JPS6138448B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a comparative inspection mechanism for photomasks,
In particular, in the photomask manufacturing process, a plurality of photomask patterns are formed on a mask substrate by copying a reticle pattern with a pattern several times to ten times the size of the photomask pattern onto the mask substrate. In this case, a comparison test is automatically performed between the reticle pattern and a formed photomask pattern, or a comparison test is performed between two photomasks having patterns with different magnifications that are copied from the same reticle pattern and have different magnifications. The present invention relates to a comparative inspection mechanism for photomasks that can be used to perform photomask comparison and inspection.

A photomask manufacturing method in which a photomask pattern is formed by reducing a reticle pattern onto a mask substrate made of glass or the like has been widely used in the past, but during this reduction process, dust, dirt, etc. may accidentally be deposited on the reticle pattern surface. There are cases where a plurality of patterns formed on a photomask are transferred as defective patterns due to the presence of a defect cause. Therefore, as a defect inspection method for photomask patterns, if an inspection device that can automatically compare and inspect the manufactured photomask and reticle is installed at the manufacturing site, it is possible to accurately inspect the presence or absence of defects in photomask patterns. I can do it. On the other hand, for the purpose of improving the yield per wafer of a certain size in the manufacture of integrated circuits, etc., the reduction rate from a reticle pattern to a photomask pattern is increased or decreased from the normal reduction rate even though the reticle pattern is the same. In some cases, a photomask is formed by reduction on a photomask substrate, and in such a case, it is desired to perform a comparison inspection between two photomasks having patterns with different reduction ratios.

However, conventionally, there has been an inspection mechanism that can perform a comparison inspection of a reticle and a photomask formed by reduction based on the reticle, or a comparison inspection of two photomasks having patterns with different reduction ratios based on the same reticle pattern. There is currently no suitable product available.

Therefore, an object of the present invention is to automatically compare and verify a reticle pattern and a photomask pattern formed by reduction from the reticle pattern, or two photomasks formed from the same reticle pattern at different reduction ratios. It is an object of the present invention to provide a comparison inspection mechanism for photomasks that can inspect the presence or absence of defective photomask patterns.

According to the present invention, a reticle having a reticle pattern or a first photomask having a plurality of patterns formed by reduction from the reticle pattern, and a first photomask having a plurality of patterns formed by reduction from the same reticle pattern and different from the first photomask pattern are provided. A second photomask having a plurality of patterns with different ratios is placed on individually movable first and second inspection stages, and a comparison and verification inspection of the patterns is performed by irradiating inspection light. In the comparison inspection mechanism, the inspection light introduced from the same light source is separately irradiated to both patterns placed on the corresponding first and second inspection stages through first and second optical systems, and One optical system of the first optical system and the second optical system is constituted by a lens system with a constant magnification, and the other optical system is constituted by a zoom lens system, and both patterns having different sizes are formed by the zoom lens. A photomask comparison/inspection mechanism is provided, which is characterized in that it is possible to perform comparison and verification by adjusting magnification to the same magnification using a system. Hereinafter, the present invention will be explained in more detail based on the accompanying drawings.

FIG. 1 is a plan view showing a reticle and a photomask having a plurality of patterns copied from the reticle pattern formed on the reticle, and as is clear from the plan view, the reticle pattern 10 of the reticle 8 is Generally, the size is several to ten times larger than each photomask pattern 12 included in the photomask substrate 14. Therefore, from the reticle pattern 10 to the photomask pattern 12
When forming a photomask pattern, a method is adopted in which a plurality of photomask patterns 12 are obtained by repeatedly copying and printing the reticle pattern 10 onto the photomask substrate 14 through an optical lens system. Therefore, if, for example, dust 10a is attached in contact with the reticle pattern 10, this dust 10a will come into contact with each photomask pattern 12 on the photomask substrate 14 and be transferred as a blemish pattern 12a, and as a result, the dust 10a will be transferred onto the photomask substrate 14. This will result in the formation of a defective pattern. 10a of dust was collected during the inspection process in the photomask manufacturing process.
By comparing and comparing the photomask with the reticle 8 that has been removed and cleaned, defective patterns can be easily detected, and photomask patterns that have passed the inspection can be compared with photomask patterns formed from the same reticle pattern 10 with different reduction ratios. If it is used as a so-called inspection master for comparison and verification inspection of another second photomask having a second photomask, it becomes possible to easily detect a defective pattern of the second photomask.

FIG. 2 is a mechanical diagram showing the overall configuration of an inspection apparatus equipped with a photomask comparison inspection mechanism according to the present invention. The apparatus is equipped with a first stage 22 and a second stage 24, and one of the first and second stages 22 and 24 has a reticle pattern 10.
A reticle 8 or a master photomask having a reticle 8 is placed as a reference for comparison inspection, and a photomask to be inspected on which a plurality of photomask patterns 12 are formed based on the reticle 8 is placed on the other stage. Both stages 22 and 24 are provided so as to be movable in the same plane or in two parallel planes, for example, in the X-axis direction perpendicular to the plane of the paper in FIG. This is achieved by a drive mechanism having respective drive sources 26 and 28. Further, the apparatus is provided with an optical mechanism for emitting comparative inspection light, which is equipped with objective microscopes 30 and 32 above the first stage 22 and the second stage 24, respectively. In both objective microscopes 30 and 32, one microscope 30 has a fixed magnification lens, and can be focused on the reticle pattern 10 or photomask pattern 12 of the first stage 22 by manual operation or by operation of an automatic focusing mechanism. A feeding mechanism is provided to allow this.
The other microscope 32 has a zoom lens, for example, a lens that can freely change the magnification to a larger or smaller magnification than the fixed magnification of the microscope 30, and can be operated manually or by an automatic focusing mechanism. Reticle pattern 10 of second stage 24
Alternatively, a feeding mechanism is provided so that the photomask pattern 12 can be focused. Note that the zoom lens of the microscope 32 is operated by a drive motor 6, which will be described later.
8. The zoom magnification can be changed by operating a DC motor, for example. A comparative inspection light such as a laser beam is emitted from the light source S through the objective microscopes 30 and 32 of these irradiation optical mechanisms toward the reticle or master photomask and photomask to be inspected on the first and second stages 22 and 24. It is becoming irradiated. That is, in FIG. 2, the laser comparison inspection light emitted from the laser light source S passes through the scanning mirror 34 and is refracted by the reflecting mirrors 36 and 38, and then passes through the corresponding microscope 3.
It was introduced in 0.32. The above-mentioned scanning mirror 34 can be rotated so that the comparative inspection light scans the reticle pattern 10 or master pattern (hereinafter referred to as reference pattern) and photomask pattern 12 on both stages 22 and 24, for example, in the Y-axis direction. It is set in . Both microscopes 30,
The comparison test laser beams that have passed through 32 pass through the reference pattern and photomask pattern 12, respectively, and then further pass through condenser lenses 40 and 42, and are received by photomal elements 44 and 46, which are well-known photoelectric elements. At this time, the photoelectric elements 44, 46
Electric signals corresponding to the pattern shapes are respectively emitted from the circuits, and after being amplified by amplifiers 48 and 50, they are both input to a signal processing circuit 52.
After the two electric signals are compared and verified, the comparison result is outputted from the output terminal of the signal processing circuit 52. That is, in the signal processing circuit 52, if there is a perfect match between the reference pattern and the photomask pattern 12, the difference between both electric signals is zero, and a defective pattern 12a is formed on the photomask together with the photomask pattern 12. If so, signal processing is realized in which the difference value between the two electrical signals is different from the zero value. In this case, in the comparison verification inspection process described above, the laser beam for comparison irradiation scans the reference pattern and the photomask pattern 12 in the Y-axis direction by the rotating operation of the scanning mirror 34, and at the same time, the reticle (or master both the first and second stages 2 on which the photomask) and the photomask to be inspected are placed.
By simultaneously moving 2 and 24 in the X-axis direction, the entire pattern area is scanned. Therefore, the signal processing circuit 52 is coupled to a control section 54 that controls the movement of both stages 22 and 24 in the X-axis direction, so that the reference pattern and the photomask pattern 12 are simultaneously moved in the X-axis direction. Both electrical signals of amplifiers 48 and 50 are activated in response to an output signal indicating that the current state is present.

Now, in carrying out the comparison inspection between the reference pattern and each photomask pattern 12, the microscope 3
0 and 32, respectively, and the zoom lens of the microscope 32 must match the magnifications of the two patterns, as will be described later. Focusing is performed manually or using an automatic focusing mechanism as an early step in the inspection process. Also, magnification matching is achieved by operating the zoom lens of the microscope 32 as described below each time between the reference pattern and each photomask pattern 12 of the photomask to be inspected. Now, assuming that both focusing and magnification matching have been achieved, the comparison verification process will be described below.

As described above, scanning in the Y-axis direction is performed by the scanning mirror 3 during the comparison inspection process between the reference pattern and the photomask pattern 12 of any one of the photomasks to be inspected.
4, the movement of the first stage 22 and the second stage 24 in the X-axis direction is performed by the reference pattern, especially the reticle pattern 1
0 has a size several to ten times larger than each photomask pattern 12, so both stages 22 and 24 are configured to move simultaneously over a movement amount matching this magnification. must be maintained. That is, for example, the reticle 8 is placed on the first stage 22.
is placed on the second stage 24, and the photomask to be inspected is placed on the second stage 24.
A configuration must be adopted in which the second stage 24 moves in the X-axis direction over the photomask dimension T ₂ in FIG. 1 while the second stage 24 moves in the X-axis direction over the reticle dimension T ₁ in FIG. 1. It is. For this purpose, a special configuration is provided for controlling the operation of the drive sources 26 and 28 by the control section 54. That is,
In the embodiment of FIG. 2, the first stage 22 is provided with a conventional optical potentiometer 56, and the second stage 24 is provided with a similar optical potentiometer 58. 58 are respectively connected to the input terminals of the control unit 54, so that the drive sources 26 and 28 move the first stage 22 in the X-axis direction over a distance _T1 at the same time, as will be described later. Further, the second stage 24 is similarly moved in the X-axis direction over a distance _T2 .

FIG. 3 shows the reticle pattern 10 and photomask pattern 12 in the X-axis direction of both stages 22 and 24.
FIG. 2 is a schematic diagram of a mechanism for matching the magnification of the image. In FIG. 3, optical potentiometers 56 and 58 are the same potentiometers as shown in FIG. A configuration in which the laser beams are received after being sequentially reflected at a width portion corresponding to between both ends of the reticle on the stage 22 and a width portion corresponding to between both ends of one chip of the photomask on the second stage. is taken. That is, in FIG. 3, on the reticle side, as the rotating mirror 60 rotates, both portions corresponding to both ends of the reticle
The laser beam reflected between R ₁ and R ₂ is received between both ends 56a and 56b of the optical potentiometer 56, while on the photomask side, the laser beam is received by the rotating mirror 6.
As the laser beam rotates, the laser beam reflected between the portions M ₁ and M ₂ corresponding to both ends of one chip of the photomask is transmitted to the portions 58a and 58 of the optical potentiometer 58.
A configuration is provided in which light is received between mirrors 60 and 8b.
In this case, the stages 22 and 24 are provided to rotate at a constant speed in order to cause the stages 22 and 24 to move at a constant speed in the X-axis direction. Note that the distance between R ₁ and R ₂ described above corresponds to the dimensional distance T ₁ described above, and the distance between M ₁ and M ₂ corresponds to the dimensional distance T ₂ described above. Now, upon reception of light, the optical potentiometers 56, 58 produce a voltage signal at their output terminals, which in the case of the optical potentiometer 56, for example, has a portion R _{1 .}
Upon receiving the laser beam reflected by
_R1 and a DC voltage V _R2 is generated by receiving the laser light reflected at the portion _R2 , so that ultimately a DC voltage value V _R1 -V _R2 is generated from the output terminal. Similarly, in the case of the optical potentiometer 58, the partial
By receiving the laser beams reflected by M ₁ and M ₂ , a DC voltage value V _M1 -V _M2 is ultimately generated from the output terminal. And these voltage values V _R1 −V _R2 , V _M1
-V _M2 are each input to the control unit 54 and D-A
After the conversion, the voltage level ratio is adjusted in the control unit 58 so as to accurately match the magnification ratio of the reticle pattern 10 and the photomask pattern 12, and the DC voltage signals are converted into DC voltage signals by A-D conversion again. After being converted, it is supplied to each DC motor of the drive sources 26 and 28. Therefore, in response to the operation of the DC motor, the first stage 22 and the second stage 24 are moved to their respective dimensional values via the drive sources 26 and 28.
It moves by the movement distance corresponding to T ₁ and T ₂ . FIG. 4 is a system diagram illustrating the above-mentioned voltage signal processing performed in the control section 54. In addition, optical potentiometers 56, 58
As is well known, generates a voltage signal proportional to the light receiving position, so the above voltage values V _R1 -V _R2 and V _M1 - V _M2
Although the ratio between the reticle pattern 10 and the photomask pattern 12 is approximately the same as the comparison between the reticle pattern 10 and the photomask pattern 12, since the magnification matching process is performed extremely precisely in the control unit 54, the error in the movement of the stages 22 and 24 in the X-axis direction is There is no possibility of errors occurring in the photomask comparison inspection that caused this. In the above, reticle pattern 1
0 and the photomask pattern of one chip of the photomask is completed, the same reticle pattern 10 is again compared and verified with the photomask pattern of one adjacent chip of the photomask. In this case, In the present invention, the zoom lens of the microscope 32 is operated to match the magnification of the reticle pattern 10 and the photomask pattern to be newly compared and inspected. The zoom lens operating mechanism of the microscope 32 will be explained below.

Now, as shown in FIG. 2, a reflecting mirror 60' serves as a zoom lens operating mechanism of the microscope 32 and distributes a light beam, such as a laser beam, emitted from a light source S' into respective patterns of the first stage 22 and the second stage 24. , optical potentiometers 62 and 64 that receive the light beams distributed by the reflecting mirror 60' after being reflected on the pattern surfaces of the first stage 22 and the second stage 24, and both optical potentiometers 62 and 64. A voltage processing unit 66 to which a voltage signal is input, and a DC motor 68 driven based on the voltage signal processed by the voltage processing unit 66 are provided. is configured to perform a zoom action (continuous change in focus). Note that the optical potentiometer 62 is fixed to the microscope 30, and the other optical potentiometer 64 is fixed to the microscope 30.
It is fixed to 2. The reflecting mirror 60' is fixedly arranged at a fixed position. The optical potentiometers 62 and 64 described above have the same function as the optical potentiometers 56 and 58 shown in FIG. the respective optical potentiometers 62, 64 when the magnifications of
The voltage processing unit 66 stores the DC voltage value from the photomask pattern, and each time the comparison inspection of one chip of photomask patterns is completed, the two-optical potentiometer 62,
The voltage processing unit 66 compares the DC voltage signal of 64 with a constant DC voltage value to calculate a magnification, and drives the DC drive motor 68 based on the voltage difference value so that the voltage difference value becomes zero value. By operating the zoom lens, it is possible to match the magnification.
After matching the magnifications in this way, the above-mentioned comparative verification test is performed on one chip of photomask patterns.

As is clear from the above description, in the present invention, when comparing and inspecting the reference pattern of a reticle or master photomask with each of a plurality of photomask patterns of a photomask to be inspected, first, the objective microscopes 30 and 32 check that the magnifications match. If the magnifications do not match, adjustments are made to match the magnifications by operating the zoom lens of one of the microscopes 32, and then a comparison inspection of both patterns is performed. It will be done. Generally, even when multiple photomask patterns are formed on one mask substrate through the same process to form the same reticle pattern, small dimensional differences occur between the multiple photomask patterns, and in the comparative inspection process, In order to obtain highly accurate inspection results, it is important to accurately match the magnification between the reference pattern for comparison inspection and each photomask pattern to be inspected in order to deal with these minute dimensional differences before performing comparison scanning. It becomes a requirement. According to the comparison inspection mechanism according to the present invention, these requirements are satisfied, so that inspection can be performed with extremely high accuracy. Note that FIG. 5 is a flowchart of the inspection process by the photomask comparison inspection mechanism according to the present invention.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing the relationship between pattern magnification between a reticle and a photomask, Fig. 2 is a mechanical diagram showing the configuration of an inspection device equipped with a comparative inspection mechanism for photomasks according to the present invention, and Fig. 3 is a comparison of the same mechanism. FIG. 4 is a system diagram showing a voltage signal processing process, and FIG. 5 is a flowchart of an inspection process using the same mechanism. 8... Reticle, 10... Reticle pattern,
12... Photomask pattern, 12a... Defective pattern, 14... Photomask substrate, 22...
First stage, 24...Second stage, 26,2
8... Drive source, 30, 32... Objective microscope, 54
...Control unit, 56, 58...Optical potentiometer, 60...Rotating mirror, 60'...Reflector, 6
2, 64... Optical potentiometer, 66... Voltage processing unit, 68... DC motor.

Claims (1)

[Claims] 1 A first photomask having a reticle having a reticle pattern or a plurality of patterns formed by reduction from the reticle pattern, and a second photomask having a plurality of patterns formed by reduction from the same reticle pattern and smaller than the first photomask pattern. In a photomask comparative inspection mechanism, two photomasks are placed on independently movable first and second inspection stages, and patterns are compared and inspected by irradiating them with inspection light. Separately irradiating the introduced inspection light to both patterns placed on the corresponding first and second inspection stages via the first and second optical systems, and one of the first and second optical systems. Comparative inspection of a photomask, characterized in that one optical system is composed of a constant magnification lens system, and the other optical system is composed of a zoom lens system, so that both patterns can be adjusted to the same magnification and compared and verified. mechanism.