JP3641378B2 - Process monitoring method for semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a process monitoring method for monitoring reliability in a manufacturing process of a semiconductor device such as an LSI. More particularly, the present invention relates to a process monitoring method for a semiconductor device that can accurately monitor the reliability of a thin oxide film such as a gate oxide film, including the influence of a cleaning process in a manufacturing process.
[0002]
[Prior art]
Conventionally, in the manufacturing process of a semiconductor device, for example, when evaluating the film quality of an oxide film, a monitor pattern is formed on a part of a semiconductor wafer (wafer-like semiconductor substrate), and a current is applied to the monitor pattern. A method of evaluating the quality of the film formed on the semiconductor wafer by QBD inspection of how many coulombs to destroy or TZBD inspection of how many volts it can withstand by applying a voltage is employed.
[0003]
For example, as shown in FIG. 4, a monitor pattern for monitoring such an oxide film is formed by placing a thin evaluation oxide film 22 as a tunnel oxide film or a gate oxide film on a semiconductor substrate 21 between LOCOS oxide films 24. A polysilicon film 25 as a conductive film is formed thereon, and a current or voltage is applied between the polysilicon film 25 and the semiconductor substrate 21 using the polysilicon film 25 as one electrode. Can be done. The size of the monitor pattern is formed between the LOCOS oxide films 24 so as to be about one to 1.5 semiconductor chips to be formed on the semiconductor wafer, and the evaluation oxide film 22 is within the range. In this process, the tunnel oxide film and the gate oxide film are formed to a thickness used for the chip. The reason why the evaluation oxide film is formed in such a uniform thickness is that a thin oxide film is formed with as large an area as possible, so that a defect is detected even if a part of the oxide film has a defect. This is because it is considered that the reliability can be increased.
[0004]
[Problems to be solved by the invention]
As described above, in manufacturing a conventional semiconductor device, a pattern for process monitoring is formed and the reliability is sufficiently ensured. However, there is still a problem that a dielectric breakdown of an oxide film may occur during use of an actual LSI or the like.
[0005]
The inventors of the present invention have made extensive investigations in order to improve the reliability of the oxide film by making it completely correspond to the inspection by the process monitor in the manufacturing process. After that, the reason why the reliability of the oxide film decreases is that the residue of the cleaning liquid from the cleaning process etc. before the formation of the oxide film remains, the watermark is formed, and the watermark deteriorates the film quality of the oxide film later And found that it is in reducing reliability.
[0006]
The present invention has been made in view of such a situation. The inspection by the process monitor is made to correspond to the reliability of the oxide film in the actual product, and the quality of the oxide film is accurately inspected by the process monitor. An object of the present invention is to provide a process monitoring method for a semiconductor device that can improve the performance.
[0007]
[Means for Solving the Problems]
As a result of intensive studies in order to make the inspection by the process monitor correspond to the reliability of the oxide film in the actual product, the present inventors have conducted a cleaning process performed before and after the formation of the oxide film as described above. It has been found that the formation of the watermark due to the above causes the deterioration of the oxide film, and that the influence of the watermark hardly appears in the conventional oxide film having a uniform thickness. That is, after the cleaning process, the semiconductor wafer is rotated by a spinner, and the cleaning liquid is scattered and dried. If the oxide film has irregularities, the cleaning liquid remains in the concave portions, and the above-described watermark is easily formed at the corners. However, in the conventional uniform oxide film having a large area, when the cleaning liquid is blown by the spinner, it almost flies and does not remain in the corners.
[0008]
The process monitoring method for a semiconductor device according to the present invention provides an oxide film for process monitoring on the surface of a wafer made of a semiconductor substrate, and a conductive pattern is formed thereon to form a monitoring pattern. A process monitoring method for evaluating the film quality of the oxide film by applying a voltage and / or current between the film and the film, wherein the monitor pattern is the same as or more than a product chip formed on the wafer It formed in a large area, and, and performing the same or more small I凹 convex and concavo-convex pattern formed on the chip for the product to form the pattern of the oxide film having a plurality.
[0009]
According to this method, an uneven pattern of an oxide film that is similar to or finer than the pattern of an actual LSI chip or the like is formed. Therefore, when drying with a spinner after cleaning, the cleaning liquid is the same as the actual pattern. When the corrosive liquid remains in the concave portion due to the scattering method, it remains in the oxide film portion of the monitor pattern as well, and the deterioration of the oxide film due to the influence can be detected by the monitor pattern.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, a process monitoring method for a semiconductor device according to the present invention will be described with reference to the drawings.
[0011]
The process monitoring method for a semiconductor device according to the present invention has an active toe of each memory cell of the EEPROM on the semiconductor substrate 1 as shown in FIG. 1 (a), which shows an EEPROM monitoring pattern having a tunnel window. A gate oxide film 2 is provided at an interval (small active region) equal to or smaller than an active (active to active) space (interval of active regions sandwiching a LOCOS oxide film). A tunnel window 3 having the same size as the tunnel window of the cell is formed. A LOCOS oxide film 4 is formed between the gate oxide films 2, and a monitor pattern 10 is formed by providing, for example, a polysilicon film 5 which is a conductive film so as to cover the entire portion of the monitor pattern. . As shown in FIG. 1B, an explanatory plan view of the pattern 10 before the polysilicon film 5 is provided is a tunnel window 3 which is a thin oxide film and a LOCOS oxide film which is not shown in FIG. 4 are formed in a matrix. The size of this tunnel window is formed in accordance with the actual cell pattern or smaller, but is usually on the order of submicron. These oxide films have different thicknesses, and the surface is uneven as shown in FIG. 1A. In particular, the tunnel window 3 is formed as a recess in the gate oxide film 2.
[0012]
In order to form the tunnel window 3, for example, a part of the gate oxide film where the tunnel window is formed is etched to expose the semiconductor layer, and then the whole is oxidized to form a thin oxide film of the tunnel window 3. At the same time, other gate oxide films and the like are oxidized and thickened, and only the tunnel window 3 is formed to be particularly thin. In order to expose the semiconductor layer in the formation portion of the tunnel window 3, a mask such as a photoresist film is formed and the gate oxide film is etched, and then the photoresist film is removed and cleaning is performed, and the cleaning liquid is blown off by a spinner. And let it dry. Thereafter, an oxide film is formed by oxidation or the like, and the tunnel window 3 is formed as described above. The tunnel window 3 and the like are formed simultaneously by the same process as the formation of the tunnel window of the cell.
[0013]
Thereafter, a conductive film is formed, for example, by depositing a polysilicon film 5 on the entire surface of the monitor oxide film, and the monitor pattern 10 is formed as an electrode for performing a reliability test of the oxide film.
[0014]
As described above, the monitor pattern 10 is about the same size as the chip formed on the wafer and about 1.5 times as large as the above-mentioned active region. The number of the wafers 11 may be smaller than the pattern), and as shown in FIG. Layers necessary for the cell, such as an interlayer insulating film and a gate insulating film, are formed at the cell formation location, and after all the wafer processes are completed, a voltage is applied between the polysilicon film 5 and the semiconductor substrate 1 described above. Alternatively, the tunnel oxide film 3 is evaluated by applying a current and examining the leakage current and breakdown voltage. That is, for example, when the applied current is sequentially increased, the number of coulombs to be destroyed (QBD) according to the current value at the time of destruction is examined by each monitor pattern, A lot can be determined to be defective.
[0015]
According to the present invention, the etching solution is left in the corners of the recesses or washed with a dirty cleaning solution, and the residual solution remains in the corners of the recesses, so that the oxidation process proceeds with the watermark formed. In such a case, the film quality can be inspected with certainty of the influence of the watermark on the oxide film. That is, the monitor pattern is formed of an oxide film pattern having the same level of irregularities as the actual memory cell pattern (actual pattern). For this reason, when cleaning liquid or the like soiled in the actual pattern remains as a watermark, it remains in the same manner in the monitor pattern, and inspection can be performed in the same state as the actual pattern. This is the idea that the reliability is improved by forming a thin oxide film to be inspected as wide as possible in the past, but the same as the actual pattern even if the thick part of the oxide film increases This is based on a change in the idea that it is important to form unevenness.
[0016]
More specifically, as described above, drying after cleaning is performed by flying with a centrifugal force by a spinner. However, the tunnel window 3 and the like described above are formed in very small concave portions of submicron order of about 0.6 μm. It has become. For this reason, even if the spinner rotates, the etching solution and the cleaning solution contained in the recesses cannot be easily blown off and remain as residues, which tend to become watermarks as described above. If the oxidation treatment is performed as it is, the oxidation proceeds with the residue remaining. Therefore, if the etching solution is completely replaced and the cleaning water is a clean solution that is not very dirty, even if the solution remains in the recess, it can be dried by heating during the oxidation treatment. If liquid remains or dirty cleaning liquid remains, a corrosive residue will accumulate even after drying. In particular, when a thin oxide film such as a tunnel window is corroded, there is a problem that dielectric breakdown is likely to occur. However, if there is dirt such as cleaning water, the monitor pattern has a fine recess of the same degree, and the corrosive residue remaining in the recess corrodes the tunnel window of the monitor pattern. Therefore, it is possible to reliably grasp the contamination of the cleaning liquid or the insufficient removal of the etching liquid.
[0017]
On the other hand, in the conventional method, since a thin oxide film is formed over a wide area, when it is dried by a spinner, it almost flies without remaining in the recess and does not remain as a watermark. Therefore, even if etching liquid remains in the actual pattern or dirty cleaning water remains, it does not remain in the monitor pattern, the influence cannot be known, and it has not been possible to monitor accurately. .
[0018]
FIG. 3 is an explanatory diagram showing another example of the monitor pattern of the present invention. This example is an example of a monitor pattern such as a CMOS or LOGIC IC, and has a two-stage LOCOS structure in which an intermediate thickness oxide film 6 having an intermediate thickness is formed between the LOCOS oxide film 4 and the gate oxide film 2. . In this example, the gate oxide film 2 is thin and its reliability is required, but its size is formed with the same width as the actual MOS pattern, so that the influence of the watermark can be reliably monitored. it can. The effect of this watermark appears surely when the size of the concave portion is about 1.2 μm square or less, and the design rule below this has a great merit of forming a monitor pattern that matches the actual pattern as in the present invention. appear.
[0019]
【The invention's effect】
According to the present invention, even if an etching solution or a dirty cleaning solution remains in a small recess, the reliability of the oxide film can be reliably monitored in consideration of the influence. As a result, the reliability of a highly integrated LSI or the like can be greatly improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of a monitor pattern used in the monitoring method of the present invention.
FIG. 2 is an explanatory diagram of an example of forming a monitor pattern on a semiconductor wafer.
FIG. 3 is an explanatory diagram of another example of a monitor pattern used in the monitoring method of the present invention.
FIG. 4 is an explanatory diagram of an example of a conventional monitor pattern.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Gate oxide film 3 Tunnel window 4 LOCOS oxide film 5 Polysilicon film 10 Monitor pattern 11 Wafer

Claims (1)

An oxide film for process monitoring is provided on the surface of a wafer made of a semiconductor substrate, and a conductive pattern is provided thereon to form a monitor pattern, and a voltage and / or current is applied between the semiconductor substrate and the conductive film. A process monitoring method for evaluating a film quality of the oxide film by applying, wherein the monitor pattern is formed in an area equal to or larger than a product chip formed on the wafer, and for the product process monitoring method of a semiconductor device that performs the same or greater than the smaller I凹 convex and concavo-convex pattern formed on the chip to form the pattern of the oxide film having a plurality.

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