KR20100028008A - Process and apparatus for changing the structure of a semiconductor layer - Google Patents

Abstract

PURPOSE: A process and an apparatus for changing the structure of a semiconductor layer are provided to improve the uniformity of the semiconductor layer by sweeping the surface of the semiconductor layer with at least two laser lights. CONSTITUTION: One area of the surface of a semiconductor layer(30) is radiated by a first laser light(35). The area of the surface of the semiconductor layer is radiated by a second laser light(27). The area of the surface of the semiconductor layer is swept in one direction by the first laser light and the second layer light. The radiation intensity of the first laser light is lower than the second laser light.

Description

PROCESS AND APPARATUS FOR CHANGING THE STRUCTURE OF A SEMICONDUCTOR LAYER}

The present invention relates to a process and apparatus for modifying the structure of a semiconductor layer with at least one first laser light and a second laser light.

It is known to use laser irradiation for the purpose of initiating thermal processes for amorphous silicon and other semiconductor materials. In this regard, semiconductor materials are irradiated, for example, for the purpose of activating doping, for crystallizing amorphous layers for three-dimensional switching circuits, and for healing crystal defects.

Crystallization of the amorphous layers and healing of crystal defects may be useful in large area displays, such as flat display screens, to produce liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays. It is used at the time of preparation of a semiconductor film. Such displays use thin-film transistors (TFTs) to switch the pixels to be displayed on the display. By irradiating the semiconductor film with laser light, the electron mobility of the semiconductor film can be particularly increased. As a result, it is possible to manufacture smaller transistors, whereby a higher resolution display can be produced with a more compact, lighter, and thinner structural design.

In order to reduce size, and to further reduce the weight and thickness of the display, and to further increase the resolutions of the display, much higher quality semiconductor materials are needed.

Publication US 2003/0024905 A1 relates to an apparatus for irradiating a semiconductor layer. In one embodiment, three laser beams generated by the laser source are reflected on the substrate aligned on the movable plane.

Publication US 2007/0178631 A1 relates to a process and an apparatus for crystallizing a semiconductor film. In one embodiment, the laser beam is split into two laser beam portions, and through the lens the two laser beam portions are focused on the same surface area of the semiconductor film.

It is an object of the present invention to make the process and apparatus for irradiating a semiconductor layer available, through which the uniformity of the semiconductor layer can be increased.

According to the invention, this object is achieved by irradiating at least one surface area of the semiconductor layer with a first laser light by a process of modifying the structure of the semiconductor layer, and with the at least one second laser light. Achieved by irradiating the at least one surface area of the semiconductor layer, wherein the first laser light and the second laser light only sweep the at least one surface area of the semiconductor layer once in one direction in succession in time The first laser light exhibits a lower radiation intensity than the second laser light, and the first laser light and the second laser light are generated from one laser beam.

At least one region of the semiconductor layer is first irradiated with laser light having a first emission intensity or energy density, and is offset in time, subsequently with laser light having a higher emission intensity or energy density than in the case of the first irradiation. By this, at least one region of the semiconductor layer can be prepared for the second irradiation by the first irradiation. By pretreating at least one region of the semiconductor layer in this way, a second investigation can result in better layer properties. For example, hydrogen may be evaporated from the deposited layers of the semiconductor layer during the first irradiation. This can happen especially without microexplosion. By first irradiation, defects (eg, contamination) in or on the semiconductor layer may also be removed without breaking the semiconductor layer. As a result, the first survey increases the efficiency of the second survey. Thus, the first survey, in particular for the second survey, widens the process window. As a result, the first irradiation and the second irradiation together produce a synergistic effect with each other, whereby the uniformity of the semiconductor layer can be increased and the surface thereof can be smoother.

Since the first laser light and the second laser light from one laser beam are generated, both irradiation or exposure can be generated by any scan procedure. As a result, the throughput can be increased with the process according to the invention with double exposure in the scanning procedure.

Moreover, two separate laser beam sources need not be provided for the purpose of generating the first laser light and the second laser light. As a result, the additional control effort to control the laser light generated by the two laser beam sources with respect to each other can be avoided. As a result, device costs can be reduced.

In the case of the first laser light and the second laser light, these laser lights are preferably laser light pulses that can be generated with the aid of a pulsed laser-light source. However, the first laser light and the second laser light may also be continuous wave laser beams.

In the semiconductor layer, preferably this semiconductor layer is an amorphous silicon layer. In particular, such a semiconductor layer may be a thin film.

By the first irradiation and the second irradiation according to the present invention, homogeneous conversion of the amorphous silicon layer to polycrystalline silicon may occur. In this process, the amorphous silicon layer can be at least partially converted to polycrystalline silicon.

In one embodiment of the invention, the first laser light and the second laser light pass (swept) in at least one region of the semiconductor layer in one direction. In particular, the first laser light and the second laser light may sweep at least one region in the same direction. As a result, the semiconductor layers of a large area can also be irradiated with the first laser light and the second laser light. At least one region of the semiconductor layer is preferably irradiated only once in each case by the first laser light and the second laser light. Instead of the term 'sweep', the term 'scan' may be used herein.

More preferably, the first laser light and the second laser light irradiate (or sweep) at least one region with a predetermined temporal separation interval and / or spatial separation interval from each other. That is, laser irradiation by a 1st laser light and a 2nd laser light arises. In this case, the temporal separation interval and / or spatial separation interval between laser irradiations can be predetermined. Due to the temporal offset or spatial offset of the laser irradiation, when the second irradiation occurs, the thermal process occurring in the semiconductor layer by the first irradiation may be terminated or in a desired state, which may be in the desired state, Subsequent thermal processes of or occur or the thermal process occurring by the first irradiation is continued. For example, during irradiation of an amorphous silicon layer, it can only be partially melted by the first irradiation. During cooling of the silicon layer (ie, after the first irradiation and before the second irradiation), crystals may grow from the molten layer. Cooling of the semiconductor layer after the first irradiation through a predetermined separation interval between the first laser light and the second laser light, i.e., through a predetermined temporal separation interval when the second irradiation after the first irradiation occurs, or The time at which the growth of the crystals is terminated can be determined. As a result, thermal process performance in and on the semiconductor layer can also be affected by a predetermined temporal separation interval between the first laser light and the second laser light.

The second irradiation of at least one region of the semiconductor layer preferably takes place after this region has cooled to almost ambient temperature after the first irradiation.

In a more preferred method, the time interval between the first laser light and the second laser light, i.e., the time interval between the first radiation in at least one region of the semiconductor layer and the at least one second radiation in at least one region of the semiconductor layer, is from 10 ms to 100 ms. In particular, this time interval may be between 1 ms and 5 ms.

In order to generate two laser light beams from one laser beam, the process of irradiating the semiconductor layer also includes dividing the laser beam into two laser beam portions having different emission intensities, and the first laser light and A process step may consist of focusing these two laser beam portions to form a second laser light. During the separation step, two laser beam portions are generated on the one hand (which forms the basis for the first laser light and the second laser light) and on the other hand have a higher emission intensity than the first laser light. Second laser light may be generated. In the case of two split laser beam portions, these laser beam portions may be ray bundles, in particular Gaussian ray bundles, which are focused to irradiate at least one region of the semiconductor layer to be first. Laser light and second laser light are formed.

The first laser light and the first laser light and the second laser light before the irradiation of at least one region of the semiconductor layer to irradiate the semiconductor layer or to sweep at least one region of the semiconductor layer at the required separation interval, 2 laser light may be collimated.

According to another embodiment of the invention, the process of irradiating a semiconductor layer also includes the following process steps: changing the distribution of the emission intensity of the two laser beam portions during the separation of the laser light, and the first Changing the direction in which the laser light and the second laser light sweep (scan) at least one region of the semiconductor layer. Through this process step, at least one region of the semiconductor layer can be intermittently scoured (scanned) in different directions by the first laser light and the second laser light. At least one region of the semiconductor layer is preferably irradiated only once in each case by the first laser light and the second laser light. Thus, for example, if a semiconductor layer having a rectangular surface is to be irradiated, the surface is irradiated alternately from circle to right and from right to left in the form of a strip until the entire surface is irradiated twice. Can be erased. As a result, the time to irradiate the entire semiconductor layer can be shortened, thereby reducing the cost.

In another preferred manner, the first laser light having a radiation intensity or energy density at which the semiconductor layer is not destroyed irradiates the semiconductor layer. For example, the emission intensity of the first laser light may be such that hydrogen is evaporated from the deposited layers of the semiconductor layer or the defect in the semiconductor layer or the defect on the semiconductor layer is removed, without breakage.

During irradiation of the amorphous silicon layer, the emission intensity of the first laser light can be selected so that the amorphous silicon layer can only be partially converted to polycrystalline silicon. In this case, the first irradiation corresponds to a pretreatment for the second irradiation, where polycrystalline silicon can be made under better conditions.

Through the process of irradiating the semiconductor layer, preferably a thin amorphous silicon layer can be irradiated, and the thickness of the amorphous silicon layer is preferably larger than 10 nm and up to 10 μm. The thickness of the amorphous silicon layer can also be larger than 10 μm.

In particular, radiant energy is introduced into the semiconductor layer by the first irradiation and / or the second irradiation over the entire thickness of the semiconductor layer, ie to the lower glass substrate.

In another preferred manner, the ratio of the emission intensity of the first laser light to the emission intensity of the second laser light is from at least 0.1 to at most 0.9, and particularly preferred values are between at least 0.25 and at most 0.45.

The improvement of the uniformity of the semiconductor layer can preferably be obtained when the first laser light and / or the second laser light have a wavelength of 190 nm to 1100 nm. The use of laser light in the green spectral region may be suitable for conventional semiconductor layer thicknesses. In a preferred embodiment, the first laser light and / or the second laser light exhibits a wavelength of 450 nm to 550 nm. In a particularly preferred manner, the first laser light and / or the second laser light exhibits a wavelength of 515 nm or 532 nm. For example, if the laser light in the green spectral region hits amorphous silicon having a layer thickness greater than 10 nm and up to 10 μm, the green laser light is absorbed over the entire thickness of the amorphous silicon layer. In comparison, when irradiating an amorphous silicon layer using laser light within a wavelength range smaller than 500 nm, the laser light is only absorbed into the thin surface layer of the amorphous silicon layer. As a result, laser light in the green spectral region can be used, in particular for the purpose of converting semiconductor layers.

The first laser light and / or the second laser light, ie the pulsed laser light, preferably exhibit a repetition frequency of 10 kHz to 250 kHz. By controlling the repetition frequency of the first laser light and / or the second laser light, the first laser light and / or the second laser light can affect the rate of sweeping at least one region of the semiconductor layer.

In another preferred manner, the geometric half width of the strip-shaped first laser light and / or the second laser light is 2 μm to 10 μm, perpendicular to the longitudinal direction of the strip, but preferably 5 μm to 6 μm.

The process of irradiating the semiconductor layer can be used for line laser beam systems and / or laser spot laser systems. As a result, in the case of the first laser light and / or the second laser light, this laser light may be a laser beam projected in a line (strip) or may be a focused laser spot.

The above-mentioned object of the invention is also achieved by a device for irradiating a semiconductor layer, which device comprises first irradiation means adapted to irradiate at least one surface area of the semiconductor layer with a first laser light, and And a second irradiating means adapted to irradiate the at least one surface area of the semiconductor layer with at least one second laser light, wherein the first irradiating means and the second irradiating means comprise the first laser light and the second irradiating means. Laser light only sweeps the at least one surface area of the semiconductor layer once in one direction in succession in time, the first irradiating means generating the first laser light having a lower emission intensity than the second laser light Let's do it.

The apparatus for irradiating the semiconductor layer may also represent means for controlling the temporal separation and / or spatial separation between the first laser light and the second laser light.

In a more preferred manner, the device for irradiating the semiconductor layer is characterized in that at least one speed at which the first laser light and / or the second laser light is moved relative to the semiconductor layer, ie the first laser light and / or the second laser light, Means for controlling at least one speed of sweeping at least one region of the semiconductor layer.

The device for irradiating the semiconductor layer may also represent a laser generating a laser beam, and a beam-splitter for generating two laser beam portions having different radiation intensities from the laser beam.

The beam splitter may preferably be configured to adjust the radiation intensity of the two laser beam portions.

The apparatus for irradiating the semiconductor layer may represent a projection lens for focusing two laser beam portions such that the first laser light and the second laser light are formed.

According to another development of the invention, the device for irradiating a semiconductor layer may represent an optical body for aiming the first laser light and the second laser light.

The invention will become apparent from the following description with reference to the accompanying drawings, based on the illustrated exemplary embodiments.

1 shows illustratively an embodiment of an apparatus for irradiating a semiconductor layer.

Such a device comprises a laser light source 10, a beam splitter 13, a mirror 16, and a projection lens 19. In the case of the laser light source 10, this is a diode-pumped Yb: YAG laser. The laser 10 generates a pulsed laser beam 21 having a repetition frequency between 10 kHz and 250 kHz. In the case of the laser beam 21, this is a single laser beam with a wavelength of 515 nm. The laser beam 21 strikes the beam splitter 13. In the case of the beam splitter 13, this may be a beam-intensity splitter. The incident laser beam 21 is divided into a transmission portion 25 and a reflection portion 33 by the beam splitter 13. In the case of the transmissive portion 25 and the reflective portion 33, this may in each case be a Gaussian ray bundle or Gaussian line beam (in particular having axial homogeneity with respect to the line). The transmissive portion 25 passes through the beam splitter 13 without being reflected and impinges on the projection lens 19, which projects the transmissive portion 25 onto the amorphous silicon layer 30. . In the case of the amorphous silicon layer 30, this is a thin silicon film. The silicon film is placed on a glass substrate (not shown). The projection lens 19 is a lens unit that realizes Gaussian focusing of the incident ray bundles 25, 33.

The portion 33 reflected from the beam splitter is reflected against the mirror 16, which reflects the reflective portion 33 onto the projection lens 19. The projection lens 19 focuses the reflective portion 33 onto the amorphous silicon layer 30. The irradiated surface of the amorphous silicon layer 30 coincides with the imaging plane of the laser beams 27 and 35.

In addition to dividing the laser beam 21 into portions having different radiation directions, the beam splitter 13 also establishes the radiation intensity of the transmission portion 25 and the radiation intensity of the reflective portion 33. In the present exemplary embodiment, the radiation intensity of the laser beam 21 is such that 30% of the radiation intensity of the laser beam 21 is supplied to the reflective portion 33 and 70% of the radiation intensity of the laser beam 21 is obtained. It is divided by the beam splitter 13 to be supplied to the transmission portion 25. As a result, two laser beams 27 and 35 having different radiant intensities can be generated using the device shown to irradiate the semiconductor layer. In this case, the laser beam 35 exhibits a lower radiation intensity than the laser beam 27.

Moreover, the two laser beams 27, 35 are projected onto the amorphous silicon layer 30 with a spatial separation gap a defined spatially separated from each other. The separation interval a depends in particular on the orientation of the optical elements constituted by the beam splitter 13, the mirror 16, and the projection lens 19, and the projection lens 19 and the amorphous silicon layer ( 30) depends on the separation gap b). All of the beam axes of the apparatus shown in FIG. 1 are in a plane.

As a result, using the apparatus shown in FIG. 1, two laser beams 27 and 35 having different radiation intensities can be generated from one laser beam 21, which are separated from each other, i. It can be projected onto the amorphous silicon layer 30 at a separation gap (a) determined at.

In order to change the ratio of the radiation intensity of the laser beam 27 to the radiation intensity of the laser beam 35, another beam splitter with different splitting ratios may be used. For example, the beam splitter 13 shown in FIG. 1 having a split ratio of 70:30 may be replaced with a beam splitter having a split ratio of 20:80.

Moreover, the laser 10 can be designed such that the radiation intensity of the laser beam 21 can be changed, so that the radiation intensity of the laser beams 27 and 35 can additionally be changed.

The laser beams 27 and 35 exhibit a wavelength of 515 nm. While irradiating amorphous silicon with laser light in the green spectral region, it can also be considered that the absorption of green laser light into silicon varies greatly with temperature. As a result, the laser beams 27 and 35 can be controlled in accordance with the temperature of the semiconductor layer to be irradiated.

The separation interval a between the laser light 27 and the laser light 35 is the position of one or more of the components consisting of the beam splitter 13, the mirror 16, and the projection lens 19. May be mechanically repositioned (eg, rotating, swiveling, or displacing). In order to increase the separation gap a between the laser beam 27 and the laser beam 35, the separation gap b between the projection lens 19 and the amorphous silicon layer 30 may be increased. Another possible method for changing the spatial separation gap a between the laser beam 27 and the laser beam 35 may also be considered. For example, one or more optical units may be provided to deflect one or both of the laser beams 27, 35.

The apparatus shown in FIG. 1 for irradiating the semiconductor layer allows the laser beams 27 and 35 to pass through the amorphous silicon layer 30 in the S1 direction, that is, they sweep (scan the amorphous silicon layer 30 in the S1 direction). It is designed to The laser beams 27 and 35 pass through the amorphous silicon layer 30 in the S1 direction at the same speed. With the amorphous silicon layer 30 fixed, the entire device (ie, all components 10, 13, 16, and 19) is moved in the S1 direction, so that the laser beams 27 and 35 can pass in the S1 direction. . However, the amorphous silicon layer 30 may also be moved in a direction opposite to the S1 direction with the device fixed. The entire device may also rotate clockwise. It is also possible to use additional optics (not shown) that project the laser beams 27 and 35 onto the amorphous silicon layer 30 while moving in the S1 direction.

FIG. 2 shows the radiation intensity distribution of the two laser beams 27 and 35 shown in FIG. 1. In this figure, the level of radiation intensity is shown on the I axis for the local distribution on the X axis.

The radiation intensities of the laser beams 27 and 35 are distributed in a substantially Gaussian form in the scan direction. The maximum radiation intensity I2 of the laser beam 35 is less than the maximum radiation intensity I1 of the laser beam 27. In FIG. 2, the ratio of radiation intensity I2 to radiation intensity I1 is approximately 0.3. The radiation intensity maximums of the laser beams 27 and 35 represent the spatial separation gap a with respect to each other. The laser beams 27 and 35 move simultaneously at a predetermined speed in the S1 direction along the amorphous silicon layer 30 shown in FIG. 1. As a result, the laser beam 35 irradiates a predetermined area of the amorphous silicon layer 30 before the laser beam 27. By irradiating the amorphous silicon layer 30 with two laser beams 27 and 35, the layer is homogeneously converted to polycrystalline silicon.

3 diagrammatically shows the irradiation of an amorphous silicon layer using two laser beams.

In the case of laser beams 27 and 35, this is the laser beam shown in FIG. 2. The laser beam 35 precedes the laser beam 27 by the separation interval a. The laser beams 35 and 27 pass through the amorphous silicon layer 30 in the S1 direction from left to right. First pass from left to right, ie start at the upper left corner of the amorphous silicon layer 30 and end at the upper right corner of the amorphous silicon layer 30.

After the two laser beams 27 and 35 have passed through the amorphous silicon layer 30 once completely from left to right, in the direction S2 which is the opposite direction of the direction S1, ie from right to left, the amorphous silicon just below the first section. Pass through certain sections or strips of layer 30. For this purpose, the orientation of the laser beam is transposed so that the laser light beam 35 'is now placed in front of the laser light beam 27'. The laser beam 35 'corresponds to the laser beam 35 and the laser beam 27' corresponds to the laser beam 27, that is, the laser beam 35 'is lower than the laser beam 27'. It shows the radiation intensity. As a result, the laser beams 35 'and 27' pass through the amorphous silicon layer 30 from the right to the left, i. The width of the section of the amorphous silicon layer 30 irradiated each time the laser beam passes (the direction perpendicular to the directions S1 and S2) depends on the width of the laser beams 35 and 27. The laser beams 35 and 27 optionally have the same width.

After the laser beams 35 'and 27' have completely passed the amorphous silicon layer 30 in the S2 direction, the orientation of the laser beam is changed back to the initial orientation (laser beams 27 and 35) and left in the S1 direction. The third pass is to the right from. In space, the third part passes just below the second part. Changes in the unidirectional directions S1 and S2 and changes in the orientation of the laser beams 35, 27 and the laser beams 35 ′, 27 ′, relative to one another, cause the entire amorphous silicon layer 30 to be irradiated at least twice from top to bottom. Until it happens. The irradiation of another amorphous silicon layer can then be carried out.

The present invention is not limited to passing the laser beam only in the direction shown in FIG. 3. For example, such irradiation may also begin at the lower right end of the amorphous silicon layer 30. The laser beam may pass through the amorphous silicon layer 30 in helical form or along a circle.

FIG. 4 schematically shows another embodiment of an apparatus for irradiating the semiconductor layer shown in FIG. 1. In FIG. 1 and FIG. 4, the same components are denoted by the same reference symbols, and new descriptions for these components are omitted. Using the apparatus shown in FIG. 4, it is possible to change the orientation of the laser beams by changing the orientation of the laser beams.

The device shown in FIG. 4 differs from the device shown in FIG. 1 in that another mirror 40 is provided. Moreover, the beam splitter 13 is designed to be rotatable or pivotable. The beam splitter 13 can rotate or pivot around an axis perpendicular to the beam axis of the laser beam 21 of the laser 10 and perpendicular to the plane of the drawing plane. Thus, the beam splitter 13 can rotate or pivot from the position shown in FIG. 1 to the position shown in FIG. 4.

As in the apparatus of FIG. 1, the laser 10 generates a laser beam 21, which strikes the beam splitter 13. The beam splitter 13 splits the laser beam 21 into a transmission portion 25 'and a reflection portion 33'. However, in the apparatus shown in FIG. 4, the reflective portion 33 ′ is reflected relative to the mirror 40 rather than the mirror 16. The mirror 40 reflects the reflective portion 33 'to the projection lens 19, and the projection lens 19 focuses the reflective portion on the amorphous silicon layer 30 as the laser beam 35'.

As in the apparatus shown in FIG. 1, the transmissive portion 25 ′ is projected on the amorphous silicon layer 30 as a laser beam 27 ′ by the projection lens 19. The laser beams 27 'and 35' irradiate the amorphous silicon layer 30 at a predetermined separation gap a from each other.

The beam splitter 13 is such that 30% of the radiation intensity of the laser beam 21 is supplied to the reflective portion 33 'and 70% of the radiation intensity of the laser beam 21 is supplied to the transmission portion 25'. The radiation intensity of the laser beam 21 is divided. In comparison with FIG. 1, in the apparatus shown in FIG. 4, the orientations of the laser beams 27 and 35 are switched. If the light beams 27 'and 35' projected onto the amorphous silicon layer 30 move in the S2 direction, the light beam 35 'with lower emission intensity is light beam 27 with higher emission intensity. ') Is ahead.

As a result, using the apparatus shown in FIG. 4, as shown in FIG. 3, the laser beam can alternately pass through the amorphous silicon layer 30, ie from left to right and right to left without interruption. have. In addition to moving the laser beams 35, 27 and 35 ′, 27 ′ in the S1 direction and the S2 direction, the apparatus shown in FIG. 4 has an upward or upward orientation of the laser beams 35, 27, 35 ′, 27 ′. Configured to shift downward. As a result, the device shown in FIG. 4 can move the laser beams 35, 27 and 35 ′, 27 ′ in all directions on the amorphous silicon layer 30. For this purpose, the apparatus shown in FIG. 4 represents a suitably designed mechanical handling device or optical deflection device (not shown).

 The continuously advancing laser beams 35, 27 and 35 ′, 27 ′ act as a double exposure of the amorphous silicon layer 30 such that the time elapsed from the first exposure until the second exposure occurs, It can be established by the separation gap a between the beams 35, 27 and 35 ', 27' and the speed of the laser beams (so-called feed speed).

The feed rate is obtained by multiplying each feed distance of the laser beams 35, 27 and 35 ', 27' per laser pulse by the repetition frequency of the laser, called the repetition rate. As a result, the time between the two exposures is equal to the separation interval between the two beams divided by the speed of travel.

5 shows the relationship between the repetition frequency (ie repetition rate) of a laser light beam and the temporal separation interval between two irradiations. In particular, for three different separation spacings (a) between two irradiations (which are denoted by curves 50, 55, and 60), the time between two irradiations (if the transfer distance per laser pulse is 1 μm) The unit is ms) and is shown for the repetition frequency (unit is kHz). The separation interval a between the two exposures is 10 μm for curve 50, 100 μm for curve 55 and 1000 μm for curve 60.

As is apparent from FIG. 5, for a repetition frequency of approximately 200 kHz and at a transport distance of 1 μm per pulse, when the spatial separation gap a between the two exposures is 10 μm (curve 50), the first exposure And the second exposure is 50 ms. If the spatial separation interval between the two exposures is greater (see curves 55 and 60), a few ms temporal separation between the two exposures is possible. As a result, in particular the temporal separation between exposures can be controlled by controlling the transport distance and / or the repetition frequency. In principle, two exposures may be controlled such that they intersect spatially.

In the case where the temporal separation between two exposures is small, the irradiated semiconductor layer (eg, amorphous silicon layer) is not cooled back to room temperature. This allows the use of additional absorption effects.

Using the present invention, in particular, the uniformity of the polycrystalline silicon layers can be increased. In addition, the surface of the semiconductor layer becomes less rough.

The increase in the uniformity of the polycrystalline structure of the semiconductor layer and the less roughness of the surface of the semiconductor layer occur both in the case of the so-called full melting process and in the case of the partial melting process.

In the case of a complete melting process, the semiconductor layer (eg amorphous silicon layer) is irradiated with laser light indicating a relatively high energy density (eg 800 mJ / cm 2). Irradiation with the laser beam of high energy density results in the melting of the semiconductor layer completely, ie to the glass surface located below the semiconductor layer. If the laser light is a pulsed laser beam that exposes the semiconductor layer only for a short time (eg 100 ns to 1000 ns), then the semiconductor layer also melts for a short time, and the side of the semiconductor layer solidifies during cooling of the semiconductor layer. Lateral crystal growth occurs.

In connection with the complete melting process, FIG. 6 shows an amorphous silicon layer 70 exhibiting a thickness of 50 nm. The area 75 of the amorphous silicon layer 70 is exposed (pre-exposure) by a laser beam having a low radiation intensity, and subsequently exposed by a laser beam having a high radiation intensity (main exposure Whereas, region 80 is only exposed (main exposure) with a laser beam of high radiation intensity.

Pre-exposure occurs at an energy density of 300 mJ / cm 2, and main exposure occurs at an energy density of 800 mJ / cm 2. The transport distance per laser beam pulse is 1 μm, the geometric half width of the laser beam in the scan direction is 6 μm, and the wavelength of the laser beam is 515 nm. The laser beam is generated at a repetition frequency of 100 kHz. As is apparent from FIG. 6, twice exposed area 75 is less rough than only once exposed area 80. The twice exposed region 75 also exhibits higher uniformity than the once exposed region 80.

In contrast to a full melting process, in the case of a partial melting process, the semiconductor layer is irradiated with laser light exhibiting a relatively low energy density (eg 500 mJ / cm 2). In this case, the semiconductor layer is only partially melted by irradiation with laser light. During the cooling after irradiation, the crystals in the non-melt regions of the semiconductor layer grow vertically upwards.

Regarding the partial melting process, FIG. 7 shows an amorphous silicon layer 85 exhibiting a thickness of 50 nm. Region 95 of amorphous silicon layer 85 is continuously exposed to a laser beam with an energy density of 200 mJ / cm 2 and a laser beam with an energy density of 500 mJ / cm 2, while region 90 is only 500 Only the laser beam with an energy density of mJ / cm 2 is exposed. The feeding distance per laser beam pulse is 1 mu m, the half width of the laser beam is 6 mu m, and the wavelength of the laser beam is 515 nm. Laser beams are generated at a repetition frequency of 100 kHz. It is clear from FIG. 7 that the area 95 exposed twice is less rough than the area 90 exposed only once. In addition, twice exposed region 95 exhibits higher uniformity than once exposed region 90.

8 schematically shows a laser system with a device for irradiating a semiconductor layer. The device shown in FIG. 1 for irradiating the semiconductor layer is integrated in the laser system shown. Like elements are denoted by like reference numerals.

The laser 10 generates a laser beam 21. The laser beam 21 passes through the telescope 105, is reflected on the mirror 110, passes through cylindrical-lesns arrays 115, and strikes the beam splitter 13. The beam splitter 13 splits the laser beam into a transmission portion 25 and a reflection portion 33.

The transmissive portion 25 passes through a first condenser lens 120 and is reflected on two mirrors 125 and 130, passes through a second condenser lens 135, and has a focusing lens having an intermediate focus. (focusing lens) 140, once again reflected on mirror 145, and is projected on a semiconductor layer (not shown) by laser lens 27 as imaging lens 150.

Reflecting portion 33 is reflected from beam splitter 13 onto mirror 16, likewise subsequently passing through optical elements 120, 125, 130, 135, 140, 145 and 150, and the laser beam The semiconductor layer is hit by the laser beam 35 separated by the separation interval a from 27. The laser beams 27 and 35 have orientations that are substantially parallel to each other in the laser system such that each of the laser beams 27 and 35 strikes substantially perpendicularly on the semiconductor layer.

In the laser system shown in FIG. 8, the imaging lens 150 is a cylindrical lens, so only the Gaussian axis (ie, the axis with Gaussian intensity distribution) is reduced and focused onto the semiconductor layer. Alternatively, a spherical objective that projects the laser beams 27 and 35 onto the semiconductor layer to be reduced to an intermediate image can be used.

The laser system shown in FIG. 8 relates to generating a laser beam in line form (line perpendicular to the plane of the drawing). However, the present invention can also be used in laser systems that generate laser light in the form of laser spots. Furthermore, the device shown in FIG. 4 for irradiating a semiconductor layer can be integrated into the laser system shown in FIG. 8.

In the above exemplary embodiments, the present invention becomes apparent on the basis of laser light pulses. However, the present invention is not limited to laser light pulses. Also, the first laser light and the second laser light may be continuous wave laser beams. In such a case, double irradiation can be realized by changing the radiation intensity of the continuous wave laser beam. In this case, sweeping of at least one region of the semiconductor layer is carried out intermittently, ie discontinuously, after the region has been irradiated twice by the same continuous wave laser beam having different radiant intensities.

Using the present invention, the surface roughness and uniformity of thin semiconductor layers, in particular polycrystalline silicon, can be increased. As a result, it is possible to produce much smaller thin film transistors, whereby higher resolution flat panel display screens can be made smaller, lighter, and with a thinner structural design.

1 is a diagram illustrating an apparatus for irradiating a semiconductor layer.

2 is a diagram illustrating the irradiation intensity distribution of two laser beams.

3 is a view showing irradiating an amorphous silicon layer with two laser beams.

4 is a schematic diagram of an apparatus for irradiating the semiconductor layer of FIG. 1 with a scanning direction opposite.

5 is a graph showing the relationship between the repetition frequency of laser light and the temporal separation interval between two irradiations.

6 shows the effect on the silicon layer in the case of a complete melting process.

7 shows the effect on the silicon layer in the case of a partial melting process.

8 is a diagrammatic representation of a laser system with a device for irradiating a semiconductor layer.

Claims (23)

As a method of changing the structure of a semiconductor layer, Irradiating at least one surface area of the semiconductor layer (30) with a first laser light (35); And Irradiating the at least one surface area of the semiconductor layer 30 with at least one second laser light 27, The first laser light 35 and the second laser light 27 sweep the at least one surface area of the semiconductor layer 30 only once in one direction in succession in time, The first laser light 35 exhibits a lower radiation intensity than the second laser light 27, The first laser light (35) and the second laser light (27) are generated from one laser beam (21). The method of claim 1, The semiconductor layer (30) is an amorphous silicon layer. The method of claim 2, And wherein said amorphous silicon layer (30) is at least partially converted to polycrystalline silicon. In one of the preceding terms, The first laser light 35 and the second laser light 27 irradiate the at least one surface area while being separated from each other by a predetermined temporal separation interval and / or spatial separation interval. How to change the structure. In one of the preceding terms, The time interval between the first laser light (35) and the second laser light (27) is between 10 ms and 100 ms, in particular between 1 ms and 5 ms. In one of the preceding terms, Dividing the laser beam 21 into two laser beam portions 25, 33 having different radiation intensities; And Focusing the two laser beam portions 25, 33 so that the first laser light 35 and the second laser light 27 are formed. How to change the structure. In one of the preceding terms, Collimating the first laser light (35) and the second laser light (27). The method according to claim 6 or 7, Altering the distribution of the radiation intensity of the two laser beam portions during dividing the laser light (21); And And changing the direction in which the first laser light 35 and the second laser light 27 sweep the at least one surface area of the semiconductor layer 30. How to change. In one of the preceding terms, The first laser light 35 is of a semiconductor intensity with an emission intensity such that defects in or on the semiconductor layer 30 are removed without evaporation or breakage of hydrogen from the deposited layers of the semiconductor layer 30. Irradiating the layer (30). The method of claim 2, The first laser light 35 modifies the structure of the semiconductor layer, characterized by irradiating the amorphous silicon layer 30 with an emission intensity at which the amorphous silicon layer 30 is only partially converted to polycrystalline silicon. Way. The method of claim 2 or 10, Wherein the thickness of the amorphous silicon layer (30) is greater than 10 nm and exhibits a maximum of 10 [mu] m. In one of the preceding terms, The ratio of the emission intensity of the first laser light 35 to the emission intensity of the second laser light 27 is at least 0.1 and at most 0.9, in particular at least 0.25 and at most 0.45. How to let. In one of the preceding terms, The wavelength of the first laser light 35 and / or the second laser light 27 is 190 nm to 1100 nm, in particular 450 nm to 550 nm, more specifically 515 nm or 532 nm. Method of changing the structure of a semiconductor layer. In one of the preceding terms, And wherein the repetition frequency of the first laser light (35) and / or the second laser light (27) is between 10 kHz and 250 kHz. In one of the preceding terms, The geometric half-width of the first laser light 35 and / or the second laser light 27 is between 2 μm and 10 μm, in particular between approximately 5 μm and 6 μm. How to change the structure of the. In one of the preceding terms, And said first laser light (35) and / or said second laser light (27) are straight-projected or focused laser spots. First irradiating means adapted to irradiate at least one surface area of the semiconductor layer 30 with the first laser light 35; And A process of irradiating the semiconductor layer using second irradiation means adapted to irradiate the at least one surface area of the semiconductor layer 30 with at least one second laser light 27, The first irradiating means and the second irradiating means are characterized in that the first laser light 35 and the second laser light 27 are at least one time of the semiconductor layer 30 once in one direction only continuously in time. Sweeping the surface area, the first irradiating means generates the first laser light 35 having a lower emission intensity than the second laser light 27, and the first laser light 35 and the first 2 The process of irradiating a semiconductor layer, characterized in that the laser light (27) is generated from one laser beam (21). The method of claim 17, And means for controlling and / or adjusting the temporal separation and / or spatial separation between the first laser light (35) and the second laser light (27). The method of claim 17 or 18, And means for controlling and / or adjusting at least one speed at which said first laser light 35 and / or said second laser light 27 move relative to said semiconductor layer. The process of investigation. The method according to any one of claims 17 to 19, A laser (10) for generating the laser beam (21); And And a beam splitter (13) for generating two laser beam portions (25, 33) having different radiation intensities from said laser beam (21). The method of claim 20, Said beam splitter (13) is adapted to adjust the radiation intensity of said two laser beam portions (25, 33). The method of claim 20 or 21, And a projection lens 19 for focusing the two laser beam portions 25, 33 so that the first laser light 35 and the second laser light 27 are formed. The process of irradiating a semiconductor layer to make. The method according to any one of claims 17 to 22, wherein The process of irradiating a semiconductor layer further comprising an optic aiming said first laser light (35) and said second laser light (27).

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