JP2006216761A - Consecutive liquid-phase film forming method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polycrystalline Si crystal liquid-phase film forming method which is capable of forming a film consecutively with high mass-productivity, and to provide its manufacturing device. <P>SOLUTION: A film forming unit is kept at a prescribed temperature. The temperature of a solute feed unit is made to vary in a prescribed range of temperature to the temperature of the film forming unit, and a melt which varies continuously in degree of supersaturation with time is supplied to the film forming unit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal film forming method of Si crystal and a liquid phase film forming apparatus, and more particularly to a liquid phase film forming method in which the surface property of a film forming layer is good and continuous film forming is possible.

  Since the liquid phase film formation method is a crystal film formation from a quasi-equilibrium state, it has the advantage that high-quality crystals close to the stoichiometric composition can be obtained, and LED (light emission) has already been established with compound semiconductors such as GaAs. Diodes) and laser diodes. Recently, liquid phase film formation of Si has been attempted for the purpose of obtaining a thick film (for example, Patent Document 1), and application to solar cells is also being studied.

  In the conventional liquid phase film-forming method, a solution containing a film-forming substance as a solute is generally cooled to a supersaturated state, and an excess solute (film-forming substance) is deposited on a substrate. As a typical film formation temperature profile, the film formation temperature is lowered from the film formation start temperature to the film formation end temperature while gradually cooling at a constant temperature decrease rate. In such a method, a relatively smooth film-forming surface can be obtained when a crystal film is formed on a commercially available mirror-finished single crystal wafer. In other cases, for example, on a polycrystalline substrate that is not sufficiently polished. When the film is formed, unevenness due to the facet surface occurs, or undulations occur in the vicinity of the crystal grain boundary, resulting in poor surface properties, which becomes a problem when applied to devices such as solar cells (Non-Patent Document 1). As a method of improving such deterioration of surface properties, a method of periodically melting back the film formation surface during crystal film formation has been proposed (Non-Patent Document 2), and film formation having a substantially flat surface with few irregularities. It was shown that a layer was obtained. In this case, as shown in FIG. 5, the temperature profile at the time of film formation decreases as a whole while repeating cooling and temperature increase. Here, Th and Tl represent the film formation start temperature and the film formation end temperature, respectively, the cooling temperature width ΔTc is for solute supersaturation in the solvent to promote film formation, and the temperature rise temperature width ΔTh is It is a value set in order to selectively dissolve out the convex portion in the solvent among the concave and convex portions formed by film formation (melt back).

  In general, when a solute (Si, GaASinP, etc.) is dissolved in a solvent using a low-melting-point metal (In, Sn, Ga, Bi, etc.), the amount of solute (solubility) dissolved in the solvent is a function of temperature. Therefore, in order to maintain a certain degree of solute supersaturation and meltback, it is necessary to increase ΔTc and ΔTh, respectively, as the film formation temperature decreases. For this reason, in the above-described method, as the film formation progresses, much time is required for cooling and raising the temperature, and there is a problem in productivity. In addition, since the film formation temperature changes, there is a difficulty in keeping the film quality of the formed crystal constant, and it takes time to return the temperature lowered after the film formation to the original film formation start temperature.

As a method for performing continuous liquid phase film formation at a constant film formation temperature, the methods disclosed in Patent Documents 2 to 4, that is, the film formation is performed with the place where the solute is dissolved in the solvent and the solvent in which the solute is dissolved. Separately from the place to perform, the temperature of the place where the solute is dissolved is controlled independently so that the temperature of the place where the film is formed is higher, and the solvent is continuously circulated between the two. A method of performing liquid phase film formation has been proposed, and crystal film formation with uniform film quality and mass productivity can be performed. However, even in these methods, the above-described problem of surface unevenness during film formation on a polycrystalline substrate has not been solved.
JP 58-89874 A Japanese Patent Laid-Open No. 3-19326 Japanese Patent Laid-Open No. 6-349751 JP 11-292893 A K. J. et al. Weber and A.M. W. Blackers: Journal of Crystal Growth 154 (1995) p54. G. Ballhorn, K.M. J. et al. Weber, S .; Armand, M.M. J. et al. Stocks and A.M. W. Blackers: Solar Energy Materials and Solar Cells 52 (1998) p. 61

  The present invention has been completed as a result of diligent research by the present inventors in order to solve the above-described problems in the prior art, and provides a liquid phase film forming method with good surface properties and high mass productivity. Objective.

  Therefore, the present invention provides a liquid phase in which film formation is performed by separating the solute supply unit and the film forming unit and controlling each temperature independently and circulating a solvent in which the solute is dissolved between the two. In the film forming method, the film forming unit is maintained at a predetermined temperature, while the temperature of the solute supply unit changes with a temperature range within a predetermined range with respect to the temperature of the film forming unit. A continuous liquid phase film forming method is provided, wherein a solvent whose supersaturation degree is changed is supplied to the film forming section.

  The present invention also includes a raw material supply mechanism that supplies a solute to a solvent, a film formation mechanism that forms a crystal film by bringing the solvent supplied with the solute into contact with a substrate, and the raw material supply mechanism and the film formation mechanism. A continuous liquid phase film forming apparatus comprising a pipe for circulating the solvent between them, and provided with means for independently controlling the temperature of the raw material supply mechanism and the temperature of the film formation mechanism. A mechanism for controlling the temperature of the mechanism within a temperature range within a predetermined range with respect to the temperature of the film forming mechanism; and a means for continuously supplying a solvent from the raw material supply mechanism to the film forming mechanism. A continuous liquid phase film forming apparatus is provided.

  According to the present invention, continuous liquid phase film formation with good surface properties and high mass productivity is possible on a polycrystalline substrate. The present invention is suitable as a method for mass production of devices requiring thickness, particularly solar cells.

  An example of a liquid phase film forming apparatus used in the liquid phase film forming method of the present invention is shown in FIG. In FIG. 1, 101 is a wafer cassette, 102 is a substrate (wafer), 103 is a film forming unit, 104 is a solvent (melt), 112 is a gate valve, and these constitute a film forming mechanism 114. The wafer cassette 101 moves up and down to immerse the wafer 102 in the solvent 104 or lift the wafer 102 from the solvent 104 to perform film formation start processing / film formation end processing. The wafer cassette 101 is also provided with a rotation mechanism, and the film thickness can be made uniform within the wafer surface and between the wafers by rotating the wafer cassette 101 during film formation. These film forming mechanisms 114 are heated by an electric furnace 108 disposed outside. A raw material supply mechanism 113 includes a 105 solute supply unit, 106 heating means (heater block), and 107 cooling means (cooling pipe). The film forming mechanism and the raw material supply mechanism are connected by a circulation pipe 110, and a heat exchanger 109 and a rotor 111 for circulating the solvent are provided in the middle of the circulation pipe. As shown in FIG. 6, the solute supply unit 105 includes several partition plates 602 installed in a solute supply container 601 made of a material such as carbon or quartz, and a raw material plate (solute) serving as a lid of the solute supply container 601. And the same material) 603 to form a solvent flow path as shown in FIG. While the solvent passes through the flow path, the solute dissolves in the solvent from the raw material plate 603 and is supplied. The solute supply unit 105 also serves as a heat exchanger. Further, these series of members are stored in the electric furnace 108.

  Next, the liquid phase film forming method and the liquid phase film forming apparatus of the present invention will be described with reference to FIG. As shown in FIG. 1, there is a film forming mechanism 114 that is maintained at a certain constant temperature T by an electric furnace 108, and a solvent 104 containing a solute enters and exits the film forming unit 103 by a rotor 111 at a constant flow rate. Similarly, the solvent fed by the rotor 111 enters the solute supply unit 105 also serving as a heat exchanger in the raw material supply mechanism 113 in the electric furnace 108, and is controlled by a temperature control mechanism including the heater block 106 and the cooling pipe 107. The solute is supplied from the raw material plate 603 forming the flow path while gradually changing to the generated temperature, and reaches saturation. At this time, if the temperature of the solute supply unit 105 is set higher than the temperature T of the film forming mechanism by ΔT1 ° C. (T + ΔT1), the solvent in which the solute is saturated at this temperature (the saturation concentration at this time is set). C1) is sent out from the solute supply unit. The solvent that has passed through the solute supply unit returns to the outside of the raw material supply mechanism, passes through a heat exchanger, drops to the same temperature T as the film formation mechanism 114, and is then sent into the film formation unit 103 in the film formation mechanism. Here, since the temperature of the solvent returns to the original temperature T, the solute becomes supersaturated. When the saturation concentration at the original temperature T is C0, the degree of supersaturation σ1 at this time is represented by (C1−C0) / C0. Therefore, if the temperature of the solute supply unit 105 is maintained at a temperature higher than that of the film forming mechanism 114 by ΔT1 ° C., a solvent having a supersaturation level σ1 always flows into the film forming unit 103. If the substrate is immersed, film formation corresponding to the degree of supersaturation σ1 is always possible. The degree of supersaturation of the solvent exiting the film forming unit 103 decreases as much as the solute is deposited in the film formation, and is sent again into the raw material supply mechanism 113 to be supplied with the solute again. Thus, liquid phase film-forming is performed continuously by circulating a solvent.

  In the above-described film forming process, if the solute supply unit 105 is held at the time T + ΔT1 for t1 and then changed to the time T−ΔT2 at t2, the amount of the solute dissolved in the solvent changes accordingly. The excess solute in the solvent is deposited on the surface of the raw material plate 603 in the solute supply unit, and the solute concentration of the solvent is adjusted. Thus, the degree of supersaturation σ2 of the solvent sent into the film forming unit 103 is σ2 = (C2−C0) / C0 when the saturation concentration at the temperature of T−ΔT2 is C2, and C2 <C0. It will be in an unsaturated state. That is, by changing the temperature of the solute supply unit 105 within a predetermined range with respect to the temperature T of the film forming unit 103, a solvent in a supersaturated to unsaturated state is continuously sent to the film forming unit over time. Is possible. Since the sizes of ΔT1 and ΔT2 can be set in a range of about 0 to several tens of degrees Celsius, the film formation and the meltback can be repeated at a substantially constant film formation temperature, so that the flatness can be continuously obtained. A crystal film-forming layer on a polycrystalline substrate having a good and uniform film quality can be obtained. Actually, as shown in FIG. 7, since the temperature of the solute supply portion changes from T + ΔT1 to T−ΔT2, it takes transition times Δt1 and Δt2. It will be responsive. Since there is a partial difference between the temperature change in the solute supply unit and the change in the degree of supersaturation of the solvent flowing into the film forming unit, a time difference (phase difference) occurs.

  High purity carbon or high purity quartz is mainly suitable as the material of the film forming unit for containing the metal solvent used in the present invention, the material of the wafer cassette that supports the wafer, and the material of the pipe for solvent circulation. Used for. In addition, the film forming mechanism is replaced with the structure in which the wafer cassette is taken in and out of the film forming unit described above, and an opening for contacting the substrate is provided in the middle of the circulation pipe. In this case, high-purity carbon is mainly used as the material of the slider.

The solvent and solute used in the present invention may be any combination as long as they are used in the conventional liquid phase film forming method. For example, when Si is used as the solute, , Sn, Bi, Ga, Sb and other metals are used. Here, when In or Sn is used as a solvent, the Si crystal obtained is electrically neutral, and the conductivity type is determined at a desired doping concentration by appropriately adding desired impurities after or during film formation. can do. For example, a p ⁻ type Si crystal can be obtained by adding a small amount of Ga as a dopant in In and forming a crystal film.

  In the method of the present invention, H2 or N2 is used as an atmosphere in which the solvent and the substrate are placed, and the pressure is generally about 10-2 Torr to 760 Torr, more preferably 10-1 Torr to 760 Torr.

  In addition, the solvent temperature in the method of the present invention is preferably controlled to be 800 ° C. or higher and 1100 ° C. or lower when In or Sn is used, depending on the type of solvent.

  The present invention can be applied not only to homoepitaxial but also to heteroepitaxial.

  When the film forming mechanism has a slider structure that can move so that the solvent and the substrate are in contact with each other at the opening of the circulation pipe, the speed of the solvent in the pipe is preferably 1 to 100 mm / min, and the moving speed of the slider is 0 to 300 mm. / Min is preferred.

  The temperature differences ΔT1 and ΔT2 between the raw material supply mechanism and the film forming mechanism are preferably in the range of 0 to 50 ° C., respectively. The holding times t1 and t2 are preferably in the range of 0 to 100 minutes. If the product of ΔT2 and t2 is too small compared to the product of ΔT1 and t1, the flatness of the substrate surface is not sufficient, or conversely if the product of ΔT2 and t2 is too high than the product of ΔT1 and t1. Since the film formation rate may be significantly reduced or only meltback may proceed, it is necessary to determine appropriately according to the desired surface condition and film formation rate. Also, if ΔT1 is excessively increased, crystal grains may be precipitated in the solvent in the pipe before reaching the substrate, so care must be taken.

  Further, in addition to the above-mentioned raw material plate, the solute can be supplied to the solvent by feeding the raw material gas into the solvent by the raw material gas introduction pipe held in the raw material supply mechanism. That is, the solvent is filled in the carbon or quartz film forming unit similar to the film forming unit of the film forming mechanism described above as the solute supply unit, and the source gas is introduced along the side wall and the bottom surface of the film forming unit. A supply pipe is provided, and the raw material is continuously supplied by blowing the raw material gas from the outside of the film forming section through this gas introduction pipe (for details, refer to Japanese Patent Laid-Open No. 11-292893). As the material for the source gas introduction pipe, high-purity carbon or high-purity quartz is preferably used as in the film forming section. For example, SiH4, Si2H6,... SinH2n + 2 (n: natural number) and other halogenated silanes such as SiH2Cl2, SiHCl3, SiCl4, SiH2F2, and Si2F6 are suitable as source gases to be used. As mentioned. Further, as the doping gas added to the source gas, PH3, PF3, AsH3, SbH3, B2H6, BF3, BCl3, Ga (CH3) 3, Ga (C2H5) 3, or the like is preferably used. Moreover, you may install the energy provision means for decomposing | disassembling source gas and / or dopant gas in the front | former stage of an inlet tube.

  In addition, it is preferable to add hydrogen (H2) to the source gas as a carrier gas or for the purpose of obtaining a reducing atmosphere that promotes crystal film formation. The ratio of the amount of the source gas and hydrogen is appropriately determined depending on the formation method, the type of the source gas, and the formation conditions, but is preferably 1: 1000 or more and 100: 1 or less (introduction flow ratio), and is 1: 100 or more. More preferably, it is 10: 1 or less.

  Hereinafter, although the place which forms a desired crystal | crystallization by the method of this invention using an Example is demonstrated in detail, this invention is not limited at all by these Examples.

Example 1
In this example, a Si layer was formed on a polycrystalline Si substrate using the liquid phase film forming apparatus having the configuration shown in FIG. In was used as a solvent, and polycrystalline Si (Si as a solute) was used as a raw material plate. A wafer cassette 101 in which five 125 mm square polycrystalline Si wafers (thickness 0.6 mm) 102 formed by the casting method are placed in a standby chamber (not shown) is placed in a standby chamber (not shown), and an In solvent 104 is accommodated. The film part 103 (crucible) was heated by the electric furnace 108 to keep the temperature of the solvent constant at 950 ° C. Next, the wafer cassette 101 kept in the standby chamber was held immediately above the film forming unit 103 by opening the gate valve 112. The gate valve was left open thereafter. The temperature of the solute supply unit 105 was adjusted to 957 ° C. by the heater block 106 (ΔT1 = 7 ° C.), and the In solvent was circulated between the raw material supply mechanism and the film formation mechanism through the circulation pipe 110. At this time, the temperature of the solvent is converted by the heat exchangers 109 and 105 from the temperature of the raw material supply mechanism to the temperature of the film forming mechanism, and from the film forming mechanism to the temperature of the raw material supply mechanism. When a sufficient time has passed, the wafer cassette 101 is lowered while rotating at a rotational speed of 10 rpm, and is put into the In solvent 104 in the film forming unit 103. When the wafer cassette 101 is completely immersed in the In solvent 104, the wafer cassette 101 is lowered. The liquid phase film formation was performed for 30 minutes while holding and rotating the position. Thereafter, the output of the heater block 106 is adjusted while flowing a cooling gas such as nitrogen through the cooling pipe 107 to adjust the temperature of the solute supply unit 105 to 947 ° C. (ΔT2 = 3 ° C.), and held for 10 minutes (= t2). At this time, the transition time (Δt2) from 957 ° C. to 947 ° C. of the temperature in the solute supply unit was 15 minutes. Thereafter, the temperature of the solute supply unit 105 was further adjusted to 957 ° C. (ΔT1 = 7 ° C., transition time Δt1 = 10 minutes), and thereafter the same process was repeated to perform film formation / meltback for a total of 3 cycles. After all the cycles are completed, the wafer cassette 101 is lifted out of the In solvent 104, temporarily stopped immediately above the film forming unit 103, and the rotation speed is increased to 120 rpm. The membrane was terminated.

  As a result of investigating the film thickness and surface state of the deposited Si layer using a step gauge and a scanning electron microscope, the average thickness of the deposited Si layer was about 35 μm, and the surface was almost flat (the height of irregularities was 1 to 1). About 3 μm) was obtained. Further, when the orientation of the deposited Si layer was measured by an ECP (Electron Channeling Pattern) method, it was found that the crystal orientation of each grain of the underlying polycrystalline Si substrate was inherited.

  For comparison, when there is no meltback process, that is, when only ΔT1 is set without setting ΔT2 in the above, the obtained Si layer has an average thickness of about 45 μm. The surface property was poor, and irregularities with a height of about 10 to 30 μm were generated.

(Example 2)
In this example, a GaAs crystal film was formed on polycrystalline GaAs using the liquid phase film forming apparatus having the configuration shown in FIG. Ga was used as the solvent, and polycrystalline GaAs (GaAs as the solute) was used as the raw material plate. A polycrystalline GaAs substrate 202 having a width of 40 mm, a length of 60 mm, and a thickness of 0.5 mm is placed on the slider 201, and the width and length of the opening 203 provided in the circulation pipe (flat pipe) 210 are set to 35 mm, The position of the slider was adjusted in advance so that the GaAs substrate 202 was not in contact with the Ga solvent at the opening 203 of the flat pipe. The Ga solvent 204 in the circulation pipe 210 was heated by the electric furnace 208 to keep the temperature of the solvent constant at 750 ° C.

  The temperature of the solute supply unit 205 was adjusted to 754 ° C. by the heater block 206 (ΔT1 = 4 ° C.), and Ga solvent was circulated between the raw material supply mechanism and the film formation mechanism through the circulation pipe 210. At this time, the temperature of the solvent is converted by the heat exchangers 209 and 205 from the temperature of the raw material supply mechanism to the temperature of the film forming mechanism, and from the film forming mechanism to the temperature of the raw material supply mechanism. When sufficient time had elapsed, the slider 201 was moved to bring the polycrystalline GaAs substrate 202 into contact with the Ga solvent at the opening 203, and in this state, liquid phase film formation was performed for 30 minutes. Thereafter, the temperature of the solute supply unit 205 is adjusted to 748 ° C. by adjusting the output of the heater block 206 while flowing a cooling gas such as nitrogen through the cooling pipe 207 (ΔT2 = 2 ° C.) and held for 10 minutes (= t2). At this time, the transition time (Δt2) from 754 ° C. to 748 ° C. of the temperature in the solute supply unit was 12 minutes. Thereafter, the temperature of the solute supply unit 205 was further adjusted to 754 ° C. (ΔT1 = 4 ° C., transition time Δt1 = 8 minutes), and thereafter the same process was repeated for a total of four cycles of film formation / meltback. After all the cycles were completed, the slider 201 was moved again to separate the GaAs substrate 202 from the Ga solvent, and the crystal film formation was completed.

  As a result of examining the film thickness and surface state of the deposited Si layer with a step meter and a scanning electron microscope, the average thickness of the deposited GaAs layer was about 10 μm, and the surface was flat (with an uneven height of 0.2 μm). ˜0.3 μm) was obtained. Further, when the orientation of the deposited GaAs layer was measured by an ECP (Electron Channeling Pattern) method, it was found that the grain orientation of each grain of the underlying polycrystalline GaAs substrate was inherited.

  For comparison, when there is no meltback step, that is, when only ΔT1 is set without setting ΔT2 in the above, the obtained epitaxial GaAs layer has an average thickness of about 15 μm. However, the surface property was poor, and irregularities with a height of about 1 to 3 μm were produced.

  Further, in the above-described embodiment, the process is started after first setting ΔT2, that is, the substrate surface is melted back and cleaned prior to film formation by making the solvent unsaturated and then contacting the substrate. And a higher quality GaAs epitaxial layer can be obtained.

(Example 3)
In this example, a Si layer was formed on a polycrystalline Si substrate using the liquid phase film forming apparatus having the configuration shown in FIG. In was used as the solvent, and SiH4 (Si as the solute) was used as the source gas. A wafer cassette 301 on which five 125 mm square polycrystalline Si wafers (thickness: 0.6 mm) 302 formed by the casting method are placed in a standby chamber (not shown), and the In solvent 304 is accommodated. The film part 303 was heated by an electric furnace 308 to keep the temperature of the solvent constant at 960 ° C. Next, the wafer cassette 301 that was waiting in the preliminary chamber was held just above the film forming unit 303 by opening the gate valve 312. The gate valve was left open thereafter. The source gas SiH4 is flowed into the source gas introduction pipe 316 together with the H2 gas (gas flow ratio SiH4: H2 = 1: 20), and into the In solvent of the film forming unit 315 from the outlet provided at the tip of the source gas introduction pipe Erupted. In this case, the ejected raw material gas is decomposed in contact with the solvent, and the solute (Si) is rapidly dissolved and supplied to the solvent, and the solvent is generated by the gas 305 (reaction product gas: H 2 or the like) generated by decomposition. The solute concentration is made uniform by stirring. The temperature of the film forming unit 315 was adjusted to 970 ° C. by the heater block 306 (ΔT1 = 10 ° C.), and the In solvent was circulated between the raw material supply mechanism and the film forming mechanism through the circulation pipe 310. At this time, the temperature of the solvent is converted by the heat exchangers 309a and 309b from the temperature of the raw material supply mechanism to the temperature of the film forming mechanism and from the film forming mechanism to the temperature of the raw material supply mechanism. After 20 minutes in this state, the wafer cassette 301 is lowered while being rotated at a rotation speed of 10 rpm and is put into the In solvent 304. When the wafer cassette 301 is completely immersed in the In solvent 304, the descent is stopped. Liquid phase film formation was performed for 20 minutes while rotating while maintaining the position. Thereafter, the output of the heater block 306 is adjusted while flowing a cooling gas such as nitrogen through the cooling pipe 307 to adjust the temperature of the film forming unit 315 to 955 ° C. (ΔT2 = 5 ° C.) and held for 7 minutes (= t2). At this time, the transition time (Δt2) from 970 ° C. to 955 ° C. of the temperature in the solute supply unit was 15 minutes. The inner wall material of the heat exchanger 309b uses the same Si as the solute, and the solute concentration of the solvent is adjusted by, for example, depositing excess solute in the solvent on the surface of the inner wall of the heat exchanger. Thereafter, the temperature of the film forming unit 315 was further adjusted to 970 ° C. (ΔT1 = 10 ° C., transition time Δt1 = 10 minutes), and thereafter the same process was repeated to perform film formation / meltback for a total of 5 cycles. After all the cycles are completed, the wafer cassette 301 is lifted out of the In solvent 304, temporarily stopped immediately above the film forming unit 303, and the number of rotations is increased to 120 rpm. The membrane was terminated.

  As a result of investigating the film thickness and surface state of the deposited Si layer using a step gauge and a scanning electron microscope, the average thickness of the deposited Si layer was about 50 μm, and the surface was almost flat (1 to About 2 μm). Further, when the orientation of the deposited Si layer was measured by an ECP (Electron Channeling Pattern) method, it was found that the crystal orientation of each grain of the underlying polycrystalline Si substrate was inherited.

  For comparison, when there is no meltback process, that is, when only ΔT1 is set without setting ΔT2 in the above, the obtained Si layer has an average thickness of about 70 μm. The surface property was poor, and irregularities with a height of about 20 to 50 μm were generated.

Example 4
In this example, an Si layer was formed on a polycrystalline Si substrate using the liquid phase film forming apparatus having the configuration shown in FIG. Sn was used as the solvent, Si2H6 (Si as the solute) as the source gas, and B2H6 as the impurity doping gas. A polycrystalline Si substrate 402 having a width of 40 mm, a length of 60 mm, and a thickness of 0.5 mm formed by the casting method is placed on the slider 401, and the width and length of the opening 403 provided in the circulation pipe (flat pipe) 410 are arranged. The thickness was set to 35 mm and 55 mm, respectively, so that the position of the slider was adjusted in advance so that the polycrystalline Si substrate 402 did not come into contact with the Sn solvent at the opening 403 of the flat pipe. The Sn solvent 404 in the circulation pipe 410 was heated by the electric furnace 408 to keep the temperature of the solvent constant at 930 ° C. Source gas Si2H6 and doping gas B2H6 were flowed to source gas introduction pipe 416 together with H2 gas (gas flow ratio Si2H6: H2 = 1: 20, B2H6 / Si2H6 = 0.03) and provided at the tip of the source gas introduction pipe The film was ejected from the outlet into the In solvent of the film forming unit 415. In this case, the ejected source gas and doping gas are decomposed in contact with the solvent, and the solute (Si) and the dopant (B) are rapidly dissolved in the solvent and supplied and decomposed and generated (reaction product gas) : H2 etc.) The solvent is stirred by 405, and the concentration of the solute and the dopant is made uniform. The temperature of the film formation unit 415 was adjusted to 935 ° C. by the heater block 406 (ΔT1 = 5 ° C.), and the Sn solvent was circulated between the raw material supply mechanism and the film formation mechanism through the circulation pipe 410. At this time, the temperature of the solvent is converted by the heat exchangers 409a and 409b from the temperature of the raw material supply mechanism to the temperature of the film forming mechanism and from the film forming mechanism to the temperature of the raw material supply mechanism. When sufficient time had elapsed, the slider 401 was moved to bring the polycrystalline Si substrate 402 into contact with the Sn solvent at the opening 403, and in this state, liquid phase film formation was performed for 30 minutes. Thereafter, the output of the heater block 406 is adjusted while flowing a cooling gas such as nitrogen through the cooling pipe 407 to adjust the temperature of the film forming unit 415 to 920 ° C. (ΔT2 = 10 ° C.), and held for 3 minutes (= t2). At this time, the transition time (Δt2) from 935 ° C. to 920 ° C. of the temperature in the solute supply unit was 15 minutes. The inner wall material of the heat exchanger 409b uses the same Si as the solute, and the solute concentration in the solvent is adjusted by, for example, depositing excess solute in the solvent on the surface of the inner wall of the heat exchanger. Thereafter, the temperature of the film forming unit 415 was further adjusted to 935 ° C. (ΔT1 = 5 ° C., transition time Δt1 = 10 minutes), and thereafter the same process was repeated for a total of four cycles of film formation / meltback. After all the cycles were completed, the slider 401 was moved again to separate the Si substrate 402 from the Sn solvent, and the liquid phase film formation was completed.

  As a result of investigating the film thickness and surface state of the deposited Si layer using a step gauge and a scanning electron microscope, the average thickness of the deposited Si layer was about 40 μm, and the surface was almost flat (1 to About 2 μm). Further, when the orientation of the deposited Si layer was measured by an ECP (Electron Channeling Pattern) method, it was found that the crystal orientation of each grain of the underlying polycrystalline Si substrate was inherited.

  For comparison, film formation was performed by the conventional meltback method, that is, the temperature profile of FIG. In was used as the solvent, Si2H6 as the source gas, and B2H6 as the impurity doping gas. A wafer cassette 801 on which five 125 mm square polycrystalline Si wafers (thickness 0.6 mm) 802 formed by the casting method are placed in a standby chamber (not shown) and a Sn solvent 804 is accommodated. The film part 803 was heated by a heater (electric furnace) 808 to keep the temperature of the solvent constant at 935 ° C. Next, the wafer cassette 801 that was waiting in the preliminary chamber was introduced into the reaction tube 807 by opening the gate valve 812, and held immediately above the film forming unit 803. The gate valve was left open thereafter. Source gas Si2H6 and doping gas B2H6 were flowed to source gas introduction pipe 816 together with H2 gas (gas flow ratio Si2H6: H2 = 1: 20, B2H6 / Si2H6 = 0.03) and provided at the tip of the source gas introduction pipe The film was ejected from the outlet 809 into the Sn solvent of the film forming unit 803. In this case, the ejected source gas and doping gas are decomposed in contact with the solvent, and the solute (Si) and the dopant (B) are rapidly dissolved in the solvent and supplied and decomposed and generated (reaction product gas) : H2 etc.) 805 stirs the solvent to make the solute concentration uniform. After the gas flow was completed after 20 minutes, the heater 808 was controlled to gradually cool the solvent in the reaction tube 807 at a rate of −1 ° C./min, and when the temperature of the Sn solvent 804 reached 930 ° C. The cassette 801 is lowered while being rotated at a rotational speed of 10 rpm and is put into the Sn solvent 804. When the wafer cassette 801 is completely immersed in the Sn solvent 804, the descent is stopped and the liquid phase is maintained while rotating and rotating. Film formation was performed for 30 minutes. Thereafter, the heater 808 is controlled again to raise the temperature of the solvent in the reaction tube 807 at a rate of 2 ° C./min. After 5 minutes, the heater 808 is controlled again to change the solvent in the reaction tube 807 to −1 ° C./min. The solution was gradually cooled at a rate of min and a liquid phase film was formed for 50 minutes. Thereafter, the temperature of the solvent in the reaction tube 807 is further increased at a rate of 2 ° C./min. After 10 minutes, the heater 808 is controlled again and the solvent in the reaction tube 807 is gradually cooled at a rate of −1 ° C./min. For 80 minutes. Thereafter, the wafer cassette 801 was lifted out of the Sn solvent 804, temporarily stopped immediately above the film forming unit 803, the number of rotations was increased to 120 rpm, and Sn partially remaining on the wafer cassette was shaken off to complete the liquid phase film formation.

  As a result of investigating the film thickness and surface state of the deposited Si layer using a step gauge and a scanning electron microscope, the average thickness of the deposited Si layer was about 40 μm, and the surface was almost flat (1 to About 2 μm). Further, when the orientation of the deposited Si layer was measured by an ECP (Electron Channeling Pattern) method, it was found that the crystal orientation of each grain of the underlying polycrystalline Si substrate was inherited. Thus, an Si layer similar in appearance to the above-described example was obtained. When the distribution of impurities (dopant) B contained in the Si layer is compared by secondary ion mass spectrometry, the concentration distribution of B in the Si layer formed by this example is almost constant (within 5% of variation). Met. On the other hand, the B concentration in the Si layer according to the comparative example was reduced to about 40% at the end of film formation compared to the concentration at the start of film formation. From this, it has been clarified that the method of the present invention enables more uniform doping to the deposited Si layer than before.

(Example 5)
In this example, an n + / p-type thin film polycrystalline Si solar cell was produced using the liquid phase film formation method of the present invention. First, using the apparatus shown in FIG. 1, a Si layer was formed on a 0.6 mm thick p + polycrystalline Si wafer (ρ = 0.02 Ω · cm) under the same conditions as in Example 1. For comparison, a film formed without a meltback step was also prepared.

  Next, thermal diffusion of P was performed on the surface of each deposited Si layer at a temperature of 900 ° C. using POCl 3 as a diffusion source to form an n + layer, and a junction depth of about 0.5 μm was obtained. The formed dead layer on the surface of the n + layer (the portion where the surface concentration is too high and the short wavelength sensitivity is deteriorated) is removed by etching after wet oxidation to obtain a junction depth having an appropriate surface concentration of about 0.2 μm. It was.

  Finally, a collector electrode (Ti / Pd / Ag (40 nm / 20 nm / 2 μm)) / SiN antireflection film (82 nm) is deposited on the n + layer and a back electrode (Al (1 μm)) by EB (Electron Beam) deposition. Each was formed on the back side of the substrate to obtain a solar cell.

  The thin-film polycrystalline Si solar cell thus obtained was measured for IV characteristics under AM1.5 (100 mW / cm 2) light irradiation. When the Si layer formed by the method of the present invention was used, The cell area was 4 cm2, the open circuit voltage was 0.62 V, the short-circuit photocurrent was 31 mA / cm2, the fill factor was 0.76, and an energy conversion efficiency of 14.6% was obtained. For comparison, when a Si layer formed without a meltback step was used, the cell area was 4 cm2, the open-circuit voltage was 0.58 V, the short-circuit photocurrent was 32 mA / cm2, the fill factor was 0.71, and the energy conversion efficiency was 13.2%. This indicates that the Si layer formed by the method of the present invention has excellent surface properties, and as a result, a good solar cell can be formed.

1 is a schematic cross-sectional view showing an example of a liquid phase film forming apparatus according to the present invention. The typical sectional view showing an example of the device which the substrate and solvent which are an example of the liquid phase film-forming device concerning the present invention touch at the opening. The typical sectional view showing an example of the device with which supply of the solute which is an example of the liquid phase film formation device concerning the present invention is performed with gas. 1 is a schematic cross-sectional view showing an example of an apparatus in which a substrate and a solvent are in contact with each other through an opening while supplying a solute as an example of a liquid phase film forming apparatus according to the present invention. The figure which shows the temperature profile of the liquid phase film-forming by the conventional method. The figure which shows the structure of the solute supply part of the apparatus of FIG. The figure explaining the relationship between the temperature change of the solute supply part of the apparatus of FIG. 1, and the change of the supersaturation degree of the solvent which flows into a film-forming part. Schematic sectional view showing an example of a liquid phase film forming apparatus according to a conventional method.

Explanation of symbols

102, 202, 302, 402, 802 Substrate (wafer)
101, 301, 801 Wafer cassette 201, 401 Slider 103, 303, 315, 415, 803 Deposition unit 203, 403 Opening 104, 204, 304, 404, 804 Solvent (melt)
105, 205 Solute supply unit 305, 405, 805 Reaction product gas 106, 206, 306, 406 Heater block 107, 207, 307, 407 Cooling pipe 807 Reaction tube 108, 208, 308, 408, 808 Electric furnace (heater)
109, 209, 309a, 309b, 409a, 409b Heat exchanger 809 Gas outlet 110, 210, 310, 410 Circulation pipe 111, 211, 311, 411 Rotor 112, 312, 812 Gate valve 113, 213, 313, 413 Raw material Supply mechanism 114, 214, 314, 414 Film formation mechanism 316, 416, 816 Gas introduction pipe 317, 417, 817 Exhaust pipe 118, 218, 318, 418 Cooling gas 319, 419, 819 Source gas and dopant gas 320, 420, 820 exhaust gas

Claims (23)

  A liquid phase film forming method in which the temperature of the solute supply unit and the film forming unit is controlled independently, and the solvent in which the solute is dissolved is circulated between the solute supply unit and the film forming unit to form a film on the substrate. Then, by maintaining the film forming unit at a predetermined temperature and changing the temperature of the solute supply unit in a temperature range within a predetermined range with respect to the temperature of the film forming unit, the degree of supersaturation is continuously increased over time. A continuous liquid phase film forming method, wherein the changed solvent is supplied to the film forming section.   The continuous liquid phase film forming method according to claim 1, wherein the solute supply unit and the film forming unit are connected via a heat exchanger.   3. The continuous liquid phase film forming method according to claim 1, wherein the temperature of the solute supply unit is controlled by a temperature control mechanism including a heating unit and a cooling unit.   4. The continuous liquid phase film formation according to claim 1, wherein the solvent circulation is performed by a solvent circulation rotor provided in a part of a pipe connecting the solute supply unit and the film formation unit. Method.   5. The continuous liquid phase film forming method according to claim 1, wherein a solvent made of a metal is used as the solvent.   6. The continuous liquid phase film forming method according to claim 5, wherein the metal is at least one selected from In, Sn, Bi, Ga, and Sb.   The continuous liquid phase film forming method according to claim 1, wherein the solute is Si.   The continuous liquid according to any one of claims 1 to 7, wherein a temperature range changing in the solute supply unit is in a range of 0 to 50 ° C in both the + direction and the-direction with respect to the temperature of the film forming unit. Phase deposition method.   The continuous liquid phase according to any one of claims 1 to 8, wherein the solute is supplied to the solvent by feeding a raw material gas into the solvent by a raw material gas introduction pipe held in the solute supply unit. Film forming method.   The continuous liquid phase film forming method according to claim 9, wherein the source gas is made of SiH 4.   The continuous liquid phase film-forming method according to claim 9, wherein the source gas is made of SinH2n + 2 (n is an integer of 2 or more).   The continuous liquid phase film forming method according to claim 9, wherein the source gas is made of a halogenated silane.   The source gas is fed into the solvent together with at least one selected from gases containing dopants of PH3, PF3, AsH3, B2H6, BF3, BCl3, Ga (CH3) 3, and Ga (C2H5) 3. The continuous liquid phase film forming method according to claim 9.   A raw material supply mechanism for supplying a solute to the solvent, a film forming mechanism for forming a crystal film by bringing the solvent supplied with the solute into contact with a substrate, and circulating the solvent between the raw material supply mechanism and the film forming mechanism A continuous liquid phase film forming apparatus provided with means for independently controlling the temperature of the raw material supply mechanism and the temperature of the film forming mechanism. Continuous liquid phase film formation comprising: means for controlling the temperature of the film mechanism within a temperature range within a predetermined range; and means for continuously supplying a solvent from the raw material supply mechanism to the film formation mechanism apparatus.   The continuous liquid phase film forming apparatus according to claim 14, wherein at least a part of the pipe is a heat exchanger.   16. The continuous liquid phase film formation according to claim 14 or 15, wherein the circulation of the solvent is performed by a solvent circulation rotor provided in a part of a pipe connecting the raw material supply mechanism and the film formation mechanism. apparatus.   The continuous liquid phase film forming apparatus according to claim 14, wherein a solvent made of a metal is used as the solvent.   18. The continuous liquid phase film forming apparatus according to claim 14, wherein the metal is at least one selected from In, Sn, Bi, Ga, and Sb.   The continuous liquid phase film forming apparatus according to claim 14, wherein the solute is Si.   20. The continuous liquid phase film forming apparatus according to claim 14, wherein a temperature of the raw material supply mechanism is controlled by a temperature control mechanism including a heating unit and a cooling unit.   21. The continuous liquid phase film forming apparatus according to claim 14, wherein the film forming mechanism includes a wafer cassette that can be inserted into and removed from a film forming unit held in the film forming mechanism.   The film forming mechanism has an opening in contact with the substrate in the middle of the circulation pipe, and is arranged so that the solvent and the substrate are in contact with each other at the opening of the pipe while holding and moving the substrate. 21. The continuous liquid phase film forming apparatus according to claim 14, wherein the apparatus is provided with a slider.   23. The continuous liquid according to claim 14, wherein the solute is supplied to the solvent by feeding a raw material gas into the solvent through a raw material gas introduction pipe held in the raw material supply mechanism. Phase deposition system.

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