JP2800060B2 - Method for manufacturing semiconductor film - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for crystallizing a semiconductor film having an amorphous phase, and more particularly, to a method for growing a crystal phase using an ion beam to obtain uniform and controlled grains. The present invention relates to a method for forming a polycrystalline semiconductor film having a diameter.

[Prior art] Conventionally, with respect to crystal growth using an ion beam, an example in which amorphous silicon formed on a silicon substrate is subjected to solid phase epitaxial growth by arsenic ion implantation (Jpn, J. Appl. Phys. 21)
(1982) Suppl. 21-1, p211) and an example of combining xenon ion implantation and substrate heating during implantation (Nuclear Instrum.
Methods Res. B 1, 9/20 (1987) p457). Further, with respect to the semiconductor film and the ion implantation on the glass substrate, an example in which germanium or silicon was ion-implanted into a polycrystalline germanium film or a silicon film deposited on quartz glass while heating, respectively, to increase the particle size (Appl. Phys.64
(1988) p2337).

These examples using an ion beam can perform solid phase growth at a lower temperature than other methods, and are expected to be applied to a lower temperature semiconductor process and a three-dimensional integrated circuit.

[Problems to be Solved by the Invention] However, in the above-described conventional crystal growth method using an ion beam, since the projected range of implanted ions is set at the center of the film, the defect density in the crystal phase is high, and In order to grow grains, it was necessary to increase the substrate temperature during ion implantation. For example, at least 800 ° C. for a polycrystalline silicon film
Heating the substrate during the above implantation is necessary, and when a material that cannot withstand this temperature is used as the substrate of the semiconductor film, serious problems such as deformation of the substrate shape and diffusion of the substrate constituent elements into the semiconductor film occur. there were.

In a known method for forming crystal nuclei in a solid phase by heat treatment, for example, a high temperature of at least 600 ° C. is required for an amorphous silicon film.

[Means for Solving the Problems] According to the present invention, there is provided a step of forming an amorphous semiconductor film containing crystals on a substrate, and the step of projecting an implanted ion from the surface of the formed amorphous semiconductor film. A crystal growth step of implanting ions so as to have a thickness greater than the thickness of the amorphous semiconductor film.

The formation of the amorphous semiconductor film containing a crystal phase can be performed, for example, by depositing a semiconductor film containing crystal nuclei on a substrate by known plasma CVD, thermal CVD, or the like, or by ion-implanting the amorphous semiconductor film deposited on the substrate. This can be realized by partially nucleating the crystal phase by injection. In order to partially form a crystal phase nucleus by the above-described ion implantation, the acceleration energy of the implanted ions is set so that the projected range of the implanted ions is larger than the thickness of the semiconductor film. Thereby, the effect of amorphization is reduced due to cascade collision of implanted ions and constituent atoms of the semiconductor film, the defect density in the crystallized region in the semiconductor film is small, and a high-quality crystal nucleus can be obtained. If the acceleration energy is smaller than the film thickness, the density of crystal nuclei increases in a region where the energy deposition is large, but the crystallinity of the crystal nuclei is inferior to the above conditions. Further, no crystal nucleus is formed at a depth where the ions do not reach in the semiconductor film. The power density of the ion beam is preferably 1 W / cm ² or more. When the power density is low, crystallization can be formed by ion implantation while heating the substrate (at 50 to 800 ° C.). The boundary value of the power density at which the substrate needs to be heated (the power density at which the generation rate of crystal nuclei greatly changes) greatly changes depending on the type of the semiconductor film or the substrate and the type of ions. The ion species used is not particularly limited, but is preferably a semiconductor constituent element, a substrate constituent element, or a rare gas element to be crystallized. In addition, under the above-described desirable conditions of the current density of the ion beam that forms the nucleation of the crystal phase, the crystal phase can be grown following the nucleation of the crystal phase. The difference between the crystal grain size due to the crystal nucleus thus formed and the crystal grain formed at the last stage increases.

The acceleration energy of the ions in the step of implanting ions from the surface of the amorphous semiconductor film according to the present invention is set so that the projected range of the implanted element is larger than the thickness of the semiconductor film. The setting is made so that the effect of amorphization due to cascade collision of atoms is reduced and the defect density in a crystallized region in the semiconductor film is reduced. If the projected range of the implanted element is smaller than the above film thickness, a portion where ions do not reach in the semiconductor film is generated, and the crystal phase hardly grows in the portion. The power density of the ion beam is desirably 0.5 to ¹ W / cm ² . Above the power density, crystal nuclei are formed and the controllability of the crystal grain size is reduced. When the power density is 0.5 W / cm ² or more, crystal growth can be performed without particularly performing substrate heating. When the power density of the ion beam is low, the crystal growth rate can be increased by heating (50 to 800 ° C.) when implanting ions into the substrate. The boundary value of the power density that requires substrate heating changes depending on the type of the semiconductor film and the substrate. In the case where the semiconductor film is a silicon film, substrate heating is not necessary if the temperature of the silicon film is 200 to 220 ° C. or higher due to the heating effect of the ion beam. At a temperature lower than this, the growth of the amorphous phase is more likely to occur than the growth of the crystal phase. Therefore, it is important for the growth of the crystal phase that the substrate be heated by an external heater to a temperature higher than this temperature. The type of ions to be implanted is not particularly limited, but is preferably a semiconductor element, a substrate element, or a rare gas element to be crystallized.

According to the present invention, a control step can be provided between the step of forming the semiconductor film including the crystal and the step of implanting ions from the surface of the formed amorphous semiconductor film. The control step is to amorphize a part of the crystal contained in the semiconductor film containing the crystal to control the density of the crystal phase or the spatial arrangement in the film prior to the subsequent crystal growth. This is performed so that a semiconductor film having a larger crystal grain size and uniform polycrystals can be obtained. It is desirable that the ion current density to be implanted is about 0.3 to 0.7 W / cm ² , and the acceleration energy of the ions is set so that the projected range of the implanted element is about the same as or larger than the thickness of the semiconductor film. desirable. If the projected range of the implanted element is smaller than the above film thickness, amorphousization does not occur at a depth where ions do not reach in the semiconductor film, which is not desirable. Above the power density, the temperature of the semiconductor film becomes 200 ° C. or higher due to the heating effect of ion implantation, and the crystal phase tends to grow. The type of ions to be implanted is not particularly limited, but is preferably a semiconductor constituent element, a substrate constituent element, or a rare gas element to be crystallized.

The following three methods can be used to control the density of the crystal phase. The first method is a method in which a focused ion beam having a predetermined diameter is scanned and irradiated on the surface of the semiconductor film under conditions for performing amorphization. The crystal in the region into which the ion beam has been implanted is amorphized, and only the portion of the crystal not irradiated with ions remains in the film. Conditions such as the accelerated voltage of the focused ion beam, the ion current density, and the amount of implantation depend on the size and density of the crystals contained in the amorphous semiconductor film, and are larger and more uniform in the subsequent crystal growth process. Is set to obtain. As a second method, an amorphous semiconductor film, which is to be a masking film for ions to be implanted, such as a SiO ₂ film, is coated on the amorphous semiconductor film to a predetermined size to expose an amorphous semiconductor film not covered with the masking film. A method of performing ion implantation on a portion can be used. In addition, the ion implantation may be performed while heating the amorphous semiconductor film.

Further, as a third method, ions are implanted into the entire film under the condition that crystal growth does not occur, that is, the condition that the growth of the amorphous phase occurs (the substrate temperature of the semiconductor film is set to 220 ° C. or lower). A method of controlling the density of a crystal phase can be used by amorphizing a crystal having a relatively small size and leaving only a crystal having a relatively large size in a film in an initial state.

Further, when light absorption is caused by the implanted ions reaching the substrate, two or more ions are implanted to react them (for example, when light absorption is caused by silicon implantation, oxygen, nitrogen or the like is ion-implanted). By forming a transparent compound (SiO ₂ or Si ₃ N _{4 in the} above example) in the substrate, light absorption can be suppressed.

[Action] According to the present invention, accelerated ions are implanted into the semiconductor film, and in the process of decelerating while losing energy, directly (elastic collision between incident atoms and semiconductor atoms) or indirectly ( The semiconductor film is locally heated to a high temperature at an atomic level by applying energy (inelastic collision between incident atoms and a semiconductor electronic system).

Since the temperature rise due to this ion beam is short and local in time, the average temperature rise of the substrate is much smaller than this, and defects caused by ion implantation cause the movement of semiconductor atoms. By promotion, crystal growth of the semiconductor film is realized at a low temperature.

In the formation of crystal nuclei and crystal growth, the acceleration energy determined so that the projected range of the implanted ions is larger than the thickness of the semiconductor film is determined by the cascade collision between the implanted atoms and the atoms constituting the semiconductor film. The defect density in the region crystallized in the semiconductor film,
It works so that good quality crystal grains can be obtained at low temperature.

[Examples] The present invention will be described below based on examples. FIGS. 1, 2, 3, and 4 show examples 1, 2, and 3 of the present invention, respectively.
It is process explanatory drawing of 3,4. 5 and 6 are diagrams showing the concentration distribution of the implanted ions of the first embodiment, and FIG. 7 is a diagram showing the concentration distribution of the implanted ions of the fourth embodiment.

Example 1 An amorphous silicon film containing crystal nuclei by a plasma CVD method using silane gas as a raw material on two kinds of glass substrates of quartz glass and alkaline earth / alumina borosilicate glass (trade name: 7059 glass, manufactured by Corning Incorporated) Was deposited to a thickness of 150 nm (FIG. 1 (a)). Next, silicon is accelerated to 18
0 keV, dose 5 × 10 ¹⁶ / cm ² , beam current density 6 μA /
Ions were implanted in cm ² without heating the substrate (FIG. 1 (b)). FIG. 5 shows the result of calculation (based on LSS theory) of the distribution of implanted silicon. These samples were compared before and after ion implantation by transmission electron microscope observation and transmission electron beam diffraction. It was confirmed that the amorphous silicon film containing crystal nuclei of about 50 nm before the ion implantation grew into a polycrystalline silicon film having crystal grains of about 600 nm. When the current density of the ion beam was changed, it became clear that the growth of crystal grains was extremely reduced at a current density of ³ μA / cm ² or less. Further, the final grain size of the crystal grains was determined by the density of the crystal nuclei, and the grain size of the crystal grains did not increase even when the dose was increased. Therefore, the crystal growth was completed when the entire region of the amorphous silicon layer changed to polycrystalline. on the other hand,
Reduce the ion beam current density to ² μA / cm ² ,
When the substrate was heated to about 00 ° C and ion implantation was performed,
A polycrystalline silicon film having the same particle size as that obtained when the substrate was not heated was obtained in each of the glass substrates.

Furthermore, in order to oxidize the silicon implanted in the substrate,
Oxygen acceleration energy 110 keV, dose 1 × 10 ¹⁷ / cm ²
It was injected (FIG. 1C). The implantation depth of oxygen was matched with that of silicon, and the implantation amount was twice that of silicon. FIG. 6 shows the oxygen concentration distribution calculated under these conditions. Thereafter, a pattern was formed on the polycrystalline silicon film, and the light absorption of the etched silicon portion was examined. As a result, a remarkable effect of suppressing light absorption was observed as compared with the case where oxygen was not injected.

Example 2 Plasma CVD was performed on the same two types of glass substrates as in Example 1.
An amorphous silicon film containing a crystal nucleus was deposited to a thickness of 150 nm by the method. On top of this, silicon oxide is sputtered
200 nm was deposited, and a square mask having a side of 500 nm was provided on the oxide film every 3 μm through a photolithographic process (FIG. 2A). Next, silicon was ion-implanted at an acceleration energy of 100 keV, a dose of 1 × 10 ¹⁶ ions / cm ² , and a beam current density of 1 μA / cm ² without heating the substrate, thereby amorphizing a portion without a mask ( FIG. 2 (b). Thereafter, the silicon oxide film was removed, and silicon was ion-implanted under the conditions of an acceleration energy of 180 keV, a dose of 5 × 10 ¹⁶ / cm ² , a beam current density of ² μA / cm ² , and substrate heating of 300 ° C. (FIG. 2). (C)). When this sample was evaluated by transmission electron microscope observation and transmission electron beam diffraction, 3 μm was observed on any of the glass substrates.
It was found that a polycrystalline silicon film having a relatively uniform grain size of about m was formed.

Example 3 Plasma CVD was performed on the same two glass substrates as in Example 1.
An amorphous silicon film was deposited to a thickness of 150 nm by the
Figure (a). Next, silicon was ion-implanted under the conditions of an acceleration energy of 180 keV, a dose of 3 × 10 ¹⁶ ions / cm ² , a beam current density of 10 μA / cm ² , and no substrate heating to form a crystal phase (FIG. 3 (b) )). Thereafter, in order to reduce the density of the crystal phase, silicon was accelerated at an acceleration energy of 180 keV and a dose of 1 × 10 ¹⁶
Ions were implanted under the conditions of the number of particles / cm ² , the beam current density: 1 μA / cm ² , and the heating of the substrate at 200 ° C., and the crystal phase having a small grain size was made amorphous (FIG. 3C). Furthermore, the remaining crystal phase is grown,
Silicon is accelerated at 180 ke to crystallize the entire film
V, dose 5 × 10 ¹⁶ / cm ² , beam current density 2μA / c
Ions were implanted under the conditions of m ² and substrate heating of 300 ° C. (FIG. 3D). When this sample was evaluated by transmission electron microscope observation and transmission electron diffraction, it was found that a polycrystalline silicon film having a particle size of about 3 μm was formed. Also, the third
The sample processed up to Fig. (C) was placed at
When a heat treatment was performed for a long time and the same evaluation was performed, it was found that a polycrystalline silicon film having a grain size of about 3 μm was formed on each of the substrates. The crystal growth by heat treatment
Lasers and lamps were also possible.

Example 4 An amorphous silicon film having a thickness of 150 nm was deposited on a single crystal gallium arsenide substrate by a sputtering method (FIG. 4A).
Next, argon was supplied at an acceleration energy of 280 keV and a dose of 5 ×.
10 ¹⁶ pieces / cm ² , beam current density 2μA / cm ² , substrate heating 250 ° C
(FIG. 4 (b)). FIG. 7 shows the distribution of the injected argon. These samples were compared before and after ion implantation by transmission electron microscope observation and transmission electron beam diffraction. It was observed that the amorphous silicon film before the ion implantation grew into a substantially uniform single crystal silicon film. The defects in the gallium arsenide substrate due to the implantation of argon could be recovered by heat treatment.

[Effects of the Invention] According to the present invention, formation of a polycrystalline semiconductor film or heteroepitaxial growth having a large grain size and a uniform grain size, which was impossible in the past, can be realized at a low temperature. According to the present invention, a substrate which cannot be used for a semiconductor due to deformation by heat or diffusion of a substrate constituent element in a conventional high temperature process by heating can be used according to the present invention.

[Brief description of the drawings]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are views for explaining a method of manufacturing a polycrystalline semiconductor film according to the present invention. Fifth
FIG. 6, FIG. 6, and FIG. 7 are diagrams for explaining the concentration distribution of ions implanted in the first to third embodiments of the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-310109 (JP, A) JP-A-60-153114 (JP, A) JP-A-61-55915 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H01L 21/20

Claims (5)

(57) [Claims] A step of forming an amorphous semiconductor including a crystal on a substrate;
A crystal growth step of implanting ions so that the projected range of the implanted ions is larger than the film thickness of the amorphous semiconductor.
A method for manufacturing a polycrystalline semiconductor film on a substrate. 2. A control step of adjusting a density and / or a position of a crystal by amorphizing a part of the crystal contained in the amorphous semiconductor film prior to the crystal growth step. 2. The method according to claim 1, further comprising: 3. The method according to claim 2, wherein said controlling step comprises implanting ions by irradiating the surface of said amorphous semiconductor film with a focused ion beam at intervals. 4. The method according to claim 1, wherein said controlling step comprises masking a surface of said amorphous semiconductor film into a predetermined shape, and thereafter implanting ions from an exposed surface of said amorphous semiconductor film which is not masked. 3. The method according to item 2. 5. The method according to claim 1, wherein said crystal growth step is a heteroepitaxial growth step in which said substrate is a single crystal semiconductor or a single crystal insulator, and said amorphous semiconductor film has a composition different from that of said substrate. Item 5. The method according to any one of Items 4 to 4.