JPH07249592A - Laser treatment method of semiconductor device - Google Patents

Abstract

PURPOSE:To improve crystallizability and to improve uniformity by applying line-shaped pulse laser beams with a relatively small output to a substrate and then applying line-shaped laser beams with a larger output nearly at right angles to the previous laser beams. CONSTITUTION:Initially, line-shaped thin and long laser beams 1 with a relatively small output are scanned and applied to a substrate ABCD from the upper to lower parts. Then, the substrate ABCD is rotated by (n/2+1/4) turn (n: natural number). Then, laser beams 4 which are larger than the initial laser beams 1 are scanned from the upper to the lower parts, thus treating the substrate ABCD and hence maintaining mass-production capability, improving the crystallizability of the substrate, and improving the uniformity of a semiconductor device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device by laser light irradiation, which is excellent in mass productivity, has a small variation, and has a high yield. In particular, the present invention is a semiconductor material which is partially or wholly composed of an amorphous component, or a substantially intrinsic polycrystalline semiconductor material, and further, which is damaged by ion irradiation, ion implantation, ion doping, or the like. The present invention relates to a method for improving crystallinity of a semiconductor material or recovering the crystallinity by irradiating a semiconductor material whose crystallinity is significantly impaired with laser light.

[0002]

2. Description of the Related Art In recent years, much research has been conducted on lowering the temperature of semiconductor device processes. The big reason is
This is because it becomes necessary to form a semiconductor element on an insulating substrate such as glass. In addition, there are demands for miniaturization of elements and multilayering of elements. In the semiconductor process, crystallizing an amorphous component contained in a semiconductor material or crystallizing an amorphous semiconductor material, or crystallinity of a semiconductor material whose crystallinity is lowered due to irradiation of ions It is necessary to recover the crystallinity or to improve the crystallinity though it is crystalline.
Conventionally, thermal annealing has been used for this purpose. When silicon is used as the semiconductor material,
By performing annealing at a temperature of 600 ° C. to 1100 ° C. for 0.1 to 48 hours or longer, crystallization of amorphous, recovery of crystallinity, improvement of crystallinity and the like have been performed.

In general, the higher the temperature, the shorter the treatment time may be, but such a thermal anneal has almost no effect at a temperature of 500 ° C. or lower. Therefore, from the viewpoint of lowering the process temperature, it has been necessary to replace the step conventionally performed by thermal annealing with another means. Laser light irradiation technology is drawing attention as the ultimate low temperature process. That is, the laser light can be applied to only the places where high energy comparable to thermal annealing is required, and it is not necessary to expose the entire substrate to high temperature. Regarding the irradiation of laser light, two methods have been roughly divided and proposed.

The first method uses a continuous wave laser such as an argon ion laser and irradiates a semiconductor material with a spot-like beam. This is a method of crystallizing the semiconductor material by melting the semiconductor material and then slowly solidifying it due to the difference in energy distribution inside the beam and the movement of the beam. Second
Is a method of crystallizing the semiconductor material by irradiating the semiconductor material with a high-energy laser pulse using a pulsed laser such as an excimer laser, instantaneously melting and solidifying the semiconductor material.

[0005]

The problem of the first method is that the processing takes a long time. This is because the maximum energy of the continuous wave laser is limited and the size of the beam spot is at most mm. On the other hand, in the second method, the maximum energy of the laser is very large, so that it was possible to further improve the mass productivity by using a large spot of several cm ² or more. However, with a commonly used square or rectangular shaped beam, it is necessary to move the beam up, down, left and right in order to process one large area substrate.
There was still room for improvement in terms of mass productivity.

In this regard, the beam is deformed linearly,
By making the width of the beam longer than the substrate to be processed and scanning the beam, a great improvement could be achieved. What remained to be solved as a problem was the uniformity of the laser irradiation effect. Since the energy of the pulsed laser changes to some extent for each pulse, it is difficult to uniformly process the entire surface of the substrate. In particular, it was an important unsolved problem to keep the characteristics uniform with respect to the overlapping portion of the laser spots.

[0007]

The present invention has been made for the purpose of solving the problem of non-uniformity. Conventionally, in order to mitigate the above-mentioned nonuniformity, it has been reported that uniformity is improved by performing preliminary irradiation with a weaker pulsed laser light before irradiation with a stronger pulsed laser light. There is. However, also in this case, the overlapping portion of the laser spots was neglected.

The present invention solves this problem by making good use of a linear laser beam. That is,
In the present invention, the substrate is processed by irradiating a linear pulsed laser light having a relatively weak output, and then irradiating a linear laser light having a stronger output at a substantially right angle to the linear laser light. To process. In this case, the absolute values of the output of the first laser light treatment and the output of the subsequent laser light treatment may be determined in consideration of the required uniformity and characteristics.

In order to make the first linear laser light and the subsequent linear laser light substantially orthogonal, the direction of the laser light may be changed, or the orientation of the substrate may be rotated about 1/4 rotation (more generally). , (N / 2 + 1/4) (where n is a natural number) may be rotated. An example of this is shown in FIG. First, by arranging the substrate (square ABCD) as shown in FIG. 1 (A) and scanning the linear elongated laser light 1 from top to bottom,
Perform substrate processing. The output of laser light is assumed to be relatively weak. As shown in FIG.
As indicated by the dotted line in (A), non-uniformity may be observed due to variations in the pulse intensity of the laser light and overlapping of laser spots. The third part of the substrate has not yet been irradiated with laser. (Fig. 1 (A))

Next, the substrate is rotated 1/4 turn. (Fig. 1
(B)) Then, the substrate is processed by scanning the laser beam 4 again from top to bottom. The output of the laser light at this time shall be larger than the output of the first laser light. (Fig. 1 (C))

[0011]

As apparent from FIG. 1, in the present invention,
The non-uniformity introduced by the subsequent laser irradiation is orthogonal to the non-uniformity created by the previous laser irradiation step. Therefore, the non-uniformities cancel each other out and are weakened. Thus, according to the present invention, a semiconductor device having good uniformity can be obtained. In the present invention, the shape of the object to be irradiated with the laser may be a film shape having no pattern, or may be a substantially completed shape of the device.

Since the present invention has features such as using a linear beam and irradiating it linearly and irradiating it twice or more times, a square or rectangular substrate is used. The shape is more efficient than the circular one because there is no wasted laser light. Of course, this does not mean that a circular substrate should not be used in the present invention. FIG. 1 is a very basic example of the present invention.
The present invention has several patterns depending on the configuration of the circuit provided on the substrate to be processed. Examples are shown below,
The present invention will be described in more detail.

[0013]

EXAMPLE FIG. 5 shows a conceptual diagram of a laser annealing apparatus used in this example. The laser light is oscillated by the oscillator 52, amplified by the amplifier 53 via the total reflection mirrors 55, 56, and further introduced into the optical system 54 via the total reflection mirrors 57, 58. The beam of laser light up to that point was a rectangle of about 3 × 2 cm ² , but this optical system 64
Is processed into a slender beam having a length of 10 to 30 cm and a width of 0.3 cm. The energy of the laser beam that passed through this optical system was 1000 mJ / shot at the maximum.

The optical path inside the optical system 54 is shown in FIG. The laser light incident on the optical system 54 passes through a cylindrical concave lens A, a cylindrical convex lens B, a horizontal fly-eye lens C, and a vertical fly-eye lens D. By passing through the fly-eye lenses C and D, the laser light changes from the Gaussian distribution type to the rectangular distribution. Further, the light passes through the cylindrical convex lenses E and F, is focused by the cylindrical lens H via the mirror G (mirror 59 in FIG. 5), and is irradiated onto the sample.

In this embodiment, the distances X ₁ and X ₂ in FIG. 6 are fixed, and the distance X ₃ between the virtual focal point I (this is caused by the difference in the curved surface of the fly-eye lens) and the mirror G. , And the distances X ₄ and X ₅ were adjusted to adjust the magnification M and the focal length F. That is, there is a relation between them: M = (X ₃ + X ₄ ) / X ₅ , 1 / F = 1 / (X ₃ + X ₄ ) + 1 / X ₅ . In this example, the total optical path length X ₆ was about 1.3 m.

By using the beam processed into such a slender beam, the laser processing capability is dramatically improved. That is, after the strip-shaped beam exits the optical system 54, the strip-shaped beam passes through the total reflection mirror 59 and is irradiated on the sample 61. However, since the beam width is longer than the sample width, the sample ends up in one direction. Only move it. Therefore, the sample stage and the driving device 60 have a simple structure and are easy to maintain. Further, the alignment operation when setting the sample is easy. In the present invention, in addition to the movement in one direction, it may have a function of rotating the sample.

On the other hand, if the beam is close to a square, it is not possible to cover the entire surface of the substrate by itself, so the sample must be moved two-dimensionally in the vertical and horizontal directions. . However, in that case, the driving device of the stage becomes complicated, and the alignment must be performed two-dimensionally, which is difficult. In particular, when the alignment is performed manually, the time loss in the process is large and the productivity is reduced. It should be noted that these devices need to be fixed on a stable mount 51 such as an anti-vibration base.

In the present embodiment, a so-called monolithic AMLCD in which peripheral circuits for driving the active matrix circuit are formed on the same substrate in an active matrix type liquid crystal display device (AMLCD) will be described. Among the elements used in such AMLCD, the outline of the manufacturing process of the thin film transistor was as follows. [1] Formation of underlying silicon oxide film and amorphous silicon film on glass substrate, and coating of crystallization accelerator (eg nickel acetate etc.) on amorphous silicon film [2] Solid phase growth Crystallization of the amorphous silicon film by the method (Example of solid-phase growth conditions: 550 ° C, 8 hours, nitrogen atmosphere) [3] Laser treatment of the crystallized silicon film (to improve crystallinity) [4] ] Formation of island-like silicon region by etching of silicon film [5] Formation of gate insulating film (silicon oxide) [6] Formation of gate electrode [7] Source by implantation of impurity element (phosphorus, boron, etc.)
Drain formation [8] Activation of implanted impurities by laser irradiation [9] Formation of interlayer insulator [10] Formation of electrodes on source / drain In this example, the crystallinity of the polycrystalline silicon film was This is related to laser light irradiation [3], which is carried out for the purpose of further enhancing the above.

In such a device, as shown in FIG. 2A, an area 22 of an active matrix circuit, a column driver 23 and a scan driver 24 are provided on the edge of a substrate 21. The circuit configurations of the column driver 23 and the scan driver 24 are almost the same. Generally, as shown in FIG. 3, a large number of thin film transistors (TFTs) are formed in the longitudinal direction of the driver region. (Fig. 3 shows a TFT of a column driver analog switch. This TFT has a large channel width (about 80
0 μm)

FIG. 2 shows a first example of this embodiment. First, as shown in FIG. 2B, an elongated linear laser beam 2
Laser processing was carried out by scanning No. 5 from the top to the bottom of the figure. Laser irradiation was performed in the atmosphere, and the substrate temperature was 200 ° C. Kr for laser
An F excimer laser (wavelength 248 nm) was used. The oscillation frequency of the laser was 10 Hz, the energy density of the laser light was 200 mJ / cm ² , and the scanning speed of the laser light was 3 mm / s. As a result, the laser beam is 300
It will shift by μm. Beam width is 0.3m
Since it is m, about 10 shots of laser light will be emitted per location.

After that, the substrate is rotated clockwise by 90 °. (FIG. 2 (C)) Then, scanning is performed again from the top to the bottom of the drawing by laser light to perform laser processing. Laser irradiation was performed in the atmosphere, and the substrate temperature was 200 ° C. At this time, the laser oscillation frequency and scanning speed are the same as those of the previous laser irradiation, and only the energy density is 300 mJ.
/ Cm ² . (Fig. 2 (D))

The final laser irradiation has a large influence on the characteristics of the semiconductor device because the energy density of the laser is large. Although the present invention significantly reduces laser variability, it is still not a complete solution. For example, look at how the lasers overlap. Figure 3
Shows the state of the column driver. In the column driver, the first laser irradiation causes an overlap in the region indicated by the alternate long and short dash line in the figure. In the subsequent laser irradiation, the laser beam moves in the longitudinal direction of the column driver, so that the region shown by the dotted line in the drawing overlaps.

Particularly in the subsequent laser irradiation, since the energy density is large, the influence on the TFT is large, and it is expected that the variation of the energy for each shot of the laser causes a large variation in the characteristics of the adjacent TFT. Actually, this fluctuation is suppressed to a sufficiently small level by the first preliminary laser irradiation, but the threshold voltage of 0.02 V or more is required in the adjacent TFT in the case where the analog switch such as the column driver is used. There should be no difference. From this point of view, the method shown in FIG. 2 is not preferable because the threshold voltage of the TFT of the column driver may vary greatly. Therefore, a method as shown in FIG. 4 can be considered.

First, the substrate is set in the same direction as that shown in FIG. In the figure, 31 is a substrate, 32 is a region of an active matrix circuit, 33 is a column driver, 34
Is a scan driver. (FIG. 3 (A)) Then, this is rotated 90 ° in the clockwise direction. (Fig. 3
(B)) In this state, laser processing is performed by scanning the laser beam 35 from the top to the bottom of the drawing. The conditions of laser irradiation were the same as in the case of FIG. That is, the oscillation frequency of the laser is 10 Hz, the energy density of the laser light is 200 mJ / cm ² , and the scanning speed of the laser light is 3 mm.
/ S. Laser irradiation was performed in the atmosphere, and the substrate temperature was 200 ° C. (Fig. 3 (C))

After that, the substrate was rotated counterclockwise.
(FIG. 3D) Then, laser processing was performed by scanning the laser beam 35 from the top to the bottom of the drawing. The laser irradiation conditions are laser energy density of 300 mJ / c.
The laser irradiation conditions were the same as those described above except that m ² was used. (FIG. 3 (E)) In this case, in the first laser irradiation, although there is an overlap like the region shown by the dotted line in FIG. 3 with respect to the column driver, when the laser light of larger energy is irradiated. Can overlap in the area indicated by the alternate long and short dash line in FIG. Therefore, variations in TFT can be significantly suppressed.

On the other hand, in the scan driver, it may be considered that the problem in the column driver in the method of FIG. However, the scan driver does not have an analog switch like a column driver, and the threshold variation of adjacent TFTs is about 0.1 V, which is sufficient. The method shown in 1) is satisfied. By further developing the present invention as described above, it is possible to further improve the uniformity of the semiconductor device. In this embodiment, the case of improving the crystallinity by laser irradiation is shown, but the same can be done in the step [8] of activating the source / drain regions after the introduction of impurities.

[0027]

According to the laser irradiation technique of the present invention, it is possible to improve the uniformity of semiconductor devices while maintaining mass productivity. INDUSTRIAL APPLICABILITY The present invention can be applied to all laser processing processes used in semiconductor device processes.
In terms of improving the uniformity of the threshold voltage of the FT, the effect is large when used in the laser irradiation process on the polycrystalline silicon film as described in the examples. In addition to the above steps, it is effective to use the present invention in the step of activating the impurity element of the source / drain in the sense that the field effect mobility of the TFT or the uniformity of the on-current is increased. As described above, the present invention is considered to be industrially useful.

[Brief description of drawings]

FIG. 1 illustrates the concept of the present invention.

FIG. 2 shows a laser processing method according to an embodiment.

FIG. 3 shows how the analog switch TFTs of the column driver of the embodiment are arranged.

FIG. 4 shows a laser processing method according to an embodiment.

FIG. 5 shows a conceptual diagram of a laser annealing apparatus used in Examples.

FIG. 6 shows a conceptual diagram of an optical system of a laser annealing apparatus used in Examples.

[Explanation of symbols]

1, 4 Laser spot (linear laser beam) 2 Laser-treated area 3 Laser-untreated area 21, 31 Substrate 22, 32 Active matrix circuit area 23, 33 Column driver 24, 34 Scan driver 25, 35 Laser Spot (linear laser beam) 51 Optical mount 52 Laser device (oscillation stage) 53 Laser device (amplification stage) 54 Beam shaping optical system 55-59 Total reflection mirror 60 Sample stage and drive mechanism 61 Sample (glass substrate)

Claims (6)

[Claims] 1. A first step of irradiating a substrate on which a semiconductor device is formed or a substrate on which an object to be a semiconductor device is formed with a linear laser beam while scanning the substrate (n / 2 + 1/4) rotation (n is a natural number), and a linear laser beam having a larger energy density than that of the laser beam used in the first step is applied to the substrate in the same direction as in the first step. And a third step of irradiating while irradiating the semiconductor device with the laser beam. 2. The laser processing method for a semiconductor device according to claim 1, wherein the substrate has a rectangular shape. 3. A first step of irradiating a silicon film formed on a substrate with a linear laser beam while scanning the substrate, and rotating the substrate by (n / 2 + 1/4) (n is a natural number). A second step; and a third step of irradiating the substrate with linear laser light having a larger energy density than the laser light used in the first step while scanning in the same direction as in the first step. A laser processing method comprising: 4. The laser processing method according to claim 3, wherein the silicon film is irradiated with high-speed ions. 5. The laser processing method according to claim 3, wherein the silicon film is a film crystallized by a solid phase growth method. 6. The laser processing method according to claim 3, wherein the silicon film is in an amorphous state.