JPH01276734A - Detector for defective chip of semiconductor wafer - Google Patents

Abstract

PURPOSE:To make it possible to test all the chips and to improve the reliability of chips, by judging the quality of focusing by a method wherein the maximum of a difference in focus values taken from the focus value data when an aligner is brought into focus is compared with the depth of focus of an optical system in the exposure process. CONSTITUTION:An aligner 2 exposes a shot portion A on a semiconductor wafer 1 and adjusts the focus to the irregularity values. A focus value when the aligner is brought into focus is inputted into a maximum value calculating portion 3. The maximum value calculating portion 3 finds a difference between a focus value FA of the shot portion A and each of focus values FB1-FB4 of surrounding shot portions B1-B4 and outputs a maximum value Dmax. When the maximum value Dmax exceeds the depth of focus df of an optical system, a judging portion 4 outputs a signal, judging that the chip is a defective one since it is out of focus. By this method, bad chips which are out of focus can be detected in the exposure process.

Description

Detailed Description of the Invention [Summary] The present invention relates to a detection device for automatically detecting defective chips due to poor exposure from among LSI chips formed on a semiconductor wafer. At the same time, the purpose of the present invention is to provide a detection device that can automatically detect out-of-focus defective chips. an exposure device that outputs a focus value signal at the time of focusing; a maximum value calculation unit that calculates a maximum difference in focus values between an exposed shot and its surrounding shots based on the focus value; and a determination section 4 that determines the quality of the chip to which the exposure shot belongs by comparing the value with the depth of focus of the optical system of the exposure apparatus.

[Industrial application field]

The present invention relates to a detection device for automatically detecting defective chips due to poor exposure from among LSI chips formed on a semiconductor wafer.

In the LSI manufacturing process, there is an exposure process for printing a predetermined pattern onto a semiconductor wafer. The exposure device has an autofocus mechanism (autofocus point tli
Each shot surface of the portion corresponding to each chip on the semiconductor chip is exposed by an autofocus mechanism.

The quality of exposure, that is, the presence or absence of focus shift, is determined by the L
Since this is directly related to the quality of the SI chip, an out-of-focus inspection step is placed after the exposure process.

[Conventional technology]

In a conventional out-of-focus inspection process, an inspector first performs a visual inspection after development, and then inspects defective shots found through the visual inspection in more detail using a microscope.

[Problem to be solved by the invention]

As mentioned above, exposure is performed using an autofocus mechanism, but if the unevenness value of the semiconductor wafer surface is large, especially if the unevenness value exceeds the depth of focus of the optical system of the exposure equipment, defocus may occur. Even though this occurs, exposure will be carried out at a focus that is considered to be appropriate within the capabilities of the autofocus timing.

This kind of focus shift should be discovered during the inspection process, but current visual inspections depend on the skill level of the inspector and are not always perfect. In some cases, the particles may not be subjected to microscopic inspection using a microscope, and the process may proceed to the next development process without being discovered.

As described above, the conventional inspection method has a problem in that defocus cannot be detected unless the image is developed. In addition, there is a risk that the current performance may be overlooked and the chip may be put into production without knowing that it is a defective chip due to a focus shift. This leads to the problem of reduced reliability.

An object of the present invention is to provide a detection device that can automatically detect out-of-focus defective chips simultaneously during exposure in an exposure process.

[Means to solve the problem]

In order to solve the above problems, the present invention includes an automatic focusing device that automatically corrects the exposure focus on the exposure shot A surface according to the unevenness value of the surface of the semiconductor wafer 1, as shown in FIG. , 7-occasion value signal F at the focused point, FB
and a maximum value calculation that calculates the maximum value Dlax8B of the difference (F-F) between the focus values of the shot A being exposed and its surrounding shots 81 to B4 based on the focus value FBFa. and a determining section 4 that determines the quality of the chip to which the exposure shot aXA belongs based on the maximum value D (=d) of the difference in focus values.

[Effect]

According to the present invention, the exposure apparatus 2 exposes a predetermined shot portion A on the semiconductor wafer 1. At this time, autofocus 8! 6. The focus fli (the height position of the exposure device or the unevenness value of the semiconductor wafer) at the focused point is input to the maximum value calculation unit 3. be done. The maximum value calculation unit 3 calculates the difference between the focus value Ft of the exposure shot A currently being exposed and the focus values FB1 to F84 of each of the surrounding shots 81 to B4, and calculates the difference when the difference is the largest. Outputs the value D (=d).

+1aX This maximum value D□8 corresponds to the maximum value of the relative unevenness difference between the shot A currently being exposed and the surrounding shots 81 to B4. If the maximum value D of this unevenness difference exceeds the depth of focus df of the optical system of the exposure device aX, defocus will always occur, so there is a high probability that the chip containing the defective focus shot will be a defective chip. Therefore, the determination unit 4 compares the maximum value D with the depth of focus d of the optical system, and determines that the maximum value Dlax is the depth of focus d.
If r is exceeded (D, x>d), it is assumed that the chip is defective due to defocus, and a detection signal is output.

As described above, according to the present invention, it is possible to detect in advance the occurrence of defective chips caused by defocus during the exposure process on eight sides of a semiconductor wafer.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

Hinoki M Tanuki First, the detection principle will be explained.

The focus shift that causes defective chips can be determined by whether the relative distance between the convex portion and the concave portion on the surface of the semiconductor wafer 1 is larger than the depth of focus of the optical system of the exposure apparatus 3. That is, the condition for determining poor focus is given by d>d, (1). Here, d is the relative distance between the convex portion and the four portions on the surface of the semiconductor wafer, and dr is the depth of focus of the optical system.

The reason why this poor focus judgment condition is satisfied is that when the relative distance d of the concave and convex portions exceeds the depth of focus dr of the optical system, it exceeds the focusing ability of the exposure device 3 using autofocus, and therefore the focus cannot be achieved. This is because it is clear that there is no focus, and therefore defocus will always occur. This defocus means that the pattern cannot be accurately transferred during printing, resulting in a defective chip.

To find the relative distance d between the convex and concave portions on the surface of the semiconductor wafer, as shown in FIG. (Ill, n) Each focus value F1 of the part B-84
(n-1, n) ・F
(m, n+1) (m+1.n) (Il, n
-1) Find the maximum value Dlax of the difference (absolute, F, F blockade) 8 surrounding shot part B
The reason why each focus value of ~B4 is determined is that accurate determination cannot be made based on only the difference from one adjacent shot portion.

Here, the differences D1 to D4 with each focus value when the shot A of interest is taken as a reference are DI "" (m, n) (l-1, n) '
""") F D 2 = l F (11,.) (T1..,
1) 1 ... (3) F D3 "" (II, n) (n+1.n) '
"") F D 4 = l F <,,. )(,,.-1)1
...(5) It is given by F. The maximum value among these focus value differences D1 to D4 is assumed to be D□8. Specifically, in FIG. 2, D is D2, which corresponds to daX in equation (1).

To summarize the above, the focus value F (,. Find the maximum value D, compare this maximum value D (=d) and the depth of focus d, and aa
x If the judgment condition of equation (1) is exceeded, the relevant shot A
The LSI chip including the LSI chip is configured to output a detection signal indicating that it is a defective product.

Figure 2 shows an outline of an embodiment of the present invention based on the above detection principle.

A defective chip detection device according to the present invention includes an exposure device 2 that irradiates an exposure beam onto a semiconductor wafer 1 placed on a wafer stage 5 whose position is adjustable in the X-Y direction, and a defective chip detection device that position (i.e. focus value)
A position detector 6 such as a potentiometer that detects FBF, focus value signals F, F, and B from this position detector 6, and a shutter signal S in the exposure device 2 are input, and based on these signals, The camera is configured to include a detection unit 7 that detects whether or not the shot A of interest is out of focus.

The exposure device 2 is equipped with an autofocus mechanism that performs automatic focusing in accordance with the uneven surface shape of the shot A of interest.

The method of the autofocus mechanism may be a known method and is not particularly limited.

The focus value signal Ft is the focus value of the shot A of interest at the time of exposure, and refers to F(4,n) in FIG. 2. The focus value signal F8 is the focus value of each surrounding shot 81 to
This is the focus value during exposure of B4, and is F(n-
1,n) (n,n+1) (l+1.n)
, F and F F (l, n-1), respectively.

Next, the general operation will be explained with reference to FIG.

During exposure, the wafer stage 5 is moved in the X and Y directions by a predetermined pitch to position the shot A of interest.Next, the exposure device 3 is moved in the Z direction by the autofocus mechanism to perform automatic focus adjustment. , during the exposure process of 0 or more in which the shutter is opened when the focus is achieved and the shot A of interest on the surface of the semiconductor wafer 1 is exposed, the focus value signal F at the time of the focus is input together with the shutter signal S as a synchronization signal. The signal is given to the detection unit 7. On the other hand, in order to detect poor focus of the shot of interest A, automatic focus adjustment is similarly performed for the surrounding shots B1 to B4, and the focus value FB for each of the surrounding shots 81 to B4 is output to the detection unit 7.

Although the details will be described later, the detection unit 7 receives each focus value signal F.
, F ~ F and shutter signal S 81
84 Next, it is detected whether or not poor focus has occurred during exposure of the shot A of interest, and a detection signal Sb to that effect is output.

The above exposure process and defective focus detection operation are repeated for all shots on the semiconductor wafer 1.

As described above, the present invention is characterized in that the occurrence of defective chips caused by defective focus is detected in advance during the exposure process, and the present invention is not inspected after the fact in a step after the exposure process, unlike the conventional method. significantly different from the original.

Gontoki Tsuta Next, a detailed circuit of the detection section 7 is shown in FIG.

The detection unit 7 receives focus value signals F , F ~
an A/D conversion circuit 8 that converts BI Fe2 into a digital value;
A counter 9 that counts the shutter signal S, a focus value storage circuit 10 that stores the A/D converted focus value signals FA''81 to FB4 in association with shot positions based on the count value of the shutter signal S, and a memory. focused (liFA).

By FB1 to FB4, the difference D1 to each focus value is
A maximum value calculation unit 11 that calculates the maximum value DIlaX of D4, a reference value setting circuit 12 that outputs a reference signal corresponding to the depth of focus df of the optical system, and a reference signal dt and the maximum value D.
(=d) to determine the presence or absence of a defective fax orcus, and a counter 9.
A defective shot storage circuit 14 stores the defective focus detection signal from the comparator circuit 13 in correspondence with the count @ff (each shot position) from .

The maximum value calculation unit 11 is a so-called high value priority circuit. That is, the difference between the focus values of the surrounding shots 81 to B4 with respect to the focus value FA of the shot of interest l-A ((2)
~ (see formula (5)) are determined by comparators 15 to 18, and the larger difference between them is determined by comparators 19 and 20 in the next stage, and the resulting difference value is determined by comparator 21 in the next stage. The switch circuit 22
．． 23, the focus value with the largest difference is sequentially selected in a tournament manner, and is finally output from the switch circuit 24 to the comparison circuit 13.

Next, a series of operations of the detection section will be explained.

The focus value FA of the shot A of interest, which is output for each shot in the exposure process and stored in the focus value storage circuit 10, and the focus values FBl to Fe of each of the surrounding shots B to B are determined by the difference in focus value in the maximum value calculation circuit 11. The maximum value D is calculated. The obtained maximum value aXDIaX is compared with the reference value dt based on equation (1), and if D > d (1aX), the exposure of the relevant shot A is determined to be a defective focus and is stored in the defective shot storage circuit 14. 0 to be done
The above processing is performed for all shots of one semiconductor wafer. When the process is completed, the position of the defective shot portion on the semiconductor wafer is clarified and transferred as production information to the next process.

〔Effect of the invention〕

As described above, according to the present invention, the maximum value of the difference between the focus value data at the time of focusing by autofocus and the depth of focus of the optical system is compared in the exposure process, and the quality of the focus is determined. Therefore, the conventional visual inspection process can be omitted.

In addition, since each shot is automatically detected, there is no need for oversights or for inspectors to rely on their senses, which is the case with visual inspections, making it possible to perform a 100% inspection.
It is expected that the reliability of the product will improve. Furthermore, since the detected information is reflected in the subsequent glossary, there is no need to process unnecessary shot-corresponding portions, which contributes to a reduction in man-hours.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is a detailed explanatory diagram of the present invention, Fig. 3 is a schematic explanatory diagram of an embodiment of the present invention, and Fig. 4 is a diagram of the detection section of an embodiment of the present invention. It is a circuit diagram. DESCRIPTION OF SYMBOLS 1... Semiconductor wafer, 2... Exposure apparatus, 3... Maximum value calculation part, 4... Judgment part. Fig. 1 Detailed explanatory diagram of the present invention Fig. 2

Claims (1)

[Claims] It has an automatic focusing device that automatically corrects the exposure focus on the exposure shot plane (A) according to the unevenness value of the surface of the semiconductor wafer (1), and the focus value signal (F_A ,
An exposure device outputs an exposure shot (A) and its surrounding shots (B_1) based on the focus value.
, B_4); and a maximum value calculation unit (3) that calculates the maximum value of the difference between the focus value (D_m_a_x) and the focus value (D_m_a_x) and the depth of focus (df) of the optical system of the exposure apparatus. 1. A defective chip detection device for a semiconductor wafer, comprising: a determination unit 4 that determines the acceptability of a chip to which the exposure shot belongs by comparing the values of the exposure shot and the exposure shot.