JPH06120508A - Substrate for semiconductor device and manufacturing method thereof - Google Patents

Abstract

PURPOSE:To avoid the deposition of an alkaline metal such as Na, etc., contained in a glass substrate in a functional film comprising a FET in the substrate for semiconductor device using a glass substrate. CONSTITUTION:In the substrate for semiconductor device to form a polycrystalline silicon film 4 on a glass substrate 1 by crystallizing an amorphous silicon film, a phosphosilicate glass film 2 containing exceeding 5mol (5) of phosphoric acid is formed on the surface of the glass substrate as the lower layer of the amorphous silicon film and then a silicon oxide film 3 is formed on the phosphosilicate glass film 2 so that Na may be taken in the phosphosilicate glass film 2 when the Na existing in the glass substrate 1 is to be deposited during the heat treatment step, etc., in the TFT manufacturing process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device substrate for forming a semiconductor element such as a thin film transistor,
In particular, the present invention relates to a semiconductor device substrate used for a large area active matrix liquid crystal display or the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display, TFTs are arranged in a matrix so that one thin film transistor (TFT) corresponds to one pixel, and each pixel is controlled by driving each TFT. It is a thing. In recent years, the active matrix type liquid crystal display described above uses an inexpensive glass substrate,
There is an urgent need for higher image quality and larger screens while incorporating peripheral circuits. To incorporate the peripheral circuit, TF
Since the current driving capability of T is required, poly-SiTF using a polycrystalline silicon layer with high carrier mobility as a channel layer
It is necessary to use T.

Conventionally, formation of a poly-Si TFT as shown in FIG. 2 has been performed by a manufacturing method including the following steps, for example. An amorphous silicon (a-Si) film is formed on a large-area insulating substrate 51 by LPCVD at 450 to 550 ° C.
Film is formed at a deposition temperature of N 2
Annealing is performed in the atmosphere to crystallize and form a poly-Si film. As the annealing method, it has been proposed to crystallize by irradiating an excimer laser absorbed by the a-Si film (H. Ku.
riyama et al .: Proceedings of IEDM'91, pp.563-56
6). The poly-Si film is patterned to form the poly-Si film island 5.
Form 2. A gate insulating film 53 is deposited so as to cover the poly-Si film island 52. Deposit a metal film and pattern this metal film to poly
-A gate electrode 54 is formed on the Si film island 52. By performing ion implantation from above, the gate electrode 54 and the poly-Si film island 52 are doped with impurities, and the source part 52b and the drain part 52c are formed with the channel layer 52a of the poly-Si film island 52 interposed therebetween. The impurities are activated by the annealing treatment. An insulating film 55 is deposited, and contact holes 56 are formed at the source and drain electrode positions. A film of aluminum is deposited and patterned to form A
The l electrode 57 is formed, the protective film 58 is further deposited, and the pad hole 59 is formed.

By the way, in order to increase the area of the liquid crystal display and reduce the cost, the insulating substrate 51 is used.
Although it is necessary to use an inexpensive glass substrate as the glass substrate, the glass substrate (aluminosilicate glass substrate) contains about 0.5 at% of an alkali metal such as sodium (Na) which is inevitably generated in the glass manufacturing process. ing. This Na, etc. is removed from the glass substrate by poly in the heat treatment process or the excimer laser irradiation process during the TFT manufacturing process.
-Heat diffusion to the Si film island 52 and deposition in the poly-Si film island 52. As a result, for example, when Na exists in the gate insulating film 53 of the TFT, the interface between the gate insulating film 53 and the channel layer 52a, etc., Na drifts in the gate insulating film 53 when the TFT is driven, and thus the gate insulating film 53 is insulated. The charge distribution in the film 53 fluctuates, and accordingly the TFT
It is conceivable that the threshold voltage (VTH) of the ON operation of the device will shift and cause instability of the device operation.

Therefore, when a glass substrate is used instead of quartz, as shown in FIG. 3, in order to prevent impurities contained in the glass substrate 61 from depositing on the poly-Si film island 52, the glass substrate 61 is prevented. And poly-Si film island 52
Between the silicon oxide film (or silicon nitride film) 6
It has been proposed to intervene 2 (1990 Spring Response Preliminary Report p.638).

[0006]

However, in the case of the silicon oxide film (silicon nitride film) 62, the glass substrate 61 is used.
However, there is a problem in that it is impossible to sufficiently prevent the precipitation of Na included in the poly-Si film island 52. N
As shown in FIG. 4, when a positive bias is applied to the gate electrode 54 while maintaining the substrate temperature at a constant temperature of 200 to 300 ° C., the influence of a on the poly-Si TFT is such that the gate applied voltage and the source portion 52 b 2 of the drain part 52c
It appears in the shift at the change position (BT stress) of the semiconductor capacitance-voltage characteristic (CV characteristic) curve between terminals. The shift change amount of this curve corresponds to the change amount of the threshold voltage.

That is, in the case where the poly-Si film island 52 to be the channel layer is directly formed on the glass substrate 61,
BT stress (substrate temperature 250 ℃, bias voltage 30
The shift value of the C-V characteristic before and after V, 30 min) is −
It was 2.0 to -3.0 (V) (the threshold voltage changed in the negative direction). When a silicon oxide film 62 (7000 angstrom) is formed between the glass substrate 61 and the poly-Si film island 52, the shift value is -2.
It was 0-3.0 (V). In addition, with the glass substrate 61
A silicon nitride film 62 is formed between the poly-Si film island 52 and the poly-Si film island 52.
In the case of forming (7000 angstrom), the shift value was -1.0 to -2.0 (V). In either case, the shift value (the amount of change in the threshold value) could not be reduced. In the above case,
The thickness of the gate insulating film 53 is 1000 Å,
The area of the gate electrode 54 was 0.785 cm ² .

The present invention has been made in view of the above circumstances, in which the alkali metal such as Na contained in the glass substrate is
It is an object of the present invention to provide a semiconductor device substrate capable of preventing deposition in a functional film forming an FT and a manufacturing method thereof.

[0009]

In order to solve the above-mentioned problems of the conventional example, a semiconductor device substrate of the present invention is a semiconductor in which a polycrystalline silicon film is obtained on a glass substrate by crystallizing an amorphous silicon film. In the device substrate, a phosphosilicate glass film containing 5 mol% or more of phosphoric acid was formed on the surface of the glass substrate below the amorphous silicon film, and a silicon oxide film was formed on the phosphosilicate glass film. It has a feature.

A method of manufacturing a semiconductor device substrate according to the present invention comprises:
In a method of manufacturing a substrate for a semiconductor device, which comprises laminating a polycrystalline silicon film obtained by crystallizing an amorphous silicon film on a glass substrate, coating the surface of the glass substrate with phosphosilicate glass containing 5 mol% or more of phosphoric acid. A step of forming a phosphosilicate glass film by firing the phosphosilicate glass, forming a silicon oxide film on the phosphosilicate glass film, and forming a polycrystalline silicon film on the silicon oxide film And a step of performing.

[0011]

According to the present invention, since the phosphosilicate glass film having a high Na absorption rate is interposed between the glass substrate and the amorphous silicon film, the heat treatment during the TFT manufacturing process, etc. When Na present in the film is precipitated, this Na is taken into the phosphosilicate glass film, and Na present in the gate insulating film of the TFT or the channel layer / gate insulating film interface of the polycrystalline silicon film can be reduced. That is, since Na is unevenly distributed in the phosphosilicate glass film, the Na concentration in the upper layer of the silicon oxide film, which is the upper layer, is reduced to about 1/1000 of that in the phosphosilicate glass film. Further, since the silicon oxide film is formed on the phosphosilicate glass film, the polycrystalline silicon film is prevented from being doped with phosphorus in the phosphosilicate glass film in the TFT manufacturing process.

[0012]

EXAMPLE An example of a semiconductor device substrate according to the present invention will be described with reference to FIG. The semiconductor device substrate 10 is formed by sequentially stacking a phosphosilicate glass film 2, a silicon oxide film 3, and a poly-Si layer 4 on a glass substrate 1. A method of manufacturing the semiconductor device substrate 10 will be described. Film formation temperature: 410 ° C., gas flow rate: SiH ₄ : O ₂ : PH ₃ : N ₂ = 900: 1180: 43 on the glass substrate 1 by atmospheric pressure CVD (hereinafter, APCVD) method.
Phosphosilicate glass containing 10 mol% of P ₂ O ₅ was deposited to a film thickness of 2000 angstroms under the condition of 0: 4000 sccm to form a phosphosilicate glass film 2, and a silicon oxide film 3 was continuously formed to a film thickness of 7000 angstroms. Deposit on.

Film formation temperature: 550 by the low pressure CVD method
° C, gas pressure: 300 mTorr, gas flow rate: SiH ₄ = 1
An a-Si film is deposited to 1000 angstrom under the condition of 00 sccm. After that, the KrF excimer laser is set to 450 m.
By irradiating the entire surface of the a-Si film with a laser power intensity of J / cm ² , annealing is performed to form a poly-Si layer 4 (FIG. 1A). Since the surface of the glass substrate 1 was covered with the phosphosilicate glass film 2, when Na contained in the glass substrate 1 was thermally diffused during the annealing, it was combined with phosphorus in the phosphosilicate glass film 2 to form the phosphosilicate glass film. 2 is absorbed into the poly-Si layer 4 and prevented from being deposited in the poly-Si layer 4.

Next, an embodiment of a method of manufacturing a thin film transistor using the semiconductor device substrate 10 will be described with reference to FIG. Po of semiconductor device substrate 10
The island-shaped polysilicon layer 11 is formed by patterning the ly-Si layer 4 by photolithography. Then E
Gate insulating film 1 by depositing SiO ₂ by CRCVD method
Form 2. The deposition conditions are SiH ₄ / N ₂ O gas flow rate:
10 sccm / 200 sccm, gas pressure: 5 × 10 ⁻³
Torr, discharge power: 100 W, film thickness: 1000 angstrom. As a film deposition method, ECRCVD
Other than the above method, LPCVD, plasma CVD, sputtering method or the like may be used.

Next, a poly-Si film is deposited by the LPCVD method and then patterned to form a gate electrode 13 on the island-shaped polysilicon layer 11. The film deposition conditions were as follows: SiH ₄ gas flow rate: 200 sccm, gas pressure: O. 5 Torr, substrate temperature: 500 ° C., film thickness: 3000 Å. As the gate electrode material, in addition to poly-Si, high melting point metals such as W, Mo, Ti, Ta and alloys thereof,
A silicide of these metals and poly-Si may be used.

Next, by ion implantation, phosphorus (P) ions are implanted into the gate electrode 13 and the island-shaped polysilicon layer 11 at an energy of 100 KeV and a dose amount of 5 × 10 ¹⁵ ions / cm ² to form the source portion 11a and the drain. The part 11b is formed (FIG. 1B).

Subsequently, in order to activate the doped ions, heat treatment is performed at 550 ° C. for 60 hours in a nitrogen atmosphere, or a KrF excimer laser is used at 300 mJ / cm 2.
^The annealing is performed by irradiating with an intensity of ² . Even by these heat treatments and annealings, Na that thermally diffuses from the glass substrate 1 is prevented from being taken up by the phosphosilicate glass film 2 and precipitated in the island-shaped polysilicon layer 11 as in the above.

Next, a SiO ₂ film as the interlayer insulating film 14 is deposited (700 nm) by a normal transistor manufacturing process.
0 angstrom), formation of contact holes 15,
Electrode 1 after deposition and patterning of Al which is a wiring material
6 is formed, a Si ₃ N ₄ film as a passivation film is deposited and patterned (not shown), and if necessary, hydrogen plasma treatment for improving characteristics such as hydrogenation is performed to perform thin film transistor (TFT). ) Is completed.

BT stress of the TFT manufactured as described above (substrate temperature 250 ° C., bias 30 V, 30 min)
When the shift value of the C-V characteristic before and after was measured, it was 0.
The value is 5 (V) or less, which is smaller than the shift value according to the structure described in the conventional example.

[0021]

According to the present invention, since the phosphosilicate glass film is formed on the glass substrate, Na existing in the glass substrate is taken into the phosphosilicate glass film in the heat treatment step in the TFT manufacturing process, After the TFT is manufactured, Na existing at the gate insulating film of the TFT or the interface between the channel layer and the gate insulating film can be reduced. As a result, the shift value of the CV characteristic before and after the BT stress in the TFT can be reduced, so that the shift value of the threshold voltage corresponding to this shift value can be reduced and the operation of the TFT is prevented from becoming unstable. In addition, a TFT having stable characteristics can be obtained.

[Brief description of drawings]

1A to 1C are manufacturing process diagrams showing a method of manufacturing a thin film transistor according to the present invention.

FIG. 2 is an explanatory cross-sectional view showing the structure of a conventional thin film transistor.

FIG. 3 is a cross-sectional explanatory view showing a structure of a conventional thin film transistor.

FIG. 4 is a graph of a CV characteristic curve showing the relationship between the bias voltage applied to the gate electrode of the TFT and the semiconductor capacitance. DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Phosphosilicate glass film, 3 ... Silicon oxide film, 4 ... Poly-Si film, 10 ... Semiconductor device substrate, 11 ... Island-like polysilicon layer, 11a ... Source part, 11b ... Drain part, 12 ... Gate insulating film,
Reference numeral 13 ... Gate electrode, 14 ... Interlayer insulating film, 15 ... Contact hole, 16 ... Electrode

Claims (2)

[Claims] 1. A semiconductor device substrate for obtaining a polycrystalline silicon film on a glass substrate by crystallizing the amorphous silicon film, wherein 5 mol of phosphoric acid is added to the surface of the glass substrate below the amorphous silicon film. % Or more of a phosphosilicate glass film is formed, and a silicon oxide film is formed on the phosphosilicate glass film. 2. A method of manufacturing a substrate for a semiconductor device, which comprises laminating a polycrystalline silicon film obtained by crystallizing an amorphous silicon film on a glass substrate, wherein the glass substrate surface contains phosphoric acid in an amount of 5 mol% or more. A semiconductor comprising: a step of depositing a phosphosilicate glass; a step of forming a silicon oxide film on the phosphosilicate glass film; and a step of forming a polycrystalline silicon film on the silicon oxide film. Method for manufacturing device substrate.