JPH041930B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor memory device for constructing a nonvolatile optical memory using a non-single crystal semiconductor including an amorphous structure.

This invention uses silicon or germanium as a main component to which hydrogen or oxygen is added, and
A non-single-crystal semiconductor to which 5×10 ¹⁶ to 1×10 ²¹ cm ^-3 of impurities selected from a group or group of the periodic table is added, and such a semiconductor is irradiated with short wavelength light of 600 nm or less, Absorption coefficient is especially 750nm
(1.65eV) to 5μ (approximately 0.3eV) near-infrared or infrared light, and long wavelength light of 5μ or more or 120 to
The present invention relates to a rewritable optical readout memory device that utilizes the reversibility of reducing the absorption coefficient of light through thermal annealing at 300°C.

The present invention relates to a forbidden band (hereinafter referred to as "within Eg") of an energy band (hereinafter referred to as "Eg") in a group of non-single crystal semiconductors whose main components are silicon and germanium.
As the recombination center density (hereinafter referred to as RC) increases, the optical absorption coefficient increases, and as a result,
Light transmission amount, especially from 750nm to 5μ (preferably from 800nm to
2μ) near-infrared or infrared light transmission becomes poor,
The present invention also relates to a nonvolatile memory device that performs optical reading using the characteristic that when RC decreases, the light absorption coefficient of near-infrared or infrared light decreases, and the amount of reading light transmitted increases.

The present invention detects the transmitted light of this light or the reflected light by providing a reflective surface on the back surface with a photo sensor, thereby constructing a semiconductor memory device for optical reading.

Conventionally, when a photoelectric conversion device or the like is manufactured using amorphous silicon, the photoelectric conversion device deteriorates due to light irradiation and its electrical conductivity decreases, which is known as the Stebla-Wronski effect.

The inventor investigated this factor in detail, and found that oxygen and hydrogen create OH groups in silicon semiconductors, which combine with or separate from silicon dangling bonds, increasing the number of recombination centers or We were able to find out that it was decreasing.

As a model, A reversible reaction process is proposed. That is, the D° level changes to D ^- or D ⁺ by irradiation with short wavelength light.
That is, the reaction shifts to the left in the above equation. the result
RC is formed at a deep level within Eg. This RC
The electrical conductivity decreases. However, D ^- and D ⁺ reversibly change to D° by far-infrared light or heat treatment at 120 to 300°C. That is, in the above equation, a reaction occurs in the right direction. The present invention actively utilizes the property that RC reversibly increases or decreases. Therefore, the intrinsic semiconductor or substantially intrinsic semiconductor (hereinafter simply referred to as layer or type semiconductor) of the present invention
Oxygen and hydrogen are actively added to this.
Specifically, oxygen was contained in an amount of 1×10 ²⁰ to 5×10 ²¹ cm ⁻³ , for example, 1×10 ²¹ cm ⁻³ , or hydrogen was contained in an amount of 1 to 40 atom %, for example, 15 atom %.

In addition, in order to easily perform such a reversible reaction (increase sensitivity), it has been found that it is effective to bring the Fermi level close to the conduction band to some extent and perform N ^- conversion. For this reason, the activation energy is set at, for example, 0.2 to 0.7 eV, preferably 0.4 to 0.6 eV in amorphous silicon. In the present invention, groups (Na, K, etc.) of the periodic table or groups (N,
P, As, Sb, etc.) were added. Typical impurities are Na, K, P, and N.

In the present invention, in order to read out the stored information, the electrical conductivity is determined by applying near-infrared or infrared light (100 to 10000 1x) of a specific intensity to a specific address from 1 to 100 μφ, for example, 2 μφ. this spot
GaAs/GaAlAs (emission wavelength 780-905 nm) or
It is irradiated with an InGaAsP (1100 to 1600 nm) semiconductor laser, and the magnitude of the transmitted or reflected light is read out as "0" or "1" by a photo sensor, such as an avalanche type silicon photo sensor.

The present invention thus demonstrates the light irradiation effect (Stebla
This is a non-contact nonvolatile semiconductor memory device that uses the Wronski effect to perform optical writing and erasing as well as optical reading.

For this reason, it is widely applied to optical disks, and since its main component is silicon, it is not a polluting material.
Furthermore, by not using expensive materials such as tellurium oxide or for magneto-optical disks, it has the great advantage of being able to achieve lower costs and higher reliability.

The present invention addresses the problem of increasing RC caused by short-wavelength light irradiation, thermal annealing, or long-wavelength light irradiation.
A decrease in RC not only leads to a change in electrical resistance, but also increases or decreases the optical absorption coefficient of the semiconductor in the near-infrared or infrared region. That is, by increasing or decreasing the number of recombination centers, the relationship between RCs or RCs
It uses the characteristic of reducing transmitted light or reflected light due to the absorption of irradiated light due to optical excitation between the conduction band (CB) and valence band (VB).

As described above, the present invention does not utilize the transformation of the crystal structure of the semiconductor itself as seen in chalcogen type semiconductors, but utilizes changes in the bonding of the bonds in the semiconductor to increase or decrease the light absorption coefficient. The purpose of the present invention is to propose a non-contact type semiconductor memory device in which detection is performed by optical reading using infrared or near-infrared light.

The contents are described below according to the drawings.

In FIG. 1, a non-single-crystal semiconductor mainly composed of silicon is formed on a substrate 4 having a reflective metal surface and has an intrinsic or substantially intrinsic conductivity type to which hydrogen and oxygen are added. Furthermore, an anti-reflection protective film was formed from silicon nitride thereon and laminated on the semiconductor.

In the drawing, the semiconductor 1 is first made of silane (Si _o
A silicide gas such as H _2o+2 n1) was formed to a thickness of 0.1 to 10 μm, for example, 3 μm, by a plasma glow discharge method (PCVD method). In the drawing, the substrate is a reflective metal 4, and oxygen and hydrogen were simultaneously added to the upper surface of the substrate to produce an amorphous silicon film by the PCVD method. This contains 1 to 30 atomic percent of hydrogen and 1×10 ²⁰ of oxygen.
~5×10 ²¹ cm ⁻³ was mixed. Na, K, P, and N were further added to this semiconductor at a concentration of 5×10 ¹⁶ to 1×10 ²¹ cm ⁻³ . Specifically, in order to add Na and K, this semiconductor is mixed with NaCl and KCl (0.1N water temperature is 100℃)
Soaked in for about 10 minutes. Na and K can be mixed into the interior simply by dipping the semiconductor in such a solution and heating it. On the other hand, P and N are preferably added as a mixture in the raw material gas of the semiconductor. This was dried and irradiated with light to improve its sensitivity as a semiconductor for the reversible process of light absorption coefficient. This semiconductor film can be manufactured using sputtering method, photo plasma CVD method, vacuum evaporation method, and reduced pressure method.
A CVD method may also be used.

In the following, a plasma glow discharge method is used, and the temperature is 100 to 400°C, for example 200°C, the pressure is 0.1 torr, and the thickness is 0.1 to 10μ, for example, 3μ.

Furthermore, a mechanical protective film that also served as an anti-reflection film was fabricated in a subsequent process of forming this semiconductor. Here, silicon nitride or a transparent conductive film was fabricated. In its manufacture, this film was formed by plasma CVD at a temperature below 300° C. to prevent the hydrogen in the semiconductor from degassing, and the structure shown in FIG. 1 was obtained.

FIG. 2 shows an energy band diagram corresponding to FIG. In this energy band diagram, semiconductor 1
When visible or ultraviolet light (light with a higher optical energy than Eg) is irradiated onto the surface, RCs (recombination centers) are formed by this irradiated light. After this, they continuously varied the wavelength of light on this semiconductor and measured the degree of light absorption. Then, this continuous light undergoes optical absorption in CB (conduction band) -RC, RC-RC, and RC-VB (valence band), and the increase in RC further increases the optical absorption coefficient. That is, it has been found that the light transmittance decreases or increases depending on the density of RC.

FIG. 3 shows the relationship between the absorption coefficient of such light and the irradiation amount of visible or ultraviolet light of 600 nm or less.

That is, in the initial state, curve 11 is changed to light with a wavelength of 500 nm or less, such as nitrogen laser (337 nm), helium cadmium laser (442 nm, 325 nm), or xenon lamp (300 nm).
For example, when irradiated with a xenon lamp (100 mW/cm ² ) for 2 hours, curve 1
1 changes to 12, 750nm (1.65eV) ~ 5μ
The light absorption characteristic (αhν) (α is the light absorption coefficient) at (approximately 0.3eV) became large. Furthermore, Na, K, P, and N were added to the sample having the characteristics of this curve 11.
The addition of this impurity increased the light absorption coefficient by about one order of magnitude, and when irradiated for 20 minutes and 2 hours under the same conditions, it changed to curves 13 and 14.

This is not because the optical Eg changes, but because the recombination center (RC) 17 is located within the forbidden band of the energy band.
occurs and exists continuously as shown in Figure 2, and light is absorbed between this RC and CB, VB, or RC, so curves 14, 13, and 12 show absorption coefficients larger than 11. Presumed.

Curve 14 shows such high light absorption characteristics.
Long wavelength light of 1μ or more or 130℃ or more, e.g. 150℃
It was found that when thermal annealing was performed, the curve decreased to 11 or 12, and the RC decreased.

The present invention is capable of absorbing infrared or near-infrared light, which is a region where the absorption coefficient changes greatly, from 0.3 to
Light with a wavelength of 1.65 eV, preferably 0.5 to 1 eV, is emitted, for example, from a semiconductor laser InGaAsP (1100 nm (1.1 eV) to
1600 nm (0.77 eV)), this light was used as read light to irradiate each of these two curves, for example, 11 and 14, and the amount of transmitted light was examined.

In curve 14, the amount of transmitted light is small, and in curve 11, it is large. These two differences are set as "0" and "1", respectively, and are used as a non-contact optical readout nonvolatile memory.

FIG. 4 shows the change in the absorption coefficient (α) when a valence or valent impurity is added.

In the drawings, 19 is the case where phosphorus is added to 11 shown in FIG. 3, and 20 is the case where sodium is added. Also, curves 15 and 16 are curve 1 in Figure 3.
4. Curve 15 is the case when sodium is added, and curve 16 is the case when phosphorus is added. Furthermore, curves 17 and 18 are "0" and "1"
indicates the judgment boundary.

As a result, it has been found that when an impurity for N conversion is added, the overall absorption coefficient increases and readout becomes easier.

A specific example of a memory device will be shown below according to an embodiment.

Embodiment 1 This embodiment is a non-volatile light-emitting memory of an optically programmable and readable ROM.

This optical memory is extremely effective when used as an optical memory disk for office automation and can be programmed and used as desired.

That is, in FIG. 5A, glass, ceramic,
An insulating substrate 4 such as an organic film (thickness of 100 to 500 μm) is coated with a first metal such as aluminum as a reflective plate 9, and a two-layer structure is formed with tin oxide to prevent a decrease in reflection due to the reaction between the metal and the semiconductor. 8 to form a reflecting plate 3. Furthermore, a non-single crystal semiconductor 1 with a large irradiation effect in which oxygen and hydrogen are added
was formed to a thickness of 3μ.

Furthermore, a protective film 2 made of silicon nitride was formed over the entire surface. Also, near the semiconductor protective film, tin oxide, SixC _1-x (0<x<1 x=0.8) was formed to a thickness of 500 mm to improve reliability. This board has a disc shape similar to a record board,
Memory writing is performed at a specific address selected arbitrarily.
Laser light 27 having a size of 0.1 to 50μ, for example 2μφ, was irradiated from the light source 35. For example, irradiation with a nitrogen laser (337 nm, 300 mW/cm ² ) was performed at 24 and 26 to form a non-light-transmitting region. On the other hand, a specific address 25 of the semiconductor is provided as a light-transmitting region.

To read the memory, as shown in FIG. Irradiated.
The photo sensor 30 then detected the magnitude of the reflected light 38 in the irradiated area. The information was then optically detected, with a value of "1" indicating a large amount of reflected light and a "0" indicating no (few) reflected light.

This time chart is shown in FIG.

That is, FIGS. 6A and 6B are memory writing. High light absorption regions 44 and 46 are selectively formed in a part of the optical disk by intense light pulse irradiation 47 and 48, as shown in FIG. 6B. 44, 45, 46 are Figure 5A
24, 25, and 26.

Also, this disk can be rewritten at 130 to 300 degrees Celsius.
All tests were carried out by leaving the sample at a temperature of, for example, 180°C for 30 minutes as a low absorption region. Furthermore, this rewrite
It may also be performed by localized irradiation with a 10.6μ carbon gas laser.

Also, readout is shown in Figures 6C and D, but an infrared laser 37 is added and the reflected light is reflected in Figure 6D.
It can be obtained as 38 and 39 as shown in FIG. At this time, the address 39 where there is little reflected light and the address 38 where there is a lot of reflected light are detected by the same optical axis type photo sensor 33 in FIG.
optical readout is now possible.

In other words, this optical memory (program ROM) uses only light irradiation to make a part of the record-like disk a high light absorption area, and the other part a relatively low light absorption area, and also for readout, the address specification is performed using light. Since the readout is performed using coaxial reflected light, non-contact optical readout is possible. For this reason, it was possible to create a ROM that allows so-called optical writing, optical or thermal rewriting, and non-contact optical reading.

The present invention differs in principle from the conventionally known non-rewritable mask type optical disk memory which is formed by selectively removing a portion of a substrate. Furthermore, it has been found that the stored information can be rewritten and is nonvolatile, making it ideal as a large-capacity optical disk memory.

As is clear from the above explanation, adding valent or valence impurities in addition to adding only O and H increases the light irradiation coefficient by about one order of magnitude or more, and as a result, the intensity of irradiation light at night for reading It is now possible to determine at least "0" or "1". In other words, it has become easier to determine whether the data is "0" or "1" when reading data. The present invention particularly applies to PI, NI, PN,
No PIN junction was provided. However, it is effective to increase or decrease the light absorption coefficient by providing these junctions and applying electrical energy to write or rewrite the memory. Furthermore, optical writing,
By increasing the contrast of rewriting, it is possible to apply the present invention to optical memories with higher precision, and furthermore, many applications based on the same technical idea are possible.

Although FIG. 1 shows the case of amorphous silicon, the same method can be applied to non-single crystal compounds or mixture semiconductors such as Ge and GexSi _1-x (0<x<1). It goes without saying that the semiconductor referred to in the present invention includes semi-insulators to the extent that the amount of oxygen added is large and a light irradiation effect exists. Furthermore, in the present invention, when thermal annealing is performed for a long time, reactions occur simultaneously at the interface between the protective film 2 and the substrate 3 and the semiconductor 1, resulting in deterioration of characteristics. Therefore, semiconductor 1 is SixC _1-x (0<x<1 x=0.8)
It was more practical to have this structure near the electrode, with the semiconductor layer doped with large amounts of hydrogen and oxygen inside.

In this way, by creating a heterojunction in terms of energy band, it is possible to prevent the formation of insulating silicon oxide at the interface between the electrode and the semiconductor at high temperatures of 150 to 300°C, resulting in high reliability. was completed.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor device using the non-single crystal semiconductor of the present invention. FIG. 2 is an energy band diagram for explaining the theory of the present invention. Third
4 shows the light absorption coefficient characteristics of a non-single crystal semiconductor. FIG. 5 shows an embodiment of the semiconductor device of the present invention. FIG. 6 shows a time chart used in the embodiment of FIG.

Claims (1)

[Claims] 1. A nonvolatile optical memory in which silicon to which hydrogen and oxygen are added or a non-single crystal semiconductor mainly composed of silicon is disposed on a substrate having a reflective surface, and a light beam is locally directed to the optical memory. means for locally or partially irradiating infrared rays or thermal energy to form a low light absorption region; and means for irradiating the high light absorption region and the low light absorption region with light. An optical memory device comprising means for emitting light and detecting the reflected light. 2. In claim 1, the non-single crystal semiconductor contains impurities selected from groups of the periodic table such as Na, K, P, N, etc. in an amount of 5×10 ¹⁶ to 1×10 ²¹
An optical memory device characterized by being doped with cm ^-3 . 3. A nonvolatile optical memory in which silicon doped with hydrogen and oxygen or a non-single crystal semiconductor mainly composed of silicon is provided on a substrate having a reflective surface, and the optical memory is locally irradiated with a light beam to remove the semiconductor. forming a high light absorption region on the optical memory; forming a low light absorption region by locally or partially irradiating the semiconductor with infrared rays or thermal energy; and forming a high light absorption region and a low light absorption region on the optical memory. An optical memory device write/read method comprising a step of reading out stored memory information by irradiating light with light and detecting the reflected light. 4 In claim 3, the non-single crystal semiconductor contains impurities selected from the groups of the periodic table such as Na, K, P, and N in an amount of 5×10 ¹⁶ to 1×10 ²¹
An optical memory device write/read method characterized by cm ^-3 doping.