JPH035056B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a semiconductor single crystal thin film on an insulating metal fluoride thin film or substrate.

(Prior Art) Generally, in order to increase the speed and density of electronic devices, it is desired to form a single crystal semiconductor thin film on an insulator. One of the methods for forming it is to use alkaline earth metal fluorides or lanthanum group metal fluorides as insulators, which can yield good single crystals and whose crystal type and lattice constant are similar to typical semiconductors.
There is a method of epitaxially growing a semiconductor single crystal thin film thereon by molecular beam epitaxy or the like. However, when a semiconductor thin film is deposited directly on these metal fluorides at high temperatures, the semiconductor is deposited in islands in the early stage of growth, and even if the film thickness is increased, the surface is not flattened and the crystallinity is poor. be.

In order to solve this problem, conventional methods have been to apply a thin film of insulating metal fluoride single crystal or a thin film on the surface of the substrate.
A method has been proposed in which an ultra-thin semiconductor film of 10 nm or less is deposited and then a single crystal of the semiconductor thin film is grown on the ultra-thin semiconductor film.

(Problem to be solved by the invention) However, in this method, the type of semiconductor
There were problems with effectiveness in the case of germanium, gallium arsenide, etc.

Therefore, the present invention aims to improve the surface flatness and crystallinity of the semiconductor thin film even if the film thickness is increased because island-like growth occurs when a semiconductor thin film is grown as a single crystal on an alkaline earth metal fluoride or a lanthanum group metal fluoride. The purpose is to solve the problem of not being improved.

(Means for Solving the Problems) A first aspect of the present invention that satisfies the above objects is to deposit an insulating metal fluoride single crystal thin film or a semiconductor ultra-thin film with a thickness of 10 nm or less on the surface of a substrate. a first step of depositing an ultra-thin semiconductor film, and a second step of irradiating an electron beam from the surface side of the sample with an energy and incident angle that passes through the ultra-thin semiconductor film and reaches the fluoride thin film or substrate. The present invention relates to a method for manufacturing a semiconductor thin film, comprising a third step of growing a single crystal of a semiconductor thin film on the ultra-thin semiconductor film.

Further, a second invention of the present invention relates to a method in which a step of irradiating the surface of a fluoride thin film or a fluoride substrate with an electron beam is added before the first step of the first invention, and the second step is omitted. The first step is to irradiate the surface of an insulating metal fluoride single crystal thin film or substrate with an electron beam, and then the surface of the thin film or substrate is coated with a thickness of 10 nm.
The present invention relates to a method for producing a semiconductor thin film, comprising a second step of depositing an ultra-thin semiconductor film with a thickness of less than m, and a third step of growing a single crystal of the semiconductor thin film on the ultra-thin semiconductor film.

Here, the term "insulating metal fluoride single crystal thin film" means a thin film deposited on a substrate made of another semiconductor material, and the term "insulating metal fluoride single crystal substrate" means that the entire substrate is made of the fluoride single crystal. shall mean consisting of.

The insulating metal fluorides used in the present invention include alkaline earth metal fluorides such as magnesium fluoride, calcium fluoride, strontium fluoride, barium fluoride, thulium fluoride, holmium fluoride, europium fluoride, and fluoride. There are lanthanum group metal fluorides such as neodymium fluoride, praseodymium fluoride, cerium fluoride, and lanthanum fluoride.

In the first aspect of the present invention, in the first step, an ultra-thin semiconductor film with a thickness of 10 nm or less, preferably 0.2 to 10 nm, is deposited on the fluoride single crystal thin film or the surface of the substrate (i.e., pre-deposited). )but,
Vacuum deposition, sputtering, etc. are used as the deposition method.

After depositing an ultra-thin semiconductor film in the first step, in the second step, an electron beam with energy that passes through this ultra-thin film and reaches the fluoride thin film or substrate is applied to the ultra-thin film at an arbitrary incident angle. Irradiate from the surface side of the deposited thin film or substrate. At this time, the electron beam irradiation is usually performed at an electron beam acceleration voltage of 100V or more.
It is carried out at 50kV with an irradiation dose in the range of 5×10 ^-5 to 5×10 ^-3 C/cm ² .

Finally, in the third step, a semiconductor thin film is grown as a single crystal on the extremely thin semiconductor film. As a method for growing a single crystal, molecular beam epitaxy, solid phase epitaxy, vacuum evaporation, etc. performed in the same vacuum chamber, as well as vapor phase growth performed after taking the crystal out of the vacuum chamber, etc. can be used.

The semiconductor ultra-thin film and the semiconductor thin film are semiconductors made of group element semiconductors of the periodic table, such as silicon and germanium, group compound semiconductors, such as indium,
Compound semiconductors of gallium, aluminum, and phosphorus, arsenic, and antimony; Group-3 compound semiconductors, such as zinc, cadmium, and sulfur, selenium, and tellurium; Group-3 compound semiconductors, such as tin, lead, and sulfur; , selenium, and tellurium.

In the second invention, the method for depositing the ultra-thin semiconductor film, the electron beam irradiation conditions, etc. are substantially the same as in the first invention.

(Examples) Next, the present invention will be explained by examples with reference to the drawings.

Example 1 (A) As shown in Figure 1a, an insulating metal fluoride single crystal thin film made of calcium fluoride (CaF ₂ ) was epitaxially grown on a silicon (Si) substrate with a thickness of 0.6 mm. The substrate 1 is kept at room temperature in a vacuum,
An ultra-thin germanium (Ge) semiconductor film 2 having a thickness of 4 nm was deposited on the above thin film by vacuum evaporation.

(B) After depositing the Ge ultra-thin film (pre-deposited Ge layer) 2, the substrate 1 with the ultra-thin film 2 was kept at 400°C, and an electron beam reflection diffraction device with an accelerating voltage of 3 kV as shown in Fig. 3 was used. A sample was prepared by applying an AC voltage to the deflection plate 5 and scanning the electron beam 4 with an energy of 3 ke V to irradiate the surface of the ultra-thin film 2 of the substrate at an incident angle of 3 degrees. did. The irradiation dose was 160 μC/cm ² . 1-1 and 1- in the figure
2 is a silicon (Si) substrate and a calcium fluoride (CaF ₂ ) layer constituting the substrate 1, 2 is a preliminary deposited Ge layer, and 6 is a screen. By the above treatment, a flat Ge ultrathin film without an island structure was obtained on the CaF ₂ layer 1-2.

(C) Next, the sample was maintained at a temperature of 600° C., and a normal Ge thin film 3 was deposited on the predeposited Ge layer of the sample by molecular beam epitaxy (MBE) to grow a single crystal.

Figures 4a and 4b show reflection medium velocity electron diffraction (RMEED) patterns after a 4 nm predeposited Ge layer was irradiated with an electron beam at a substrate temperature of 400°C. In this case, since the purpose was to observe the diffraction pattern, the electron beam remained fixed without being scanned. The halo diffraction pattern shown in Figure 4a indicates that the predeposited Ge layer is still amorphous at this stage. However, in FIG. 4b, when this film was irradiated with a sufficient amount of electron beams, it showed a streaky pattern, indicating that the film was crystallized while remaining atomically flat. When the area that was not irradiated with the electron beam at this time was observed, it still showed a halo pattern, and it was found that the change shown in FIG. 4b was due to the electron beam irradiation. FIG. 4c shows the diffraction pattern when the substrate temperature is 600°C. 600 with this spot-like pattern.
Ge easily crystallizes on CaF ₂ when heated to ℃, but the surface is uneven, and the electron diffraction pattern reveals that Ge aggregation occurs. When this sample is irradiated with an electron beam, this spot-like pattern gradually changes to a streak-like pattern, which is more streaky than that shown in Figure 4b.
In other words, it was found that the film had good crystallinity.

Next, as shown in FIGS. 5a to 5d, samples were prepared in the same manner as described above except that the thickness of the preliminary deposited layer was changed to 3 nm, except that a non-irradiated area was provided in addition to an electron beam irradiated area for comparison. Surface SEM photographs of the irradiated and non-irradiated areas of these samples are shown in Figures 5a and b, respectively, and the back scattering (RBS) spectra are shown in Figure 5c, respectively.
and d. The SEM photograph shows that the surface of the electron beam irradiated area is extremely flat, while the non-irradiated area is extremely rough. Also, according to the backscattering spectrum, the minimum scattering yield (X _nio ) is 8 in the irradiated area.
%, and a significant improvement of 16% in the non-irradiated area.

Next, we investigated the dependence of crystallinity on electron beam current density and irradiation dose. The current density dependence during irradiation is the seventh
As shown in the figure, the crystallinity remained the same even if the value was changed by one order of magnitude, but it was found that the change in the irradiation amount significantly affected the crystallinity and surface flatness as shown in FIG. This indicates that electron beam irradiation is an integral effect of the irradiation dose, and that the heating effect of the electron beam, which depends on the irradiation rate, is not essential.

Next, an electron beam is used to knock on Ge.
-on) effect, that is, the effect of electron beam irradiation on Ge, preliminary deposition was performed after electron beam irradiation on the CaF ₂ surface, and the results were similar to those obtained when the preliminary deposited layer was irradiated with the electron beam as described above. Got the same result. This revealed that it is necessary to irradiate the fluoride with the electron beam, and that the effect of irradiating Ge is not important. However, directly on the CaF ₂ surface irradiated with the electron beam,
It has been shown that MBE growth results in island-like growth rather than layered growth, and it has become clear that layered growth can only be achieved by combining electron beam irradiation and pre-deposition.

Next, a method of performing preliminary deposition after irradiating the CaF ₂ surface with an electron beam and then growing a semiconductor thin film as a single crystal will be further explained in Example 2.

Example 2 Ge semiconductor ultra-thin film 2 in step (A) of Example 1
The calcium fluoride layer is provided on the silicon substrate 1 by substantially reversing the order of the step of depositing the calcium fluoride and the step of irradiating the electron beam 4 in step (B), as shown in FIG. 2a.
The substrate was kept at 400°C as shown in Example 1.
The method described in
An ultra-thin germanium film of 4 nm was deposited, and then a Ge thin film 3 shown in FIG. 1c was grown as a single crystal.

The thus obtained sample was used as a sample, and its surface SEM photograph is shown in Figure 8a, and its RBS spectrum is shown in Figure 8b. The SEM photograph shows that the surface is extremely flat. In addition, the minimum scattering yield (X _nio ) is 8% in the irradiated area according to the backscattering spectrum.
It can be seen that this is a significant improvement compared to 16% in the non-irradiated area shown in Figure 5d.

(Effects of the Invention) As explained above, according to the method of the first aspect of the present invention, when a semiconductor thin film is grown as a single crystal on an insulating metal fluoride single crystal thin film or a substrate, the semiconductor film is initially grown. The problem is that the film grows in the form of islands and unevenness occurs on the surface of the film even after the film becomes thick, or when the initially formed islands coalesce, crystal defects enter the coalescing interface, causing growth. The problem of deterioration of film crystallinity is solved. As a result, a single crystal semiconductor thin film with a flat surface and good crystallinity is formed on the insulating metal fluoride.

Moreover, the method of the second invention also suppresses the island-like growth of the semiconductor thin film in the initial stage, and has the effect that a semiconductor thin film with a flat surface and good crystallinity can be grown as a single crystal on the insulating metal fluoride. can get.

[Brief explanation of the drawing]

Figure 1 is a process diagram of the first invention method of the present invention, Figure 2 is a process diagram of the second invention method of the invention, and Figure 3 is a perspective view of the electron beam reflection diffraction apparatus used in the examples. , Figures 4a, b and c show the state of the crystals after electron beam irradiation on the predeposited Ge layer of Example 1, and Figures 5a and b is an SEM photograph showing the crystal structure of the surface of the electron beam irradiated area and non-irradiated area when the thickness of the preliminary deposited layer was 3 nm in Example 1;
Figures 5c and d are graphs showing the relationship between the number of channels and the backscattering yield according to the backscattering spectrum;
Figure 7 is a diagram showing the relationship between electron irradiation dose and minimum scattering yield, Figure 7 is a diagram showing the relationship between electron irradiation rate and minimum scattering yield, and Figure 8a is a diagram showing the relationship between electron irradiation dose and minimum scattering yield. FIG. 8b is a SEM photograph showing the crystal structure of the surface, and is a graph showing the relationship between the number of channels and the backscattering yield based on the backscattering spectrum of the same sample. 1...Substrate, 1-1...Silicon substrate, 1-2...
...CaF ₂ layer, 2... semiconductor ultra-thin film, 3... semiconductor thin film, 4... electron beam, 5... deflection plate, 6... screen.

Claims (1)

[Claims] 1. A first step of depositing an insulating metal fluoride single crystal thin film or a semiconductor ultra-thin film 2 with a thickness of 10 nm or less on the surface of the substrate 1, and after depositing the semiconductor ultra-thin film 2. , semiconductor ultrathin film 2
a second step of irradiating the electron beam 4 from the surface side with an energy and an incident angle that reaches the fluoride thin film or substrate 1 through the fluoride film; and a second step of growing a semiconductor thin film 3 as a single crystal on the semiconductor ultra-thin film 2. A method for manufacturing a semiconductor thin film, characterized by comprising three steps. 2. A first step of irradiating the surface of the insulating metal fluoride single crystal thin film or substrate 1 with an electron beam, and then applying a thickness to the surface of the thin film or substrate 1.
A method for manufacturing a semiconductor thin film, comprising: a second step of depositing an ultra-thin semiconductor film 2 of 10 nm or less; and a third step of growing a single crystal of a semiconductor thin film 3 on the ultra-thin semiconductor film 2.