JPH0530909B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a film by vapor phase chemical reaction.

In recent years, a reaction vessel is filled with a photochemically reactive gas consisting of silicon hydrogen compound gas mixed with mercury vapor, a substrate is placed there, and ultraviolet rays at wavelengths of 253.7 nm and 184.9 nm from a mercury lamp are irradiated from outside the reaction vessel. , by depositing amorphous silicon (hereinafter referred to as a-Si) on a substrate through a photosensitization reaction of mercury, or by adding a gas containing oxygen atoms or nitrogen atoms, an insulating film of silicon dioxide or silicon nitride can be formed. Research is being conducted on depositing protective films.
(Publication of Patent Publication No. 54-163792, Nikkei Electronics, February 15, 1982 issue) However, the coatings formed by this method, such as a-Si, silicon dioxide, and silicon nitride, cannot be applied to the process of microelectronic circuits. At the time, there was a problem that the mercury used as a photosensitizer had an adverse effect.

Therefore, recently, without using mercury photosensitizer,
A method has been announced in which a photochemically reactive gas consisting of disilane is directly photodecomposed by irradiating it with ultraviolet light with a wavelength of 184.9 nm from a low-pressure mercury lamp, and a-Si is deposited on a substrate. (Jap.J.Appl.Phys. 22 (1983)
L46) The film formed by this method can eliminate the harmful effects of mercury mentioned above, however, the film formation rate is 0.025 nm/
It is slow, about seconds, and is far from practical use. By the way, CHEMICAL PHYSICS LETTERS
1 (1968), pp. 595-596, etc., silane and higher-order hydrogenated silicon have a large absorption range for ultraviolet rays at wavelengths of 190 nm or less, especially 160 nm or less, so if 160n like this
If ultraviolet rays containing wavelengths of m or less can be directly irradiated onto these photochemically reactive gases, it is possible to directly photodecompose silicon thin films from silane, which have a film formation rate that is sufficient for practical use without the use of mercury sensitizers. It may be possible to provide a film formation method in which the film is deposited on a substrate.

However, if such a photochemical reaction is to be realized using an independent light source and reaction tank, the material for the light intake window of the reaction tank should be a stable and easy-to-handle substance that transmits light up to the shortest wavelength, such as sprodiel. There is synthetic quartz, but its transmission wavelength is 160 nm or more, so it can be used from outside the reaction tank through a window.
It is difficult to incorporate light of 160 nm or less on an industrial scale.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a film forming method for forming a silicon thin film on a substrate without the adverse effects of mercury when applied to a process for forming a microelectronic circuit. Its features include a discharge region where a discharge gas for ultraviolet radiation selected from rare gases, hydrogen, deuterium, or a mixture thereof is supplied, a substrate is placed, and a silane gas with a flow rate of 1 SCCM or more is supplied. Alternatively, a reaction region in which high-order silicon hydride is supplied alone or together with a carrier gas is surrounded by a single container without division, and ultraviolet rays with a wavelength of 160 nm or less are emitted from the plasma formed by the discharge gas. The discharge gas is turned into plasma for a finite continuous time of several seconds or more so that the intensity reaches 1 mW/cm ² or more on the substrate, and the silane or high-order hydrogenated silicon is converted into plasma using a mercury sensitization reaction. The purpose of the present invention is to cause a photochemical reaction on or near the substrate by direct irradiation of ultraviolet rays having a wavelength of 160 nm or less emitted from plasma, and as a result, form a thin film of silicon on the substrate.

Some embodiments of the present invention will be described below based on the drawings.

In FIG. 1, reference numeral 1 denotes a discharge region, opposite to which a pair of electrodes 2 are arranged, and a discharge gas for ultraviolet radiation such as rare gas, hydrogen, or deuterium is supplied from a pair of pipes 3. It is becoming more and more common. Reference numeral 4 denotes a pipe for supplying silane alone or together with a carrier gas, and is opened facing the reaction area 7 where the substrate 6 placed on the substrate holding table 5 is disposed. The position is between the pair of electrodes 2 and is sufficiently far away from the center of the plasma positive column formed by discharge. Reference numeral 13 denotes a pump that exhausts the discharge gas and the photoreactive gas, but the exhaust may be performed from another direction of the pipe 8. 9 is a pipe for supplying a protective gas to prevent photolysis reaction products from accumulating on the electrode when the device is used for a long period of time; It is good to make it flow. A rare gas such as argon is ideal as the protective gas, and can be used as is as a discharge gas. There are various ways to flow these discharge gas and protective gas.
structure may be adopted. Similarly, photoreactive gases
If it is desired to use it as a discharge gas, it is sufficient to exhaust it from the pipe 8, and the exhaust method and structure can be changed in various designs as necessary.

By the way, using the device with the above configuration, ultraviolet rays with a wavelength of 160 nm or less emitted from plasma can be
Directly illuminate the substrate or its vicinity,
If the photoreactive gas is photodecomposed by a photochemical reaction and the decomposition products are deposited on the substrate 6, the rate of film formation of amorphous silicon is extremely fast even without using a mercury sensitization reaction. When argon is used as a discharge gas, ultraviolet rays with wavelengths of 106.7 nm, 104.8 nm, etc. are emitted;
m, 129.6nm, for hydrogen, 121.6nm, 102.6nm
UV rays are emitted. These light beams directly hit the silane on or near the substrate 6 without being interrupted. Rare gases other than those listed above are also available.
It emits ultraviolet rays with a wavelength of 100 mm or less, and these also
It is estimated that this contributes to the direct photodecomposition of silane. Furthermore, if the pressure of the discharge gas is high, a continuous spectrum is also emitted in addition to the emission line. To give an example, if 50 SCCM to 200 SCCM of argon is flowed as a discharge gas for ultraviolet radiation, and a plasma is formed with a power consumption of 2500 W due to discharge, a plasma of about 5 cm will be formed.
The distant substrate 6 is directly irradiated with ultraviolet rays with a wavelength of 160 nm or less and an intensity of 8 mW/cm ² , and when silane is supplied as a photoreactive gas at a flow rate of 20 SCCM, even without using a mercury sensitization reaction, An amorphous silicon film is formed on the substrate 6 at an extremely fast film formation rate of 1 nm/sec or more. Therefore, normally, in a solar cell, etc., it is sufficient to have an amorphous silicon film with a thickness of about 600 nm on the substrate 6, and in the above example, it is sufficient to maintain stable discharge continuously for 10 minutes. Depending on the application, the film thickness may vary.
In some cases, even a wavelength of about 100 nm may be sufficient, so a stable discharge of approximately 100 seconds or more is sufficient. Of course, if the intensity of the ultraviolet rays is high and the film thickness can be thin, the plasma formation time can be short. Furthermore, if the temperature of the substrate 6 can be increased by heating it with infrared rays or by adding a heater to the substrate holding table, it is possible to heat the substrate 6 not only with a thin film of amorphous silicon but also with a large amount of silicon. Crystal thin films and single crystal thin films can also be obtained. Although it depends on the conditions, if the temperature of the substrate 6 is 700 to 800° C. or higher, it becomes a single crystal, but if it is a polycrystal, it may be a little lower.

The wavelength of the vacuum ultraviolet rays emitted from the discharge gas for ultraviolet radiation is determined by the type of gas, so for example, hydrides or halides of arsenic, boron, or phosphorus, which emit UV rays well, may be mixed. The plasma may be formed by a high frequency capacitive coupling type, an inductive coupling type, a microwave type electrodeless type, or by ECR heating.

Furthermore, if hydrogen compounds or halides of arsenic, phosphorus, or boron are mixed into the carrier gas or photoreactive gas, amorphous silicon films doped with arsenic, phosphorus, or boron as impurities can also be obtained. It will be done.

Here, I would like to introduce some of the comparative experimental studies.While evacuating the container to a pressure of about 2 Torr, 10 SCCM of argon gas and 10 SCCM of silane were introduced.
Figures 3 and 4 show the measurement results of the emitted light from the plasma when 5SCCM was flowing and a mercury reservoir maintained at 60°C was connected to the vessel and when it was not. Figure 3 shows the case where it communicates with the mercury reservoir, and Figure 4 shows the case where it does not communicate with the mercury reservoir.The scale of the vertical axis in Figure 3 is enlarged to 2.5 times that of Figure 4. be. As can be seen from this, when it is in communication with a mercury reservoir, the radiation from mercury is added, but the radiation from argon is weaker than when it is not communicating with a mercury reservoir. In other words, without mercury, the radiation from argon is even stronger. It was also confirmed that the film formation rate was almost the same, and mercury sensitization was not necessarily required. In addition, the temperature of the plasma is determined by using an electrode that has a filament with good electron emissivity, such as an electrode that has a tungsten filament coated with an alkaline earth metal oxide used in fluorescent lamp electrodes and is sintered. By using an electrode in which the base metal is impregnated, coated, or mixed with an alkali metal oxide, discharge can be maintained with relatively low power energy, and the plasma temperature is also considerably lower than that of RF plasma. Therefore, it is estimated that the damage to the film formed on the substrate is also smaller than that in the film forming method using RF plasma. Regarding the temperature of this plasma, see J.Quant.Spectrosc.Radiant.
Transfer 23 (1980) 1, Proc.Phys.Soc. 92
(1967) 896., Atomic Transition Probabilities.
Vol., NSRDS-NBS 22 (1969), etc. Even if calculations are made using data such as 7600
Compared to ~11,000 degrees Kelvin, when the electrodes of the fluorescent lamp are used, the plasma temperature is about 4,600 to 5,700 degrees Kelvin, which is roughly 1/2 the temperature.

By the way, from the viewpoint of film quality, if you want to make a good quality film, as mentioned above, place the substrate at a position sufficiently far away from the center of the plasma positive column, that is, at a position far enough away that almost no plasma charged particle damage will occur. At the same time, consideration should be given to ensuring that the substrate is not located downstream in the flow of discharge gas, and that the substrate is located upstream in the flow of photoreactive gas relative to the plasma. Effective.

However, if the film quality is not a big problem, the substrate may be intentionally placed near the plasma or at the center of the plasma positive column in order to increase the film formation rate. When placed near the plasma, charged particle damage can be slightly reduced by placing a grid electrode between the plasma and the substrate to repel ions directed toward the substrate.

Regarding the flow rate of silane, according to an experiment using a 100 mmφ silicon wafer substrate, if the irradiation intensity of ultraviolet rays having a wavelength of 30 SCCM or more and a wavelength of 160 nm or less is 8 mW/cm ² or more on the substrate, A film formation rate of approximately 1 nm/sec or more can be obtained, making it suitable for practical use.

The above film forming method does not utilize mercury sensitization reaction, so there is no problem of mercury contamination of the film quality. Since it is not a device, there is no problem of ``fogged windows'', and plasma formation is convenient because ordinary continuous discharge type power supplies can be used. In particular, if the power supply device can be designed to be compact, there is a great economic advantage in that it occupies a small area in the clean room.

Further, another improved embodiment will be described. The plasma formed in the discharge region has various shapes such as spherical, rugby ball, and linear (rod-shaped) depending on the formation method, but the semiconductor wafer that is the substrate is generally circular in size from 3 to 5 inches. It is surprisingly difficult to uniformly irradiate the entire wafer with ultraviolet rays from these plasmas. In that case, it is recommended to form three to five rod-shaped plasmas, whose power consumption can be controlled independently, lined up in a plane. good. FIG. 2 is a perspective view of the main part, and shows paired electrodes 2a-2a, 2b-
2b,... are arranged to protrude into the discharge area,
Between 2c and 2c in the center is driven by a 2500W power supply,
b-2b and 2d-2d are 2000W, 2a- at both ends
2a and 2e-2e are each driven by a power supply of 1600W, and when more ultraviolet rays are emitted from the plasma toward the edge of the substrate surface, the intensity of the ultraviolet rays on the substrate surface is made uniform. Ru. This uniformity of the intensity of ultraviolet rays on the substrate surface can also be used when the discharge area and the reaction area are separated by an ultraviolet transmitting window. The lamp may be configured as a lamp having five sets of electrodes that can be controlled. Also, 2a-
It is not necessary that the distances between the electrodes 2a, 2b-2b, etc. are all the same. Rather, in the above example,
The distance between the electrodes is 2a-2a, 2e-2e<2b-2b, 2d-
Even better is 2d<2c-2c.

As can be understood from the description of the embodiments above, the present invention provides a discharge region to which a discharge gas for ultraviolet radiation selected from a rare gas, hydrogen or deuterium, or a mixture thereof is supplied, and a substrate. The reaction area where silane or high-order silicon hydride with a flow rate of 1 SCCM or more is supplied alone or together with a carrier gas is treated in one container without division, and the plasma formed by the discharge gas is removed. The discharge gas is turned into plasma for a finite continuous time of several seconds or more so that the emitted ultraviolet rays with a wavelength of 160 nm or less reach the substrate with an intensity of 1 mW/cm ² or more, and the silane or higher-order hydrogenated Silicon is directly irradiated with ultraviolet rays containing wavelengths of 160 nm or less emitted from plasma without using a mercury sensitization reaction to cause a photochemical reaction on or near the substrate, and as a result,
A thin film of silicon is formed on the substrate, and there is no mercury contamination, the film formation speed is practical, there is no problem of "cloudy windows" as mentioned above, and the power supply is small. It has the advantage of being easy to design.

In addition, if uniformity of the UV irradiation intensity on the substrate is required, multiple sets of rod-shaped plasma may be created regardless of the type or pressure of the discharge gas, and the thickness and length of each plasma may be adjusted individually. The size and distance of the pair of electrodes may be changed, and the power consumption may be independently controlled.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an apparatus used in an embodiment of the present invention, FIG. 2 is a perspective view of the same, and FIGS. 3 and 4 show the measurement results of emitted light. DESCRIPTION OF SYMBOLS 1... Discharge area, 2... Electrode, 5... Substrate holding stand, 6... Substrate, 7... Reaction area.

Claims (1)

[Claims] 1. A discharge region to which a discharge gas for ultraviolet radiation selected from a rare gas, hydrogen or deuterium, or a mixture thereof is supplied, and a substrate are arranged,
Silane or high-order silicon hydride with a flow rate of 1 SCCM or more is supplied alone or together with a carrier gas, and the reaction area is surrounded in one container without division, and radiated from the plasma formed by the discharge gas. The discharge gas is turned into plasma for a finite continuous time of several seconds or more so that ultraviolet rays with a wavelength of 160 nm or less reach the substrate with an intensity of 1 mW/cm ² or more, and the silane or high-order hydrogenated silicon is Without using a mercury sensitization reaction, a photochemical reaction occurs directly on or near the substrate by direct irradiation of ultraviolet rays with a wavelength of 160 nm or less emitted from plasma, and as a result, a thin film of silicon is formed on the substrate. A film forming method characterized by forming a film. 2. The film forming method according to item 1, wherein the silicon thin film is made of amorphous silicon. 3. The film forming method according to item 1, wherein the silicon thin film is made of polycrystal or single crystal. 4 Plasma is formed by a discharge generated between a pair of electrodes placed opposite each other in a discharge region, and the electrodes contain an oxide of an alkali metal or alkaline earth metal as an electron radioactive substance such as tungsten or 2. The method of forming a film according to item 1, wherein the film is deposited on, impregnated with, or mixed with triated tungsten. 5. The film forming method according to item 1, wherein the plasma is formed by an electrodeless type discharge such as a high frequency capacitive coupling type, an inductively coupled type, or a microwave type. 6. The film forming method according to item 1, wherein the discharge gas for ultraviolet radiation contains at least one hydride or halide selected from indium, antimony, arsenic, phosphorus, and boron. 7. The film forming method according to item 1, wherein a hydride or halide of arsenic, phosphorus, indium, antimony, or boron is mixed in the silane, high-order silicon hydride, or carrier gas. 8. The film forming method according to item 1, wherein the substrate is placed at a position sufficiently far from the center of the plasma positive column to the extent that charged particle damage does not occur. 9. The film forming method according to item 4, wherein an electrode protection gas is supplied near the electrode. 10. The film forming method according to item 1, wherein the plasma is formed by ECR heating. 11. The film forming method according to item 1, wherein a grid electrode is disposed between the plasma and the substrate.