JP2667664B2 - Manufacturing method of silicon single crystal thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to low-temperature formation of a silicon single crystal thin film. BACKGROUND OF THE INVENTION With the high integration of semiconductor devices, low temperature formation methods for silicon epitaxial substrates have been attracting attention. Various approaches have been taken for this purpose. However, for example,
Thermal CVD of monosilane: In (Ch emical V apor D eposition chemical vapor deposition) method requires a high temperature of about 1000 to 1100 ° C.. At such a high temperature, solid phase diffusion or autodoping of impurities from the substrate at the time of film formation is unavoidably caused, so that it is difficult to obtain a high-quality epitaxial thin film. We found that when fluorosilane was added to a mixed gas of silane and hydrogen and decomposed by mercury-sensitized CVD, epitaxial growth on a silicon substrate occurred at a substrate temperature of 300 ° C. It was clarified from the results of the thermal analysis test of hydrogen that the film formed in 1 contains a considerable amount of hydrogen. It is considered that the incorporation of hydrogen into the film is undesirable because it has a problem in the manufacture of semiconductor devices. As a result of further studies to solve such a problem, the present inventors have found that when a mixed gas of silane, fluorosilane, and hydrogen is introduced onto a substrate to form a film while keeping the substrate temperature at 600 ° C. or higher, hydrogen is generated. The present inventors have found that a silicon single crystal thin film containing no silicon can be obtained, and completed the present invention. DISCLOSURE OF THE INVENTION That is, the present invention is a method for producing a silicon single crystal thin film, which comprises introducing a mixed gas consisting of silane, fluorosilane and hydrogen onto a heated single crystal substrate to grow a single crystal thin film. . Hereinafter, the present invention will be described in detail. The present invention is basically characterized by adding fluorosilane to a mixed gas of hydrogen and silane. As the fluorosilane used in the present invention, fluorosilane or fluorodisilane of monosilane represented by SiH _4-n F _n (n is an integer of 1 to 4), particularly Si
₂ F ₆ is effectively used. The silane is Si _m H _{2m + 2}
Monosilane, disilane, trisilane and the like represented by (m is an integer of 1 to 3) are effectively used. In the present invention, such a fluorosilane-containing gas is introduced onto a heated substrate to form a single crystal thin film by the CVD method. In a particularly preferred embodiment, the single crystal thin film is grown on a single crystal substrate, and a silicon wafer or sapphire is preferably used as the substrate. That is, in summary, the present invention provides a mixed gas of hydrogen and silane gas mixed with fluorosilane at 600 ° C.
This is a method of forming a silicon single crystal thin film by guiding it onto the heated single crystal substrate and forming a film by the CVD method. Concerning the mixed gas ratio, it is convenient to express it as a supply flow rate (capacity) ratio of the raw material gas to the forming apparatus for forming the single crystal thin film. Preferred fluorosilane / silane ratios range from 0.1 to 50, more preferably 0.2 to 20. Fluorosilane /
When the silane ratio is about 0.1 or lower, polycrystals are easily formed when the substrate temperature is around 600 ° C. or lower. On the other hand, if the ratio of fluorosilane / silane exceeds 50, the growth rate of the single crystal thin film is decreased, which is not preferable. The preferred hydrogen / (fluorosilane + silane) ratio is 5
It is in the range of 500, more preferably 50-200. A single crystal thin film tends to be formed in a region where the hydrogen / (fluorosilane + silane) ratio is relatively large, but if the amount of hydrogen added is too large, the growth rate of the single crystal thin film decreases, which is not preferable. The substrate temperature during film formation is effectively 600 ° C. or higher, more preferably 700 ° C. or higher, and even more preferably 800 ° C. or higher. When the substrate temperature during film formation is lower than 600 ° C., a polycrystalline thin film is easily formed. The higher the substrate temperature during film formation, the higher the single crystal thin film formation rate tends to be. However, a high temperature of 1000 ° C. or higher is not necessary in practice, and it is not preferable from the viewpoint of forming a low temperature thin film. The method of heating the substrate is not a critical factor and is not particularly limited. For example, induction heating with a high frequency using a carbon susceptor coated with SiC and heating with an infrared lamp using a quartz susceptor are both useful. Also, the method of forming the mixed gas is not a critical factor and is not particularly limited. For example, it is useful to introduce a premixed gas outside the forming apparatus or to mix hydrogen in the outside forming apparatus so as to satisfy the above-mentioned dilution degree. Of course, there is no problem in using fluorosilane or silane diluted with hydrogen. In the present invention, the pressure in the forming apparatus is not a critical factor. The pressure of the mixed gas during film formation may be normal pressure or reduced pressure. A good single crystal thin film can be obtained by appropriately changing the gas flow rate ratio and the substrate temperature during film formation. [Preferred Embodiments for Carrying Out the Invention] Next, preferred embodiments of the present invention will be described.
Substrate introduction / extraction means, substrate holding means, substrate heating means,
A cleaned silicon substrate is placed in a thin film forming apparatus having at least gas introduction means and gas discharge means. After heating to 1000 to 1200 ° C in a hydrogen stream to expose a clean substrate surface, the temperature is lowered to a predetermined film forming temperature of 600 ° C or higher. Thereafter, a raw material gas consisting of silane, fluorosilane and hydrogen is flown at a predetermined flow rate to form a single crystal thin film on the substrate by the CVD method. The gas is switched to hydrogen at a time required to achieve the required film thickness in consideration of the film forming speed, and then the temperature is lowered and the heat is removed to take out the wafer. [Effects of the Invention] The silicon single crystal thin film obtained in the present invention is a good silicon single crystal thin film that is formed at a low substrate temperature of 1000 to 600 ° C. and does not contain hydrogen. The present invention provides an extremely useful technique in the field of semiconductor device manufacturing, in which a semiconductor thin film or a low-temperature forming technique for a semiconductor device is eagerly awaited as the semiconductor device is highly integrated. Further, the present invention is an excellent technique in terms of pollution prevention because it does not require harmful mercury unlike the mercury-sensitized CVD method. Furthermore, it can be said that this technique is superior from the practical point of view because it achieves higher speed film formation than the mercury-sensitized CVD method. Example The present invention was carried out using a thin film forming apparatus equipped with a substrate loading / unloading means, a substrate holding means, a substrate heating means, a gas introducing means, and a gas discharging means. The cleaned n-type silicon wafer (100) was introduced by using the substrate loading / unloading means and set on the substrate holding means. While introducing hydrogen gas at a flow rate of 2 per minute from the gas introducing means, the gas is discharged from the gas discharging means and the inside of the forming apparatus is kept at a normal pressure to raise the temperature of the substrate to 1120 ° C. Cleaned up. Thereafter, the substrate temperature was lowered to a predetermined film forming temperature, and the hydrogen gas was switched to a mixed gas. This mixed gas is a mixture of hydrogen, silane, and fluorosilane at a predetermined flow rate ratio. After depositing a film by the CVD method for 30 minutes, the mixed gas was switched to hydrogen gas, and the substrate temperature was lowered to room temperature while flowing hydrogen gas at 2 per minute. Thereafter, the substrate was taken out using the substrate introduction / extraction means. After observing the surface by backscattered electron diffraction (RHEED) and confirming that a single crystal thin film has grown by the appearance of streak-like diffraction images, a hydrogen desorption test from the single crystal thin film was performed using a heating analyzer. did. Tables 1 and 2 show gas flow ratios, substrate temperatures during film formation, and RH of the examples and comparative examples.
The measurement result by EED and the measurement result of hydrogen release test are shown.
In the items of the RHEED measurement results in the table, ⊚ indicates that the diffraction image was a streak-like good single crystal thin film, and ○ indicates that the diffraction image showed a streak-like shape, but the crystallinity was a little. The inferior single crystal thin film indicates that the diffraction pattern did not show a streak pattern and that the single crystal thin film was not formed. Further, in the items of the results of the hydrogen release test in the table, a circle indicates that hydrogen was not detected. Further, impurities (carbon, carbon, etc.) in the single crystal film obtained in Example 5 were used.
Analysis of oxygen and nitrogen) elements by secondary ion mass spectrometry (SIMS) indicated that the carbon concentration was 1 × 10 ¹⁷ Atoms / cm ³ , oxygen concentration 5 × 10 ¹⁷ atoms / cm ³ , and nitrogen concentration were below the limit of quantification (1 × 10 ¹⁷ atoms / cm ³ ). Example 5
When the conductivity of the single crystal thin film obtained in step 1 was measured, it was 1000 Ω.
Good results were obtained with cm.

Claims (1)

(57) [Claims] A highly gaseous mixture of silane, fluorosilane and hydrogen, wherein the hydrogen / (fluorosilane + silane) ratio is in the range of 50 to 200, is introduced onto a substrate heated to 600 ° C. or higher, and ultraviolet light is introduced. CVD without irradiation
A method for producing a silicon single crystal thin film, characterized by being formed by a method. 2. Preparation of fluorosilane _{SiH 4-n F n (n} = 1~4) fluoro monosilane or Si ₂ F ₆ Scope first claim of claims is fluoro disilane represented. 3. The method according to claim 1, wherein the silane is Si _m H _2m + ₂ (m = 1 to 3). 4. 2. The method according to claim 1, wherein the substrate is a single crystal substrate.