JPS62136020A - Aligning method - Google Patents

Abstract

PURPOSE:To improve a superposing accuracy in an aligning method by automatically measuring a displacement of adjacent shot region as a designated shot region when detecting an impossibility of a displacement measurement in the designated shot region. CONSTITUTION:Three conditions that used shot regions are all both side automatic alignment (AA), a pair of shot regions are separated at a predetermined distance or longer, and two shot regions of the same direction are not displaced more than a certain degree in upward and downward directions are required for the shot region used for a TTL global alignment. A displacement of the AA mark is measured in a designated shot region S0. When the measurement is impossible, it is moved to a shot position SS adjacent to the designated shot region, and a displacement in the shot region which has satisfied all the three conditions is measured as the shot region instead of the designated shot region. Thus, an accurate alignment can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates particularly to an alignment method for an apparatus for printing or exposing circuit patterns used in the manufacture of high-density integrated circuit chips such as semiconductor memories and arithmetic devices.

[Conventional technique #I] Conventional TTL (Through The Len
s) In the global alignment method, if the amount of deviation could not be measured in a specified shot area during deviation measurement, the method was to restart the global alignment from the beginning or to bus the deviation measurement in that shot area. . Therefore, if the amount of deviation cannot be measured, the operation of the apparatus is stopped and an operator is required to carry out the above processing, which has the drawback of reducing the throughput of the exposure apparatus.

[Object of the invention] The present invention solves the above-mentioned difficulties and achieves extremely high overlay accuracy,
The purpose of the present invention is to provide an alignment method with high productivity (speed), high flexibility, and simple configuration.

[Explanation of Examples] Hereinafter, the present invention will be explained in detail using the drawings.

Figure 1 shows TTL to which the 7-line method of the present invention is applied.
1 is a schematic configuration diagram of a semiconductor printing apparatus using a global alignment method. In the same figure, XYS indicates the wafer
XY stage to move in the Y direction, XM, YM
A drive motor drives X Y S in the X and Y directions, WS is a θ stage that rotates the wafer in the θ direction, WF is the wafer, and OA detects the pre-alignment mark and roughly aligns the wafer. This is an off-axis microscope for performing this. In addition, LN is a printing projection lens, R8 is a reticle stage that moves the reticle in the X, Y, and θ directions, RT is a reticle, PT is a circuit pattern drawn on the reticle RT, Ll is a printing illumination device, MR, M
L is a mirror, DR, DL are photoelectric detectors, CB is CP
It is a control box equipped with a control circuit consisting of a central processing unit (U), memory, etc.

FIG. 2 shows an example of a shot layout of a wafer WF, which is an object to be exposed. In the figure, PMl and PM2 are pre-alignment marks used for pre-alignment, which will be described later. 1 to 45 indicate each shot area where exposure is performed. SO indicates a designated shot area used for global alignment, and SS indicates a shot area adjacent to the designated shot area SO. Here, the shot area numbered 25 is set as the designated shot area. Further, LN indicates a printing projection lens when exposing the shot area IfA1.

FIG. 3 is a flowchart for explaining the procedure for wafer baking using the alignment method of the present invention, and FIG. 4 is a flowchart for explaining the alignment method of the present invention. This is detailed information about deviation measurement, etc.

Next, with reference to FIGS. 2 and 3, the procedure for baking a wafer using the apparatus shown in FIG. 1 will be explained.

In FIG. 3, first, when the semiconductor printing operation is started, reticle RT is set on reticle stage R8 in step S1. Next, in step S2, the reticle RT and the burn-in projection lens LN are correctly aligned using the reticle flymen 1 to marks provided on the burn-in projection lens LN. Next, step S
In step 3, the wafer WF to be actually baked is placed on the XY stage
Set it on top of YS. In step S4, pre-alignment marks PMI and PM2 as shown in FIG. 2 are applied with a lateral force by an off-axis microscope OA provided outside the projection lens to roughly align the reticle RT and wafer WF. Next, in step S5, TTL global alignment, which will be described later, is performed to accurately align the reticle RT and wafer W.
Perform positioning of F. After accurately aligning the reticle RT and the wafer WF, in step S6, the XY stage XYS is driven to align the shot area of the wafer WF, which is the actual printing position, with the printing projection lens N.
Exposure is performed in step S7.

Next, in step S8, it is determined whether printing has been completed for all shot areas on one wafer WF, and if it has not been completed, the process returns to step $6. When the baking of one wafer is completed for the entire shot area, the baked wafer WF is carried out from the XY stage XYS in step S9. In step S10, it is checked whether the pre-designated number of 10 wafers has been completely baked, and if it has not been finished, the process returns to step S3.
If the process has ended, the process returns to step S1 and the above-described operations are performed again.

Next, a method of global alignment in the apparatus shown in FIG. 1 will be explained with reference to FIGS. 2 and 4.

First, the requirements for the shot area used for TTL global alignment will be explained. The shot area used for TTL global alignment requires the following three conditions in terms of alignment accuracy and the like.

1) All shot areas used must be in both-eye auto alignment (AA) mode.

2) A pair of shot areas are separated by a certain distance (span) or more.

3) Two shot areas in the same direction should not have a vertical deviation θ (tilt) of more than a certain degree.

From the above, explanation will be given based on FIG. 4.

First, in step S11, in a designated shot area used for TTL global alignment, the deviation from the AA mark in that shot area is measured. next,
In step 812, it is checked whether the measurement in step S11 was possible, and if it was possible, step 813
Then, the process moves to the next designated shot area position and returns to step 811. If measurement is not possible in step 812,
In step 814, the camera moves to a shot position adjacent to the designated shot area, and in that shot area, step 81
Condition 1) mentioned earlier in Step 5 is set to Condition 2) in Step 816.
In addition, in step S11, it is checked whether condition 3) is satisfied, and a shot area that satisfies all three conditions is set as a shot area in place of the designated shot area. Next, in step 318, the deviation m is measured in the shot area in the same manner as in step 311, and further in step 319, confirmation is performed in the same manner as in step 812.
If measurement is possible, the process advances to step S13.

Furthermore, if each condition is not satisfied in step S15 or 816, or if measurement is impossible in step 319, the process moves to the next adjacent shot position in step 820, and the processes from step 815 onwards are repeated. Also, step 31
If condition 7 is not met, that is, condition 1 mentioned earlier)
If condition 2) is satisfied but condition 3) is not satisfied, it is determined that there is no shot area that can replace the designated shot area, and in step 821, it is determined whether to pass or remeasure (retry) the shot area. Let the operator decide, and if it passes, proceed to step 813,
To retry, return to step 311. Note that the adjacent shot areas are sequentially selected according to the selection conditions described below. Therefore, if condition 3) regarding the inclination is not satisfied, it can be determined that there is no shot area that can replace the designated shot area.

As described above, if it is impossible to measure the amount of deviation with the designated shot under the three conditions, a shot that can replace the designated shot can be automatically searched for.

Next, a method for selecting adjacent shots will be described.

In FIG. 2, if the shot number of the global alignment designated shot area SO is 25, the shots adjacent to this shot are 8 shots (shot numbers 13°14, 15.24.26) as shown in the figure.
．． 27.28.29) Yes. Here, the following conditions for adjacent shot selection are set based on conditions 1) and 2) of the three conditions shown above.

4) Select a shot area where the span is not shortened as much as possible and no tilt occurs.

5) If the span becomes short and tilt occurs, select a shot area with as little tilt as possible.

6) If there are two shot areas satisfying the same condition, select the one with the smaller shot number first.

If adjacent shots are selected based on the above three conditions, the order of selection of the eight adjacent shots is shot NO.
, 26-+ N O, 24-+ N O, 134 N O
,27-) NO,14→No,28→N015→
The result is No. 29, and adjacent shots can be selected. Based on this, if it is impossible to measure the amount of deviation in global alignment in a certain shot area, shot areas may be selected one after another based on the above conditions.

[Effects of the Invention] As explained above, according to the present invention, in TTL global alignment, when it is impossible to measure the amount of deviation in the specified shot area, a shot area that can replace the specified shot area is automatically searched for and measured. This prevents the equipment from stopping when deviation measurement is impossible, and is effective in improving throughput.

Furthermore, by using the method described above, it is possible to measure the amount of deviation in a replacement shot area for a specified shot area that would have passed using conventional methods, making it possible to perform alignment with higher precision. It has the effect of

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a semiconductor printing apparatus to which the alignment method of the present invention is applied. FIG. 2 is a diagram showing the spot arrangement and marks on a wafer. FIG. 3 is a diagram showing the alignment method of the present invention. FIG. 4 is a flowchart for explaining the TTL global alignment method of the present invention. XYS...XY stage, WS...θ stage, W
F...Wafer, LN...Printed projection lens, R8...
・Reticle stage, RT... Reticle, Ll...
Burning lighting device, CB...Control box, PMI, PM2...Pre-alignment mark, SO
...Specified shot area, SS...Adjacent shot area.

Claims (1)

[Claims] In global alignment performed using shot areas on a wafer, if it is detected that it is impossible to measure the amount of deviation in the specified shot area for global alignment, the adjacent shot area of the specified shot area is automatically specified. An alignment method characterized by performing alignment by measuring the amount of deviation as a shot area.