various methods described in the following documents can be appropriately employed (references SIMOX: K. Izumi, M. Doken and H. Aryoshi: “C.M.O.S. devices fabrication on buried SiO 2). layered by oxygen im- portation into silicon ", Electron. Lett., 14, 593-594 (1978), Smart-Cut: Industrial Research Committee, Electronic Materials August, pp. 83-87 (1997), ELTRAN:" K Sakaguchi et al., “Current Progress in Epitaxy Layer Transfer (ELTRAN)”, IEICE TRANS. ELEC. RON, VOL.E80 C, NO.3, pp378-387, March 1997).

  In the second step (S2) of the method of the present invention, carbon ions are implanted into the silicon layer 2 between the buried oxide film layer 3 and the oxide film layer 4 in the silicon substrate 10 described above, so that silicon and carbon This is a step of obtaining the semiconductor substrate 20 having the carbon-containing layer 7 in which is mixed. Here, there is no restriction | limiting in particular about the quantity of the carbon ion inject | poured into the silicon layer 2, and the distribution of the carbon ion in the layer 7, According to the objective, it can select suitably. The carbon ion implantation method and apparatus are not particularly limited, and a conventionally known method and apparatus can be used (reference documents JKN Lindner, A. Frönwieser, B. Rauschenbach, and B. Stritzker, Fall Meeting). of the Materials Research Society, Boston, USA (1994), Mater. Res. Syn. Proc, Vol. 354 (1995), 171).

  In the present invention, immediately after carbon ion implantation, the carbon atom concentration at the interface between the carbon-containing layer 7 and the buried oxide film layer 3 (on the carbon-containing layer 7 side) is 15 atom% or more, and the carbon-containing layer 7 and the oxide film layer 4 The ion implantation conditions were adjusted so that the carbon atom concentration at the interface (on the carbon-containing layer 7 side) was 15 atom% or more and the maximum value of the carbon atom concentration in the carbon-containing layer 7 was 55 atom% or less. Do the injection. The carbon atom concentration at the buried oxide layer 3 / carbon-containing layer 7 interface (carbon-containing layer 7 side) is 15 atom% or more, and the carbon atom concentration at the oxide film layer 4 / carbon-containing layer 7 interface (carbon-containing layer 7 side) is 15 atom%. % Or more is extremely important in order to achieve good surface roughness. When the carbon atom concentration at the buried oxide film layer 3 / carbon-containing layer 7 interface (carbon-containing layer 7 side) or the oxide film layer 4 / carbon-containing layer 7 interface (carbon-containing layer 7 side) is less than 15 atom%, after annealing, On top of the single crystal carbon silicon film layer 5, a transition layer composed of polysilicon carbide grains and Si crystals begins to appear, and the surface roughness after the completion of all the processes deteriorates. On the other hand, the carbon atom concentration at the buried oxide film layer 3 / carbon-containing layer 7 interface (carbon-containing layer 7 side) is 15 atom% or more and the carbon atom concentration at the oxide film layer 4 / carbon-containing layer 7 interface (carbon-containing layer 7 side). Is set to 15 atom% or more, the transition layer disappears and a good surface roughness can be realized. More preferably, in order to stably realize a good surface roughness, the buried oxide film layer 3 / carbon-containing layer 7 interface (carbon-containing layer 7 side) and the oxide film layer 4 / carbon-containing layer 7 interface (carbon-containing layer). 7 side) is preferably 25 atom% or more.

  Setting the maximum value of the carbon atom concentration in the carbon-containing layer 7 to 55 atom% or less is extremely important in order to maintain the crystallinity of the single crystal carbon silicon film layer 5. If the maximum value of carbon atom concentration in the carbon-containing layer 7 exceeds 55 atom%, after annealing, defects consisting of minute carbon grains appear in the single crystal carbon silicon film layer 5, and the crystal of the single crystal carbon silicon film layer 5 is crystallized. Deteriorate the sex. On the other hand, when the maximum value of the carbon atom concentration in the carbon-containing layer 7 is set to 55 atom% or less, it is possible to suppress the appearance of the above-described carbon particles. More preferably, the maximum value of the carbon atom concentration in the carbon-containing layer 7 is desirably 50 atom% or less in order to stably suppress the carbon particles.

Further, in the present invention, when the thickness of the silicon layer 2 is tsoi, the peak of the carbon atom concentration of the carbon-containing layer 7 is located at a position of tsoi × 1/4 to tsoi × 3/4 from the bottom of the oxide film layer 4. It is extremely important to adjust to When the peak position of the carbon concentration deviates from this range, the carbon atom concentration is lowered, so that it is distributed in an island shape at the interface between the oxide film layer 4 and the silicon layer 2 or at the interface between the silicon layer 2 and the oxide film layer 3. This is because a silicon region is formed. The carbon-containing layer 7 obtained by such carbon ion implantation is changed into the silicon carbide single crystal layer 5 under the annealing condition of the next third step. Moreover, conventionally known carbon ion implantation conditions can be preferably applied conventionally (reference documents J. K. L. Lindner, A. Frönwieser, B. Rauschenbach and B. Stritzker, Fall Meeting of the Materials Research Center). USA (1994), Mater.Res.Syn.Proc, Vol.354 (1995), 171), for example, the implantation energy of carbon ions is approximately 100 to 200 keV, and the implantation amount of carbon ions is 7 × 10 ^{17 to} 8 × 10 ¹⁷ cm ^−2. Is appropriate.

  The third step (S3) of the method of the present invention is a step of obtaining the semiconductor substrate 30 in which the carbon-containing layer 7 is exposed by removing the surface oxide film layer 4 of the semiconductor substrate 20 having the carbon-containing layer 7 obtained. . Here, the method for removing the surface oxide film is not particularly limited, but generally known methods and apparatuses can be preferably used. Specifically, etching with acid is preferable, and dilute hydrofluoric acid or ammonium fluoride can be used as the liquid phase etchant. By this etching, the oxide film 4 on the surface is removed, and the carbon-containing layer 7 having a surface with very high flatness is exposed. The third step of the present invention includes a subsequent cleaning step with pure water.

  In the fourth step (S4) of the method of the present invention, the semiconductor substrate 30 obtained above is annealed to change the contained carbon and silicon into single crystal silicon carbide by heat, so that the thin surface oxide film 6 is obtained. And a step of obtaining the semiconductor substrate 40 having the single crystal silicon carbide film layer 5. The annealing conditions are not particularly limited as long as the contained carbon reacts with silicon to form single crystal silicon carbide. In the present invention, the atmosphere in which the annealing conditions are performed is not particularly limited, but the annealing is preferably performed in a small amount of oxidizing atmosphere so that the buried oxide film does not change greatly under the annealing conditions. Specifically, the substrate 60 is heat-treated in an argon gas atmosphere containing about 0.5% by volume of oxygen at a temperature of 1100 ° C. or higher and lower than the silicon melting point. The time required for this heat treatment is about 10 hours.

  In the fifth step (S5) of the method of the present invention, the surface oxide film 6 formed in the previous step is removed, and the silicon semiconductor whose surface layer portion is composed of the silicon oxide layer 3 and the single crystal silicon carbide layer 5 is removed. In this step, the substrate 50 is obtained. Here, the same removal method and apparatus as those in the third step above can be used. That is, the method for removing the surface oxide film is not particularly limited, but generally known methods and apparatuses can be preferably used. Specifically, etching with acid is preferable, and dilute hydrofluoric acid or ammonium fluoride can be used as the liquid phase etchant. By this etching, the oxide film 6 on the surface is removed, and the single crystal carbon silicon film layer 5 having a surface with very high flatness is exposed.

  Hereinafter, the method of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

A plurality of SOI substrates using a (111) n-type float zone silicon wafer having a diameter of 150 mm are prepared and heat-treated in a dry oxidation atmosphere at 1100 ° C., and a surface of 360, 370, 400, 430, 440 nm is formed on each wafer. An oxide film was formed. At this time, the thickness of the silicon layer between the surface oxide film and the buried oxide film and the thickness of the buried oxide film were adjusted to 120 nm and 150 nm, respectively. Thereafter, carbon ion (C +) implantation was performed at a wafer heating temperature of 550 ° C., an acceleration energy of 180 keV, and a dose of 7.5 × 10 ¹⁷ / cm ² to form a carbon-containing layer between the surface oxide film and the buried oxide film. After the implantation, for some samples, concentration profiles in the substrate depth direction of the implanted carbon ions were obtained by Rutherford backscattering (RBS) measurement. The peak positions of the carbon concentration were 20, 29, 61, 88, and 101 nm, respectively, immediately below the surface oxide film. After the injection, the oxide film layer formed on each sample was removed with diluted hydrofluoric acid. Subsequently, each sample was annealed in a vertical high-temperature heat treatment furnace at 1350 ° C. in an Ar + 0.5 volume% O ₂ atmosphere for 10 hours. Thereafter, the cross-sectional structure near the surface of each sample was evaluated by cross-sectional TEM. It was confirmed that single crystal silicon carbide was formed for the samples with the first surface oxide film thickness of 370, 400, and 430 nm, but the first surface oxide film thickness was 360 nm. In the sample, a poly-SiC layer of about 10 nm was observed on the buried oxide film side, and an Si region distributed in an island shape on the surface oxide film side. In the first sample having a surface oxide film thickness of 440 nm, a poly-SiC layer having a thickness of about 15 nm on the surface oxide film side and an Si region distributed in an island shape on the buried oxide film side were confirmed. Surface roughness (RMS) was evaluated with an atomic force microscope (AFM) for samples having surface oxide films of 370, 400, and 430 nm. The surface roughness (RMS) of each sample having a surface oxide film of 370 nm, 400 nm, and 430 nm was 0.41 nm, 0.42 nm, and 0.35 nm, respectively, and a surface roughness of 0.5 nm (RMS) or less was achieved. Subsequently, in order to evaluate the surface roughness of the interface between the single crystal silicon carbide and the buried oxide film, the single crystal silicon surface of each sample was attached to the silicon substrate, and the silicon substrate under the buried oxide film was removed by polishing. Subsequently, the buried oxide film layer was removed with diluted hydrofluoric acid to expose the interface between the single crystal silicon carbide and the buried oxide film layer. Surface roughness (RMS) was evaluated with an atomic force microscope (AFM). The surface roughness (RMS) of each sample having a surface oxide film of 370 nm, 400 nm, and 430 nm was 0.49 nm, 0.45 nm, and 0.47 nm, respectively, and a surface roughness of 0.5 nm (RMS) or less was achieved.

  INDUSTRIAL APPLICABILITY The present invention can be used for manufacturing a silicon semiconductor substrate suitable for manufacturing power devices and optoelectronic devices.

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Silicon layer 3, 4 Oxide film 5 Silicon layer 6 Surface oxide film 7 Carbon containing layer 10, 20, 30, 40, 50 Silicon semiconductor substrate

Claims (6)

A method for producing a silicon semiconductor substrate, wherein the surface layer portion of the silicon substrate is composed of a silicon oxide layer and a single crystal silicon carbide layer, wherein the following steps are sequentially performed:
(1) A silicon semiconductor substrate whose surface layer portion is composed of a buried silicon oxide film layer and a surface silicon oxide film layer is prepared,
(2) implanting carbon ions into the silicon layer between the buried oxide film layer and the oxide film layer in the silicon substrate to form a carbon-containing layer in which silicon and carbon are mixed;
(3) removing the surface oxide film layer;
(4) heat-treating the silicon substrate to form the carbon-containing layer as a silicon carbide film layer;
(5) A step of removing an oxide film formed on the surface of the silicon substrate.   The carbon atom concentration on the carbon-containing layer side at the interface between the carbon-containing layer between the surface silicon oxide film and the buried oxide film and the surface silicon oxide film is 15 atom% or more, and the carbon atom concentration in the carbon-containing layer is The method for manufacturing a silicon semiconductor substrate according to claim 1, wherein the ion implantation conditions are adjusted so that the maximum value is 55 atom% or less.   The carbon atom concentration on the carbon-containing layer side at the interface between the carbon-containing layer between the surface silicon oxide film and the buried oxide film and the buried oxide film is 15 atom% or more, and the maximum carbon atom concentration in the carbon-containing layer is The method for manufacturing a silicon semiconductor substrate according to claim 1, wherein the ion implantation conditions are adjusted so that the value is 55 atom% or less.   When the thickness between the surface silicon oxide film and the buried oxide film is defined as tsoi, the peak of the carbon atom concentration of the carbon-containing layer is expressed as tsoi × 1/4 or more tsoi × 3 / from the lower part of the surface silicon oxide film. The method for manufacturing a silicon semiconductor substrate according to any one of claims 1 to 3, wherein the position is adjusted to 4 or less.   5. The method of manufacturing a silicon semiconductor substrate according to claim 1, wherein the carbon ions are implanted in a state where the silicon substrate is heated to a temperature of 400 ° C. or higher and 1000 ° C. or lower.   The method for manufacturing a silicon semiconductor substrate according to claim 1, wherein the silicon substrate is manufactured by a Czochralski method or a float zone method.

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