Method of manufacturing semiconductor device and semiconductor manufacturing apparatus

A method of manufacturing a semiconductor device includes forming a film along a surface of a semiconductor substrate in a first surface area state having a first surface area by supplying a reaction gas at a first flow rate. The method further includes detecting a transition from the first surface area state to a second surface area state having a second surface area different from the first surface area. The method still further includes forming the film by changing the flow rate of the reaction gas from the first flow rate to a second flow rate different from the first flow rate after detecting the transition from the first surface area state to the second surface area state.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-196633, filed on, Sep. 26, 2014 the entire contents of which are incorporated herein by reference.

FIELD

Embodiments disclosed herein generally relate to a method of manufacturing semiconductor device and a semiconductor manufacturing apparatus.

BACKGROUND

Three-dimensionalization of semiconductor devices may cause an increase in the surface area of the structures formed above the semiconductor substrate during the manufacturing process flow. When forming a film by CVD (Chemical Vapor Deposition) for example, the supply of reaction gas increases as the surface area of the underlying structure becomes greater. Thus, formation of a film above a semiconductor substrate having a large surface area requires a large amount of reaction gas, which in turn increases the cost of semiconductor device manufacturing.

DESCRIPTION

In one embodiment, a method of manufacturing a semiconductor device includes forming a film along a surface of a semiconductor substrate in a first surface area state having a first surface area by supplying a reaction gas at a first flow rate. The method further includes detecting a transition from the first surface area state to a second surface area state having a second surface area different from the first surface area. The method still further includes forming the film by changing the flow rate of the reaction gas from the first flow rate to a second flow rate different from the first flow rate after detecting the transition from the first surface area state to the second surface area state.

In one embodiment, a semiconductor manufacturing apparatus includes a reaction chamber configured to process a semiconductor substrate; amass flow controller configured to control a flow rate of a reaction gas being provided into the reaction chamber; and a controller. The controller is configured to be capable of executing a control to form a film along a surface of the semiconductor substrate so that a surface area of the semiconductor substrate makes a transition from a first state having a first surface area to a second state having a second surface area different from the first surface area. The film is formed by supplying the reaction gas at a first flow rate when in the first state, and after detecting the transition from the first state to the second state, the controller is capable of executing a control to form a film by changing the flow rate of the reaction gas to a second flow rate different from the first flow rate.

EMBODIMENTS

Embodiments are described herein with reference to the accompanying drawings. The drawings are schematic and are not necessarily consistent with the actual relation between thickness and planar dimensions as well as the ratio of thicknesses between different layers, etc. The same element may be illustrated in different dimensions or ratios in different figures. Further, directional terms such as up, down, left, and right are used in a relative context with an assumption that the surface, on which circuitry is formed, of the later described semiconductor substrate faces up and thus, do not necessarily correspond to the directions based on gravitational acceleration. In the drawings referred to in the following description, elements that are identical or similar in function, structure, etc. to those already illustrated or described are identified with identical or similar reference symbols and may not be re-described.

Further, in the following description, an XYZ orthogonal coordinate system is used for convenience of explanation. In the coordinate system, the X direction and the Y direction each indicate a direction parallel to the surface of a semiconductor substrate and crossing one another. The direction crossing both the X direction and the Y direction is referred to as the Z direction.

First Embodiment

FIG. 1is one example of a schematic view illustrating the structure of semiconductor manufacturing apparatus100of the first embodiment. In the first embodiment, semiconductor manufacturing apparatus100is described through a CVD (Chemical Vapor Deposition) apparatus application. Semiconductor manufacturing apparatus100is provided with reaction chamber10hereinafter also referred to as chamber10, mass flow controller26hereinafter also referred to as MFC26, and central processing unit28hereinafter also referred to as CPU28.

Chamber10contains shower head12and stage heater14. Semiconductor substrate18may be placed on stage heater14, in which case, stage heater14may serve as a heater for controlling the temperature of semiconductor substrate18. Lifter pins16are provided at the upper portion of stage heater14. Exhaust tube20communicates with the interior of chamber10. Exhaust tube20is provided with automatic pressure controller22hereinafter also referred to as APC22.

Shower head12and MFC26are interconnected by gas supply tube32. MFC26is configured to control the flow rate of reaction gas. Thus, reaction gas is fed through gas supply tube32at a controlled flow rate and supplied into chamber10from shower head12. The gas supplied into chamber10forms a film above the surface of semiconductor substrate18. The reaction gas which was not consumed in the reaction is exhausted, as exhaust gas24, from chamber10through exhaust tube20.

CPU28serves as a controller configured to control various components of semiconductor manufacturing apparatus100. CPU28is provided with a memory portion not illustrated and an interface portion also not illustrated. The memory portion is configured to store various programs and parameters used in the control. The interface portion is configured to establish connection with the components of semiconductor manufacturing apparatus100and send/receive various signals to/from the components.

Chamber10serves as a reaction chamber for forming one or more films above the surface of semiconductor substrate18by CVD. MFC26is configured to control the amount of reaction gas being supplied from gas supply tube32into chamber10through shower head12. MFC26and CPU23are interconnected by signal line36. The amount of gas supply is controlled by MFC26based on the instructions provided from CPU28through signal line36.

APC22is capable of controlling or adjusting the pressure inside chamber10. APC22is an automatic pressure controller configured to control the pressure inside chamber10by varying the flow rate of gas passing through exhaust tube20. For example, APC22is capable of controlling the pressure inside chamber10to a predetermined pressure. APC22is disposed in the path of exhaust tube20. A valve may be provided inside APC22for example, and APC22may be configured to control the flow rate of exhaust gas24discharged from exhaust tube20by varying the degree of openness of the valve. The degree of openness of the valve provided in APC22is also hereinafter simply referred to as the degree of openness, or the opening of APC22. APC22and CPU28are interconnected by signal line34. Information regarding the openness of APC22is sent to CPU28through signal line34.

Next, a description will be given on one example of a manufacturing method of a semiconductor device of the first embodiment with referenceFIG. 2A,FIG. 2B, andFIG. 2C.FIGS. 2A to 2Care examples of vertical cross sectional views describing one example of a sequence of process steps for manufacturing the semiconductor device of the first embodiment. Further, graph line50of the graph inFIG. 3indicates the variation, i.e. change, in the surface area of semiconductor substrate18during the manufacturing process flow of semiconductor device120.

Semiconductor device120includes film40. Film40is formed on semiconductor substrate18. A silicon substrate may be used for example as semiconductor substrate18. Film40may be an insulating film or a conductive film. Film40may also be a stack of films. One example of film40may be a stack of a silicon oxide film and a silicon nitride film.

Film40is provided with trenches42and trenches44. Trenches42extend in the up and down direction also referred to as the Z direction. Trenches44extend in the left and right direction or the lateral direction also referred to as the X direction and are centered on trenches42. Trenches42and44taken together exhibit a cross section looking like a fish bone for example as illustrated inFIGS. 2A, 2B, and 2Cin which trenches44extend in the left and right direction (X direction) so as to be centered on trenches42extending in the Z direction. Trenches42and trenches44are elongate trenches extending into the page in the front and rear direction also referred to as the Y direction as viewed inFIGS. 2A, 2B, and 2C. Trenches42and trenches44increase the surface area of semiconductor device120, i.e. the surface area of semiconductor substrate18surface. In the embodiments disclosed herein, semiconductor substrate18surface is inclusive of film40. The surface area of semiconductor substrate18surface is the sum of surface areas of trenches42, trenches44, and the upper surface of CVD film48.FIG. 2Aillustrates a first state. In the first state, the surface area of semiconductor substrate18amounts to a first surface area obtained by the sum of the surface areas of trenches42, trenches44, and the upper surface of film40. Film40is also herein after referred to as a pre-deposited film. Region A indicated inFIG. 3represents the first state and the surface area of region A also referred to as the first surface area is indicated by graph line50a. For example, the first surface area is approximately 50 times the surface area of a flat semiconductor substrate18.

The cross section shaped like, but not limited to, a fish bone configured by trenches42and trenches44is an example of a shape having a large surface area. In an alternative embodiment, the cross section may be configured by trenches extending in the up and down direction for example.

Next, CVD film48is formed above film40having trenches42and trenches44formed therein as described above. In other words, CVD film48is formed above semiconductor substrate18in the first state. CVD film48may be an insulating film or a conductive film for example. In this example, CVD film48is a conductive film comprising tungsten (W). Film formation by CVD is carried out with conditions that provide good coverage. Formation of CVD film48above semiconductor substrate18in the first state progresses conformally along trenches42, trenches44, and surface46of film40.

Then, trenches44are filled with CVD Film48as illustrated inFIG. 2B. As trenches44are filled with CVD film48, the total surface area of the first state is reduced by the surface area of trenches44. Because trenches44are formed substantially throughout the surface of semiconductor substrate18, the surface areas of trenches44sum up to a significantly large amount. Thus, the total surface area becomes significantly small by the loss of surface area occupied by trenches44.FIG. 2Billustrates a second state. In the second state, the total surface area of semiconductor substrate18amounts to a second surface area obtained by the sum of the surface areas of trenches42and the upper surface of surface46bof CVD film48. Region B indicated inFIG. 3represents the second state and the surface area of region B also referred to as the second surface area is indicated by graph line50b. For example, the second surface area is approximately 5 times the surface area of a flat semiconductor substrate18.

As the formation of CVD film48further progresses, trenches42are also filled with CVD film48and CVD film48is formed further above surface46as illustrated inFIG. 2C. Because trenches42are filled with CVD film48, the total surface area of semiconductor substrate18is reduced by the surface area of trenches42. The total surface area of semiconductor substrate18surface ultimately becomes substantially equal to the surface area of surface46cof CVD film48covering film40and trenches42which is in turn substantially equal to the surface area of a flat semiconductor substrate18surface. In other words, the total surface area of semiconductor substrate18surface become substantially equal to the surface area of a flat semiconductor substrate18, being approximately one times the surface area of a flat semiconductor substrate18.FIG. 2Cillustrates a third state. In the third state, the total surface area of semiconductor substrate18amounts to a third surface area corresponding to the surface area of surface46c, i.e. the surface area of the planar portion. Region C indicated inFIG. 3represents the third state and the surface area of region C also referred to as the third surface area is indicated by graph line50c.

There are no trenches42nor trenches44in the third state and thus, the formation of CVD film48progresses over a flat surface. As a result, the formation of CVD film48may progress with a focus on increasing the speed of film formation with less focus on improving coverage. Formation of CVD film48in the third state may be accelerated by increasing the temperature of semiconductor substrate18by increasing the temperature of stage heater14. Accelerating CVD film48formation allows improvement in the throughput of CVD film48formation process.

As the formation of CVD film48progresses along the surface of semiconductor substrate18provided with trenches42and44, the vertical cross section of semiconductor device120changes its shape as illustrated inFIGS. 2A, 2B, and 2Cand the surface area of semiconductor device120varies as indicated by graph line50ofFIG. 3. That is, the total surface area of semiconductor device120is gradually reduced in the listed sequence of the first surface area represented by graph line50a, the second surface area represented by graph line50b, and the third surface area represented by graph line50c.

FIG. 3is a graph indicating the relation of the flow rate of reaction gas and the surface area of semiconductor substrate18surface. InFIG. 3, the lateral axis indicates the time of film formation, whereas the left vertical axis indicates the gas flow rate of reaction gas used in the film formation and the right vertical axis indicates the total surface area of semiconductor substrate18surface. In CVD, the amount (flow rate) of reaction gas used in film formation is correlated with the surface area of semiconductor substrate18surface along which the film is to be formed. As described earlier, semiconductor substrate18surface is inclusive of the pre-deposited film40in which trenches42and trenches44are formed. This means that the gas flow rate can increase/decrease as the surface area becomes greater/smaller.

As indicated inFIG. 3, the surface area of semiconductor substrate18surface represented by graph line50is gradually reduced as indicated by graph lines50a,50b, and50c. However, when film formation by CVD is carried out without detecting and considering the variation in the surface area of semiconductor substrate18surface, gas is supplied at constant flow rate as indicated by gas flow rate52and gas flow rate54.

However, as the surface area of semiconductor substrate18surface is gradually reduced, the amount of gas actually being used exhibits the flow rates indicated by first gas flow rate52a, second gas flow rate52b, and third gas flow rate52c. Excess reaction gas is exhausted without being used in the reaction for causing film formation. Thus, supply of reaction gas exceeding the flow rate of reaction gas required in the film formation results in a waste of reaction gas. In this example, gas amount56occupying the region above graph line52becomes a waste. In the first embodiment, the flow rate of reaction gas is adjusted in correlation with the detected variation, represented by graph lines50a,50b, and50cof graph line50, in the total surface area of semiconductor substrate18surface where CVD film48is formed. First gas flow rate52a, second gas flow rate52b, and third gas flow rate52crepresenting the gas flow rates used in the actual film formation may be obtained experimentally.

For example, tungsten may be formed by CVD at a pressure of 10,000 Pa and a temperature of 300 degrees Celsius using WF6(tungsten hexafluoride) as a material gas and H2(hydrogen) as a reduction gas. The speed of film formation is 0.3 nm/sec for example when the tungsten film is formed above a flat 300 mm semiconductor substrate180, that is, above semiconductor substrate18in the third state having the third surface area.

FIG. 4is one example of a flow chart indicating the process flow for manufacturing the semiconductor device of the first embodiment. Reference will be made toFIG. 1toFIG. 3whenever found appropriate. Reaction gas is supplied into chamber10at first gas flow rate52awith semiconductor substrate18surface of semiconductor device120in the first state (step S401). The surface of semiconductor substrate18is structured as illustrated inFIG. 2A. The surface area of the surface of semiconductor substrate18in the first state may be given for example by the sum of the surface areas of trenches42, trenches44, and the upper surface of CVD film48. The surface area of the surface of semiconductor substrate18in the first state may also be referred to as a first surface area. In this example, tungsten is used as an example of CVD film48formed by CVD. CVD film48, which is a tungsten film in this example, is formed along the surface of semiconductor substrate18which is inclusive of the surface of film40including the surfaces of trenches42and the surfaces of trenches44(step S402).

Then, the surface of semiconductor substrate18is placed in the second state illustrated inFIG. 2Bas the formation of CVD film48progresses (step S403). In the second state, semiconductor device120is structured as illustrated inFIG. 2B. The surface area of the surface of semiconductor substrate18in the second state may be given for example by the sum of the surface areas of trenches42and the upper surface of CVD film48. The surface area of the surface of semiconductor substrate18in the second state may also be referred to as a second surface area. The surface area of the surface of semiconductor substrate18is reduced in the second state as compared to the first state.

In the second state, the pressure inside chamber10is reduced as will be later described and thus, APC22is controlled in the direction to close the valve in order to keep the pressure inside chamber10constant. Stated differently, the opening, i.e. the degree of openness of APC22is reduced (step S404).

Upon detecting the reduction of APC22opening, CPU28controls MFC26to change the flow rate of reaction gas to second gas flow rate52b. More specifically, CPU28monitors the opening of APC22and when determining that the opening of APC22has become equal to or less than a predetermined value, CPU28sends instructions to MFC26through signal line36to change the gas flow rate to second gas flow rate52b. Upon receiving the instructions, MFC26executes a control to change the gas flow rate to second gas flow rate52b(step S405).

Next, a description will be given on how the variation in the opening of APC22is fed back to MFC26. The formation of tungsten by CVD described earlier is driven by the reaction expressed by chemical formula (1) given below which takes place inside chamber10.
WF6(g)+3H2(g)→W(s)+6HF(g)  (1)

WF6and H2are reaction gases and WF6serves as a material gas and H2serves as a reduction gas. In the reaction expressed by formula (1), a total of 4 mol of reaction gas, containing 1 mol of WF6serving as a material gas and 3 mol of H2serving as a reduction gas, is introduced into chamber10. The reaction produces 6 mol of HF when the reaction gas is fully consumed in the reaction. This means that 6 mol of gas is produced when 4 mol of reaction gas is introduced.

Suppose a total of 2000 sccm of reaction gas, containing 500 scorn of material gas (WF6) and 1500 sccm of reduction gas (H2), is supplied to semiconductor substrate18in the first state having the first surface area.

As described earlier, the first surface area is approximately 50 times of the surface area of a flat semiconductor substrate18. The reaction gases being fully consumed in the reaction taking place above semiconductor substrate18for forming CVD film48will result in 3000 sccm of HF. APC22is controlled to a degree of openness corresponding to the gas flow rate of 3000 sccm and thereby keeps the pressure inside chamber10constant.

Then, semiconductor substrate18surface makes the transition to the second state having the second surface area as the formation of CVD film48progresses. Meanwhile, the reaction gas continues to be supplied at the flow rate of 500 sccm for WF6and 1500 sccm for H2until the variation, i.e. change, in the opening of APC22is detected by CPU28. The second surface area is approximately five times the surface area of a flat semiconductor substrate18as described earlier. As the surface area of semiconductor substrate18is reduced from the first surface area to the second surface area, the amount of gas used in the reaction expressed in formula (1) amounts to 50 sccm for WF6and 150 sccm for H2. The reaction gases unconsumed in the reaction are exhausted as unreacted gas. In the reaction taking place in the second state, 2100 sccm of exhaust gas24is exhausted since 300 sccm of HF produced by the reaction of 50 sccm of WF6and 150 sccm of H2is also exhausted simultaneously. Thus, in this example, the amount (flow rate) of exhaust gas24is reduced from 3000 sccm to 2100 sccm as the surface area is reduced from the first surface area being 50 times the surface area of a flat semiconductor substrate180to the second surface area being 5 times the surface area of a flat semiconductor substrate18, meaning that the pressure inside chamber10is reduced. In order to keep the pressure inside chamber10constant, a control is executed to reduce the opening of APC22. That is, when a transition is made from the first state having the first surface area to the second state having the second surface area, the opening of APC22is reduced. In this example, opening of APC22is reduced by making adjustments in the degree of openness of the valve in the direction to close the valve.

FIG. 5is one example of a graph schematically indicating the variation in the opening of APC22. InFIG. 5, the lateral axis represents the time of film formation, the vertical axis represents the APC opening, region A represents the first state having the first surface area, and region B represents the second state having the second surface area. As the result of variation in the flow rate of exhaust gas24in the above described manner caused by the variation in the state of semiconductor device120from the first state to the second state at time T, the opening of APC22is reduced, i.e. changed, in the direction to close the degree of openness of APC22.

In the first embodiment, CPU28is configured to detect the variation in the opening of APC22. When determining that the opening of APC22has become equal to or less than a predetermined degree of openness, CPU28is configured to send instructions to MFC26to change the gas flow rate from first gas flow rate52ato second gas flow rate52b. Upon receiving the instructions, MFC26is configured to change the gas flow rate from first gas flow rate52ato second gas flow rate52b(step S405).

Next, as the formation of CVD film48progresses based on second gas flow rate52b(step S406), trenches42are filled with CVD film48to place semiconductor device120in the third state (step S407) in which semiconductor substrate18surface has the third surface area as illustrated inFIG. 2C. Because the surface area of semiconductor substrate18surface is reduced from the second surface area to the third surface area, the pressure inside chamber10is reduced as was the case in the above described reaction and the opening of APC22is reduced (step S408). The variation in the opening of APC22is detected by CPU28and upon determining that the opening of APC22has become equal to or less than a predetermined degree of openness, CPU28is configured to send instructions to MFC26to change the gas flow rate from second gas flow rate52bto third gas flow rate52c. MFC26is configured to change the gas flow rate from second gas flow rate52bto third gas flow rate52cin the above described manner (step S409).

Next, formation of CVD film48progresses based on third gas flow rate52c(step S410), and the formation is ended when reaching the desired thickness (step S411). The semiconductor device of the first embodiment is manufactured in the above described manner.

In the first embodiment described above, CPU28is capable of detecting the transition from the first state having the first surface area to the second state having the second surface area and the transition from the second state having the second surface area to the third state having the third surface area based on the opening of APC22. As a result, CPU28is allowed to instruct MFC26to change the gas flow rate to a level which is suitable with the variation in the surface area of semiconductor substrate18. More specifically, CPU28is capable of detecting the variation, i.e. decrease in the surface area of the surface of semiconductor substrate18by monitoring the opening of APC22. It is thus, possible to control or adjust the flow rate of reaction gas to a level which is suitable with the variation in the surface area of semiconductor substrate18in real time. By controlling the supply of reaction gas to an appropriate flow rate for film formation in real time, it is possible to save excessive supply of gas which may amount to gas amount56indicated inFIG. 3for example. It is thus, possible to reduce the supply of reaction gas and consequently reduce the manufacturing cost of the semiconductor device.

The first embodiment was described based on, but not limited to, an example in which tungsten was formed as CVD film43. Different reactions may result depending upon the material being formed and/or reaction gases, etc. being used. Thus, the transitions from the first state to the second state and from the second state to the third state may take different forms from the examples described above. For instance, the opening of APC22may increase in some examples. The same is applicable to the second, third, and fourth examples described hereinafter.

Second Embodiment

In the first embodiment described above, variation in the surface area of semiconductor substrate18surface is detected by monitoring the opening of APC22. The supply of gas is thereby controlled to an appropriate flow rate depending upon the variation in the surface area of semiconductor substrate18surface. In the second embodiment, the variation in the surface area of semiconductor substrate18surface is detected by detecting the variation, i.e. change, in the ratio of chemical species contained in exhaust gas24.

As was the case in the first embodiment, suppose a total of 2000 sccm of reaction gas, containing 500 sccm of material gas (WF6) and 1500 sccm of reduction gas (H2), is supplied to semiconductor substrate18in the first state having the first surface area in the second embodiment. In such case, the reaction gases being fully consumed in the reaction taking place above semiconductor substrate18will produce 3000 sccm of HF. Thus, exhaust gas24resulting from the reaction will contain HF.

Next, when a transition is made to the second state having the second surface area as the formation of CVD film48progresses, amount of gas used in the reaction expressed by formula (1) amounts to 50 sccm of WF6and 150 sccm of H2when 500 sccm of WF6and 1500 sccm of H2are supplied. The reaction produces 300 sccm of HF. The reaction gases unconsumed in the reaction are exhausted as unreacted gas. In this example, a total of 1800 sccm of material gas containing 450 sccm of WF6and 1350 sccm of H2are unconsumed in the reaction. Thus, the flow rate of exhaust gas24amounts to a total of 2100 sccm containing 300 sccm of HF, 450 sccm of WF6, and 1350 sccm of H2. It is possible to detect the variation in the surface area of semiconductor substrate18surface by detecting the variation in the ratio of chemical species contained in exhaust gas24. It is thus, possible to control the supply of gas to an appropriate flow rate in real time depending upon the variation in the surface area of semiconductor substrate18surface. The same is applicable when a transition is made from the second state having the second surface area to the third state having the third surface area.

The ratio of chemical species contained in exhaust gas24may be measured by a mass spectrometer. For example, the mass spectrometer may be disposed in exhaust tube20illustrated inFIG. 1and connected to CPU28so that the measurements of the mass spectrometer may be monitored by CPU28.

In the second embodiment described above, CPU28is capable of detecting the transition from the first state having the first surface area to the second state having the second surface area and the transition from the second state having the second surface area to the third state having the third surface area based on the ratio of chemical species contained in exhaust gas24. As a result, CPU28is allowed to instruct MFC26to change the gas flow rate to a level which is suitable with the variation in the surface area of semiconductor substrate18. More specifically, CPU28is capable of detecting the variation in the surface area of the surface of semiconductor substrate18by monitoring the ratio of chemical species contained in exhaust gas24. The second embodiment is thus, capable of achieving the advantages similar to those of the first embodiment.

Third Embodiment

Next, a description will be given on a third embodiment. In the third embodiment, the variation in the surface area of semiconductor substrate18surface is detected by detecting the variation in the heater power of stage heater14.

As described earlier, semiconductor device120makes a transition from the first state having the first surface area to the second state having the second surface area as the formation of CVD film48progresses. Stage heater14is configured to be capable of keeping the temperature of semiconductor substrate18constant. The amount of heat dissipation from semiconductor substrate18surface is reduced as the surface area of semiconductor substrate18is reduced. The reduced heat dissipation makes it difficult for the temperature of semiconductor substrate18to be lowered and thus, an adjustment is made to lower the heater power of stage heater14. As a result, the heater power of stage heater14is reduced when the transition is made from the first state having the first surface area to the second state having the second surface area. Thus, it is possible to detect the variation in the surface area of semiconductor substrate18surface by detecting the variation in the heater power of stage heater14. The supply of gas can be controlled to an appropriate flow rate depending upon the variation in the surface area of semiconductor substrate18surface.

The heater power of stage heater14is controlled for example by CPU28. CPU28keeps track of the value of heater power supplied to stage heater14. CPU28is capable of controlling MFC26by detecting the variation, i.e. change, in the value of heater power. For example, it is possible to determine that the value of heater power has been changed when for example three different values have been detected in a second-by-second monitoring of the heater power value. The same is applicable when a transition is made from the second state having the second surface area to the third state having the third surface area.

In the third embodiment described above, CPU28is capable of detecting the transition from the first state having the first surface area to the second state having the second surface area and the transition from the second state having the second surface area to the third state having the third surface area based on the detection of variation in the value of heater power. As a result, CPU28is allowed to instruct MFC26to change the gas flow rate to a level which is suitable with the variation in the surface area of semiconductor substrate18. More specifically, CPU28is capable of detecting the variation in the surface area of the surface of semiconductor substrate18by monitoring the value of heater power. The third embodiment is thus, capable of achieving the advantages similar to those of the first embodiment.

Fourth Embodiment

Next, a description will be given on a fourth embodiment. In the fourth embodiment, variation in the surface area of semiconductor substrate18surface is detected by detecting the variation in the value of current being supplied for driving lifter pin16provided at the upper surface of stage heater14. The value of current being supplied for driving lifter pin16is also hereinafter referred to as lifter drive current value.

In the fourth embodiment, lifter pin16is controlled so that semiconductor substrate18is spaced by a predetermined distance from the surface of stage heater14. The distance between the surface of stage heater14and semiconductor substrate18may be less than 1 mm, for example. Thus, radiation heat coming from stage heater14will reach semiconductor substrate18and thereby allow temperature control of semiconductor substrate18. Lifter pin16is capable of lifting semiconductor substrate18upward from the underside of semiconductor substrate18. Lifter drive current value supplied to lifter pin16varies depending upon the weight of semiconductor substrate18. For example, the lifter drive current value may become greater as the weight of semiconductor substrate18becomes heavier.

The speed of film formation along trenches42, trenches44, and surface46is substantially the same when CVD film48is formed by CVD. The speed of film formation may be defined as the thickness of film being formed in a given time period. Thus, the amount of film formation throughout semiconductor substrate18becomes greater as the surface area becomes greater. The amount of film formation may be measured by weight. Thus, the amount of increase in the weight of semiconductor substrate18in a given time period becomes greater as the surface area of semiconductor substrate18becomes greater and becomes smaller as the surface area of semiconductor substrate18becomes smaller. Thus, the amount of increase, i.e. the increasing gradient hereinafter also referred to as the gradient, in the lifter drive current value supplied to lifter pin16becomes greater as the surface area of semiconductor substrate18becomes greater.

FIG. 7is one example of a graph indicating the variation in the lifter drive current value supplied to lifter pin16related to time of film formation. The lateral axis represents the time of film formation and the vertical axis represents the lifter drive current value. In region A representing the first state having the first surface area, the gradient of the amount of film formation, i.e. the gradient of the amount of weight increase is large, being larger than region B for example. This is because the first surface area of the first state is large, being approximately 50 times the surface area of a flat semiconductor substrate18as mentioned in the example of the first embodiment. As a result, a large or steep gradient is observed in the amount of increase in the lifter drive current value supplied to lifter pin16.

In contrast, in region B representing the second state having the second surface area, the gradient of the amount of film formation is small, being smaller than region A for example. This is because the second surface area of the second state is small, being approximately 5 times the surface area of a flat semiconductor substrate18as mentioned in the example of the first embodiment. As a result, a small or gradual gradient is observed in the amount of increase in the lifter drive current value supplied to lifter pin16. The gradient of the lifter drive current value becomes smaller at time T when the transition is made from the first state to the second state. It is possible to detect the variation in the surface area of semiconductor substrate18surface by detecting the variation, i.e. change, in the gradient of the lifter drive current value. Thus, it is possible to control the supply of gas to an appropriate flow rate depending upon the variation in the surface area of semiconductor substrate18surface. The same is applicable to the transition from the second state having the second surface area and the third state having the third surface area.

FIG. 6illustrates one example of the structure of semiconductor manufacturing apparatus100of the fourth embodiment. Lifter pin16is connected to CPU28by way of signal line38. CPU28is configured to control lifter pin16through signal line38. The lifter drive current value supplied to lifter pin16is controlled for example by CPU28. Semiconductor manufacturing apparatus100is provided with lifter pin16or a mechanism not shown configured to detect the location of semiconductor substrate18. The lifter drive current value is controlled by the above described configuration to enable a control to space semiconductor substrate18away from the surface of stage heater14by a predetermined distance. The lifter drive current value, used for controlling lifter pin16to space semiconductor substrate18away from the surface of stage heater14by a predetermined distance, varies depending on the weight of semiconductor substrate18. For example, the lifter drive current value becomes greater as the weight of semiconductor substrate18becomes greater as illustrated inFIG. 7.

CPU28is configured to monitor the lifter drive current value and detect the variation in the surface area of semiconductor substrate18by detecting the variation in the gradient of the amount of increase in the lifter drive current value. As illustrated inFIG. 7, a change is observed in the gradient or the inclination of the straight line representing the lifter drive current value at time T. For example, a change in the gradient may be determined as follows. The lifter drive current value is detected every 1 second and the gradient of the lifter drive current value is detected for every 1 second. A change in the gradient is determined to have occurred when a different gradient value has been encountered for 3 consecutive times. The change in the gradient of the amount of increase of the lifter drive current value may be detected in the above described manner. CPU28is capable of controlling MFC26to specify an appropriate gas flow rate depending upon the variation in the surface area of semiconductor substrate18surface detected by detection of change in the gradient of the lifter drive current value.

in an alternative embodiment, semiconductor substrate18may be lifted away from the surface of stage heater14by lifter pin16at a regular interval of 1 second for example during the formation of CVD film48and the lifter drive current value measured at this timing may be monitored.

In the fourth embodiment described above, CPU28is capable of detecting the transition from the first state having the first surface area to the second state having the second surface area and the transition from the second state having the second surface area to the third state having the third surface area based on the detection of variation in the value of lifter drive current of lifter pin16. As a result, CPU28is allowed to instruct MEC26to change the gas flow rate to a level which is suitable with the variation in the surface area of semiconductor substrate18. More specifically, CPU28is capable of detecting the variation in the surface area of the surface of semiconductor substrate18by monitoring the value of lifter drive current. The fourth embodiment is thus, capable of achieving the advantages similar to those of the first embodiment.

OTHER EMBODIMENTS

The embodiments described above may be applied to various type of semiconductor devices including storage devices such as a NAND type or a NOR type flash memory, EPROM, DRAM, and SRAM; and logic devices.