JP3054310B2 - Laser processing method for semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, active research has been made on lowering the temperature of semiconductor device processes. The main reason is that
This is because a semiconductor element has to be formed on an insulating substrate such as glass. In addition, there is a demand accompanying miniaturization of elements and multilayering of elements. In a semiconductor process, the crystallization of an amorphous component or an amorphous semiconductor material contained in a semiconductor material, or the crystallinity of a semiconductor material that was originally crystalline but has been reduced in crystallinity due to irradiation with ions. In some cases, it is necessary to recover the crystallinity or to improve the crystallinity, although the crystallinity may be required.
Conventionally, thermal annealing has been used for such a purpose. When silicon is used as a semiconductor material,
By performing annealing at a temperature of 600 ° C. to 1100 ° C. for 0.1 to 48 hours or more, amorphous crystallization, recovery of crystallinity, improvement of crystallinity, and the like have been performed.

[0003] In general, the higher the temperature, the shorter the processing time may be. However, at a temperature lower than 500 ° C, there is almost no effect. Therefore, from the viewpoint of lowering the temperature of the process, it has been necessary to replace the step conventionally performed by thermal annealing with another means. Laser light irradiation technology is attracting attention as the ultimate low-temperature process. In other words, laser light can be applied only to a required portion with high energy equivalent to thermal annealing, and it is not necessary to expose the entire substrate to a high temperature. Regarding the irradiation of laser light, roughly two methods have been proposed.

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

[0005]

The problem with the first method is that it takes a long time to process. This is because the maximum energy of the continuous wave laser is limited, and the beam spot size is at most mm. On the other hand, in the second method, the maximum energy of the laser was very large, and therefore, mass productivity could be further improved 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 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,
Significant improvement was achieved by making the width of the beam longer than the substrate to be processed and scanning this beam. What remained to be improved was the uniformity of the laser irradiation effect. Since the energy of the pulse oscillation laser varies to some extent for each pulse, it has been difficult to uniformly process the entire surface of the substrate. In particular, it has been an important unsolved problem to keep the characteristics uniform with respect to the overlapping portions of the laser spots.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the problem of non-uniformity. Conventionally, it has been reported that in order to reduce the above-mentioned non-uniformity, uniformity is improved by performing preliminary irradiation with a weaker pulsed laser beam before irradiation with a strong pulsed laser beam. I have. However, also in this case, the overlapping portion of the laser spot has been 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 beam with a relatively weak output, and then, at a substantially right angle to the linear laser beam, by irradiating a linear laser beam with a stronger output. Process. In this case, the absolute values of the output of the first laser beam processing and the output of the subsequent laser beam processing 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 perpendicular to each other, the direction of the laser light may be changed, or the direction of the substrate may be changed by about 1/4 turn (more generally, , (N / 2 + ／) (where n is a natural number). This example is shown in FIG. First, a substrate (square ABCD) is arranged as shown in FIG. 1 (A), and a linear elongated laser beam 1 is scanned from top to bottom.
Performs substrate processing. The output of the laser light is relatively weak. The part 2 irradiated with the laser light has the structure shown in FIG.
As shown by a dotted line in (A), non-uniformity may be observed due to variations in pulse intensity of laser light and overlapping laser spots. Three portions of the substrate have not yet been irradiated with the laser. (Fig. 1 (A))

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

[0011]

As is apparent from FIG. 1, in the present invention,
The non-uniformity caused by the subsequent laser irradiation is orthogonal to the non-uniformity caused by the previous laser irradiation step. For this reason, the non-uniformity is offset and weakened. As described above, 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 a device having a substantially completed device shape.

In the present invention, since a linear beam is used, and the beam is irradiated almost twice or more, and the beam is irradiated almost twice or more, a square or rectangular substrate is used as the substrate. Shapes are more efficient than circular ones because there is no wasted laser light. Of course, this does not mean that a circular substrate must 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 a circuit provided on a substrate to be processed. Examples are shown below,
The present invention will be described in more detail.

[0013]

FIG. 5 is a conceptual diagram of a laser annealing apparatus used in this embodiment. The laser light is oscillated by an oscillator 52, amplified by an amplifier 53 via total reflection mirrors 55 and 56, and further introduced into an optical system 54 via total reflection mirrors 57 and 58. The laser beam up to that time is a rectangle of about 3 × 2 cm ² ,
It is processed into an elongated beam having a length of 10 to 30 cm and a width of 0.3 cm. The energy of the laser beam passing through this optical system was 1000 mJ / shot at 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 these 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, passes through the mirror G (mirror 59 in FIG. 5), is focused by the cylindrical lens H, and is irradiated on 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 (which 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 relationship between them, M = (X ₃ + X ₄ ) / X ₅ , and 1 / F = 1 / (X ₃ + X ₄ ) + 1 / X ₅ . In this example, the total length X ₆ of the optical path was about 1.3 m.

By using a beam processed into such an elongated beam, the laser processing ability has been dramatically improved. That is, after the strip-shaped beam exits the optical system 54 and irradiates the sample 61 through the total reflection mirror 59, the beam width is longer than the sample width. You only have to move it. Accordingly, the sample stage and the driving device 60 have a simple structure and are easy to maintain. Further, the operation of alignment (alignment) when setting the sample is also easy. In the present invention, it is only necessary to have a function of rotating the sample in addition to the movement in one direction.

On the other hand, if the beam is nearly square, it is impossible to cover the entire surface of the substrate by itself, and 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 it is difficult to perform positioning in two dimensions. In particular, when the alignment is performed manually, time loss in the process is large and productivity is reduced. These devices need to be fixed on a stable gantry 51 such as an anti-vibration table.

In this embodiment, a so-called monolithic AMLCD in which a peripheral circuit for driving an active matrix circuit is formed on the same substrate in an active matrix liquid crystal display (AMLCD) will be described. Among the elements used in such an AMLCD, an outline of a manufacturing process of a thin film transistor was as follows. [1] Formation of a base silicon oxide film and an amorphous silicon film on a glass substrate, and application of a crystallization promoter (eg, nickel acetate, etc.) on the amorphous silicon film [2] Solid phase growth Of amorphous silicon film by solidification (example of solid phase growth conditions: 550 ° C., 8 hours, nitrogen atmosphere) [3] Laser treatment of 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 / injection of impurity element (phosphorus, boron, etc.)
Formation of drain [8] Activation of implanted impurities by laser irradiation [9] Formation of interlayer insulator [10] Formation of electrode on source / drain In this example, the crystallinity of the polycrystalline silicon film was [3] laser beam irradiation performed for the purpose of further enhancing the laser beam irradiation.

In such an apparatus, 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, a large number of thin film transistors (TFTs) are formed in the longitudinal direction of the driver region as shown in FIG. (FIG. 3 shows a TFT of an analog switch of a column driver. 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.
5 was scanned from top to bottom in the figure to perform laser processing. Laser irradiation was performed in the air, and the substrate temperature was 200 ° C. Kr as laser
An F excimer laser (wavelength 248 nm) was used. The laser oscillation frequency 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. 0.3m beam width
m, so that about 10 shots of laser light are irradiated at one location.

Thereafter, the substrate is rotated 90 ° clockwise. (FIG. 2 (C)) Then, the laser beam is again scanned from the top to the bottom in the figure to perform laser processing. Laser irradiation was performed in the air, and the substrate temperature was 200 ° C. In this case, the laser oscillation frequency and scanning speed were the same as those of the previous laser irradiation, and only the energy density was 300 mJ.
/ Cm ² . (FIG. 2 (D))

The last laser irradiation has a large effect on the characteristics of the semiconductor device because the energy density of the laser is large. Although the present invention has significantly reduced laser variability, it is still not a complete solution. For example, look at how lasers overlap. FIG.
Shows a column driver. In the column driver, the first laser irradiation causes an overlap in a region indicated by a dashed line in the figure. In the subsequent laser irradiation, since the laser beam moves in the longitudinal direction of the column driver, an overlap occurs in a region indicated by a dotted line in the drawing.

In particular, since the energy density is large in the subsequent laser irradiation, the influence on the TFT is large, and it is expected that the variation in the energy of each shot of the laser will greatly change the characteristics of the adjacent TFT. In practice, this variation is kept sufficiently small by the initial preliminary laser irradiation, but even if an analog switch such as a column driver is used, a threshold voltage of 0.02 V or more is applied to an adjacent TFT. There must be no difference. From such a viewpoint, the method as shown in FIG. 2 is not preferable because the threshold voltage of the TFT of the column driver may greatly vary. Therefore, a method as shown in FIG. 4 can be considered.

First, the substrate is set in the same direction as in FIG. In the figure, 31 is a substrate, 32 is an active matrix circuit area, 33 is a column driver, 34
Is a scan driver. (FIG. 3 (A)) And this is rotated 90 degrees clockwise. (FIG. 3
(B) In this state, laser processing is performed by scanning the laser beam 35 from the top to the bottom of the figure. The conditions for laser irradiation were the same as in 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 air, and the substrate temperature was 200 ° C. (FIG. 3 (C))

Thereafter, 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 figure. Laser irradiation conditions are as follows: laser energy density is 300 mJ / c
except that the m ² was the same as the previous laser irradiation conditions. (FIG. 3 (E)) In this case, in the first laser irradiation, although the column driver overlaps as shown by the dotted line in FIG. 3, when the laser light of higher energy is irradiated, Can overlap the area indicated by the dashed line in FIG. Therefore, variation in TFT is 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, in a scan driver, there is no analog switch like a column driver, and a variation in the threshold value of an adjacent TFT is about 0.1 V is sufficient. Such a variation can be reduced by a general method of the present invention (for example, FIG. 1). In the method shown in (2). By further developing the present invention, the uniformity of the semiconductor device can be further improved. In this embodiment, the case where the crystallinity is improved by laser irradiation has been described. However, the same operation can be performed in the step [8] of activating the source / drain regions after the impurity is introduced.

[0027]

According to the laser irradiation technique of the present invention, the uniformity of a semiconductor device can be improved while maintaining mass productivity. The present invention can be used for all laser processing processes used for semiconductor device processes.
In terms of improving the uniformity of the threshold voltage of the FT, the effect is great when used in the step of irradiating the polycrystalline silicon film with laser as described in the embodiment. In addition, in order to increase the field effect mobility of the TFT or the uniformity of the on-current, it is effective to use the present invention in the step of activating the source / drain impurity elements in addition to the above steps. Thus, the present invention is considered to be industrially useful.

[Brief description of the drawings]

FIG. 1 illustrates the concept of the present invention.

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

FIG. 3 shows the arrangement of analog switch TFTs in the column driver of the embodiment.

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

FIG. 5 is a conceptual diagram of a laser annealing apparatus used in the example.

FIG. 6 is a conceptual diagram of an optical system of a laser annealing apparatus used in the example.

[Explanation of symbols]

1, 4 laser spot (linear laser beam) 2 laser treated area 3 non-laser treated 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 gantry 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)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/268

Claims (6)

(57) [Claims] 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; 2 + ／) rotation (n is a natural number), and a laser beam used in the first step for the substrate .
A third step of irradiating a linear laser beam having a large energy density while scanning in the same direction as the first step. 2. The method of claim 1, wherein the substrate is rectangular. 3. A first step of irradiating a silicon film formed on a substrate with a linear laser beam while scanning the same, and rotating the substrate by (n / 2 + 1/4) (n is a natural number). A second step, and the laser light used for the substrate in the first step .
A third step of irradiating a linear laser beam having a large energy density while scanning in the same direction as the first step. 4. The method of claim 3, laser treatment wherein the silicon film in which ions are irradiated. 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 method of claim 3, the silicon film is laser treatment wherein the Oh <br/> Rukoto in amorphous.