Raw material gas supply apparatus, raw material gas supply method and storage medium

In a raw material gas supply apparatus, a control unit obtains an offset value of (m3−(m1+m2)), m1, m2 and m3 being respective measurement values of first and second mass controllers, and a mass flow meter, by supplying a carrier gas and a dilution gas in a state where the carrier gas flows through a bypass channel. Further, the control unit obtains an actual measurement value of a flow rate of the raw material by subtracting the offset value from (m3−(m1+m2)) obtained by supplying the carrier gas and dilution gas in a state where the carrier gas flows through the inside of a raw material container and calculating a difference between a target value of the flow rate of the raw material and the actual measurement value, and adjusts a set value of the first mass flow controller such that the flow rate of the raw material becomes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application Nos. 2015-194887 and 2015-241520 filed on Sep. 30 and Dec. 10, 2015, respectively, the entire contents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to a technique for supplying a sublimated raw material together with a carrier gas to a film forming unit.

BACKGROUND OF THE INVENTION

A film forming process, one of the semiconductor manufacturing processes, is performed by ALD (Atomic Layer Deposition) in which a raw material gas and a reactant gas for oxidizing, nitriding or reducing the raw material gas are alternately supplied, CVD (Chemical Vapor Deposition) in which a raw material gas is decomposed in a vapor phase or made to react with a reactant gas, or the like. As for the raw material gas used in the film forming process, a sublimated gas of the raw material is used in order to extremely reduce the amount of impurities introduced into a substrate and increase a density of crystal after film formation. For example, the raw material gas is used for a film forming apparatus for forming a high dielectric film by ALD.

In such a film forming apparatus, a raw material gas is obtained by vaporizing (sublimating) a raw material by heating a raw material container in which a solid or liquid raw material is accommodated. A carrier gas is supplied into the raw material container, and the raw material is supplied into a processing chamber by the carrier gas. The raw material gas is combination of the carrier gas and a gaseous raw material. In controlling a thickness, a quality or the like of a film formed on a semiconductor wafer (hereinafter, referred to as “wafer”), it is required to accurately control an amount of the vaporized raw material (flow rate of the raw material contained in the raw material gas).

However, the amount of the vaporized raw material in the raw material container is changed by the filling amount of the raw material. When the raw material is in a solid state, the amount of the vaporized raw material is varied by non-uniform distribution of the raw material in the raw material container or by the change in the grain size or the like. Further, when the raw material is in a solid state, the temperature of the raw material container is decreased by loss of heat caused by sublimation (referred to as “vaporization” in this specification) of the raw material. Since, however, convection does not occur in the raw material container in which the solid raw material is accommodated, the distribution of the temperature in the raw material container tends to be non-uniform. Therefore, the vaporized amount of the raw material tends to be unstable.

Recently, along with the trend toward miniaturization of a wiring pattern formed on a wafer, there is required a method capable of stabilizing a film thickness or a film quality. Although the ALD method is advantageous in that a raw material gas can be supplied within a short period of time, there is still a need for a method capable of controlling a raw material supply amount to a set value.

Japanese Patent Application Publication No. 1993-305228 discloses a technique for detecting and controlling a total mass flow of a non-evaporated gas in a system to a constant level in the case of supplying a carrier gas to a liquid raw material evaporation unit and introducing a buffer gas into the system. In that case, however, differences between the flow rate meters are not considered.

In a raw material gas supply apparatus disclosed in Japanese Patent Application Publication No. 2014-145115, since a mass flow meter is calibrated by a flow rate of a carrier gas, in a state that the flow rate of the carrier gas is set to a set value by a mass flow controller, the difference between the set value of the flow rate of the carrier gas and the flow rate measured by the mass flow meter indicates the amount of the sublimated raw material in the case where the set value of the flow rate of the carrier gas is zero. Japanese Patent Application Publication No. 2014-145115 discloses a technique for obtaining an amount of the sublimated raw material gas by multiplying the difference between the set value of the flow rate of the carrier gas and the flow rate measured by the mass flow meter by a proportional coefficient. However, the object of the present disclosure is not solved by such a technique.

SUMMARY OF THE INVENTION

In view of the above, the present disclosure provides a technique for stabilizing a supply amount of a sublimated raw material in the case of supplying a raw material gas containing a gas obtained by sublimating a solid or liquid raw material to a film forming unit.

In accordance with an aspect, there is provided a raw material gas supply apparatus for supplying a raw material gas obtained by vaporizing a solid or liquid raw material in a raw material container along with a carrier gas to a film forming unit for performing a film forming process on a substrate through a raw material gas supply line, the apparatus including:

a carrier gas supply line for supplying a carrier gas to the raw material container;

a bypass channel branched from the carrier gas supply line and connected to the raw material gas supply line while bypassing the raw material container;

a dilution gas supply line connected to the raw material gas supply line at a downstream side of a connection portion to which the bypass channel is connected, the dilution gas supply line serving to allow a dilution gas to join with the raw material gas;

a first mass flow controller and a second mass flow controller connected to the carrier gas supply line and the dilution gas supply line, respectively;

a mass flow meter provided in the raw material gas supply line at a downstream side of a joining portion to which the dilution gas supply line is connected;

a switching mechanism configured to selectively allow a carrier gas to flow through an inside of the raw material container or through the bypass channel; and

a control unit configured to execute: a first step of obtaining an offset value that is a value of (m3−(m1+m2)), m1, m2and m3being respective measurement values of the first mass controller, the second mass flow controller and the mass flow meter, by supplying the carrier gas and the dilution gas in a state where the carrier gas flows through the bypass channel; a second step of obtaining an actual measurement value of a flow rate of the raw material by subtracting the offset value from a value of (m3−(m1+m2)) obtained by supplying the carrier gas and dilution gas in a state where the carrier gas flows through the inside of the raw material container and calculating a difference between a target value of the flow rate of the raw material and the actual measurement value; and a third step of adjusting a set value of the first mass flow controller such that the flow rate of the raw material becomes the target value based on relationship between the difference, increase/decrease in the flow rate of the raw material, and increase/decrease in the flow rate of the carrier gas.

In accordance with another aspect, there is provided a raw material gas supply method for supplying a raw material gas obtained by vaporizing a solid or liquid raw material in a raw material container along with a carrier gas to a film forming unit for forming a film on a substrate by using a raw material gas supply apparatus including: a carrier gas supply line for supplying a carrier gas to the raw material container; a bypass channel branched from the carrier gas supply line and connected to the raw material gas supply line while bypassing the raw material container; a dilution gas supply line connected to the raw material gas supply line at a downstream side of a connection portion to which the bypass channel is connected, the dilution gas supply line serving to allow a dilution gas to join with the raw material gas; a first mass flow controller and a second mass flow controller connected to the carrier gas supply line and the dilution gas supply line, respectively; a mass flow meter provided in the raw material gas supply line at a downstream side of a joining portion to which the dilution gas supply line is connected; and a switching mechanism configured to selectively allow a carrier gas to flow through an inside of the raw material container or through the bypass channel, the method including:

obtaining an offset value that is a value of (m3−(m1+m2)), m1, m2and m3being respective measurement values of the first mass controller, the second mass flow controller and the mass flow meter, by supplying the carrier gas and the dilution gas in a state where the carrier gas flows through the bypass channel;

obtaining an actual measurement value of a flow rate of the raw material by subtracting the offset value from a value of (m3−(m1+m2)) obtained by supplying the carrier gas and dilution gas in a state where the carrier gas flows through the inside of the raw material container and calculating a difference between a target value of the flow rate of the raw material and the actual measurement value; and

adjusting a set value of the first mass flow controller such that the flow rate of the raw material becomes the target value based on relationship between the difference, increase/decrease in the flow rate of the raw material, and increase/decrease in the flow rate of the carrier gas.

In accordance with still another aspect, there is provided a storage medium storing a computer program used for a raw material gas supply apparatus for vaporizing a solid or liquid raw material in a raw material container and supplying the vaporized raw material, as a raw material gas, along with a carrier gas to a substrate through a raw material gas supply line, wherein the computer program has a group of steps for performing the raw material gas supply method described above.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an exemplary configuration in which a raw material gas supply apparatus of the present disclosure is applied to a film forming apparatus will be described. As shown inFIG. 1, a film forming apparatus includes: a film forming unit40for forming a film on a wafer100as a substrate by using an ALD method; and a raw material gas supply unit10including a raw material gas supply device for supplying a raw material gas to the film forming unit40. In this specification, it is assumed that a gas including a carrier gas and a (sublimated) raw material flowing along with the carrier gas is referred to as a raw material gas.

A raw material gas supply unit10includes a raw material container14accommodating WCl6as a raw material. The raw material container14contains WCl6in a solid state at a room temperature. The raw material container14is covered by a jacket-shaped heating unit13having a resistance heating element. The raw material container14is configured to control a temperature in the raw material container14by increasing/decreasing the amount of power supplied from a power supply (not shown) based on a temperature of a gas phase part in the raw material container14which is detected by a temperature detector (not shown). A temperature of the heating unit13is set to a level, e.g., 160° C., at which the solid raw material is sublimated and WCl6is not decomposed.

Inserted into the gas phase part above the solid raw material in the raw material container14are a downstream end portion of a carrier gas supply line12and an upstream end portion of a raw material gas supply line32. A carrier gas supply source11for supplying a carrier gas, e.g., N2gas, is provided at the upstream end of the carrier gas supply line12. A first mass flow controller (MFC)1, a valve V3, and a valve V2are installed in the carrier gas supply line12in that order from the upstream side.

A valve V4, a valve V5, a mass flow meter (MFM)3that is a flow rate measuring unit, and a valve V1are installed in the raw material gas supply line32in that order from the upstream side. Reference numeral8in the drawing denotes a pressure gauge for measuring a pressure of a gas supplied from the raw material gas supply line32. A downstream end portion of the raw material gas supply line32is referred to as a gas supply line45because a reactant gas or a replacement gas to be described later flows therein. A downstream end of the dilution gas supply line22for supplying a dilution gas joins with the upstream side of the MFM3in the raw material gas supply line32. A dilution gas supply source21for supplying a dilution gas, e.g., N2gas, is provided at an upstream end of the dilution gas supply line22. A second mass flow controller (MFC)2and a valve V6are installed in the dilution gas supply line22in that order from the upstream side. A portion between the valves V2and V3in the carrier gas supply line12and a portion between the valves V4and V5in the raw material gas supply line32are connected by a bypass channel7having a valve V7. The valves V2, V4and V7correspond to a switching mechanism.

Next, the film forming unit40will be described. The film forming unit40includes a mounting table42for horizontally supporting a wafer W in, e.g., a vacuum chamber41, and a gas inlet43for introducing a raw material gas or the like into the vacuum chamber41. The mounting table42has a heater (not shown). A gas supply line45is connected to the gas inlet43. A gas from the raw material gas supply unit10is supplied into the vacuum chamber41through the gas inlet. A vacuum exhaust unit44is connected to the vacuum chamber41via a gas exhaust line46. Pressure control valves47and48constituting a pressure control unit94for controlling a pressure in the film forming unit40are provided in the gas exhaust line46. The gas supply line45joins with a reactant gas supply line50for supplying a reactant gas that reacts with a raw material gas and a replacement gas supply line56for supplying a replacement gas. The other end of the reactant gas supply line50is branched into an H2gas supply line54connected to a reactant gas supply source52for supplying a reactant gas, e.g., H2gas, and an inert gas supply line51connected to an inert gas supply source53for supplying an inert gas, e.g., N2gas. The other end of the replacement gas supply line56is connected to a replacement gas supply source55for supplying a replacement gas, e.g., N2gas. Notations V50, V51, V54and V56in the drawing denote valves installed in the reactant gas supply line50, the inert gas supply line51, the H2gas supply line54, and the replacement gas supply line56, respectively.

As will be described alter, when a W (tungsten) film is formed by the film forming unit40, a raw material gas containing WCl6and H2gas as a reactant gas are alternately supplied and a replacement gas for replacing an atmosphere in the vacuum chamber41is supplied between the supply of the raw material gas and the reactant gas. The raw material gas is intermittently supplied to the film forming unit40while alternately repeating a supply period and a pause period. The supply of the raw material gas is controlled by controlling on/off of the valve V1. The valve V1is configured to be opened/closed by a control unit9to be described later. “ON” indicates an open state of the valve V1. “OFF” indicates a closed state of the valve V1.

The raw material gas supply unit10includes the control unit9. As shown inFIG. 2, the control unit9includes a CPU91, a program storage unit92, and a memory93for storing a processing recipe of a film forming process performed on the wafer100. Reference numeral90in the drawing denotes a bus. The control unit9is connected to a pressure control unit94connected to the valve groups V1to V7, the MFC1, the MFC2, the MFM3, and the film forming unit40. The control unit9is also connected to a host computer99. A film forming recipe of a lot of the wafer100to be loaded into the film forming apparatus is transmitted from the host computer99and stored in the memory93.

The processing recipe is information on a processing condition and a sequence of film formation of the wafer100which is set for each lot. The processing condition includes a process pressure, timing of supplying a gas to the film forming unit40and timing of stopping the supply in the ALD method, a raw material gas flow rate, and the like. Hereinafter, the ALD method will be briefly described. First, WCl6gas as a raw material gas is supplied for, e.g., one second and then the valve V1is closed to allow WCl6gas to be adsorbed onto the surface of the wafer100. Next, a replacement gas (N2gas) is supplied into the vacuum chamber to replace the atmosphere in the vacuum chamber41. Thereafter, a reactant gas (H2gas) is supplied together with a dilution gas (N2gas) into the vacuum chamber41. As a consequence, a W (tungsten) film of an atomic layer is formed on the surface of the wafer100by hydrolysis and dechlorination reaction. Then, the replacement gas is supplied into the vacuum chamber41to replace an atmosphere in the vacuum chamber41. Accordingly, a cycle of sequentially supplying the raw material gas containing WCl6, the replacement gas, the reactant gas and the replacement gas into the vacuum chamber41is repeated multiple times. As a result, a W film is formed.

In the ALD method, the cycle of sequentially supplying the raw material gas, the replacement gas, the reactant gas, and the replacement gas is repeated multiple times. Therefore, the timing of an ON signal and the timing of an OFF signal are determined by the recipe that specifies such a cycle. For example, the supply and the supply stop of the raw material gas are performed by the valve V1. Accordingly, a period from the ON signal to the OFF signal of the valve V1corresponds to a raw material gas supply period and a period from the OFF signal to the ON signal of the valve V1corresponds to a period in which the raw material gas supply is stopped. When the ALD method is used for obtaining measured flow rates of the raw material in the MFCs1and2and the MFM3, the measured flow rates may be unstable due to the intermittent supply of the raw material gas for a short supply period. To that end, in this example, a value obtained by dividing an integration value of the measurement values of the MFCs1and2and the MFM3in one cycle of ON and OFF of the valve V1by the time period of one cycle is used (evaluated) as a measurement output value (measured value), as will be described in detail later.

The memory93stores therein information, e.g., a relational equation, indicating a relationship between increase/decrease in a flow rate of the carrier gas at a heating temperature of the raw material container14, e.g., 160° C., and increase/decrease in a flow rate of a vaporized raw material supplied to the raw material gas supply line32together with the carrier gas. This relational equation is approximated as a linear expression as shown in the following Eq. (1).
Increase/decrease in flow rate of vaporized raw material=k(constant)×increase/decrease in flow rate of carrier gas   Eq. (1)

The program stored in the program storage unit92has a group of steps for executing the operation of the raw material gas supply unit10. The term “program” includes software such as a process recipe or the like. The group of steps includes a step of integrating measurement outputs of the flow rates of the MFCs1and2and the MFM3in the supply period and performing an operation while using the integration value as the flow rate in the supply period. The integration process may be performed by a hard configuration using a time constant circuit. The program is stored in a storage medium, e.g., a hard disk, a compact disk, a magnet optical disk, a memory card, or the like and installed in a computer.

The operation of the film forming apparatus according to the embodiment will be described with reference to the flow chart shown inFIG. 3. In this case, one lot includes two or more wafers100, e.g., 25 wafers100. First, the power of the film forming apparatus is ON and, then, a carrier accommodating a wafer100of a leading lot (the first lot processed after the power of the film forming apparatus is ON) is loaded onto a carrier stage. In this case, the steps1,2and4are executed in that order, and an offset value is obtained under the condition of the processing recipe of the leading lot.

Hereinafter, the offset value will be described.FIG. 4shows a difference between a sum (m1+m2) of the measurement value m1of the MFC1and the measurement value m2of the MFC2and a measurement value m3of the MFM3in the case of supplying a carrier gas and a dilution gas respectively from the carrier gas supply source11and the dilution gas supply source21by using the raw material gas supply unit10to the film forming unit40through the MFM3. The difference (m3−(m1+m2)) obtained during a period from time t0to t100indicates a value obtained in the case of supplying the carrier gas to the raw material gas supply line32through the bypass channel7without passing through the raw material container14. During the period from the time t0to the time t100, the gas flowing through the MFM3is combination of the carrier gas supplied from the carrier gas supply line12and the dilution gas supplied from the dilution gas supply line22. However, the difference between the measurement value m3of the MFM3and the sum (m1+m2) of the measurement value m1of the MFC1and the measurement value m2of the MFC2is not zero as shown inFIG. 4. Such a difference caused by individual differences among the MFM3, the MFC1, and the MFC2corresponds to an offset value.

Next, the process of obtaining the offset value will be described. The offset value is obtained by setting the set values of the MFCs1and2to the respective flow rates of the carrier gas and the dilution gas which are determined based on the target value of the raw material gas flow rate stored in the processing recipe. The timing of opening/closing the valve V1is set to be the same as that in the cycle of supplying the raw material gas to the film forming unit40and stopping the supply in the processing recipe. A pressure in the process of obtaining the offset value is set to a level determined by the processing recipe.

The set value of the MFC1is determined based on the flow rate of the carrier gas which enables the raw material to be supplied at a target flow rate in a state the raw material container14is filled with the solid raw material at a maximum level. The relationship between the increase/decrease in the flow rate of the raw material and the increase/decrease in the flow rate of the carrier gas is stored in, e.g., the memory93. The pressure in the film forming unit40is set to a set pressure in the processing recipe by the pressure control unit94. The control of the temperature of the film forming unit40requires time and the vaporized raw material may be adhered to a low-temperature portion and solidified. Therefore, the temperature of the film forming unit40is set in advance to a film forming temperature, e.g., 170° C.

When the flow rate of the raw material is small and the total flow rate of the raw material gas diluted by the dilution gas is determined as the total flow rate of the carrier gas and the dilution gas, a set value of the flow rate of the dilution gas is obtained by subtracting the set value of the flow rate of the carrier gas from the total flow rate. When the flow rate of the raw material is included in the total flow rate, the target value of the supply amount of the raw material is considered as, e.g., a weight per unit time. Therefore, the total flow rate and the flow rate of the carrier gas for supplying the raw material are obtained based on the target value of the supply amount of the raw material and the processing pressure. Accordingly, the set value of the flow rate of the dilution gas is obtained by subtracting the sum of the supply amount of the raw material and the flow rate of the carrier gas from the total flow rate.

Next, the valves V3, V5, V6and V7are opened and the valve V1is opened/closed at the same timing as opening/closing timing of the valve V1in the processing recipe after the time t0. In this case, an operation of opening the valve V1for one second and closing the valve V1for one second is repeated 100 times from time t0to t100. The vacuum chamber41has already been vacuum-evacuated. Accordingly, the carrier gas flows at a flow rate corresponding to the set value of the MFC1from the carrier gas supply source11to the raw material gas supply line32through the carrier gas supply line12and the bypass channel7(bypass flow). In the raw material gas supply line32, the carrier gas is mixed with the dilution gas supplied from the dilution gas supply line22, and the raw material gas diluted with the dilution gas flows through the MFM3. The gaseous mixture of the carrier gas and the dilution gas is intermittently supplied to the film forming unit40.

The measurement values of the flow rates in the MFCs1and2and the MFM3during the period from the time t0to the time t100are obtained. InFIG. 5, (a) shows a state of the valve V1for supplying the raw material gas and blocking the supply of the raw material gas. The ON period corresponds to the raw material gas supply period. The OFF period corresponds to a period in which the raw material gas supply is stopped. InFIG. 5, (b) shows variation of a measurement output (measured value) of the flow rate of the raw material gas which is measured by the MFM3during the period from the time t0to the time t100. Since the opening period of the valve V1is short, the measurement output of the flow rate of the raw material gas which is measured by the MFM3abruptly increases after the ON instruction of the valve V1and abruptly decreases after the OFF instruction of the valve V1. A ratio of the supply period and the supply-stop period in (a) ofFIG. 5is merely an example for convenience of illustration.

Therefore, the measurement value of the flow rate is obtained by dividing, by a time period T of one cycle of supplying the raw material gas and stopping the supply, an integration value obtained by integrating the measured outputs of the flow rates of the MFM3and the MFCs1and2during one cycle by the control unit9. In this case, based on the ON instruction of the valve V1shown in (a) ofFIG. 5, the integration operation of the gas flow rate is started at the time t0and completed at the time t1at which the next ON instruction of the valve V1is outputted. The period from the time t0to the time t1is set to one cycle.

Further, values (integration value/(t1−t0)) obtained by dividing the integration value of the flow rates in the MFCs1and2and the MFM3from the time t0to the time t1by the time period T of one cycle, i.e., the period (t1−t0) from the time t0to the time t1, are respectively set to the measurement values m1, m2and m3of the MFC1, the MFC2and the MFM3from the time t0to the time t1.

The values of m1to m3in the respective cycles from time t0to time t1, from time t1to time t2. . . are obtained and the value of (m3−(m1+m2)) in each cycle is obtained as shown inFIG. 6. The average of the values of (m3−(m1+m2)) during 100 cycles from the time t0is set to the offset value.

Referring back toFIG. 3, when the offset value obtained in the step S4is within a tolerable range, “YES” is selected in a step S5and the processing proceeds to a step S6. A first wafer100is loaded into the film forming unit40and processed, so that an actual measurement value m of the flow rate of the raw material is obtained. The offset value indicates the difference between the MFM3, and the MFC1and the MFC2. When the difference is too large, it is considered that there is a reason other than the measurement differences between the MFM3, and the MFC1and the MFC2. Therefore, the tolerance range of the difference that may be considered as individual variations of the MFM3, the MFC1and the MFC2is determined in advance.

In the step S6, the raw material container14is heated to, e.g., 160° C., by the heating unit13of the raw material container14. Accordingly, the solid raw material is sublimated and the concentration of the raw material in the raw material container14is increased to a level close to a saturated concentration. Then, the wafer100is loaded into the film forming unit40and the actual measurement value m of the flow rate of the raw material which will be described later is obtained. In other words, the flow rate of the carrier gas and the flow rate of the dilution gas are set to levels stored in the processing recipe and the pressure of the film forming unit40is set to a level determined by the processing recipe. At time ta, the valve V7is closed and the valves V2and V4are opened. Accordingly, the carrier gas is supplied at a flow rate set by the MFC1from the carrier gas supply line12into the raw material container14and the raw material vaporized in the raw material container14flows together with the carrier gas to the raw material gas supply line32. Also, the dilution gas flowing from the dilution gas supply line22to the raw material gas supply line32joins therewith. After the time ta, the valve V1is opened/closed at the same timing as the opening/closing timing of the valve V1in the processing recipe. In this example, the operation of opening the valve V1for one second and closing the valve V1for one second is repeated. Thus, the raw material gas mixed with the dilution gas is sent to the film forming unit (autoflow). Accordingly, the carrier gas is supplied to the raw material container14and the raw material gas is supplied to the film forming unit40while setting the flow rate of the carrier gas, the flow rate of the dilution gas, the pressure of the film forming unit40and the interval of opening/closing the valve V1to those in the process of obtaining the offset value.

As a consequence, as shown in (c) ofFIG. 5, the measurement value of the raw material gas abruptly increases after the ON instruction of the valve V1up to a level higher than the measurement value from the time t0to the time t100and immediately decreases after the OFF instruction of the valve V1.

In the processing of the first wafer100, as in the period from the time t0to the time t100, the integration values of the flow rates in the MFCs1and2and the MFM3from the time tato the time ta+1are divided by the time period T of one cycle, i.e., the period (ta+1−ta) from the time tato the time ta+1. The values thus obtained, i.e., (integration value/(ta+1−ta)), are respectively set to the measurement values m1, m2and m3of the MFCs1and2and the MFM3from the time tato the time ta+1. The value of (m3−(m1+m2)) in each cycle is obtained by subtracting the sum of the measurement value m1of the MFC1and the measurement value m2of the MFC2from the measurement value m3of the MFM3in each cycle of the gas supply. The value of (m3−(m1+m2)) in each cycle after the time tacorresponds to the flow rate of the raw material obtained by subtracting the sum of the flow rate of the carrier gas and the flow rate of the dilution gas from the total flow rate of the raw material gas diluted by the dilution gas and supplied to the film forming unit40, as shown inFIG. 4.

However, as described above, there is a difference between the measurement value of the MFM3and the sum of the measurement value m1of the MFC1and the measurement value m2of the MFC2, which is caused by the difference in the measurement outputs of the MFM3and the MFCs1and2. The value corresponding to the difference is the offset value. Therefore, an actual measurement value m of the flow rate of the raw material supplied to the film forming unit40is obtained by obtaining the average of the values (m3−(m1+m2)) in the respective cycles of the raw material gas supply after the time tashown inFIGS. 4 and 5and then subtracting the offset value during the period from the time t0to the time t100from the average. The actual measurement value m is converted to a value of the raw material (mg/min) by the following Eq. (2).
Raw material(mg/min)=Flow rate(sccm)of Raw material×0.2(Conversion Factor)/22400×(Molecular weight (WCl6:396.6)of Raw material 1)×1000   Eq. (2)

Then, in a step S7, N is set to 2 and the processing proceeds to a step S8. When the actual measurement value m of the flow rate of the raw material is within the set range, “YES” is selected in the step S8and the processing proceeds to a step S9. In the step S9, the same processing performed on the first wafer100is performed on a second (N=2) wafer100, and the actual measurement value m of the flow rate of the raw material is obtained.

On the other hand, when the actual measurement value m of the flow rate of the raw material in an (N-1)thwafer, i.e., the first wafer100in this case, is not within the range (set range), “NO” is selected and the processing proceeds to a step S21. Next, when the actual measurement value m of the flow rate of the raw material is not a value determined as an error (abnormal value), the processing proceeds to a step S22.

In the step S22, the flow rate of the raw material is controlled by controlling the flow rate of the carrier gas. As described above, the increase/decrease a1in the flow rate of the carrier gas and the increase/decrease Δm in the flow rate of the raw material flowing together with the carrier gas are approximated as a linear expression y=k(x) as shown inFIG. 7on the assumption that y indicates the increase/decrease in the flow rate of the raw material and x indicates the increase/decrease in the flow rate of the carrier gas. Accordingly, the measured value of the flow rate of the raw material is in proportion to the measured value m1of the MFC1. Since the difference between the actual measurement value m of the flow rate of the raw material and the target value of the flow rate of the raw material may be set to the increase/decrease Δm in the flow rate of the raw material, the equation Δm=k×a1is satisfied and a1can be calculated. a1thus calculated is added to the current measurement value of the MFC1. It is possible to set the measurement value of the MFC1becomes to (m1+a1) by adding a1to the current set value of the MFC1since the MFC1is controlled such that the set value of the flow rate becomes the measurement value. By adding a1to the measurement value of the MFC1, the total flow rate of the raw material gas diluted by the dilution gas which is supplied to the film forming unit40is increased and, thus, the pressure is changed. Therefore, a1is subtracted from the current set value of the MFC2so that the value obtained by subtracting a1from the current measurement value m2of the MFC2, i.e., (m2−a1), becomes the measurement value. Then, the process proceeds to a step S9and an actual measurement value m of the flow rate of the raw material by processing an Nthwafer100is obtained.

Thereafter, the process proceeds to a step S10. Since the second wafer100is not the last wafer100, “NO” is selected. In a step S11, N is set to 3 and the process returns to the step S8. In the step S8, it is determined whether or not the actual measurement value m of the flow rate of the raw material in the film forming process of an (N-1)thwafer100, i.e., the second wafer100in this case, is within the set range. When the actual measurement value m of the flow rate of the raw material is within the set range, the process proceeds to the step S9and an actual measurement value m of the flow rate of the raw material for processing the third wafer100is obtained by using the set value of the flow rate of the carrier gas in the processing of the second wafer100. When the actual measurement value m of the flow rate of the raw material in the second wafer100is not within the set range, the flow rate of the carrier gas is controlled in the steps S21and S22and the third wafer100is processed. By repeating the steps S8to S11, all wafers of the lot are sequentially processed.

FIG. 8shows an example of the actual measurement value m of the flow rate of the raw material for each wafer100as described above. For example, when the actual measurement value m of the flow rate of the raw material in the film forming process for the fourth wafer100is not within the set range in the step S9, the steps S10and S11are executed. After N is updated to 5, the process proceeds to the step S8. Since the actual measurement value m of the flow rate of the raw material in the film forming process of the fourth wafer100is not within the set range, the process proceeds to the step S21. Next, when the actual measurement value m of the flow rate of the raw material is not a value determined as an error (abnormal value) as shown inFIG. 8, the process proceeds to the step S22to control the flow rate of the raw material by controlling the flow rate of the carrier gas.

The wafers100are processed in the above-described manner. In the case of the final wafer100, i.e., the 25thwafer in this example, “YES” is selected in the step S10and the process is completed.

Next, a subsequent lot will be described. When the subsequent lot is loaded onto the carrier stage, the step S1and S2are executed. Since the current lot is not the leading lot, “NO” is selected in the step S2and the process proceeds to a step S3. In the step S3, it is determined whether or not the processing recipe for the wafer100of the current lot is different from the processing recipe for the wafer of the prior lot (previous lot). Specifically, it is determined whether the flow rate of the raw material (target value of the flow rate of the raw material) in the processing recipe, the set pressure of the film forming unit40, and the cycle of supplying the raw material gas and stopping the supply in the film forming process are the same as those in the previous processing recipe. When any one of them is different, “YES” is selected and the process proceeds to the step S4. In the step S4, the target value of the flow rate of the raw material, the set pressure of the film forming unit40, and the cycle of supplying the raw material gas and stopping the supply in the film forming process are set based on the processing recipe for the wafer100of the current lot (subsequent lot). The offset value is obtained as in the case of the previous lot and the process proceeds to the step S5. When the offset value is within the tolerable range, the process proceeds to the step S6and the step S6and the subsequent steps are executed.

When the processing recipe in the subsequent lot, e.g., the flow rate of the raw material (target value of the flow rate of the raw material) in the processing recipe, the set pressure of the film forming unit40, and the cycle of supplying the raw material gas and stopping the supply in the film forming process, is the same as the processing recipe in the prior lot (previous lot), “NO” is selected in the step S3and the process proceeds to the step S6. The step S6and subsequent steps are executed by using the offset value used in the previous lot.

When the offset value obtained based on the processing recipe of the lot is not within the tolerable range, “NO” is selected in the step S5and the processing proceeds to a step S30. After an alarm is activated in the step S30, the processing is completed. In this case, any error may be caused due to a factor other than the individual variations of the MFM3, the MFC1and the MFC2and, thus, a maintenance is performed.

When the actual measurement value m of the flow rate of the raw material in the Nthwafer100is not within the set range and is a value determined as an error (abnormal value) in the step S8, the process proceeds from the step S8to the step S21and “YES” is selected in the step S21. Therefore, the process proceeds to the step S30and the alarm is activated. After the process is completed, the maintenance of the raw material gas supply unit10is performed.

In the above embodiment, the flow rate of the carrier gas is controlled based on the difference between the target value and the actual measurement value of the flow rate of the raw material in the case of supplying the carrier gas to the raw material container14, discharging the vaporized raw material together with the carrier gas from the raw material container14, diluting the vaporized raw material with the dilution gas, and supplying the vaporized raw material diluted with the dilution gas to the film forming unit40. The actual measurement value of the flow rate of the raw material is obtained by subtracting the offset value corresponding to the individual variation of the respective measurement devices from the difference between the sum of the measurement values of the flow rates of the carrier gas and the dilution gas and the sum of the measurement values of the flow rates of the vaporized raw material, the carrier gas and the dilution gas. Therefore, the individual differences among the respective measurement devices are cancelled out and the accurate actual measurement value of the flow rate of the raw material can be obtained. Since the supply amount of the carrier gas is controlled based on the actual measurement value, the supply amount of the raw material for each wafer100becomes stable.

When the ALD method is performed, the integration value of the measurement output in one cycle of supplying the raw material gas and stopping the supply in each measurement device is considered as the measurement value of the flow rate. Therefore, the instability of the measurement caused by increase/decrease in the gas flow rate during a short period of time can be prevented. Accordingly, the measurement value of the gas flow rate can be stably obtained. As a result, the supply amount of the raw material gas for each wafer100becomes stable.

In measuring the actual measurement value of the flow rate of the raw material in the steps S6to S10, the actual measurement value m of the flow rate of the raw material may be measured before the processing of the wafer100of a lot. For example, the actual measurement value m of the flow rate of the raw material may be measured by performing dummy processing performed by supplying the raw material gas without loading the wafer100into the vacuum chamber41under the same condition as that of the processing recipe in the corresponding lot. Accordingly, the accuracy of the flow rate of the raw material gas in the processing of the first wafer100can be increased.

For example, a pre-coating process of controlling a condition of the vacuum chamber41by supplying a film forming gas to the vacuum chamber41and depositing a film on an inner surface of the vacuum chamber41is performed before the processing of a lot in the film forming apparatus or after the cleaning of the vacuum chamber41. The actual measurement value m of the flow rate of the raw material may be measured in this pre-coating process.

The measurement values m1to m3of the flow rates may be calculated by dividing, by a time period nT of n cycles, an integration value obtained by integrating measurement outputs of the flow rates of the MFM3and the MFCs1and2during n (n being 2 or more) cycles of supplying the raw material gas and stopping the supply by the control unit9.

In order to satisfy the condition of the pre-coating process, it is preferable to ensure a high accuracy of the flow rate of the raw material gas supplied to the vacuum chamber41. The accuracy of the flow rate of the raw material gas can be increased by performing the dummy processing before the pre-coating process and measuring the actual measurement value m of the flow rate of the raw material. For example, the actual measurement value m of the flow rate of the raw material is obtained by the dummy processing as in the step S6shown inFIG. 3. Then, it is determined whether or not the actual measurement value m of the flow rate of the raw material is within the set range (step S8). When the actual measurement value m of the flow rate of the raw material is not within the set range, the pre-coating process may be performed after the flow rate of the carrier gas is adjusted.

The actual measurement value m of the flow rate of the raw material may be obtained by, e.g., the integration value in one cycle of supplying the raw material and stopping the supply, and the supply amount of the raw material may be controlled in real time during the film forming process of one wafer100. For example, the variation is obtained by performing a PID operation by using the difference between the target value of the flow rate of the raw material and the actual measurement value m of the flow rate of the raw material which is obtained in the cycle T1of supplying the raw material and stopping the supply at a certain time. The supply amount of the raw material in a next cycle, of the cycle T, of supplying the raw material and stopping the supply may be controlled based on the variation.

The present disclosure may be used for a film forming apparatus by using a CVD method. In the CVD method, a film is formed on the wafer100by continuously supplying a raw material gas to the film forming unit40and also by continuously supplying a reactant gas. In the CVD method, the measurement outputs of the flow rates of the MFM3and the MFCs1and2in a state where the flow rate of the raw material gas is stable may be respectively set to the measurement values m1to m3of the MFM3and the MFCs1and2.

Further, in the CVD method, the actual measurement value m of the flow rate of the raw material is measured at an interval of, e.g., 0.1 sec, in the raw material supply period in processing of one wafer100. When the actual measurement value m of the flow rate of the raw material at a certain time is not within the set range, the actual measurement value m of the flow rate of the raw material may be immediately controlled to be within the set range.

Since the flow rate of the raw material is controlled in real time, it is not required to obtain the actual measurement value m of the flow rate of the raw material by the processing of the first wafer100and the dummy processing.

The raw material accommodated in the raw material container14is not limited to a solid raw material and may be a liquid raw material. When the flow rate of the carrier gas is controlled in the step S22, the flow rates of the carrier gas which respectively correspond to the actual measurement value and the target value of the flow rate of the raw material are obtained using a function, e.g., a linear expression, in which the flow rate of the carrier gas is made to correspond to the flow rate of the raw material and, then, the flow rate of the carrier gas may be controlled based on the difference between the flow rates of the carrier gas.

Further, a tank for temporally storing the raw material gas at the upstream side of the valve V1may be provided at the downstream side of the MFM3. In this case, the raw material gas stored in the tank can be supplied at once to the film forming unit40, so that the flow rate of the raw material supplied to the film forming unit per unit time can be increased. Accordingly, the opening period of the valve V1can be shortened, which makes it possible to shorten the processing time of the wafer100.

When the wafer100is processed by the ALD method, a plurality of films having different film qualities is consecutively formed. Thus, a plurality of ALDs different from each other in at least one of the flow rate of the raw material and the supply period of the raw material gas (supply period of the raw material gas in one cycle) may be performed. For example, the film forming process performed on the wafer100includes first ALD and second ALD. The first ALD and the second ALD are performed under different conditions of the flow rate of the raw material and the supply period of the raw material gas. For example, in the case of performing a film forming process by executing a cycle of supplying the raw material and stopping the supply 100 times, there may be used a processing recipe in which the supply period of the raw material gas and the flow rate of the raw material in 50 cycles of the first ALD are different from the supply period of the raw material gas and the flow rate of the raw material in 50 cycles of the second ALD. In that case, the offset value in the first ALD and the offset value in the second ALD are obtained in the process of obtaining the offset value of the step S4shown inFIG. 3.

In the step S6shown inFIG. 3, the actual measurement value m of the flow rate of the raw material supplied from the raw material container14is obtained by using the offset value of the first ALD in the film forming process using the first ALD and by using the offset value of the second ALD in the film forming process using the second ALD.

Further, the steps S8, S21and S22shown inFIG. 3may be applied to the respective actual measurement values m.

When the offset value is obtained in the step S4shown inFIG. 3, a recipe including a calculation parameter in which a process parameter that greatly affects the offset value is selected from the processing recipe may be used.

For example, as shown inFIG. 9, the memory93of the control unit9stores a calculation recipe93aand a calculation recipe format93bas a pattern for creating the calculation recipe93a. The program storage unit92stores therein a processing program92afor performing the operation of the raw material gas supply unit10which is shown in the flowchart ofFIG. 3and a recipe creating program92bfor creating the calculation recipe93a.

The processing recipe will be described before the description of the calculation recipe format93b. The processing recipe specifies the sequence of the process performed on the wafer100of each lot.FIG. 10schematically shows an example of the actual processing recipe. The processing recipe shown inFIG. 10includes “step number” indicating an execution sequence, “execution time” of each step, “on/off of the valve V1”, “repeating step” and “the number of repetition” indicating a step number to be executed after the completion of the corresponding step, “flow mode” indicating switching between bypass flow and autoflow by the manipulation of the valves V2, V4and V7, “carrier N2” indicating a carrier gas flow rate (sccm), “offset N2” indicating a dilution gas flow rate (sccm), and “pressure (Torr)” of the film forming unit40. “Bypass flow” indicates a method of supplying the carrier gas to the raw material gas supply line32through the bypass channel7while bypassing the raw material container14and supplying a gaseous mixture of the carrier gas and the dilution gas to the film forming unit40. “Autoflow” indicate a method of supplying the carrier gas to the raw material container14, supplying the carrier gas containing the vaporized raw material to the raw material gas supply line32, and supplying the raw material gas to the film forming unit40. The processing recipe shown inFIG. 10includes a part for supply of the raw material gas of a film forming recipe for the wafer100, and a part for supply and supply-stop of the replacement gas and the reactant gas is omitted.

The following is description on the operation based on the processing recipe shown inFIG. 10. The wafer100is loaded into the vacuum chamber41and waits for50seconds. In the step2, the pressure of the film forming unit40is controlled to 80 Torr. Next, the flow rate of the carrier gas is set to 300 sccm and the flow rate of the dilution gas is set to 1100 sccm. The operation of opening the valve V1for 0.4 sec and closing the valve V1for 0.3 sec is repeated 40 times. Then, the pressure of the film forming unit40is controlled to 40 Torr. The flow rate of the carrier gas is set to 700 sccm and the flow rate of the dilution gas is set to 600 sccm. The operation of opening the valve V1for 0.4 sec and closing the valve V1for 0.3 sec is repeated30times. Thereafter, the supply of the raw material to the film forming unit40is stopped and the vacuum chamber41is evacuated to a predetermined vacuum level. In other words, in the processing recipe, the first ALD shown in the steps3and4and the second ALD shown in the steps6and7are performed on the wafer100.

Next, the calculation recipe format93bwill be described. As in the case of the processing recipe, the calculation recipe format93bincludes “step number”, “execution time”, “on/off of the valve V1”, “repeating step”, “the number of repetition”, “flow mode”, “carrier N2” indicating a flow rate (sccm) of the carrier gas, “offset N2” indicating a flow rate (sccm) of the dilution gas, and “pressure (Torr)” of the film forming unit40, as shown inFIG. 11. In the calculation recipe format93b, parameters that affect the acquisition of the offset value are blank and parameters that do not affect the acquisition of the offset value are common as those of the processing recipe. For example, in the calculation recipe format93b, “execution time” in the steps3and4and the steps6and7, “carrier N2” and “offset N2” in the steps3to7, “pressure” in the steps2to8are blank. The values corresponding thereto can be recorded for each processing recipe. In addition, “flow mode” in the steps1to9is set to the bypass flow, and the number of repetition in the steps4and7is set to 10.

In the calculation recipe92a, the flow mode and the number of repetition of opening/closing of the valve V1are different from those of the processing recipe. This is because actual supply of the raw material is not required. In the processing recipe, the film forming process is performed by repeating the opening/closing of the valve V1100 times. However, the difference in the number of repetition of the opening/closing of the valve V1does not affect the offset value. Therefore, the time required to obtain the offset value is shortened by reducing the number of repetition of the opening/closing of the valve V1. Although it is not included in the recipes shown inFIGS. 10 to 12, a small amount of the raw material gas remaining in the raw material gas supply line32may be supplied to the film forming unit40and, thus, the reactant gas is not supplied.

Next, the recipe creating program92bwill be described. When the process proceeds to the step S4shown inFIG. 3, the processing recipe corresponding to the current lot shown inFIG. 10is sent from the host computer to the memory93of the control unit. The recipe creating program92breads out from the processing recipe the items corresponding to the blank portions of the calculation recipe format93b, i.e., values of “carrier N2” and “offset N2” in the steps3to7, “pressure” of the film forming unit40in the steps2to8, and “execution time” in the steps3and4and in the steps6and7. The read-out values are recorded in the blank portions of the calculation recipe format93bshown inFIG. 11. Accordingly, the calculation recipe93ashown inFIG. 12is created and stored in the memory93.

The offset value is obtained by using the calculation recipe93acreated by the recipe creating program92b. As will be described in the following verification test, the offset value is affected by the flow rates of the carrier gas and the dilution gas and also by the temperature of the film forming unit40. Further, the offset value is affected by the pressure of the film forming unit40and by the opening/closing cycle of the valve V1even if the flow rate of the carrier gas is constant. When the offset value is obtained, the temperature is not considered because the temperature of the film forming unit40is already set to the film forming temperature.

Therefore, an accurate offset value for each processing recipe can be obtained by setting the calculation recipe92ain which the opening/closing time of the valve V1, the flow rates of the carrier gas and the dilution gas, and the set value of the pressure of the film forming unit40are recorded for each processing recipe. Accordingly, the accuracy of the actual measurement value of the flow rate of the raw material which is obtained by subtracting the offset value from the measurement value of the flow rate of the raw material is increased. In addition, since the calculation recipe92ais used as described above, the load of data processing is decreased.

In the case of consecutively performing the film forming process on the wafers100of each lot under the same processing recipe, as the wafers100are processed, the remaining amount of the raw material in the raw material container14is decreased. When the flow rates of the carrier gas and the dilution gas are controlled in the steps S21and S22shown inFIG. 3, the temperature of the raw material gas is changed due to the difference in the temperature between the carrier gas and the dilution gas and, thus, the offset value may be gradually deviated. To that end, the offset value may be changed when the number of processed wafers100reaches a predetermined number or when the supply time of the raw material gas reaches a predetermined time. For example, when a next lot is processed after completion of the processing of the current lot, there may be provided a step in which “YES” is selected and the processing proceeds to the step S4when the number of processed wafers100reaches the predetermined number after the step S2inFIG. 3and “NO” is selected and the process to proceed to the step S3when the number of processed wafers100does not reach the predetermined number. Accordingly, the offset value is corrected even when the individual deviations of the MFM3, the MFC1and the MFC2are increased due to the increase in the number of processed wafers or in the processing time in the case of consecutively performing the same processing recipe. Hence, the actual measurement value m of the flow rate of the raw material can be obtained with high accuracy. The offset value may also be obtained by stopping the processing of a lot during the processing of the lot.

For example, when the effect of the offset value on the pressure of the film forming unit40is small, the offset value may be obtained by allowing the gas to flow from the raw material gas supply line32through a bypass line that bypasses the film forming unit40.

The following test was executed to verify the relationship between the processing recipe and the offset value. The offset value was obtained by using the film forming apparatus according to the embodiment by using different processing recipes in which the pressure and the temperature of the film forming unit40, the cycle of supplying the raw material gas and stopping the supply, and the flow rates of the carrier gas and the dilution gas are varied.

FIG. 13is a characteristic view showing a relationship between the offset value and the flow rate of the carrier gas in an example in which the offset value was obtained by using a processing recipe in which the flow rate of the dilution gas is set to zero.FIG. 14is a characteristic view showing a relationship between the offset value and the total flow rate of the carrier gas and the dilution gas in an example in which the offset value was obtained by using a processing recipe in which the carrier gas and the dilution gas are supplied. InFIGS. 13 and 14, the relationship therebetween was obtained while varying the temperature of the film forming unit40.

The result shows that the offset value tends to be increased by increasing the flow rates of the carrier gas and the dilution gas as can be seen fromFIGS. 13 and 14. However, even when the flow rates of the carrier gas and the dilution gas are constant, the offset value has variation due to the set values of the processing recipe such as the temperature and the pressure of the film forming unit40, the opening/closing cycle of the valve V1and the like. Therefore, when the processing parameters are changed as described above, it is preferable to obtain the offset value by using the changed processing parameters.

While the present disclosure has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the present disclosure as defined in the following claims.