JP5084185B2 - Manufacturing method of semiconductor thin film - Google Patents

Description

  The present invention relates to a method for manufacturing a semiconductor thin film, and particularly to a method for manufacturing a crystallized semiconductor thin film by making a laser beam incident on an amorphous semiconductor thin film.

  A method for manufacturing a polycrystalline silicon thin film disclosed in Patent Document 1 below will be described with reference to FIGS. 6A to 6C.

  As shown in FIG. 6A, a silicon oxide film 101 is formed on the glass substrate 100. A cylindrical recess 102 is formed in the silicon oxide film 101. The diameter of the recess 102 is in the range of 50 nm to 150 nm, and the depth is about 750 nm. An amorphous silicon film 103 having a thickness of about 30 nm to 150 nm is formed in the recess 102 and on the silicon oxide film 101.

As shown in FIG. 6B, the laser beam 105 is incident on the amorphous silicon film 103. As the laser beam 105, for example, a XeCl excimer laser having a wavelength of 308 nm and a pulse width of 150 ns to 250 ns is used. Note that the glass substrate 100 is heated to a temperature in the range of 200 ° C. to 400 ° C. during laser irradiation. Most of the laser beam incident on the amorphous silicon film 103 is absorbed near the surface of the amorphous silicon film 103. This is because the absorption coefficient of amorphous silicon at a wavelength of 308 nm is about 0.139 nm ⁻¹ . A non-melted portion remains at the bottom of the recess 102, and the other portions are almost completely melted. Thereby, the crystal growth of silicon after laser irradiation starts first near the bottom of the recess 102 and proceeds to the vicinity of the surface of the amorphous silicon film 103.

  Several crystal grains can be generated at the bottom of the recess 102. If the planar cross-sectional dimension of the recess 102 is set to one crystal grain or a little smaller than that, only one crystal grain reaches the opening of the recess 102. Crystal growth proceeds in the in-plane direction of the amorphous silicon film 103 using the crystal grains reaching the opening of the recess 102 as seed crystals. Thereby, as shown in FIG. 6C, substantially single crystal grains 108 are formed.

  In Patent Document 2 below, a second silicon oxide film is conformally deposited on the inner surface of a recess having a diameter of about 1 μm and a depth of about 800 nm formed in the first silicon oxide film, thereby reducing the diameter of the recess. A technique for reducing the size to about 0.1 μm is disclosed. A crystallization propulsion film such as Ni is deposited on the bottom surface of the reduced recess. A first amorphous silicon film is deposited thereon. The first amorphous silicon film, the crystallization promoting film, and the second silicon oxide film are removed until the upper surface of the first silicon oxide film is exposed. As a result, the crystallization promoting film remains only in the recess, and the first amorphous silicon film remains thereon.

  After the removing step, by depositing the second amorphous silicon film, the plane orientation can be aligned with the (111) plane.

Japanese Patent Laid-Open No. 2005-26330 JP 2005-56894 A

  In the method disclosed in Patent Document 1, the aspect ratio of the recess for generating growth nuclei must be about 5 to 15. When the aspect ratio of the recesses becomes large, it becomes difficult to fill the recesses with an amorphous silicon film with good reproducibility.

  In the method disclosed in Patent Document 2, since the dimension of the flat cross section of the recess to be filled with the amorphous silicon film is reduced to about 0.1 μm, the amorphous silicon film is filled therein. Is more difficult.

  An object of the present invention is to provide a method of manufacturing a crystallized semiconductor thin film using a recess having a smaller aspect ratio than the conventional one.

According to one aspect of the present invention,
(A) forming a plurality of recesses having a planar shape including a circle having a diameter of 150 nm and being included in a circle having a diameter of 300 nm and having a depth of 200 nm or more and 500 nm or less on the substrate surface;
(B) As before Symbol the recess is filled, on the substrate, forming an amorphous or polycrystalline silicon film state,
(C) a portion of the silicon film, the Rukoto is incident first laser pulse, a step of melting the silicon film by heating the silicon film to the middle of the depth direction of the recess,
(D) providing a delay time from the time of incidence of the first laser pulse, and causing the second laser pulse to be incident on the same position within a period in which the molten state of the silicon film is maintained, thereby causing the recess There is provided a method for producing a semiconductor thin film, comprising the steps of growing only the crystal grains grown from one of the growth nuclei to the opening of the recess and crystallizing the silicon film .

  Even if the aspect ratio of the concave portion is reduced by making the second laser pulse incident at the same position in a state where the thermal influence of the first laser pulse remains, almost one crystal is formed with respect to one concave portion. A polycrystalline film in which grains are arranged can be formed.

  A method for manufacturing a semiconductor thin film according to an embodiment will be described with reference to FIGS.

  As shown in FIG. 1A, a silicon oxide film 2 having a thickness of 500 nm is formed on a base substrate 1 made of silicon. The silicon oxide film 2 can be formed by, for example, well-known chemical vapor deposition (CVD). A large number of recesses 3 are formed in the silicon oxide film 2. Each of the recesses 3 has a depth of 500 nm, and its flat cross section is a circle having a diameter of 0.19 μm.

  FIG. 2A shows an in-plane arrangement of the recess 3. The recesses 3 are arranged at positions corresponding to lattice points of a square lattice having a lattice interval D of 0.6 μm.

Returning to FIG. 1A, the description will be continued. The inner surface of the recess 3 and the upper surface of the silicon oxide film 2 are covered with a silicon oxide film 4 having a thickness of 30 nm. The silicon oxide film 4 can be formed by, for example, CVD using tetraethylorthosilicate (TEOS) and ozone (O ₃ ) as source gases.

An amorphous silicon film 5 having a thickness of 100 nm is deposited on the substrate so that the inside of the recess 3 is embedded. The amorphous silicon film 5 can be formed by, for example, CVD using silane (SiH ₄ ).

As shown in FIG. 1B, a pulsed laser beam 10 is incident on the amorphous silicon film 5. The pulse laser beam 10 is, for example, a second harmonic of an Nd: YAG laser. In place of the Nd: YAG laser, a solid-state laser such as an Nd: YLF laser or an Nd: YVO ₄ laser may be used.

FIG. 3A shows a timing chart of the pulse laser beam 10. First, the first laser pulse _{P 11} is incident. After the delay time TD, a second laser pulse P ₁₂ is incident on the same position. In this specification, the incidence of the first laser pulse P _{11 and} the incidence of the second laser pulse P ₁₂ are collectively referred to as “one shot”. Pulse width PW of the first laser pulse _{P 11} and the second laser pulse _{P 12} is in the range of 100Ns～200ns. The pulse energy density of the first laser pulse P ₁₁ on the surface of the amorphous silicon film 5 is 0.6 J / cm ² , and the second laser pulse P ₁₂ on the surface of the amorphous silicon film 5 is The pulse energy density is 1.0 J / cm ² . This pulse energy density is large enough to melt the amorphous silicon film 5.

The delay time TD from the incident first laser pulses _{P 11} until the second laser pulse _{P 12} is incident is 500 ns. The delay time TD is the length of the thermal effects of the first laser pulse P ₁₁ is sufficiently remained, i.e. the length of the molten state is maintained. The “molten state” includes a supercooled state. In this way, a laser processing method in which the next laser pulse is incident within a short time in which the thermal influence of the first incident laser pulse remains sufficiently within one shot is referred to as a “double pulse method”. . More generally, a method of configuring one shot with three or more laser pulses is referred to as a “multi-pulse method”. In this embodiment, the double pulse method is employed, but a multi-pulse method may be employed.

After irradiation of one shot consists of first laser pulses P ₁₁ and the second laser pulse P ₁₂ of, the following shots of configuration as first laser pulses P ₂₁ in the second laser pulses P ₂₂ Done. The time interval T from the irradiation of one shot to the irradiation of the next shot is 1 ms. That is, the shot repetition frequency is 1 kHz.

  FIG. 3B shows the shape of the beam cross section on the surface of the amorphous silicon film 5. The beam cross section is a rectangle that is long in the y-axis direction, and has a length L of 2.5 mm and a width W of 0.25 mm. Since the grating interval D shown in FIG. 2A is 0.6 μm, the number of the concave portions 3 arranged in the width direction in one beam cross section is 400 or more.

  In the laser beam irradiation step, the number of shots incident on the same portion of the surface of the amorphous silicon film 5 may be 1, or may be 2 or more, for example, 10. When the number of shots incident on the same location is 10, as an example, the substrate may be stationary and 10 shots may be incident on the same location, or the base substrate 1 may have an overlap rate of 90%. Irradiation may be performed while moving in the x-axis direction. When laser irradiation is performed while the base substrate 1 is moved, the first laser pulse and the second laser pulse constituting one shot have a very short delay time TD, so that they are in substantially the same region. It can be considered to be incident. The overlap ratio between shots means a ratio of a portion that overlaps an area irradiated with the next one shot in an area irradiated with one shot.

  As shown in FIG. 1C, the amorphous silicon film 5 is temporarily melted and crystallized halfway in the depth direction in the recess 3. Thereby, the polycrystalline silicon film 5a is formed. Amorphous silicon remains in the deep region of the recess 3.

  FIG. 2B schematically shows a plan view of the substrate after laser irradiation. Crystals grow from the growth nuclei generated in the recess 3. After the crystal growth reaches the opening of the recess 3, the crystal grows in the in-plane direction. When the crystals grown from the two recesses 3 adjacent to each other collide, the crystal growth stops and a grain boundary 6 is formed at the collision portion. Since the recesses 3 are arranged at lattice points of a square lattice, one crystal grain 7 exhibits a planar shape close to a square.

  FIG. 4 shows an electron micrograph (SEM photograph) after the surface layer portion of the actually produced polycrystalline silicon film 5a is sco-etched. It can be seen that approximately square crystal grains are regularly arranged in a matrix. The crystal orientation of each crystal grain was measured using an electron back scattering pattern (EBSP) method. As a result, it was found that the crystal orientation was constant in one crystal grain in both the direction perpendicular to the substrate surface and the two directions perpendicular to each other in the substrate surface. That is, it was confirmed that each of the crystal grains is a single crystal. It was also found that there were the most crystal grains in which the <001> direction was perpendicular to the substrate surface.

  Further, when the cross section of the substrate passing through the recess 3 was observed with an electron microscope (SEM), the interface between the amorphous silicon in the recess 3 and the crystallized silicon was approximately about the upper surface of the silicon oxide film 2. It was found to be located at a depth of 200 nm.

  Since the bottom and side surfaces of the recess 3 formed in the above embodiment are covered with the silicon oxide film 4 having a thickness of 30 nm, the substantial diameter of the recess is 0.13 μm and the depth is 0.47 μm. The aspect ratio of this recess is about 3.6. In the conventional crystallization by laser irradiation, the aspect ratio of the recesses has to be about 5-15. This is because it is necessary to generate only one growth nucleus in one recess. A portion shallower than the depth of 0.2 μm in the silicon film 5 in the recess 5 was melted, and a portion deeper than that was not melted. The substantial depth of the concave portion 3 can be considered as the depth of the melted portion, that is, 0.2 μm. In this case, the substantial aspect ratio is about 1.5. Even when the aspect ratio of the recess 3 is about 1.5, the same effect as in the above embodiment can be expected.

  By adopting the multi-pulse method as in the embodiment, it is possible to form crystal grains distributed corresponding to the distribution of the recesses even if the aspect ratio is smaller than 5. When the multi-pulse method is adopted, even if a plurality of growth nuclei are generated in one recess, only the crystal grains grown from one growth nucleus grow to the opening of the recess and grow from other growth nuclei. Does not grow to the opening of the recess. For this reason, even if the aspect ratio is reduced, almost one crystal grain 7 is formed for one recess 3 on the surface of the polycrystalline silicon film 5a.

  The polycrystalline silicon film shown in FIG. 4A is formed by allowing only one shot to enter the same location. In FIG. 4A, a black line like a grain boundary is observed in one crystal grain corresponding to one recess. This is considered to be a crystal defect such as dislocation.

  The polycrystalline silicon film shown in FIG. 4B is formed by making a laser beam incident while moving the incident position under the condition of an overlap rate of 90%. In this case, a 10-shot laser pulse is incident on the same location. It can be seen that the crystal defect density decreases. A straight line appearing in one crystal grain corresponding to one recess is a boundary between two single crystals constituting a twin. This boundary has less influence on carrier mobility than ordinary crystal defects. Thus, by making a plurality of shots enter the same location, crystal defects can be eliminated and the crystal quality of the crystal grains can be improved.

  In the case of forming a thin film transistor (TFT) in a polycrystalline silicon film, it is possible to form one TFT in one crystal grain by disposing a recess at a position where the TFT is disposed. With crystal grains whose <001> direction is perpendicular to the substrate surface, it is possible to form TFTs having higher field-effect mobility than crystal grains whose <111> direction is perpendicular to the substrate surface.

  FIG. 5A shows another example of the arrangement of the recesses 3. In the embodiment shown in FIG. 2A, the concave portions 3 are arranged at the positions of the lattice points of the square lattice. In the example shown in FIG. 5A, the recesses 3 in even-numbered rows of lattice points of the square lattice are shifted by a half pitch in the row direction. That is, the recess 3 is arranged at the position of the lattice point of the triangular lattice.

  FIG. 5B shows the positional relationship between the recesses 3 and the crystal grains 7. A crystal grain 7 formed by crystal growth in the in-plane direction around one recess 3 has a substantially hexagonal planar shape. In the embodiment shown in FIG. 2B, the growth from the four recesses 3 collides at one point, but in the example shown in FIG. 5B, the growth from the three recesses 3 collides at one point. By reducing the number of crystal grains colliding at one point, the swell at the position of the grain boundary can be lowered.

  In the embodiment described above, the planar shape of the recess 3 is a circle having a diameter of 0.19 μm, but other sizes and shapes may be used. For example, a planar shape including a circle having a diameter of 150 nm and included in a circle having a diameter of 300 nm may be used. Further, when the recess 3 is shallow, crystal grains grown from a plurality of growth nuclei reach the opening of the recess 3. In order to form one crystal grain for one recess, the depth of the recess 3 is preferably 200 nm or more (aspect ratio is 1.5 or more). If the recess 3 is made too shallow, crystal grains grown from a plurality of seed crystals generated at the bottom of the recess 3 reach the upper surface, so that a plurality of crystal grains are formed for one recess. If the recess 3 is made too deep, it becomes difficult to bury the inside with amorphous silicon. For this reason, it is preferable that the depth of the recessed part 3 shall be 500 nm or less. In the conventional method, the aspect ratio of the recesses had to be 5 or more, but in this embodiment, even if the aspect ratio is 4 or less, a polycrystalline silicon thin film in which the recesses and crystal grains substantially correspond to each other is formed. be able to.

  In the above embodiment, the second harmonic of a solid-state laser such as an Nd: YAG laser is used, but other lasers may be used. For example, a laser having a center wavelength in the wavelength range of 520 to 540 nm may be used.

The delay time TD since the first laser pulses P ₁₁ in one shot is incident to the second laser pulse P ₁₂ is incident, the thermal effects of the first laser pulse P ₁₁ is sufficiently remained in time, in order to enter the second laser pulses P ₁₂ of, preferably to a delay time TD and 1μs or less.

  In the above embodiment, a silicon substrate is used as the base substrate 1, but a substrate made of other materials may be used. For example, a glass substrate may be used. Further, the recess may be formed directly on the glass substrate without forming the silicon oxide film 2. In this case, it is not necessary to form the silicon oxide film 4 that covers the inner surface of the recess.

  In the above embodiment, the amorphous silicon film 5 is filled in the recess 3, but the polycrystalline silicon film may be filled in the recess 3. When the polycrystalline silicon film is formed, the crystal grains are irregularly distributed, but crystal grains distributed corresponding to the recesses 3 can be formed by crystallization by the method according to the above embodiment.

  In the above embodiment, the bottomed recess is filled with the silicon film, but the recess (penetrating hole) penetrating the substrate may be filled with the silicon film. In this case, the inside of the through hole is completely filled with the silicon film by the silicon film deposited on the side surface of the recess that penetrates the substrate.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

(1A) and (1B) are cross-sectional views of a substrate in the course of production for explaining a method for producing a semiconductor thin film according to an embodiment, and (1C) is a substrate and a polycrystal produced thereon. It is sectional drawing of a silicon film. (2A) is a plan view showing the distribution of recesses, and (2B) is a plan view showing the relationship between the recesses and crystal grains. (3A) is a timing chart of the laser pulse, and (3B) is a diagram showing a cross section of the laser beam on the substrate. It is a SEM photograph after carrying out Secco etching of the polycrystalline silicon film produced by the method by an example. (5A) is a plan view showing another example of the distribution of recesses, and (5B) is a plan view showing the relationship between the recesses and crystal grains. It is sectional drawing of the board | substrate in the middle of manufacture for demonstrating the preparation methods of the conventional polycrystalline silicon film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base substrate 2, 4 Silicon oxide film 3 Recessed part 5 Amorphous silicon film 5a Polycrystalline silicon film 6 Grain boundary 7 Crystal grain 10 Laser beam 100 Silicon substrate 101 Silicon oxide film 102 Recessed part 103 Amorphous silicon film 105 Laser beam 108 Crystal grain

Claims (6)

(A) forming a plurality of recesses having a planar shape including a circle having a diameter of 150 nm and being included in a circle having a diameter of 300 nm and having a depth of 200 nm or more and 500 nm or less on the substrate surface;
(B) As before Symbol the recess is filled, on the substrate, forming an amorphous or polycrystalline silicon film state,
(C) a portion of the silicon film, the Rukoto is incident first laser pulse, a step of melting the silicon film by heating the silicon film to the middle of the depth direction of the recess,
(D) providing a delay time from the time of incidence of the first laser pulse, and causing the second laser pulse to be incident on the same position within a period in which the molten state of the silicon film is maintained, thereby causing the recess And a step of growing only the crystal grains grown from one of the growth nuclei to the opening of the recess to crystallize the silicon film . 2. The method of manufacturing a semiconductor thin film according to claim 1 , wherein the first laser pulse and the second laser pulse have a center wavelength within a wavelength range of 520 nm to 540 nm. 2. The method of manufacturing a semiconductor thin film according to claim 1 , wherein the first laser pulse and the second laser pulse are second harmonics of an Nd: YAG laser, an Nd: YLF laser, or an Nd: YVO ₄ laser. Wherein in step c, the first method for manufacturing a semiconductor thin film according to any one of claims 1 to 3 time is 1μs or less from the entrance of the laser pulse to the entrance of the second laser pulse. When the incidence of the incident of the first laser pulse and the second laser pulse is defined as one shot, in the step c, according to claim 1-4 for entering a plurality of shots at the same position of the silicon layer A manufacturing method of a semiconductor thin film given in any 1 paragraph. The first laser pulse and the manufacturing method of a semiconductor thin film according to any one of claims 1 to 5 pulses width of the second laser pulses is in the range of 100Ns～200ns.