JP2002373859A - Crystal growing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce impurities in a polysilicon film formed by a solid phase growth or a laser annealing in a solid phase growing method from an amorphous silicon (a-Si) film to the polysilicon (p-Si) film. SOLUTION: A crystal growing method comprises a process for moving impurities in an amorphous silicon film 24 or a polysilicon film 24a formed by vapor-phase growing the film 24 into an impurity capturing layer 23 formed on or under the film 24 by heating to capture the impurities in the layer 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a crystal, and more particularly, to amorphous silicon (a-Si).
The present invention relates to a method for solid-phase growth from silicon to polysilicon (p-Si).

[0002]

2. Description of the Related Art In view of an increase in the amount of information, a liquid crystal display (LCD) that can display a large amount of characters and display characters or images is desired.
For this reason, a non-linear element is added to the picture element to give an equivalently sharp threshold characteristic to a liquid crystal that does not have a sufficient sharpness of the threshold characteristic, thereby increasing the display capacity while maintaining a high display contrast.

One of such nonlinear elements is a thin film transistor (TFT). At present, application of an amorphous silicon (a-Si) film is mainly used. However, in recent years, in order to improve a response speed, a reduction in resistance and an increase in on-current have been demanded. I have.
For this reason, use of a semiconductor film made of p-Si having better crystallinity than a-Si has been studied. There are the following four main methods for forming a polysilicon film.

A method of growing a polysilicon film directly on a heated glass substrate by a CVD method (a method of forming a polysilicon film by a CVD method); melting an a-Si film by laser annealing; (A method of forming a polysilicon film by laser annealing) by heating the a-Si film at a temperature of about 600 ° C. for about 40 hours to crystallize and grow the polysilicon film (A method of forming a polysilicon film by solid-phase growth), a method of forming a polysilicon film by solid-phase growth and a method of forming a polysilicon film by laser annealing in combination, There is a method of forming a silicon film.

[0005]

SUMMARY OF THE INVENTION However, CVD
In the method of forming a polysilicon film by the method, the heating temperature is high, which has an adverse effect on the glass substrate.

In the method of forming a polysilicon film by laser annealing and the method of forming a polysilicon film by solid phase growth, when impurities (light element or heavy metal element) are mixed in the a-Si film, the Since impurities accumulate in crystal grain boundaries or the like during heating during solid phase growth or cooling during laser annealing, the electrical characteristics of the TFT formed in the polysilicon film do not improve. For example, an increase in leakage current is caused.

Further, as already known, a-Si
By intentionally doping impurities such as Ni into the film, the solid phase growth temperature can be further lowered and the growth rate can be increased. However, in this case, a larger amount of impurities accumulate at crystal grain boundaries and the like.

In particular, when a metal that forms silicide as described above accumulates at a crystal grain boundary or the like, the formation of silicide causes a sudden deterioration in the electrical characteristics of the TFT formed in the polysilicon film.

Further, when both solid phase growth and laser annealing are used, impurities accumulated in the crystal grain boundaries and the like due to the heating of the solid phase growth are re-dissolved because the crystal temperature rises to near the melting point of the crystal during laser annealing. At the time of cooling, it is frozen on defects and crystal grain boundaries in the polysilicon film. Therefore, a large amount of impurities are included in the polysilicon film.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and provides a crystal growth method capable of reducing impurities in a polysilicon film formed by solid phase growth or laser annealing. The purpose is to provide.

[0011]

According to a first aspect of the present invention, there is provided a crystal growth method, wherein an impurity trapping layer formed above or below an amorphous silicon film is provided in the amorphous silicon film. The method according to claim 2, further comprising a step of moving and capturing impurities in the polysilicon film formed by solid-phase growing the amorphous silicon film by heating. The invention according to claim 3, wherein in the growing method, after the impurity in the amorphous silicon film or the polysilicon film is captured by the impurity capturing layer, the impurity capturing layer is removed. Item 3. In the crystal growth method according to Item 1 or 2, the impurity trapping layer is a semiconductor layer having a different density, distribution or size of crystal defects with respect to the polysilicon film. And wherein there claim 4
According to a fifth aspect of the present invention, there is provided the crystal growth method according to the first or second aspect, wherein the impurity trapping layer is a semiconductor layer having a different lattice constant from the polysilicon film. The invention relates to the crystal growth method according to claim 1 or 2, wherein the impurity trapping layer is a semiconductor layer containing phosphorus or boron. The invention according to claim 6 is the invention according to claims 1 to 5. In the crystal growth method according to any one of the first to sixth aspects, the heating for moving the impurities is performed by irradiation with a laser beam, and the invention according to the seventh aspect is any one of the first to sixth aspects. The amorphous silicon film before the solid phase growth is doped with nickel or copper at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more.

The operation of the present invention will be described below.

In order to lower the solid phase growth temperature and improve the growth rate, a high concentration (concentration 1) is intentionally contained in the a-Si film.
× 10 ¹⁷ cm ^-3 or more) nickel (Ni) or copper (Cu)
Doping with impurities such as is performed.

According to the present invention, the impurity trapping layer formed above or below the a-Si film is provided in the a-Si film or in the a-Si film.
The impurities in the p-Si film formed by solid-phase growth of the i film are moved and captured by heating. Thus, p-
Impurities are removed from the Si film. In particular, after capturing the impurities in the impurity capturing layer, by removing the impurity capturing layer,
Even when heat treatment is performed later, it is possible to prevent impurities from returning to the p-Si film again. This gives p
-Leakage current of a transistor or the like formed in the Si film can be reduced.

After the p-Si film is solid-phase grown,
Since the p-Si film is heated by irradiating laser light when the impurities in the Si film are moved to be captured by the impurity capturing layer, the crystal grain size of the p-Si film is increased, The crystallinity of the film can be improved. Thus, p-
The mobility of carriers such as a transistor formed in a Si film can be increased to reduce resistance and increase on-state current.

As the impurity trapping layer, a semiconductor layer having a different density, distribution or size of crystal defects with respect to the p-Si film, a semiconductor layer having a different lattice constant with respect to the p-Si film, or phosphorus or boron is used. A contained semiconductor layer can be used. These impurity trapping layers are all p-S
distortion occurs at the interface with the i-film or at the impurity trapping layer itself,
It is considered that impurities are captured by this distortion.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

(1) First Embodiment of the Present Invention FIG. 1 is a flowchart showing a process sequence of a crystal growth method according to a first embodiment. 2 (a) to 2 (d),
3A and 3B are cross-sectional views showing a crystal growth method according to the first embodiment, and show a case of the flowchart of FIG.

First, an a-Si film 2 having a thickness of about 50 nm is formed on a glass substrate 1 shown in FIG. 2A by a CVD method, and then an aqueous solution of nickel acetate is applied and dried.
A nickel film (Ni film) 3 (not shown) is formed (FIG. 2).
(B)).

Next, a heat treatment is performed at a temperature of 550 ° C. for 4 hours to diffuse Ni into the a-Si film 2 and a.
P-Si film 2 having crystal grains 4 by solid-phase growth of -Si
a is formed. At this time, since Ni is diffused in the a-Si film 2a, the solid-phase growth temperature is lowered.
In the film 2a, Ni having a large diffusion coefficient accumulates at the crystal grain boundaries 5, and further reacts with Si to form silicide. FIG. 2C shows a state after the Ni film 3 is removed. FIG. 2D shows a state after the crystal grain boundaries have been removed by etching.

T of p-Si solid-phase grown by doping with Ni
The EM photograph is shown in FIG. Silicide in the black part in the center
It can be seen that it is formed. FIG. 4A shows a SIM.
The secondary ions of Ni are counted by S, and Ni in the depth direction is counted.
It is the figure converted into density distribution. Represented by a linear scale on the horizontal axis
Depth (nm), and the vertical axis represents p− expressed on a logarithmic scale.
Nickel concentration (cm) in Si film 2a^-3). Average
About 1 × 10¹⁹cm ^-3Of Ni. What
The beam diameter of SIMS is several μm, and Ni is
Because the crystal defects accumulate within the diameter, the measured Ni concentration
The degree is considered to average the amount of Ni existing in the beam diameter.
available. Further, FIG. 6A shows a recess on the surface of the p-Si film 2a.
It is a photograph of the crystal surface showing the result of observing the convexity, and the surface is
It is flat.

Next, Secco etching is performed using an etching solution comprising a mixed solution of potassium dichromate, hydrofluoric acid and water.
Thereby, as shown in FIG. 2D, etching proceeds along crystal defects including the crystal grain boundaries 5. At the same time, Ni accumulated at the crystal grain boundaries 5 is also removed. FIG. 6B shows p
-It is a photograph of the crystal surface which shows the result of having observed the unevenness | corrugation of the surface after etching the Si film 2a, The black part is removed by etching and it is dented. FIG. 4B is a diagram showing the concentration distribution of Ni in the depth direction. The horizontal axis and the vertical axis are the same as in FIG. Ni in the p-Si film 2a was greatly reduced, and the concentration became about 1 × 10 ¹⁸ cm ⁻³ or less on average.

Next, as shown in FIG.
A new a-Si film 6 having a thickness of about 200.
It is formed by the VD method.

Next, the p-Si film is solid-phase grown from the a-Si film 6 by irradiating a laser beam, and the surface is flattened. Thus, as shown in FIG. 3B, a p-Si film 7 as an element forming layer is formed on the glass substrate 1 as a whole.

FIG. 4C is a diagram showing the concentration distribution of Ni in the depth direction. The horizontal axis and the vertical axis are the same as in FIG. Ni in the p-Si film 7 of FIG. 3B is maintained at a concentration of about 1 × 10 ¹⁸ cm ⁻³ or less on average. FIG.
(C) is a photograph of the crystal surface showing the result of observing the irregularities on the surface of the p-Si film 7, and it can be seen that it is flat. Further, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

As described above, according to the first embodiment,
Lower the solid phase growth temperature and increase the growth rate
Therefore, intentionally high concentration (concentration of 1 × 10
¹⁷cm ^-3Above), doping with Ni
Impurities accumulate in crystal defects such as grain boundaries 4.
However, the crystal defects are etched by selective etching.
As a result, Ni is removed from the p-Si film 2a.

As a result, it is possible to reduce the leakage current of the transistor and the like formed on the p-Si film 7.

After the etching of the crystal defects, the a-Si
By coating the film 6 and performing laser annealing, the concave portions of the etching traces can be filled and the surface can be flattened.
This facilitates formation of elements such as transistors on the p-Si film 7.

The solid phase growth method shown in the flowchart of FIG. 1 is also possible. That is, the p-Si film 2a is formed without forming the a-Si film 6 after the selective etching of the crystal defect.
May be directly heated by laser annealing or the like. Thereby, the crystal grain size of the p-Si film 2a can be further increased, and the surface can be flattened.

(2) Second Embodiment of the Present Invention FIG. 7 is a flowchart showing a process sequence of a crystal growth method according to a second embodiment. 8 (a) to 8 (d),
FIGS. 9A and 9B are cross-sectional views showing a crystal growth method according to the second embodiment, and show the case of the flowchart of FIG. The difference from the first embodiment is that after the step of solid-phase growth of the p-Si film and before the step of selectively etching crystal defects, p-Si
This includes a step of heating the Si film to increase the crystal grain size of the p-Si film.

First, an a-Si film 12 having a thickness of about 50 nm is formed on a glass substrate 11 shown in FIG. 8A by a CVD method, and then an aqueous solution of nickel acetate is applied and dried. A nickel film (Ni film) 13 is formed (FIG. 8B).

Next, a heat treatment is performed at 550 ° C. for 4 hours to diffuse Ni into the a-Si film 12 and
After the solid phase growth, the p-Si film 1 having the crystal grains 14a is formed.
2a is formed. At this time, the N-
Since i is diffused, Ni accumulates at the crystal grain boundaries 15a in the p-Si film 12a, and further reacts with Si to form silicide. FIG. 8C shows a state after the Ni film 13 has been removed.

FIG. 1 is a TEM photograph of the Ni state shown in FIG.
It is shown in FIG. The left part of the figure shows Ni silicide. FIG. 10A is a diagram showing the Ni concentration distribution in the depth direction acquired in the same manner as FIGS. 4A to 4C. The horizontal axis shows the depth (nm) expressed on a linear scale, and the vertical axis shows the nickel concentration (c) in the p-Si film 12a expressed on a logarithmic scale.
m- ³ ). On average, it contains about 1 × 10 ¹⁹ cm ⁻³ of Ni. FIG. 12A shows the p-Si film 12.
4 is a photograph of a crystal surface showing a result of observing irregularities on the surface a. In the photograph, a protrusion was observed, but the height of the protrusion was approximately several nm.

Next, as shown in FIG.
Laser annealing is performed on the film 12a. As a result, the crystal grains 14a further grow in solid phase, and the crystal grains 14b
Becomes

Next, as shown in FIG. 9A, Secco etching is performed to selectively etch crystal defects including the crystal grain boundaries 15b. At this time, Ni accumulated at the crystal grain boundary 15b is also removed at the same time. FIG. 10B is a diagram showing the concentration distribution of Ni in the depth direction. The horizontal axis and the vertical axis are the same as in FIG. N in p-Si film 12a
i is decreasing from the side closer to the surface, and is approximately 1 × 10
It is distributed at ¹⁸ to 1 × 10 ¹⁹ cm ⁻³ .

Next, as shown in FIG. 9B, the p-Si film 12b is further solid-phase grown by irradiating a laser beam, and the surface is flattened. Thereby, the glass substrate 1
P-Si film 12c as an element forming layer as a whole
Is formed. FIG. 10C is a diagram showing the concentration distribution of Ni in the depth direction. The horizontal axis and the vertical axis are the same as in FIG. Ni in the p-Si film 12c is approximately 1 × 10 ¹⁸ to 1
× 10 ¹⁹ cm ^-3 is maintained. FIG. 12B shows p-
It is a photograph of the crystal surface showing the result of observing the irregularities on the surface of the Si film 12c, and it can be seen that the projections are flat apart from the projections. Further, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

When an element such as a transistor is formed on the p-Si film 12c, the protrusion may be removed by polishing (CMD), and since the protrusion is small, it is not obstructed to form the element. Conceivable.

As described above, according to the second embodiment, in order to lower the solid phase growth temperature and improve the growth rate, the a-Si film 12 is intentionally made to have a high concentration (concentration 1 ×). 1
In the case of doping with Ni (0 ¹⁷ cm ⁻³ or more), a larger amount of impurities accumulate in crystal defects 15 b such as crystal grain boundaries. However, by etching the crystal defects 15 b by selective etching, p- Ni is removed from inside the Si film 12b. Thereby, the leakage current of the transistor and the like formed on the p-Si film 12c can be reduced.

After the step of solid-phase growth of the p-Si film 12b and before the step of selectively etching crystal defects, the p-Si film 12a is heated by laser light irradiation, Since the method includes the step of increasing the crystal grain size of the -Si film 12a, the crystallinity of the p-Si film 12b is further improved. This makes it possible to increase the mobility of carriers of a transistor or the like formed in the p-Si film 12c to reduce resistance and increase on-current.

Further, since laser annealing is performed after the crystal defect is etched to further solid phase growth, the crystal grain size can be further increased and the surface can be flattened. This facilitates formation of an element such as a transistor on the p-Si film 17.

The solid phase growth method shown in the flowchart of FIG. 7 is also possible. That is, an a-Si film may be formed after selective etching of crystal defects, and may be heated by laser annealing or the like. Thereby, the surface can be further flattened.

(3) Third and Fourth Embodiments of the Invention FIGS. 13A to 13D are cross-sectional views showing a crystal growth method according to a third embodiment. The difference from the first and second embodiments is that an impurity trapping layer is provided.

First, as shown in FIG. 13A, a silicon oxide film 22 having a thickness of about 200 nm is formed on a glass substrate 21. Further, after forming an a-Si film having a thickness of about 20 nm, the a-Si film is annealed by irradiating a laser beam to the a-Si film at two stages of energy of, for example, 220 mJ and 330 mJ,
P-Si film (impurity capture layer) 23 having a crystal grain size of about 10 nm
To form The temperature was 1410 at the time of laser light irradiation.
Although the temperature is on the order of ° C., the required energy of the laser beam differs depending on the laser irradiation device.

Next, as shown in FIG.
An a-Si film 24 having a thickness of about 50 nm and Ni
After forming the film 25 in order, as shown in FIG. 13C, a heat treatment is performed at a temperature of 550 ° C. for 4 hours to form a-Si.
Ni is diffused into the film 24 and the p-Si film 24a is grown in a solid phase.

Next, as shown in FIG. 13D, after the Ni film 25 is removed, laser annealing is performed to further grow the solid phase to increase the crystal grain size. Thus, a p-Si film 24b as an element formation layer is formed. At this time, Ni moves by heating, and p-Si
The film is captured by the film 23.

FIG. 14A shows the result of investigation of the concentration distribution of Ni in the p-Si film (impurity trapping layer) 23 and the p-Si film 24b. The horizontal axis indicates the depth (nm) expressed on a linear scale, and the vertical axis indicates the Ni concentration (cm ^-3 ) expressed on a logarithmic scale. For comparison, the same experiment was performed on a sample having no p-Si film (impurity trapping layer) 23, and the concentration distribution of Ni in the p-Si film 24b was examined. The result of the investigation is shown in FIG.

According to the results of the investigation, a large amount of Ni is p-Si
It is trapped in the film (impurity trapping layer) 23, and the Ni concentration in the p-Si film 24b is reduced by that amount. The effect is remarkable as compared with the comparative example.

Further, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

As described above, according to the third embodiment, a-
P-Si film (impurity trapping layer) formed under Si film 24
23, a p- film formed by solid-phase growth of an a-Si film 24 is formed.
Ni in the Si film 24a is moved and captured by heating. Thereby, Ni is removed from the p-Si film 24a. As a result, it is possible to reduce the leakage current of the transistor and the like formed on the p-Si film 24b.

After the p-Si film 24a is solid-phase grown, the p-Si film 24a is heated by laser light irradiation, so that the crystal grain size of the p-Si film 24b is increased.
The crystallinity of the p-Si film 24b can be improved.
This makes it possible to increase the mobility of carriers such as transistors formed in the p-Si film 24b, reduce the resistance, and increase the on-current.

In the above description, p is used as the impurity trapping layer.
Although a p-Si film 23 having a different density, distribution or size of crystal defects is used for the -Si film 24a or 24b, as a fourth mode, as shown in FIG.
It is also possible to use a semiconductor layer having a different lattice constant for the i film 24a or 24b, for example, a SiGe film 26.

Also in this case, the Ni concentration distribution in the p-Si film 24b is as shown in FIG. 16A as in the third embodiment. That is, Ni is captured by the SiGe film 26,
The Ni concentration in the p-Si film 24b can be reduced. FIG. 16B shows an experimental result of a sample having no SiGe film 26.

(4) Fifth Embodiment of the Invention FIGS. 17A to 17D are cross-sectional views showing a crystal growth method according to a fifth embodiment. The difference from the third and fourth embodiments is that a phosphorus-containing p-Si film 29 is formed as an impurity trapping layer on a solid-phase grown Ni-containing p-Si film 28. .

First, as shown in FIG. 17A, a silicon oxide film 22 is formed on a glass substrate 21. continue,
In the same manner as described above, the a-Si film is doped with Ni (impurity) and solid-phase grown to form the p-Si film 28. The Ni concentration distribution in the p-Si film 28 at this time is shown in FIG.
Shown in

Next, as shown in FIG.
A p-Si film (impurity capture layer) 29 containing phosphorus having a concentration of about 1 × 10 ²⁰ cm ⁻³ is formed on the Si film 28 by a CVD method.

Next, as shown in FIG. 17C, the p-Si film 28 is heated by applying laser annealing.
Ni inside the p-Si film 29 is moved into the p-Si film 29 to form the p-Si film 2.
9 and grow the crystal grain size of the p-Si film 28a to a large value.

Next, as shown in FIG.
When the Si film 29 is removed, the formation of the element formation layer is completed. FIG. 18B shows the Ni concentration distribution in the p-Si film 28a at this time. That is, Ni decreases from the surface of the p-Si film 28a. Further, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

According to the fifth embodiment, the p-Si film 28
After the p-Si film (impurity trapping layer) 29 is formed thereon, Ni in the p-Si film 28a is moved into the p-Si film 29 by heating and is captured by the p-Si film 29, so that p −
Ni in the Si film 28a can be reduced. Thus, when a transistor or the like is formed on the p-Si film 28a, the leakage current of the transistor can be reduced and the performance can be improved.

Also, after Ni is captured by the p-Si film 29, the p-Si film 29 is removed to prevent the Ni from returning to the p-Si film 28a again even if a heat treatment is applied later. Can be prevented.

Further, after the solid phase growth, laser annealing is further performed to further perform the solid phase growth to increase the crystal grain size, so that the mobility of carriers in the p-Si film 28a is increased, -The performance of the transistor formed on the Si film 28a can be improved.

The impurity trapping layer 29 may be made of very small crystalline p-Si or a semiconductor having a different lattice constant, for example, SiGe.

(5) Sixth Embodiment of the Present Invention FIGS. 19A to 19E are cross-sectional views showing a crystal growth method according to a sixth embodiment. The difference from the fifth embodiment is that the p-Si film 30 containing Ni grown by solid phase is partially etched to form a plurality of p-S
After air isolation to the i-film 30a, a p-S containing phosphorus as an impurity trapping layer is formed between the p-Si films 30a.
This means that the i film 32 is embedded and Ni is captured therein.

First, as shown in FIG. 19A, a silicon oxide film 22 is formed on a glass substrate 21. continue,
In the same manner as described above, the a-Si film is doped with Ni (impurity) and solid-phase grown to form the p-Si film 30. FIG. 20A shows the Ni concentration distribution in the p-Si film 30 at this time.
Shown in

Next, as shown in FIG.
After a resist mask 31 is formed in a region on the Si film 30 where an element formation layer is to be formed, the p-Si film 30 is selectively etched by the resist mask 31 and removed. As a result, the element formation layer 30a remains on the silicon oxide film 22.

Next, as shown in FIG. 19C, the resist mask 31 is left as it is, and a concentration of about 1 × 10 ²⁰
p-Si film containing phosphorus at cm ^-3 (impurity trapping layer)
32 is formed by a CVD method. A p-Si film 32 is buried between the element forming layers 30a.

Next, the resist mask 31 is removed,
The p-Si film 32 buried between the element formation layers 30a is left by lift-off.

Next, as shown in FIG. 19D, by irradiating laser light from the surface of the element forming layer 30a and the surface of the p-Si film 32 and heating, the Ni in the p-Si film 30a is converted into p-type. The p-Si film 32 is moved into the Si film 32 and captured by the p-Si film 32, and the crystal grain size of the p-Si film 30b is increased.

Next, as shown in FIG. 19E, when the p-Si film 32 is removed by utilizing the difference in etching rate, the formation of the element formation layer 30b is completed. P at this time
FIG. 20B shows the Ni concentration distribution in the -Si film 30b. That is, the Ni concentration in the p-Si film 30b decreases,
× 10 ¹⁷ cm ^-3 . Further, as a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

According to the sixth embodiment, after a plurality of p-Si films 30a to be element forming regions are air-isolated, the p-Si film containing phosphorus as an impurity trapping layer is formed between the p-Si films 30a. Since the film 32 is embedded and Ni is captured therein, Ni in the p-Si film 30b can be reduced. Thus, when a transistor or the like is formed on the p-Si film 30b, the leakage current of the transistor can be reduced and the performance can be improved.

After Ni is captured by the p-Si film 32, the p-Si film 32 is removed to prevent the Ni from returning to the p-Si film 30b even if a heat treatment is performed later. Can be prevented.

Further, after the solid-phase growth, laser annealing is further performed to further perform solid-phase growth to increase the crystal grain size. Therefore, the mobility of carriers in the p-Si film 30b is increased, -The performance of the transistor formed on the Si film 30b can be improved.

The impurity trapping layer 32 may be made of very small crystalline p-Si or a semiconductor having a different lattice constant, for example, SiGe.

(6) Seventh Embodiment of the Present Invention FIGS. 21A to 21D are cross-sectional views showing a crystal growth method according to a seventh embodiment. A feature of the seventh embodiment is that impurity trapping layers are formed above and below a p-Si film 34 serving as an element formation layer. In the seventh embodiment, a SiGe film 33 is formed below a p-Si film 34, and a p-Si film 35 containing phosphorus is formed on the p-Si film 34.

First, as shown in FIG. 21A, a silicon oxide film 22 is formed on a glass substrate 21. continue,
After a SiGe film (impurity trapping layer) 33 having a thickness of about 20 nm and an a-Si film having a thickness of about 50 nm are sequentially formed, the a-Si film is doped with Ni (impurity) in the same manner as described above. The p-Si film 34 is formed by growing. FIG. 22A shows the Ni concentration distribution in the p-Si film 34 at this time.

Next, as shown in FIG.
A p-Si film (impurity trapping layer) 35 containing phosphorus having a concentration of about 1 × 10 ²⁰ cm ⁻³ is formed on the Si film 34 by a CVD method.

Next, as shown in FIG. 21C, the p-Si film 34 is heated by laser annealing.
Ni in the SiGe film 33 and the p-Si film 35 is moved to be captured in the SiGe film 33 and the p-Si film 35, and the crystal grain size of the p-Si film 34a is increased.

Next, as shown in FIG.
When the Si film 35 is removed, the formation of the element formation layer 34a is completed. FIG. 22 (b) shows the Ni concentration distribution in the p-Si film 34a at this time. That is, the Ni of the p-Si film 34a is
The concentration decreased to 1 × 10 ¹⁷ cm ⁻³ or less. Furthermore,
As a result of Raman scattering measurement, it was confirmed that the quality of the crystal was good.

According to the seventh embodiment, since the impurity trapping layers 33 and 35 are formed above and below the p-Si film 34 serving as an element forming layer, Ni in the p-Si film 34a can be reduced. Can be. Thus, when a transistor or the like is formed on the p-Si film 34a, the leakage current of the transistor can be reduced and the performance can be improved.

Further, by removing the p-Si film 33 after capturing Ni in the p-Si film 35, the amount of Ni returning to the p-Si film 34a again can be reduced even if a heat treatment is performed later. Can be done.

Further, after solid phase growth, laser annealing is further performed to further perform solid phase growth to increase the crystal grain size. Therefore, the mobility of carriers in the p-Si film 34a is increased, -The performance of the transistor formed on the Si film 34a can be improved.

The impurity trapping layers 33 and 35 may be made of very small crystalline p-Si or a semiconductor having a different lattice constant, for example, SiGe.

In the above embodiment, Ni is intentionally introduced into the a-Si film. However, it is also effective when impurities (light elements or metal elements) are present in the a-Si film from the beginning. .

Although the method for removing impurities in the crystal growth method of the present invention is applied to a p-Si film grown by solid phase, it can be applied to a p-Si film grown by a CVD method. is there.

[0084]

As described above, according to the present invention, a-S
In the impurity trapping layer formed above or below the i film, p-S formed in the a-Si film or by solid-phase growth of the a-Si film
Since the impurities in the i film are moved and captured by heating, the impurities are removed from the p-Si film. This allows
Leakage current of a transistor or the like formed in the p-Si film can be reduced.

In particular, after the impurities are trapped in the impurity trapping layer, the impurity trapping layer is removed, so that the impurities can be prevented from returning to the p-Si film even if heat treatment is performed later. .

Further, when the impurities in the p-Si film are moved to be captured by the impurity capturing layer, the p-
Since the Si film is heated, the crystal grain size of the p-Si film can be increased, and the crystallinity of the p-Si film can be improved. Thus, the mobility of carriers such as a transistor formed in the p-Si film can be increased to reduce the resistance and increase the on-current.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a process sequence of a crystal growth method according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view (part 1) illustrating a crystal growth method according to the first embodiment of the present invention.

FIG. 3 is a sectional view (part 2) illustrating a crystal growth method according to the first embodiment of the present invention.

FIG. 4 is a view showing a Ni concentration distribution in an element formation layer in the crystal growth method according to the first embodiment of the present invention.

FIG. 5 is a crystal thin film photograph showing a surface state of a p-Si film in the crystal growth method according to the first embodiment of the present invention.

FIG. 6 is a crystal thin film photograph showing a surface state of a p-Si film in the crystal growth method according to the first embodiment of the present invention.

FIG. 7 is a flowchart showing a process sequence of a crystal growth method according to a second embodiment of the present invention.

FIG. 8 is a sectional view (part 1) illustrating a crystal growth method according to a second embodiment of the present invention.

FIG. 9 is a cross-sectional view (part 2) illustrating a crystal growth method according to the second embodiment of the present invention.

FIG. 10 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a second embodiment of the present invention.

FIG. 11 is a crystal thin film photograph showing a surface state of a p-Si film in a crystal growth method according to a second embodiment of the present invention.

FIG. 12 is a crystal thin film photograph showing a surface state of a p-Si film in a crystal growth method according to a second embodiment of the present invention.

FIG. 13 is a cross-sectional view showing a crystal growth method according to a third embodiment of the present invention.

FIG. 14 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a third embodiment of the present invention.

FIG. 15 is a cross-sectional view illustrating a crystal growth method according to a fourth embodiment of the present invention.

FIG. 16 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a fourth embodiment of the present invention.

FIG. 17 is a sectional view illustrating a crystal growth method according to a fifth embodiment of the present invention.

FIG. 18 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a fifth embodiment of the present invention.

FIG. 19 is a sectional view illustrating a crystal growth method according to a sixth embodiment of the present invention.

FIG. 20 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a sixth embodiment of the present invention.

FIG. 21 is a cross-sectional view showing a crystal growth method according to a seventh embodiment of the present invention.

FIG. 22 is a diagram showing a Ni concentration distribution in an element formation layer in a crystal growth method according to a seventh embodiment of the present invention.

[Explanation of symbols]

1,11,21 glass substrate, 2,6,12,24 a-Si film, 2a, 12a, 12b, 24a, 24b, 28,30,
30a, 34 p-Si film, 3, 13, 25 Ni film, 4, 14a, 14b crystal grain, 5, 15a, 15b crystal grain boundary, 7, 12c, 28a, 30b, 34a p-Si film (element formation layer ), 22 silicon oxide film, 23 p-Si film (impurity trapping layer), 26,33 SiGe film (impurity trapping layer), 29,32,35 phosphorus-containing p-Si film (impurity trapping layer), 31 resist mask.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H01L 29/786 H01L 29/78 627G F-term (Reference) 5F052 AA02 AA11 CA02 CA08 DA02 DB01 EA16 FA06 FA19 HA08 JA01 5F110 AA01 AA06 AA07 BB01 DD02 DD13 GG01 GG02 GG13 GG19 GG25 GG33 GG34 GG36 GG44 PP01 PP03 PP29 PP34 QQ19 QQ28

Claims (7)

[Claims] An impurity trapping layer formed above or below an amorphous silicon film is moved by heating impurities in the amorphous silicon film or in a polysilicon film formed by solid-phase growth of the amorphous silicon film. A crystal growth method, comprising a step of capturing by means of a crystal. 2. The crystal growth method according to claim 1, wherein said impurity trapping layer is removed after impurities in said amorphous silicon film or said polysilicon film are trapped by said impurity trapping layer. . 3. The crystal growth method according to claim 1, wherein the impurity trapping layer is a semiconductor layer having a different density, distribution or size of crystal defects with respect to the polysilicon film. . 4. The crystal growth method according to claim 1, wherein the impurity trapping layer is a semiconductor layer having a different lattice constant from the polysilicon film. 5. The crystal growth method according to claim 1, wherein the impurity trapping layer is a semiconductor layer containing either phosphorus or boron. 6. The crystal growth method according to claim 1, wherein the heating for moving the impurities is performed by laser light irradiation. 7. The method according to claim 1, wherein the amorphous silicon film before the solid phase growth is doped with nickel or copper having a concentration of 1 × 10 ¹⁷ cm ⁻³ or more. Crystal growth method.