# Patent

## Title
Method for manufacturing semiconductor device

## Abstract

In a manufacturing method for a semiconductor device, a main body wafer having an interlayer insulating film is formed, and a monitor wafer on which a monitor element is formed is provided. Characteristics of the main body wafer are copied onto the monitor element by simultaneously processing the main body wafer and the monitor wafer through BPSG densification during formation of the interlayer insulating film. The characteristic of the monitor element is measured by checking a process influence of the monitor element. Manufacturing conditions are set in accordance with the process influence of the monitor element. Variations in electric characteristics of the main body wafer are reduced in accordance with the set manufacturing conditions.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a manufacturing method for a semiconductor device. In particular the invention relates to a manufacturing method for a semiconductor device including a method of monitoring halfway through a manufacturing process of the semiconductor device and a method of reflecting monitoring information to its subsequent manufacturing process.
2. Description of the Related Art
Upon manufacturing any products, product-to-product variation (production variation) impairs uniformity in product characteristics (inclusive of function, performance, and shape). To prevent it, a manufacturer faces an agonizing choice between relaxing a production specification to keep a production yield at a certain level (decrease in quality) and complying with a product specification to thereby cause reduction in production yield (increase in cost). Under such circumstances, regarding a manufacturing method for a semiconductor device as a typical method for mass-production of goods as well, some improvement have been made and tried on a manufacturing method by combining a cost-oriented manufacturing method with a quality-oriented manufacturing method. Prior to explanation about the improved manufacturing method, generally-employed manufacturing methods for a semiconductor device are first described.
A semiconductor device is provided in a form of a semiconductor chip (for example, 0.5 mm in thickness, 10 mm in length, 8 mm in width) on which a number of electronic elements such as transistors, resistors, capacitors, diodes and wirings for electrically connecting the electronic elements together are formed, and the chip is housed in a package according to the environment it is actually used. The packaged chip is incorporated into an electronic device such as a computer, a mobile telephone, a gene console, etc., for variety of use. A manufacturing process for the semiconductor device consists of, as shown in a macro-manufacturing process flow of FIG. 2, a pre-manufacturing process X for lot-production of several dozens of wafers on which a number of semiconductor chips are assigned and a post-manufacturing process Y for separating the semiconductor chips assigned on the waters from one another to be housed in packages and subjected to product testing. The post-manufacturing process V hence includes package assembly and product testing. Electric characteristics of a semiconductor device are nearly determined at the time of placing the semiconductor chip on a wafer, in other words, upon the completion of the pre-manufacturing process X although there are a few exceptions, i.e., FPLD (digital IC), fuse memory, and such other semiconductor devices whose functions are determined by a user after the completion of the post-manufacturing process Y. It is assumed throughout The following description that a characteristic variation due to the post-manufacturing process Y is negligible. In this specification, description of the manufacturing process for the semiconductor device is therefore exclusively focused on the pre-manufacturing process X. Description of the post-manufacturing process Y will accordingly be omitted hereafter.
Here, the pre-manufacturing process X for the semiconductor device will be described with reference to a typical and simplified manufacturing process flow of 3 in which basic processes are shown. A semiconductor device manufactured by utilizing these processes is also called a CMOS semiconductor device.
1. Field Oxide Film Formation
Insulating films partially different in thickness are selectively formed near the surfaces of a semiconductor substrate, in this example a P-type semiconductor substrate, through thermal oxidation etc. (FIG. 3, Step J).
2. N well Formation
Phosphorous ions for N well formation are selectively implanted into the semiconductor substrate surface, for example, to thereby form an N well (FIG. 3, Step K).
3. Isolation with LOCOS
BF2 ions for P-type channel stopper formation are selectively implanted into the P-type semiconductor substrate surface and its vicinities, for example, after which an element isolation insulating film and channel stopper are selectively formed by using a LOCOS method etc. (FIG. 3, Step L).
4. Channel Doping
Phosphorus ions for controlling a threshold voltage are selectively implanted into the semiconductor substrate surface in an active region for element formation where a transistor is formed later to thereby form an impurity Step M).
5. Gate Oxide Film Formation
An oxide film near the semiconductor substrate surface in the active region for element formation is removed to form a gate oxide film through thermal oxidation etc. (FIG. 3, Step N).
6. Polysilicon Gate Formation
A poly-crystalline silicon (polysilicon) gate is selectively formed on the gate oxide film through chemical vapor deposition (CVD), photolithography, and etching (FIG. 3, Step O).
7. Source/Drain Formation
After an oxide film is formed on the P-type semiconductor substrate surface by CVD or thermal oxidation, impurity ions for forming source/drain (SD) regions are implanted to the polysilicon gate and the oxide film in desired regions of the active region for the element formation in a self-alignment manner to thereby form an N-type source region, an N-type drain region, a P-type source region, and a P-type drain-region (FIG. 3, Step P).
8. Interlayer Insulating Film Formation
An oxide film is deposited on the P-type semiconductor substrate surface by CVD or the like to thereby form an interlayer insulating film (FIG. 3, Step Q).
9. Contact Hole Formation
A contact hole is selectively formed onto an interlayer insulating film through photolithography- and etching Step R).
10. Metal Wiring Formation
A metal wiring is selectively formed on the interlayer insulating film through sputtering, photolithography, etching, etc. (FIG. 3, Step S).
11. Protective Film
A protective film is deposited on the metal wiring and an opening is selectively formed in a desired region (metal wiring in an external connection terminal region etc.) (FIG. 3, Step T).
12. Wafer Inspection
A semiconductor chip and an IC tester are electrically connected through a wafer prober to test electric characteristics etc. of the semiconductor device (FIG. 3, Step U).
As mentioned above, the semiconductor device is manufactured through a lengthy or long-term manufacturing process. More specifically, the manufacturing process is very complicated and consists of well over 100 steps.
The electric characteristics of the semiconductor device are determined depending on characteristics of circuit elements in the semiconductor chip. As well known in the art, the electric characteristic of a MOS transistor, which is a typical circuit element of the semiconductor device, is approximately represented by the following equation: (1) for unsaturated state:

Id=μC(W/L) (Vg−Vt)Vd  (1)

where

Id: drain current of a transistor
μ: carrier mobility of the transistor
C: gate capacitance per, unit area of the transistor
W: gate width of the transistor
L: gate length of the transistor.
Vg: gate-source voltage of the transistor
Vd: drain-source voltage of the transistor
Vt: threshold voltage of the transistor
As apparent from the equation (1), the current characteristics of the transistor are determined by many characteristic parameters. Further, the threshold voltage Vt is derived from the following equation (2):

Vt=VF+2.F+(QA+QB)/C  (2)

where

VF: flat band voltage
.F: shift in Fermi level due to impurity
QA: interface charge per unit area at an interface between the oxide film and the silicon surface
QB: charge per unit area of deletion layer
C: gate capacitance per unit area of the transistor
The electric characteristics of the transistor manufactured through the manufacturing process including-well over 100-steps may vary due to an influence of the long-term manufacturing process. In commercializing a semiconductor device, a product specification is determined by balancing the quality with the cost while taking the variations into account, and a circuit is designed such that the electric characteristics of the semiconductor device comply with the product specification. In some cases, however, high quality, e.g., high precision, should precede the cost as a result of reflecting the strong demand from the market. The characteristic parameter sensitive to the variations in electric characteristics, such as the threshold voltage Vt may largely vary between wafers, among the same lot, and in the same semiconductor chip as well as between lots. Heretofore, there is an increasing demand for realization of a manufacturing method which absorbs and lowers the variations of parameters having a large contribution to the variation in electric characteristics of the semiconductor device, such as the threshold voltage Vt.
Up to now, a manufacturing method for a semiconductor device has been proposed, with which the aforementioned problem is solved and the variations in the threshold voltage Vt are reduced. The manufacturing method is completed by adding, for example, a step of reducing variations of FIG. 14, to the typical manufacturing process flow of FIG. 2. The step of reducing the variations includes a quality check step F of measuring and checking a quality of a half-completed product in the middle of the manufacturing process, a condition setting step G of setting a manufacturing condition in a variation reduction step H included in the subsequent manufacturing process for the semiconductor device, based on the measurement information, and the variation reduction step H of absorbing and reducing the variations in electric characteristics under the set manufacturing condition for manufacturing the semiconductor device. The above three steps are regarded as being extended from the wafer inspection step (FIG. 3, Step U).
A first prior art aiming to solve the aforementioned problem provides a feed-back type manufacturing method including: measuring (or simulating) the threshold voltage Vt of an electronic element in a half-completed semiconductor chip during manufacture under existing manufacturing conditions adjusting and determining the next manufacturing conditions for manufacturing the next lot based on the existing manufacturing conditions for the semiconductor device and the measurements; reducing variations in the threshold voltage Vt of the semiconductor device; and reducing variations in electric characteristics (see JP 2002-083958 A (p. 8, FIG. 1), for example). A second prior art aiming to solve the aforementioned problem provides a trimming type manufacturing method including: adjusting values (e.g., resistance value) of passive elements in a half-completed semiconductor chip; absorbing variations in the threshold voltage Vt etc. for each chip; and reducing variations in electric characteristics of a semiconductor device (see JP 07-086521 A (p. 5, FIG. 1), for example). These prior arts will be described in brief below, but detailed description will be referred to each publication.
The feed-back type manufacturing method as the conventional manufacturing method for the semiconductor device aimed to reduce production variations is a method of setting the next manufacturing condition based on the existing manufacturing condition of the manufacturing process in the case of manufacturing another semiconductor device. More specifically, it is a manufacturing method including: measuring the threshold voltage Vt of a semiconductor product manufactured under the existing manufacturing condition; measuring or evaluating a quality of the semiconductor device in course of manufacture (FIG. 15, Step F) and then revising and determining the next manufacturing condition based on the existing criteria (FIG. 15, Step G); and manufacturing the next semiconductor device under the next manufacturing condition (FIG. 15, Step H) to reduce the variations in electric characteristics of the semiconductor device. According to this feed-back type manufacturing method, the next manufacturing condition is adjusted based on information on current variations to thereby reduce the variations in electric characteristics of the semiconductor device. A specific method of determining the next manufacturing condition is shown in FIG. 15.
The trimming type manufacturing method as another typical manufacturing method for a semiconductor device aimed to reduce the production variation uses a trimming circuit as shown in FIG. 18. In the trimming circuit of FIG. 18 resistors 220 and 221 are electrically connected in series between external input terminals 300 and 301. Fuses 230 and 231 are connected to the resistors 220 and 221 in parallel, respectively. A gate electrode of a transistor 210 is connected to a node between the resistors 220 and 221. A drain region of the transistor 210 is connected to an external input/output terminal 303 through an internal circuit 240 while a source region thereof is connected to an external input/output terminal 304 through an internal circuit 241. The fuses 230 and 231 of the trimming circuit of this semiconductor device are formed of polysilicon but may be formed of aluminum etc. as a metal thin film. Note that, pairs of the resistors 220, 221 and of the fuses 230, 231 may be provided in plural as needed.
The trimming type manufacturing method includes: measuring and checking the quality of the half-completed semiconductor device midway through the manufacturing process (FIG. 16, Step F); and determining fuse cutout portions in the trimming circuit so as to absorb variations of individual semiconductor chips (FIG. 16, Step G) and trimming the individual semiconductor chips (FIG. 16, Step H) to thereby reduce the variations in electric characteristics of the semiconductor device.
However, the conventional manufacturing methods involve the following problems. With the feed-back type manufacturing method as the prior art of FIG. 15, initial conditions for new manufacturing process are first set by, for example, analogizing and referring from/to the existing manufacturing process (existing technique) and then a product is manufactured by way of trial or simulation through all the steps under the initial manufacturing conditions. Next, the quality is measured and checked, after which the initial manufacturing conditions are revised based on the preset criteria to determine the next manufacturing conditions. Thus, the quality check step F and the manufacturing condition setting step G cannot be applied to the semiconductor device in course of manufacture. The wafer inspection result of the completed semiconductor device can be fed back for improving the next manufacturing conditions to thereby improve the manufacturing process. However, this is not directly contributable to reduction in variations of the semiconductor device in course of manufacture.
With the trimming type manufacturing method as the prior art of FIG. 16, the half-completed semiconductor device itself is measured midway through, the manufacturing process, and hence the quality check step F and the manufacturing condition setting step G can be applied to the semiconductor device in course of manufacture. However, in this method, quality damage is caused on the semiconductor device at the time of measurement (due to the contact type measurement in most cases) or a trimming circuit is provided in the semiconductor device for reflecting measurements therein in advance. As a result, this redundant circuit leads to an increase of chip area of the semiconductor device, resulting in lowering of mass-production efficiency and final increase in cost.
SUMMARY OF THE INVENTION
The present invention has an object to provide a manufacturing method for a semiconductor device, which enables reduction in variation of a half-completed semiconductor device without increasing a chip area of the semiconductor device.
A manufacturing method for a semiconductor device according to the present invention includes: a pre-manufacturing process X for manufacturing a wafer (hereinafter, referred to as “main body wafer”) where the semiconductor device to be completed as a product is formed; and a monitor wafer manufacturing process (FIG. 1, Step Z) for manufacturing a wafer (hereinafter, referred to as “monitor wafer”) where a monitor element 200 in FIG. 4 is formed, in which the main body wafer manufacturing process X and the monitor wafer manufacturing process Z share a monitoring step (FIG. 1, Step C) of copying a quality of the semiconductor device on the monitor element 200, the main body wafer manufacturing process X includes a variation reduction step (FIG. 1, step H) after the monitoring step C, and the monitor wafer manufacturing process Z includes a quality check step (FIG. 1, Step F) of measuring characteristics of the monitor element 200 after the monitoring step C and its subsequent condition setting step (FIG. 1, Step G) of setting a manufacturing condition in the variation reduction step H based on measurement information. The aforementioned manufacturing method for a semiconductor device is now referred to as a “feed-forward manufacturing method” herein.
An embodiment of the present invention will be described in detail later. To explain it in brief, as shown in FIG. 1, variations of the semiconductor device are copied to the monitor element 200 (FIG. 4) in the course of manufacture (FIG. 1, step C), a quality of the half-completed semiconductor device is checked (FIG. 1, Step F), a quality of the completed semiconductor device is estimated based on the measured information (FIG. 1, Step G1), the manufacturing conditions of a variation reduction step in the subsequent manufacturing process are set in an analog fashion based on the estimated information (FIG. 1, Step G2), and the variations in electric characteristics are reduced under the newly set manufacturing conditions to complete the manufacture of the semiconductor device (FIG. 1, Step H). Variations in electric characteristics of the semiconductor device in the course of manufacture can thus be reduced considerably. In other words, according to the present invention, the variations of the semiconductor device can be reduced without causing any quality damage on the semiconductor device to be completed as a product and also without requiring any redundant circuit.
Further, by forming the monitor element 200 on which the quality of the semiconductor device is copied in an amplifying manner on a monitor wafer and utilizing it, monitoring can be performed in a short time and at low costs to thereby obtain measurement information sufficient in terms of both quality and quantity since the monitor wafer is only subjected to a short-term process unlike the main body wafer which is subjected to a long-term process. Thus, the manufacturing conditions for the quality check step F can be made more precisely. The feed-forward manufacturing method of the present invention accordingly enables a further reduction in variations in electric characteristics of the semiconductor device and realizes a manufacturing method for a semiconductor device capable of manufacturing the semiconductor device with high quality and high yields.



BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a conceptual view illustrative of a manufacturing process flow of a feed-forward manufacturing method according to the present invention;
FIG. 2 is a flowchart of a typical macro-manufacturing process flow for a semiconductor device;
FIG. 3 is a flowchart of a typical manufacturing process flow of a pre-manufacturing process of a manufacturing method for a semiconductor device;
FIG. 4 is a schematic diagram showing a monitor element 200 used in an embodiment of the present invention;
FIG. 5 is a sectional view illustrative of a typical manufacturing method for a semiconductor device used in an embodiment of the present invention in the step order;
FIG. 6 is a sectional view illustrative of a typical manufacturing method for a semiconductor device used in an embodiment of the present invention in the step order;
FIG. 7 is a sectional view illustrative of a typical manufacturing method for a semiconductor device used in an embodiment of the present invention in the step order;
FIG. 8 is a sectional view illustrative of a typical manufacturing method for a semiconductor device used in an embodiment of the present invention in the step order;
FIG. 9 is a sectional view illustrative of a typical manufacturing method for a semiconductor device used in an embodiment of the present invention in the step order;
FIG. 10 is a sectional view illustrative of a typical manufacturing method for a semiconductor device used in an embodiment of the present invention in the step order;
FIG. 11 is a sectional view illustrative of a typical manufacturing method for a semiconductor device used in an embodiment of the present invention in the step order;
FIG. 12 is a sectional view illustrative of a typical manufacturing method for a semiconductor device used in an embodiment of the present invention in the step order;
FIG. 13 is a sectional view illustrative of a typical manufacturing method for a semiconductor device used in an embodiment of the present invention in the step order;
FIG. 14 is a conceptual view illustrative of a manufacturing process flow which is aimed to absorb variations in electric characteristics in a conventional manufacturing method for a semiconductor device;
FIG. 15 is a flowchart illustrative of a manufacturing process flow which is aimed to absorb variations in electric characteristics in a manufacturing method for a semiconductor device of Prior Art 1 (first prior art);
FIG. 16 is a flowchart illustrative of a manufacturing process flow which is aimed to absorb variations in electric characteristics in a manufacturing method for a semiconductor device of Prior Art 2 (second prior art);
FIG. 17 is a flowchart illustrative of a flow for determining manufacturing conditions used for a feed-back applied manufacturing method of Prior Art 1;
FIG. 18 is a schematic-circuit diagram showing a trimming circuit used for a trimming applied manufacturing method of Prior Art 2;
FIG. 19 is a sectional view illustrative of a typical DDD process used in an embodiment of the present invention in the step order.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a conceptual view illustrative of a manufacturing process flow of a manufacturing method for a semiconductor device according to the present invention. A manufacturing method according to an embodiment of the present invention includes: a main body wafer manufacturing process X for manufacturing a wafer where the semiconductor device to be completed as a product is formed; and a monitor wafer manufacturing process Z for manufacturing a wafer (hereinafter, referred to as “monitor wafer”) where a monitor element 200 which is shown in FIG. 4 is formed. The main body wafer manufacturing process X and the monitor wafer manufacturing process Z share a monitoring step C alone. The monitoring step C is important as a step of copying on the monitor element 200 formed on the monitor wafer, a quality of the semiconductor device formed on the main body wafer.
A manufacturing process flow (FIG. 3) is basically applied to the main body wafer manufacturing process X. The monitoring step C of FIG. 1 is selected from the manufacturing process flow of FIG. 3 as needed. As the monitoring step C, plural steps may be selected. It is assumed here that steps preceding a step specified as the monitoring step C, for example, a gate oxide film formation step N are each referred to as a “main body pre-process step” B, while steps in a manufacturing process succeeding the monitoring step C are each referred to as a “main body post-process step” D. The main body post-process step D includes a variation reduction step H. As the variation reduction step H, plural steps may be set corresponding to the monitoring step C as needed. Steps are selected from the manufacturing process flow of FIG. 3 as a subsequent pre-process step D1 and a subsequent post-process step D2 upstream and downstream of the variation reduction step H, respectively, as needed.
The pre-manufacturing process X for the semiconductor device applied in the embodiment of the present invention will be described in detail with reference to step-order sectional views (FIGS. 5 to 13, and 19). The embodiment of the present invention is not limited to the step-order sectional views but is applicable to any pre-manufacturing process for a typical semiconductor device. Needless to say, the present invention is not limited to a manufacturing method for a MOS semiconductor device but is applicable to a manufacturing method for a bipolar semiconductor device, a compound semiconductor, or the like.
1. Field Oxide Film
Insulating films partially different in thickness are selectively formed near the surface of a semiconductor substrate, for example, a P-type semiconductor substrate 102 through thermal oxidation etc. to thereby form an oxide film 103 having a thickness of about 300 to 1,000 nm and an oxide film 104 having a thickness of about 50 to 100 nm. Here, the P-type semiconductor substrate is used but an N-type semiconductor substrate can be used as well (FIG. 5).
2. N well
Impurity ions, for example, phosphorous ions are implanted into the main body wafer surface in an impurity amount of about 3.0×1012/cm2 to thereby form an impurity doped region for forming an N well 111. This step is called a well impurity doping step. Next, impurities doped into the main body wafer through ion implantation are electrically inactive unless otherwise treated and thus subjected to activation through heat treatment and recovered from damage upon ion implantation. In order to form a PMOS transistor inside the N well 111, the N well 111 needs to have some depth. Typically, the requisite depth is about 1 to 3 mm for the miniaturized transistor and about 3 to 8 mm for the high-breakdown voltage transistor. To obtain an impurity profile necessary for the heat treatment, thermal diffusion is carried out under the conditions of 1,100 to 1,200° C. for several to over ten hours with an electric furnace, for example. This is called a “well thermal diffusion step” (FIG. 6). The well thermal diffusion step is such that plural (about 150) large-diameter wafers are simultaneously processed at high temperature for a long time. Here, the N well 111 is used, but a P well or both the N well and the P well can be used.
3. LOCOS
B or BF2 ions for selectively forming a P-type channel stopper 142 are selectively implanted into a portion near the P-type semiconductor substrate 102 surface, for example, after which an element isolation insulating film 130 and the P-type channel stopper 142 are selectively formed by using a LOCOS method etc. (FIG. 7). In the case of forming the element isolation oxide film using the LOCOS method, the thermal oxidation step is such that plural (about 150) large-diameter wafers are simultaneously processed at high temperature and high oxidation rate for a long time.
4. Channel Doping
Phosphorous, As, B, or BF2 ions for controlling a threshold voltage are selectively implanted into the semiconductor substrate surface in an active region 132 for element formation where a MOS transistor is formed later, for example, to thereby form an impurity doped region 201. In some cases, as a region corresponding to the impurity doped region 201, plural regions may be separately formed according to requirement for a conductivity type of the MOS transistor, the threshold voltage, etc. Some specifications of the semiconductor device may impose too narrow tolerance on an ion implantation amount etc. (FIG. 8). Even if a channel doping step M and its subsequent step, i.e., a gate oxide film step N are carried out in reverse order, the same semiconductor device can be obtained.
5. Gate Oxide Film
An oxide film near the semiconductor substrate surface in the active region 132 for element formation is removed to form a gate oxide film 161 through thermal oxidation etc. (FIG. 9). Here, the thickness of the gate oxide film 161 is arbitrarily set according to the specifications of the semiconductor device, but is an important process parameter for determining a threshold voltage of the MOS transistor. After that (after the formation of the gate oxide film 161), phosphorous, B, or BF2 ions for controlling a threshold voltage may be selectively implanted, for example, into the semiconductor substrate surface in the active region 132 for element formation where the MOS transistor is formed later to thereby form the impurity doped region 201 as shown in FIG. 8.
6. Polysilicon
A polysilicon gate 170 is selectively formed on the gate oxide film 161 through CVD, photolithography, or etching (FIG. 10). Here, a process width of the polysilicon gate 170 is arbitrarily set according to the specifications of the semiconductor device, but is an important process parameter for determining a drive power of the MOS transistor. Also, after that, although not shown here, the oxide film is formed and then a second polysilicon layer for resistor may be formed.
7. Source/Drain Formation
After an oxide film 164 is formed on the P-type semiconductor substrate 102 surface by CVD or thermal oxidation, phosphorous, As, B, or BF2 ions for forming source/drain regions are implanted to the polysilicon gate 170 and the oxide film 164 in desired regions of the active region 132 for element formation in a self-alignment manner, for example, to thereby form an N-type source region 181, an N-type drain region 191, a P-type source region 182, and a P-type drain region 192 (FIG. 11). Here, the source region and drain region may each have a low-concentration impurity region called “lightly doped drain (LDD)” and a low-concentration impurity region called “double diffused drain” (DDD) and formed by diffusing impurities in a nitrogen or diluted oxygen atmosphere at about 900 to 1,100° C. The source/drain regions may have a low-concentration impurity region 134 formed by thermally diffusing impurities doped through ion implantation before forming the source/drain regions in a source/drain formation step P, at about 900 to 1,100° C. in a nitrogen or diluted oxygen atmosphere (FIG. 19). This step is hereinafter referred to as a DDD step.
8. Interlayer Insulating Film
An oxide film is deposited on the P-type semiconductor substrate 102 surface by CVD or the like and annealed at about 800 to 900° C. in a diluted oxygen atmosphere to thereby form an interlayer insulating film 163 (FIG. 12).
9. Contact Hole, Metal Wiring, and Protective Film
A contact hole 250 is selectively formed in a desired region of the interlayer insulating film 163 by photolithography or etching, and the contact hole is made smooth through wet etching, reflow technique, or the like. A metal wiring 260 is selectively formed through sputtering, photolithography, etching, or the like. A protective film 270 is deposited by CVD etc. and an opening is selectively formed in a desired region (in an external connection terminal region or the like). Here, the case of forming the single-layer metal wiring 260 is described, but plural layers may be laminated through an interlayer insulating film as the metal wiring. Also, the metal wiring may be formed such that a barrier metal forms a lower layer thereof and an antireflection film forms an upper layer. In addition, an annealing step for recovery from process damage may be carried out in a hydrogen atmosphere at 350 to 450° C. (FIG. 13).
EMBODIMENT
The monitor wafer manufacturing process Z as a feature of the present invention includes: a monitor wafer pre-process step (FIG. 1, Step A); a step of copying characteristics of a main body wafer by simultaneously processing the main body wafer and monitor wafer (FIG. 1, Step C); a monitor post-process step for the monitor element 200 (FIG. 1, Step E); a step of measuring characteristics of the monitor element 200 (FIG. 1, Step F); and a step of setting manufacturing conditions in the variation reduction step H (FIG. 1, Step G). Here, the monitoring step C of copying the quality of the half-completed main body wafer on the monitor wafer aims at simultaneously processing the main body wafer and the monitor wafer in the same apparatus. In this embodiment, a MOS diode shown in FIG. 4 is used as the monitor element 200 where the quality of the half-completed semiconductor device is copied in the monitoring step C. Hereinafter, an embodiment of the feed-forward type manufacturing method according to the present invention will be described in detail centering on a monitor wafer manufacturing process Z.
1. Monitor Pre-Process Step
The monitor element shown in FIG. 4 is described below.
Phosphorous, As, B, or BF2 ions for controlling a threshold voltage are implanted, for example, into a portion near the surface of the P-type semiconductor substrate 102 in a concentration about 10 to 50% lower than the P-type semiconductor substrate for the main body wafer to thereby form an impurity doped region. Here, the ion implantation step is desirably carried out under the same conditions as the semiconductor device whose process condition is to be predicted. This is because the variations in the ion implantation step are further reduced. The reason for using the low-concentration semiconductor substrate in this case is to improve the monitoring sensitivity.
Next, the gate oxide film 161 is formed. The gate oxide film 161 is formed with substantially the same thickness and processing conditions as those for the semiconductor device of the main body wafer. The number of monitor wafers to be inserted is determined in consideration of correlation between a variation tolerance of the threshold voltage of the MOS transistor and a variation range in a BPSG densification step. Also, the manufacturing process for the monitor wafer preceding the monitoring step C is preferably simpler than the manufacturing process for the main body wafer preceding the monitoring process C. More specifically, the monitor pre-process step A of this embodiment dispenses with the N well step K and the LOCOS step L unlike the main body pre-process step B and is preferably a simple and short-term process in terms of cost performance (FIG. 1, Step A).
2. Monitoring Step
The monitoring step C is important as a step of copying a quality of the half-completed main body wafer on the monitor wafer. In short, this is a step of accurately copying on the monitor wafer a process influence (monitor condition) by which the parameter having a high rate of contribution that influences the quality of the completed semiconductor device can be estimated. In the description of this embodiment, an interlayer insulating film formation step Q involving the large production variations is used as the monitoring step C by way of example.
A BPSG (Borophosilicate class) film 163 is formed on the gate oxide film 161 formed on the monitor water under the same processing conditions as those for the main body wafer, after which in the BPSG densification (reflow) step, the wafer as a monitoring target (monitor wafer) is processed simultaneously with the semiconductor device of the main body wafer. The BPSG densification step in the interlayer insulating film formation step Q is a step of thermally densifying the BPSG film (interlayer insulating film: silicon oxide film containing boron, phosphorous, or the like) deposited in advance by CVD or the like. Plural (about 150) large-diameter waters are simultaneously processed at a relatively high temperature of about 800 to 900° C. (in terms of the process after the source/drain formation). Thus, this step involves large production variations. The production variations caused in this step result from variations due to defects etc. around an interface between the gate oxide film 161 and the semiconductor substrate 100 and are obviously observed as variations in threshold voltage of the MOS transistor.
The monitor wafer is processed simultaneously with the main body wafer having undergone the main body pre-process step B. Simultaneous processing is only intended to more accurately copy the process influence, so if the processing conditions are the same between the main body wafer and the monitor wafer, simultaneous processing for the main body wafer and the monitor wafer is not the requisite for the present invention. This concerns copy accuracy. In order to make a more accurate copy reflecting the process influence, simultaneous processing is preferred. Similarly, the monitor wafer is determined for an insertion position and the number of wafers to be inserted in consideration of correlation between a variation tolerance and a range of variation due to defects etc. around the interface between the gate oxide film 161 and the semiconductor substrate 100 (FIG. 1, Step C).
3. Monitor Post-Process Step
In light of high-sensitivity amplification and measurement of the process influence of the monitor wafer processed simultaneously with the main body wafer (FIG. 1, Step C), in the monitor wafer post-process step (FIG. 1, Step E), the metal wiring 260 is formed on the BPSG film 163 thus formed (FIG. 1, Step E).
4. Quality Check Step
Next, the process influence of the monitor element 200 is checked (Step F). In this embodiment, the variations in impurity concentration profile of the impurity doped region 201 are derived from capacitance-voltage (CV) characteristics of the monitor element 200 of the monitor wafer to obtain information on measurements of the threshold voltage Vt or flat band voltage Vf (FIG. 1, Step F).
5. Characteristic Estimation Step
The gate oxide film thickness of the semiconductor devices mounted in great numbers on each wafer and impurity concentration profile are estimated from the measurement information. Based on the correlation between the known threshold voltage Vt of the monitor wafer and the threshold voltage Vt of the transistor formed on the main body wafer, the estimation information for estimating the threshold voltage Vt of the main body wafer is created (FIG. 1, Step G1).
6. Condition Setting Step
In this embodiment, an alloy step in a metal wiring formation step S in the main body post-process step D is selected as the variation reduction step H. According to the estimation information, alloy conditions of the metal wiring formation step S are determined in an analog fashion so as to sufficiently reduce the variations in the threshold voltage Vt. The alloy conditions of the metal wiring formation step S are determined for each wafer or every several wafers according to the estimation information or the installation position and number of monitor wafers (FIG. 1, Step G2).
7. Variation Reduction Step
The main body wafer having undergone the monitoring step C is subjected to the alloy step in the metal wiring formation step S for the main body wafer for each wafer or every several wafers under the alloy conditions determined in the condition setting step G2 (FIG. 1, Step H).
8. Subsequent Post-Process Step
Here, the main body wafer having undergone the variation reduction step H passes through the subsequent post-process steps including a wafer inspection step U and thus the pre-manufacturing process X ends.
As understood from the above description, the monitoring step C is a step of accurately copying a quality of the main body wafer on the monitor wafer. Note that the wafer pre-process step A and the monitor post-process step E need to be steps of forming the monitor element 200 such that the copied quality variation is amplified and measured.
Here, the monitoring step C or variation reduction step H may be selected in consideration of process characteristics. Also, the monitoring step C or variation reduction step H may be set in plural but is preferably set taking into account a cost. Further, the present invention is also applicable to the step causing the damage and the damage recovery step in the manufacturing process.
The present invention is directed to applications to manufacture of typical semiconductor devices and thus is applicable in a wide field of applications. For example, when the present invention is applied to manufacture of a semiconductor device including both a MOS transistor requiring a high-voltage operation and a MOS transistor requiring a low-voltage low-current operation, more specifically, a power management semiconductor device that controls charge/discharge of a lithium-ion battery, an effect of the present invention that realizes a semiconductor device with high quality and low cost can be exerted fully. However, needless to say, the present invention is not limited thereto.

## Claims

1. A manufacturing method for a semiconductor device, comprising the steps of:
selecting as a monitoring step, one step from a plurality of steps in a main body wafer manufacturing process for manufacturing a main body wafer on which the semiconductor device is formed, the monitoring step comprising BPSG densification in an interlayer insulating film formation step;
selecting as a variation reduction step, one step from main body post-process steps succeeding the monitoring step;
a monitor wafer manufacturing process for manufacturing a monitor wafer on which a monitor element is formed, the monitor wafer manufacturing process comprising a monitor pre-process step, the monitoring step, a quality check step of measuring a characteristic of the monitor element formed under the same condition as the main body wafer, and a condition setting step of setting a manufacturing condition in the variation reduction step based on a process influence measured in the quality check step; and
performing the main body post-process step under the manufacturing condition set in the condition setting step.

2. A manufacturing method for a semiconductor device according claim 1; wherein the variation reduction step comprises the step of subjecting the main body wafer to an alloy step during a metal wiring formation step for the main body wafer.

3. A manufacturing method for a semiconductor device according to claim 1; wherein the quality check step comprises measuring a capacitance-voltage characteristic of the monitor element.

4. A manufacturing method for a semiconductor device according to claim 1; wherein the monitoring step further comprises the step of copying onto the monitor element characteristics of the main body wafer by simultaneously processing the main body wafer and the monitor wafer through BPSG densification during formation of the interlayer insulating film.

5. A manufacturing method for a semiconductor device, comprising the steps of:
forming a main body wafer having an interlayer insulating film;
providing a monitor wafer on which a monitor element is formed;
copying onto the monitor element characteristics of the main body wafer by simultaneously processing the main body wafer and the monitor wafer through BPSG densification during formation of the interlayer insulating film;
measuring a characteristic of the monitor element by checking a process influence of the monitor element;
setting manufacturing conditions in accordance with the process influence of the monitor element; and
reducing variations in electric characteristics of the main body wafer in accordance with the set manufacturing conditions.

6. A manufacturing method for a semiconductor device according to claim 5; wherein the reducing step comprises the step of subjecting the main body wafer to an alloy step during a metal wiring formation step for the main body wafer.

7. A manufacturing method for a semiconductor device according to claim 5; wherein the measuring step comprises measuring a capacitance-voltage characteristic of the monitor element.