JP2807296B2 - Manufacturing method of semiconductor single crystal layer - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor single crystal layer in which a semiconductor single crystal layer is formed on an insulating film, and particularly relates to a method for manufacturing a semiconductor single crystal layer from a substrate seed portion. The present invention relates to a method for manufacturing a semiconductor single crystal layer using lateral crystal growth.

(Prior Art) Conventionally, three-dimensional ICs have been developed for the purpose of improving the degree of integration and increasing the speed of device operation.
In order to realize an IC, a technology for forming a semiconductor single crystal layer on an insulating film is essential. In silicon devices, SOI (Silicon O
n Insulater techniques such as a melt recrystallization method using an electron beam or a laser beam, a solid phase epitaxial growth method, and the like have been actively developed. Among them, the solid phase epitaxial growth method is a promising technique because a single crystal layer can be formed at a low temperature.

Further, in a device in which a polycrystalline semiconductor layer has been conventionally used, element reliability may be improved by monocrystallizing the polycrystalline semiconductor layer. For example, in a floating type EPROM, a polycrystalline silicon layer is used as a floating gate, and an oxide film of polycrystalline silicon is used as an insulating film on the floating gate. The oxide film on the polycrystalline silicon is usually formed by thermally oxidizing the polycrystalline silicon. However, when the oxidation temperature is lowered, irregularities such as protrusions are formed on the surface of the polycrystalline silicon, and thus there is a problem that the insulating characteristics are deteriorated. In order to avoid this problem, it is conceivable to use a silicon single crystal layer for the floating gate. By making the floating gate a single crystal layer, the insulating characteristics of the insulating film on the floating gate are dramatically improved. Even in such a device, a solid phase epitaxial growth method is effective as a method for forming a silicon single crystal layer.

FIG. 4 is a cross-sectional view showing a conventional silicon single crystal layer manufacturing process using a solid phase epitaxial growth method. First,
As shown in FIG. 4 (a), an insulating film 2 is formed on a silicon substrate 1.
Is formed, and a part of the insulating film 2 is removed to form the substrate seed portion 3. At this time, the native oxide film 4
Is formed. Next, by performing heat treatment at a high temperature of 1000 ° C. in a hydrogen (H ₂ ) atmosphere, the natural oxide film 4 on the substrate seed portion 3 is removed as shown in FIG. 4B. continue,
Amorphous silicon film 5 on insulating films 2 and 3
To form Next, as shown in FIG.
By annealing at a low temperature of 50 ° C., the silicon single crystal layer 7 is subjected to solid phase epitaxial growth. At this time, the natural oxide film 4 enters the amorphous silicon film 5 and disappears or becomes extremely thin.

However, this type of method has the following problems. That is, when the native oxide film 4 on the substrate seed portion 3 is thick, a silicon single crystal layer 6 containing many crystal defects 7 is formed after the epitaxial growth, and it is important to remove the native oxide film 4. In the step of removing the native oxide film 4 on the substrate seed portion 3, the surface of the insulating film 2 is etched and damaged, so that the surface of the insulating film 2 becomes uneven. During the solid phase growth, irregularities on the surface of the insulating film 2 due to damage cause nuclei other than the substrate seed portion 3. For this reason, it has been difficult to form a single crystal layer over a long distance in the lateral direction from the substrate seed portion 3.

Further, when the floating gate of the EPROM is formed in a silicon single crystal layer by the solid phase epitaxial growth method, damage to the insulating film deteriorates the insulating characteristics of the insulating film, and significantly deteriorates the reliability of the device function.

(Problems to be Solved by the Invention) As described above, conventionally, when a semiconductor single crystal layer is formed on an insulating film by a solid phase epitaxial growth method, it is necessary to remove a natural oxide film on a substrate seed portion before growth. In addition, the natural oxidation removing step forms irregularities on the surface of the insulating film on the base, which serves as a nucleus, which causes a problem that the single crystal layer does not grow in the lateral direction and a problem that the insulating characteristics of the insulating film deteriorate.

The present invention has been made in consideration of the above circumstances, and an object thereof is to enable a single crystal layer to grow laterally on an insulating film from a substrate seed portion, and to form a large area single crystal layer. It is another object of the present invention to provide a method for manufacturing a semiconductor single crystal layer, which can improve the insulating characteristics of an insulating film.

[Means for Solving the Problems] The gist of the present invention resides in that a semiconductor layer is formed on an insulating film before the seed opening in order to prevent the formation of irregularities in the underlying insulating film due to the etching of the seed opening. Is to be formed.

That is, the present invention relates to a method for manufacturing a semiconductor single crystal layer in which a semiconductor single crystal layer is formed on an insulating film by utilizing crystal growth from a substrate seed portion. A first semiconductor thin film is formed thereon, and then a portion of the insulating film and the first semiconductor thin film is opened to form a substrate seed portion serving as a nucleus for crystal growth. Remove the natural oxide film on the part,
Then, a second semiconductor thin film is formed on the first semiconductor thin film and the substrate seed portion, and thereafter, the first and second semiconductor thin films are heat-treated to be crystallized.

(Operation) According to the present invention, after forming an insulating film, a first semiconductor thin film is formed on the insulating film, and thereafter, a substrate seed portion,
In order to form the second semiconductor thin film, in an etching step for removing a natural oxide film on the substrate seed portion, the insulating film is covered with the first semiconductor thin film. Therefore, there is no possibility that the surface of the insulating film is damaged and unevenness is generated. Therefore,
Generation of nuclei other than the substrate seed portion on the surface of the insulating film can be prevented, and the insulating characteristics of the insulating film do not deteriorate.

(Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples.

FIG. 1 is a sectional view showing a manufacturing process of a semiconductor crystal layer according to the first embodiment of the present invention. First, as shown in FIG. 1 (a), an SiO ₂ film (insulating film) 12 is formed on a silicon single crystal substrate 11 by thermal oxidation to a thickness of 200 °, and a first amorphous silicon film is formed thereon. 13 is formed to a thickness of 500 mm. The amorphous silicon film 13 is formed by thermally decomposing silane (SiH ₄ ) or disilane (Si ₂ H ₆ ) at a temperature of 500 to 550 ° C. by an LP-CVD method.

Next, as shown in FIG. 1 (b), a substrate seed portion 14 is provided by selectively etching the first amorphous silicon film 13 and the insulating film 12. At this time, a natural oxide film 15 is formed on the surface of the silicon film 13 and the surface of the substrate seed portion 14 with a slight amount of oxygen or due to any cause.

Next, after exposing the sample to a hydrogen fluoride gas to remove the natural oxide film 15, a second amorphous silicon film 13 and a second substrate seed portion 14 are formed on the first amorphous silicon film 13 as shown in FIG. An amorphous silicon film 16 is formed to a thickness of 500 mm. The formation of the second amorphous silicon film 16 is performed by thermally decomposing silane or disilane by LPCVD in the same manner as the formation of the first amorphous silicon film 13. In the step of removing the native oxide film 15, the surface of the underlying insulating film 12 is covered with the first amorphous silicon film 13, so that the surface of the film 12 does not have irregularities.

Next, an annealing process is performed in a nitrogen atmosphere at a temperature of 550 to 650 ° C. to form an amorphous silicon film as shown in FIG.
13 and 16 are changed to a single crystal silicon layer 17. This crystallization is
This is a solid phase epitaxial growth from the substrate seed portion 14.

By doing so, the silicon single crystal can be formed only up to 10 μm from the substrate sheet portion in the prior art, whereas in this embodiment, the defect-free silicon single crystal layer 17 can be formed up to a region 15 μm or more from the substrate seed portion 14. It became possible to obtain. This is considered to be because the surface of the underlying insulating film 12 is in a flattened state, and crystal growth always proceeds from the substrate seed portion 14. Note that the surface of the first amorphous silicon film 13 has irregularities due to the etching process for removing the natural oxide film 15, and the irregularities on the surface of the silicon film 13 are reduced by the second amorphous silicon film 16. Since it is buried, the unevenness does not become a nucleus for crystal growth, and there is no problem.

Thus, according to the method of the present embodiment, since the first amorphous silicon film 13 is formed on the insulating film 12 before providing the substrate seed portion 14, the natural oxide film 15 on the substrate seed portion 14 is removed. In this case, inconveniences such as unevenness on the surface of the insulating film 12 can be prevented beforehand in the etching step. Therefore, the silicon single crystal layer 17 can be formed by lateral growth from the substrate seed portion 14, and a large area single crystal layer can be realized on the insulating film 12. In addition, since there is no unevenness due to damage on the surface of the insulating film 12, the insulating characteristics of the insulating film 12 can be improved.

FIG. 2 is a process sectional view for explaining the method of the second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

This embodiment differs from the first embodiment in the step of forming an amorphous silicon film. That is, in this embodiment, first, as shown in FIG. 2A, an SiO ₂ film (insulating film) 12 and a first polycrystalline silicon film 23 are formed on a silicon single crystal substrate 11 by thermal oxidation. Here, the first polycrystalline silicon film 23 was formed by thermally decomposing silane or disilane at a temperature of 600 ° C. or higher using the LP-CVD method.

Next, as shown in FIG. 2 (b), the substrate seed portion 14 is provided by performing selective etching of the polysilicon 23 and the insulating film 12 in the same manner as in the first embodiment. At this time,
The natural oxide film 15 is formed on the surface of the first polycrystalline silicon film 23 and on the substrate seed portion 14 as described above. Thereafter, after removing the natural oxide film 15, a second polycrystalline silicon film 26 is formed by LPCVD as shown in FIG. 2 (c).

Next, as shown in FIG. 2 (d), silicon, arsenic or boron is ion-implanted into the first and second polycrystalline silicon films 23 and 26 to thereby form the first and second polycrystalline silicon films 23 and 26. 26 is made amorphous. In addition, due to this ion implantation, a natural oxide film slightly remaining on the substrate seed portion 13 is also dispersed and removed. Thereafter, similarly to the first embodiment, the amorphous silicon films 13 and 16 are converted into the silicon single crystal layer 17 by solid phase epitaxial growth by annealing at a temperature of 550 to 600 ° C. in a nitrogen atmosphere. .

Even in such a process, it is possible to prevent the occurrence of unevenness on the surface of the insulating film 12, and the same effect as that of the above-described embodiment method can be obtained.

FIG. 3 is a process sectional view for explaining the method of the third embodiment of the present invention, and shows an example in which the present invention is applied to the manufacture of an EPROM.

First, as shown in FIG. 3 (a), a silicon single crystal substrate
Element isolation oxide film 32, gate oxide film (insulating film) 33 on 31
After forming the first amorphous silicon film 34 on the entire surface by LPCV
Formed by thermal decomposition of silane or disilane by Method D. Subsequently, as shown in FIG. 3B, a photoresist 35 is applied on the first amorphous silicon film 34, and the resist 35 where the substrate seed portion is to be formed is removed. Then, the substrate seed portion 36 is provided by dry-etching the oxide films 32 and 33 using the resist 35 as a mask. At this time,
On the substrate seed portion 36, a natural oxide film 37 is formed.

Next, as shown in FIG. 3C, a second amorphous silicon film 38 is formed on the first amorphous silicon film 34 and in the substrate seed portion 36 by heat of silane or disilane by the LPCVE method. Formed by decomposition. Subsequently, in a nitrogen or argon gas atmosphere, 5
By annealing at a low temperature of 00 to 550 ° C., the third
As shown in FIG. 4D, the first and second amorphous silicon films 3 are formed.
4,38 silicon single crystal layer by solid phase epitaxial growth
Change to 39. Then, phosphorus, arsenic or boron is diffused into the silicon single crystal layer 39. Here, the silicon single crystal layer 39 is used as a floating gate. Also, the substrate seed section
The silicon single crystal layer 39 on 36 is removed.

Then, as shown in FIG. 3 (e), a silicon single crystal layer
A thermal oxide film 41 is formed on 39, a polycrystalline silicon film 42 is further formed thereon, and phosphorus is diffused into the polycrystalline silicon film 42 to form a control gate. Next, as shown in FIG. 3 (f), the polycrystalline silicon film 42, the thermal oxide film 41 and the silicon single crystal layer 39 are selectively etched into a gate electrode shape.
Subsequently, arsenic is ion-implanted into the substrate 31 using the polycrystalline silicon film 42 and the silicon single crystal 39 as a mask to form an n ⁻ -type diffusion layer 43, thereby completing the EPROM cell shown in the figure.

The doping of the floating gate 39 can be performed before the solid phase growth. Since the solid phase growth rate of the polycrystalline silicon layer to which phosphorus or arsenic is added is high, the solid phase growth after adding phosphorus or arsenic to amorphous silicon has a larger substrate seed portion over a larger area. Epitaxial growth can be performed up to a region distant from the vicinity.

Thus, according to the method of this embodiment, the floating gate 39 can be made of a silicon single crystal layer without deteriorating the withstand voltage of the thermal oxide film (gate oxide film) 33 below the floating gate 39. The withstand voltage of the thermal oxide film (silicon oxide film) 41 on the gate 39 can be improved.

Increasing the area of the substrate sheet portion 36 is against the trend of improving the degree of integration. Therefore, since it is desirable to reduce the area ratio of the substrate seed portion 36 as much as possible,
A semiconductor device in which the substrate seed portion 36 exists at least at a rate of one for every two elements is effective. Actually, by the method shown in FIG. 1, a region 15 μm or more away from the substrate seed portion.
Since it is possible to form a single crystal layer to the area of 200 [mu] m ^2, the substrate seed unit 1 for elements of a single element area 20 [mu] m ²
The seed area ratio can be reduced by the ratio of about 10 elements per element.

Note that the present invention is not limited to the above-described embodiments. In the embodiment, the hydrogen fluoride (HF) gas is used as the step of removing the natural oxide film. However, the heat treatment may be performed in a fluorine nitrogen (NF ₃ ) or hydrochloric acid (HCl) gas atmosphere instead. Further, the semiconductor to be crystallized is not limited to silicon, and germanium, GaAs, and other semiconductors can be used. Further, the crystal growth method from the substrate seed portion is not limited to the solid phase epitaxial growth method, and a melt recrystallization method using an electron beam or a laser beam can also be used. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described above in detail, according to the present invention, by forming a semiconductor layer on an insulating film before opening a seed, it is possible to prevent the formation of irregularities on the underlying insulating film. it can. Therefore, the single crystal layer can always be grown in the lateral direction from the substrate seed portion, so that a single crystal layer having a large area can be obtained and the insulating characteristics of the insulating film can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a manufacturing process of a semiconductor single crystal layer according to the method of the first embodiment of the present invention. FIG. 2 is a process sectional view for explaining the method of the second embodiment of the present invention. FIG. 3 is a process sectional view for explaining the method of the third embodiment of the present invention, and FIG. 4 is a process sectional view for explaining the conventional method. 11: silicon single crystal substrate, 12: thermally oxidized SiO ₂ film (insulating film), 13: first amorphous silicon film, 14: substrate seed part, 15: natural oxide film, 16: Second amorphous silicon film, 17 single crystal silicon layer, 23 first polycrystalline silicon film, 26 second polycrystalline silicon film.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/20

Claims (3)

(57) [Claims] A step of forming an insulating film on a semiconductor substrate;
Forming a first semiconductor thin film on the insulating film, forming a substrate seed portion serving as a nucleus for crystal growth by opening a part of the insulating film and the first semiconductor thin film;
Removing a native oxide film on the semiconductor thin film and the substrate seed portion; forming a second semiconductor thin film on the first semiconductor thin film and the substrate seed portion;
And a step of heat-treating and crystallizing the second semiconductor thin film. 2. The method according to claim 1, wherein the step of crystallizing the first and second semiconductor thin films is a solid phase growth from the substrate seed portion. 3. A process for forming the first and second semiconductor thin films, comprising forming a polycrystalline silicon film and then implanting ions into the polycrystalline silicon film to form an amorphous silicon film. The method for producing a semiconductor single crystal layer according to claim 1 or 2, wherein: