JPH10163109A - Light beam annealing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the explosive emission of hydrogen in the annealing of a body to be annealed containing hydrogen, and to perform surely crystallization by annealing. SOLUTION: In a light beam annealing method for performing annealing by the sweeping application of light beams, a first process for applying light beams with a first energy to a hydrogenated body 1 to be annealed and for evaporating hydrogen contained in the body 1 to be annealed, and a second process for crystallizing the body 1 to be annealed by applying light beams with a second energy that is larger than the first energy to the body 1 to be annealed after the first process is conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical beam annealing method, and more particularly to a method for annealing a crystal-containing object containing a volatile substance, that is, a crystallization annealing of a hydrogenated silicon amorphous (a-Si: H) thin film or the like. It relates to a preferred light beam annealing method.

[0002]

2. Description of the Related Art Plasma CVD (Chemical Vapor Depos)
hydrogenated amorphous silicon (hereinafter, referred to as a-Si: H) containing 10 atomic% of hydrogen atoms formed by the above-described method.
By crystallizing the film under normal temperature atmosphere by pulsed laser irradiation with high energy, a high-quality polycrystalline silicon film having high carrier mobility can be manufactured at low temperature. By applying such a technique, a thin film transistor (TFT) made of a polycrystalline silicon thin film becomes 30
(T, Same)
shima and S, Usui; Materials Research Society Sympos
ium Proceedings Vol. 71 (1986) pp. 435-440).

In the case of performing the above-described light beam annealing by pulsed laser irradiation, annealing such as crystallization for an amorphous thin film or annealing for recrystallization of a polycrystalline thin film is performed, as shown in FIG. 1, for example. The spot s of the pulsed laser light is applied to the annealed body 1, for example, a wafer having the a-Si: H amorphous layer 3 formed on the glass substrate 1, by annealing the a-Si: H thin film on the a-Si: H thin film. For example, it is performed by sweeping over the entire region to be subjected to the crystallization process, for example, as shown by an arrow in a zigzag pattern. In this case, in order to obtain an annealing effect such as crystallization or recrystallization over a required depth (thickness) from the surface, the surface must be crystallized or recrystallized, that is, sufficient energy equal to or more than the energy that can be annealed. Requires great energy. However, when the object to be annealed is a material containing a volatile substance, particularly hydrogen, such as the above-described a-Si: H, when pulse laser irradiation with a large energy is performed rapidly, hydrogen of the volatile substance hydrogen Explosive emissions occur, hindering good crystallization or recrystallization. Therefore, annealing of such a material is usually performed a plurality of times, for example, five times, and a sweeping operation is repeated, and as shown in FIG. A method of sequentially increasing the laser energy to, for example, 230 mJ / cm ² is employed.

[0004] However, repeating the sweeping a plurality of times while sequentially changing the energy of the light beam as described above has an industrial problem such as an increase in the annealing time and an increase in the number of pulses.

[0005]

SUMMARY OF THE INVENTION The present invention avoids the explosive release of hydrogen during the above-described annealing treatment of the hydrogenated object to be annealed, and further complicates the operation by repeatedly sweeping the light beam. The purpose of the present invention is to solve problems such as work time and pulse number.

[0006]

The light beam annealing method according to the present invention is a light beam annealing method in which annealing is performed by sweeping irradiation of a light beam. A first step of irradiating a beam to evaporate hydrogen contained in the object to be annealed, and after the first step, irradiating the object to be annealed with a light beam having a second energy larger than the first energy And a second step of crystallizing the object to be annealed.

According to the above-described method of the present invention, as the light beam is swept, the energy of the first step and the second step is gradually increased to the level of the energy capable of performing the desired annealing at the desired depth. As a result, the explosive ejection due to the progressive evaporation of volatile substances, particularly hydrogen, in the object 1 to be annealed is avoided, and a decrease in the crystallinity of the non-uniform crystallization characteristics due to the annealing can be avoided. At the same time, the conventional repeated sweeping of the light beam a large number of times can be limited to one or a small number of times, so that the working time can be shortened and the number of pulses can be reduced even when the light beam is irradiated with pulses. .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, a step of irradiating a hydrogenated object to be annealed with a light beam having a first energy to evaporate hydrogen contained in the object to be annealed, Irradiating the object to be annealed with a light beam having a second energy larger than the first energy to crystallize the object to be annealed.

An example in which a polycrystalline silicon layer is formed in a TFT manufacturing process will be described. in this case,
As shown in FIG. 1 and FIG. 2, an object to be annealed 1 having an amorphous layer 3 such as an a-Si: H layer formed by a CVD method on various substrates 2 such as a glass plate is prepared.

Then, as shown in FIG. 1, for example, a light beam spot s by a laser beam from a XeCl excimer laser is formed on the amorphous layer 3 of the object 1 to be annealed, ie, the a-Si: H layer. In FIG. 1, the trajectory of the zigzag pattern is drawn left and right as indicated by an arrow, and sweeping is performed only once along a parallel line.

In this case, the energy distribution of the light beam spot s is divided into a plurality of stages, for example, seven stages, from the front side to the rear side in the sweep direction of the spot s, and the a-Si: H layer 2 is formed.
Crystallized surface, i.e. from the energy E ₁ for example 170 mJ / cm ² reaches 1400 ° C. to melt, substantially for example up energy E ₇ for example 250 mJ / cm ² can be crystallized over the required thickness for example 1000Å The energy is distributed to the equally divided energies E _{1 to} E ₇ . Then, as shown in FIG. 1, the sweep of the light beam is performed from left to right with respect to odd-numbered sweep lines b ₁ , b ₃ , b ₅ }, and even-numbered sweep lines b ₂ , b ₄ , b ₆ ‥‥
As shown in FIG. 3, when the reciprocating sweeping is performed in two directions such that the spot s is changed from right to left without changing the vertical and horizontal relationship of the spot s, the distribution is symmetrical in both directions. However, when the sweep direction of the light beam is one specific direction, for example, from left to right in the direction of the solid arrow in FIG. 3, the energy distribution is in front of the spot s, that is, In other words, when only the distribution where the spot irradiation starts at each position on the amorphous layer 2 of the body 1 to be annealed has low energy and the energy increases toward the rear, and the sweep direction is reverse, the non- Only the distribution of the reverse inclination shown in the line diagram is assumed.

In order to obtain a spot s having such an energy distribution, the laser beam is generated by changing the light transmittance with respect to the wavelength of the laser beam one-dimensionally from the center to both sides in the sweep direction. It can be obtained by passing through an optical filter F that changes concentrically.

As shown in FIG. 4, for example, this filter F can be formed by laminating filter plates f (f ₁ , f ₂ ‥‥) of the number of filters corresponding to the number of steps of the energy distribution to be obtained. For example, when it is desired to obtain the seven-stage energy distribution symmetrical as shown in FIG. 3, the width (diameter) W ₁ corresponding to the spot width Ws as shown in FIG.
Has a high light transmittance portion h ₁ in the center, the sides or around the filter plates f ₁ having a low light transmittance portion b _1, shown from the inner edge of its high light transmittance portion h _1, in FIG. 3 high light transmittance portion h ₂ a has both sides or peripheral projecting inwardly by the width corresponding to the step width of the energy E ₁ of the first stage is a filter plate f ₂ having a low light transmittance portion b _2, successively each A filter f ₃を having a high light transmittance portion h ₃ ‥‥ h ₇ protruding inward by a width corresponding to the step width of the step and having a low light transmittance portion b ₃ ‥‥ b ₇ on both sides or around the same. It may use an optical filter F by laminating a f _7.

The filter plates f _{1 to} f of this optical filter F
Each low light passing rate of _{7 b 1, b 2, b} 3 ‥‥ b 7 are respectively selecting the transmittance for example, 93%. When a light beam L having a required energy for annealing, for example, a XeCl excimer laser beam is transmitted through the filter F, a stepwise energy distribution shown in FIG.

The laser beam having this energy distribution is swept at a sweep speed of, for example, 5 mm / sec according to the sweep pattern shown in FIG. 1, and a pulse width of, for example, 30 × 10 ^-9 sec, which is sufficiently smaller than the sweep speed. And a pulsed laser beam having a pitch. When the amorphous layer 2 is annealed with a-Si: H in this manner, the inhibition of crystallization and non-uniformity due to the ejection of hydrogen are avoided, excellent crystallization is performed, and fine and uniform crystal grains are formed. The generated polycrystalline Si layer having good carrier mobility was obtained. A drain current I _D − of a so-called thin film transistor TFT in which a field-effect transistor is manufactured on the Si layer, using the drain voltage V _D as a parameter.
Measurement of the gate voltage V _G characteristics exhibited excellent properties as shown in Figure 5.

In the above-described example, the energy of the light beam has a stepwise distribution. However, in some cases, the energy may be a distribution that changes continuously.

In the above-described example, the present invention is applied to the annealing for crystallization of the amorphous layer 2 of a-Si: H. In addition, silicon germanium containing a volatile substance such as hydrogen, The present invention can be applied to various anneals such as crystallization of each amorphous layer of silicon carbide or recrystallization annealing of microcrystalline polycrystal such as a microcrystalline silicon layer.

[0018]

According to the above-described method of the present invention, as viewed from the object 1 to be annealed, at each position to be annealed, as the light beam spot s is swept, its energy distribution gradually, stepwise or continuously. In each part, the energy is increased to the extent that the desired required depth of annealing can be performed, so that the hydrogen evaporation of the volatile substance in the annealed object 1 progresses temporarily by one sweep at each position. Explosive ejection of hydrogen by heat treatment can be avoided, and a reduction in the crystallinity of the crystallization non-uniformity rate due to the annealing treatment can be avoided, and the conventional multiple repetitive sweeps of the light beam can be limited to one or a few. The working time can be shortened, and the number of pulses can be reduced, for example, when the light beam is pulsed.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of a light beam sweep of an example of the method of the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is a light beam energy distribution diagram of an example of the method of the present invention.

FIG. 4 is a sectional view of an example of an optical filter.

5 is a I _D -V _G characteristic diagram of the obtained a TFT by using the present invention method.

FIG. 6 is an explanatory diagram of a conventional method.

[Description of Signs] 1) Annealed object, F} Optical filter

Continuation of the front page (72) Inventor Setsuo Usui 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (1)

[Claims] In a light beam annealing method in which annealing is performed by sweeping irradiation of a light beam, a hydrogenated object to be annealed is irradiated with a first energy light beam, and hydrogen contained in the object to be annealed is A second step of irradiating the object to be annealed with a light beam having a second energy larger than the first energy to crystallize the object to be annealed after the first step And a light beam annealing method.