Method and apparatus for simulating an oxidation process in a semiconductor device manufacturing step

[0003] 1. Field of the Invention

[0004] The present invention generally relates to a process simulating method, a process simulator, and a recording medium for recording a process simulation program. More specifically, the present invention is directed to such a process simulating method for simulating an oxidation process in a semiconductor device manufacturing step for an LSI and the like. Also, the present invention is directed to a process simulator for the above-described process simulating method, and also to a recording medium for recording a process simulation program.

[0005] 2. Description of the Related Art

[0006] Conventionally, process simulators are practically available in order to predict internal physical amounts and shapes such as impurity profiles of various elements for constituting semiconductor devices such as LSIs by calculating an oxidation process, a diffusion process, an ion implantation process in manufacturing steps of these LSIs with employment of computers. When such a process simulator is employed, manufacturing processes of the respective elements for constituting the semiconductor device such as the LSI can be optimized as a desk plan in such a manner that the semiconductor device such as the LSI has a desirable electric characteristic. As a consequence, the manufacturing cost can be considerably reduced and the time can be largely shortened, as compared with the actual manufacture of the semiconductor device as a trial case.

[0007] To calculate the manufacturing steps for the various sorts of elements by using the computer, the model formulae have been installed in the process simulator with respect to each of the processes. Among these processes, as to the oxidation process, for example, the following simulation method is known. That is, the formula of Deal-Grove (see formula (22)) disclosed in Japanese publication “VLSI Designing/Manufacturing Simulation” written by M. MORISUE issued by CMC K. K., in 1987, pages 62 to 63 is differentiated with respect to time to thereby obtain the formula (23). Then, this formula (23) is solved to simulate the temporal change in the film thickness of the silicon oxide film (SiO₂, simply referred to as an “oxide film” hereinafter).

[0008] In the formulae (22) and (23), symbol “t” indicates a time instant in the oxidation process, symbol “T_OX” shows a film thickness of an oxide film at a present time instant, and symbol “T^P_OX” indicates a film thickness of an oxide film at a preceding time instant, and also symbols “A” and “B” are parameters related to oxidation speed. The formula (23) is applied to an one-dimensional oxidation case such that a flux of an oxidizing agent does not depend upon a place:

[0009] T_OX²+AT_OX=B(t+τ)  (22)

[0010] $\begin{array}{cc}\frac{d{T}_{\mathrm{OX}}}{dt}=\frac{B}{\left(2T_{\mathrm{OX}}^P+A\right)}& \left(23\right)\end{array}$

[0011] On the other hand, very recently, in connection with the high integration in semiconductor devices such as LSIs and VLSIs, namely in conjunction with very fine structures of structural elements for constituting these semiconductor devices, these structural elements are isolated by employing LOCOS (Local Oxidation of Silicon) structures and trench structures in order to avoid electrical adverse influences caused by these structural elements. As a consequence, also in process simulators, oxide film shapes in these LOCOS structures and trench structures are required to be simulated. When these oxide film shapes are simulated, since fluxes of oxidizing agents differ from each other, depending on places, the simulation for the oxide film shapes should be carried out at least in the two-dimensional manner, which is completely different from the one-dimensional oxidation.

[0012] The two-dimensional oxidation simulation as to the LOCOS structure is disclosed in Japanese publication “Semiconductor Process Device Simulation Technique” written by S. ISOMAE, published by REALIZE publisher, in 1990, on pages 79 to 89. Also, the method for determining the time step “Δt” equal to the unit time of the oxidizing agent diffusion within the oxide film during the oxidation process is described in “Two-Dimensional Oxidation” by DAEJE CHIN et al., IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. ED-30, No. 7, July 1983.

[0013] Now, the conventional two-dimensional oxidation process simulating method disclosed in the last-mentioned publication will be described with reference to a flow chart shown in FIG. 5 and a sectional structure view of an LSI under manufacture indicated in FIG. 6.

[0014] In the flow chart of FIG. 5, at the first step SA1, the time instant variable “t” used to count up a time elapse in the oxidation process is set to zero. Subsequently, the simulating operation is advanced to the step SA2. At this step SA2, the Laplace equation indicated in the above-described formula (24) as to the oxide film 1 is solved to calculate oxidizing agent (oxidant) density C^S_OXat the boundary surface between the oxide film 1 and the silicon substrate 2 (will be referred to as “a boundary surface between an oxide film/a silicon substrate” hereinafter). Then, the simulating operation is advanced to the further step SA3. In the following formula (24), symbol D_OXshows the diffusion coefficient of the oxidizing agent within the oxide film 1:

[0015] D_OX∇²C_OX=0  (24).

[0016] At the step SA3, the film thickness T^S_OXof the oxide film 1 of the side wall in the LOCOS structure at the time instant “t” is calculated. Thereafter, the process operation is advanced to the step SA4.

[0017] At the step SA4, the calculated value of this film thickness T^S_OXis substituted for the below-mentioned formula (25) so as to calculate the time step “Δt” equal to the unit time of the oxidizing agent diffusion within the oxide film 1 during the oxidation process. Subsequently, the simulating process is advanced to the step SA5. It should be understood that symbol “ΔT_OX” shown in the formula (25) is a desirable film thickness increase amount of the oxide film 1 per 1 time step Δt. This formula (25) is substantially same as the formula [23] disclosed in page 748 of the last-mentioned publication “Two-Dimensional Oxidation”. $\begin{array}{cc}\Delta t=\left(\frac{2T_{\mathrm{OX}}^S+A}{B}\right)\Delta T_{\mathrm{OX}}& \left(25\right)\end{array}$

[0018] At the step SA5, the time instant “t” is advanced only by the time step Δt. In other words, after the time step Δt is added to the time instant variable “t”, this simulating process is advanced to the step SA6.

[0019] At this step SA6, after the calculation is made of deformation in the shape of the oxidation film as to the time instant “t”, the simulating process is advanced to the further step SA7.

[0020] At this step SA7, the judgment is made as to whether or not the time instant “t” reaches an ending time instant of the oxidation process. If the judgment result is “NO”, then the simulating process is returned to the step SA2, at which the process operations defined from the step SA2 to the step SA6 are repeatedly performed. Then, in the case that the time instant “t” has reached the ending time instant of the oxidation process, since the judgement result of the step SB8 becomes “YES”, a series of simulation work is accomplished.

[0021] As previously explained, in accordance with the conventional process simulating method, as indicated in FIG. 6, the time step “Δt” is determined in such a manner that the increased value of the film thickness T^S_OXof the oxide film of the side wall in the LOCOS structure is continuously made equal to the film thickness ΔT_OX.

[0022] On the other hand, in the above-explained conventional process simulating method, the film thickness T^S_OXof the side wall in the LOCOS structure is employed as the present film thickness of the oxide film 1 which is required to determine the time step “Δt”. As a consequence, this conventional process simulating method owns such a drawback that this process simulating method cannot be applied to any of the oxidation process simulation methods. That is, when the respective structural elements for constituting a semiconductor device such as an LSI own arbitrary shapes other than the LOCOS structure, this conventional oxidation process simulating method cannot be used to simulate this oxidation process.

[0023] The present invention has been made to solve the above-described problem, and therefore, has an object to provide a process simulating method, a process simulator, and a recording medium for recording a process simulation program, capable of properly calculating a time step in an oxidation process even when the respective structural elements for constituting a semiconductor device such as an LSI own arbitrary shapes.

[0024] To achieve the above-described object, a process simulating method, as recited in claim 1 of the present invention, is featured by such a process simulating method for simulating an oxidation process in a step for manufacturing a semiconductor device, comprising: a first step in which a two-dimensional Laplace equation related to an oxidizing agent diffusion within an oxide film is solved to thereby calculate oxidizing agent concentration C^S_OXat a boundary surface between an oxide film/a silicon substrate; a second step in which the oxidizing agent density C^S_OXis substituted for the below-mentioned formula (1) so as to calculate an effective film thickness of the oxide film as to all of a plurality of preset modes on the boundary surface between the oxide film/the silicon substrate; the formula (1) is defined by such that equilibrium oxidizing agent concentration within the oxide film is “C*”, an oxidation reaction coefficient at the boundary surface between the oxide film/the silicon substrate is “k”, a mass transfer coefficient at a boundary surface between an atmosphere/an oxide film is “h”, a diffusion coefficient of an oxidizing agent within the oxide film is “D”, and a parameter related to an oxidation speed is equal to “A” given by the below-mentioned formula (2): $\begin{array}{cc}{T}_{\mathrm{OX}}^E=\frac{A}{2}·\frac{\frac{h}{h+k}·C^{*}-C_{\mathrm{OX}}^S}{C_{\mathrm{OX}}^S},\mathrm{and}& \left(1\right)\\ A=2D\left(\frac{1}{h}+\frac{1}{k}\right);& \left(2\right)\end{array}$

[0025] a third step for calculating a minimum value T^M_OXof the film thickness T^E_OX; and a fourth step in which both the minimum value T^M_OXand a desirable film thickness increase amount ΔT_OXof the oxide film per a time step Δt are substituted for the below-mentioned formula (3) to thereby calculate the time step “Δt”, the time step “Δt” being equal to unit time of the oxidizing agent diffusion within the oxide film in the oxidation process; $\begin{array}{cc}\Delta t=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}},& \left(3\right)\end{array}$

[0026] wherein: another parameter B related to an oxidation speed, expressed in a right hand of the above-described formula (3), is given by the below-mentioned formula (4), and symbol “N₁” shown in a right hand of the below-mentioned formula (4) is a parameter determined by an oxidation sort: $\begin{array}{cc}B=\frac{2D{C}^{*}}{N_1}.& \left(4\right)\end{array}$

[0027] Also, to achieve the above-described object, a process simulating method, as recited in claim 2 of the present invention, is featured by the process simulating method according to claim 1 wherein: the process simulating method is comprised of, instead of the fourth step, a fifth step in which the minimum value T^M_OX, a maximum film thickness increase amount ΔT^MM_OXand also a minimum film thickness increase amount ΔT^M_OXwith respect to the oxide film thickness increase amount ΔT_OX, and a preceding time step Δt^Pare substituted for the below-mentioned formula (5) related to a maximum time step Δt^MM, the below-described formula (6) related to a minimum time step Δt^M, and the below-mentioned formula (7) directed to such a time step Δt which should be calculated when a ratio of a present time step to the preceding time step Δt^Pis assumed as “R”, whereby the time step Δt is calculated: $\begin{array}{cc}\Delta t^{\mathrm{MM}}=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}}^{\mathrm{MM}}& \left(5\right)\\ \Delta t^M=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}}^M& \left(6\right)\end{array}$  Δt=max{Δt^M,min(Δt^P×R,Δt^M)}  (7).

[0028] Furthermore, a process simulator, as recited in claim 3 of the present invention, is featured by such a process simulator for simulating an oxidation process in a step for manufacturing a semiconductor device, comprising: first means in which a two-dimensional Laplace equation related to an oxidizing agent diffusion within an oxide film is solved to thereby calculate oxidizing agent concentration C^S_OXat a boundary surface between an oxide film/a silicon substrate; second means in which the oxidizing agent density C^S_OXis substituted for the below-mentioned formula (8) so as to calculate an effective film thickness of the oxide film as to all of a plurality of preset modes on the boundary surface between the oxide film/the silicon substrate; the formula (8) is defined by such that equilibrium oxidizing agent concentration within the oxide film is “C*”, an oxidation reaction coefficient at the boundary surface between the oxide film/the silicon substrate is “k”, a mass transfer coefficient at a boundary surface between an atmosphere/an oxide film is “h”, a diffusion coefficient of an oxidizing agent within the oxide film is “D”, and a parameter related to an oxidation speed is equal to “A” given by the below-mentioned formula (9): $\begin{array}{cc}{T}_{\mathrm{OX}}^E=\frac{A}{2}·\frac{\frac{h}{h+k}·C^{*}-C_{\mathrm{OX}}^S}{C_{\mathrm{OX}}^S},\mathrm{and}& \left(8\right)\\ A=2D\left(\frac{1}{h}+\frac{1}{k}\right);& \left(9\right)\end{array}$

[0029] third means for calculating a minimum value T^M_OXof the film thickness T^E_OX; and fourth means in which both the minimum value T^M_OXand a desirable film thickness increase amount ΔT_OXof the oxide film per a time step Δt are substituted for the below-mentioned formula (10) to thereby calculate the time step “Δt”, the time step “Δt” being equal to unit time of the oxidizing agent diffusion within the oxide film in the oxidation process; $\begin{array}{cc}\Delta t=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}},& \left(10\right)\end{array}$

[0030] wherein: another parameter B related to an oxidation speed, expressed in a right hand of the above-described formula (10), is given by the below-mentioned formula (11), and symbol “N₁” shown in a right hand of the below-mentioned formula (11) is a parameter determined by an oxidation sort: $\begin{array}{cc}B=\frac{2D{C}^{*}}{N_1}.& \left(11\right)\end{array}$

[0031] Also, to achieve the above-described object, a process simulator, as recited in claim 4 of the present invention, is featured by the process simulator according to claim 3 wherein: the process simulator is comprised of, instead of the fourth means, fifth means in which the minimum value T^M_OX, a maximum film thickness increase amount ΔT^MM_OXand also a minimum film thickness increase amount ΔT^M_OXwith respect to the oxide film thickness increase amount ΔT_OX, and a preceding time step Δt^Pare substituted for the below-mentioned formula (12) related to a maximum time step Δt^MM, the below-described formula (13) related to a minimum time step Δt^M, and the below-mentioned formula (14) directed to such a time step Δt which should be calculated when a ratio of a present time step to the preceding time step Δt^Pis assumed as “R”, whereby the time step Δt is calculated: $\begin{array}{cc}\Delta t^{\mathrm{MM}}=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}}^{\mathrm{MM}}& \left(12\right)\\ \Delta t^M=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}}^M& \left(13\right)\end{array}$  Δt=max{Δt^M,min(Δt^P×R,Δt^M)}  (14).

[0032] Also, to achieve the above-described object, a process simulator, as recited in claim 5 of the present invention, is featured by the process simulator according to claim 3 wherein: the process simulator is arranged by a computer including at least: a memory unit for previously storing thereinto a program to simulate the oxidation process of the semiconductor device manufacturing step; and a central processing unit for controlling the operations of the first to fourth means, and the memory unit.

[0033] Moreover, a recording medium, as recited in claim 6 of the present invention, is featured by such a recording medium for recording thereon a process simulation program used to simulate an oxidation process in a step for manufacturing a semiconductor device, wherein: the process simulation program causes a computer to execute: a first step in which a two-dimensional Laplace equation related to an oxidizing agent diffusion within an oxide film is solved to thereby calculate oxidizing agent concentration C^S_OXat a boundary surface between an oxide film/a silicon substrate; a second step in which the oxidizing agent density C^S_OXis substituted for the below-mentioned formula (15) so as to calculate an effective film thickness of the oxide film as to all of a plurality of preset modes on the boundary surface between the oxide film/the silicon substrate; the formula (15) is defined by such that equilibrium oxidizing agent concentration within the oxide film is “C*”, an oxidation reaction coefficient at the boundary surface between the oxide film/the silicon substrate is “k”, a mass transfer coefficient at a boundary surface between an atmosphere/an oxide film is “h”, a diffusion coefficient of an oxidizing agent within the oxide film is “D”, and a parameter related to an oxidation speed is equal to “A” given by the below-mentioned formula (16): $\begin{array}{cc}{T}_{\mathrm{OX}}^E=\frac{A}{2}·\frac{\frac{h}{h+k}·C^{*}-C_{\mathrm{OX}}^S}{C_{\mathrm{OX}}^S},\mathrm{and}& \left(15\right)\\ A=2D\left(\frac{1}{h}+\frac{1}{k}\right);& \left(16\right)\end{array}$

[0034] a third step for calculating a minimum value T^M_OXof the film thickness T^E_OX; and a fourth step in which both the minimum value T^M_OXand a desirable film thickness increase amount ΔT_OXof the oxide film per a time step Δt are substituted for the below-mentioned formula (17) to thereby calculate the time step “Δt”, the time step “Δt” being equal to unit time of the oxidizing agent diffusion within the oxide film in the oxidation process; $\begin{array}{cc}\Delta t=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}},& \left(17\right)\end{array}$

[0035] wherein: another parameter B related to an oxidation speed, expressed in a right hand of the above-described formula (17), is given by the below-mentioned formula (18), and symbol “N₁” shown in a right hand of the below-mentioned formula (18) is a parameter determined by an oxidation sort: $\begin{array}{cc}B=\frac{2D{C}^{*}}{N_1}.& \left(18\right)\end{array}$

[0036] Also, to achieve the above-described object, a recording medium, as recited in claim 7 of the present invention, is featured by the recording medium for recording thereon a process simulation program, according to claim 6, wherein: the process simulating method is comprised of, instead of the fourth step, a fifth step in which the minimum value T^M_OX, a maximum film thickness increase amount ΔT^MM_OXand also a minimum film thickness increase amount ΔT^M_OXwith respect to the oxide film thickness increase amount ΔT_OX, and a preceding time step t^Pare substituted for the below-mentioned formula (19) related to a maximum time step Δt^MM, the below-described formula (20) related to a minimum time step Δt^M, and the below-mentioned formula (21) directed to such a time step Δt which should be calculated when a ratio of a present time step to the preceding time step Δt^Pis assumed as “R”, whereby the time step Δt is calculated: $\begin{array}{cc}\Delta t^{\mathrm{MM}}=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}}^{\mathrm{MM}}& \left(19\right)\\ \Delta t^M=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}}^M& \left(20\right)\end{array}$  Δt=max{Δt^M,min(Δt^P×R,Δt^M)}  (21).

[0037] The above and further objects, novel features and advantages of the present invention will more fully become obvious upon an understanding of the following detailed description taken in connection with the accompanying drawings, in which:

[0038] FIG. 1 is a flow chart for describing a process simulating method according to a first embodiment of the present invention;

[0039] FIG. 2 illustratively shows an example of an effective film thickness T^E_OXof an oxide film in a semiconductor element having a LOCOS structure according to the first embodiment;

[0040] FIG. 3 illustratively represents another example of an effective film thickness T^E_OXof an oxide film in a semiconductor element having a trench shape according to the first embodiment;

[0041] FIG. 4 is a flow chart for describing a process simulating method according to a second embodiment of the present invention;

[0042] FIG. 5 is a flow chart for explaining one example of the conventional process simulating method; and

[0043] FIG. 6 is an explanatory diagram for explaining the problems of the conventional process simulating method.

[0044] Referring now to drawings, various preferred embodiments of the present invention will be described in detail.

[0045] FIG. 1 is a flow chart for describing a process simulating method according to a first preferred embodiment of the present invention. It should be understood that this first process simulating method is installed as a process simulation program into a process simulator for a utilization purpose.

[0046] The process simulator is arranged by employing a computer containing a CPU (central processing unit), an internal storage apparatus such as a ROM (read-only memory) and a RAM (random access memory), and an external storage apparatus such as an FDD (floppy disk drive), a HDD (hard disk drive), and a CD-ROM (compact disk-ROM) driver. This computer further contains an input device such as a keyboard and a mouse, and also a display device. This process simulator is furthermore constituted by other data processing apparatus. The above-described process simulating method is recorded as a process simulation program on such a recording medium as an FD (floppy disk) and an HD (hard disk), and also a CD-ROM. This recording medium may be realized by employing a semiconductor memory, for instance, a ROM.

[0047] Referring now to FIG. 1 and FIG. 2, a description will be made of operations of the process semiconductor with employment of the above-described arrangement.

[0048] In the flow chart of FIG. 1, at a first step SB1, a time instant variable “t” used to count up a time elapse in the oxidation process is set to zero. Subsequently, the simulating operation is advanced to a step SB2.

[0049] At this step SB2, the Laplace equation indicated in the above-described formula (24) as to an oxide film 1 is solved to calculate oxidizing agent density C^S_OXat a boundary surface between an oxide film/a silicon substrate. Then, the simulating operation is advanced to a further step SB3.

[0050] At the step SB3, the value of the oxidizing agent density C^S_OXis entered into a formula (47) so as to calculate an effective film thickness T^E_OXof the oxide film 1 over all of nodes on the boundary surface between the oxide film/the silicon substrate. Thereafter, this simulating process is advanced to a step SB4. It should be noted that the method for determining the node is described in, for instance, Japanese Unexamined Patent Application No. 9-017738 opened in 1997. In the above-described formula (47), symbol “C*” indicates equilibrium oxidizing agent density within the oxide film 1, symbol “k” shows an oxidation reaction coefficient at the boundary surface between the oxide film/the silicon substrate, depending upon a temperature, and symbol “h” represents a mass transfer coefficient at a boundary surface between an atmosphere/the oxide film 1, depending upon a temperature. Similar to the above-described formulae (22) and (23), symbol “A” indicates a parameter related to an oxidation speed. This oxidation speed “A” is given by the below-mentioned formula (48). In this formula (48), symbol “D” denotes an oxidation agent diffusion coefficient within the oxide film 1, depending upon a temperature. $\begin{array}{cc}{T}_{\mathrm{OX}}^E=\frac{A}{2}·\frac{\frac{h}{h+k}·C^{*}-C_{\mathrm{OX}}^S}{C_{\mathrm{OX}}^S}& \left(47\right)\\ A=2D\left(\frac{1}{h}+\frac{1}{k}\right)& \left(48\right)\end{array}$

[0051] Now, a method for conducting the above-described formula (47) will be explained. A growing speed of the oxide film 1 is directly proportional to a flux of an oxidizing agent such as O₂and H₂O at the boundary surface between the oxide film/the silicon substrate. In a primary oxidation model, a flux F₁of an oxidation agent at the boundary surface between the atmosphere/the oxide film, a flux F₂of an oxidation agent within the oxide film 1, and a flux F₃of an oxidation agent at the boundary surface between the oxide film/silicon substrate are reserved. In other words, the following formula (49) can be satisfied:

[0052] F₁=F₂=F₃  (49)

[0053] The growing speed of the oxide film 1, the flux F₁, the flux F₂, and the flux F₃are given in accordance with the below-mentioned formulae (50) to (53). In these formulae (50) to (53), symbol “N” shows a parameter, and symbol “C_OX” represents oxidizing agent density at the boundary surface between the atmosphere/the oxide film 1. $\begin{array}{cc}\frac{d{T}_{\mathrm{OX}}^E}{dt}=\frac{F_3}{N}& \left(50\right)\end{array}$  F₁=h(C*−C_OX)  (51)

[0054] $\begin{array}{cc}{F}_2=-D\frac{\partial C}{\partial X}=D\frac{C_{\mathrm{OX}}-C_{\mathrm{OX}}^S}{T_{\mathrm{OX}}^E}& \left(52\right)\end{array}$  F₃=kC^S_OX  (53)

[0055] Since F₂=F₃can be satisfied based upon the above-explained formula (49), the following formula (54) is obtained from the right hand of the above-described formula (52) and the right hand of the above-described formula (53): $\begin{array}{cc}{C}_{\mathrm{ox}}=\frac{{\mathrm{kT}}_{\mathrm{OX}}^E+D}{D}{C}_{\mathrm{OX}}^S& \left(54\right)\end{array}$

[0056] Since F₁=F₂can be satisfied based upon the above-explained formula (49), the following formula (55) is obtained from the right hand of the above-described formula (51) and the right hand of the above-described formula (52):

[0057] DC^S_OX=−hT^E_OXC*+(hT^E_OXD)C_OX  (55)

[0058] As a consequence, when the formula (54) is substituted for the formula (55) to be rearranged as to the effective film thickness T^E_OXof the oxide film 1, the above-described formula (47) is obtained.

[0059] Referring to the simulating operation by the process simulator, a minimum value T^M_OXis calculated from the effective film thickness T^E_OXof the oxide film 1 at a step SB4, which has been calculated on the boundary surface between the oxide film/silicon substrate. Then, this simulating process is advanced to a further step SB5.

[0060] At this step SB5, both the effective minimum value T^M_OXof the film thickness of the oxide film 1 and a desirable film thickness increase amount ΔT_OXof the oxide film 1 per 1 time step “Δt” are substituted for the below-mentioned formula (56) so as to calculate a time step “Δt”. Thereafter, the simulating process is advanced to a step SB6. $\begin{array}{cc}\Delta t=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}}& \left(56\right)\end{array}$

[0061] It should be understood that similar to the above-described formulae (22) and (23), symbols “A” and “B” show parameters related to oxidation speeds, depending upon temperatures. The parameter “A” is given by the formula (48), whereas the parameter “B” is given by the formula (57). Also, symbol “N₁” of a right hand of the below-mentioned formula (57) represents a parameter determined based upon an oxidation sort. $\begin{array}{cc}B=\frac{2D{C}^{*}}{N_1}& \left(57\right)\end{array}$

[0062] At a step SB6, a time instant “t” is advanced only by the time step Δt. In other words, after the time step Δt is added to the time instant variable “t”, this simulating process is advanced to a step SB7.

[0063] At this step SB7, after a calculation is made of deformation in the shape of the oxidation film as to the time instant “t”, the simulating process is advanced to a further step SB8.

[0064] At this step SB8, a judgment is made as to whether or not the time instant “t” reaches an ending time instant of the oxidation process. If the judgment result is “NO”, then the simulating process is returned to the step SB2, at which the process operations defined from the step SB2 to the step SB7 are repeatedly performed. Then, in the case that the time instant “t” has reached the ending time instant of the oxidation process, since the judgement result of the step SB8 becomes “YES”, a series of simulation work is accomplished.

[0065] As previously explained, in accordance with the process simulating method of this first embodiment, even when the respective elements for constituting the semiconductor device own arbitrary shapes, the time step “Δt” can be calculated based upon the minimum value T^M_OXof the effective film thickness of the oxide film 1.

[0066] FIG. 2 illustratively indicates an example of the effective film thickness T^E_OX(indicated by arrows) of the oxide film 1 at all of the nodes on the boundary surface between the oxide film/the silicon substrate as to the oxidation process simulation in the respective elements of the semiconductor device having the LOCOS structure. As can be seen from this drawing, an effective film thickness T^E_OX1of the oxide film 1 at a side wall portion of the LOCOS structure is made coincident with the actual film thickness of the oxide film 1 in the side wall portion of the LOCOS structure. On the other hand, since the oxidizing agent is not diffused under a nitride film 3, the oxidizing agent concentration at the boundary surface between the oxidation film/the silicon substrate is decreased, and an effective film thickness T^E_OX5of the oxide film 1 under the nitride film 3 becomes thicker than the actual film thickness of the oxide film 1.

[0067] FIG. 3 illustratively indicates an example of the effective film thickness T^E_OX(indicated by arrows) of the oxide film 1 at all of the nodes on the boundary surface between the oxide film/the silicon substrate as to the oxidation process simulation in the respective elements of the semiconductor device having the trench structure. As can be seen from this drawing, an effective film thickness T^E_OX1of the oxide film 1 at such a trench portion where the nitride film 3 is not present is made coincident with the actual film thickness of the oxide film 1. On the other hand, since the oxidizing agent is not diffused under the nitride film 3, the oxidizing agent concentration at the boundary surface between the oxidation film/the silicon substrate is decreased, and an effective film thickness T^E_OX5of the oxide film 1 under the nitride film 3 becomes thicker than the actual film thickness of the oxide film 1.

[0068] Next, a second embodiment will now be explained. FIG. 4 is a flow chart for describing a process simulating method according to this second embodiment of the present invention. This process simulating method of the second embodiment is different from the above-explained process simulating method of the first embodiment with respect only to a step SC5 instead of the above-explained step SB5. Accordingly, only this different step SC5 will be explained in the following description.

[0069] That is, at this step SC5, the following calculations are carried out. The minimum value T^M_OXof the effective film thickness of the oxide film 1, a maximum film thickness increase amount ΔT^MM_OXand a minimum film thickness increase amount ΔT^M_OXwith respect to a desirable oxide film thickness increase amount ΔT_OX, and a preceding time step Δt^Pare substituted for the below-mentioned formula (58) related to a maximum time step Δt^MM, the below-mentioned formula (59) concerning a minimum time step Δt^M, and the above-mentioned formula (53) related to the time step Δt to be calculated, respectively, to obtain a time step Δt. Thereafter, the simulating process is advanced to a step SB6. Also, in the below-explained formula (60), symbol “R” indicates a ratio of the present time step to the preceding time step. $\begin{array}{cc}\Delta t^{\mathrm{MM}}=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}}^{\mathrm{MM}}& \left(58\right)\\ \Delta t^M=\left(\frac{2T_{\mathrm{OX}}^M+A}{B}\right)\Delta T_{\mathrm{OX}}^M& \left(59\right)\end{array}$  Δt=max{Δt^M,min(Δt^P×R,Δt^M)}  (60)

[0070] As previously described, in accordance with the process simulating method of the second embodiment, the desirable oxide film thickness increase amount ΔT_OXcan be restricted into such a range between the minimum film thickness increase amount ΔT^M_OXand the maximum film thickness increase amount T^MM_OX. Also, since the time step Δt can be increased/decreased with reference to the preceding time step Δt^P, the high precession analysis can be obtained.

[0071] While the present invention has been described with reference to the drawings, the present invention is not limited to the above-described embodiments, but may be modified, changed, and substituted without departing from the technical spirit and scope of the present invention.

[0072] As previously described in detail, in accordance with the process simulating method, the process simulator, and the recording medium for recording the process simulation program of the present invention, there are advantages as follows. That is, the effective film thicknesses of the oxide film 1 as to the respective nodes on the boundary surface between the oxide film/the silicon substrate are calculated. Based upon the minimum film thickness of the oxide film 1, the unit time (time step) of the oxidizing agent diffusion within the oxide film 1 in the oxidation process can be calculated. Even when the respective elements for constituting the semiconductor device such as the LSI own the arbitrary shapes, the time step can be properly calculated.

[0073] As a consequence, the simulation in the oxidation process can be realized in a high speed and in high precision.

[0074] It is thus apparent that the present invention should by no means be limited to the illustrated embodiment and various modification and changes may be suggested without departing from the scope and spirit of the invention.

[0075] Finally, the present application claims the priority of Japanese Patent Application No. Hei9-193893 filed on Jul. 18, 1997, which is herein incorporated by reference.