JP2005303052A - Manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a semiconductor device capable of obtaining the semiconductor device whose S value is excellent in an electric characteristic in a region lower than the threshold value, in the semiconductor using nearly single-crystalline grains of a semiconductor material in the channel forming region thereof. <P>SOLUTION: A base film 11 is formed on a substrate 10, a grain-filter 12 is used as the starting point of the crystallization of a semiconductor film, and the semiconductor film is formed. Then, laser annealing is carried out to crystallize the semiconductor film, and the nearly single-crystalline grains 15a are formed. Thereafter, the semiconductor film 15 is made thinner to obtain a desired thickness by a method such as thermal oxidation etc. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a semiconductor device.

  In an electro-optical device such as a liquid crystal display device or an organic EL (electroluminescence) display device, pixel switching is performed using a thin film circuit including a semiconductor device. In a conventional semiconductor device, an active region such as a channel formation region is formed using an amorphous silicon film. A semiconductor device in which an active region is formed using a polycrystalline silicon film has also been put into practical use. By using the polycrystalline silicon film, electric characteristics such as field effect mobility can be improved and the performance of the semiconductor device can be improved as compared with the case where an amorphous silicon film is used.

In order to further improve the performance of a semiconductor device, a technique for forming a semiconductor film made of large crystal grains and forming a channel formation region of the semiconductor device with substantially single crystal grains has been studied. For example, a technique has been proposed in which a fine hole (concave portion) is formed on a substrate and a semiconductor film is crystallized using this hole as a starting point for crystal growth to form a substantially single crystal grain having a large grain size. . By forming a semiconductor device using a silicon film having a large crystal grain size formed by using this technique, a single semiconductor device formation region (particularly, a channel formation region) is configured with a single substantially single crystal grain. It becomes possible to do. This makes it possible to realize a semiconductor device having excellent electrical characteristics such as field effect mobility. (For example, see Non-Patent Document 1 or Non-Patent Document 2.)
“Single Crystal Thin Film Transistors” (IBM Technical DISCLOSURE BULLETIN Aug. 1993 pp 257-258) “Advanced Excimer-Laser Crystallization Techniques of Si Thin-Film For Location Control of Large Grain on Glass” (R. Ishihara et al., Proc.

By the way, when a semiconductor device is formed using substantially single crystal grains formed by the above-mentioned literature and the electrical characteristics thereof are actually examined, the field effect mobility can be realized as a very large value of about 500 cm ² / Vs. The subthreshold hold swing (S value), which is the electrical characteristic of the subthreshold region, is 0.45 V / dec. It has been confirmed by experiments by the inventors of the present application that it is large as described above and inferior to the same characteristic (about 0.2 V / dec.) Of a normal polycrystalline silicon thin film semiconductor device. This is because, in the configuration of the semiconductor device described in the above-mentioned document, the film thickness of the silicon film serving as the channel formation region is set to about 250 nm or more, so that the total number of crystal defects included therein increases. It is considered that the S value has deteriorated.

  Therefore, an object of the present invention is to provide a method for manufacturing a semiconductor device that can obtain a semiconductor device having excellent field effect mobility and S value in a semiconductor device formed using a substantially single crystal.

  In order to achieve the above object, the present invention provides a method of manufacturing a semiconductor device using a semiconductor film formed on a substrate and using the semiconductor film, and serves as a starting point when the semiconductor film is crystallized on the substrate. A starting point forming step for forming a power starting point, a semiconductor film forming step for forming the semiconductor film on the substrate on which the starting point is formed, a heat treatment is performed on the semiconductor film, and the starting point is substantially centered. A heat treatment step for forming substantially single crystal grains, a thinning step for thinning the semiconductor film, and a patterning step for patterning the semiconductor film to form a semiconductor device region to be a source, drain region, and channel formation region And an element formation step of forming a gate insulating film and a gate film on the semiconductor device region to form a semiconductor device.

  According to the above method for manufacturing a semiconductor device, it is possible to manufacture a semiconductor device that realizes characteristics equivalent to or higher than the S value of a normal polycrystalline silicon thin film semiconductor device. The density of crystal defects contained in substantially single crystal grains is estimated to be very small compared to the crystal defect density in a semiconductor film used in a normal polycrystalline silicon thin film semiconductor. When the thickness is increased, the total number of crystal defects increases, and as a result, the S value of the semiconductor device formed there becomes a large value. Therefore, in the present invention, an excellent semiconductor device is obtained by thinning the semiconductor film to an appropriate film thickness, reducing the absolute number of defects contained in substantially single crystal grains, and using it for a channel formation region. It makes it possible.

  In the semiconductor device manufacturing method of the present invention, the semiconductor film is formed in a thickness of 50 nm to 300 nm in the semiconductor film formation step.

  According to the above method for manufacturing a semiconductor device, the semiconductor film can be stably crystallized, and an excellent semiconductor device can be obtained. When the thickness of the semiconductor film is 50 nm or more, the semiconductor film can be stably formed on the starting point of crystallization, and crystallization can be performed more satisfactorily. Further, the crystal grain size increases as the thickness of the semiconductor film is increased. However, since the crystal grain size only needs to satisfy a desired size, the semiconductor film only needs to have a certain thickness. When the thickness of the semiconductor film is 300 nm, a crystal grain size large enough to manufacture a semiconductor device can be obtained. If the semiconductor film is made thicker than this, productivity will be reduced, and the load on the heat treatment apparatus for crystallization will increase.

  In the semiconductor device manufacturing method of the present invention, the thinning step includes a semiconductor film oxidation step. The oxidation step is preferably a thermal oxidation of a semiconductor film.

  According to the above method for manufacturing a semiconductor device, it is difficult to damage the semiconductor film during the thinning process, and an excellent semiconductor device can be manufactured. When a silicon film is used as the semiconductor film, the surface of the silicon film becomes a silicon oxide film when the silicon film is oxidized. In this way, the silicon film becomes thinner by the amount of oxidation. Since the oxidation reaction proceeds while forming a good semiconductor film / oxide film interface on the surface of the semiconductor film, the semiconductor film is hardly damaged, and good semiconductor film quality can be maintained even after thinning. The oxide film formed by oxidizing the semiconductor film may be peeled off or used as it is as a gate insulating film. Examples of the oxidation include thermal oxidation and plasma oxidation. Thermal oxidation is suitable for reducing the thickness of a semiconductor film because the oxidation rate can be made relatively high and the oxidation can be made relatively thick. Further, since the semiconductor film is exposed to a high temperature atmosphere of about 1000 ° C. during thermal oxidation, the film quality of the semiconductor film is improved. Since it is difficult to oxidize thickly by plasma oxidation, it is not suitable for thinning a semiconductor film, but it is possible to make it thin a little. Plasma oxidation has the advantage that it can be performed at a temperature at which a glass substrate can be used (for example, about 500 ° C.).

  In the semiconductor device manufacturing method of the present invention, the thinning step includes a chemical mechanical polishing step of the semiconductor film.

  According to the semiconductor device manufacturing method described above, since the semiconductor film surface can be planarized simultaneously with the thinning of the semiconductor film, the interface characteristics between the semiconductor film and the gate insulating film are improved. Further, the thinning process can be performed at a temperature at which the glass substrate can be used (for example, about 500 ° C.). When thinning by oxidizing the semiconductor film, the oxidation rate depends on the crystallinity and surface orientation of the surface of the semiconductor film. Therefore, if there are variations in crystallinity and surface orientation on the surface of the semiconductor film, There is a problem that the film thickness of the semiconductor film varies. However, such a problem hardly occurs when the semiconductor film is thinned by a chemical mechanical polishing process, and a uniform thinning can be realized. In addition, when thinning a patterned semiconductor film, the thinning by oxidation causes the semiconductor film to be oxidized not only in the film thickness direction but also in the lateral direction. It is necessary to perform patterning in consideration of direction oxidation. However, such a problem hardly occurs when the semiconductor film is thinned by a chemical mechanical polishing process, and the patterning of the semiconductor film is easy.

  In the semiconductor device manufacturing method of the present invention, the thinning step includes a semiconductor film etching step.

  According to the semiconductor device manufacturing method described above, since the semiconductor device manufacturing apparatus can be used, the semiconductor film can be easily reduced in thickness. Further, the thinning process can be performed at a temperature at which the glass substrate can be used (for example, about 500 ° C.).

  In addition, the semiconductor device manufacturing method of the present invention is characterized in that the film thickness of the semiconductor film is set to 45 nm or less by the thinning step.

  According to the method for manufacturing a semiconductor device described above, an excellent semiconductor device having a very small S value can be manufactured.

  Preferably, the patterning step is performed so that at least the starting portion and the vicinity thereof are not included in the channel formation region. Crystal grains formed around the starting point may have crystal defects at the starting point and in the vicinity thereof, and crystallinity may be disturbed. Therefore, by avoiding the channel formation region from including the semiconductor film in the starting portion and the vicinity thereof, the channel formation region can be prevented from including a semiconductor film having poor crystallinity, and the characteristics of the semiconductor device can be improved. Further improvement is possible.

  Preferably, the above-described starting point portion is a recess formed in the substrate. As a result, it is possible to easily form a portion to be a starting point for crystallization.

  Preferably, the heat treatment in the heat treatment step described above is performed under a condition that a non-molten portion remains in the semiconductor film in the recess and other portions are melted. As a result, the crystallization of the semiconductor film after the heat treatment starts from the inside of the recess that is in a non-molten state, particularly near the bottom, and proceeds to the periphery. At this time, by appropriately setting the size of the recess, only one crystal grain reaches the upper portion (opening) of the recess. In the melted portion of the semiconductor film, crystallization is performed with one crystal grain reaching the upper portion of the recess as a nucleus, so that a substantially single crystal semiconductor film (approximately Single crystal grains) can be formed.

  Preferably, the heat treatment is performed by pulse laser irradiation having a pulse width of 150 ns to 250 ns. By using a laser having a relatively long pulse width as described above, the melting time of the semiconductor film becomes long, and it becomes possible to promote the growth of crystal grains from the concave portion that is the starting point of crystal growth.

  Preferably, the semiconductor film formed on the substrate is an amorphous or polycrystalline silicon film. As a result, it is possible to form substantially single-crystal silicon crystal grains in a range with the starting point being substantially the center, and to form a semiconductor device using these high-quality silicon crystal grains.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The manufacturing method of this embodiment includes (1) a step of forming a silicon film on a glass substrate for use as a source region, a drain region, and a channel formation region of a semiconductor device, and (2) using the formed silicon film. Forming a semiconductor device. Hereinafter, each process will be described in detail.

(Example 1)
FIG. 1 is an explanatory diagram for explaining a process of forming a silicon film. As shown in FIG. 1A, a silicon oxide film 11 as a base film is formed on a quartz substrate 10 as a substrate. The substrate may be a single crystal silicon substrate, or a glass substrate or a plastic substrate may be used if the temperature in the subsequent manufacturing process is sufficiently low. The silicon oxide film 11 as the base film is preferably formed by a film forming method such as a plasma chemical vapor deposition method (PECVD method), a low pressure chemical vapor deposition method (LPCVD method), or a sputtering method.

  Next, recesses (hereinafter referred to as “grain filters”) 12 are formed in the silicon oxide film 11 as the base film. The grain filter is a starting point portion to be a starting point when crystallization of a semiconductor film to be performed later, and is a hole for growing only one crystal nucleus. The grain filter 12 is preferably formed in a cylindrical shape having a diameter of about 50 nm to about 150 nm and a height of about 750 nm, for example. The grain filter 12 may have a shape other than a cylindrical shape (for example, a prism shape).

  The grain filter 12 is, for example, a photo having an opening that exposes and develops a photoresist film applied to a silicon oxide film using a mask in which the grain filter 12 is arranged to expose the formation position of the grain filter 12. A resist film (not shown) is formed on the silicon oxide film 11 as a base film, and reactive ion etching is performed using the photoresist film as an etching mask, and then the silicon oxide film 11 as a base film is formed. It can be formed by removing the photoresist film. In the case of forming a grain filter 12 having a smaller diameter, it is possible to reduce the hole diameter of the recess by depositing a silicon oxide film by a method such as PECVD or LPCVD after removing the photoresist film. .

  Next, as shown in FIG. 1B, an amorphous silicon film 13 as a semiconductor film is formed on the silicon oxide film 11 as a base film and in the grain filter 12 by a film forming method such as LPCVD. To do. The thickness of the amorphous silicon film 13 is set to 50 nm or more and 300 nm or less. Instead of the amorphous silicon film 13, a polycrystalline silicon film may be formed.

  Here, the amorphous silicon film 13 needs to be thick enough to embed the grain filter 12. For example, if the diameter of the grain filter is 50 nm, the amorphous silicon film has a thickness of 30 nm. More than about is required. If a silicon film thinner than this is deposited, the grain filter is not sufficiently embedded and a gap is formed. In addition, when the diameter of the grain filter is made smaller than 50 nm, the film thickness of the amorphous silicon film can be reduced in principle, but such a grain filter having such a small diameter can be stably formed. This is very difficult in the manufacturing process, and further, amorphous silicon cannot be sufficiently supplied to the inside of the grain filter when the amorphous silicon film is deposited. For these reasons, the minimum thickness of the amorphous silicon film 13 is 30 nm in order to stably perform substantially single crystal grain growth of silicon described later. Although the minimum film thickness is 30 nm, the crystal growth of the semiconductor film can be performed better when the semiconductor film is thicker. In the experiments by the inventors of the present application, good crystallization can be performed if the thickness of the semiconductor film is 50 nm or more.

  As the amorphous silicon film is thicker, larger single crystal grains can be formed. In the experiments conducted by the present inventors, the maximum crystal grain size was about 3.0 μm when the amorphous silicon film thickness was 50 nm. However, when the amorphous silicon film thickness was 100 nm, the maximum crystal grain size was about When the amorphous silicon film thickness was 250 nm, the maximum crystal grain size was about 6.5 μm (FIG. 2A). In this way, larger crystal grains can be formed when the amorphous silicon film is thicker, but problems arise when the film is too thick. First, there is an upper limit to the film thickness that can be deposited due to device limitations. If the film thickness is too thick, the film may be peeled off. Further, when the film thickness is increased, it takes time to form the film, and the productivity is lowered. Furthermore, the heat treatment apparatus for crystallization is burdened, and if it is too thick, crystallization cannot be sufficiently performed due to the restrictions of the apparatus. In the experiments by the present inventors, the maximum film thickness of the amorphous silicon film is about 300 nm. When the film thickness is 300 nm or less, the above-described problems do not occur, and crystal grains having a size sufficient for manufacturing a semiconductor device can be obtained.

Next, as shown in FIG. 1C, the silicon film 13 is irradiated with a laser beam 14 as a heat treatment. This laser irradiation is preferably performed using, for example, a XeCl pulse excimer laser having a wavelength of 308 nm and a pulse width of about 200 ns so that the energy density of the laser light 14 is about 0.4 to 1.5 J / cm ^2. It is. By performing laser irradiation under such conditions, most of the irradiated laser light 14 is absorbed near the surface of the silicon film 13. This is because the absorption coefficient of amorphous silicon at the wavelength of XeCl pulse excimer laser light (308 nm) is relatively large at 0.139 nm ⁻¹ .

  Here, as the excimer laser light to be irradiated, it is preferable to use an excimer laser light having a pulse width of about 150 ns to 250 ns, rather than an excimer laser light having a pulse width of about 20 ns to 30 ns, which is conventionally used. This is because the melting time of the silicon film is remarkably increased by irradiating the excimer laser light having such a relatively long pulse width. This is reported in "Experimental and numerical narrative of surface melt dynamics in 200 ns-excimer laser crystallisation, in 38 ns, E. Fos. Yes. The size of the crystal grains when the molten silicon film is solidified and crystallized depends on the multiplication of the crystal growth rate and the melting time. That is, when the melting time of the silicon film is increased by irradiating the excimer laser beam having a relatively long pulse width, a large substantially single crystal grain can be formed accordingly. For example, in the experiments of the present inventors, by irradiating a silicon film sample at room temperature with the excimer laser light having the relatively long pulse width, for example, in the case of a silicon film thickness of 100 nm, the diameter is approximately 4 μm. The formation of crystal grains is confirmed (FIG. 2 (a)). On the other hand, R. mentioned above. In Ishihara et al., A conventional excimer laser having a relatively short pulse width is used, and the maximum single crystal grain size when the silicon film thickness is 90 nm is about 2.5 μm (FIG. 2B). ). Although the silicon film thicknesses of these two are slightly different, by using the excimer laser having a long pulse width, it is possible to realize the growth of a crystal grain about several tens of percent. The same applies to other silicon film thicknesses as shown in FIG.

  Furthermore, in the experiments by the inventors of the present application, the silicon film sample is heated to about 200 ° C. during the irradiation with the excimer laser having a long pulse width, so that the maximum single crystal grain size of about 7 μm is obtained in the sample having a silicon film thickness of 100 nm. In the sample with the same film thickness of 150 nm, formation of large crystal grains of about 8 μm was confirmed. This is because the silicon film was melted for a long time by heating the sample. The heating temperature of the silicon film sample during excimer laser irradiation is preferably about 200 ° C. to about 500 ° C.

  On the other hand, techniques for crystallizing a silicon film using a laser having a long pulse width are also disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2000-36464 and 7-283151. However, in these techniques, the silicon film does not have a starting point as a starting point for crystallization, and the place where crystal growth starts is not controlled. In other words, irradiation with laser light having a long pulse width increases the melting time of the silicon film, but crystal nuclei are generated at random positions and crystal grains grow from the respective crystal nuclei. There is no significant change in the size of the grains compared to the conventional one. On the other hand, in this embodiment, since the starting point of crystallization of the silicon film is controlled by forming a recess (grain filter), crystal growth starts preferentially from here, and laser irradiation with a long pulse width is performed. Due to the effect of increasing the melting time, as described above, the formation of crystal grains several tens of percent larger than the conventional one is realized.

  By appropriately selecting the laser irradiation conditions described above, the silicon film 13 remains in the non-molten state inside the grain filter 12, particularly in the vicinity of the bottom, and the other portions are almost completely melted. To be in a state. Thereby, the crystal growth of silicon after laser irradiation starts first in the vicinity of the unmelted silicon in the grain filter 12 and proceeds to the vicinity of the surface of the silicon film 13, that is, the substantially completely melted portion.

  Several crystal grains may be generated inside the grain filter 12 after the laser irradiation. At this time, by setting the cross-sectional dimension of the grain filter 12 (in this embodiment, the diameter of a circle) to be about the same as or slightly smaller than one crystal grain, the grain filter 12 has an upper portion (opening). Will reach only one crystal grain. As a result, in the substantially completely melted portion of the silicon film 13, crystal growth proceeds with the crystal grains reaching the upper part of the grain filter 12 as nuclei. As shown in FIG. A substantially single crystal grain 15 a of silicon centering on the filter 12 is formed.

  FIG. 3 is a plan view showing substantially single crystal grains 15 a of silicon formed on the substrate 10. As shown in the figure, the substantially single crystal grains 15 a of silicon are formed in a range with the grain filter 12 as a substantial center. Using such substantially single crystal grains 15a, a semiconductor device is formed as described below.

  4 mainly focuses on the gate electrode 19, the source region 20, the drain region 21, and the channel formation region 22 in the semiconductor device using a part of the substantially single crystal grain 15 a of silicon shown in FIG. 3 as the semiconductor device region. And it is the top view which abbreviate | omitted and showed the structure other than that. In the semiconductor device T of this embodiment, the grain filter 12 is included in the source 20 or drain region 21 of the semiconductor device region, and more preferably, the region including the grain filter 12 that is likely to cause disorder in crystallinity is a channel. They are arranged so as not to be included in the formation region 22. Specifically, the grain filter 12 is preferably separated from the channel formation region 22 by about 0.5 μm to 1 μm.

  Next, a process for forming the semiconductor device T shown in FIG. 3 will be described. FIG. 5 is an explanatory diagram illustrating a process of forming the semiconductor device T. This figure shows a cross-sectional view in the AA ′ direction shown in FIG. 4.

  FIG. 5A is the same as FIG. 1D, and shows that the silicon film 13 is crystallized by laser irradiation to form substantially single crystal grains 15a.

According to the experiments by the present inventors, the defect density N _bk in the substantially single crystal grain of silicon formed in this way is estimated to be about 3.2 × 10 ¹⁶ cm ⁻³ eV ⁻¹ . This is an extremely small value compared with the defect density of 10 ¹⁸ cm ^-3 eV ^-1 in the polycrystalline silicon film by the conventional laser crystallization technique, and an excellent substantially single crystal grain having a low defect density is obtained by this method. You can see that However, the film thickness of the silicon film containing the substantially single crystal grains is the same as that of the R.P. When set to about 250 nm or more as described in the literature of Ishihara et al., The total number of defects in the substantially single crystal grain becomes large, and the S value of the semiconductor device formed there is realized by a conventional polycrystalline silicon semiconductor device. This is inferior to the S value (about 0.2 V / dec.). Accordingly, in the present invention, in view of the defect density in the substantially single crystal grains, a silicon film after crystallization is realized in order to realize a characteristic equivalent to or better than that of a conventional polycrystalline silicon semiconductor device in a semiconductor device using the defect density. The film thickness is reduced to an appropriate film thickness.

  The S value of the semiconductor device can be obtained by the following equation.

S value = kT / q · ln10 · (1+ (qN _bk t _si + qD _it ) / C _ox )
Here, k is the Boltzmann coefficient, T is the absolute temperature, q is the elementary charge, N _bk is the defect density in the silicon film, t _si is the silicon film thickness, D _it is the interface state density, and C _ox is the silicon oxide film It is the capacity per unit area. From this equation, the S value is reduced by further reducing the silicon film thickness (the film thickness of the substantially single crystal grains), which is superior to the conventional polycrystalline silicon thin film semiconductor device.

  In the thinning process for thinning the silicon film 15 as a semiconductor film, an oxidation process, a chemical mechanical polishing process, a wet etching process, a dry etching process, or the like of the semiconductor film is used. The thinning process may be performed using one of the above processes, or the thinning process may be performed by combining two or more.

When an oxidation process is used for the thinning process, the semiconductor film is hardly damaged during the thinning process, and an excellent semiconductor device can be manufactured. In particular, thermal oxidation can make the oxidation rate relatively high and can make the oxidation relatively thick, so that it is suitable for thinning the semiconductor film. Further, since the semiconductor film is exposed to a high temperature atmosphere of about 1000 ° C., the quality of the semiconductor film is improved.
Hereinafter, a process for thinning a semiconductor film by thermal oxidation will be described. After the substrate is inserted into a heat treatment furnace having a temperature of 800 ° C., nitrogen and a slight amount of oxygen are allowed to flow into the heat treatment furnace so that the atmosphere in the heat treatment furnace is an atmosphere in which the oxygen in the nitrogen is about 10 ppm to 1%. The temperature is increased at a rate of about 4 ° C. to 20 ° C. per minute, and the temperature in the heat treatment furnace is set to 1000 ° C. If the temperature rising rate is as low as about 4 ° C., the temperature controllability is improved, but it takes a long time to raise the temperature, so the productivity is lowered. On the other hand, if the rate of temperature increase is as high as 20 ° C., the temperature controllability is deteriorated, but the temperature increase time is shortened, so the productivity is improved. When the above temperature increasing process is performed in a 100% nitrogen atmosphere, there is a problem that a hole is formed in the semiconductor film. As described above, when the oxygen in the nitrogen atmosphere is about 10 ppm, an ultrathin oxide film is formed on the semiconductor film, so that it is possible to prevent a hole from being formed in the semiconductor film. Here, if the oxygen concentration is too high, such as about 1% or more, the oxide film thickness becomes thick. Since this oxide film is formed at a low temperature, the film quality is poor, and when it becomes a gate insulating film, it causes deterioration in characteristics and reliability of the thin film semiconductor element. Therefore, in the above temperature rising process, the oxygen concentration is kept sufficiently low, such as 10 ppm to 1%, so that holes are not formed in the semiconductor film and a gate insulating film with poor film quality is not grown more than necessary. There is a need to. After the temperature rises, the atmosphere in the heat treatment furnace is set to 2% oxygen or 100% oxygen in nitrogen, and the silicon film 15 is oxidized to form a silicon oxide film 16 (FIG. 5B). The lower the oxygen concentration in nitrogen, the easier the stress generated at the interface between the silicon film and the silicon oxide film is relaxed. On the other hand, the higher the oxygen concentration in nitrogen, the higher the oxidation rate, so that the oxidation time is shortened and the productivity is improved. Then, when the silicon oxide film 16 is peeled off, a thinned silicon film 15 can be obtained as shown in FIG. Here, the thinning process may be performed once, or may be thinned little by little in a plurality of times. Even if a chemical mechanical polishing process, a wet etching process, a dry etching process, or the like is used in a thinning process for thinning the silicon film 15 as a semiconductor film, the thinned silicon film 15 shown in FIG. 5C is obtained. be able to.

With the thermal oxidation of about 1000 ° C., forming a gate insulating film (silicon oxide film) as the interface state density D _it between the silicon film and the silicon oxide film on the order of ¹⁰ 10 cm ^-2 eV ^-1 If the method reported in “Low temperature formation of high quality SiO ₂ / Si interface using ECR-PECVD” (D. Abe et al., AM-LCD 2001, p. 98) is used, a glass substrate is formed. The gate insulating film (silicon oxide film) can be formed so as to be 3.0 × 10 ¹⁰ cm ⁻² eV ⁻¹ even in a low-temperature process that can be used. If the interface state density D _it is assumed to be ^{3.0 × 10 10 cm -2 eV -1} , in the semiconductor device formed in the gate insulating film thickness 82.5 nm, S value by the 180nm the silicon film thickness About 0.2 V / dec. Therefore, it is preferable to reduce the silicon film thickness to 180 nm or less. Further, by setting the silicon film thickness to 110 nm, the S value is about 0.15 V / dec. Therefore, it is more preferable that the silicon film thickness is reduced to 110 nm or less. Further, by setting the silicon film thickness to 45 nm, the S value is about 0.1 V / dec. Therefore, it is very preferable that the silicon film thickness be reduced to 45 nm or less. Here, as an example, the silicon film 15 is thinned to 55 nm.

  Next, as shown in FIG. 6A, the silicon film 15 is patterned into a desired shape. Then, the silicon film 15 is oxidized by the above-described thermal oxidation method to form a silicon oxide film 17 as a first gate insulating film having a thickness of about 30 nm to 35 nm. At this time, the thickness of the silicon film 15 is about 40 nm. Plasma oxidation may be used instead of thermal oxidation.

Next, as shown in FIG. 6B, a silicon oxide film 18 as a second gate insulating film is formed on the silicon oxide film 17 as the first gate insulating film by a chemical vapor deposition method (CVD method). Deposit about 50 nm thick. For example, a low pressure chemical vapor deposition method (LPCVD method) is used to form the second gate insulating film. Although the gate insulating film has a two-layer structure, the effect of the present invention is not lost even by one layer. Next, the gate electrode 19 is formed. Examples of the material of the gate electrode include a polycrystalline silicon film into which an impurity element is implanted, and a metal film such as tantalum and aluminum. Then, a source region 20, a drain region 21, and a channel formation region 22 are formed in the silicon film 15 by performing so-called self-aligned ion implantation in which an impurity element serving as a donor or acceptor is implanted using the gate electrode 19 as a mask. For example, in this embodiment, phosphorus (P) is implanted as an impurity element, and then heat treatment is performed to activate the impurity element to form an N-type semiconductor device. Needless to say, a P-type semiconductor device can also be formed. Note that the impurity element may be activated by irradiation with a XeCl excimer laser adjusted to an energy density of about 200 mJ / cm ² to 400 mJ / cm ² .

  Next, as shown in FIG. 6C, a silicon oxide film 25 as an interlayer insulating film is formed on the upper surfaces of the silicon oxide film 18 and the gate electrode 19. Next, contact holes are formed through the interlayer insulating film 25, the second gate insulating film 18, and the first gate insulating film 17 to reach the source region 20 and the drain region 21, respectively. A source electrode 23 and a drain electrode 24 are formed by embedding and patterning a metal such as aluminum or tungsten by a film forming method such as sputtering. The semiconductor device T of this embodiment is formed by the manufacturing method described above.

  As described above, in this embodiment, by reducing the film thickness of the silicon film 15, the total number of crystal defects in the substantially single crystal grains 15a of silicon can be reduced, and a semiconductor device having good characteristics can be obtained. . Further, since the silicon film in the grain filter 12 and its neighboring region is arranged so as not to be included in the channel forming region 22, it is avoided that the channel forming region 22 includes a silicon film having poor crystallinity, The characteristics of the semiconductor device can be further improved. Further, when the substantially single crystal grain 15a is formed, an excimer laser having a relatively long pulse width of about 150 ns to 250 ns is used, so that even if the silicon film 15 is relatively thin, the large substantially single crystal grain 15a is formed. Can be formed.

(Example 2)
FIG. 7 is an explanatory diagram of a silicon film thinning process in the second embodiment. In FIG. 7A, 110 is a quartz substrate, 111 is a silicon oxide film as a base film, 112 is a grain filter, 115 is a silicon film after crystallization, and 115a is a substantially single crystal grain of silicon. It is the same as the process of manufacturing FIG.

  In Example 1, the thinning process was performed after this, but in Example 2, the silicon film 115 was patterned as shown in FIG. 7B.

  Then, as in Example 1, the silicon film 115 as a semiconductor film is thinned. As a thinning process for thinning the silicon film 115 as a semiconductor film, an oxidation process, a chemical mechanical polishing process, a wet etching process, a dry etching process, or the like of the semiconductor film is used. The thinning process may be performed using one of the above processes, or the thinning process may be performed by combining two or more.

  When the semiconductor film is thinned by an oxidation process before patterning the semiconductor film, the substrate may be warped or the semiconductor film may be damaged by stress generated at the interface between the semiconductor film and the oxide film. However, if the semiconductor film is oxidized after patterning as in the second embodiment, the substrate has a region where the semiconductor film exists and a region where the semiconductor film does not exist, so that stress is not applied to the entire substrate. Warpage and damage to the semiconductor film can be prevented.

  When an oxidation process or a wet etching process is used for the thinning process, the semiconductor film is oxidized or etched in the lateral direction. Therefore, it is necessary to pattern the semiconductor film in consideration of it in advance.

  When the semiconductor film is thinned, it becomes as shown in FIG.

  Thereafter, a semiconductor device is manufactured in the same manner as in the first embodiment.

  As described above, in this embodiment, by thinning the semiconductor film after patterning the semiconductor film, it is possible to reduce the influence of stress caused by the thinning by the oxidation process, and to prevent the warpage of the substrate and the damage to the semiconductor film. it can.

  As described above, according to the present invention, when forming a substantially single crystal grain of a semiconductor used in a channel formation region of a semiconductor device, the thickness of the semiconductor is reduced to an appropriate value. It is possible to realize an S value equal to or greater than that of the crystalline silicon thin film semiconductor device. As a result, it is possible to obtain a semiconductor device with excellent characteristics having excellent field effect mobility and S value.

  The semiconductor device according to the present invention can be used as a switching element of a liquid crystal display device or a drive element of an organic EL display device.

  These display devices can be applied to various electronic devices. Examples include mobile phone display units, video camera viewfinders and display units, portable personal computer (so-called PDA) display units, head mounted display image display sources, rear and front projector image display sources, and the like. Can be mentioned.

  The display device using the semiconductor device of the present invention is not limited to the above-described example, and can be applied to any electronic apparatus to which an active or passive matrix liquid crystal display device and organic EL display device can be applied. For example, in addition to this, it can also be used for a fax machine with a display function, a finder for a digital camera, a portable TV, an electronic notebook, an electric bulletin board, a display for advertisements, and the like.

It is explanatory drawing explaining the process of forming a silicon film. It is explanatory drawing explaining the maximum particle size of the substantially single crystal grain of silicon. It is a top view which shows the substantially single crystal grain of the silicon | silicone formed on the board | substrate. 1 is a plan view showing a semiconductor device formed using substantially single crystal grains of silicon, mainly focusing on a gate electrode, a source region, a drain region, and a channel formation region, and omitting other configurations. It is explanatory drawing explaining the thin film formation process of a silicon film. It is explanatory drawing explaining the process of forming a semiconductor device. It is explanatory drawing explaining the patterning process and thinning process of a silicon film in Example 2. FIG.

Explanation of symbols

10, 110 Quartz substrates 11, 111 Silicon oxide film 12, 112 Grain filter 13 as a base film Silicon film 14 as a semiconductor film Laser light 15, 115 Silicon films 15a, 115a after crystallization substantially single crystal grains 16 of silicon Silicon oxide film 17 by thinning process Silicon oxide film 18 as first gate insulating film Silicon oxide film 19 as second gate insulating film 19 Gate electrode 20 Source region 21 Drain region 22 Channel formation region 23 Source electrode 24 Drain electrode 25 Interlayer Silicon oxide film T as an insulating film Semiconductor device

Claims (7)

A method of manufacturing a semiconductor device using a semiconductor film formed on a substrate, the semiconductor film comprising:
A starting point forming step for forming a starting point to be a starting point when the semiconductor film is crystallized on the substrate;
A semiconductor film forming step of forming the semiconductor film on the substrate on which the starting portion is formed;
A heat treatment step of performing a heat treatment on the semiconductor film to form a substantially single crystal grain having the origin portion as a substantial center;
A thinning process for thinning the semiconductor film;
Patterning the semiconductor film to form a semiconductor device region to be a source, drain region and channel forming region; and
Forming a semiconductor device by forming a gate insulating film and a gate film on the semiconductor device region, and a method for manufacturing the semiconductor device.   2. The method of manufacturing a semiconductor device according to claim 1, wherein, in the semiconductor film forming step, the semiconductor film is formed to have a thickness of 50 nm to 300 nm.   The method of manufacturing a semiconductor device according to claim 1, wherein the thinning step includes a semiconductor film oxidation step.   The method of manufacturing a semiconductor device according to claim 3, wherein the oxidation step is thermal oxidation of a semiconductor film.   The method of manufacturing a semiconductor device according to claim 1, wherein the thinning step includes a chemical mechanical polishing step of a semiconductor film.   6. The method of manufacturing a semiconductor device according to claim 1, wherein the thinning step includes a semiconductor film etching step. The method of manufacturing a semiconductor device according to claim 1, wherein the thickness of the semiconductor film is 45 nm or less by the thinning step.

Images