JP3027092B2 - Method of forming porous silicon light emitting layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a porous silicon light emitting layer. More specifically, the present invention relates to a method for forming a porous silicon light emitting layer for improving the luminance of photoluminescence light emission of a porous silicon light emitting layer obtained by anodizing a surface layer of a silicon substrate by anodization and improving the light emitting characteristics.

[0002]

2. Description of the Related Art When anodizing single crystal silicon in an aqueous solution of hydrofluoric acid, if the anodic current density exceeds a certain value, mirror-like electropolishing occurs. If the anodic current density is below a certain value, a porous layer is formed. It is known that Anodization is performed by placing a silicon single crystal and a platinum plate in a solution containing hydrofluoric acid as a main component, and holding the silicon single crystal on the anode and the platinum plate on the cathode. It is generally known that when a silicon single crystal is immersed in hydrofluoric acid, its surface is terminated with hydrogen atoms. The anodization reaction for forming the porous layer starts from this state, and the mechanism is shown in FIG.

[0003] First, by the application of a voltage, the hole reaches the silicon surface, F ^- ions of the silicon surface Si
Attack the -H bond to form a Si-F bond (step 1). Then, due to the influence of the polarity of the bonded F atom, another F ^- ion attacks the Si-H bond, and H ₂
Form molecules and cause injection of electrons into the electrodes (steps 2 and 3). Due to the polarization by the population of Si-F, S
The electron density of the i-Si bond decreases, and the bond becomes weaker. Therefore, it is attacked by HF or H ₂ O and detaches from the surface (steps 4 and 5). However, the remaining silicon surface is still terminated with hydrogen atoms. The anodization reaction proceeds in this manner.

Here, if silicon atoms are desorbed from a flat silicon surface at the atomic level by the above reaction, a depression of the atomic size remains. This geometrical change induces non-uniformity of the charge distribution on the surface, resulting in selective concentration of holes in the recessed area. By repeating the above reaction, the unevenness on the surface is emphasized, and a porous layer having a large number of pores is formed. This reaction is restricted by holes, so that the porous layer can be thickened as much as a voltage is applied.

[0005] The porous layer formed as described above has a thickness of 19
In 1990, by Hamham, Xe lamp and He-C
Irradiation with ultraviolet light such as d laser (325 nm) has been found to cause photoluminescence emission in the visible region (LT Canham; Appl, Ph.
ys, Lett. 57 (1990) 1046). This fact is due to the physical concern that silicon, which is an indirect transition type semiconductor, emits light, and the OEIC with a single material can be realized by fusing and combining the device technology of silicon with the porous layer that emits light. So various researches are being actively conducted.

[0006]

The porous silicon light-emitting layer formed by the conventional method utilizing the above-described anodization method originally had low light emission intensity. In addition, since the surface of the porous silicon light emitting layer is terminated with hydrogen, hydrogen atoms are released by light irradiation, and thus a tangling bond is generated, which further reduces the light emission intensity. Had a problem.

[0007]

The porous silicon light-emitting layer emits light in a microcrystalline region on the order of several nanometers. In order to improve the light-emitting characteristics, the tangent of silicon, which is a non-light-emitting center existing in the microcrystal, is required. It is necessary to effectively terminate the ring bond. Therefore, the inventors of the present invention have conducted intensive studies and have found that ions having high electronegativity are introduced into a film as terminal atoms of a tangling bond using an ion implantation method, leading to the present invention.

Thus, according to the present invention, after ions having high electronegativity are implanted into an arbitrary depth of the silicon substrate, the porous silicon light emitting layer is selectively formed only in the ion-implanted region of the silicon substrate by anodization. And a method for forming a porous silicon light emitting layer, characterized by forming According to the method of the present invention, ions having a high electronegativity are locally or uniformly introduced into a silicon substrate using an ion implantation method to selectively emit strong light only in a region of an arbitrary depth. A high quality porous silicon light emitting layer having excellent light emitting characteristics as shown can be obtained.

The silicon substrate that can be used in the present invention includes a Czochralski (CZ) method, a floating (FZ) method,
Those produced by either method can be used. Further, either the p-type or the n-type conductivity may be doped in advance. Examples of the impurity imparting the p-type include boron and the like, and examples of the impurity imparting the n-type include phosphorus, arsenic, and antimony.

Next, ions having a high electronegativity are implanted into the silicon substrate. As ions with high electronegativity,
For example, oxygen, fluorine, chlorine, nitrogen, bromine and the like can be mentioned. The ion implantation depends on the type of ions to be implanted, but has a kinetic energy of 0 to 30 MeV and an implantation amount of 1 ×.
It is performed under the condition of 10 ¹³ -1 × 10 ¹⁷ / cm ² . By this implantation, the implanted ions can be distributed to a desired region in the silicon substrate. Further, a plurality of types of the above ions may be simultaneously implanted. Here, the ions are assumed to be oxygen ions, and the ion implantation condition is set to a kinetic energy of 0 to 10 M
It is more preferable to set the eV and the implantation dose to 1 × 10 ¹⁴ to 1 × 10 ¹⁶ / cm ² . Under these conditions, 0
An oxygen ion-implanted layer having a peak concentration of 1 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ³ is formed at a depth of 10 to 10 μm, preferably 0 to 5 μm. A porous silicon light emitting layer with little deterioration in light emission intensity can be obtained.

Further, when ions are implanted into the same silicon substrate with a plurality of different kinetic energies, a plurality of light emitting layers can be formed in the depth direction, and a multilayer light emitting layer can be realized. Furthermore, by arbitrarily selecting an ion-implanted portion in the substrate surface, only a desired region can be used as a light emitting layer, and when combined with the multilayered light emitting layer, a three-dimensional light emitting layer can be realized. can do.

The peak concentration, distribution broadening, and implantation depth of an implantation region formed in a silicon substrate by ion implantation are determined by the LSS theory (Mat.Fys.Medd.Da).
n. Vid. Selsk 33, No. 14 (196
It can be obtained from the correspondence table of the ion type, the acceleration voltage and each characteristic value based on 3)). Furthermore, the ion implantation layer may be diffused by performing an annealing process after the ion implantation. The conditions of this annealing treatment are 800 to 900
C. for 10 to 60 minutes is appropriate.

Next, the silicon substrate is modified into a porous layer based on the known anodization method. This anodization method can be performed as follows. First, the silicon substrate is connected to the anode. Next, both electrodes are immersed in an electrolytic solution using platinum as a cathode. As an electrolytic solution that can be used at this time, hydrofluoric acid, hydrofluoric acid and ethyl alcohol, hydrofluoric acid and methyl alcohol, and the like can be used. It is preferable from the viewpoint of shortening. Also,
The composition of the mixed solution of hydrofluoric acid and ethyl alcohol is H
It is more preferable that F: H ₂ O: C ₂ H ₅ OH = 1: 1: 2 (volume ratio) because the processing time can be further shortened.

Next, depending on the ion implantation depth and the pore diameter of the porous silicon luminescent layer to be obtained, the current reaches the implanted ion layer at a current density of ² to 200 mA / cm ² depending on the ion implantation depth and the pore size of the porous silicon light emitting layer to be obtained. By passing an electric current for only a certain time, an electrochemical reaction occurs, and a porous layer including a porous silicon light emitting layer is formed. In this reaction, since the holes control the reaction, the porous layer can be made thicker as long as a voltage is applied.

Here, prior to the formation of the porous silicon light emitting layer, an intermediate layer resistant to the electrolytic solution used in the anodizing method is formed to form a porous layer having a more uniform thickness with higher precision. can do. The method of forming the intermediate layer is as follows. First, when hydrofluoric acid is used as an electrolytic solution, a silicon substrate is irradiated with carbon ions under the conditions of 1 to 6 MeV, 1 × 10 ¹⁶ to 1 × 10 ¹⁸ / cm ² . Next, an annealing process is performed on the silicon substrate to form an intermediate layer made of silicon carbide in the silicon substrate. The annealing treatment is performed at 1200 to 1400 ° C. and 2-1.
It can be performed for 0 hours in an atmosphere of an inert gas such as Ar. Since the intermediate layer made of silicon carbide has resistance to hydrofluoric acid, only the silicon layer above the intermediate layer can be made porous, and the thickness can be controlled precisely. .

[0016]

After a high electronegativity ion is implanted into an arbitrary depth of a silicon substrate, a porous silicon light emitting layer is selectively formed only in an ion implantation region of the silicon substrate by anodization. Since the surface of the porous silicon light-emitting layer is terminated with ions having high electronegativity instead of being terminated with hydrogen, a light-emitting layer with almost no deterioration in emission intensity due to light irradiation can be obtained.

Next, when the ion having a high electronegativity is oxygen or fluorine, a high-luminance porous silicon light emitting layer can be obtained. Further, if ions having high electronegativity are implanted at a depth of 0 to 5 μm from the surface of the silicon substrate, a porous silicon light emitting layer with high brightness and high intensity can be obtained.

[0018]

【Example】

Embodiment 1 The present invention will be described below with reference to FIG. The following examples are exemplifications, and the present invention is not limited to the following materials, steps and conditions. First, oxygen ions 2 were implanted on a boron-doped p-type silicon substrate 1 under the conditions of a kinetic energy of 4 MeV and 1 × 10 ¹⁵ / cm ² (see FIG. 1A). Here, FIG. 6 shows the actual concentration distribution of oxygen in the silicon substrate in the depth direction measured by mass spectrometry. According to this figure, 2.9 × 10 ¹⁹ / cm ³ oxygen ions are located at a depth of about 3.3 μm from the surface.
Are shown to be distributed at high concentrations.

Next, based on the following method, the surface layer of the silicon substrate 1 was subjected to anodization to transform it into a porous layer 3 (see FIG. 1B). This anodization method is performed based on FIG. 3. In a reaction cell 4, an anode composed of a p-type silicon substrate 1 and a cathode composed of a platinum electrode 5 are HF: H ₂ O =
It was immersed in a 1: 1 (volume ratio) hydrofluoric acid solution 6. When an electric current was applied to the anode and the cathode at a current density of 20 mA / cm ² for about 13 minutes, an electrochemical reaction occurred, and a porous layer 3 having a thickness of 20 μm was formed on the surface layer of the p-type silicon substrate 1.

Observation of the obtained porous layer with a high-resolution electron microscope reveals that a layer having a different pore size, that is, a porous silicon luminescent layer 31 is formed in a region where oxygen is distributed at a high concentration of about 3 μm from the surface of the substrate 1. It turned out that it was. FIG. 2 shows the measurement results of the cross-sectional photoluminescence of the porous silicon light emitting layer. As is clear from the figure, it can be seen that high intensity photoluminescence emission is generated from a region where oxygen is distributed at a high concentration at a depth of about 3 μm from the surface. The photoluminescence was measured at room temperature by irradiating light of 4880 ° emitted from an Ar ion laser.

FIG. 5 shows a photoluminescence spectrum in a region where oxygen is distributed at a high concentration. As is clear from the figure, it can be seen that light emission in the visible region can be obtained.

Example 2 A plurality of different kinetic energies of 240 KeV and 4 MeV
At 1 × 10¹⁵Pieces / cm ^TwoOxygen ions to p-type silicon base
Poured into plates. Next, a current density of 20 mA / cm ^TwoAnd about
Electrochemical reaction occurs by passing current for 13 minutes,
20 μm thick porous layer on the surface layer of p-type silicon substrate 1
Was formed. This porous layer has a depth of about 60 from the surface.
The porous silicon light emitting layer is formed in the area of 00Å and about 3 μm.
Was made.

In addition to the above-described method, a three-dimensional light emitting region can be realized by selective ion implantation in a plane.

[0024]

According to the present invention, after a high electronegativity ion is implanted into an arbitrary depth of a silicon substrate, a porous silicon light emitting layer is selectively formed only in an ion implantation region of the silicon substrate by anodization. Accordingly, instead of terminating the surface of the porous silicon light emitting layer with hydrogen, the surface is terminated with ions having a high electronegativity, so that it is possible to obtain a light emitting layer in which the light emission intensity hardly deteriorates due to light irradiation. In addition, by changing the kinetic energy of ion implantation, a light-emitting layer having a desired thickness can be formed at a desired depth, and a multi-layer and three-dimensional light-emitting layer can be realized.

Next, when the ion having a high electronegativity is oxygen or fluorine, a porous silicon light emitting layer with high luminance can be obtained. Further, by implanting ions having a high electronegativity at a depth of 0 to 5 μm from the surface of the silicon substrate, a porous silicon light emitting layer having high luminance and high intensity can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic manufacturing process diagram of a porous silicon light emitting layer of the present invention.

FIG. 2 is a distribution diagram of photoluminescence intensity when the emission wavelength of the porous silicon light-emitting layer obtained in the example of the present invention is fixed at 7000 °.

FIG. 3 is a schematic view of a reaction cell used for an anodization method.

FIG. 4 is a schematic explanatory view of a mechanism for forming a porous silicon light emitting layer by anodization.

FIG. 5 is a diagram showing a photoluminescence spectrum of a porous silicon light emitting layer obtained in an example of the present invention.

FIG. 6 is a depth distribution of oxygen in a silicon substrate after ion implantation according to an example of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 p-type silicon substrate 2 oxygen ions 3 porous layer 31 porous silicon light-emitting layer 4 anodizing reaction cell 5 platinum electrode 6 hydrofluoric acid solution

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Junichi Tanaka 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside (72) Inventor Hiroshi Taniguchi 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (72) Inventor Yoshiro Akagi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-6-125112 (JP, A) JP-A-5-55627 (JP, A JP-A-5-335624 (JP, A) JP-A-5-251741 (JP, A) JP-A-5-218494 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 33/00 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A method for forming a porous silicon light emitting layer selectively only in an ion-implanted region of a silicon substrate by anodization after implanting ions having a high electronegativity into an arbitrary depth of the silicon substrate. Characteristic method of forming a porous silicon light emitting layer. 2. The method according to claim 1, wherein the ion having a high electronegativity is oxygen or fluorine.