JP4410894B2 - Semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device having a light emitting function.
[0002]
[Prior art]
High integration of so-called LSIs, which are composed of MIS transistors represented by Si-MOS transistors, has been steadily progressed by miniaturization of individual transistors for 30 years since the 1970s. . Even today, DRAMs having a gigabit degree of integration are appearing on the market, and various methods for further improving the performance of future integrated circuits are being considered. For example, a high dielectric film is used for the gate insulating film, a SiGe-based material is used for the channel, and a structure such as SOI (Silicon (Semiconductor) On Insulator) is used to achieve individual transistor performance. Improvements are being considered.
[0003]
However, on the other hand, it has been pointed out that the key to improving the performance of future LSIs is to solve the signal propagation delay in the wiring. In fact, as for logic LSIs, products using Cu wiring instead of conventional Al wiring have appeared on the market. In addition, for the purpose of reducing the capacitance between wirings, research on an interlayer insulating film having a low dielectric constant has been actively conducted.
[0004]
However, simply changing the material of the wiring and insulating film does not provide an essential solution to improve the signal propagation speed of the wiring, and in the near future, information is exchanged between LSI chips and within the chip using optical signals. The realization of the technology to perform is predicted. For this reason, research on mounting a surface emitting semiconductor laser using a group III-V semiconductor on a Si substrate and material research on fabricating a light emitting device with Si itself or SiGe having good compatibility with Si have been actively conducted. ing. In particular, the latter research is attractive because it is possible to fabricate electronic devices and optical devices monolithically on a Si substrate when the future is considered.
[0005]
However, Si and SiGe are indirect transition semiconductors, and generally the emission intensity is extremely weak. In recent research, there are nanocrystals such as Si, SiGe, Ge and the like that have a high possibility of practical use as Si-based luminescent materials. It has been reported that when these are made in a material with a large energy gap such as SiO ₂ and excited by light such as a laser, relatively strong light emission occurs.
[0006]
Further, by doping a rare earth element such as Er into a base material in which oxygen atoms coexist, or doping into an insulator with a large gap such as SiO ₂ , light emission due to the inner-shell transition of Er ions is extremely high. It has been reported to become stronger.
[0007]
[Problems to be solved by the invention]
As described above, although light emission from various types of semiconductor nanocrystals and Er has been reported as a research of materials, research and proposals on what kind of device structure is useful as a light emitting device have been made so far. Little has been done.
[0008]
Nanocrystals, Er, and the like can obtain high luminous efficiency by doping a material having a large band gap such as SiO ₂ . However, these results are due to photoexcitation and electron beam excitation, and since the base material is an insulator even if an electrical contact is made directly to the insulating film because of the current injection method used in ordinary devices. Almost no current flows and satisfactory light emission intensity cannot be obtained.
[0009]
Therefore, the present invention has been made in view of the above problems, and can easily and reliably obtain high light emission efficiency, has excellent compatibility with a conventional Si-MOS transistor structure, and can be used for an optical interconnect. Therefore, an object of the present invention is to provide a semiconductor device capable of significantly improving the performance of an LSI.
[0010]
[Means for Solving the Problems]
As a result of intensive studies on the above problems, the present inventors have arrived at the invention shown below.
[0011]
In the first configuration of the present invention, a semiconductor device having a MIS transistor structure including a gate electrode and a source / drain is configured as a light emitting element. That is, in the gate insulating film, there is a light emitting substance that is at least one selected from a semiconductor nanocrystal including a group IV, a semiconductor microcrystal including a group IV, a polycrystal or a single crystal of a compound semiconductor, a rare earth element, and a fluorescent substance. A voltage that generates hot electrons is applied to the source / drain, a bias voltage is applied to the gate electrode, conductive carriers are injected into the gate insulating film, and the gate insulating film emits light. It is characterized by damaging.
[0014]
The gate insulating film is preferably formed by laminating a plurality of types of insulating films.
[0015]
In this case, the plurality of types of insulating films include a first insulating film in the vicinity of the gate electrode and a second insulating film spaced from the gate electrode through the first insulating film, The light emitting material is added to the second insulating film, and the first insulating film has a larger band gap that acts as an energy barrier against the carriers than the second insulating film. preferable.
[0016]
According to the second configuration of the present invention, when a semiconductor device having a MIS type transistor structure including a gate electrode and a source / drain is manufactured, a light emitting substance is formed in the gate insulating film when the gate insulating film is formed. Is added.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.
[0018]
(Configuration of light emitting element)
In this example, a MIS transistor type light emitting element (MIS type light emitting element) is illustrated as a semiconductor device having a light emitting function.
FIG. 1 is a schematic cross-sectional view showing the main configuration of the MIS type light emitting device of this embodiment, where (a) shows an n-channel type and (b) shows a p-channel type.
[0019]
This MIS type light emitting device is configured in substantially the same manner as a normal Si-MOSFET, and silicon oxide is formed on the source / drain 2 formed on the surface layer of the Si-semiconductor substrate 1 and on the channel between the source / drain 2. This is a three-terminal device having a gate electrode 4 patterned through a gate insulating film 3 made of a film (SiO ₂ film).
[0020]
The main feature of the light emitting element is that the gate insulating film 3 is formed thicker (about 50 nm to 500 nm) than that of a normal Si-MOSFET, and the gate insulating film 3 is doped with a light emitting substance. Suitable materials for the light-emitting material include semiconductor nanocrystals such as Si, SiGe, and Ge, polycrystals and microcrystals of direct transition semiconductors, and rare earth elements such as Er and Eu, and fluorescence such as ZnS: Mn. Substances. Here, the conductivity type of the channel of the light-emitting element may be n-type or p-type, but should be selected in consideration of the light-emitting mechanism of each light-emitting substance. It is preferable to use an n channel when injecting electrons into the p channel and a p channel when holes are injected.
[0021]
As a material of the gate insulating film 4, Si ₃ N ₄ , Al ₂ O ₃ , TiO ₂ or the like can be used in addition to SiO ₂ .
[0022]
Needless to say, the gate electrode 4 is desirably a transparent electrode in accordance with the wavelength band of light emission. For example, ITO (InSnO) or the like may be used as an electrode material that is transparent in the visible range. Moreover, it is also suitable as a structure in which a window is opened in a part of the gate metal 4 to extract emitted light.
[0023]
(Function of MIS type light emitting element)
The light emitting function of the MIS type light emitting element configured as described above will be described in general with reference to FIG. 2 and an n channel light emitting element (see FIG. 1A) as an example.
[0024]
If the channel length and the applied voltage between the source / drain 2 are set so that a relatively large electric field is applied between the source / drain 2, the channel conduction electrons gain energy by the electric field and have high energy, so-called hot Become an electron. Under such circumstances, when a relatively large positive bias voltage is applied to the gate electrode 4, some of the electrons in the channel thermally exceed the potential barrier of the gate insulating film 3, or a Fowler-Nordheim type tunneling process. Is injected into the gate insulating film 3. Light emission is caused by a plurality of processes in the gate insulating film 3 caused by the injected electrons.
[0025]
Based on the overall function of the MIS type light emitting device, the light emission process for each light emitting material doped in the gate insulating film 3 will be described.
[0026]
(1) Semiconductor nanocrystal, polycrystalline or fine particles of direct transition semiconductor, or fluorescent material such as ZnS: Mn In this case, as shown in FIG. 3, electrons injected in the gate insulating film 3 are accelerated by the gate voltage. However, it collides with the material containing the luminescent material and causes an ionization process to form electron-hole pairs due to excitation between bands, or ionization occurs due to the loss of some inner-shell electrons as in Mn. . Thereafter, when the electron-hole pair is recombined, light emission between bands occurs, or in Mn or the like, light emission specific to the fluorescent material is caused by electron capture or inner-shell transition. This process is similar to the cathode luminescence that emits light when the sample is accelerated and irradiated with thermionic and field emission electrons emitted from the electron gun (applied to a cathode ray tube of a television).
[0027]
(2) Rare earth elements such as Er and Eu In this case, as in (1), there is a method of embedding the rare earth elements in the gate insulating film 3 made of SiO ₂ or the like together with a semiconductor material serving as a host. As far as the previous reports are concerned, the luminous efficiency is high in the method of directly doping the rare earth element therein to obtain light emission of wavelength 1.54 μm resulting from the electron transition of the inner shell of the atom of the rare earth element. As shown in FIG. 4, in any case, in the solid, for example, Er is mainly ionized to trivalent cations, and the electrons captured by these ions cause a transition in the f orbit of the atomic core. Thus, light emission with a wavelength of 1.54 μm occurs. Alternatively, as in the case of (1), it is conceivable that Er loses core electrons due to impact ionization and emits light due to electron capture and core transition.
[0028]
(3) n-type or p-type doped semiconductor nanocrystals, direct transition semiconductor polycrystals or fine particles, as light emitting materials here, such as III-V and II-VI group compound semiconductors directly in the gate insulating film 3 Polycrystalline transition semiconductors, semiconductor nanocrystals, or semiconductor nanocrystals such as Si, SiGe, and Ge having high emission efficiency are formed, and these are doped n-type or p-type. In this case, as shown in FIG. 5, when electrons or holes serving as minority carriers are injected into the gate insulating film 3 from the channel into these luminescent materials, recombination with the majority carriers originally present in the luminescent materials occurs. As a result, light emission corresponding to the band gap occurs. Here, for example, an n-channel transistor is preferably used when the light-emitting substance is doped p-type, and a p-channel transistor is preferably used when the light-emitting substance is doped n-type.
[0029]
Unlike the MIS type light emitting device of the present embodiment, in a light emitting device having a two-terminal device structure having no source / drain (for example, a diode type light emitting device), not only a very large gate voltage needs to be applied but also injection is performed. Since the number of carriers to be generated is small, the emission intensity is weakened. On the other hand, in the present embodiment, a light emitting portion is formed in the gate insulating film 3 having the MIS transistor structure, and a voltage large enough to generate hot electrons (holes) between the source / drain 2 is applied. Since hot electrons (holes) are injected by applying a bias in an appropriate direction to 4, a larger number of carriers can be injected into the gate insulating film 3 than in the conventional element structure, and the emission intensity can be increased.
[0030]
Furthermore, in the MIS type light emitting device of this embodiment, the number of hot carriers that cause light emission can be independently controlled by the source / drain voltage and the gate voltage. In terms of the cathode luminescence analogy, the filament voltage of the electron gun corresponds to the source / drain voltage, and the acceleration voltage (extraction voltage) corresponds to the gate voltage. Therefore, the energy distribution of injected electrons (holes) can be controlled by adjusting these voltages.
[0031]
(Manufacturing method of light emitting element)
Hereinafter, the manufacturing method of the above-described light emitting device of this embodiment will be described in the order of steps.
FIG. 6 is a schematic cross-sectional view showing the method for manufacturing the MIS type light emitting device of this embodiment. Here, an n-channel MOS type light emitting element is illustrated.
[0032]
First, as shown in FIG. 6A, a p-type Si-semiconductor substrate 1 is prepared, and a SiO ₂ film 11 containing a luminescent material is formed on the substrate 1 to a film thickness of about 50 nm to 500 nm by a CVD method or the like. . Specifically, after a thermal oxide layer (lower layer) 12 is formed on the surface of the substrate 1, Si nanocrystals are grown on the thermal oxide layer 12. Then, an oxide layer (upper layer) 14 is formed by CVD or the like so as to cover the Si layer 13 made of Si nanocrystals, and the SiO ₂ film 11 is formed so as to wrap the Si layer 13 between the lower layer 12 and the upper layer 14.
[0033]
In this case, Si nanocrystals may be grown and formed on the lower layer film 12 in a state of being doped n-type or p-type depending on the situation.
[0034]
Here, as another method for forming the SiO ₂ film 11, the CVD method is used to set a larger proportion of Si in the source gas than when ordinary SiO ₂ is deposited (Si rich), and on the substrate 1. There is also a method of depositing SiO ₂ . In this case, the SiO ₂ film 11 is formed in such a way that unreacted fine Si nanocrystals are contained in SiO ₂ due to Si rich at the time of deposition. Further, after SiO ₂ is formed on the substrate 1, doping may be performed so that Si is ion-implanted into the SiO ₂ .
[0035]
As the semiconductor nanocrystal, Ge, SiGe or the like may be used instead of Si. Further, instead of semiconductor nanocrystals, semiconductor microcrystals including group IV, polycrystals or single crystals of compound semiconductors such as GaAs, rare earth elements such as Er and Eu, and fluorescent materials such as ZnS: Mn are formed. May be.
[0036]
Further, instead of SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , TiO ₂ or the like is also suitable as a material.
[0037]
Subsequently, as shown in FIG. 6B, a polycrystalline silicon film is formed on the SiO ₂ film 11 to a thickness of about 20 nm, and photolithography and subsequent dry etching are performed on the polycrystalline silicon film and the SiO ₂ film 11. And patterning into an electrode shape. As a result, the gate electrode 4 is formed on the substrate 1 with the gate insulating film 3 interposed therebetween.
[0038]
Subsequently, as shown in FIG. 6C, n-type impurities are ion-implanted into the surface layer of the substrate 1 using the gate electrode 4 as a mask. Specifically, for example, phosphorus (P) is ion-implanted as an n-type impurity at an acceleration energy of 50 to 100 keV and a dose of 5 × 10 ¹⁵ / cm ² . Then, by subjecting the substrate 1 to a predetermined annealing process, the source / drain 2 is formed on the surface layer of the substrate 1 on both sides of the gate electrode 4.
[0039]
Thereafter, the MOS type light emitting device is completed through formation of an interlayer insulating film covering the gate electrode 4, formation of various wiring layers electrically connected to the gate electrode 4 and the source / drain 2, and the like.
[0040]
This MOS type light emitting element is expected to be applied to various devices by being arrayed and integrated. Specifically, various drive circuits including a display of an image display device, a DRAM-type storage integrated circuit arranged with a storage capacitor, and a logic operation integrated circuit arranged in the same manner as a CMOS transistor It is suitable for mounting on a circuit or the like.
[0041]
As described above, according to the MIS type (mainly MOS type) light emitting element of the present embodiment, high light emission efficiency can be obtained easily and reliably, and it has good consistency with the conventional Si-MOS structure transistor. Since it has a structure, it can be integrated on a Si substrate. Further, since it can be used as a monolithic light emitting element on a Si substrate necessary for an optical interconnect, it is possible to solve the problem of wiring delay, which is a main factor that hinders performance improvement due to high integration of LSI.
[0042]
-Modification-
Hereinafter, various modifications of the MIS type light emitting device of this embodiment will be described. In addition, about the component similar to the light emitting element of this example, the same code | symbol is described and description is abbreviate | omitted.
[0043]
(Modification 1)
Here, as shown in FIG. 7, the gate insulating film 21 is formed in a three-layer structure in which an SiO ₂ layer 22, an Si ₃ N ₄ layer 23, and an SiO ₂ layer 24 are laminated in this order, and an Si ₃ N ₄ layer is formed. The light emitting material is added into the layer 23.
[0044]
In this case, SiO ₂ has a larger energy gap than Si ₃ N ₄ , and therefore SiO ₂ films 22 and 24 are implanted by sandwiching Si ₃ N ₄ with SiO _{2 as} shown in FIG. Functions as an energy barrier for carriers. The carriers for this purpose are confined in Si ₃ N ₄ , so that the phenomenon that the carriers escape to the gate electrode 4 side can be suppressed, and a further higher emission intensity can be obtained.
[0045]
(Modification 2)
Here, as shown in FIG. 9, the upper layer 14, which is a component of the gate insulating film 3, is formed thicker than the lower layer 12.
[0046]
In this case, as shown in FIG. 10, the Si layer 13 to which the luminescent material is added is arranged such that the distance from the Si layer 13 to the gate electrode 4 is longer than the distance to the channel. is there. Since the distribution of the gate voltage to the upper layer and the lower insulating film is different, the upper layer 14 effectively functions as an energy barrier against the injected carriers. As a result, it is possible to suppress the phenomenon that carriers escape to the gate electrode 4 side, and a further higher light emission intensity can be obtained.
[0047]
(Modification 3)
Here, as shown in FIG. 11, a gate insulating film 31, the dielectric film 32, the SiO ₂ layer 33 and the dielectric film 34 is formed on the multi-layer structure formed by laminating in this order, wherein in the SiO ₂ layer 33 Add luminescent material. The dielectric films 32 and 34 are configured by laminating material films having different dielectric constants. Specifically, the SiO ₂ layer 41, the Si ₃ N ₄ layer 42, the SiO ₂ layer 43, and the Si ₃ N ₄ layer, respectively. 44 has a four-layer structure in which the layers are laminated in this order. Although a four-layer structure is illustrated here, it is also suitable as a further multilayer structure.
[0048]
In this case, if the so-called Bragg reflection effect due to the difference in dielectric constant between SiO ₂ and Si ₃ N ₄ is used, light emission of an arbitrary wavelength can be selected from a light emitter having a broad emission wavelength, or induced if conditions permit. It is also possible to cause release.
[0049]
【The invention's effect】
According to the present invention, high light emission efficiency can be obtained easily and reliably, it is excellent in consistency with a conventional Si-MOS transistor structure, can be used for an optical interconnect, and performance due to high integration of LSI. It becomes possible to solve the problem of wiring delay, which is the main factor that hinders improvement.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a main configuration of a MIS type light emitting device of an embodiment.
FIG. 2 is a schematic diagram for explaining a light emitting function of the MIS type light emitting device of the present embodiment.
FIG. 3 is a schematic diagram for explaining a light emitting function of another example of the MIS light emitting element of the present embodiment.
FIG. 4 is a schematic diagram for explaining a light emitting function of another example of the MIS light emitting element of the present embodiment.
FIG. 5 is a schematic diagram for explaining the light emitting function of another example of the MIS light emitting element of the present embodiment.
FIG. 6 is a schematic cross-sectional view showing a method of manufacturing the MIS type light emitting device of the present embodiment in the order of steps.
7 is a schematic cross-sectional view showing the main configuration of a MIS light-emitting element of Modification 1. FIG.
FIG. 8 is a schematic diagram for explaining a light emitting function of a MIS light emitting element of Modification 1;
9 is a schematic cross-sectional view showing the main configuration of a MIS light-emitting element of Modification 2. FIG.
10 is a schematic diagram for explaining a light emitting function of a MIS light emitting element according to a second modification. FIG.
11 is a schematic cross-sectional view showing the main configuration of a MIS light-emitting element of Modification 3. FIG.
[Explanation of symbols]
1 Si- semiconductor substrate second source / drain 3,21,31 gate insulating film 4 gate electrode 11 SiO ₂ film 12 thermally oxidized layer (lower layer)
13 Si layer 14 Oxide layer (upper layer)
22, 24, 33, 41, 43 SiO ₂ layer 23, 42, 44 Si ₃ N ₄ layer 32, 34 Dielectric film

Claims (3)

A semiconductor device having a MIS type transistor structure having a gate electrode and a source / drain,
In the gate insulating film, a semiconductor nanocrystal including a group IV, a semiconductor microcrystal including a group IV, a polycrystalline or single crystal of a compound semiconductor, a light emitting material selected from a rare earth element and a fluorescent material is added. And
A voltage for generating hot electrons is applied to the source / drain and a bias voltage is applied to the gate electrode to inject conductive carriers into the gate insulating film, thereby causing the gate insulating film to emit light. Semiconductor device.   The semiconductor device according to claim 1, wherein the gate insulating film is formed by stacking a plurality of types of insulating films. The plurality of types of insulating films include a first insulating film in the vicinity of the gate electrode and a second insulating film spaced from the gate electrode through the first insulating film, and the second insulating film The light-emitting substance is added to the film, and the first insulating film has a larger band gap that acts as an energy barrier against the carriers than the second insulating film. The semiconductor device according to claim 2 .

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