JP2000311856A - Polycrystalline silicon film and semiconductor device having it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin film transistor a high mobility stably by an arrangement wherein the lattice strain of a polysilicon film in the direction parallel with the surface thereof is an elongation strain of specified value in any direction. SOLUTION: A polysilicon film 2 is formed on a substrate 1, e.g. a glass substrate coated or not coated with an insulating amorphous film. Elongation lattice strain in the range of 3×10-3-5×10-5 exists on the surface of the polysilicon film 2 in all parallel directions. The polysilicon film 2 is obtained, for example, by depositing an amorphous silicon film of 100 nm thick or less on the substrate 1 by plasma CVD and crystallizing the amorphous silicon film through laser irradiation under optimized conditions of energy density and irradiation times using a large area collective excimer laser annealing system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polycrystalline silicon film suitable for a thin film transistor and a semiconductor device having the same, and more particularly to a polycrystalline silicon film capable of stably obtaining a high mobility and a semiconductor device having the same. .

[0002]

2. Description of the Related Art Conventionally, a polycrystalline silicon film (polysilicon film) has been formed on a thin film transistor (TFT). For example, as described in JP-A-8-139018, an amorphous silicon film is It has been believed that a low-temperature polysilicon film of only {111} orientation crystallized by annealing generally satisfies the necessary and sufficient conditions for high mobility.

[0003]

However, even if the mobility of a TFT comprising a MOS type field effect transistor using a laser crystallized polysilicon film satisfies the above conditions, the mobility of a manufacturing apparatus and a crystallization method is actually high. However, there is a problem that it greatly changes depending on the condition (1). That is, if there is a time when the mobility becomes high accidentally, it is always the case that the mobility becomes low without understanding the cause. Therefore, it is difficult to stably supply a laser-crystallized polysilicon film having high mobility, and only inefficient production with a low yield rate has been achieved. For this reason, it is clear that there are physical properties closely related to the mobility other than the {111} orientation, but it is unclear what they are.

The present invention has been made in view of the above problems, and has as its object to provide a polycrystalline silicon film capable of stably obtaining a thin film transistor having a high mobility and a semiconductor device having the same. .

[0005]

In the polycrystalline silicon film according to the present invention, the lattice strain in a direction parallel to the surface is an expansion strain of 3 × 10 ^{−3 to} 5 × 10 ⁻³ in any direction. It is characterized by the following.

Another polycrystalline silicon film according to the present invention is characterized in that the difference between the maximum value and the minimum value of the lattice strain in a direction parallel to the surface is 1 × 10 ⁻³ or less.

In the present invention, it is preferable that both of these conditions are satisfied.

[0008] These polycrystalline silicon films can be formed by crystallizing an amorphous silicon film by laser irradiation.

The lattice strain may be a value obtained by an energy dispersive grazing incidence X-ray diffraction method.

In the present invention, since the lattice strain in the direction parallel to the surface is appropriately defined, it is possible to stably obtain a high mobility without depending on the manufacturing apparatus and crystallization conditions. Become.

A semiconductor device according to the present invention is characterized in that any one of the polycrystalline silicon films is formed on a substrate.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive experiments and research conducted by the present inventors to solve the above-mentioned problems, the mobility of a TFT is
It is closely related to the lattice strain of the polysilicon film, and it has been found that by defining the lattice strain in an appropriate range, a TFT having a high mobility can be obtained stably.

More specifically, the inventors of the present invention have measured lattice distortion by an energy dispersive grazing incidence X-ray diffraction (SR-EDGID) method using synchrotron radiation which has recently been performed. Was. The SR-EDGID method can be performed using, for example, a measuring device described in Japanese Patent No. 2615452. When measuring the lattice distortion of the polysilicon film using this apparatus, for example, the incident angle of X-rays on the sample surface is set to 0.5 degrees, and the diffraction angle (2θ) is set to 27 degrees. The details such as the basic arrangement of each component in the measurement of lattice strain by the SR-EDGID method are described in, for example, “A. T.
anikawa and K. Akimoto, Jpn. J. Appl. Phys., 36, 57
59 (1997) ".

FIG. 9 is obtained by the SR-EDGID method.
FIG. 3 is a graph showing an energy dispersive X-ray spectrum. What
This spectrum has an energy density of 500 (mJ /
cm ^TwoPolysilicon film crystallized under conditions
It is. From such an energy dispersive X-ray spectrum
The procedure for analyzing the lattice distortion is as follows. First, get
Apply the appropriate smoothing to the spectra obtained. Next
Creates a spectrum divided by the spectrum of the substrate only
(Background removal). Then peak top
By fitting with a suitable peak function
Get position E. In addition, powder silicon without strain introduced
For the reference, the peak position E_rTo
obtain. Then, the strain ε of the sample is calculated from the following equation (1).

[0015]

Ε = (E _r / E) −1

The mechanism of the mobility fluctuation conceived by the inventors of the present invention based on such experimental facts is as described below, and contradicts the conventional view that the smaller the distortion, the better. Was.

When an amorphous silicon film on a glass substrate is laser-crystallized to form a polysilicon film, a tensile strain occurs in the polysilicon film due to a temperature gradient during the crystallization. When a polysilicon film having a relatively large particle size is to be formed, a glass substrate inevitably does not melt, and a temperature condition in an extremely narrow range where only silicon is completely dissolved is required. Therefore, in such a case,
The temperature gradient in the vertical direction of the polysilicon film during crystallization increases, and the tensile strain generated thereby also increases.

If the uniformity of laser irradiation is impaired during crystallization for some reason, lattice defects occur in the crystal grains, and the tensile strain is relaxed. Since the relaxation of the extensional strain is caused by showing anisotropy in the crystal orientation, the orientational difference occurs in the extensional strain. Lattice defects not only cause carrier scattering by themselves, but also decrease mobility, and also reduce mobility near the surface by forming irregularities on the surface of the polysilicon film. In addition, the relaxation of the extensional strain of the polysilicon film increases irregularities generated at the crystal grain boundary on the surface, and the difference in the orientation of the extensional strain causes wavy irregularities on the crystal grain surface. This is based on the same principle as that the creased paper is kept flat by pulling it evenly from the periphery. In the case of paper as well, if the pulling force is reduced, the unevenness of the fold increases, and if the paper is pulled only in one direction, a wave is generated in a direction perpendicular to the pulling direction. In the case of an elastic sheet such as a vinyl film instead of paper, such a phenomenon is more prominent.

Hereinafter, a polycrystalline silicon film according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a sectional view showing a polycrystalline silicon film according to an embodiment of the present invention.

The polysilicon film 2 of this embodiment is formed on a substrate 1. The substrate 1 is, for example, a glass substrate or a substrate on which an insulating amorphous film is formed. The polysilicon film 2 has a thickness of 3 in all directions parallel to its surface.
There is a lattice strain of stretching from × 10 ^{-3 to} 5 × 10 ^-5 . Even when the lattice strain is not within the above range, the difference between the crystal orientation of the lattice strain in a direction parallel to the surface between the maximum value and the minimum value may be 1 × 10 ⁻³ or less. .

The polysilicon film 2 is formed, for example, by depositing an amorphous silicon film having a thickness of 100 nm or less on a glass substrate 1 by a plasma CVD method, and using a large area batch excimer laser annealing apparatus to obtain the energy density and the number of irradiation times. Can be obtained by performing laser irradiation under optimized conditions to crystallize the amorphous silicon film.

In the polysilicon film 2 thus manufactured, a high mobility of 100 (cm ² / V · sec) or more can be obtained. Note that the type of glass of the substrate 1, the laser annealing apparatus, the annealing uniformity, the density of the amorphous silicon film, and the like also affect the irradiation conditions.
If the lattice strain inside is within the above range, 100 (cm ² /
V.sec) or higher.

In particular, when forming the polysilicon film 2, it is preferable to pay attention to the following points in order to improve the uniformity of microscopic crystallization.

First, in order to prevent carbon atoms from adhering to the surface, the substrate 1 is not exposed to organic molecules (such as CO 2 and ethanol) at least until crystallization of the amorphous silicon film. In particular, it is preferable to take a measure such as using a clean room or an atmosphere in a laser annealing apparatus through an organic filter.

Second, the microscopic flatness of the window of the resonator made of MgF ₂ or the like of the excimer laser device and the window of the chamber made of quartz or the like are kept at a certain level or more according to the laser beam used. . For example, when a laser beam having a wavelength of 308 nm is used, the unevenness of the surface of the window material is 3 nm in a 300 nm square whose one side length is almost equal to the wavelength, that is, about 1/100 or less of the wavelength. If that is enough.
In addition, it is necessary to remove deposits that inhibit these.

In addition to these conditions, if there is a factor that inhibits uniformity depending on the manufacturing site,
You need to get rid of it.

In other words, manufacturing a laser-crystallized polysilicon film having a lattice strain within the range of the present invention is performed by monitoring for the above-mentioned cautionary notes and any other mobility-reducing factors and controlling them. It can be said that it is equivalent to

[0028]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples that fall outside the scope of the claims. FIG. 2 is a cross-sectional view illustrating a method for manufacturing a polysilicon film.

First, an amorphous silicon film having a thickness of 75 nm was deposited by a plasma CVD method on a substrate having an SiO ₂ film 12 having a thickness of 50 nm formed on a glass substrate 11 by a CVD method. Next, the amorphous silicon film is irradiated with a laser under the conditions of an energy density of 400 (mJ / cm ² ) and an irradiation frequency of 3 using a large-area batch excimer laser annealing apparatus, whereby the amorphous silicon film is irradiated. Was crystallized to form a laser-crystallized polysilicon film 13.

In order to prevent carbon atoms from adhering to the surface of the amorphous silicon film, the substrate and the amorphous silicon film are not exposed to organic molecules at least during the period from the formation of the amorphous silicon film to the crystallization thereof. I did it.

FIG. 3 and Table 1 below show the energy density during laser irradiation and the resulting lattice distortion of the interplanar spacing in each of the examples and comparative examples. In FIG. 3, ● represents $ 22.
The lattice distortion in the {0} plane is shown, and the lattice distortion in the {111} plane is shown.

[0032]

[Table 1]

As shown in Table 1 above, Example No. Example No. 1 satisfies the range defined in claim 3. Example No. 2 satisfies the range defined in claim 2. 3 satisfies the range defined in claim 1. On the other hand, Comparative Example N
o. No. 4 does not satisfy any of the ranges.

Then, a MOSFET was manufactured by performing the following steps using the polysilicon film as described above. FIG. 4 is a sectional view showing the MOSFET.

First, an SiO ₂ film 22 was deposited on a glass substrate 21 by a CVD method. Next, a tungsten silicide electrode 24 was formed at a predetermined position. Thereafter, an n ⁺ -polysilicon electrode 25 covering the tungsten silicide electrode 24 was selectively formed. Next, the polysilicon film 23 of each embodiment or comparative example as described above was formed on the entire surface.

Further, a plasma C is formed on the polysilicon film 23.
The SiO ₂ film 26 was formed by the VD method. Then, Si
A polysilicon electrode 28 was formed on the O ₂ film 26, and a contact hole reaching the tungsten silicide electrode 24 was formed in these multilayer films. Next, an aluminum electrode film 27 was formed on the entire surface so as to fill the contact hole. Then, the source electrode 29, the gate electrode 30, and the drain electrode 31 are formed by patterning the aluminum electrode film 27 and the polysilicon electrode 28 into predetermined shapes, and the above-described polysilicon film 23 exists immediately below the gate electrode 30. MOS transistor to be completed.

Note that these steps include a photoresist step, an ion implantation step, a plasma CVD film growth step, a sputter film deposition step, and the like as appropriate.

Then, the mobility of the MOS transistor thus manufactured was measured. As a result, the average value in the lot was equal to that of Example No. 44 (cm ² / V
Second), Example No. In Example 2, 121 (cm ² / V ·
Second), Example No. 84 at 3 (cm ² / V ·
Second), Comparative Example No. 21 at 4 (cm ² / V · sec)
Met. FIG. 5 is a graph showing the relationship between the average values of lattice strain in two directions on the horizontal axis and the mobility on the vertical axis. FIG. 6 is a graph showing the relationship between the lattice strain in two directions on the horizontal axis and the mobility on the vertical axis.

As shown in FIGS. 1
In Nos. 3 to 3, since the lattice strain is within the range of the present invention,
High mobility was obtained. On the other hand, in Comparative Example 4, since the lattice strain did not satisfy the range of the present invention, the mobility was low. Thus, there is a correlation that the larger the lattice strain and the smaller the azimuth difference, the higher the mobility.

As described above, the polysilicon film 23
Is formed immediately below the gate electrode 30, but even if it is formed in other regions, the mobility is usually not significantly affected.

The standard deviation within the lot was determined in Example No.
In Example 1, 13 (cm ² / V · sec) was obtained. In Example 2, 2 (cm ² / V · sec) was obtained. In Comparative Example No. 3, 28 (cm ² / V · sec). 9 in 4
(Cm ² / V · sec). Further, the standard deviation of the mobility average value in the five production lots is shown in Example No. In Example No. 1, 5 (cm ² / V · sec) was obtained. In Example 2, 3 (cm ² / V · sec) was obtained. 19 in 3
(Cm ² / V · sec), Comparative Example No. 7 in 4 (cm ²
/ V · sec). With this alone, the variation within a lot or between lots does not seem to correlate with the lattice strain,
When compared by a value (variation rate) divided by the mobility, there is a correlation that the larger the lattice strain and the smaller the azimuth difference, the smaller the variation. FIG. 7 is a graph showing the relationship between the average values of the lattice strain in two directions on the horizontal axis and the fluctuation rate on the vertical axis. FIG. 8 is a graph showing the relationship between the lattice strains in two directions on the horizontal axis and the fluctuation rate on the vertical axis. In FIGS. 7 and 8, .largecircle. Indicates the variation between lots, and .DELTA. Indicates the variation between lots.

[0042]

As described in detail above, according to the present invention,
Since the lattice strain in the direction parallel to the surface is appropriately defined, a high mobility can be stably obtained without depending on the manufacturing apparatus and crystallization conditions. Further, a thin film transistor with improved mobility uniformity can be supplied stably. In particular, when the lattice strain is within the range defined in claim 2, the effective mobility is 100 (cm ² / cm ² ).
V · sec) can be supplied stably.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a polycrystalline silicon film according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a method for manufacturing a polysilicon film.

FIG. 3 is a graph showing a relationship between laser energy and lattice distortion.

FIG. 4 is a sectional view showing a MOSFET.

FIG. 5 is a graph showing a relationship between an average value of lattice distortion and mobility.

FIG. 6 is a graph showing a relationship between a difference in lattice strain and mobility.

FIG. 7 is a graph showing a relationship between an average value of lattice strain and a variation rate.

FIG. 8 is a graph showing a relationship between a difference in lattice strain and a variation rate.

FIG. 9 is a graph showing an energy dispersive X-ray spectrum obtained by the SR-EDGID method.

[Explanation of symbols]

1, 11, 21; substrates 2, 13, 23; polysilicon films 12, 22, 26; SiO ₂ film 24; tungsten silicide electrode 25; n ⁺ -polysilicon electrode 27; aluminum electrode film 28; polysilicon electrode 29; Source electrode 30; gate electrode 31; drain electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenji Sera 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Fujio Okumura 5-7-1 Shiba, Minato-ku, Tokyo Japan F-term in the electric company (reference)

Claims (6)

[Claims] 1. A polycrystalline silicon film, wherein the lattice strain in a direction parallel to the surface is an extensional strain of 3 × 10 ^{−3 to} 5 × 10 ⁻³ in any direction. 2. The method according to claim 1, wherein the difference between the maximum value and the minimum value of the lattice distortion is 1
2. The polycrystalline silicon film according to claim 1, wherein the thickness is not more than × 10 ⁻³ . 3. A polycrystalline silicon film, wherein a difference between a maximum value and a minimum value of lattice strain in a direction parallel to the surface is 1 × 10 ⁻³ or less. 4. An amorphous silicon film formed by crystallizing an amorphous silicon film by laser irradiation.
4. The polycrystalline silicon film according to any one of items 3 to 3. 5. The polycrystalline silicon film according to claim 1, wherein the lattice strain is a value obtained by an energy dispersive grazing incidence X-ray diffraction method. 6. A semiconductor device, wherein the polycrystalline silicon film according to claim 1 is formed on a substrate.