JP3859978B2 - Device for forming a laterally extending crystal region in a semiconductor material film on a substrate - Google Patents

Description

[0001]
TECHNICAL FIELD The present invention relates to a method for processing a semiconductor material for a semiconductor integrated device.
[0002]
Background of the invention Semiconductor devices can be formed in a layer or film of silicon, for example on a quartz or glass substrate. This technology is used in the manufacture of image sensors and active matrix liquid crystal display (AMLCD) devices. In the latter case, each transistor acts as a pixel controller in a regular array of thin film transistors (TFTs) on a suitably transparent substrate. In a commercially available AMLCD device, the thin film transistor is formed in a hydrated amorphous silicon film (a-Si: H TFT).
[0003]
In order to enhance the switching characteristics of the TFT, polycrystalline silicon is used instead of amorphous silicon. The polycrystalline structure is obtained, for example, by crystallizing (ELC) the deposited amorphous or microcrystalline silicon film with an excimer laser.
[0004]
However, unsatisfactory results occur when using randomly crystallized polycrystalline silicon. In the case of small grain polysilicon, device performance is limited by a large number of large angle grain boundaries, for example in the active channel region of a TFT. Large grain polysilicon is superior in this regard, but the presence of significant grain structure irregularities in one TFT compared to another TFT results in non-uniform device characteristics in the TFT array.
[0005]
Summary of the invention In order to improve device characteristics and device non-uniformity, a technique of laterally solidifying a semiconductor film on a substrate is applied. This technique, referred to as artificially controlled super lateral growth (ACSLG), exposes a part of the film with a suitable radiation pulse, for example a laser beam pulse, and melts the film locally over its entire thickness. Including doing. As the molten semiconductor material solidifies, a crystal structure grows from a predetermined, completely unmelted portion of the film.
In a first preferred embodiment of this technique, the exposed structure is a first semiconductor film supported by a substrate, a heat resistant film on the first semiconductor film, and a second semiconductor on the heat resistant film. Including membrane. In this embodiment, both the front and back sides of the structure are exposed with pulses.
[0006]
In the preferred second embodiment, the lateral solidification proceeds from the first region through the constricted second region to the third region intended as the device region. In this embodiment, exposure from one side is used in conjunction with the area to be heated through the substrate.
In the third preferred embodiment, the expanded single crystal region is formed by repeatedly irradiating the beam, stepping the radiation pattern in the lateral direction, and repeating the melting and solidification.
Beneficially, this technique can be used in the manufacture of high-speed liquid crystal displays, in which the pixel controller and / or driver circuit is formed as a single crystal or as a regular / quasi-regular polycrystalline film. To do. Other applications include image sensors, static random access memory (SRAM), silicon on insulator (SOI) devices, and three-dimensional integrated circuit devices.
[0007]
Description of preferred embodiments Specific embodiments experimentally implemented and variations thereof will be described below. Several explicit or inherent modifications are common to the embodiments, and further modifications will be apparent to those skilled in the art within the scope of the claims. For example, using a semiconductor material other than silicon, such as germanium, silicon-germanium, germanium arsenide or indium phosphide. It also includes using a substrate of a suitable material such as silicon, quartz, glass or plastics that is considered for stability, inertness and heat resistance under processing conditions. It also includes using a radiation beam other than a laser beam, such as an electron beam or an ion beam.
[0008]
First embodiment The projection exposure apparatus of FIG. 1 includes an excimer laser 11, a mirror 12, a beam splitter 13, a variable focus field lens 14, a patterned projection mask 15, and an imaging lens 16 having two elements. A sample stage 17, a variable attenuator 18, and a converging lens 19. By using this projection device, radiation pulses can be simultaneously supplied to the front side surface and the rear side surface of the sample 10 on the stage 17.
[0009]
In the case of the first embodiment of this technique, as shown in FIG. 2, a “double layer” (DL) including a transparent substrate 20, a first amorphous silicon film 21, a SiO ₂ film 22, and a second amorphous silicon film 23 is shown. ) A sample structure was prepared. The film thickness of the amorphous silicon film was 100 nm, and the film thickness of the SiO ₂ film was 500 nm. Another heat resistant material such as silicon nitride or high temperature glass can be used for the film 22.
[0010]
When pattern projection is performed on the second or top silicon film 23 and broad beam irradiation is performed on the first or bottom silicon film 21, the first silicon film 21 is adjusted as an included sacrificial layer, and the top silicon film 23 The lateral crystallization rate at can be maximized. The role of these films can be reversed when the pattern is projected onto the first film through the substrate. In the film on which the pattern is projected, particles solidified in the lateral direction are formed, for example, a processed film that is well suited for TFTs.
[0011]
The structure according to FIG. 2 is prepared by sequentially depositing amorphous silicon, SiO ₂ track amorphous silicon on a quartz substrate in a low pressure chemical vapor volume. Other suitable deposition methods for amorphous or microcrystalline deposition include, for example, plasma enhanced chemical vapor deposition (PECVD), evaporation, or sputtering.
[0012]
The sample is placed on the stage 17 of the projection exposure apparatus shown in FIG. The mask 15 has a simple strip pattern with a width of 50 μm at various separation distances of 10 to 100 μm.
[0013]
The mask pattern is projected onto the sample at various reduction ratios ranging from 3-6. The energy density on the rear side is controlled by the variable attenuator 18. The sample is irradiated at room temperature using a 30 ns XeCl excimer laser with a wavelength of 308 nm, and the crystal is transparent in this wavelength range. This laser is commercially available under the trade name LambdaPhysik Compex 301. In the case of a glass substrate, longer wavelengths such as 348 nm are required.
[0014]
Beam irradiation is performed at a fixed front energy density and various rear energy densities. The evaluated front energy density is about 1.0 J / cm ² at the sample surface. The rear energy density is 170 to 680 mJ / cm ² .
In order to test following irradiation, the entire film was subjected to defect etching using a Secco etchant and tested using a scanning electron microscope (SEM). The largest non-uniform particles were obtained with a backside energy density of 510 mJ / cm ² . These grains grow laterally from the two sides of the strip-like region and form two grain rows at well-defined grain boundaries on the centerline of the strip.
Even if the resulting individual crystal is not sufficient to form the entire active channel region of the TFT, the crystal can be regular or can act as the active channel region of a TFT, for example as illustrated in FIG. 3A or 3B. A quasi-regular polycrystalline structure is formed. A source electrode 31, a drain electrode 32 , a gate electrode 33, and an active channel region 34 are shown. In FIG. 3A, the active channel region includes both particle trains generated as described above. For sufficiently large particles, such as in FIG. 3B, the active channel region can be formed as a single row of particles.
[0015]
In the processing method according to the first embodiment, the role of the bottom sacrificial layer 21 can be understood as the role of a heating susceptor that accumulates energy when heated by a beam, and the maximum effect is obtained when this film is melted. It is done. The accumulated heat is released during solidification. This reduces the extent to which the top film 23 loses heat due to conduction. Therefore, in order to obtain the maximum benefit, it is important that the structure being exposed is appropriately dimensioned. If the SiO ₂ film 22 is too thin, the heat dissipation of the silicon films 21 and 23 is combined, and the advantage of forming the film 21 cannot be obtained. On the other hand, if the film 22 is too thick for the thermal diffusion distance of the physical process, the film 21 will act poorly on the conversion of the top film 23. With respect to the bottom membrane 21, its thickness must be selected so that this membrane has a sufficient amount of heat. However, if the film 21 is thicker, more energy is required to melt the film.
[0016]
Instead of exposing the pattern on the silicon layer 23, the desired pattern can be defined by a deposited mask layer patterned by, for example, a proximity mask, contact mask or photolithography.
In a masking variant, the mask layer can act to reduce heating in the area under the mask, for example by absorbing or reflecting incident radiation. Alternatively, when an appropriate mask material having an appropriate thickness is used, a complementary antireflection effect is realized, and additional energy can flow into the semiconductor film under the mask material. For example, this effect can be exerted on the silicon film by using a SiO ₂ film. This modification has the advantage that the mask layer acts as a restraining member for the molten semiconductor material and prevents the molten semiconductor layer from agglomerating or deforming into a lump due to the action of surface tension.
[0017]
Second Embodiment The exposure apparatus of FIG. 4 includes an excimer laser 41, a prism deflector 42, a focusing lens 43, a vacuum chamber 44, and a hot stage 45 in which a sample is arranged.
In the second embodiment using the exposure apparatus of FIG. 4 of the present invention, the sample structure of FIG. 5 includes a substrate 50, a thermal oxide film 51, a first patterned amorphous silicon film 52, a SiO ₂ film 53, A second patterned amorphous silicon film 54 and a further deposited SiO ₂ film 55 are included. Typical thicknesses are 100 nm for the thermal oxide film 51, 100 nm for the amorphous silicon film 52, 210 nm for the SiO ₂ film 53, 120 nm for the amorphous silicon film 54, and 170 nm for the SiO ₂ film 55. And
[0018]
This sample structure is obtained by depositing an amorphous silicon film 52 on a thermal oxide film 51 on a silicon wafer 50 by low pressure chemical vapor deposition (LPCVD). The silicon film 52 is coated with a photoresist, then exposed and developed with a stepper, and the silicon film 52 is subjected to reactive ion etching with SF ₆ / O ₂ plasma to form a pattern. The obtained pattern of the first level island of the silicon film 52 is shown in FIG. 6A as viewed from above. This pattern is composed of three areas: a rectangular main island area 523 used as a device, a rectangular “tail” area 521, and a “bottleneck” area 522 connecting the tail area 521 and the main island area 523. The These dimensions are selected as follows. The tail region 521 is 20 × 10 μm, the bottom neck region 522 is 5 × 3 μm, and the main island region 521 has different dimensions in the range of 10 × 10 μm to 50 × 50 μm.
[0019]
The first level island plasma - Enhan scan de vapor deposition by (PECVD) to form a SiO ₂ film 53 is deposited amorphous silicon on the upper side. Amorphous silicon is patterned using a photolithography process to form “second level islands” 54 with dimensions of 5 × 5 μm. The second level island 54 is located directly above the tail region 521 and acts as a beam blocking area during exposure. Finally, a PECVD SiO ₂ layer is formed over the entire structure.
[0020]
For processing, the sample is placed on a refractory graphite hot stage in a vacuum chamber at a pressure of 10 ^-5 Torr. If another suitable heating device is available, the vacuum treatment can be omitted. Heating is performed until the substrate temperature reaches 1000 to 1200 °, which requires a rise time of about 3 minutes. The sample is held at the final substrate temperature for about 2 minutes before exposure. Sample temperature is monitored intermittently with a directly attached thermocouple and continuously with a digital infrared thermometer. The sample is exposed with a single excimer laser pulse at an energy density that is high enough to completely melt all first level islands in the tail area except the beam shading area area.
[0021]
In order to analyze the microstructure, the exposed sample was subjected to Secco etching. For samples exposed at a substrate temperature of 1150 ° C., Nomarski micrographs of the Segou etched samples show that 20 × 20, 40 × 40 and 50 × 50 μm islands are completely converted to single crystal islands (SCI) It has been shown. The defect pattern of the etched sample shows that the main island region contains small-angle subboundaries similar to those observed in zone melting recrystallization, in addition to the planar defects recognized in SLG studies. Suggests. For substrate temperatures as low as 1100 ° C., only small islands of 20 × 20 μm were converted to single crystal islands without large angle grain boundaries. In the case of lower substrate temperatures of 1050 and 1000 ° C., large-angle grain interfaces are generated on 20 × 20 μm islands.
[0022]
The solidification process of the second embodiment can be understood based on FIGS. That is, at the time of exposure, the second level square region 54 shields most of the beam energy incident on this region, and complete melting in the area where the beam of the tail region 521 is shielded is prevented. The remaining portion of the exposed first level region is completely melted as shown in FIG. 6B. When the film is cooled through the substrate, the liquid-solid interface in the region where the beam is shielded becomes insufficiently cooled, and the silicon particles 61 start to grow rapidly outward from the beam shielding region. Within the tail region, many particles 61 are quickly combined and only one or several preferably located particles grow towards the bottleneck 522. The bottleneck portion 522 has a form in which one particle expands to the main island region 523 through the bottleneck portion. When the substrate temperature is sufficiently high and the main island region 523 is small enough to prevent agglomeration in the rapidly cooled liquid, the main island 523 is formed by lateral growth of one particle grown through the bottleneck portion 522. The whole is converted into a single crystalline region.
[0023]
Thus, useful conversion of the main island region 523 to a single crystal form requires an appropriate combination of substrate temperature and island region size. The molten silicon must be maintained at a sufficiently high temperature for a characteristic time to solidify a specific volume longer than the characteristic time required for complete conversion by lateral solidification. This characteristic conversion time depends mainly on the distance to be converted, i.e. the lateral dimensions of the main island, so that the characteristic conversion time is comparable to the average lateral growth distance that can be achieved in the liquid before solidification is triggered. It is necessary to relate the island size to the substrate temperature. Compared to zone melting recrystallization, the technique of the present invention can recrystallize very thin films with a thickness of, for example, 100 nm or less.
[0024]
Instead of blocking the beam, the seed region can be defined by complementary masking using an antireflective coating, as described in the first embodiment. Alternatively, the seed region can be defined by exposure.
[0025]
Third embodiment The projection exposure apparatus of Fig. 7 includes an excimer laser 71, a mirror 72, a variable focus field lens 74, a mask 75 on which a pattern is formed, a two-element imaging lens 76, a sample stage 77, and a variable. An attenuator 78 is included. The sample 70 is placed on the sample stage 77. By using this apparatus to generate a sharp beam, a single crystal silicon region can be grown in stages by a sequential lateral aggregation (SLS) process. Alternatively, beam shaping can be performed using a proximity mask or contact mask.
[0026]
The sample structure shown in FIG. 8 includes a substrate 80, a thermal oxide film 81, and an amorphous silicon film 82.
In the following description, the technology of the third embodiment will be described with reference to FIGS. 9A to 9F, FIGS. 10A to 10F showing two examples of the first modification, and FIGS. 11A to 11B showing the second modification. To do.
[0027]
Starting from an amorphous silicon film 82 patterned in a rectangular shape in this example (FIG. 9A), a region 91 of the silicon film 82 bounded by two broken lines is exposed with a pulse, and the silicon in this region is completely exposed. It is melted (FIG. 9B) and then the molten silicon in region 91 is re-solidified (FIG. 9C). Here, the region 91 has a strip shape, and the exposure of the region 91 can be performed by masked exposure or using a proximity mask. When re-solidifying the molten silicon in the region 91, two particle rows grow explosively from the boundary portion of the broken line in the region 91 toward the center of the region 91. The growth of the two rows of particles is a characteristic lateral growth up to a final distance 92. In the remaining part of the region 91, a finely grained polycrystalline region 93 is formed. Preferably, the width of the strip is selected so that the two particle rows approach each other without refocusing during resolidification. Although not excluded from the present invention, increasing the width does not contribute to processing efficiency. Narrowing the width tends to be undesirable. The reason for this is that the length of the semiconductor must be shortened in the subsequent steps, and the semiconductor surface may become irregular at the position where particles growing from opposite directions come together during the solidification process. . An oxidation cap layer can be formed on the silicon film to slow the aggregation and reduce the distortion of the surface of the silicon film to make the surface smooth.
[0028]
The adjacent area to be exposed is defined by shifting (stepping) the sample in the direction of crystal growth relative to the mask projection or proximity mask. The shifted (stepped) region 94 is bounded by the two dashed lines in FIG. 9D. The shift distance is such that the next region to be exposed overlaps with the previously exposed region so that one crystal row is partially melted while the other crystal row is completely melted as shown in FIG. 9E. Set. Upon re-solidification, a row of partially melted crystals is produced. As shown in 9F, it becomes longer. In this embodiment, it is possible to grow single crystal grains having a desired length by repeatedly cysting the exposed portion.
If the pattern of the exposed area is not a single strip but is chevron 101 as defined by the dashed line in FIG. 10A, the exposure areas shown in FIGS. 10B-10F are shifted by shifting in the same order. Particle growth expands from the top of the edge of the formed chevron pattern. In this way, single crystal regions can be grown with increasing width and length.
[0029]
The large-area single crystal region is illustrated in FIG. 11A, and an exposure region that is sequentially shifted (stepped) into a patterned amorphous silicon film having a tail region 111, a thin bottleneck region 112, and a main island region 113. It can be grown by forming. The cross sections of the regions 111, 112, and 113 in FIGS. 11A-11C are similar to those shown in FIG. 5 except that the radiation-shielding amorphous silicon region 54 and the second silicon dioxide layer 55 are not present. The exposure area defined by the masked exposure or proximity mask is illustrated by the area bounded by the dashed lines in FIGS. 11A-11C, which grows a single particle from the tail area 111 through the bottleneck area 112. FIG. 5 shows sequential lateral shift (stepping) of the exposure region to form a single crystal island region 113.
[0030]
The sequential lateral melting and resolidification of the embodiments of FIGS. 9A-9F, FIGS. 10A-10F and FIGS. 11A-11C is performed by chemical vapor deposition on silicon dioxide coated on a quartz substrate and having a thickness of 100-240 nm. An amorphous silicon film deposited by (CVD) was used. The formation of the single crystal strip was confirmed by an optical scanning electron microscope of the defect etching sample.
[0031]
Optionally, the substrate can be heated to reduce the beam energy required for melting or to increase the lateral growth distance per step. This advantage can be realized by exposing the sample on the stage shown in FIG. 1 from two directions.
[0032]
Alternative processing and applications By using semiconductor films formed according to the present invention, for example, pattern definition, etching, impurity implantation, deposition of insulating layers, contact formation, and interconnection of patterned metal layers. Integrated semiconductor devices can be manufactured by such well established other techniques. In a preferred thin film semiconductor transistor, at least the active channel region has a single crystal regular or at least nearly regular microstructure, for example as shown in FIGS. 3A and 3B.
Of particular note is that such a TFT is included in the liquid crystal display device shown diagrammatically in FIG. This device includes a substrate 120 in which at least the display window portion 121 is transparent. The display window 121 includes a regular array of pixels 122, each pixel including a TFT pixel controller. Each pixel controller can be individually addressed by the driver 123. Preferably, the pixel controller and / or driver circuit is formed of a semiconductor material formed based on the technique of the present invention.
Other applications include image sensors, static random access memory (SRAM), silicon-on-insulator (SOI) devices, and three-dimensional integrated circuit devices.
[Brief description of the drawings]
FIG. 1 is a diagram of a projection exposure apparatus that can be used as a first embodiment of this technique.
FIG. 2 is an enlarged diagrammatic side view of a sample structure for the first embodiment.
3A and 3B are enlarged schematic top views of a TFT device microstructure that can be formed in the semiconductor material of the first embodiment. FIG.
FIG. 4 is a diagram of an exposure apparatus that can be used in the second embodiment of this technique.
FIG. 5 is an enlarged diagrammatic side view of the sample structure of the second embodiment.
6A-6D are diagrammatic top views of the sample structure of FIG. 5 in sequential processing steps.
FIG. 7 is a diagram of an exposure apparatus that can be used in the third embodiment.
FIG. 8 is an enlarged diagrammatic side view of the sample structure of the third embodiment.
9A-9F are diagrammatic side views of the sample structure of FIG. 8 in sequential steps of the first form of the first variation of the process.
10A-10F are diagrammatic side views of the sample structure of FIG. 8 in sequential steps of the second type of first modification of the process.
FIGS. 11A-11C are diagrammatic side views of a sample structure in sequential steps of a second variation of the process. FIGS.
FIG. 12 is a schematic top view of a liquid crystal display device including a TFT.

Claims (15)

An apparatus for forming a crystal region extending laterally in a semiconductor material film on a substrate,
(A) a pulsed radiation beam source for generating a pulsed radiation beam;
(B) with each having a predetermined intensity pattern for exposing the semiconductor material film, masked with sufficient energy order to melt the exposed portions of the semiconductor material film throughout its thickness A beam mask for forming radiation beam pulses;
(C) the on board while said at least a portion of the semiconductor material film is exposed by the radiation beam pulse which is masked, thereby holding the semiconductor material layer, said semiconductor material layer on the substrate, is the mask A sample moving stage that moves in a direction transverse to the radiation beam pulse,
If the sample moving stage is located at the first position, the first portion of the semiconductor material film, and exposed by the radiation beam pulse which is masked over the its entire thickness of the semiconductor material of the first portion melted, along the boundary of the said semiconductor material is solidified first portion of the first portion to form at least one semiconductor crystal, the semiconductor crystal and the portion of the immediately preceding to the next process,
Wherein the sample moving stage is moved to the next position, in this position, the next portion of the semiconductor material layer to said at least one semiconductor crystal and partially overlap, and the exposure by the radiation beam pulse masked the semiconductor material of the next portion was melted throughout its thickness, the expanding at least one of the semiconductor crystal by growing laterally solidifying the molten said semiconductor material of said next part,
The repeatedly moving the sample moving stage to another position, at that location, after a portion of the immediately preceding solidified, the another portion of the semiconductor material film, and exposed by the beam pulse masked, the another portion immediately before An apparatus for expanding the at least one semiconductor crystal until a desired crystal region is formed by partially overlapping with at least one semiconductor crystal of the portion and growing in a lateral direction.   2. The apparatus of claim 1, wherein the pulsed radiation beam source is a pulsed laser, the apparatus comprising a first optical path through which a radiation beam pulse propagates from a laser to the beam mask.   3. The apparatus according to claim 2, wherein the pulsed laser is a pulsed excimer laser.   3. The apparatus of claim 2, wherein the first optical path comprises a field lens that projects radiation beam pulses from the laser onto a beam mask.   3. The apparatus according to claim 2, wherein the beam mask is a projection mask.   3. The apparatus according to claim 2, wherein the mask is a proximity mask.   The apparatus according to claim 2, wherein the mask is a contact mask.   3. The apparatus of claim 2, wherein the first optical path includes a variable attenuator that attenuates the intensity of the radiation beam pulse from the laser.   The apparatus of claim 2, wherein the first optical path includes at least one beam steering mirror.   2. The apparatus of claim 1, wherein a pulsed radiation beam source is a laser, the beam mask is a projection mask, and a second radiation beam pulse propagated from the beam mask to a semiconductor material on a sample moving stage. A device having an optical path. The apparatus according to claim 10, wherein the second optical path, apparatus including an objective lens for focusing on a portion of the semiconductor material film to be exposed to masked radiation beam pulse at the sample moves on the stage.   The apparatus of claim 10, wherein the second optical path includes a variable attenuator that attenuates the masked radiation beam pulse.   12. The apparatus of claim 11, wherein the second optical path comprises at least one beam steering mirror.   The apparatus of claim 1, wherein the beam mask defines an intensity pattern of each masked radiation beam pulse, the intensity pattern comprising at least one strip shape that exposes the semiconductor material film. .   The apparatus of claim 1, wherein the beam mask defines an intensity pattern of each masked radiation beam pulse, the intensity pattern including at least one chevron shape that exposes the semiconductor material film.

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