Method for manufacturing germanium semiconductor device and germanium semiconductor device

Abstract

To provide a method for manufacturing a germanium semiconductor device and a germanium semiconductor device capable of growing germanium crystal layers of a sufficient thickness in a short time.SOLUTION: A method for manufacturing a germanium semiconductor device according to the present invention comprises a processes of forming a trench 11 parallel to<010>on a main surface 10a of a silicon substrate 10 having a {100} plane orientation, and embedding germanium 20 in the trench 11 by chemical vapor deposition. The chemical vapor deposition is performed under pressure conditions where a raw material gas is supplied as a molecular flow.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a germanium semiconductor device and a germanium semiconductor device. [Background technology]

[0002] In recent years, the development of optoelectronic integration technology using silicon photonics has progressed. The basic optical components of silicon photonics are silicon (Si)-based optical waveguides and germanium (Ge) photodetectors, and compact optical modules that monolithically integrate these on the same substrate (see Patent Document 1) are expected to be applied to communication systems.

[0003] Regarding germanium semiconductor technology, Patent Document 2 describes a stress-enhanced MOS transistor and its manufacturing method. This manufacturing method includes the steps of forming a trench on a silicon substrate near a channel region, epitaxially growing a first SiGe layer to fill a part of the trench, and epitaxially growing a second SiGe layer having a lower germanium concentration than the first SiGe layer to completely fill the trench. The silicon substrate has a (100) crystal plane orientation, the channel region is oriented in the

[0110] direction, and the side of the trench has a (011) crystal plane orientation. In the step of epitaxially growing the first SiGe layer, the growth conditions are adjusted so that the growth rate is higher on the (011) crystal plane than on the (100) crystal plane. In this way, by initially increasing the germanium content of the SiGe layer and then decreasing it, it is possible to suppress a decrease in contact resistance while ensuring compressive stress in the longitudinal direction of the transistor channel.

[0004] Although not related to germanium semiconductor technology, Patent Document 3 describes the formation of a p-type epitaxial layer in a plurality of first trenches formed in the surface layer of an n-type silicon substrate. The n-type silicon substrate has a (100) surface or a surface equivalent thereto, and the plurality of first trenches are formed in the (100) surface of the n-type silicon substrate. <001> The first trench extends in the direction of the epitaxial layer, and the side surfaces of the first trench are configured as (010) and (0-10) planes. Therefore, voids are unlikely to remain when a pn junction is formed by embedding and growing an epitaxial layer in the trench, and this makes it possible to achieve a structure with a low interface state density. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5761754 [Patent Document 2] JP 2010-510684 A [Patent Document 3] JP 2013-102213 A Summary of the Invention [Problem to be solved by the invention]

[0006] In order for a germanium photoreceiver that receives near-infrared light to receive light that propagates in free space rather than light that propagates through an optical waveguide, it needs high light-receiving sensitivity, and for this purpose, a germanium crystal layer of sufficient thickness of about several microns is required. However, when forming a germanium crystal layer of sufficient thickness on a silicon substrate, there is a problem that crystal growth takes time and manufacturing efficiency is low.

[0007] Therefore, an object of the present invention is to provide a method for manufacturing a germanium semiconductor device that is capable of growing a germanium crystal layer of sufficient thickness in a short period of time. Another object of the present invention is to provide a germanium semiconductor device that has a germanium crystal layer of sufficient thickness, thereby enabling the light receiving sensitivity of a photodetector to be increased. [Means for solving the problem]

[0008] In order to solve the above problems, the method for manufacturing a germanium semiconductor device according to the present invention comprises the steps of: forming a silicon substrate having a {100} surface orientation on a main surface of the silicon substrate; <010> The method includes the steps of forming a trench parallel to a direction of growth of germanium and embedding germanium in the trench by chemical vapor deposition, the chemical vapor deposition being carried out under pressure conditions in which a source gas is supplied as a molecular flow.

[0009] According to the present invention, the crystal growth of germanium can be promoted not only from the bottom surface of the trench but also from the sidewall surface, so that a germanium crystal layer having a sufficient thickness can be formed in a short period of time.

[0010] In the present invention, the pressure condition is preferably equal to or less than 100 Pa. This makes it possible to promote the growth of germanium crystals not only from the bottom surface of the trench but also from the sidewall surface, thereby shortening the time required to fill the trench with germanium.

[0011] The method for manufacturing a germanium semiconductor device according to the present invention preferably further comprises the step of forming a silicon protective film covering an upper surface of the germanium buried in the trench, thereby improving the reliability of the germanium buried in the trench and increasing the lattice distortion of the germanium to lower the band gap energy and shift the optical absorption wavelength to a longer wavelength.

[0012] A germanium semiconductor device according to the present invention comprises a silicon substrate having a {100} surface orientation and having a trench formed in a main surface thereof, and a germanium crystal layer embedded in the trench, <010> It is characterized in that it is formed parallel to the direction.

[0013] According to the present invention, it is possible to realize a germanium photodetector having enhanced light receiving sensitivity by using a germanium crystal layer having a sufficient thickness.

[0014] In the present invention, the width of the trench is preferably 1 μm or less. If the width of the trench is 1.0 μm or less, the time required to fill the trench with germanium can be shortened by crystal growth from the sidewall surface of the trench.

[0015] In the present invention, the depth of the trench is preferably 2 μm or more, and more preferably 3 μm or more. If the depth of the trench is 2 μm or more, the thickness of the germanium crystal layer can be 2 μm or more, and the light absorptance of the germanium receiver can be 50% or more. Furthermore, if the depth of the trench is 3 μm or more, the thickness of the germanium crystal layer can be 3 μm or more, and the light absorptance of the germanium receiver can be 70% or more.

[0016] In the present invention, the sidewall surface of the trench is preferably an inclined surface with an inclination angle of 1 degree or more and 10 degrees or less with respect to the vertical surface. When the inclination angle of the sidewall surface 11a is 0.3 degrees or more and 10 degrees or less, cavities are unlikely to occur when germanium is embedded, and the quality of the germanium crystal layer can be improved.

[0017] In the present invention, it is preferable that a plurality of the trenches are provided at equal intervals on the main surface of the silicon substrate. Also, it is preferable that the step of forming the trenches includes forming a plurality of the trenches at equal intervals on the main surface of the silicon substrate. This makes it possible to realize a germanium photodetector that has not only high photosensitivity per unit area but also a large photodetection area.

[0018] The germanium semiconductor device according to the present invention preferably further comprises a silicon protective film covering an upper surface of the germanium crystal layer, which increases the reliability of the germanium crystal layer in the trench and increases the lattice distortion of germanium to lower the band gap energy and shift the optical absorption wavelength to a longer wavelength. Effect of the Invention

[0019] According to the present invention, it is possible to provide a germanium semiconductor device having enhanced light receiving sensitivity due to a germanium crystal layer having a sufficient thickness, and also to provide a method for manufacturing a germanium semiconductor device that is capable of growing a germanium crystal layer of sufficient thickness in a short period of time. [Brief description of the drawings]

[0020] [Figure 1] 1(a) and (b) are diagrams showing the structure of a germanium semiconductor device according to a first embodiment of the present invention, where FIG. 1(a) is a schematic plan view and FIG. 1(b) is a schematic sectional view taken along line XX in FIG. 1(a). [Diagram 2] FIG. 2 is a schematic perspective view showing the configuration of a trench. [Diagram 3] 3(a) to 3(c) are process diagrams illustrating a method for manufacturing a germanium semiconductor device. [Figure 4] 4(a) and (b) are schematic diagrams for explaining the crystal growth mechanism of germanium in the trench. [Diagram 5] 5(a) and (b) are diagrams showing the configuration of a germanium semiconductor device according to a second embodiment of the present invention, where FIG. 5(a) is a schematic plan view and FIG. 5(b) is a schematic sectional view taken along line XX in FIG. 5(a). [Figure 6] FIG. 6 is a schematic cross-sectional view showing the structure of a germanium semiconductor device according to the third embodiment of the present invention. [Figure 7] 7(a) and (b) are explanatory diagrams of trench patterns according to a comparative example and an embodiment, where FIG. 7(a) is a plan view of a silicon wafer, FIG. 7(b) is a plan view of a trench pattern according to a comparative example, and FIG. 7(c) is a plan view of a trench pattern according to an embodiment. [Figure 8] 8(a) and (b) are TEM images showing the state of a germanium crystal layer embedded in a trench, where FIG. 8(a) shows the state of germanium embedded in a trench according to a comparative example, and FIG. 8(b) shows the state of germanium embedded in a trench according to an embodiment. [Figure 9] FIG. 9 is a schematic cross-sectional view showing an evaluation model of a germanium semiconductor device, where (a) shows a comparative example, (b) shows Example 1, and (c) shows Example 2. [Figure 10] FIG. 10 is a diagram showing the lattice strain distribution of an evaluation model according to a comparative example of a germanium semiconductor device. [Figure 11] FIG. 11 is a diagram showing the lattice strain distribution of an evaluation model according to the first embodiment of a germanium semiconductor device. [Figure 12] FIG. 12 is a diagram showing the lattice strain distribution of an evaluation model according to the second embodiment of a germanium semiconductor device. [Figure 13] FIG. 13 is a graph showing changes in lattice distortion and optical absorption wavelength of the evaluation model according to Example 1, in which (a) is a graph showing the relationship between the thickness of the germanium crystal layer and the magnitude of lattice distortion, and (b) is a graph showing the relationship between the thickness of the germanium crystal layer and the band gap energy as well as the optical absorption wavelength. [Figure 14] FIG. 14 is a graph showing changes in lattice distortion and optical absorption wavelength of the evaluation model according to Example 2, in which (a) is a graph showing the relationship between the thickness of the germanium crystal layer and the magnitude of lattice distortion, and (b) is a graph showing the relationship between the thickness of the germanium crystal layer and the band gap energy as well as the optical absorption wavelength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0022] 1(a) and (b) are diagrams showing the structure of a germanium semiconductor device according to a first embodiment of the present invention, where FIG. 1(a) is a schematic plan view and FIG. 1(b) is a schematic sectional view taken along line XX in FIG. 1(a).

[0023] 1(a) and (b), a germanium semiconductor device 1 includes a silicon substrate 10 having a main surface 10a that is a (001) plane or a crystal plane equivalent thereto, a trench 11 formed in the main surface 10a of the silicon substrate 10, and a germanium crystal layer 20 embedded in the trench 11. The crystal plane equivalent to the (001) plane of the silicon substrate 10 is generally expressed as a {100} plane.

[0024] The silicon substrate 10 is, for example, an n-type silicon substrate, and the trench 11 is formed parallel to the

[0010] direction of the silicon substrate 10. Therefore, as shown in FIG. 2, the surface orientation of the sidewall surface 11a of the trench 11 is a (100) surface or a (-100) surface, and has a crystallographically equivalent crystal surface to the main surface 10a. The surface orientation of the bottom surface 11b of the trench 11 is a (001) surface, similar to the main surface 10a of the silicon substrate 10. The trench 11 may be formed parallel to the

[0100] direction of the silicon substrate 10. In this case, the surface orientation of the sidewall surface 11a of the trench 11 is a (010) surface or a (0-10) surface, and is a crystallographically equivalent crystal surface to the main surface 10a. In other words, the trench 11 parallel to the

[0100] direction is equivalent to the trench 11 parallel to the

[0010] direction.

[0025] It is preferable that the length L of the trench 11 is as long as possible, so that the area of ​​the germanium crystal layer 20 can be made as large as possible, thereby increasing the light receiving area of ​​the germanium photodetector.

[0026] The depth D of the trench 11 is 2 μm or more. This allows the germanium crystal layer 20 to be formed with sufficient thickness within the trench 11, and a germanium receiver with high light receiving sensitivity capable of receiving light propagating through free space can be realized. It is more preferable that the depth D of the trench 11 is 3 μm or more. By setting the depth D of the trench 11 to 2 μm or more, the optical absorptance of near-infrared light with a wavelength of about 1.55 μm can be increased to 50% or more. Furthermore, the thickness of the germanium crystal layer 20 can be set to 3 μm or more, and the optical absorptance of near-infrared light with a wavelength of about 1.55 μm can be increased to 70% or more.

[0027] The width Wt of the trench 11 is preferably 1.0 μm or less. If the width Wt of the trench 11 is too wide, it takes a long time to fill the trench 11 with the germanium crystal layer 20. On the other hand, if the width Wt of the trench 11 is too narrow, it becomes difficult to form the trench 11 and fill the trench 11 with the germanium crystal layer 20. Therefore, the width Wt of the trench 11 is preferably 0.3 μm or more. In this way, if the width Wt of the trench 11 is 0.3 μm or more and 1.0 μm or less, the time required to fill the trench 11 with the germanium crystal layer 20 can be shortened by crystal growth from the sidewall surface 11a of the trench 11.

[0028] The sidewall surface 11a of the trench 11 is preferably slightly inclined, and the angle of the inclined surface with respect to the vertical surface is preferably 0.3 to 10 degrees. When the sidewall surface 11a is slightly inclined, cavities are less likely to occur when germanium is embedded, and the quality of the germanium crystal layer 20 can be improved. When the inclination angle of the sidewall surface 11a is greater than 10 degrees, the deviation of the plane orientation of the sidewall surface 11a with respect to the (100) plane or the (-100) plane becomes large, the effect of promoting the crystal growth of germanium from the sidewall surface 11a becomes small, and the amount of germanium embedded becomes insufficient, making it impossible to obtain a germanium crystal layer 20 with a sufficient thickness. Also, when the inclination angle is less than 0.3 degrees, the effect of inclining the sidewall surface 11a cannot be obtained.

[0029] The germanium crystal layer 20 has a conductivity type opposite to that of the silicon substrate 10, and forms a pn junction with the silicon substrate 10. For example, when the silicon substrate 10 is an n-type semiconductor, the germanium crystal layer 20 is a p-type semiconductor. In this case, the germanium crystal layer 20 is a p - Germanium layer and p + It is preferable that the germanium layers are laminated in this order. It is also possible that the silicon substrate 10 is a p-type semiconductor and the germanium crystal layer 20 is an n-type semiconductor.

[0030] When the germanium crystal layer 20 is embedded in the trench 11, not only its bottom surface but also its side surface is bound by silicon, so that tensile strain is generated in the germanium crystal layer 20 due to the difference in thermal expansion coefficient between germanium and silicon. When the lattice strain in the germanium crystal increases, the band gap energy of germanium decreases. As a result, the optical absorption wavelength of germanium can be lengthened, and a wideband photoreceiver that covers the wavelengths of the L band can be realized.

[0031] 3(a) to (c) are process diagrams illustrating a method for manufacturing the germanium semiconductor device 1. FIG.

[0032] 3(a), a silicon substrate 10 having a {100} plane orientation is prepared in the manufacture of the germanium semiconductor device 1. The silicon substrate 10 may be a bulk silicon wafer, an epitaxial silicon wafer, or an SOI (Silicon On Insulator) wafer.

[0033] Next, as shown in FIG. 3(b), a trench 11 having a depth of 2 μm or more is formed in the main surface 10a of the silicon substrate 10. In forming the trench 11, after forming a SiO2 film on the main surface 10a of the silicon substrate 10, the SiO2 film is patterned by photolithography and dry etching to form a SiO2 mask 22. This exposes the trench formation region of the main surface 10a of the silicon substrate 10. Next, the trench 11 is formed in the main surface 10a of the silicon substrate 10 by dry etching using the SiO2 mask 22.

[0034] Usually, the direction in which a silicon substrate (silicon chip) is cut from a silicon wafer and the direction of wiring on the silicon substrate 10 are determined by the direction of the silicon substrate 10. <110> The main surface 10a of the silicon substrate 10 is usually set in the (001) direction. <110> In the case where a trench 11 is formed parallel to the direction, the plane orientation of the sidewall surface 11a of the trench 11 is a (1-10) plane or a (-110) plane, and is not a crystal plane equivalent to the main surface 10a. <110> Tilt 45 degrees from the direction <010> Since trench 11 is formed parallel to the direction, the plane orientation of sidewall surface 11a of trench 11 can be the (100) plane or the (-100) plane, and a crystal plane equivalent to main surface 10a can be formed.

[0035] 3(c), a germanium crystal layer 20 is formed inside the trench 11 exposed from the opening of the SiO2 mask 22. The germanium crystal layer 20 is preferably formed by UHVCVD (Ultra-High Vacuum CVD), in which the furnace pressure during crystal growth is set to a low pressure of 100 Pa or less. At this time, the germanium crystal layer 20 is deposited only inside the trench 11 and not on the upper surface of the SiO2 mask 22, so that the germanium crystal layer 20 can be selectively grown inside the trench 11.

[0036] Thereafter, a pair of electrode patterns (not shown) connected to the silicon substrate 10 and the germanium crystal layer 20, respectively, are formed, thereby completing the trench-filled germanium semiconductor device 1.

[0037] 4(a) and (b) are schematic diagrams for explaining the crystal growth mechanism of germanium in the trench 11. FIG.

[0038] For example, when the trench 11 is formed along the

[0110] direction of the silicon substrate 10, the surface orientation of the sidewall surface 11a of the trench 11 perpendicular to the (001) surface, which is the main surface 10a of the silicon substrate 10, is the (1-10) surface or the (-110) surface. In this case, as shown in FIG. 4(a), the germanium crystal growth from the sidewall surface 11a is suppressed, and the germanium crystal growth occurs mainly from the bottom surface 11b. Therefore, it takes a long time to fill the trench 11 with the germanium crystal layer 20. Usually, the typical value of the germanium crystal growth rate on the (001) surface of the silicon substrate is about 10 nm / min, and since it is necessary to form a low-temperature buffer layer with a slow growth rate in the initial growth stage, it takes nearly 10 hours of growth time to form a germanium crystal layer of 3 μm or more.

[0039] On the other hand, when the trench 11 is formed along the

[0010] direction tilted by 45 degrees from the

[0110] direction of the silicon substrate 10, the surface orientation of the sidewall surface 11a of the trench 11 perpendicular to the (001) surface, which is the main surface 10a of the silicon substrate 10, is the (100) or (-100) surface (see FIG. 2). Here, chemical vapor deposition is performed under pressure conditions in which the source gas is supplied as a molecular flow so that the source gas molecules reach the bottom of the trench 11. The mean free path of the source gas is larger than the depth D of the trench 11, so that the source gas can be supplied to the bottom and sidewall surfaces inside the trench. As shown in FIG. 4(b), crystal growth occurs from the sidewall surface 11a of the trench 11 at the same growth rate as the bottom surface 11b. If the width W of the trench 11 is, for example, 1 μm, regardless of the depth D of the trench 11, the germanium crystal layer 20 grows 0.5 μm from both sidewall surfaces 11 a of the trench 11 until the interior of the trench 11 is completely filled.

[0040] As described above, the method for manufacturing the germanium semiconductor device 1 according to the present embodiment is to form a silicon substrate 10 having a {100} plane on the main surface 10a. <010> A trench 11 parallel to the direction is formed, and a germanium crystal layer 20 is formed in the trench 11 by chemical vapor deposition. This promotes crystal growth of germanium not only from the bottom surface 11b of the trench 11 but also from the side wall surface 11a, and allows a germanium crystal layer 20 having a thickness of 2 μm or more to be formed in a short period of time.

[0041] 5(a) and (b) are diagrams showing the configuration of a germanium semiconductor device according to a second embodiment of the present invention, where FIG. 5(a) is a schematic plan view and FIG. 5(b) is a schematic sectional view taken along line XX in FIG. 5(a).

[0042] 5(a) and (b), this germanium semiconductor device 1 has a plurality of trenches 11 arranged at equal intervals at a predetermined pitch on a silicon substrate 10, and a germanium crystal layer 20 embedded in each trench 11. The other configurations are the same as those of the first embodiment.

[0043] In order to increase the light receiving efficiency of the germanium photodetector, it is desirable to make the area of ​​the germanium crystal layer 20 as large as possible. However, as described above, when attempting to form the germanium crystal layer 20 over the entire main surface 10a of the silicon substrate 10, the crystals grow only in the vertical direction, which causes a problem that it takes a long time to form a germanium crystal layer with a sufficient thickness of 2 μm or more.

[0044] In contrast, in this embodiment, a germanium crystal layer 20 of sufficient thickness can be formed in a short time by crystal growth in the lateral direction from the sidewall surface 11a as well as vertical direction from the bottom surface 11b of each trench 11. The silicon region between two adjacent trenches 11, 11 becomes a dead space where the germanium crystal layer 20 cannot be provided, but since light that reaches the silicon region is attracted to the germanium crystal layer 20, which has a higher refractive index than silicon, there is no particular problem even if some silicon region exists. The light absorption rate of the germanium crystal layer 20 increases in proportion to its area, but increases exponentially with respect to its thickness. In other words, the light absorption efficiency increases dramatically when the thickness of the germanium crystal layer 20 is thicker than the area, so increasing the thickness of the germanium crystal layer 20 is very effective in increasing the light receiving sensitivity of the germanium photodetector.

[0045] As described above, according to this embodiment, it is possible to ensure both the thickness and area of ​​the germanium crystal layer 20, and it is possible to further increase the light receiving sensitivity of the germanium photodetector.

[0046] FIG. 6 is a schematic cross-sectional view showing the structure of a germanium semiconductor device according to the third embodiment of the present invention.

[0047] As shown in Fig. 6, the germanium semiconductor device 1 is characterized in that the entire upper surface of the silicon substrate 10, including the upper surface of the germanium crystal layer 20 embedded in the trench 11, is covered with a silicon protective film 12 (Si cap). The other configurations are the same as those of the first embodiment. When the upper surface of the germanium crystal layer 20 is covered with the silicon protective film 12, not only the bottom and side surfaces of the germanium crystal layer 20 but also the upper surface are bound by silicon, so that the tensile strain generated in the germanium crystal layer 20 due to the difference in thermal expansion coefficient with silicon can be increased. When the tensile strain in the germanium crystal increases, the band gap energy of germanium decreases, so that the light absorption wavelength of germanium can be lengthened.

[0048] In order to lengthen the light absorption wavelength, it is better to increase the lattice distortion of the germanium crystal layer 20 as much as possible, and to achieve this, it is desirable to make the cross-sectional aspect ratio of the germanium crystal layer 20 as close to 1 as possible. However, when the cross-sectional aspect ratio is brought closer to 1, the thickness (≒ trench depth D) of the germanium crystal layer 20 becomes thin, and the light receiving sensitivity decreases. Therefore, in designing a Ge light receiver, it is necessary to prioritize the light receiving sensitivity while finding a balance between the two.

[0049] Although a preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention.

[0050] For example, in the above embodiment, a germanium semiconductor device and a method for manufacturing the same that are suitable for manufacturing a germanium photodetector having high light receiving sensitivity are given as examples, but the present invention is not limited to such applications and can be applied to various germanium semiconductor devices and methods for manufacturing the same that require the formation of a thick germanium crystal layer. EXAMPLES

[0051] <Evaluation of crystal growth of trench-filled Ge> The face orientation is {100} and the orientation flat is <110> A 4-inch silicon wafer 10W (see FIG. 7(a)) was prepared, and 25 silicon chips 10C having the same pattern were formed on the main surface of the wafer. Each silicon chip 10C had a formation region E1 for a trench pattern (see FIG. 7(b)) according to a comparative example extending in the <-110> direction, <110> tilted 45 degrees from the direction <010> A formation region E2 for a trench pattern (see FIG. 7(c)) according to the embodiment extending in the X-direction was provided. That is, both the trench pattern according to the comparative example and the trench pattern according to the embodiment were simultaneously formed on the same silicon wafer 10W. These trench patterns were formed by photolithography and RIE (Reactive Ion Etching).

[0052] The trench pattern of the comparative example had five trenches 11 extending in the <-110> direction arranged at intervals of 20 μm, with the length L of the trenches 11 being 10 mm, the width Wt of the trenches 11 being 0.6 μm, the depth D of the trenches 11 being 1 to 2 μm, and the space width Ws between adjacent trenches 11, 11 being 20 μm.

[0053] The trench pattern according to the embodiment is: <010> The comparative example was the same as the comparative example, except that five trenches 11 extending in the direction were arranged at intervals of 20 μm.

[0054] Next, germanium was embedded in the trench 11. The germanium was formed by ultra-high vacuum chemical vapor deposition (UHVCVD) using GeH4 as the source gas, and a molecular flow region with a pressure of 10 Pa or less in the growth furnace was used. Specifically, the growth conditions were set so that a germanium crystal layer with a thickness of 0.5 μm was obtained on the {100} plane.

[0055] After the germanium crystal layer was completely embedded in the trenches 11, the silicon wafer 10W was subjected to FIB (Focused Ion Beam) processing. In the FIB processing, a Pt protective film was formed in advance by sputtering on the main surface of the silicon wafer 10W on which the germanium embedded layer was formed, and then the silicon wafer 10W was cut in a direction perpendicular to the extension direction of the trenches 11 (the direction of the dashed line C in Figures 6(b) and (c)). Then, the cross section of the germanium crystal layer was observed by a TEM (Transmission Electron Microscope).

[0056] 8(a) and (b) are TEM images showing the state of a germanium crystal layer embedded in a trench, where FIG. 8(a) shows the state of germanium embedded in a trench according to a comparative example, and FIG. 8(b) shows the state of germanium embedded in a trench according to an embodiment.

[0057] As shown in Fig. 8(a), in the trench pattern according to the comparative example formed in the < - 110> direction, germanium could be embedded in the depth region with a height T of about 0.5 μm from the bottom surface, but the inside of the trench could not be sufficiently filled with germanium. Therefore, a cavity surrounded by a Pt protective film was generated above the germanium. This incomplete embedding state of germanium resulted in the same outcome in all the trenches of the 25 silicon chips. This is presumably because the crystal growth of germanium from the sidewall surface of the trench was suppressed. When the sidewall surface of the trench is not vertical, crystal growth occurs not only from the bottom surface but also from the sidewall surface in the initial stage of growth. However, when the sidewall surface becomes almost vertical and the {110} plane with a slow growth rate appears, the crystal growth stops, so a sufficient amount of germanium could not be embedded inside the trench.

[0058] On the other hand, as shown in Fig. 8(b), in the trench pattern according to the example formed in the <010> direction, germanium could be embedded in the depth region with a height T of about 0.9 μm from the bottom surface. This sufficient embedding state of germanium resulted in the same outcome in all the trenches of the 25 silicon chips. This is presumably because the crystal growth of germanium from the sidewall surface occurred in the same way as from the bottom surface.

[0059] <Consideration of the Influence of Strain in Ge Crystal on the Optical Absorption Wavelength> The influence of strain in the Ge crystal on the optical absorption wavelength of Ge was evaluated by simulation.

[0060] <Comparative Example: Ge Film Structure> The lattice strain and bandgap energy of a 1 - μm - thick Ge film (conventional structure) formed on the entire upper surface of the Si substrate were evaluated by simulation. As shown in Fig. 9(a), the thickness of the Si substrate was assumed to be 0.625 mm, and a region with a width of 1 mm and a depth of 1 mm was assumed. Also, the thermal expansion coefficient of Ge was 5.9×10 -6 [1 / K], and the thermal expansion coefficient of Si was 2.6×10 -6 [1 / K].

[0061] Next, the magnitude of strain ε in the X, Y, and Z directions that occurs in Ge when the temperature of the evaluation model of this comparative example is lowered from 600°C to 25°C. xx , ε yy , ε zz was calculated. The results are shown in Figure 10. The calculation results are summarized in Table 1. In Table 1, ε total is the magnitude of strain in three directions ε xx , ε yy , ε zz and is equivalent to the volume change rate of Ge.

[0062] [Table 1]

[0063] As shown in Figure 10 and Table 1, in the case of the Ge film, the magnitude of strain in the X and Y directions was the same, and a tensile strain of 0.188% was induced. On the other hand, the magnitude of strain in the Z direction was -0.1419%. This is because no force was acting in the film thickness direction, but the lattice itself was pulled laterally in the plane, resulting in a compressive strain being induced in the Ge film thickness direction. The sum of the strains in the three directions, ε total =ε xx +ε yy +ε zz was 0.2357%.

[0064] From the obtained lattice distortion, the band gap energy Eg at the gamma point of the energy band structure of Ge was calculated using the following first-order approximation formula.

number

[0065] As a result, the band gap energy Eg of Ge was 0.7809 eV, and the absorption edge wavelength was 1588 nm.

[0066] Also, in Table 1, Eg C-HH is the band gap energy between the conduction band and the heavy hole valence band at the gamma point of Ge, Eg C-LHshows the calculated band gap energy between the conduction band and the light hole valence band at the gamma point of Ge. C-HH and Eg C-LH is the band gap energy that takes into account the separation of the upper end of the valence band due to the heavy holes and light holes that are ignored in the first-order approximation formula, and has a high approximation accuracy. It can be calculated using the following formula.

number

[0067] As a result of the above calculation, Eg C-HH The absorption edge wavelength was 1575 nm. C-LH was 0.7746 eV and the absorption edge wavelength was 1601 nm.

[0068] <Example 1: Ge buried wire structure / no Si cap> The evaluation model of Example 1 had a structure in which a trench was formed on the top surface of a 0.625 mm thick Si substrate, and Ge was embedded in the trench (see FIG. 9(b)). In addition, an area with a width of 1 mm and a depth of 1 mm was assumed. The trench width was 1 μm, the length (depth) was 1 mm, and there were five trench depths: 1, 2, 3, 4, and 5 μm. In this evaluation model, the side and bottom surfaces of Ge were bound to Si, but the top surface of Ge was left open without being covered with a Si cap.

[0069] Next, the magnitude ε of the strain in the X, Y, and Z directions of the Ge when the temperature of the evaluation model in Example 1 is lowered from 600°C to 25°C is xx , ε yy , ε zz The results are shown in Figure 11 and Figures 13(a) and (b). The calculation results are summarized in Table 2.

[0070] [Table 2]

[0071] In the case of the Ge buried wire structure, the strain in the Y direction, εyy was unchanged compared to the Ge film. The strain in the X direction, ε xx The compressive strain in the Z direction, ε zz increases, and for trench depths (Ge film thicknesses) of 2 μm or more, the strain becomes tensile. The sum of the strains in the three directions, ε total It was found that is minimum when the trench depth (Ge film thickness) is 1 μm (i.e., the cross-sectional aspect ratio is 1), and increases with the Ge film thickness to reach a value similar to that of the Ge film.

[0072] When the Ge film thickness is 1 μm (minimum value), the band gap energy Eg between the conduction band and the heavy hole valence band at the gamma point is C-HH The absorption edge wavelength is 1569 nm. The band gap energy Eg between the conduction band and the light hole valence band at the gamma point of Ge is C-LH The band gap energy is 0.7818 eV and the absorption edge wavelength is 1586 nm. Compared to the Ge film, the band gap energy is larger and the absorption edge wavelength is smaller.

[0073] On the other hand, when the Ge film thickness is 5 μm (maximum), the band gap energy Eg between the conduction band and the heavy hole valence band at the gamma point is C-HH The absorption edge wavelength is 1578 nm. The band gap energy Eg between the conduction band and the light hole valence band at the gamma point is C-LH The band gap energy and absorption edge wavelength were 0.7762 eV and 1597 nm, respectively, which are similar to those of the Ge film.

[0074] <Example 2: Ge buried wire structure / with Si cap> The evaluation model of Example 2 had a structure in which a trench was formed on the top surface of a 0.623 mm thick Si substrate, Ge was embedded in the trench, and the entire top surface of the Si substrate was covered with a 2 μm thick Si film (see FIG. 9(c)). In addition, an area with a width of 1 mm and a depth of 1 mm was assumed. The trench width was 1 μm, the length (depth) was 1 mm, and there were five trench depths: 1, 2, 3, 4, and 5 μm. In this evaluation model, Ge is bound not only to the side and bottom surfaces but also to the Si on the top surface.

[0075] Next, the magnitude ε of the strain in the X, Y, and Z directions of the Ge when the temperature of the evaluation model in Example 2 is lowered from 600°C to 25°C is xx , ε yy , ε zz The results are shown in Figure 12 and Figures 14(a) and (b). The calculation results are summarized in Table 3.

[0076] [Table 3]

[0077] When the entire circumference of the Ge-embedded wire is covered with Si, the strain in the Z direction, ε xx The sum of the strains in the three directions, ε total is maximum when the trench depth (Ge film thickness) is 1 μm (i.e., the cross-sectional aspect ratio is 1). Although it decreases with increasing Ge film thickness, it is still larger than that in the case of the Ge film.

[0078] When the Ge film thickness is 1 μm (minimum value), the band gap energy Eg between the conduction band and the heavy hole valence band at the gamma point of Ge is C-HH The absorption edge wavelength is 1592 nm. This is about 20 nm larger than the absorption edge wavelength of 1575 nm for the Ge film. The band gap energy Eg between the conduction band and the light hole valence band at the gamma point of Ge C-LH The absorption edge wavelength was 1603 nm. C-LHis the same as in the case of the Ge film, and the absorption edge wavelength is almost the same, but the heavy holes have a larger density of states than the light holes, and contribute significantly to the optical absorption coefficient. C-HH Since the optical absorption coefficient increases in the energy (wavelength) region where the absorption coefficient is reduced, the light receiving characteristics are improved.

[0079] On the other hand, when the Ge film thickness is 5 μm (maximum value), the band gap energy Eg between the conduction band and the heavy hole valence band at the gamma point of Ge is C-HH The absorption edge wavelength is 1580 nm. The band gap energy Eg between the conduction band and the heavy hole valence band at the gamma point of Ge is C-LH The absorption edge wavelength was 1602 nm, and the Eg C-HH Since the optical absorption coefficient is increased, the light receiving characteristics are improved. [Explanation of symbols]

[0080] 1 Germanium semiconductor devices 10 Silicon substrate 10C Silicon Chip 10W Silicon Wafer 10a: Main surface of silicon substrate 11. Trench 11a Trench sidewall 11b Bottom of trench 12 Silicone protective film 20 Germanium crystal layer 22 SiO2 mask D Trench pattern depth E1, E2 Trench pattern formation area L Length of trench pattern Ws Trench pattern spacing Wt Width of trench pattern

Claims

1. forming a trench parallel to a <010> direction in a main surface of a silicon substrate having a {100} surface orientation; and filling the trench with germanium by chemical vapor deposition. The depth of the trench is 2 μm or more, 4 is a schematic diagram showing a method for manufacturing a germanium semiconductor device according to the present invention; FIG. 5 is a schematic diagram showing a method for manufacturing a germanium semiconductor device according to the present invention;

2. 2. The method for producing a germanium semiconductor device according to claim 1, wherein the width of said trench is 1 [mu]m or less.

3. 3. The method for manufacturing a germanium semiconductor device according to claim 1, wherein a sidewall surface of the trench is inclined at an angle of 0.3 degrees or more and 10 degrees or less with respect to a vertical surface.

4. 4. The method for producing a germanium semiconductor device according to claim 1, wherein the pressure condition is 100 Pa or less.

5. 5. The method for manufacturing a germanium semiconductor device according to claim 1, wherein the step of forming the trenches comprises forming a plurality of the trenches at equal intervals in the main surface of the silicon substrate.

6. 6. The method for manufacturing a germanium semiconductor device according to claim 1, further comprising the step of forming a silicon protection film covering an upper surface of said germanium buried in said trench.

7. a silicon substrate having a {100} surface orientation and a trench formed in a main surface; a germanium crystalline layer embedded in the trench; The depth of the trench is 2 μm or more, 4. A germanium semiconductor device, comprising: a first insulating layer formed on said first insulating film; a second insulating layer formed on said first insulating film;

8. 8. The germanium semiconductor device according to claim 7, wherein the width of said trench is 1 [mu]m or less.

9. 9. The germanium semiconductor device according to claim 7, wherein a sidewall surface of the trench is inclined at an angle of 0.3 degrees or more and 10 degrees or less with respect to a vertical surface.

10. 10. The germanium semiconductor device according to claim 7, wherein a plurality of said trenches are provided at equal intervals.

11. 11. The germanium semiconductor device according to claim 7, further comprising a silicon protective film covering an upper surface of said germanium crystal layer.

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