JP3114226B2 - Method for manufacturing thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a thin film transistor using a poly-Si layer and a method for manufacturing the same.

[0002]

2. Description of the Related Art Poly- on an insulating substrate such as glass.
As a technique for forming a Si thin film transistor (hereinafter referred to as “TFT”), there is an excimer laser annealing technique.
This is a technique in which an a-Si layer deposited on a substrate is crystallized by an excimer laser to obtain a good poly-Si layer. As a technique for manufacturing a poly-Si layer using conventional excimer laser annealing, K.K. Se
"High-Performance T by Ra et al.
FT's Fabricated by XeCl E
xicimer LaserAnnealing of
Hydrogenated Amorphous-S
Ilicon Film, "IEEE Trans.
Electron Device, vol. ED -3
6, no 12, pp. 2868-2872 Dec
1989. There are the following. A method of manufacturing a conventional poly-Si TFT using such a poly-Si layer by crystallizing the a-Si layer into a poly-Si layer will be described with reference to FIG.

First, an a-Si layer is deposited on a substrate 11 and annealed with an excimer laser of a single energy density light to form a poly-Si layer 12 (FIG. 1- (a)). After the layer 12 is patterned into an island shape, a gate insulating film (SiO ₂ ) 13 and a poly-Si layer are sequentially deposited, and the poly-Si layer is patterned to form a gate electrode 14 (FIG. 1- (b)). The source (S) / drain (D) portions 16 and 17 are formed by ion implantation using the gate electrode 14 as a mask (FIG. 1- (c)). Subsequently, an interlayer insulating film 15 is deposited, contact portions for wiring are opened in the ion-implanted S and D portions 16 and 17, and Al is deposited and patterned to form a wiring 1.
8, 19 (FIG. 1- (d)). Finally, it was protected by a passivation film 20 such as SiN _x (FIG. 1).
(E)).

However, in such a conventional manufacturing method,
There is a disadvantage that various characteristics of the NMOS and PMOS TFTs in the substrate tend to be non-uniform. For example, as shown in FIG. 4, the field effect mobility μ increases as the irradiation energy density J of the laser increases, but the variation in the substrate becomes significant in the NMOS TFT. Further, as shown in FIG. 5, the breakdown voltage Vbd between the source (S) and the drain (D) decreases as the energy density J increases, and in particular, the PMOST
The variation of that of FT becomes significant. This PMOSTF
The tendency of T is also observed for the leakage current value. Therefore, when fabricated by the conventional laser irradiation method, NMOS, PM
Irradiation at a relatively high energy density to obtain high field-effect mobility for both OSs causes variations in characteristics and deterioration in Vbd and leak current values. Therefore, it has been difficult to manufacture a device having high field-effect mobility with high uniformity.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art and provides a highly uniform and high-performance poly-
This is to provide a SiTFT.

[0006]

According to the present invention, there is provided a method of manufacturing a TFT in which an a-Si layer deposited on an insulating substrate is crystallized by excimer laser irradiation to form a poly-Si layer. when the crystallized poly-Si layer by irradiation of the excimer laser, the a-Si layer is rather high than the threshold energy density to be crystallized poly-Si layer, the poly-Si at the location irradiated
Energy remaining inside the grain of the layer and at the grain boundary
Irradiating the first energy density light Energy density, then the po formed by the first energy density beam
The method is characterized by irradiating a second energy density light capable of melting a defect remaining inside the grain and the grain boundary of the ly-Si layer.

Here, the surface flatness means that the average film thickness is T
_AVE , the maximum thickness is defined as T _MAX, and the minimum thickness is defined as T _MIN . Surface flatness (%) = (T _MAX −T _MIN ) / T _AVE × 100

[0008]

According to the present invention, first, the a-Si layer is crystallized and pol
rather higher than the threshold energy density as a y-Si layer,
Gray of the poly-Si layer at the irradiated location
Density at which defects remain inside the grain and at grain boundaries
By irradiating the first energy density light, poly
Determine good grain size in the Si layer.
At this time, it is preferable to irradiate first energy density light lower than the energy density at which the surface flatness of the poly-Si layer becomes 40%.

In the poly-Si layer manufactured in this step, many defects inside the grains and at the grain boundaries remain. So, inside this grain and the grain boundary
By irradiating the second energy density light capable of melting the remaining defects to poly-Si, the number of defects in the poly-Si layer can be reduced by converting the defective portion into poly-Si.

[0010]

The present invention will be described in detail below with reference to embodiments. 1 is the same as FIG. 1 except for the excimer laser annealing step.
I will explain using. First, LPCVD on quartz substrate 11
1000 angstrom a at 550 ° C.
A -Si layer was deposited. This is excimer laser (KrF,
The poly-Si layer 12 has an oscillation wavelength λ = 248 nm).
I made it. In this case, the entire surface of the substrate is first exposed to an energy density of 27.
A poly-Si layer is irradiated with a beam of 0 mJ / cm ^2, followed by irradiating again the entire substrate surface with a beam of energy density of 450 mJ / cm ² (Fig. 1- (a)). Subsequently, the poly-Si layer 12 is patterned into an island shape, and a gate insulating film 13 is formed on the poly-Si layer 12 by LPCVD.
0 angstrom of SiO ₂ is deposited and LPC
3000 angstroms poly-S by VD method
An i-layer was deposited, and the upper poly-Si layer was patterned to form a gate electrode 14 (FIG. 1- (b)). Subsequently, ions are implanted using the gate electrode as a mask to form source / drain portions 16 and 17 (FIG. 1C), and the interlayer insulating film 15 is formed.
After 7000 Å of SiO ₂ was deposited by LPCVD, contact portions for wiring were opened. Next, after performing a hydrogenation treatment at 350 ° C., A
1SiCu was deposited and patterned to form wirings 18 and 19 (FIG. 1- (d)). Finally, 1 μm SiN _x is pC
It was deposited by the VD method and patterned to form a protective film 20 (FIG. 1- (e)).

FIG. 2 shows the characteristics of the field-effect mobility μ of the poly-Si TFT fabricated by annealing with a plurality of energy density lights.
FIG. 3 shows the characteristics of. The field effect mobility μ is NMOS, P
Although both MOSs are about 20% smaller, μ =
A sufficiently high value of 60 cm ² / V · s is realized in a form in which variations in the substrate are reduced. In addition, the source-drain breakdown voltage Vbd shown in FIG. 5 has been significantly improved and made uniform, and this tendency has been observed in other characteristics such as other leak current values and threshold voltages. Therefore, it has been found that annealing with a plurality of energy density lights in this way can improve and uniformize various other characteristics while having sufficiently high field effect mobility.

The reason for the overall improvement and uniformity of such characteristics can be understood from the observation of the cross section of the poly-Si layer by a transmission electron microscope (hereinafter referred to as "TEM") shown in FIG. ( A ) of FIG. 6 is a single energy density light of 270 mJ / cm ² , and ( B ) is 450 mJ / c.
FIG. 3 is a schematic diagram of a cross section of a poly-Si layer when each is annealed with m ² single energy density light. As the energy density increases, each grain constituting the poly-Si layer increases, and the inside of the grain and the grain boundary become clear. However, the flatness of the surface is deteriorated accordingly.

Meanwhile, FIG. 6 in the case of the above-described embodiment (C)
Shown in Already grain size by the energy density light 270mJ / cm ² irradiated to the previously determined, then almost no change of the surface flatness in energy density light 450 mJ / cm ² is irradiated, the grain inside and the grain boundary Defects can be melted. Accordingly, defects in the inside of the grain and at the grain boundary are reduced without deteriorating the surface flatness, so that various characteristics of the TFT are improved.
In addition, it is considered that there is less variation in the energy distribution in the laser beam than in the case of single irradiation with high energy density light of 450 mJ / cm ² .
In order to melt single-crystal silicon with an excimer laser, a very high energy density of about 1000 mJ / cm ² is required. Since it is considered that the structure has a structure similar to a-Si, only a defective portion can be melted with light having a relatively low energy density than poly-Si.

The energy density of the first energy density light (270 mJ) to be applied to the a-Si layer in the above embodiment.
/ Cm ² ) is between the threshold energy density at which the a-Si layer is crystallized to become a poly-Si layer and the energy density at which the surface flatness of the poly-Si layer crystallized from the a-Si layer becomes 40%. Energy density.

The former a-Si layer is crystallized and poly
-Threshold energy density E _TH (180 m
J / cm ² ) is obtained from the energy density dependence of the X-ray diffraction intensity ((111) peak) of the poly-Si layer obtained after irradiating the a-Si layer of the embodiment shown in FIG. 7 with an excimer laser. Was. In FIG. 7, as the energy density increases, the crystallinity of the grains constituting the poly-Si layer changes to the threshold energy density E _TH (180 mJ / cm ² ).
It can be seen that it has improved at the border.

The energy density at which the surface flatness is 40% or less is poly-Si by TEM.
It was determined from the layer cross section.

Second Energy Density It is necessary to irradiate the energy density of the light with the energy density necessary to melt the defects inside the grains and at the grain boundaries. In the embodiment, the energy density of the second energy density light is set to 45.
0 mJ / cm ² and 180 from the first energy density light.
mJ / cm ² was increased, but a large energy density 30 mJ / cm ² or more than at least a first energy density is required. Note that J = 270 + 270 or J = 450
Irradiation of the same energy density light such as +450 or J = 2
When the energy density difference between the first energy density light and the second energy density light such as 70 + 290 is small, the TFT characteristics are determined by the first energy density light, and the effect of uniformity is very small.

The present invention is not limited to the conditions of the embodiment described above, and similar effects can be obtained under the following conditions. 1. Excimer laser devices are not limited to KrF, but include XeCl and A
Other oscillation wavelengths such as rF may be used. 2. The method of forming a-Si is not limited to the LPCVD method, but may be a method formed by another p-CVD method, a sputtering method, or an evaporation method. 3. The substrate is not limited to a quartz substrate, but may be another insulating substrate such as sapphire, glass, or an organic film. 4. Regarding the irradiation of a plurality of energy density lights, not only the two-step irradiation of the first energy density light / the second energy density light as in the present embodiment, but also the first energy density light / the second energy Multi-stage irradiation such as density light / third energy density light / fourth energy density light is also effective. 5. Regarding 4, it is similarly effective to irradiate multi-stage energy-density light to those already converted into poly-Si by furnace annealing instead of the first energy-density light irradiation.

[0019]

According to the excimer laser annealing process of the present invention, the poly-Si layer can reduce defects inside grains or at grain boundaries without substantially changing the surface flatness. Poly-Si TFT NMOS and PMOST
In both FTs, various characteristics such as the field effect mobility can be improved and made uniform, and the characteristics in the substrate can be made uniform.

[Brief description of the drawings]

FIG. 1 illustrates a manufacturing process of a poly-Si TFT.

FIG. 2 shows poly-Si obtained according to an embodiment of the present invention.
4 shows the field effect mobility of a TFT.

FIG. 3 shows poly-Si obtained according to an embodiment of the present invention.
This shows the source-drain breakdown voltage of the TFT.

FIG. 4 shows a poly-Si TFT obtained by a conventional technique.
3 shows the energy density dependence of the field-effect mobility of FIG.

FIG. 5 shows a poly-Si TFT obtained by a conventional technique.
3 shows the energy density dependence of the source-drain breakdown voltage of FIG.

FIG. 6 is a schematic diagram of a poly-Si cross section showing how the obtained poly-Si grains are different depending on an excimer laser irradiation method.

FIG. 7 shows the energy density dependence of X-ray diffraction intensity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 poly-Si layer 13 Gate insulating film 14 Gate electrode 15 Interlayer insulating film 16, 17 Source / drain part 19, 18 Wiring 20 Passivation film

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 29/786 H01L 21/20 H01L 21/324 H01L 21/336 JICST file (JOIS)

Claims (4)

(57) [Claims] An amorphous silicon (hereinafter referred to as "a-Si") layer deposited on an insulating substrate is crystallized by excimer laser irradiation to form polycrystalline silicon (hereinafter referred to as "poly-Si").
In a method of manufacturing a thin film transistor having a layer of “Si”), when the a-Si layer is crystallized by excimer laser irradiation to form a poly-Si layer, the a-Si layer is crystallized to become a poly-Si layer. than the threshold energy density rather high, the poly-Si layer at the location irradiated
With defects inside grain boundaries and grain boundaries
Irradiating the first energy density light ghee density, then have a higher energy density than the first energy density beam, the grain inside the poly-Si layer formed by the first energy density beam and Gray
Irradiating a second energy density light capable of melting a defect remaining at the boundary of the thin film transistor. 2. The method according to claim 1, wherein said first energy density light is a-
The surface flatness of the poly-Si layer crystallized from the Si layer
Energy density lower than 40% energy density
2. The thin film transistor according to claim 1, wherein
Manufacturing method. 3. The method according to claim 2, wherein the second energy density light is the first energy density light.
Said pol formed by irradiation of energy density light of
Energy density that changes the surface flatness of the y-Si layer
Claims characterized by having a lower energy density
3. A method of manufacturing the thin film transistor according to claim 1.
Law. 4. The method according to claim 1, wherein the second energy density light is the first energy density light.
30mJ / cm ² or more larger than the energy density light of
An energy density is provided.
A method of manufacturing the thin film transistor according to claim 3.
Construction method.