Patent Grant
7259081
The present invention relates to techniques for processing of films, and more particularly to techniques for processing films to obtain a substantially uniform grain region for placing at least an active region of a thin-film transistor (“TFT”) therein.
Semiconductor films, such as silicon films, are known to be used for providing pixels for liquid crystal display devices. Such films have previously been processed (i.e., irradiated by an excimer laser and then crystallized) via excimer laser annealing (“ELA”) methods. However, the semiconductor films processed using such known ELA methods often suffer from microstructural non-uniformities, which manifest themselves in availing a non-uniform performance of thin-film transistor (“TFT”) devices fabricated on such films. The non-uniformity generally stems from the intrinsic pulse-to-pulse variations in the output energy of the excimer lasers irradiating the semiconductor films. The above-described non-uniformity could manifest itself in, for example, a noticeable difference in a brightness level of the pixels in one area of the display as compared to the brightness in other areas thereof.
Significant effort has gone into the refinement of “conventional” ELA (also known as line-beam ELA) processes in the attempt to reduce or eliminate the non-uniformity. For example, U.S. Pat. No. 5,766,989 issued to Maegawa et al., the entire disclosure of which is incorporated herein in its entirety by reference, describes the ELA methods for forming polycrystalline thin film and a method for fabricating a thin-film transistor. This publication attempts to address the problem of non-uniformity of characteristics across the substrate, and provide certain options for apparently suppressing such non-uniformities.
However, the details of the beam-shaping approach used in conventional ELA methods make it extremely difficult to reduce the non-uniformities in the semiconductor films. This is especially because the energy fluence described above may be different for each beam pulse, and thus non-uniformity may be introduced into sections of the semiconductor thin film upon irradiation, solidification and crystallization.
Techniques for fabricating large grained single crystal or polycrystalline silicon thin films using sequential lateral solidification are known in the art. For example, in U.S. Pat. No. 6,322,625 issued to Im and U.S. patent application Ser. No. 09/390,537, the entire disclosures of which are incorporated herein by reference, and which is assigned to the common assignee of the present application, particularly advantageous apparatus and methods for growing large grained polycrystalline or single crystal silicon structures using energy-controllable laser pulses and small-scale translation of a silicon sample to implement sequential lateral solidification have been described. In these patent documents, it has been discussed in great detail that at least portions of the semiconductor film on a substrate are irradiated with a suitable radiation pulse to completely melt such portions of the film throughout their thickness. In this manner, when the molten semiconductor material solidifies, a crystalline structure grows into the solidifying portions from selected areas of the semiconductor film which did not undergo a complete melting. This publication mentions that the small grain growth in regions in which nucleation may occur. As is known in the art, such nucleation generates small grained material in the area of the nucleation.
As was previously known to those having ordinary skill in the art of a sequential lateral solidification (“SLS”) as described in U.S. Pat. No. 6,322,625, which utilizes the irradiation of a particular area using beam pulses whose cross-sectional areas are large, it is possible for the nucleation to occur in such areas before a lateral crystal growth is effectuated in such area. This was generally thought to be undesirable, and thus the placement of the TFT devices within these area was avoided.
While certain TFT devices do not require a high performance level, they require good uniformity in certain applications. Accordingly, it may be preferable to generate substrates which include the semiconductor films that allow uniform small-grained material to be produced therein, without the need for a multiple irradiation of the same area on the semiconductor thin film.
One of the objects of the present invention is to provide an improved process and system to which can produce generally uniform areas on the substrate films such that the TFT devices can be situated in such areas. Another object of the present invention is to allow such areas to be nucleated (based on the threshold behavior of the beam pulse), and then solidified, such that upon re-solidification, the nucleated area becomes a region with uniform small grained material. It is also another object of the present invention to increase the speed to process the semiconductor films for their use with the liquid crystal displays or organic light emitting diode displays. It is still another object of the present invention to allow each irradiated area of the semiconductor thin film to be irradiated once, without the need to re-irradiate a substantial portion thereof, while still providing a good uniform material therein.
In accordance with at least some of these objectives as well as others that will become apparent with reference to the following specification, it has now been determined that the nucleated and small grained material have an extremely good uniformity (e.g., uniform grains). It was also ascertained that the grain size in such nucleated areas does not vary even in a significant manner if the beam pulses melting these areas have fluctuating energy densities. This is particularly the case when the beam's energy density stays above the required threshold for fully melting these areas throughout their thickness. For example, in the case of a semiconductor film which has a thickness of approximately 0.1 μm, the energy density of each beam pulse should be above 50 mJ/cm2. Further, the uniformity in the thin film was found to be insensitive to a spatial non-uniformity of the beam incident on the semiconductor film so long as the minimum intensity of the beam is above the above-described threshold.
In one exemplary embodiment of the present invention, a process and system for processing a semiconductor thin film sample are provided. in particular, a beam generator can be controlled to emit at least one beam pulse. With this beam pulse, at least one portion of the film sample is irradiated with sufficient intensity to fully melt such section of the sample throughout its thickness. Such beam pulse may have a predetermined shape. This portion of the film sample is allowed to re-solidify, and the resolidified portion is composed of a first area and a second area. Upon the re-solidification thereof, the first area includes large grains, and the second area has a small-grained region formed through nucleation. The first area surrounds the second area and has a grain structure which is different from a grain structure of the second area. The second area is configured to facilitate thereon an active region of a thin-film transistor (“TFT”).
In another exemplary embodiment of the present invention, the first area has a first border and a second border which is provided opposite and parallel to the first border of the first area. Also, the second area has a third border and a fourth border which is provided opposite and parallel to the third border of the second area. A distance between the first border and the second border is smaller than a distance between the third border and the fourth border. The second area preferably corresponds to at least one pixel. In addition, the second area may have a cross-section for facilitating thereon all portions of the TFT. It is also possible for a portion of the first area to contain thereon a small section of the TFT. A size and a position of the first area with respect to the second area can be provided such that there is no effect or a negligible effect on a performance of the TFT by the first area.
According to yet another embodiment of the present invention, the thin film sample can be translated for a predetermined distance. With a further beam pulse, a further portion of the film sample can be irradiated. The further portion is provided at a distance from such portion that substantially corresponds to the predetermined distance. This further portion of the film sample is allowed to re-solidify, the re-solidified portion being composed of a third area and a fourth area. In addition, the third area can surround the fourth area, and at least one section of the third area at least partially overlaps at least one section of the first area. Further, upon the re-solidification thereof, the third area has laterally grown grains, and the fourth area has a nucleated region. The fourth area can also be composed of edges which are provided away from edges of the second area. Furthermore, the fourth area may be composed of edges which are approximately border edges of the second area, and the edges of the fourth area may not necessarily extend into any section of the first area. The beam pulse may have a fluence which is substantially the same as a fluence of the further beam pulse (or different therefrom).
In still another embodiment of the present invention, the thin film sample can be translated for a predetermined distance. Then, a further portion of the film sample can be irradiated using the beam pulse. The further portion is provided at a distance from such portion that substantially corresponds to the predetermined distance. The film sample may be a pre-patterned silicon thin film sample or a continuous silicon thin film sample. In addition, the thin film sample can be translated for a predetermined distance, and a further portion of the film sample may be irradiated using at least one beam pulse. The further portion is preferably provided at a distance from this portion that substantially corresponds to the predetermined distance. In addition, the film sample can be delivered to a first relative pre-calculated position of the further portion of the film sample to be irradiated. After such delivery, the film sample may be provided at a second relative pre-calculated position whose distance is different from the predetermined distance.
According to further embodiment of the present invention, the thin film sample can again be translated for a predetermined distance. Then, the translation of the film sample may be stopped, and vibrations of the film sample to allowed to settle. Thereafter, a further portion of the thin film is irradiated using at least one beam pulse, with the further portion being provided at a distance from such portion that substantially corresponds to the predetermined distance. Then, the portion of the film sample is irradiated with a further beam pulse, and allowed to re-solidify. A fluence of the beam pulse is different from a fluence of the further beam pulse (e.g., less than the fluence of the beam pulse).
According to still further embodiment of the present invention, a location of the first area is determined so as to avoid a placement of the active region of the TFT thereon. The beam pulse preferably includes a plurality of beamlets, and the first and second areas are irradiated by the beamlets. The semiconductor thin film sample may be a silicon thin film sample, and possibly composed of silicon, germanium or an alloy thereof. The semiconductor thin film may have a thickness approximately between 100 Å and 10,000 Å. Portions of the beam pulse can be masked to produce at least one masked beam pulse, such that the masked beam pulse is used to irradiate the portion of the film sample. The large grains provided in the first area may be laterally-grown grains, and the laterally-grown grains of the first area can be equiaxed grains.
According yet another embodiment of the present invention, a semiconductor thin film sample is provided which has a first area and a second area. The first area preferably has large grains therein. The second area is surrounded by the first area and includes a region formed through nucleation of at least one section of the semiconductor thin film in which the second area is situated. The structure of the grains of the first area is different from a structure of the grains of the second area. The second area is preferably configured to facilitate thereon an active region of a thin-film transistor (“TFT”).
The accompanying drawings, which are incorporated and constitute part of this disclosure, illustrate a preferred embodiment of the invention and serve to explain the principles of the invention.
It should be understood that various systems according to the present invention can be utilized to generate, nucleate, solidify and crystallize one or more areas on the semiconductor (e.g., silicon) film which have uniform material therein such that at least an active region of a thin-film transistor (“TFT”) can be placed in such areas. The exemplary embodiments of the systems and process to achieve such areas, as well as of the resulting crystallized semiconductor thin films shall be described in further detail below. However, it should be understood that the present invention is in no way limited to the exemplary embodiments of the systems, processes and semiconductor thin films described herein.
Certain systems for providing a continuous motion SLS are described in U.S. patent application Ser. No. 09/526,585 (the “'585 application”), the entire disclosure of which is incorporated herein by reference. Substantially solar systems according to the exemplary embodiment of the present invention can be employed to generate the nucleated, solidified and crystallized portions of the semiconductor film described above on which it is possible to situate the active regions of the TFT device. In particular, the system according to the present invention is used on a sample 170 which has an amorphous silicon thin film thereof that is being irradiated by irradiation beam pulses to promote the nucleation, subsequent solidification and crystallization of the particular areas of the semiconductor thin film. The exemplary system includes a beam source 110 (e.g., a Lambda Physik model LPX-315I XeCl pulsed excimer laser) emitting an irradiation beam (e.g., a laser beam), a controllable beam energy density modulator 120 for modifying the energy density of the laser beam, a MicroLas two plate variable attenuator 130, beam steering mirrors 140, 143, 147, 160 and 162, beam expanding and collimating lenses 141 and 142, a beam homogenizer 144, a condenser lens 145, a field lens 148, a projection mask 150 which may be mounted in a translating stage (not shown), a 4×-6× eye piece 161, a controllable shutter 152, a multi-element objective lens 163 for focusing a radiation beam pulse 164 onto the sample 170 having the semiconductor thin film to be processed mounted on a sample translation stage 180, a granite block optical bench 190 supported on a vibration isolation and self-leveling system 191, 192, 193 and 194, and a computing arrangement 100 (e.g., a general purpose computer executing a program according to the present invention or a special-purpose computer) coupled to control the beam source 110, the beam energy density modulator 120, the variable attenuator 130, the shutter 152 and the sample translation stage 180.
The sample translation stage 180 is preferably controlled by the computing arrangement 100 to effectuate translations of the sample 170 in the planar X-Y directions, as well as in the Z direction. In this manner, the computing arrangement 100 controls the relative position of the sample 40 with respect to the irradiation beam pulse 164. The repetition and the energy density of the irradiation beam pulse 164 are also controlled by the computer 100. It should be understood by those skilled in the art that instead of the beam source 110 (e.g., the pulsed excimer laser), the irradiation beam pulse can be generated by another known source of short energy pulses suitable for completely melting throughout their entire thickness selected areas of the semiconductor (e.g., silicon) thin film of the sample 170 in the manner described herein below. Such known source can be a pulsed solid state laser, a chopped continuous wave laser, a pulsed electron beam and a pulsed ion beam, etc. Typically, the radiation beam pulses generated by the beam source 110 provide a beam intensity in the range of 10 mJ/cm2 to 1 J/cm2, a pulse duration (FWHM in the range of 10 to 103 nsec, and a pulse repetition rate in the range of 10 Hz to 104 Hz.
While the computing arrangement 100, in the exemplary embodiment of the system shown in
As illustrated in
The semiconductor thin film 175 can be irradiated by the beam pulse 164 which is patterned using the mask 150 according to a first exemplary embodiment of the present invention as shown in
A first exemplary embodiment of the process according to the present invention shall now be described with reference to the irradiation of the semiconductor thin film 175 of the sample 170 as illustrated in
After the sample 170 is conceptually subdivided into columns 205, 206, 207, etc., a pulsed laser beam 111 is activated (by actuating the beam source 110 using the computing device 100 or by opening the shutter 130), and produces the pulsed laser beamlets 164 which impinges on a first location 220 which is away from the semiconductor thin film 175. Then, the sample 170 is translated and accelerated in the forward X direction under the control of the computing arrangement 100 to reach a predetermined velocity with respect to the fixed position beamlets in a first beam path 225.
In one exemplary variation of the process of the present invention, the pulsed beamlets 164 can reach a first edge 210′ of the sample 170 preferably when the velocity of the movement of the sample 170 with respect to the pulsed laser beam 149 reaches the predetermined velocity. Then, the sample 170 is continuously (i.e., without stopping) translated in the −X direction at the predetermined velocity so that the pulsed beamlets 164 continue irradiating successive portions of the sample 170 for an entire length of a second beam path 230.
After passing the first edge 210′, the beam pulse 164 impinges and irradiates a first area 310 of the semiconductor thin film 175, preferably with enough intensity to completely melt such area throughout its thickness, as illustrated in
The first laterally-grown region 318 is formed by laterally growing the grains from the borders between the unmelted portions of the semiconductor thin film 175 and the first melted area 310. The grains in the first laterally-grown region 318 grown from these borders toward the center of the first melted area for a predetermined distance, to reach the first small- ed region 315 and form a border there between. This predetermined distance is controlled by the rate of re-solidification of the first melted area 310. For example, the predetermined distance can be between 1 μm and 5 μm. Therefore, the first laterally-grown region 318 is significantly smaller that the first small-grained region 315 which it surrounds. Generally, the grains of the region 315 are smaller than he grains of the region 318. However, the small-grained material in the first small-grained region 315 provides a good uniformity for the placement of the TFT devices, and at least the active regions thereof, in such uniform small-grained region. For the purposes of the present invention, it is undesirable to position the active regions of the TFT devices on such small-grained regions.
Thereafter, as shown in
The translation and irradiation of the first conceptual column 205 of the semiconductor thin film 175 continues until all areas 310, 320, . . . , 380, 390 (and their respective small-grained regions 315, 325, . . . , 385, 395 and laterally-grown regions 318, 328, . . . , 388, 398) in this first conceptual column 205 is continued until the pulsed beamlets 164 reach a second edge 210″ of the sample 170, as illustrated in
While being away from the sample 170 and the second edge 210″, the sample is translated in a −Y direction to a third location 247 via a fourth beam path 245 so as to be able to irradiate the sections of the semiconductor thin film 175 along the second conceptual column 206. Then, the sample 170 is allowed to settle at that location 247 to allow any vibrations of the sample 170 that may have occurred when the sample 170 was translated to the third location 247 to cease. Indeed, for the sample 170 to reach the second conceptual column 206, it is translated approximately ½ cm for the columns having a width (in the −Y direction) of ½ cm. The sample 170 is then accelerated to the predetermined velocity via a fourth beam path 250 in the −X direction so that the impingement of the semiconductor thin film 175 by the beam pulse 164 reaches, and then bypasses the second edge 210″.
Thereafter, the sample 170 is translated along a fifth beam path 255, and the exemplary process described above with respect to the irradiation of the first column 205 may then be repeated for the second conceptual column 206 to irradiate further areas 410, 420, and their respective small-grained regions 415, 425 and laterally-grown regions 418, 428 while translating the sample in the +X direction. In this manner, all conceptual columns of the sample 170 can be properly irradiated. Again, when the beam pulse 164 reaches the first edge 210′, the translation of the sample 170 is decelerated along a sixth beam path 260 to reach a fourth location 265. At that point, the sample 170 is translated in the −Y direction along the seven beam path 270 for the beam pulse to be outside the periphery of the sample 170 to reach fifth location 272, and the translation of the sample 170 is allowed to be stopped so as to remove any vibrations from the sample 170. Thereafter, the sample 170 is accelerated along the eighth beam path 275 in the −X direction so that the beam pulse 164 reaches and passes the first edge 210′ of the sample 170, and the beam pulse 164 irradiates and completely melts certain areas in the third conceptual column 207 so that they can crystallize in substantially the same manner as described above for the areas 310, 320, . . . , 380, 390 of the first conceptual column 205 and the areas 410, 420, . . . of the second conceptual column 206.
This procedure may be repeated for all conceptual columns of the semiconductor thin film 175, for selective columns of particular sections of the thin film 175 which are not necessarily conceptually subdivided into columns. In addition, it is possible for the computing arrangement 100 to control the firing of the beam 111 by the beam source 110 based on the predefined location stored in the storage device of the computing arrangement 100 (e.g., instead of irradiating the semiconductor thin film 175 by setting predetermined pulse durations). For example, the computing arrangement 100 can control the beams source 110 to generate the beam 111 and irradiate only at the predetermined locations of certain areas of the thin film 175 with its corresponding beam pulse 164, such that these locations are stored and used by the computing arrangement 100 to initiate the firing of the beam 111 which results in the irradiation by the beam pulse only when the sample 170 is translated to situate those areas directly in the path of the beam pulse 164. The beam source 110 can be fired via the computing arrangement 100 based on the coordinates of the location in the X direction.
In addition, it is possible to translate the sample 170 in a manner which is not necessary continuous, when the path of the irradiation of the beam pulse 164 points to the areas on the semiconductor thin film 175 to be melted and crystallized. Thus, it is possible for the translation of the sample 170 to be stopped in the middle of the sample 170, with the area in the middle being irradiated, completely melted, and then re-solidified and crystallized. Thereafter, the sample 170 can be moved so that another section of the semiconductor thin film 175 is arranged in the path of the beam pulse 164, such that the translation of the sample is then stopped again and the particular section is irradiated and completely melted in accordance with the exemplary embodiment of the process described in great detail above, as well as the embodiments of the process which shall be described below.
According to the present invention, any mask described and shown herein and those described and illustrated in the '535 application may be used for the process and system according to the present invention. For example, instead of using the mask shown in
Similarly to the area 310 in
In addition, it is possible to utilize a third embodiment of a mask 150″ according to the present invention as shown in
In step 1027, the sample 170 is positioned to point the beam pulse 164 to impinge the first column of the semiconductor thin film. Then, in step 1030, the portions of the semiconductor thin film are irradiated and filly melted throughout their entire thickness using a masked intensity pattern or a shaped beam pulse (e.g., using the mask 150 or merely shaping the beam). Thereafter, the irradiated portions of the semiconductor thin film are allowed to solidify and crystallize such that the certain areas of the solidified portions have been nucleated and include uniform material therein so as to allow at least the active regions of the TFT devices to be placed entirely therein. In step 1035, it is determined whether the irradiation for the current conceptual column by the beam pulse has been completed. If no, in step 1045, the sample is continued to be irradiated with the next beam pulse 164. However, if in step 1035, it is determined that the irradiation and crystallization of the current conceptual column is completed, then it is determined in step 1045 whether there are any further conceptual columns of the sample 170 to be processed. If so, the process continues to step 1050 in which the sample 170 is translated to that the beam pulse 164 is pointed to the next conceptual column to be processed according to the present invention. Otherwise, in step 1055, the exemplary processing has been completed for the sample 170, and the hardware components and the beam 111 of the system shown in
Then, in step 1130, the resultant beam 149 is passed through the mask 159 to shape the beam pulse, and shape the edge portions of the resultant pulse. Then, the sample 170 is continuously translated along the current column in step 1135. In step 1140, during the translation of the sample 170, the portions of the semiconductor thin film 175 are irradiated, and fully melted throughout their entire thickness, e.g., using a masked intensity pattern beam pulse to allow the irradiated portions to be crystallized. This irradiation of the portions of the semiconductor thin film 175 can be performed when the beam pulses 164 reach particular locations on the sample 170, which are pre-assigned by the computing arrangement 100 and stored in the storage device thereof. Thus, the beam source 110 can be fired upon the sample 170 reaching these locations with respect to the beam pulses 164. Thereafter, the irradiated portions of the semiconductor thin film 175 are allowed to solidify and crystallize such that the certain areas of the solidified portions have been nucleated, and include the uniform material therein so as to allow the active regions of the TFT devices to be placed thereon. Such processing is continued until the end of the current conceptual column on the semiconductor thin film 175 (e.g., the edge of the sample 170) is reached. In step 1145, it is determined whether there are any further conceptual columns of the sample 170 are to be processed. If so, the process continues to step 1150 in which the sample is translated so that the beam pulse 164 is pointed to the next conceptual column to be processed according to the present invention. Otherwise, in step 1155 is performed, which is substantially the same as that of step 1055 of
The foregoing merely illustrates the principles of the invention. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. For example, while the above embodiment has been described with respect to at least partial lateral solidification and crystalization of the semiconductor thin film, it may apply to other materials processing techniques, such as micro-machining, photo-ablation, and micro-patterning techniques, including those described in International patent application no. PCT/US01/12799 and U.S. patent application Ser. Nos. 09/390,535, 09/390,537 and 09/526,585, the entire disclosures of which are incorporated herein by reference. The various mask patterns and intensity beam patterns described in the above-referenced patent application can also be utilized with the process and system of the present invention. It should also be understood that while the systems and processes described above are directed for processing, e.g., semiconductor thin films, these techniques and systems can also be used to process other films, including metal thin films, etc.
It will thus be appreciated that those skilled in the art will be able to devise numerous systems and methods which, although not explicitly shown or described herein, embody the principles of the invention and are thus within the spirit and scope of the present invention.
This application is a national phase of Internation Patent Application No. PCT/US03/025946, filed Aug. 19, 2003, published on Feb. 26, 2004 as International Patent Publication No. WO 04/017379, which claims priority from United States Provisional Application No. 60/405,084, which was filed on Aug. 19, 2002, each of which are incorporated by reference in their entireties herein, and from which priority is claimed.
The U.S. Government may have certain rights in this invention pursuant to the terms of the Defense Advanced Research Project Agency award number N66001-98-1-8913.
| Filing Document | Filing Date | Country | Kind | 371c Date |
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| Publishing Document | Publishing Date | Country | Kind |
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| WO2004/017379 | 2/26/2004 | WO | A |
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| 04017379 | Feb 2004 | WO |
| 04017380 | Feb 2004 | WO |
| 04017381 | Feb 2004 | WO |
| 04017382 | Feb 2004 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20050202654 A1 | Sep 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60405084 | Aug 2002 | US |
