JPH10150002A - Method for manufacturing semiconductor film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform optimum laser annealing and obtain a highly reliable semiconductor film with less nonuniformity by irradiating the film with pulsed laser beams through an insulating transparent board. SOLUTION: Laser beams projected into an optical system pass through a cylindrical concave lens A, a cylindrical convex lens B, a fly eye lens C in the horizontal direction and a fly eye lens D in the vertical direction. The laser beam distribution changes to rectangular distribution from the previous Gaussian distribution after passing through the fly eye lenses C and D. Furthermore, after passing through the cylindrical convex lenses E and F, the laser beams are focused by a cylindrical lens H through a mirror G. Then, the beams are applied on a sample. The beams are processed into fine and long beams to improve processability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser annealing method which is excellent in reliability and mass productivity, has small variations, and has a high yield. In particular, the present invention relates to a laser annealing method for a coating which has been damaged by ion irradiation, ion implantation, ion doping, or the like, and whose crystallinity has been significantly impaired.

[0002]

2. Description of the Related Art In recent years, active research has been made on lowering the temperature of semiconductor device processes. One of the reasons is
This is because a semiconductor element has to be formed on an insulating substrate such as glass. Laser annealing technology is attracting attention as the ultimate low-temperature process.

[0003]

However, conventionally,
The laser annealing conditions and the like differed depending on each apparatus and the conditions of the coating, and were not sufficiently studied. As a result, there has been a consensus that the laser annealing technology has a very large variation and that it will never be put to practical use. The purpose of the present invention is to present such previously unrecognized conditions,
The goal is to obtain reproducible results by laser annealing.

[0004]

SUMMARY OF THE INVENTION The present inventor has found that a film can be used as a semiconductor in a state where the film is amorphous or very similar in crystallinity is deteriorated due to damage such as ion irradiation, ion implantation and ion doping. We were looking for optimization of laser annealing conditions for the purpose of activating the coatings that could not show the characteristic, but in that case,
We found that the optimum conditions fluctuated not only depending on the energy conditions of the laser beam, but also on the impurities contained and the number of shots of the laser pulse.

In the present invention, the coating to be activated is a coating mainly composed of a group IV element such as silicon, germanium, an alloy of silicon and germanium, and silicon carbide. These coatings are 100 to 10000
Is the thickness. It is known that a laser having a short wavelength of 400 nm or less may be used for laser annealing of these films in consideration of light transmission.

For example, it is generally considered that when the energy density of a laser is high, activation is sufficiently performed and the sheet resistance is reduced. However, in practice, when phosphorus is contained as an impurity, even if such a tendency is apparently obtained, when the impurity is boron,
Conversely, it deteriorates at high energy. Also, when annealing with pulse laser increases the number of pulse shots,
It is believed that the variability of the results will be small,
As the number of shots increases, the morphology of the coating deteriorates,
It became clear that a phenomenon that micro-variation increased also occurred.

It is considered that this is because crystal nuclei grow large in the coating by repeated laser irradiation. As a result, distribution occurs at a size of about 0.1 to 1 [mu] m in a very homogeneous coating film. In particular, it was remarkable in a region where the energy of the laser was large.

In addition, it is necessary that the film is not exposed to the atmosphere at the time of laser annealing, but is covered with a transparent film having a thickness of 3 to 300 nm, typically 10 to 100 nm. Was found. As such a film, silicon oxide or silicon nitride is suitable for the purpose of transmitting a laser beam. However, a film containing silicon oxide as a main material is usually used because this film needs to be used as a gate oxide film. Of course, for the purpose of passivating the mobile ions, phosphorus or boron may be doped into this. If the Group IV coating was not coated with such a transparent coating, the heterogeneity described above was further accelerated.

In order to obtain a flatter (homogeneous) film while satisfying such conditions, the energy density of the irradiated laser beam is set to E [mJ / cm ² ] and the number of shots of the laser pulse is set to N. [Times], it was found that there was a relationship of log ₁₀ N ≦ A (EB). A and B differ depending on the impurities contained in the film. When the impurities are phosphorus, A = −0.02 and B = 350.
When the impurity is boron, A = −0.02, B = 300
Met. In the present invention, a transparent substrate may be used instead of a transparent film. That is, the laser treatment method in this case is a pulse-like laser having a wavelength of 400 nm or less and a pulse width of 50 nsec or less, which is formed on an insulated transparent substrate and is mainly composed of a group IV element and irradiated with high-energy impurity ions. In a laser annealing method for activating a semiconductor by irradiating light, the pulsed laser light is applied to the coating through the insulating transparent substrate, and the energy density E [mJ
/ Cm ² ] and the number N of irradiation pulses, log ₁₀ N ≦ −
A laser processing method having a relationship of 0.02 (E-350). Hereinafter, the present invention will be described in more detail with reference to Examples.

[0010]

In this embodiment, an impurity is introduced into a film (semiconductor film) made of a group IV element to give one of N-type and P-type,
Further, an impurity is introduced into a part of the film by using a mask, and the other of the N type and the P type is given to the part. FIG. 1 shows a conceptual diagram of a laser annealing apparatus used in this embodiment.
The laser light is oscillated by the oscillator 2, and the total reflection mirrors 5, 6
, And is introduced into the optical system 4 via total reflection mirrors 7 and 8. The laser beam up to that time has a rectangular shape of about 3 × 2 cm ² , but the optical system 4 has a length of 10 to 30 cm and a width of 0.3 mm.
It is processed into an elongated beam of about 1 to 1 cm. The energy of the laser beam passing through this optical system is up to 1000 mJ
/ Shot.

The optical path inside the optical system 4 is shown as 5. The laser light incident on the optical system 4 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 9 in FIG. 1), 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. 5 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 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.

Processing into such an elongated beam is as follows:
This is for improving workability. In other words, the strip-shaped beam exits the optical system 4 and is irradiated on the sample 11 via the total reflection mirror 9, but is longer than the width of the sample.
The sample need only be moved in one direction. Therefore, the sample stage and the driving device 10 have a simple structure and are easy to maintain. Further, the operation of alignment (alignment) when setting the sample is also easy.

On the other hand, if the beam is close to a square, it is impossible to cover the entire surface of the substrate by itself. Therefore, 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 1 such as a vibration isolator.

The sample is 100 mm in length and 100 to 300 in width.
mm glass substrates (e.g., Corning 705
No. 9 glass). The laser used was a KrF laser (wavelength 248 nm, pulse width 30 nsec).

An amorphous silicon film (semiconductor film) having a thickness of 100 .ANG.
It was formed to have a thickness of 10,000 (for example, 1000) (100 nm). This was crystallized by annealing at 600 ° C. for 48 hours. Then, this was patterned into an island shape. further,
A silicon oxide film having a thickness of 70 nm was formed by a sputtering method, and phosphorus was doped on the entire surface of the substrate. At this time, a so-called ion doping method was used, and phosphine PH ₃ was used as a plasma source. The acceleration voltage was 80 kV. Further, a part of the substrate was masked, and boron was implanted by an ion doping method. The plasma source is diborane B ₂ H
_{At 6} , the accelerating voltage was 65 kV. That is, phosphorus is implanted into the masked portions, resulting in N-type,
Phosphorus and boron are implanted into the unmasked portions, resulting in a P-type.

Then, lasers of various energy densities and shot numbers were irradiated to activate the laser, the sheet resistance was measured, and the morphology was observed with an optical microscope. 2 to 4 show the results.

FIG. 2 shows the relationship between the sheet resistance of a silicon film into which phosphorus ions have been implanted, the energy density of laser light, and the number of shots. The dose of phosphorus is 2 × 10 ¹⁵ cm ⁻² . Laser energy density of 200 mJ / cm ²
In the following, a large number of shots were required for activation, and still a high sheet resistance of about 10 kΩ / □ was obtained, but at 200 mJ / cm ² or more, 1 to 10
Sufficient activation was achieved by laser irradiation of the shot.

FIG. 3 shows laser activation of a silicon film (semiconductor film) into which boron ions (4 × 10 ¹⁵ cm ⁻² ) have been implanted. Again, at an energy density of 200 mJ / cm ² or less, the activation was insufficient and a large number of shots were required. On the other hand, in the range of 200 to 300 mJ / cm ² , a sufficiently low sheet resistance was obtained in 1 to 10 shots.
With laser irradiation of 300 mJ / cm ² or more, the sheet resistance was rather increased. Especially 200mJ / c
Contrary to the case of m ² or less, the sheet resistance increased as the number of shots increased, because the uniformity of the film deteriorated due to the large number of laser irradiations, and the crystal grain boundaries grew.

In an actual process, laser annealing is performed on both the P-type region and the N-type region at the same time. Therefore, when the energy density of the laser is set to 350 mJ / cm ² , the N-type region is sufficiently activated, but the characteristics of the P-type region are rather deteriorated. Therefore, under the conditions of the present embodiment, the energy density is 200 to 300 mJ /
The range of cm ² , especially the range of 250-300 mJ / cm ² , was preferred. The number of pulses is preferably 1 to 100 pulses.

As described above, the morphology of the coating changes due to the laser annealing. However, when the number of shots, the energy density and the morphology are actually examined, the results shown in FIG. 4 are obtained. here,
Annealing Pulse means the number of laser shots. The black circles in the figure indicate points where a change occurs in the surface morphology of phosphorus-doped silicon, and the white circles indicate points of change in boron-doped silicon. In the figure, the upper right region shows a poor (rough) state of the morphology of the film surface, and the lower left region shows a good (flat) state of the morphology. It can be seen that phosphorus-doped silicon has higher resistance to laser. from this result,
The conditions for performing laser annealing so as not to change the surface morphology are as follows: when the energy density of the irradiated laser beam is E [mJ / cm ² ] and the number of shots of the laser pulse is N [times], log ₁₀ N ≦ A (EB), and when the impurity is phosphorus, A = −0.02, B
= 350, and when the impurity is boron, A = −0.
02, B = 300.

When the morphology is rough, the characteristics of silicon are significantly deteriorated in some parts, so that the variability becomes extremely large. Actually, in a silicon film having a poor morphology (coarse surface), the variation in sheet resistance was 20% or more. In order to reduce the variation, it is necessary to satisfy the above conditions and set an appropriate laser energy density.

For example, if the laser energy density is 250
When mJ / cm ² is used, the number of laser shots is desirably 10 or less. When the laser energy density is 280 mJ / cm ² , the number of laser shots is desirably 1 to 3 times. When laser annealing was performed under such conditions, the variation in sheet resistance could be suppressed to 10% or less.

[0024]

According to the present invention, optimum laser annealing is performed, and a highly reliable semiconductor film with little variation can be obtained. Thus, the present invention is considered to be industrially useful.

[Brief description of the drawings]

FIG. 1 shows a conceptual diagram of a laser annealing apparatus used in Examples.

FIG. 2 shows the relationship between the sheet resistance, laser energy density and the number of shots of a laser-annealed silicon film (phosphorus-doped, N-type) obtained in an example.

FIG. 3 shows the relationship between the sheet resistance, laser energy density, and shot number of a laser-annealed silicon film (phosphorus and boron-doped, P-type) obtained in an example.

FIG. 4 shows the relationship between the morphology of the silicon film obtained in the example, the laser energy density, and the number of shots.

FIG. 5 shows a conceptual diagram of an optical system of a laser annealing apparatus used in the example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical gantry 2 Laser device (oscillation stage) 3 Laser device (amplification stage) 4 Beam shaping optical system 5-9 Total reflection mirror 10 Sample stage and drive mechanism 11 Sample (glass substrate)

Claims (5)

[Claims] A step of forming a semiconductor film on a substrate, oscillating a first laser beam from an oscillator, passing the first laser beam through an optical system to form a second laser beam having a virtual focus, A step of focusing the cross section of the second laser light in a specific direction by a lens disposed at a position farther than the focal point, and irradiating the semiconductor film with the focused laser light,
Moving the substrate in the specific direction. A step of forming a semiconductor film on a substrate, oscillating a first laser beam from an oscillator, passing the first laser beam through an optical system to form a second laser beam having a virtual focus, A step of focusing the cross section of the second laser light in a specific direction by a lens disposed at a position farther than the focal point, and irradiating the semiconductor film with the focused laser light,
Moving the substrate in the specific direction, wherein the magnification M of the lens is M = (distance between the virtual focus and the lens) / (distance between the lens and the semiconductor film)
A method for manufacturing a semiconductor film, comprising: A step of forming a semiconductor film on a substrate, oscillating a first laser beam from an oscillator, passing the first laser beam through an optical system to form a second laser beam having a virtual focus, A step of focusing the cross section of the second laser light in a specific direction by a lens disposed at a position farther than the focal point, and irradiating the semiconductor film with the focused laser light,
Moving the substrate in the specific direction, wherein the focal length F of the lens is 1 / F = 1 / (distance between the virtual focus and the lens) + 1 / (the lens and the semiconductor film And a distance from the semiconductor film). 4. The method according to claim 1, wherein the laser light used is an excimer laser. 5. The method according to claim 1, wherein the cross section of the second laser beam has a rectangular intensity distribution.