JP2623276B2 - Method for manufacturing thin film semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a thin film semiconductor device,
The present invention relates to a method for manufacturing a thin film semiconductor device suitable for an active matrix type display.

(Prior Art) A conventional method for manufacturing a polycrystalline silicon (abbreviated as Poly-Si) thin film transistor (abbreviated as TFT) used for an active matrix type display is disclosed in “Nikkei Electronics”, September 10, 1984, p. As described below, impurity atoms are introduced into the semiconductor layer by an ion implantation method, and thereafter, thermal activation is performed at about 600 ° C. to form source and drain regions.

In a display using a TFT formed by the above-described ion implantation method, in order to improve the image quality of the display, it is necessary to reduce the reverse leakage current of the TFT by reducing the thickness of Poly-Si.

In order to reduce the thickness of Poly-Si, a shallow junction must be formed in the source region and the drain region.
However, when the Poly-Si film thickness is about 600 ° or less,
In the ion implantation method, impurity atoms penetrate the semiconductor layer, and a good junction cannot be formed.

As a new impurity introduction method replacing the ion implantation method, see IEE ELECTRON DEVICE LETTER, EDL-6, (1985) p.291 (IEE
E Electron Dev. Lett., EDL-6, (1985) P291), or a laser doping method described in JP-A-61-14762.
The plasma doping method described in Japanese Unexamined Patent Publication (Kokai) No. HEI 9-124 has been studied.

(Problems to be Solved by the Invention) In the laser doping method, a semiconductor substrate is placed in a gas containing an impurity to be doped, and a semiconductor layer is melted by irradiating a laser beam from above to dissolve the semiconductor layer. This is to dope atoms into a semiconductor.

In this laser doping method, a shallow junction can be formed, but sufficient impurity atoms are not necessarily introduced into the surface of the semiconductor substrate, and a low sheet resistance cannot be obtained.

On the other hand, in the plasma doping method, a gas containing impurities to be doped is turned into plasma by a high frequency or DC bias, and impurity atoms are doped into a semiconductor.

In this plasma doping method, more impurity atoms are introduced into a semiconductor than in the laser doping method. However, in the plasma doping method, the impurity atoms are not sufficiently activated by the heat treatment at about 600 ° C. or less, and if the activation of the impurity atoms is performed only by the heat treatment, a temperature of about 800 ° C. or more is required. There is a problem that doping due to diffusion occurs and rearrangement of impurities occurs.

As an activation method other than heat treatment, as described in JP-A-56-24954, an impurity atom is introduced into a semiconductor substrate by an ion implantation method, and thereafter, the impurity atom is irradiated with a laser beam. There is a way to activate.

However, when this method is used for the plasma doping method, irregularities are generated on the surface of the Poly-Si, and then the TFT is formed.
However, good characteristics cannot be obtained even if the above is prepared.

An object of the present invention is to introduce a sufficient amount of activated impurity atoms into thin Poly-Si formed on the surface of an insulating substrate such as a glass substrate, and to form a shallow, good junction. And a method of manufacturing a thin film semiconductor device.

(Means for Solving the Problems) The object of the present invention is to provide a step of introducing impurity atoms into a semiconductor layer in a plasma state as shown in FIG. 3 and a step of introducing hydrogen atoms introduced into the semiconductor layer simultaneously with the impurity atoms. This is achieved by employing a step of removing by a heat treatment step at about 600 ° C. and a step of activating impurity atoms in the semiconductor layer by irradiating a pulsed laser beam in an ultraviolet light region. .

(Function) When impurity atoms are brought into a plasma state and introduced into Poly-Si, a sufficient amount (10 ²¹ cm ⁻³ ) of impurities is introduced into the Poly-Si surface region. However, since impurity atoms are generally introduced into the reaction chamber as hydrides such as PH ₃ and B ₂ H ₆ , hydrogen atoms are also brought into a plasma state, which is introduced into the poly-Si at a concentration higher than the impurity atom concentration. You.

Therefore, if an attempt is made to activate impurity atoms by laser irradiation immediately after plasma doping, hydrogen atoms rapidly become poly-
It gets out of the Si substrate and makes irregularities on the Poly-Si surface.

On the other hand, slowly heat the substrate in advance to about 600 ° C.
When the heat treatment is performed while maintaining the temperature, hydrogen gradually escapes from the Poly-Si substrate, and the surface of the Poly-Si is maintained in a smooth state. On the other hand, activation of impurities does not sufficiently occur only by the heat treatment at about 600 ° C. described above. This is considered to be due to residual hydrogen in the Poly-Si or the escape of hydrogen.

Next, when an excimer laser, which is a pulsed laser in the ultraviolet light region having a large absorption coefficient with respect to Si (silicon), is irradiated, only a thin region from the Poly-Si surface is melted for a short time (0.1 μs). During recrystallization, the impurity atoms are S
Nearly 100% activation occurs in the lattice position of i.

FIG. 2 is a diagram showing an example of the relationship between the laser light intensity and the sheet resistance when a sample that has been subjected to heat treatment after plasma doping is irradiated with a laser.

As is evident from the figure, as the laser beam intensity increases, the sheet resistance decreases, and the laser beam intensity decreases by about 150 m.
At the point of J / cm ² , the sheet resistance saturates and reaches a value of about 2 × 10 ³ Ω / □.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a TFT showing a manufacturing method according to an embodiment of the present invention.

Reference numeral 1 denotes a glass substrate having a strain temperature of about 640 ° C. Substrate 1 for 550
℃, low pressure CVD (Low Pressure CVD, LPCV)
An LPCVD film 2 is deposited on the surface of the substrate 1 at a pressure of 1 Torr by the method D). The deposition time is 25 minutes and the film thickness is 500Å.

After this film is formed into an island pattern through an island photoetching process, a SiO ₂ film 5 for a gate insulating film is deposited on the entire surface of the LPCVD film 2 by a normal pressure CVD method at a thickness of 1000 ° [FIG.

Next, a Poly-Si film for the gate electrode 6 is
Deposit 2000mm at 50 ° C and 1 Torr. After that, the gate electrode 6 and the gate insulating film 5 are formed by photoetching.

Subsequently, using 1% PH ₃ as a raw material, phosphorus is converted into plasma with a high frequency of 13.56 MHz and doped into a Poly-Si substrate maintained at 300 ° C. to form a source region 3 and a drain region 4. At this time, the gate electrode 6 is also doped with phosphorus. The pressure is 1 Torr and the doping time is 30 minutes.

Next, the substrate is slowly heated to 600 ° C. in N ₂ , and heat treatment is performed for 4 hours to remove hydrogen atoms introduced into the substrate.

Subsequently, XeCl excimer laser having a wavelength of 308 nm and being a pulsed laser is irradiated to activate the impurity atoms. The laser beam intensity is 300 mJ / cm ² [FIG.

Next, phosphor glass (abbreviated to PSG) is deposited at 480 ° C. for 5000 ° to form a passivation film 7 (FIG. 3C).

Next, after a photo-etching step for contact, an Al electrode 8 is deposited by 6000 ° by sputtering [FIG.

Thus, the TFT is completed. TFT channel width of the present embodiment,
Channel length, 50 [mu] m respectively, and 10 [mu] m, the drain current I _D - reverse leakage current was determined from the gate voltage V _G curve (V _G = -5V, Reese drain voltage V _SD = 10V) is 5 × 10 ^-12 A indicates that the bonding characteristics are good.

(Effect of the Invention) According to the present invention, a sufficient amount of activated impurity atoms can be introduced into thin Poly-Si on a glass substrate,
A shallow, good junction can be formed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a manufacturing process of one embodiment of the present invention. FIG. 2 is a diagram showing the relationship between laser energy density and sheet resistance. FIG. 3 is a block diagram showing an outline of the present invention. 1 ... glass substrate, 2 ... LPCVD film, 3 ... source region,
4 ... Drain region, 5 ... Gate insulating film, 6 ... Gate electrode, 7 ... Passivation film, 8 ... Al electrode

Claims (3)

(57) [Claims] 1. A method for manufacturing a thin film semiconductor device having an insulating substrate and a semiconductor layer formed on the insulating substrate, comprising: introducing impurity atoms into a semiconductor layer in a plasma state; Removing the hydrogen atoms introduced simultaneously with the impurity atoms by heat treatment, and irradiating the surface of the semiconductor layer with laser light,
Activating the impurities introduced into the semiconductor layer. 2. The method according to claim 1, wherein a wavelength of said laser light is in an ultraviolet region. 3. The method for manufacturing a thin film semiconductor device according to claim 1, wherein said laser light is a pulsed laser light.