JP2007142291A - Semiconductor structure and its growing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor structure which has a high-quality Ge epitaxial layer using a thin buffer layer, and to provide its growing method. <P>SOLUTION: The semiconductor structure has an Si substrate, an SiGe layer of a thickness equal to or smaller than the critical thickness which is formed on it and contains a Ge composition ≥20% and ≤80%, and a Ge epitaxial layer which is formed on the SiGe layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a structure in which a crystal layer having lattice mismatch such as germanium (Ge) is epitaxially grown on a single crystal substrate such as a silicon (Si) substrate, and a growth method thereof. The present invention relates to a structure of a buffer layer formed on a substrate before crystal layer growth for growth and a growth method thereof.

  The technique of growing a Ge epitaxial layer on a Si substrate is an indispensable technique for forming a Ge photodetector, a high electron mobility device, or the like on the Si substrate. However, since there is a 4.2% lattice mismatch between Si and Ge, the Ge epitaxial layer grown directly on the Si substrate has a large number of threading dislocations and a large surface roughness. The quality for doing so was insufficient.

  For this reason, various methods for growing a Ge layer having a low threading dislocation density (TDD) and a flat surface have been proposed. In these proposals, a method is used in which a thick buffer layer having a graded composition from a composition close to Si to a composition close to Ge and having sufficiently relaxed internal strain is grown on the Si substrate before the growth of the Ge layer. ing. A method in which this thick buffer layer is combined with chemical mechanical polishing (CMP) has also been proposed.

  In Patent Document 1, as a buffer layer for growing a Ge layer on a Si substrate, a gradient composition SiGe layer in which the Ge composition is changed at a rate of 10% Ge per μm in the thickness direction is first changed from 0% Ge to 50%. Then, a uniform cap layer is grown and then flattened by CMP. Thereafter, a gradient composition SiGe layer is grown from 50% Ge to 75% Ge at the same Ge composition change rate, and the temperature is further increased. Is a technique for growing a graded composition SiGe layer from 75% Ge to 92% Ge at the same Ge composition change rate. In this method, the total growth film thickness for forming the buffer layer is 10 μm or more, and it is necessary to use a CMP process in the middle.

  In Patent Document 2, as a buffer layer for growing a ZnSe layer on a Si substrate, a SiGe epitaxial layer having a Ge composition of 0.9% is formed with a film thickness of 0.5 to 0.8 μm and a film thickness of 0 from the Si substrate side. It is disclosed to use a laminated structure in which a SiGe epitaxial layer having a Ge composition of 0.95% with a thickness of 0.5 to 0.8 μm and a Ge epitaxial layer with a thickness of 0.5 to 0.8 μm and several μm are grown in this order. . Furthermore, an annealing process at 650 ° C. to 800 ° C. is performed every time each layer is grown. Even in this method, the growth thickness of the two SiGe epitaxial layers ranges from 1 μm to 1.6 μm.

The methods according to Patent Document 1 and Patent Document 2 have a problem that a long growth time is required to grow a thick buffer layer on the order of μm, and productivity is lowered. Furthermore, when a CMP process or the like is employed, equipment for the process is required, and further, a processing time for the process is required, leading to a problem that productivity is lowered. Furthermore, even if such a method is adopted, there is a problem that the average surface roughness (RMS) is reduced only to several nm.
Japanese Patent No. 3535527 JP 2005-303246 A

  An object of the present invention is to provide a new buffer layer film structure and a method for growing a crystal layer having lattice mismatch such as germanium (Ge) with high quality on a single crystal substrate such as a silicon (Si) substrate. A growth method is proposed, and an extremely thin buffer layer is employed to shorten the growth time and to achieve a reduction in threading dislocation density and surface flatness.

In view of the above problems, an object of the present invention is to provide a semiconductor structure having a high-quality Ge epitaxial layer employing a thin buffer layer and a growth method thereof.

  The semiconductor structure and the growth method thereof according to the present invention are configured as follows in order to achieve the above object.

  The semiconductor structure of the present invention (corresponding to claim 1) includes a Si substrate, a SiGe layer having a Ge composition of 20% or more and 80% or less formed on the Si substrate, and a SiGe layer on the SiGe layer. And a Ge epitaxial layer formed thereon.

A semiconductor structure according to the present invention (corresponding to claim 2) is characterized in that, in the above-described configuration, the thickness of the SiGe layer is in the range of 5 nm to 20 nm.

  The semiconductor structure of the present invention (corresponding to claim 3) includes a Si substrate, a SiGe layer having a Ge composition of 20% or more and 50% or less formed thereon, and a Ge epitaxial layer formed on the SiGe layer. And the thickness of the SiGe layer is in the range of 5 nm to 50 nm.

The growth method of the present invention (corresponding to claim 4) is a method of growing a Ge layer on a Si substrate, wherein the Ge composition has a thickness of not more than a critical film thickness on the Si substrate, and the Ge composition is not less than 20% and not more than 80%. A step of epitaxially growing the SiGe layer, and a step of forming a Ge layer on the SiGe layer.
A growth method according to the present invention (corresponding to claim 5) is a method of growing a Ge layer on a Si substrate, wherein the Ge composition has a thickness of not more than a critical film thickness on the Si substrate, and the Ge composition is not less than 20% and not more than 80%. A step of epitaxially growing the SiGe layer and a step of forming a Ge layer on the SiGe layer, wherein the thickness of the SiGe layer is in the range of 5 nm to 20 nm.
The growth method of the present invention (corresponding to claim 6) is a method of growing a Ge layer on a Si substrate, wherein a SiGe layer having a Ge composition of 20% to 50% is epitaxially grown on the Si substrate; Forming a Ge layer on the SiGe layer, wherein the thickness of the SiGe layer is in the range of 5 nm to 50 nm.

  The present invention has the following effects. According to the present invention, an extremely thin buffer layer can be used to shorten the growth time, and an epitaxial layer having a flat surface and no threading dislocations can be obtained.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments (examples) of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a basic film structure of a semiconductor structure when a Ge layer is epitaxially grown on a Si substrate through a SiGe buffer layer as one embodiment of the present invention. In FIG. 2 is a SiGe buffer layer, 3 is a Ge seed layer, and 4 is a Ge layer.

  The film structure of the semiconductor structure according to the first embodiment of the present invention will be described with reference to FIG. In FIG. 1, 1 is a Si (100) substrate, 2 is a SiGe buffer layer having a Ge composition of 50% and a uniform composition in the film thickness direction, and the film thickness is 13 nm. 3 is a Ge seed layer with a film thickness of 30 nm, and 4 is a Ge layer with a film thickness of 1 μm.

Subsequently, as a second embodiment of the present invention, a semiconductor structure growth method of the first embodiment will be described.
First, the Si (100) substrate 1 was cleaned by DHF treatment and heat-treated at 750 ° C. in vacuum before epitaxial growth. The SiGe buffer layer 2 having a Ge composition of 50% was grown to a thickness of 13 nm and a substrate temperature of 450 ° C. The Ge layer was grown using a two-stage growth process. In the first stage, the Ge seed layer was grown to a thickness of 30 nm at a substrate temperature of 350 ° C., and then in the second stage, the Ge layer was grown to a thickness of 1 μm at a substrate temperature of 550 ° C.

As a first comparative example, the same sample as that of the first example except that the SiGe buffer layer 2 having a Ge composition of 50% and a film thickness of 2 nm was formed in the film configuration of FIG. The production conditions were also the same as those in Example 2 except that the thickness of the SiGe buffer layer 2 was 2 nm.

  As a second comparative example, the same sample as that of the first embodiment except that a 10 nm-thickness Si buffer layer was used in place of the SiGe buffer layer 2 in the film configuration of FIG. The production conditions were the same as in the second example except that the growth temperature of the Si buffer layer was 520 ° C. and the growth temperature of the Ge seed layer 3 was 370 ° C.

According to the first and second examples, the SiGe buffer layer 2 having a Ge composition of 50% was grown in layers over the entire film thickness without agglomerating into islands. Further, the SiGe buffer layer having a thickness of 13 nm and having a Ge composition of 50% is in a range equal to or less than the critical thickness when epitaxially grown on the Si substrate, and was grown without causing threading dislocations due to strain relaxation. Therefore, the unevenness on the surface of the buffer layer due to the influence of island-like agglomeration and the unevenness due to the cross-hatch structure due to the influence of threading dislocation were not observed, and the flatness of the surface of the buffer layer 2 after growth was very good. Here, the critical film thickness means the maximum thickness at which threading dislocations do not appear on the surface of the SiGe buffer layer.

Further, according to the first and second embodiments, the Ge seed layer 3 is also grown flat on the buffer layer 2, and the average surface roughness (RMS) of the Ge seed layer 3 immediately after the growth is 1.32 nm. It was recognized that the average surface roughness (RMS) of the Ge seed layer 3 after raising the temperature to 550 ° C., which is the growth temperature of the Ge epitaxial layer, was 0.13 nm, and the flatness was further improved. FIG. 2A shows a scanning electron microscope (SEM) photograph of the surface of the Ge seed layer formed in the second comparative example using the Si buffer layer, and FIG. 2C shows a scanning electron microscope of the surface of the Ge seed layer formed in the second embodiment. (SEM) A photograph is shown. In the second comparative example, RMS has pits on the order of 60 nm and the RMS is as coarse as 2.14 nm, whereas in the second example, no pit is seen and the RMS is flat at 1.32 nm. As a result, the surface of the Ge epitaxial layer 4 formed on the Ge seed layer 3 of the first and second examples was also extremely flat.

  3A and 3B are cross-sectional TEM photographs of the sample grown by the method of the second comparative example, FIGS. 4A and 4B are cross-sectional TEM photographs of the sample grown by the method of the second embodiment, and FIGS. 5A and 5B are the first It is a cross-sectional TEM photograph of the sample grown by the method of the comparative example. Thus, in both the first comparative example and the second comparative example, threading dislocations extend in the Ge epitaxial layer, but in the method grown in the second embodiment, the dislocations are confined in the buffer layer, No threading dislocations extend in the epitaxial layer.

  As described above, according to the first and second inventions, the use of a buffer layer as thin as 13 nm shortens the growth time and provides a remarkable effect that a high-quality Ge epitaxial layer can be obtained.

The film structure of the semiconductor structure of the third embodiment of the present invention will be described with reference to FIG. In FIG. 1, 1 is a Si (100) substrate, 2 is a uniform SiGe buffer layer with a Ge composition of 25% in the film thickness direction, and the film thickness is 20 nm. 3 is a Ge seed layer with a film thickness of 30 nm, and 4 is a Ge layer with a film thickness of 1 μm.

Subsequently, as a fourth embodiment of the present invention, a semiconductor structure growth method of the third embodiment will be described.
First, the Si (100) substrate 1 was cleaned by DHF treatment and heat-treated at 750 ° C. in vacuum before epitaxial growth. The SiGe buffer layer 2 having a Ge composition of 25% was grown to a thickness of 20 nm and a substrate temperature of 520 ° C. The Ge layer was grown using a two-stage growth process. In the first stage, the Ge seed layer was grown to a thickness of 30 nm at a substrate temperature of 350 ° C., and then in the second stage, the Ge layer was grown to a thickness of 1 μm at a substrate temperature of 550 ° C.

According to the third and fourth examples, the SiGe buffer layer 2 having a Ge composition of 25% was grown in layers over the entire film thickness without agglomerating into islands. Furthermore, the SiGe buffer layer having a Ge composition of 25% with a film thickness of 20 nm is in the range below the critical film thickness when epitaxially grown on the Si substrate, and was grown without causing threading dislocations due to strain relaxation. Therefore, the flatness of the surface of the buffer layer 2 after the growth was very good.

  Further, according to the third and fourth embodiments, the Ge seed layer 3 is also grown flat on the buffer layer 2, and the average surface roughness (RMS) of the Ge seed layer 3 immediately after the growth is 1.52 nm. It was confirmed that the average surface roughness (RMS) of the Ge seed layer 3 after raising the temperature to 550 ° C., which is the growth temperature of the Ge epitaxial layer, was 0.15 nm and the flatness was further improved. FIG. 2B shows a scanning electron microscope (SEM) photograph of the surface of the Ge seed layer formed in the second example. Similar to the second embodiment, no pits are seen in this embodiment, and the RMS is flat at 1.52 nm. As a result, the surface of the Ge epitaxial layer 4 formed on the Ge seed layer 3 of the third and fourth examples was also extremely flat. Also in this example, no elongation of threading dislocations into the Ge epitaxial layer was observed.

As described above, according to the third and fourth inventions, by using a buffer layer as thin as 20 nm, the growth time is shortened, and a remarkable effect is obtained in that a high-quality Ge epitaxial layer is obtained.

As can be understood from the description in the above embodiments, the present invention does not cause a cross-hatch structure due to the influence of threading dislocations by setting the buffer layer thickness to a critical thickness or less, and the Ge composition of the buffer layer. By controlling the thickness of the Si seed layer to 80% or less, island-shaped growth is suppressed, and the surface of the buffer layer on which the Ge seed layer is grown is maintained flat by this method. It has been confirmed that if the Ge composition exceeds 80%, the possibility of island-like growth is extremely high. On the other hand, when the Ge composition is less than 20%, the density of the growth nuclei of the Ge seed layer grown on the buffer layer is lowered and the surface roughness is increased. The critical film thickness of the SiGe buffer layer is larger than 20 nm even when the Ge composition is 80%. If the film thickness is 20 nm or less, threading dislocations do not occur in the buffer layer within the range of Ge composition of 20 to 80%. The critical film thickness of the SiGe buffer layer is greater than 50 nm even when the Ge composition is 50%. If the film thickness is 50 nm or less, threading dislocations do not occur in the buffer layer within the range of the Ge composition of 20 to 50%.

Further, when the Ge seed layer and the Ge epitaxial layer are grown, in the first to fourth examples, dislocations are confined in the buffer layer, but as can be seen from the results of the first comparative example, the buffer layer thickness When the thickness is as thin as 2 nm, dislocations extend into the Ge layer. According to the inventors' investigation, the buffer layer thickness is required to be 5 nm or more.

  In the first to fourth embodiments of the present invention, the Si (100) substrate is used as the semiconductor substrate, the Ge layer is used as the epitaxial layer, and the SiGe layer is used as the buffer layer. However, the present invention is not limited to these.

  INDUSTRIAL APPLICABILITY The present invention is used for growing a crystal layer having lattice mismatch such as germanium (Ge) with high quality on a single crystal substrate such as a silicon (Si) substrate and shortening the growth time.

It is a longitudinal cross-sectional view which is a figure which shows the film | membrane structure of the semiconductor structure based on 1st Example of this invention. It is a figure which shows the surface state of Ge seed layer which concerns on 1st Example of this invention, and a comparative example. It is a figure which shows the surface state of Ge seed layer which concerns on 1st Example of this invention, and a comparative example. It is a figure which shows the surface state of Ge seed layer which concerns on 1st Example of this invention, and a comparative example. It is a cross-sectional TEM photograph which shows the semiconductor structure which concerns on the 2nd comparative example of this invention. It is a cross-sectional TEM photograph which shows the semiconductor structure which concerns on the 2nd comparative example of this invention. It is a cross-sectional TEM photograph which shows the semiconductor structure based on the 2nd Example of this invention. It is a cross-sectional TEM photograph which shows the semiconductor structure based on the 2nd Example of this invention. It is a cross-sectional TEM photograph which shows the semiconductor structure based on the 2nd Example of this invention. It is a cross-sectional TEM photograph which shows the semiconductor structure based on the 2nd Example of this invention.

Explanation of symbols

1 Si substrate 2 SiGe buffer layer 3 Ge seed layer 4 Ge epitaxial layer

Claims (6)

  A Si substrate, a SiGe layer having a Ge composition with a thickness less than or equal to a critical film thickness formed on the Si substrate and having a Ge composition of 20% or more and 80% or less, and a Ge epitaxial layer formed on the SiGe layer, Semiconductor structure.   2. The semiconductor structure according to claim 1, wherein the thickness of the SiGe layer is in the range of 5 nm to 20 nm.   It has a Si substrate, a SiGe layer having a Ge composition of 20% or more and 50% or less formed thereon, and a Ge epitaxial layer formed on the SiGe layer, and the thickness of the SiGe layer is 5 nm or more and 50 nm. A semiconductor structure characterized by being in the following range.   A method of growing a Ge layer on a Si substrate, the step of epitaxially growing a SiGe layer having a Ge composition of 20% or more and 80% or less on the Si substrate to a thickness of a critical film thickness or less, and on the SiGe layer And a step of forming a Ge layer.   The growth method according to claim 4, wherein the thickness of the SiGe layer is in the range of 5 nm to 20 nm. A method of growing a Ge layer on a Si substrate, comprising: epitaxially growing a SiGe layer having a Ge composition of 20% to 50% on the Si substrate; and forming a Ge layer on the SiGe layer. And a thickness of the SiGe layer is in the range of 5 nm to 50 nm.

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