JP3065528B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor device using a semiconductor having a microcrystal structure having lattice distortion.

[0002] SUMMARY OF THE INVENTION The present invention is mainly composed gaseous hydrogen or hydrogen (remainder inert gas such as argon) impurity concentration in the atmosphere than 5 × 10 ¹⁸ cm ^-3 in the semiconductor data - sputter the target Thus, by thermally crystallizing an amorphous semiconductor having an oxygen concentration of 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less, lattice strain of an oxygen concentration of 7 × 10 ¹⁹ cm ⁻³ or less can be obtained. The present invention relates to a semiconductor device using a semiconductor having a microcrystal structure.

[0003]

2. Description of the Related Art Hitherto, a polycrystalline semiconductor device has been manufactured by forming a polycrystalline semiconductor film by forming the polycrystalline semiconductor film at a temperature of 550 to 900.degree. C. by a low pressure CVD method, and using this polycrystalline semiconductor film.

It is also known to form microcrystals by a plasma CVD method.

[0005]

2. Description of the Related Art When a non-single-crystal semiconductor film is obtained by a low-pressure CVD method, there is a problem that it is difficult to form a film uniformly on a large-area substrate.

Further, when microcrystals are formed by the plasma CVD method, there is a problem that the film formation process takes a long time. Also, if left in the air, there is a problem that natural oxidation occurs and the film itself is not dense.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a microcrystalline semiconductor having lattice distortion by thermally crystallizing a non-single-crystal semiconductor that does not undergo dense spontaneous oxidation obtained by an industrially mass-produced sputtering method. It is an object of the invention. Then, it is intended to use it for an active region of an insulated gate field effect semiconductor device, particularly for a channel formation region.

[0008]

According to the present invention, the average crystal grain size is 5 to 400 mm.
And the hydrogen content therein is 5 atomic% or less. In particular, the feature is that oxygen as an impurity is set to 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less. And by giving each microcrystal a lattice strain, its crystal interfaces are in close contact with each other microscopically,
They try to eliminate the barrier for carriers at the grain boundaries.

For this reason, at a polycrystalline grain boundary having no lattice distortion, oxygen and the like segregate there and a barrier (barrier) hinders the movement of carriers. In the present invention, however, such lattice distortion causes a barrier. Since it is negligible or negligible, the electron mobility has an extremely superior feature of 5 to 300 cm ² / Vsec.

The present invention relates to an amorphous (amorphous or very similar) semiconductor film (hereinafter a-Si) formed by sputtering on a substrate in an atmosphere containing hydrogen or hydrogen and an inert gas containing hydrogen as a main component. ), And a step of crystallizing the amorphous semiconductor film obtained by the sputtering method at a temperature of 450 to 700 ° C, typically 600 ° C.

[0011]

【Example】

(Embodiment 1) In this embodiment, a magnetron type
The a-Si film produced by the RF (high frequency) sputtering apparatus is thermally crystallized to have lattice distortion, the average crystal grain size is as small as 5 to 400 mm, and the content of hydrogen is 5 to 5 mm.
Atomic% or less and oxygen as an impurity is 7 × 10 ¹⁹
A polycrystalline silicon semiconductor layer of quasi-crystal (also referred to as semi-amorphous Quasi-crystal or Semi-amrphas) having a size of cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less was formed. A thin film transistor was manufactured using this microcrystalline silicon semiconductor layer.

FIG. 1 shows a manufacturing process of the thin film transistor manufactured in this embodiment.

First, a silicon oxide film (12) is formed on a glass substrate (11).
Was formed to a thickness of 200 nm by magnetron type RF sputtering under the following conditions. O ₂ 100% atmosphere Deposition temperature 150 ° C RF (13.56MHz) output 400W Pressure 0.5 Pa Single crystal silicon is used as target

Furthermore, a high-purity magnetron RF
A-Si film (1
3) is deposited to a thickness of 100 nm.

In this sputtering method, the back pressure was set to 1 × 10 ⁻⁷ Pa or less, and exhaust was performed using a turbo molecular pump and a cryopump. The amount of the supplied gas had a purity of 5N (99.999%) or more, and the additional gas used was 4N or more of argon used as needed. Data - single crystal silicon be 5 × 10 ¹⁸ cm ^-3 or less in the oxygen concentration target, for example an oxygen concentration of 1 × 10 ¹⁸ cm ^-3, the oxygen as an impurity in the film formed was very small.

The film formation conditions were a hydrogen content ratio of 20 to 100% and an argon content ratio of 80 to 0%, for example, a hydrogen content of 100%. Under such an atmosphere, H ₂ / (H ₂ + Ar) = 100% (partial pressure ratio), deposition temperature 150 ° C. RF (13.56 MHz) output 400 W, total pressure 0.5 Pa, and a high-purity Si target as a target.

Thereafter, the a-Si film (1) is heated at a temperature of 450 to 700 ° C., for example, 600 ° C. for 10 hours in hydrogen or an inert gas, in this embodiment, 100% hydrogen atmosphere.
The thermal crystallization of 3) was performed. It was so-called microcrystal (or semi-amorphous).

The impurity purity in the amorphous silicon film formed by this method and in the film crystallized by heat treatment was examined by SIMS (Secondary Ion Equivalent Analysis). Then, among the impurity concentrations during the film formation, oxygen was 8 × 10 ¹⁸ cm ⁻³ and carbon was 3 × 10 ¹⁶ cm ⁻³ . Hydrogen had a concentration of 4 × 10 ²⁰ cm ⁻³ , which was equivalent to 1 atomic% when the density of silicon was 4 × 10 ²² cm ⁻³ . These were examined on the basis of the oxygen concentration of the target single crystal silicon of 1 × 10 ¹⁸ cm ⁻³ . In this SIMS analysis, the distribution in the depth direction (depth profile) of the film after film formation was examined, and the minimum value was used as a reference. This is because the surface has silicon oxide which is naturally oxidized with the atmosphere.
These values did not change significantly even after the crystallization treatment, and the oxygen impurity concentration was 8 × 10 ¹⁸ cm ⁻³ . In this embodiment, the oxygen is increased just in case, for example N ₂ O
Was added at 0.1 cc / sec and 10 cc / sec. Then, the oxygen concentration after crystallization increased to 1 × 10 ²⁰ cm ⁻³ and 4 × 10 ²⁰ cm ⁻³ . However, when such a coating was used, at the same time, crystallization could be performed only by increasing the temperature required for crystallization to 700 ° C. or more, or increasing the crystallization time by at least 5 times or more. That is, considering industrially the softening temperature of the glass of the substrate, the treatment at 700 ° C. or lower, preferably 600 ° C. or lower is important, and it is also important to further reduce the time required for crystallization. However, no matter how much impurities such as oxygen concentration are reduced, it is experimentally impossible to crystallize an a-Si semiconductor by thermal annealing at 450 ° C. or lower.

Further, in the present invention, as a result of using such a high-quality sputtering apparatus, the oxygen concentration during film formation becomes 1 × 10 ²⁰ cm ⁻³ or more due to leakage from the apparatus. In such a case, such characteristics of the present invention cannot be expected.

[0021] It is the oxygen concentration of 7 × 10 ¹⁹ cm ^-3 or less in the as of nuclear, and the heat treatment temperature was determined to be 450 to 700 ° C.. Of course, in the case of germanium, or in the case of a compound semiconductor of silicon and germanium, the annealing temperature could be lowered by about 100 ° C.

This microcrystalline semiconductor has lattice distortion, and as shown in the laser Raman analysis data shown in FIG. 4, it has shifted to the lower wave number side as compared with single crystal silicon.

Hereinafter, a method for manufacturing an insulating gate type field effect transistor which is a semiconductor device of the present invention will be described. That is, device isolation patterning is performed on the thermally crystallized microcrystalline silicon semiconductor obtained by the method of the present invention, and FIG.
The shape of (a) was obtained.

Next, an n ⁺ a-Si film (14) was formed to a thickness of 50 nm by magnetron RF sputtering under the following conditions. The film formation conditions are a hydrogen partial pressure ratio of 20 to 99% or more (80% in this embodiment), an argon partial pressure ratio of 80 to 0% (in this embodiment,
In an atmosphere with a PH ₃ partial pressure ratio of 0.1% to 10% (1% in the embodiment), a film formation temperature of 150 ° C. RF (13.56 MHz) output 400 W, a total pressure of 0.5 Pa, and a single crystal (oxygen Concentration 1 × 10 ¹⁸ cm
^-3 ) Si was used as a target.

In order to manufacture a semiconductor layer having one conductivity type, a PCVD method may be used. Further, after forming the active layer, impurities (for example, B (boron), P (phosphorus), As (arsenic)) may be added by ion implantation to form a source and a drain. Thereafter, gate region patterning was performed to obtain the shape shown in FIG.

Next, a gate silicon oxide film (15) was formed to a thickness of 100 nm by magnetron type RF sputtering under the following conditions to obtain the shape shown in FIG. 1 (c). Oxygen atmosphere 100% pressure 0.5pa, film formation temperature 100 ° C RF (13.56MHz) output 400W Single crystal silicon target or synthetic quartz target was used.

Next, contact hole opening and patterning were performed to obtain the shape shown in FIG. Finally, an aluminum electrode (16) is formed to a thickness of 300 nm by vacuum deposition and patterned to obtain the shape shown in FIG. 1 (e). Thereafter, a hot hydrogen annealing is performed at 375 ° C. in a 100% hydrogen atmosphere. This was performed for 30 minutes at a temperature to complete a thin film transistor. This hydrogen thermal annealing is for reducing the interface level between the polycrystalline silicon semiconductor and the silicon oxide insulating film and improving the device characteristics.

In the thin film transistor shown in FIG. 1E, S is a source electrode, G is a gate electrode, and D is a drain electrode. In addition, the size of the channel portion (17) of the thin film transistor manufactured in this example in FIG.
× 100 μm.

The above is the method of manufacturing a thin film transistor using the polycrystalline silicon semiconductor layer manufactured in this embodiment. In order to show the effect of the present invention, the a-Si layer shown in FIG. Five examples were prepared in which the concentration of hydrogen and the concentration of oxygen mixed involuntarily were changed as conditions for forming (13) by a magnetron type RF sputtering method. Five examples of the method are described below.

[0030] (Example 2) This example of a channel forming region in the production process FIGS. 1 (a) the partial pressure ratio of the atmosphere during sputtering of making the (13) H ₂ / Example 1 ( (H ₂ + Ar) = 0% (partial pressure ratio), and the others were produced in the same manner as in Example 1. The oxygen concentration had 2 × 10 ²⁰ cm ⁻³ .

[0031] (Example 3) the partial pressure ratio of the atmosphere during sputtering of making the (13) of this embodiment serves as a channel formation region in the fabrication method in the Embodiment 1 FIG. 1 (a) H ₂ / ( (H ₂ + Ar) = 20% (partial pressure ratio), and the others were produced in the same manner as in Example 1. The oxygen concentration during the film formation was 7 × 10 ¹⁹ cm ⁻³ .

[0032] (Example 4) The partial pressure ratio of the atmosphere during sputtering of making the (13) of this embodiment serves as a channel formation region in the fabrication method in the Embodiment 1 FIG. 1 (a) H ₂ / ( (H ₂ + Ar) = 50% (partial pressure ratio), and the others were produced in the same manner as in Example 1. The oxygen concentration during the film formation was 3 × 10 ¹⁹ cm ⁻³ .

[0033] (Example 5) the partial pressure ratio of the atmosphere during sputtering of making the (13) of this embodiment serves as a channel formation region in the fabrication method in the Embodiment 1 FIG. 1 (a) H ₂ / ( (H ₂ + Ar) = 80% (partial pressure ratio), and the others were produced in the same manner as in Example 1. The oxygen concentration during the film formation was 1 × 10 ¹⁹ cm ⁻³ .

The results of comparison of the electrical characteristics of the above embodiments are shown below. FIG. 2 is a diagram showing the completed channel portion (carrier mobility μ (FIELD in (17) of FIG. 6E) of Examples 1 to 5).
MOBILITY) and the hydrogen partial pressure ratio during sputtering (P _H / P
_TOTA = is H ₂ / a graph showing the relationship between the (H ₂ + Ar)).
Table 1 below shows the correspondence between the plot points in FIG. 2 and the examples.

[0035]

[Table 1]

[0036] When the hydrogen partial pressure according to Figure 2 is 0% since the oxygen concentration is also ^{2 × 10 20 cm -3, 3} × 10 -1 cm 2 V / sec and very small, and the other, the present invention Remarkably high mobility 2cm ² / Vs at 20% or more and oxygen concentration 7 × 10 ¹⁹ cm ^-3 or less
It can be seen that μ (FIELD MOBILITY) is obtained not less than ec.

This is presumed to be because, when hydrogen was added, oxygen in the chamber in the sputter was converted to water, which could be positively removed by a cryopump. FIG. 3 shows the threshold voltage and the hydrogen partial pressure ratio during sputtering (P _H / P _TOTAL = H ₂
/ (H ₂ + Ar)) is a graph.

Hydrogen partial pressure ratio (P _H / P _TOTAL = H ₂ / (H ₂ + Ar))
And the corresponding example numbers are the same as those in Table 1. As the threshold voltage is lower, the operating voltage for operating the thin film transistor, that is, the gate voltage may be lower,
Considering that good characteristics as a device can be obtained, the result of FIG. 3 shows that a normally-off state with a threshold voltage of 8 V or less is obtained by sputtering with a high hydrogen partial pressure ratio of 20% or more. Can be. That is, a device using a microcrystalline silicon semiconductor layer obtained by obtaining an a-Si film shown in (13) of FIG. 1A to be a channel forming region and recrystallizing the a-Si film. It can be seen that (the thin film transistor in this example) shows good electrical characteristics.

FIG. 3 shows a laser Raman spectrum of a polycrystalline silicon semiconductor layer obtained by thermally crystallizing an a-Si film. FIG.
Table 2 shows the relationship between the symbols shown in Table 2 and the example numbers and the hydrogen partial pressure ratio during sputtering.

[0040]

[Table 2]

Referring to FIG. 4, the curve (4) is compared with the curve (42).
3) That is, comparing the case where the hydrogen partial pressure ratio is 0% and the case where the hydrogen partial pressure ratio is 100% at the time of sputtering when forming an a-Si semiconductor layer to be a channel formation region ((17) in FIG. 1E). ,
When crystallized by thermal annealing, the Raman spectrum when the partial pressure ratio of hydrogen at the time of sputtering is 100% has remarkable crystallinity, and the average crystal grain size is 5 to 5 times the half width. 400Å typically 50-300Å. Then, it shifts to a lower wave number side than the peak value of 520 cm ^{-1 of} single crystal silicon, and clearly has lattice distortion. This clearly shows the features of the present invention. In other words, the effect of producing an a-Si film by a sputtering method to which hydrogen is added appears only when the a-Si film is thermally crystallized.

With such a lattice strain, the fine crystal grains are forcibly shrunk to each other, so that the close contact at the crystal grain boundaries becomes stronger, and the energy barrier for the carriers at the crystal grain boundaries also increases. Segregation of impurities such as oxygen hardly occurs. As a result, high carrier mobility can be expected.

In general, when the drain voltage VD is low in a thin film transistor that is a field effect transistor, the relationship between the drain current ID and the drain voltage VD is expressed by the following equation. ID = (W / L) μC (VG-VT) VD (Solid.State electronics.Vol.24.No.11.pp.1059.198
1.Printed in Britain) In the above equation, W is the channel width, L is the channel length, μ
Is the carrier mobility, C is the capacitance of the gate oxide film, VG
Is fixed as the gate voltage and VT is fixed as the threshold voltage.

Ar was used as the inert gas at the time of the above sputtering, but other inert gas such as He or a reactive gas such as SiH ₄ or Si ₂ H ₆ which was made into a plasma was used as an atmosphere gas. May be used by adding to some of them. In the formation of the a-Si film by the magnetron type RF sputtering method of the present embodiment, the hydrogen concentration is 5 to 100%, and the film formation temperature is room temperature to 500%.
In the range of ° C., the RF output can be arbitrarily selected in the range of 500 Hz to 100 GHz and the output in the range of 100 W to 10 MW, and may be combined with a pulse energy source. Further, light sputtering (wavelength: 100 to 500 nm or less) may be performed by applying more powerful light irradiation energy.

In this method, light atoms called hydrogen are made more plasma, positive ions required for sputtering are efficiently generated, and hydrogen or hydrogen atoms are uniformly added to a film formed by sputtering. As a result, This is for the purpose of forming a semiconductor film in which oxygen is mixed at a concentration of 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less.

In the present invention, the amorphous semiconductor film is simply abbreviated as an a-Si film in the specification. However, this mainly uses silicon semiconductors, but germanium, SixGe _1-x
(0 <x <1). This may be a P or N type semiconductor as well as an intrinsic semiconductor.

Further, the other reactive gas may be applied to the above means.

[0048]

According to the constitution of the present invention, in the step of thermally crystallizing a non-single-crystal semiconductor obtained by an industrially useful sputtering method to obtain a polycrystalline semiconductor, it becomes difficult to perform thermal crystallization which is a problem. The problem could be solved, and a high-performance thin film transistor could be manufactured using this polycrystalline semiconductor layer.

[Brief description of the drawings]

FIG. 1 shows manufacturing steps of Examples 1 to 6.

FIG. 2 shows a relationship between a partial pressure ratio of hydrogen added during formation of an a-Si film to be a channel formation region and mobility of carriers in the thin film transistor manufactured in this example in a manufacturing process of the thin film transistor manufactured in this example. It is shown.

FIG. 3 shows a relationship between a partial pressure ratio of hydrogen added when an a-Si film serving as a channel formation region is manufactured and a threshold value of a thin film transistor manufactured in the present embodiment in a manufacturing process of the thin film transistor manufactured in this embodiment. It shows the relationship.

FIG. 4 shows a Raman spectrum of a polycrystalline silicon semiconductor manufactured in this example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Glass substrate 12 ... Silicon oxide film 13 ... Active layer of microcrystalline semiconductor 14 ... n ⁺ a-Si film 15 ... Gate oxide film 16 ... Aluminum electrode 17 ... Channel forming region S ... source electrode G ... gate electrode D ... drain electrode

Claims (3)

(57) [Claims] 1. A insulated gate field effect semiconductor device, a semiconductor layer on the glass substrate to contact said semiconductor layer
A gate insulating film and a gate electrode in contact with the gate insulating film
When have, the semiconductor layer, Raman spectrum is 52
0 cm ^-1 shifted to the lower frequency side , average crystal grain size is 5 to 40
0 °, and the oxygen concentration is 7 × 10 ¹⁹ atoms / cm ³ or less.
A semiconductor device having an electron mobility of 5 to 300 cm ² / Vsec . 2. The semiconductor device according to claim 1, wherein the semiconductor layer is formed of silicon.
Compound of germanium, silicon, germanium or silicon
A semiconductor device characterized by being made of an object. 3. An insulated gate field effect semiconductor device.
Contact with the semiconductor layer on the glass substrate and the semiconductor layer
A gate insulating film and a gate electrode in contact with the gate insulating film
And the semiconductor layer has a Raman spectrum of 52
0cm ^-1 Silicon and germanium shifted to lower frequencies
With an oxygen concentration of 7 × 10 ¹⁹ atoms / cm ^Three Less than
A semiconductor device, characterized in that: