JPH05218430A - Polycrystal silicon film transistor and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Objective] To obtain a high-performance polycrystalline silicon thin film transistor having high electric field effect mobility and low leakage current electrical characteristics. [Structure] The thickness of the polycrystalline silicon thin film forming the channel region, the drain region and the source region made of the polycrystalline silicon thin film is 250 Å to 750 Å, and the hydrogen content concentration is 5 × 10 ²⁰ atom cm ⁻³ or more. Further, the polycrystalline silicon thin film obtained by the CVD method is melted and recrystallized and then subjected to hydrogen plasma treatment.
Do not apply heating temperature above 0 ° C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high performance polycrystalline silicon thin film transistor and a method of manufacturing the same.

[0002]

2. Description of the Related Art Polycrystalline silicon thin film transistors having polycrystalline silicon as a channel region have a wide range of applications such as driving elements for liquid crystal displays and integrated circuits. In order to apply a polycrystalline silicon thin film transistor to such various elements, it is important to obtain high field effect mobility and reduce leakage current.

Conventionally, as an example of a polycrystalline silicon thin film transistor having such good characteristics, Japanese Patent Laid-Open No. 64-469 has been used.
The one described in Japanese Patent No. 68 is known. This one is
The polycrystalline silicon thin film is melted by laser irradiation, solidified again, and then subjected to hydrogen plasma treatment to form a polycrystalline silicon thin film having a trapped charge density of 8 × 10 ¹¹ cm ^-2 or less, which is used as a channel region. Thus, a polycrystalline silicon thin film transistor with high transconductance is obtained.

That is, in this conventional technique, from the relationship between the trapped charge density and the field effect mobility as shown in FIG. 4, the trapped charge density is lowered to increase the field effect mobility, thereby increasing the mutual conductance. It is an attempt to raise it.

However, the relationship between the trapped charge density and the field effect mobility as shown in FIG. 4 can be grasped for the first time by evaluating the electrical characteristics of the completed polycrystalline silicon thin film transistor. Further, the calculation of the value of the trapped charge density requires a calculation formula based on an assumption, so that a unique value of the trapped charge density cannot always be obtained in consideration of various characteristics of the polycrystalline silicon thin film transistor. For these reasons, it is impossible to investigate the physical properties of the polycrystalline silicon thin film during the manufacturing process of the polycrystalline silicon thin film transistor, control the film quality, and predict the electrical characteristics of the completed polycrystalline silicon thin film transistor.

Further, when the thickness of the polycrystalline silicon thin film forming the channel region of the polycrystalline silicon thin film transistor is different, the field effect mobility is different even if the trapped charge density is the same. It is known that the trapped charge density increases with the mobility, and the drive voltage cannot be reduced. This is because when a polycrystalline silicon thin film is formed thickly, the average grain size of silicon crystal grains increases and the field effect mobility increases, while the grooves between crystal grains deepen and the trapped charge density at grain boundaries increases. This is because. Therefore, it is possible that the trapped charge density is high but the electric field mobility is also high. Therefore, even if only the trapped charge density of the polycrystalline silicon thin film is controlled, a high-performance polycrystalline silicon thin film transistor cannot be obtained unless an appropriate film thickness of the polycrystalline silicon thin film forming the channel region is set.

Further, the trapped charges in the polycrystalline silicon thin film can be obtained only by the steps of once melting and then solidifying the polycrystalline silicon thin film which becomes the channel region described in the above-mentioned prior art, and the step of subsequently performing hydrogen plasma treatment. It is not possible to control the density. In particular, when manufacturing a polycrystalline silicon thin film transistor as a driving device for a liquid crystal display or the like, it is important to control the temperature of a process involving heating after hydrogen plasma treatment. The reason is that if a step involving heating at 400 ° C. or higher is added after the hydrogen plasma treatment, hydrogen in the polycrystalline silicon thin film is released and the trapped charge density increases.

Therefore, in order to obtain a high-quality polycrystalline silicon thin film that constitutes a high-performance polycrystalline silicon thin film transistor, a step involving heating at 400 ° C. or higher is performed after the step of melting and re-solidifying, and then performing a hydrogen plasma treatment. It is necessary to exclude the step which is performed before and after the hydrogen plasma treatment, which involves heating at 400 ° C. or higher.

[0009]

Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a high-performance polycrystalline silicon thin film transistor having high electric field effect mobility and low leakage current electrical characteristics. To get.

[0010]

[Means for Solving the Problems] The problem is that the thickness of the polycrystalline silicon thin film is set to 250 Å to 750 Å and the hydrogen concentration existing in the channel region, the drain region and the source region is 5 × 10 ²⁰ atom cm ^-3 or more. What to do,
And a step of forming a polycrystalline silicon thin film to be a channel region, a drain region and a source region by a vapor phase chemical vapor deposition method, a step of melting the polycrystalline silicon thin film once and then solidifying it again, and This can be solved by manufacturing the thin film by a step of subjecting the thin film to hydrogen plasma treatment, and a step of not heating at 400 ° C. or higher after the step of hydrogen plasma treatment.

An embodiment of the present invention will be described below with reference to the drawings. The following examples show various characteristics of a polycrystalline silicon thin film that was once melted by the laser recrystallization method and then solidified again.

FIG. 1 shows the hydrogen concentration in a polycrystalline silicon thin film forming a channel region and both source and drain electrode regions of a polycrystalline silicon thin film transistor by SIMS (Se).
Condary Ion Mass Spectrometry). After removing all the films laminated above the gate insulating film of the completed polycrystalline silicon thin film transistor, the hydrogen concentration from the gate insulating film to the polycrystalline silicon thin film and the insulating substrate was analyzed. Such an analysis can be easily performed at any time after forming the polycrystalline silicon thin film in the manufacturing process of the polycrystalline silicon thin film transistor.

As shown in FIG. 1, the hydrogen concentrations in the polycrystalline silicon thin films (polycrystalline silicon regions) of Sample A and Sample B are remarkably different. Sample A was obtained by performing hydrogen plasma treatment after the completion of the polycrystalline silicon thin film transistor, and the hydrogen concentration in the polycrystalline silicon thin film was 5
The film thickness is 500Å at × 10 ²⁰ atom cm ⁻³ . On the other hand, the polycrystalline silicon thin film of Sample B was not subjected to hydrogen plasma treatment. FIG. 2 shows the electrical characteristics of the polycrystalline silicon thin film transistor configured by using the polycrystalline silicon thin films having different hydrogen concentrations as described above.

As is apparent from FIG. 2, the electrical characteristics of the polycrystalline silicon thin film transistor of sample A formed by using the polycrystalline silicon film having a high hydrogen concentration are the same as those of sample B not subjected to the hydrogen plasma treatment. compared,
Obviously it has two advantages. First, a high operating current showing high field effect mobility, and second, a low leak current and a large on / off ratio can be easily obtained. That is, when hydrogen of 5 × 10 ²⁰ atom cm ⁻³ or more is contained in the polycrystalline silicon thin film, not only the silicon crystal grain boundary but also the trapped charge density in the silicon crystal grain is reduced, the potential barrier is lowered, and the electric field is reduced. It can be seen that not only the effect mobility is increased, but also the effect of reducing the leak current generated via the trap level near the drain electrode is produced. Since such a high performance polycrystalline silicon thin film transistor can be used with a low driving voltage, power consumption can also be reduced.

FIG. 3 shows that even if the hydrogen content concentration in the polycrystalline silicon added by the hydrogen plasma treatment is the same, if the film thickness of the polycrystalline silicon thin film forming the channel region of the polycrystalline silicon thin film transistor is different, the electrical characteristics are changed. It can be said that they can be different. The film thickness of the polycrystalline silicon thin film in the channel region of the polycrystalline silicon thin film transistors of Samples A, C, D and E shown in FIG. 3 are 500Å, 750Å, 1000Å and 200Å, respectively.

As is clear from the electrical characteristics of these samples A, C, D and E, the leak current increases as the thickness of the polycrystalline silicon forming the channel region increases. In order to ensure proper operation, it is better that the leak current is low, but the operating current of a transistor composed of a polycrystalline silicon thin film with a film thickness of 200Å is 500Å
It is lower than the operating current of the transistor made of the polycrystalline silicon thin film. This is because even if the trapped charge density in the polycrystalline silicon thin film is the same, if the thickness of the polycrystalline silicon thin film is smaller than 250 Å, the sheet resistance of the source and drain electrode regions and the contact resistance with the wiring material become remarkably large. This is because the effective drain-source electrode voltage (VDS) applied to the channel region decreases.

Therefore, if the thickness of the polycrystalline silicon thin film is smaller than 250 Å, a sufficient on / off ratio cannot be obtained. When the thickness of the polycrystalline silicon thin film forming the channel region of the polycrystalline silicon thin film transistor is 250 Å or more, the operating current decreases as the thickness increases. This is because even if the concentration of hydrogen contained in the polycrystalline silicon thin film is the same, the scattering of conduction carriers due to the charges formed by the unterminated silicon bond causes the increase in the thickness of the crystal grain boundary or crystal. This is because it easily occurs inside. In the case of a polycrystalline silicon thin film transistor having a channel width and an effective channel length of 10 μm and a gate applied voltage of 10 V, in order to obtain an operating current of 1 μA or more, the thickness of the polycrystalline silicon thin film needs to be 750 Å or less. For the above reasons, it is appropriate that the thickness of the polycrystalline silicon thin film forming the active region of the high-performance polycrystalline silicon thin film transistor is 250 Å or more and 750 Å or less, and the hydrogen concentration thereof is 5 × 10 ²⁰ atom cm ⁻³ or more. It can be said that

Next, a method of manufacturing such a polycrystalline silicon thin film transistor will be described. In this manufacturing method, a polycrystalline silicon thin film to be a channel region, a drain region and a source region is formed on a substrate by a well-known chemical vapor deposition method (CVD method), and then this polycrystalline silicon thin film is subjected to a laser recrystallization method. It is once melted and then solidified again by a melt recrystallization method such as an electron beam recrystallization method.
The film thickness of the polycrystalline silicon thin film after re-solidification is 250Å ~
It should be in the range of 750Å. After that, the solidified and recrystallized polycrystalline silicon thin film is subjected to a hydrogen plasma treatment so that the concentration of contained hydrogen in the polycrystalline silicon thin film is 5 × 10 ²⁰ atom cm ⁻³ or more.

In various steps after this hydrogen plasma treatment step, it is a very important requirement not to heat above 400 ° C. That is, when the polycrystalline silicon thin film after the hydrogen plasma treatment is heated to 400 ° C. or higher, hydrogen is released from the polycrystalline silicon thin film and the hydrogen content concentration becomes less than 5 × 10 ²⁰ atom cm ⁻³ . This is to prevent separation. Therefore, when the substrate on which the polycrystalline silicon thin film is formed is heated for some reason after the hydrogen plasma treatment, it is necessary to suppress the heating temperature to 400 ° C. or lower, preferably 350 ° C. or lower. .. For this reason, 40
If it must be heated above 0 ° C., it should be done before the hydrogen plasma treatment step. As a result, the contained hydrogen concentration can be maintained at 5 × 10 ²⁰ atom cm ⁻³ or more, and high field effect mobility can be provided.

[0020]

As described above, according to the present invention,
Thickness formed by melt recrystallization method such as laser recrystallization method using a 750Å following the polycrystalline silicon thin film above 250 Å, polycrystalline silicon thin film transistor 5 × 10 the hydrogen concentration in the channel region ²⁰ the atom cm ^{- 3}
As described above, a high-performance polycrystalline silicon thin film transistor having high electric field effect mobility and low leak current electrical characteristics can be realized. Further, unlike the case where the quality of the polycrystalline silicon thin film is controlled only by the trapped charge density, after the polycrystalline silicon thin film is formed, the contained hydrogen concentration can be grasped at any time during the polycrystalline silicon thin film transistor manufacturing process by SIMS analysis. This makes it possible to control the film quality of the polycrystalline silicon thin film. Therefore, the electrical characteristics of the completed transistor can be predicted by optimizing the film thickness of the polycrystalline silicon thin film and the concentration of hydrogen contained therein, which can facilitate process control for producing a high-performance polycrystalline silicon thin film transistor. In addition, by keeping the maximum temperature of the step after the hydrogen plasma treatment lower than 400 ° C., it is possible to prevent the contained hydrogen from being released and improve the reliability of the polycrystalline silicon thin film transistor.

[Brief description of drawings]

FIG. 1 is a graph showing the results of SIMS analysis in a polycrystalline silicon thin film.

FIG. 2 is a graph showing electrical characteristics of a thin film transistor in which polycrystalline silicon thin films having different contained hydrogen concentrations are used as active regions.

FIG. 3 is a graph showing electrical characteristics of a thin film transistor having polycrystalline silicon thin films having different thicknesses as active regions.

FIG. 4 is a graph showing the relationship between field effect mobility and trapped charge density of a polycrystalline silicon thin film transistor in the prior art.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H01L 21/336 9056-4M H01L 29/78 311 H 9056-4M 311 Y

Claims (2)

[Claims] 1. A polycrystalline silicon thin film is used as a channel region,
In a polycrystalline silicon thin film transistor used as a drain region and a source region, the thickness of the polycrystalline silicon thin film is 250 Å to 750 Å and the hydrogen concentration existing in the channel region, the drain region and the source region is 5 × 10 ²⁰ atom cm ^-3 or more. And a polycrystalline silicon thin film transistor. 2. A step of forming a polycrystalline silicon thin film which becomes a channel region, a drain region and a source region by a vapor phase chemical vapor deposition method, and a step of once melting the polycrystalline silicon thin film and then solidifying it again. A method of manufacturing a polycrystalline silicon thin film transistor, comprising: a step of subjecting this polycrystalline silicon thin film to hydrogen plasma treatment; and a step without heating at 400 ° C. or higher after this hydrogen plasma treatment step.