JP3844537B2 - Method for manufacturing polycrystalline semiconductor film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a polycrystalline semiconductor film suitable for manufacturing a thin film transistor (TFT) used in an active matrix type liquid crystal display device or the like.
[0002]
[Prior art]
A liquid crystal display device is advantageous in that it is thin and lightweight, can be driven at a low voltage and consumes less power, and is widely used in various electronic devices. In particular, in recent years, an active matrix type liquid crystal display device in which an active element such as a thin film transistor is provided for each pixel has come to be superior in terms of display quality, comparable to a CRT (cathode-ray tube). It is also used for displays such as portable televisions and personal computers.
[0003]
By the way, the thin film transistor is usually formed by forming a polycrystalline silicon thin film on a transparent glass substrate and using the polycrystalline silicon thin film (Japanese Patent Laid-Open No. 64-76715, etc.).
9A and 9B are cross-sectional views showing a conventional polycrystalline silicon thin film manufacturing method and a subsequent thin film transistor manufacturing method in the order of steps, and FIG. 10 is a cross-sectional view showing the manufactured thin film transistor.
[0004]
First, as shown in FIG. 9A, an amorphous silicon film 33 is formed on a transparent glass substrate 34. Then, the amorphous silicon film 33 is repeatedly irradiated with a trapezoidal laser beam (pulse) 51 about 20 shots per location as indicated by a broken line in the beam profile (energy distribution in the beam width direction). Thereby, the amorphous silicon in the portion irradiated with the laser is polycrystallized, and the polycrystalline silicon film 35 can be obtained.
[0005]
Next, the laser beam 51 is moved to the next irradiation region, and the laser beam 51 is irradiated in the same manner as described above. By irradiating the amorphous silicon film 33 with the laser light 51 in this manner, the amorphous silicon is polycrystallized to selectively form the polycrystalline silicon film 35. In this case, the crystal grain size of silicon is small in one irradiation, and the crystal grain size gradually increases by repeatedly irradiating the laser beam 51. As the laser light source, an excimer laser is usually used because amorphous silicon can be polycrystallized without increasing the temperature of the substrate.
[0006]
Next, as shown in FIG. 9B, only the polycrystalline silicon film 35 in the region where the thin film transistor is to be formed is left, and the remaining portions of the polycrystalline silicon film 35 and the amorphous silicon film 33 are removed. Thereafter, a gate insulating film 40 and a gate electrode film 39 are sequentially formed on the entire surface, and the gate insulating film 40 and the gate electrode film 39 are patterned to expose both end sides of the polycrystalline silicon film 35.
[0007]
Thereafter, impurities are introduced at a high concentration into the exposed polycrystalline silicon film 35 to form a high-concentration impurity region 41 to be a source / drain region.
Next, an interlayer insulating film 37 is formed on the entire surface, a contact hole reaching the impurity region 41 is formed in the interlayer insulating film 37, and then a metal film such as aluminum (Al) is embedded on the entire surface so as to fill the contact hole. Then, the metal film is patterned into a predetermined shape to form source / drain electrodes 38 and wiring (not shown). Thereby, the thin film transistor shown in FIG. 10 is completed.
[0008]
[Problems to be solved by the invention]
However, in the conventional method for forming a thin film transistor described above, the polycrystalline silicon crystal grains do not become large unless laser light is irradiated for about 20 shots per part, so that workability is poor and a long time is required for manufacturing. That is, the carrier mobility of the thin film transistor is related to the crystal grain size of the polycrystalline silicon film 35, and the carrier mobility increases as the crystal grain size increases. On the other hand, generally, the higher the energy density of the laser beam 51 irradiating the amorphous silicon film 33, the larger the grain size of the polycrystalline silicon. However, the energy density of the laser beam 51 has a certain value (hereinafter referred to as microcrystallization). If the threshold value is exceeded, the grain size of polycrystalline silicon becomes extremely small. Therefore, the energy density of the laser beam 51 is preferably as high as possible below the microcrystallization threshold. However, it is extremely difficult to precisely control the energy density of the laser beam 51. For this reason, conventionally, a laser pulse whose energy density per shot is lower than the microcrystallization threshold is repeatedly irradiated many times. This increases the crystal grain size of polycrystalline silicon.
[0009]
An object of the present invention is to provide a method for manufacturing a polycrystalline semiconductor film, which can form a polycrystalline semiconductor film having a large crystal grain size and suitable for manufacturing a thin film transistor.
[0010]
[Means for Solving the Problems]
The problems described above are the step of forming an amorphous semiconductor film on the substrate, the energy density at the center of the beam is set to be equal to or higher than the microcrystallization threshold of the amorphous semiconductor film, and the energy is increased toward the end in the beam width direction. A method of manufacturing a polycrystalline semiconductor film comprising the step of irradiating the amorphous semiconductor film with a laser beam having a beam profile having a lower inclined portion to polycrystallize the amorphous semiconductor.
[0011]
FIG. 11 is a diagram illustrating Raman spectra of single crystal silicon (c-Si), polycrystalline silicon (p-Si), and amorphous silicon (a-Si) examined by Raman scattering spectroscopy. However, in FIG. 11, the horizontal axis is the wave number, and the vertical axis is the Raman intensity. As is apparent from FIG. 11, only a broad spectrum can be obtained with amorphous silicon (a-Si), but a peak is observed in the vicinity of 520 cm ^{-1 with} single crystal silicon (c-Si). In polycrystalline silicon (p-Si), a peak appears slightly on the lower wavenumber side than 520 cm ⁻¹ . The closer the peak intensity and wave number of polycrystalline silicon (p-Si) are to the value of single crystal silicon (c-Si), the better the crystallinity of polycrystalline silicon, and the higher the carrier mobility when a thin film transistor is formed.
[0012]
12, the position of the beam width direction on the horizontal axis, taking the laser energy on the vertical axis, the beam center portion average energy density of ^{300mJ / cm 2, 340mJ / cm} 2 and the laser light of 380 mJ / cm ² of (flat portion) FIG. 5 is a diagram showing the beam profile of FIG. 1 together with a crystallization threshold value and a microcrystallization threshold value. When polycrystallizing amorphous silicon using a laser beam, it is necessary to irradiate the amorphous silicon film with a laser beam having an energy exceeding a crystallization threshold (about 180 to 200 mJ / cm ² ). For energy above the crystallization threshold, the crystal grain size obtained increases with increasing energy. However, when the energy of the laser light exceeds the microcrystallization threshold (about 360 mJ / cm ² ), the crystal becomes very small in size.
[0013]
Further, 520 cm ^over time 13 to the polycrystalline silicon film produced by a laser beam having a trapezoidal beam profile shown in FIG. 12 is irradiated to the amorphous silicon, was subjected to Raman measurement while scanning the beam width direction It is a figure which shows the change of the Raman peak intensity observed in ¹ vicinity. As shown in FIG. 13, the Raman intensity distribution reflects the beam profile. When the energy density of the laser beam is 300 to 340 mJ / cm ² , the Raman intensity distribution increases in a similar manner as the energy density increases. . However, when the energy density exceeds the microcrystallization threshold, the Raman intensity in the portion exceeding the microcrystallization threshold decreases rapidly. As a result of observing the crystal state of this boundary portion using a transmission microscope (TEM), the crystal grain size of polycrystalline silicon is about 0.01 μm or less in the portion corresponding to the flat portion of the beam profile. In contrast, it was observed that the crystal grain size was extremely large at 1 μm or more in the regions on both sides. Therefore, when a thin film transistor is formed in a region where the crystal grain size is large, a thin film transistor having a high carrier mobility can be obtained.
[0014]
That is, in the present invention, laser light having a beam profile having an inclined portion in which the average energy density is equal to or higher than the microcrystallization threshold value of the amorphous semiconductor and the energy decreases toward the end in the beam width direction is applied to the amorphous semiconductor film. Irradiate. Then, there is a portion of energy slightly lower than the microcrystallization threshold in the inclined portion, and a polycrystalline semiconductor region having a large crystal grain size can be obtained. That is, according to the present invention, a polycrystalline semiconductor film suitable for forming a thin film transistor can be obtained even by one-time laser light irradiation.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
(First embodiment)
1 and 2 are cross-sectional views showing an example in which the method for manufacturing a polycrystalline semiconductor film according to the first embodiment of the present invention is applied to the manufacture of a thin film transistor in the order of steps.
[0016]
First, as shown in FIG. 1A, a silicon oxide (SiO ₂ ) film (not shown) having a thickness of about 1000 mm and a thickness are formed on a transparent glass substrate 4 by plasma CVD (chemical vapor deposition). The amorphous silicon (a-Si: H) film 3 having a thickness of about 500 mm is continuously formed. In this case, the conditions for forming the silicon oxide film are as follows: the flow rate of SiH ₄ gas is 20 sccm, the flow rate of N ₂ O gas is 2000 sccm, the pressure is 100 Pa, and the RF (high frequency) output is 300 W. The conditions for forming the amorphous silicon film 3 are, for example, that the flow rate of SiH ₄ gas is 200 sccm, the flow rate of H ₂ gas is 800 sccm, the pressure is 100 Pa, and the RF output is 80 W.
[0017]
Next, the substrate 4 is subjected to heat treatment in a nitrogen atmosphere at a temperature of about 450 ° C. for 1 hour, thereby dehydrogenating the amorphous silicon film 3. Thereafter, laser annealing is performed. That is, as shown in FIG. 1B, the laser beam 1 (the broken line in the figure indicates the beam profile) output from the XeCl excimer laser under the condition that the temperature of the substrate 4 is room temperature in a nitrogen atmosphere is converted to an amorphous silicon film. 3 is irradiated to polycrystallize amorphous silicon. In this case, as shown in FIGS. 3A and 3B, the laser beam 1 has a trapezoidal shape having a slope portion 1b having a relatively gentle beam profile, and irradiates the amorphous silicon film 3 in a band shape. It has become. The average energy density of the flat portion 1a of the laser beam 1 is about 380 mJ / cm ² . Note that the width of the flat portion 1a of the beam profile needs to be smaller than the interval between the thin film transistors to be formed.
[0018]
The laser beam 1 having such a profile can be obtained by shaping the laser beam output from the laser oscillator with a profiler including a beam homogenizer, a kamaboko lens, a mirror, and the like.
A portion of the amorphous silicon irradiated with the laser beam 1 is polycrystallized to obtain a polycrystalline silicon film 5. In this case, the portion of the polycrystalline silicon film 5 corresponding to the inclined portion 1b of the beam profile has a larger crystal grain size toward the inner side, and the portion corresponding to the flat portion 1a has a smaller crystal grain size (see FIG. 13). .
[0019]
Next, as shown in FIG. 1C, the polycrystalline silicon film 5 formed by the laser annealing described above is patterned into an island shape. That is, the amorphous silicon and fine silicon crystal portions are selectively removed to leave the polycrystalline silicon film 5a made of polycrystalline silicon having a relatively large crystal grain size only in the region where the thin film transistor is to be formed.
[0020]
Thereafter, a gate insulating film 10 made of SiO ₂ is formed to a thickness of about 1000 mm on the entire surface of the substrate 4 by plasma CVD, and then a gate electrode film made of aluminum (Al) is formed on the gate insulating film 10 by sputtering. 9 is formed to a thickness of 3000 mm.
Next, as shown in FIG. 2A, the gate electrode film 9 and the gate insulating film 10 are patterned into a predetermined shape by using a photolithography technique to expose both ends of the polycrystalline silicon film 5a. The exposed portion is doped with phosphorus (P) at a high concentration to form an n ⁺ region 11 to be a source / drain region.
[0021]
Next, as shown in FIG. 2B, an interlayer insulating film 7 made of SiN is formed on the entire surface by plasma CVD to a thickness of 3500 mm, and then aligned with the n ⁺ region 11 of the interlayer insulating film 7. A contact hole 12 is formed in the portion.
Next, as shown in FIG. 2C, aluminum is sputtered over the entire surface to fill the contact holes 12 with aluminum, and an aluminum film for wiring is formed on the interlayer insulating film 7, and this aluminum film is patterned into a predetermined shape. Then, wiring (not shown) and source / drain electrodes 8 are formed. Thereby, the thin film transistor is completed.
[0022]
In the present embodiment, amorphous silicon is polycrystallized using a laser beam 1 having a trapezoidal beam profile and having an average energy density at the beam central portion (flat portion) slightly larger than the microcrystallization threshold. Therefore, the polycrystalline silicon film 5a made of polycrystalline silicon having a large crystal grain size can be formed in the portion corresponding to the inclined portion 1b of the beam profile of the laser beam 1 by one irradiation of the laser beam 1. Therefore, there is no need to repeatedly irradiate the same portion with the laser beam over and over as in the conventional case, and the workability is significantly improved.
[0023]
In the present embodiment, laser annealing is performed in a nitrogen atmosphere, but laser annealing may be performed in vacuum instead. In this embodiment, the substrate temperature during laser annealing is set to room temperature, but laser annealing may be performed while heating the substrate. In this embodiment, a polycrystalline silicon film is formed using a laser beam having a trapezoidal beam profile. However, the beam profile of the laser beam may be triangular as shown in FIG. 4, for example. As shown, it may be Gaussian (regular curve) shape.
[0024]
(Second Embodiment)
6 and 7 are cross-sectional views showing an example in which the method for manufacturing a polycrystalline semiconductor film according to the second embodiment of the present invention is applied to the manufacture of a thin film transistor in the order of steps.
First, as shown in FIG. 6A, a plasma CVD method is used to form a first silicon oxide film (SiO ₂ ) film (not shown) having a thickness of about 1000 mm on the transparent glass substrate 24. An amorphous silicon (a-Si: H) film 23 having a thickness of about 500 and a second silicon oxide film 26 having a thickness of about 500 are continuously formed. In this case, the conditions for forming the first silicon oxide film are as follows: the flow rate of SiH ₄ gas is 20 sccm, the flow rate of N ₂ O gas is 2000 sccm, the pressure is 100 Pa, and the RF output is 300 W. The conditions for forming the amorphous silicon film 26 are as follows: the flow rate of SiH ₄ gas is 200 sccm, the flow rate of H ₂ gas is 800 sccm, the pressure is 100 Pa, and the RF output is 80 W. Further, the conditions for forming the second silicon oxide film 23 are as follows: the flow rate of SiH ₄ gas is 20 sccm, the flow rate of N ₂ O gas is 2000 sccm, the pressure is 100 Pa, and the RF output is 300 W.
[0025]
Next, as shown in FIG. 6B, the amorphous silicon film 23 is dehydrogenated by performing a heat treatment for 1 hour at a temperature of 450 ° C. in a nitrogen atmosphere, and then in a nitrogen atmosphere, XeCl An excimer laser is used to irradiate the surface of the amorphous silicon film 23 with the laser beam 1 having an energy density of 340 mJ / cm ^{2 at} the center of the beam under the condition that the substrate temperature is room temperature. In this case, the beam profile of the laser beam 1 has a trapezoidal shape as in the first embodiment. In the present embodiment, since the silicon oxide film 26 having a refractive index lower than that of the amorphous silicon film 23 is formed on the amorphous silicon film 23, reflection of the laser light 1 can be reduced. Therefore, compared to the first embodiment, even if the energy of the laser beam 1 is low, the amorphous silicon is polycrystallized and the polycrystalline silicon film 25 is obtained. Even if a silicon nitride film is formed instead of the silicon oxide film 26, the same effect can be obtained.
[0026]
Next, as shown in FIG. 6C, the silicon oxide film 26 is removed. Thereafter, as shown in FIG. 7A, the polycrystalline silicon film 25 is patterned into an island shape. That is, the amorphous silicon and the fine silicon crystal portion are selectively removed to leave the polycrystalline silicon film 25a made of polycrystalline silicon having a relatively large crystal grain size only in the region where the thin film transistor is to be formed. Thereafter, a gate insulating film 30 made of SiO ₂ is formed to a thickness of 1000 mm on the entire surface by plasma CVD. Then, a gate electrode film 29 made of aluminum is formed on the gate insulating film 30 to a thickness of 3000 mm by sputtering.
[0027]
Next, as shown in FIG. 7B, the gate electrode film 29 and the gate insulating film 30 are patterned into a predetermined shape to expose both ends of the polycrystalline silicon film 25a, and n-type is exposed to the exposed portions. Impurities are ion-doped at a high concentration to form n ⁺ regions 31 to be source / drain regions.
Next, after an interlayer insulating film 27 made of SiN is formed on the entire surface by plasma CVD, a contact hole reaching the n ⁺ region 31 is selectively formed in the interlayer insulating film 27. Then, a wiring layer that fills the contact hole with aluminum or the like and covers the interlayer insulating film 27 is formed, and the wiring layer is patterned to form a source / drain electrode 28 and wiring (not shown). Thereby, the thin film transistor is completed.
[0028]
In the present embodiment, in addition to obtaining the same effect as in the first embodiment, the reflection of laser light is suppressed by the silicon oxide film 26 formed on the amorphous silicon film 23. Even if the energy of the laser light is lowered, the amorphous silicon is polycrystallized.
(Third embodiment)
FIG. 8 is a schematic view showing a method for manufacturing a polycrystalline semiconductor film according to the third embodiment of the present invention.
[0029]
First, the amorphous silicon film 3 is formed on the transparent glass substrate 4. Next, as indicated by a broken line in the figure, the laser beam 1 is moved in the beam width direction at intervals shorter than the beam inclined portion 1b. In this case, as in the first and second embodiments, the laser beam 1 has an average energy density at the center of the beam that is slightly larger than the microcrystallization threshold, and uses a trapezoidal beam profile. As a result, the portion irradiated by the inclined portion 1b is sequentially changed to polycrystalline silicon having a large crystal grain size, so that a polycrystalline silicon film 5 having a large and uniform crystal grain size and a large area can be formed. .
[0030]
【The invention's effect】
As described above, according to the present invention, the energy density at the center of the beam is equal to or higher than the microcrystallization threshold of the amorphous semiconductor layer, and the beam profile has an inclined portion where the energy decreases toward the end in the beam width direction. Since the amorphous semiconductor layer is irradiated with the laser beam having the amorphous semiconductor layer, the amorphous semiconductor layer is polycrystallized, so that a polycrystalline silicon film having a large crystal grain size can be formed by one laser beam irradiation. Thereby, workability | operativity improves and the time which manufacture requires can be shortened remarkably. In addition, by using a polycrystalline semiconductor film manufactured by the method of the present invention, a thin film transistor with high carrier mobility can be formed, and the performance of a liquid crystal display device or the like can be further improved. .
[Brief description of the drawings]
FIG. 1 is a sectional view (No. 1) showing an example in which a method for producing a polycrystalline semiconductor film according to a first embodiment of the present invention is applied to the production of a thin film transistor.
FIG. 2 is a sectional view (No. 2) showing an example in which the method for producing a polycrystalline semiconductor film according to the first embodiment of the present invention is applied to the production of a thin film transistor.
FIG. 3 is a diagram showing a beam profile of laser light applicable to the present invention.
FIG. 4 is a diagram showing another example of a beam profile of laser light applicable to the present invention.
FIG. 5 is a diagram showing still another example of a beam profile of laser light applicable to the present invention.
6 is a cross-sectional view (No. 1) showing an example in which the method for manufacturing a polycrystalline semiconductor film according to the second embodiment of the present invention is applied to the manufacture of a thin film transistor. FIG.
FIG. 7 is a sectional view (No. 2) showing an example in which the method for producing a polycrystalline semiconductor film according to the second embodiment of the present invention is applied to the production of a thin film transistor.
FIG. 8 is a schematic view showing a method for manufacturing a polycrystalline semiconductor film according to a third embodiment of the present invention.
FIG. 9 is a cross-sectional view showing a conventional polycrystalline silicon thin film manufacturing method and a subsequent thin film transistor manufacturing method in the order of steps.
FIG. 10 is a cross-sectional view showing a thin film transistor after manufacture.
FIG. 11 is a diagram showing Raman spectra of single crystal silicon (c-Si), polycrystalline silicon (p-Si), and amorphous silicon (a-Si) examined by Raman scattering spectroscopy.
FIG. 12 is a diagram showing a beam profile of a laser beam together with a crystallization threshold value and a microcrystallization threshold value.
13 is around 520 cm ⁻¹ when Raman measurement is performed while scanning a polycrystalline silicon film formed by irradiating amorphous silicon with a laser beam having the trapezoidal beam profile shown in FIG. 12; It is a figure which shows the change of the Raman peak intensity observed in this.
[Explanation of symbols]
1, 51 Laser beam 4, 24, 34 Transparent glass substrate 3, 23, 33 Amorphous silicon film 5, 25, 25a, 35 Polycrystalline silicon film 7, 37, 37 Interlayer insulating film 8, 28, 38 Source / drain electrode 9 , 29, 39 Gate electrode film 10, 30, 40 Gate insulating film 11, 31 n ⁺ region 12 Contact hole 26 Silicon oxide film

Claims (6)

Forming an amorphous semiconductor film on the substrate;
A laser beam having a beam profile in which the energy density at the center of the beam is set to be equal to or higher than the microcrystallization threshold of the amorphous semiconductor film and has an inclined portion whose energy decreases toward the end in the beam width direction is applied to the amorphous semiconductor film. And a step of polycrystallizing an amorphous semiconductor by irradiation. 2. The polycrystalline semiconductor film according to claim 1, wherein the amorphous semiconductor film is irradiated with the laser light after forming at least one of a silicon oxide film and a silicon nitride film on the amorphous semiconductor film. Production method. The method of manufacturing a polycrystalline semiconductor film according to claim 1, wherein a beam profile of the laser beam is trapezoidal. The method of manufacturing a polycrystalline semiconductor film according to claim 1, wherein a beam profile of the laser beam is triangular. The method for manufacturing a polycrystalline semiconductor film according to claim 1, wherein a beam profile of the laser beam has a normal curve shape. 3. The polycrystalline semiconductor film according to claim 1, wherein the amorphous semiconductor layer is polycrystallized by moving the laser light in the beam width direction at intervals shorter than the width of the inclined portion. Manufacturing method.

Images