JPH08293448A - Measuring method for superposing accuracy - Google Patents

Abstract

PURPOSE: To provide a measuring method for superposing accuracy that is not limited by sort of superposed regions. CONSTITUTION: A substrate 12 includes a superposed region 5, a photosensitive material pattern 6, a peripheral region 7, and electrodes 8-11. The peripheral region 7 is formed through a doping process and a step forming process prior to a superposed region 5 forming process. A mask is superposed on the superposed region 5, which is a doped region formed through the precedent process. Here, the position of the superposed region 5 and that of the photosensitive material pattern 6 are recognized by different methods based on different principles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring overlay accuracy during a mask overlay process in semiconductor manufacturing.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor device, a step of forming a film of a photosensitive material, a step of superposing a mask on a region to be superposed formed in a previous step, and a light or electron beam or X-ray through the mask. In the step of forming a photosensitive material pattern by the step of irradiating a line and the step of removing the photosensitive material in unnecessary portions (hereinafter, the above steps are collectively referred to as a mask overlapping step) The overlay accuracy of the mask with respect to the overlay area is determined by visually observing with an optical microscope the monitor pattern that is simultaneously formed in each mask overlay step or the main pattern that constitutes the semiconductor device. It was measuring accuracy.

However, in the miniaturization of semiconductor devices, it has become impossible to measure the overlay accuracy of the mask with respect to the overlay area by the above visual observation. Therefore, instead of visual observation, the overlapped region and the photosensitive material pattern are respectively recognized as an arbitrary reference position or a relative position from the arbitrary reference region (hereinafter, referred to as position recognition).
However, a method of measuring the relative position of the photosensitive material pattern with respect to the overlapping area, that is, the overlay accuracy of the mask with respect to the overlapping area is performed.

A conventional method of measuring mask overlay accuracy will be described. FIG. 3 is a plan view of a measurement mark used in a conventional mask overlay accuracy measuring method. 4 is a cross-sectional view taken along the line AB of FIG. In the figure, 1 is a superposed area, 2 is a photosensitive material pattern, 3 is a peripheral area or substrate, and 4 is a reference position. Conventionally, the method of measuring the overlay accuracy of the photosensitive material pattern 2 with respect to the overlay area 1 is to recognize the position by the difference in the reflectance of light generated from the film quality or the step (hereinafter referred to as contrast). There is. That is, the overlapped region 1 recognizes the position with respect to the reference position 4 based on the contrast with the peripheral region 3. Further, the photosensitive material pattern 2 recognizes the position with respect to the reference position 4 based on the contrast with the overlapping region 1. The positions of the overlapping area 1 and the photosensitive material pattern 2 are recognized from the same reference position 4. Therefore, by calculating the relative position of the photosensitive material pattern 2 with respect to the overlapping area 1,
It is possible to measure the overlay accuracy of the mask with respect to the overlay area 1.

[0005]

However, in the conventional position recognition of the overlapped region 1, the contrast generated due to the difference in film quality due to the presence or absence of LOCOS, polysilicon, metal, or the like, or the step difference in the case of the same film quality is recognized. I was going. Therefore, the overlapped region 1 is limited to only the region formed by the process of performing wet or dry etching after the mask overlapping process is completed. Therefore, for example, a region (hereinafter referred to as an impurity introduction region) formed by an impurity injection process or an impurity diffusion process (hereinafter, the impurity injection process and the impurity diffusion process are collectively referred to as an impurity introduction process) at the time of mask superposition process. It was not possible to measure the overlay accuracy of the mask with respect to.

Further, in the case of a solid-state image pickup device, the solid-state image pickup device has a transfer channel in the V direction (hereinafter referred to as a transfer channel region), a region for performing photoelectric conversion and charge accumulation of the photodiode (hereinafter, the photodiode). Regions), regions for separating the transfer channel from the substrate and the photodiode region (hereinafter referred to as separation regions), and the like, the characteristics of the solid-state imaging device deteriorate when the relative position changes. Therefore, in the mask superposing step, the transfer channel region, the photodiode region or the separation region must be used as the superposed region 1 to superpose other regions. In this case, when the masks are superposed as the superposed regions 1 such as LOCOS,
Since it is not a region where overlay accuracy is originally required, it is not possible to obtain overlay accuracy required for the required characteristics of the solid-state imaging device. However, the transfer channel region, the photodiode region, and the isolation region are all formed by the mask superposing step and the impurity introducing step after the mask superposing step. Therefore, the conventional overlay measurement method cannot recognize the position of the transfer channel region, the photodiode region, or the separation region by contrast. For this reason,
With the transfer channel region, the photodiode region, or the separation region as the overlapping region 1, it is impossible to measure the overlay accuracy in the mask overlaying process for forming the other regions.

The same applies to the bipolar transistor. The bipolar transistor must form an emitter region in the base region. In this case,
When the relative position of the emitter region with respect to the drain region changes, the characteristics of the bipolar transistor deteriorate. However, like the solid-state imaging device, the base region is formed by the mask superposing step and the impurity introducing step after the mask superposing step. Therefore, the conventional overlay measuring method cannot measure the overlay accuracy in the mask overlay process for forming the emitter region with the base region as the overlay region 1.

For the above reasons, the solid-state image pickup device and the bipolar
The la-transistor cannot measure the overlay accuracy with respect to the desired overlay area 1. Therefore, it is impossible to correct the overlay deviation during the mask overlay process, and there is a problem that the characteristics of the solid-state imaging device and the bipolar transistor are deteriorated.

In view of the above-mentioned problems, the present invention provides a method of measuring the overlay accuracy with the overlay region 1 to be obtained in the overlay process of masks of a solid-state image pickup device, a bipolar transistor and the like.

[0010]

In order to solve the above-mentioned problems, the method of measuring the overlay accuracy of the present invention provides a method of recognizing the position of the overlay area and the photosensitive material pattern in the mask overlay step. It is different from the position recognition.

Further, according to the present invention, the superposition accuracy is measured by further recognizing the position of the overlapped region and the position of the photosensitive material pattern, which is characterized by being the impurity introduction region.

[0012]

By the above-described method of measuring the overlay accuracy, it is possible to measure the overlay accuracy of the solid-state imaging device and the region to be overlaid 1 which is required in the step of overlaying the mask of the bipolar transistor.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of measuring overlay accuracy according to the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of a measurement mark used in a method of measuring overlay accuracy of a mask showing an embodiment of the present invention. Further, FIG. 2 shows C of FIG.
FIG.

In the figure, reference numeral 5 is an overlapping area, 6 is a photosensitive material pattern, 7 is a peripheral area, 8, 9, 10 and 11.
Is an electrode, 12 is a substrate, and 13 is a reference position for recognizing the position of the photosensitive material pattern 6.

The peripheral region 7 is formed by an impurity introducing process and a step forming process in the preceding process of forming the overlapped region 5. The present invention is characterized in that the overlapped region 5 is an impurity introduction region. Another feature is that the recognition of the position of the overlapped region 5 and the recognition of the position of the photosensitive material pattern 6 are performed by a method using a different principle.

In the present embodiment, the peripheral region 7 is used as a reference region for recognizing the position of the impurity introduction region which is the overlapping region 5. The method will be described below. When a predetermined voltage is applied between the electrodes 8 and 9, the current flows in the peripheral region 7 below the overlapped region 5. At that time, the current flows in the peripheral region 7
By the sheet resistance value and the geometrical shape of the current path narrowed by the overlapped region 5, a constant resistance is received, and the relative positions of the overlapped region 5 and the peripheral region 7 are changed, The current changes accordingly. Therefore,
The current value flowing between the electrodes 8 and 9, the electrodes 9 and 10, the electrodes 10 and 11, and the electrodes 11 and 8 is measured. By comparing the respective current values, the position of the overlapping region 5 can be recognized with the peripheral region 7 as a reference region.

The position of the photosensitive material pattern 6 is recognized as follows.
The peripheral area 7 is used as a reference area. The method will be described below. The photosensitive material pattern 6 recognizes the position with respect to the reference position 13 based on the contrast with the substrate 12. Similarly, the peripheral region 7 recognizes the position with respect to the reference position 13 based on the contrast with the substrate 12. Photosensitive material pattern
The positions of the peripheral area 7 and the peripheral area 7 are recognized from the same reference position 13. Therefore, by calculating the relative position of the photosensitive material pattern 6 with respect to the peripheral area 7, the photosensitive material pattern 6 is defined with the peripheral area 7 as a reference area.
The position can be recognized.

As described above, the overlapping area 5 and the photosensitive material pattern 6 are used for position recognition with the peripheral area 7 as a reference area. Therefore, by calculating the relative position of the photosensitive material pattern 6 with respect to the overlapping area 5, the overlay accuracy of the mask with respect to the overlapping area 5 can be measured.

Conventionally, in the method of measuring the overlay accuracy in the mask overlay process, the position of the overlay region 5 is recognized by the difference in film quality due to the presence or absence of LOCOS, polysilicon, metal, or the like, or when the film quality is the same. Was carried out by generating contrast due to the step. Therefore, the overlapped region 5 is limited to only the region formed by the step of performing wet or dry etching after the mask overlapping step.

Further, conventionally, as a method of measuring the overlay accuracy of different impurity introduction regions, the measurement is carried out after the mask overlay step and the impurity introduction step are completed. For this reason, the overlay accuracy cannot be measured during the mask overlay process, and the overlay deviation cannot be corrected during the mask overlay process.

However, according to the method of the present invention, the overlay accuracy can be measured during the mask overlaying process even when the overlay region 5 is an impurity introduction region. Therefore, by performing the advance processing of an arbitrary number of wafers and performing the advance measurement of the overlay accuracy, it is possible to correct the overlay deviation obtained from the advance measurement when processing the remaining wafers. Further, when it is determined that the characteristic of the semiconductor device is deteriorated due to the misalignment, the photosensitive material pattern 6 may be removed to reprocess the mask overlaying process.
Therefore, it is possible to prevent the characteristics of the semiconductor device from being deteriorated due to the misalignment of the masks during the mask superimposing process, and increase the yield rate of the semiconductor devices.

In particular, in the case of a solid-state image pickup device, the characteristics of the solid-state image pickup device are deteriorated when the relative positions of the regions formed by the impurity introduction process such as the transfer channel region, the photodiode region and the separation region are changed. Therefore, in the mask superposing step, the transfer channel region, the photodiode region or the separation region must be used as the superposed region 5 to superpose other regions.

The same applies to the bipolar transistor. In the bipolar transistor, the emitter region must be formed in the base region formed by the mask overlapping process and the impurity introducing process. In this case, when the relative position of the emitter region with respect to the base region changes, the characteristics of the bipolar transistor deteriorate.

Therefore, the overlay accuracy measuring method of the present invention is particularly useful for a semiconductor device such as a solid-state image pickup device or a bipolar transistor which requires overlay accuracy of different impurity introduction regions.

While the above invention has been described in detail by way of illustration and example method for clarity of understanding, it will be apparent that certain changes and modifications may be made within the scope of the appended claims. In particular, in this embodiment, the position of the overlapped region 5 is recognized by using the difference in sheet resistance between the overlapped region 5 and the peripheral region 7. However, in the present invention, it is obvious that the position of the overlapping region 5 can be recognized by other methods.

[0026]

As described above in detail, according to the present invention, even when the region to be superposed is the impurity introduced region, it is possible to correct the misalignment during the mask superposing process. is there. Therefore, in the mask overlaying process, the preceding wafer is processed, the overlay accuracy is measured, and the overlay deviation obtained from the measurement result of the preceding wafer during the processing of the main body wafer can be corrected. it can. Further, when it is determined that the characteristics of the semiconductor device are deteriorated due to the misalignment, it is possible to reprocess the mask superimposing step by removing the photosensitive material pattern. Therefore, it is possible to prevent the characteristics of the semiconductor device from being deteriorated due to the misalignment of the masks during the mask superimposing process, and increase the yield rate of the semiconductor devices.

[Brief description of drawings]

FIG. 1 is a plan view of a measurement mark showing an embodiment of a method for measuring overlay accuracy according to the present invention.

FIG. 2 is a sectional view taken along the line C-D of FIG. 1 showing an embodiment of the overlay accuracy measuring method of the present invention.

FIG. 3 is a plan view of a measurement mark showing a conventional method of measuring overlay accuracy.

FIG. 4 is a cross-sectional view taken along the line AB of FIG. 3, showing a conventional method of measuring overlay accuracy.

[Explanation of symbols]

 5 Overlaid Area 6 Photosensitive Material Pattern 7 Peripheral Area 8 Electrode 9 Electrode 10 Electrode 11 Electrode 12 Substrate 13 Reference Position

Claims (2)

[Claims] 1. A method of measuring overlay accuracy, characterized in that, in the mask overlay step, position recognition of a region to be overlapped and position recognition of a photosensitive material pattern are performed by different methods. 2. An overlay accuracy characterized by performing position recognition of a region to be overlapped, which is an impurity introduction region, and position recognition of a photosensitive material pattern, in a mask overlaying process. Measuring method.