JP2005039224A - Laser recrystallization method for active layer of low-temperature polycrystalline silicon thin-film-transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser recrystallization method for an active layer of a low-temperature polycrystalline silicon thin-film-transistor. <P>SOLUTION: A silicon spacer (poly-spacer) is formed on the side wall of an active layer of a thin-film-transistor by Anisotropic Plasma Etching with single directivity. A laser transverse direction recrystallization mechanism is provided by the silicon spacer (poly-spacer), and after laser recrystallization is carried out, the shrinkage phenomena or exfoliation phenomena of the active layer are prevented. According to the present invention, an excessive mask is not required but silicon crystal grains in a channel can be enlarged. This allows an element property and the degree of element uniformity to be enhanced, and an effect for saving a process cost to simultaneously be attained. This technique will turn into an important technique in future for a low-temperature polycrystalline silicon thin-film-transistor (LTPS-TFTs) area. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a laser recrystallization method of a low-temperature polycrystalline silicon thin film transistor active layer, and in particular, an extra mask is not required and silicon crystal grains in a channel can be enlarged, thereby improving device characteristics and device uniformity. At the same time, it relates to a method that can achieve the effect of saving process costs.

In general, not only does the price of conventional amorphous silicon thin film transistor liquid crystal displays (a-si TFT LCDs) fall, but low temperature polycrystalline silicon (LTPS) thin film transistor liquid crystal displays have expanded their application area in small dimensions, Polycrystalline silicon thin-film transistor liquid crystal displays are advantageous in various aspects such as analysis, brightness, dimensions, and electromagnetic interference, and are therefore high in mobile terminal equipment such as personal portable information devices, digital cameras, and mobile phones. Occupancy rate is gained.

In the conventional laser annealing low-temperature mixed crystal silicon thin film transistor (LTPS-TFTs) manufacturing steps, first, the transistor active layer is formed after laser recrystallization, so the size of the silicon crystal grain is limited by the thickness of the thin film. In other words, the silicon crystal grains that cannot be enlarged and are non-uniform in size are scattered in the transistor active layer, so that the electrical characteristics of the elements are different and the uniformity is deteriorated, but the transistor active layer is formed. Then, if laser recrystallization is performed, the active layer has a surface tension caused by the melting of the entire silicon thin film.
This method cannot be applied to the production of low temperature mixed crystal silicon thin film transistors LTPS-TFTs.

In addition, since an insulating layer with relatively poor heat transfer efficiency is provided below the active layer of devices such as thin film transistors (TFTs) and MOS field effect transistors (SOI-MOSFETs) on silicon insulating layers, the devices can operate at high currents. when it is, the temperature of the active layer is increased at the moment, since the descent movement of the carrier is in the active layer, by a technician involved, the channel width W, in parallel a large number of small channel widths W _i Natural heat generation effect (Self-heating)
FIG. 7 shows a conventional method for solving the spontaneous heating effect (Self-heating Effect).

The main object of the present invention is to provide a method capable of improving the field effect carrier mobility of low-temperature mixed crystal silicon thin film transistors (LTPS-TFTs) and reducing the difference between the devices, and when this method is used to manufacture a transistor. If the channel width is small, the silicon crystal grains in the channel will be large, and if the transistor that drives the pixel is manufactured, the resolution of the display can be greatly improved, and the process window for laser recrystallization (process The window is widened, the electrical characteristics of the mixed crystal silicon thin film transistor are improved, and the difference between the elements is reduced to improve the uniformity and yield.

Another object of the present invention is to provide a mechanism having a mechanism for triggering lateral recrystallization in molten silicon after continuous wave (CW) excimer or excimer laser annealing. No extra mask is required for the process, field effect carrier mobility is greatly improved and device characteristics are improved, and thick silicon spacer (poly-spacer) shrinks when the active layer is irradiated with laser If the high energy laser is used to scan the dog-bone-shaped active layer in the source-drain direction, the transistor channel can be used. In addition, a unique silicon crystal grain condition is obtained, and a mixed crystal silicon thin film transistor with high performance and good uniformity is obtained. Register can be produced by the present invention, when the channel width W to achieve a large element relatively, by parallel multiple smaller channel widths W _i, can satisfy the needs of each current, thereby slightly larger silicon The self-heating effect of the device can be improved while holding the crystal grains in the channel.

In order to achieve the above object, the present invention provides:
Providing a substrate, step 1;
Step 2 of forming a buffer oxide layer (Buffer Oxide) on the substrate;
Depositing amorphous silicon thin film layer (amorphous silicon) on the buffer oxide layer (Buffer Oxide);
Furthermore, a low-temperature oxide layer (Low) is formed on the amorphous silicon thin film layer (amorphous silicon).
Temperature Oxide) is deposited, and the low temperature oxide layer (Low Temperature Oxide) is used as a stopper for silicon thin film dry etching, a heat retaining layer to prevent heat dissipation during laser annealing, and a silicon spacer after recrystallization ( Step 4, which is regarded as a hard mask for removing silicon-spacer,
Thereafter, the photoresist layer (Photoresist) is used as a hard mask, and the low-temperature oxide layer is completely etched away by anisotropic plasma etching, and then the amorphous silicon thin film layer below is locally etched away,
When the photoresist layer is removed and another amorphous silicon thin film layer is deposited, the amorphous silicon thin film underneath is connected to the amorphous silicon thin film, and anisotropic plasma etching is performed. When the silicon spacer is formed on the edge of the active layer, and then the continuous wavelength laser or excimer laser recrystallization of the amorphous silicon thin film active layer is performed, the silicon crystal grains of the active layer are expanded, and finally the anisotropic plasma Etching to completely remove the low temperature oxide layer above the silicon spacer and the active layer.

  According to the present invention, it is possible to enlarge the silicon crystal grains in the channel without requiring an extra mask, thereby improving device characteristics and device uniformity, and at the same time achieving the effect of saving process costs.

FIGS. 1 to 7 are a conceptual diagram of a cross section in the vertical current direction of the molding of the present invention, a top view as viewed from the opposite position of the transistor of the present invention, a scanning electron microscope (SEM) diagram of the present invention, and a continuous wavelength (continuous) in the present invention. Wave, CW) Conceptual diagram of active layer pattern orientation and laser scanning direction when using laser recrystallization, and the self-heating effect of conventional relatively large channel width transistors (Self-heating)
It is a conceptual diagram of the method of solving Effect. As shown in the drawing, the laser recrystallization method of the low-temperature polycrystalline silicon thin film transistor active layer of the present invention includes:
Providing step 1 and substrate 1;
Step 2 of forming a buffer oxide layer 2 (Buffer Oxide) on the substrate 1;
Amorphous silicon thin film layer 3 (amorphous) on the buffer oxide layer 2 (Buffer Oxide)
step 3 for depositing silicon)
Further, the low-temperature oxide layer 4 (Low
Temperature Oxide) is deposited, and the low-temperature oxide layer 4 is used as a stopper layer for silicon thin film dry etching (Anisotropic Plasma Etching), a heat insulating layer for preventing heat dissipation during laser annealing, or a silicon spacer after recrystallization. (Step 4), which is a hard mask for removing (silicon-spacer),
Thereafter, the low-temperature oxide layer 4 is completely removed by anisotropic plasma etching 8 using the photoresist layer 5 as a hard mask, and then the amorphous silicon thin film layer 3 below is locally removed by etching. Step 5 and
When the photoresist layer 5 is removed and another amorphous silicon thin film layer 3a is deposited, the amorphous silicon thin film 3 under the original is interconnected with the amorphous silicon thin film 3a and is anisotropic. In the plasma etching 8, silicon spacers are formed on the edge of the active layer, followed by continuous wavelength laser or excimer laser recrystallization 9 of the active layer of the amorphous silicon thin film. And a step 6 of completely removing the silicon spacer 7 and the low-temperature oxide layer 4 above the active layer by anisotropic plasma etching 8.

As described above, the silicon spacer may include a spacer composed of a mixed crystalline silicon film and an amorphous silicon film. In addition, the silicon spacer manufactured in Step 6 includes the thin film transistor (TFT) and the active layer edge of the MOS field effect transistor (SOI-MOSFET) on the silicon insulating layer (including filling the active layer edge). In addition, this method can be applied to both high and low temperature processes. In step 6, the edge of the active layer of the MOS field effect transistor (SOI-MOSFET) on the silicon insulating layer of the silicon spacer is fabricated and then laser recrystallized. The main purpose of this silicon spacer is to Make a ladder and recrystallize the silicon thin film laterally. In step 6, the silicon spacer material covered with the sidewall of the active layer of the thin film transistor may be a dielectric (eg, Oxide, Nitride, Metal oxide, etc.) or a metal (eg, aluminum Al, tungsten W, molybdenum Mo, chromium). The material may be replaced with a material such as Cr ...). Finally, after the silicon spacer is selectively removed (or left as it is), the subsequent process is continued. In step 6, the active layer is first recrystallized from the active layer by a method such as excimer laser annealing (ELA), solid phase growth (SPC), or metal induced solid phase growth (MILC). Later, a silicon spacer may be fabricated on the edge of the active layer of the thin film transistor or the MOS field effect transistor (SOI-MOSFET) on the silicon insulating layer.

After the silicon spacer 7 is fabricated at the edge of the active layer amorphous silicon thin film layer 3, it can be recrystallized with respect to the active layer having a dog-bone shape with a high energy continuous wavelength laser, or By recrystallizing 9 by excimer laser annealing, a temperature ladder is created in the active layer, and the silicon crystal grains are expanded (see Fig. 3).
FIG. 4 shows the relative positions of the gate 10 (Gate), the source 11 (Source), and the drain 12 (Drain). As can be seen from FIG. 4, in this process, the silicon spacer 7 is an active layer (amorphous). If the silicon thin film layer 3) surrounds the entire periphery and the subsequent anisotropic plasma etching 8 cannot completely remove the silicon spacer 7, the crystalline characteristics of the silicon spacer 7 are not good. It does not affect the electrical characteristics of the transistor, it is difficult to conduct the silicon spacer 7 by voltage, which is advantageous for current.

FIG. 5 shows the distribution of polycrystal grains (Poly-Si Grains) obtained by excimer laser recrystallization in a channel. According to the present invention, relatively large silicon grains are obtained in a transistor channel. The reason for this is that, after laser irradiation, the entire relatively thin channel region is melted, but in the region where the relatively thick silicon spacer 7 is partially melted and the entire region is melted, This is because the silicon spacer 7 is used as a seed to trigger inward recrystallization, and as can be seen from FIG. 5, no shrinkage deformation phenomenon occurs at the edge of the active layer. In this method, after the entire silicon thin film is melted, the shrinkage effect due to surface tension (Shrinkage
FIG. 6 shows the best situation of the active layer figure orientation and the laser scanning direction when recrystallizing with a continuous wavelength laser in this method, and FIG. This method solves the heat generation effect. In the present invention, by using the above-described method, a relatively large channel width W is changed in parallel with a large number of small channel widths W _i. Therefore, the natural heat generation effect of the element can be improved while holding a slightly large silicon crystal grain in the channel.

According to the above detailed description, those who understand this technology well understand that the present invention achieves the above-mentioned object, so file an application for a patent in accordance with the provisions of the Patent Law.

The above description is merely a better embodiment of the present invention, and does not limit the scope of the present invention. Equivalent modifications and changes may be made in accordance with the scope of the claims and the contents of the present invention. It is included in the claims of the invention.

It is a section conceptual diagram of the perpendicular current direction of fabrication of the present invention. FIG. 2 is a conceptual cross-sectional view in the vertical current direction of the molding of the present invention continued from FIG. 1. FIG. 3 is a conceptual cross-sectional view in the vertical current direction of the molding of the present invention continued from FIG. 2. It is a top view seen from the opposing position of the transistor of invention. It is a SEM (Scanning Electron Microscope) figure of the present invention. In this invention, it is a conceptual diagram of an active layer figure orientation and a laser scanning direction when using continuous wave (continuouswave, CW) laser recrystallization. It is a conceptual diagram of a conventional method for solving a spontaneous heating effect (Self-heating Effect) of a relatively large channel width transistor.

Explanation of symbols

1 Board
2 Buffer oxide layer 3, 3a Amorphous silicon thin film layer
4 Low temperature oxide layer
5 Photoresist layer
7 Silicone spacer
8 Anisotropic plasma etching 9 Continuous wavelength laser or excimer laser recrystallization of active layer of amorphous silicon thin film 10 Gate 11 Source 12 Drain

Claims (8)

Providing a substrate, step 1;
Step 2 of forming a buffer oxide layer (Buffer Oxide) on the substrate;
Depositing amorphous silicon thin film layer (amorphous silicon) on the buffer oxide layer (Buffer Oxide);
Furthermore, a low-temperature oxide layer (Low) is formed on the amorphous silicon thin film layer (amorphous silicon).
Temperature Oxide) is deposited, and the low-temperature oxide layer is used as a stopper layer for silicon thin film dry etching in the post-process, a heat insulating layer that prevents heat dissipation when laser annealing, or a silicon spacer after recrystallization. (Step 4) used as a hard mask to remove (poly-spacer),
Thereafter, the photoresist layer (Photoresist) is used as a hard mask, and the low-temperature oxide layer is completely etched away by anisotropic plasma etching, and then the amorphous silicon thin film layer below is locally etched away,
When the photoresist layer is removed and another amorphous silicon thin film layer is deposited, the amorphous silicon thin film underneath is connected to the amorphous silicon thin film, and anisotropic plasma etching is performed. When the silicon spacer is formed on the edge of the active layer, and then the continuous wavelength laser or excimer laser recrystallization of the amorphous silicon thin film active layer is performed, the silicon crystal grains of the active layer are expanded, and finally the anisotropic plasma Etching to completely remove the low temperature oxide layer above the silicon spacer and active layer by etching, and
A method for laser recrystallization of a low-temperature polycrystalline silicon thin film transistor active layer, characterized in that: 2. The low-temperature multi-layer according to claim 1, wherein the silicon spacer includes a spacer composed of a polycrystalline silicon film and an amorphous silicon film. Laser recrystallization method of crystalline silicon thin film transistor active layer. The silicon spacer manufactured in step 6 further includes a thin film transistor (TFT) and an edge of an active layer of a MOS field effect transistor (SOI-MOSFET) on a silicon insulating layer. A method for laser recrystallization of a low-temperature polycrystalline silicon thin film transistor active layer according to claim 1. In step 6, the edge of the active layer of the MOS field effect transistor (SOI-MOSFET) on the silicon insulating layer of the silicon spacer is fabricated and then laser recrystallized. The main purpose of this silicon spacer is to create a temperature ladder. The method for laser recrystallization of a low-temperature polycrystalline silicon thin film transistor active layer according to claim 1, wherein the method is for producing and recrystallizing a silicon thin film laterally. In step 6, the silicon spacer covered with the sidewall of the active layer of the thin film transistor is a dielectric (eg, Oxide, Nitride, Metal oxide ...) or metal (eg, aluminum Al, tungsten W, molybdenum Mo, chromium Cr ...). 2. The method of laser recrystallization of a low-temperature polycrystalline silicon thin film transistor active layer according to claim 1, wherein the material may be replaced with a material such as 6. The laser reactivation of a low-temperature polycrystalline silicon thin film transistor active layer according to claim 5, wherein the dielectric is selected from an oxide, a nitride, and a metal oxide. Crystal method. 6. The laser recrystallization method of a low-temperature polycrystalline silicon thin film transistor active layer according to claim 5, wherein the metal is selected from aluminum (Al), tungsten (W), molybdenum (Mo), and chromium (Cr). . In Step 6, the active layer is first recrystallized from the active layer by a method such as excimer laser annealing (ELA), solid phase growth (SPC), or metal induced solid phase growth (MILC). 2. The low-temperature polycrystalline silicon thin film transistor active layer according to claim 1, wherein a silicon spacer may be formed on an edge of the active layer of the thin film transistor or the MOS field effect transistor (SOI-MOSFET) on the silicon insulating layer. Laser recrystallization method.