JPH0560644B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an alignment apparatus, and more particularly to an apparatus used for aligning an integrated circuit pattern with a wafer in a semiconductor printing apparatus or the like.

[Prior Art] Conventionally, in this type of alignment apparatus, fluctuations in the relative positional relationship between the off-axis alignment scope and the printing projection lens have occurred during the operation of the apparatus. When this variation occurs, alignment accuracy is degraded when alignment is performed by off-axis alignment and exposure is performed. Therefore, it is necessary to measure the amount of change over time in the relative positional relationship between the off-axis alignment scope and the printed projection lens, and to make appropriate corrections to the measurement results from the off-axis alignment scope when performing off-axis alignment. Hereinafter, this correction will be referred to as baseline correction.

Conventionally, this baseline correction has been performed by exposing a wafer using off-axis alignment, calculating the amount of deviation from the exposure result, and inputting the amount of deviation into the apparatus. As a result, the correction values were not reflected immediately in the alignment operation, which hindered improvements in accuracy and productivity, and the calculation and input of the correction values required manual intervention, which could lead to operational errors.

[Object of the Invention] In view of the problems of the conventional method described above, the object of the present invention is to automatically measure the baseline correction value and immediately reflect the correction value in the alignment operation of the device, thereby achieving high precision and high accuracy. An object of the present invention is to provide an alignment device that performs alignment for productivity.

[Description of Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an alignment device according to an embodiment of the present invention. In the same figure, XYS is an XY stage that moves the wafer in the X and Y directions;
XM, YM are XY stage XYS respectively
WS is the wafer stage that rotates the wafer in the θ direction, WF is the wafer,
LN is a printed projection lens, RS is a reticle X, Y,
Reticle stage that moves in the θ direction, RT is the reticle, PT is the circuit pattern drawn on the reticle RT, LI is the printing illumination device, MR, ML are the mirrors,
DR and DL are photoelectric detectors, and CB is a control box equipped with a control circuit consisting of a CPU (central processing unit), memory, etc.

In addition, SL and SR are off-axis alignment scopes, MON is a monitor that displays images of the off-axis alignment scope, and JS is a joystick that allows the operator to perform manual alignment by moving the wafer in the X, Y, and θ directions. It is.

FIG. 2 shows an example of a shot layout of a wafer WF, which is an object to be exposed. In the figure, numerals 1 to 45 indicate shot areas where exposure is performed. In addition, WML and WMR are off-axis alignment marks used for off-axis alignment, and S20L and S20R are shot area 2 marks used for TTL alignment in shot area 20.
The TTL alignment marks S25L and S25R that are in a predetermined relationship with respect to the center of the shot area 20 are TTL alignment marks in the shot area 25 that are also in a predetermined relationship with the center of the shot area 20. Note that the positional relationship between the center of the shot area 20 and the alignment mark WML is the same as that between the center of the shot area 25 and the alignment mark WMR, and the shot areas 20 and 25 are close to the alignment marks WML and WMR, respectively. preferable.

FIG. 3 is a flowchart for explaining the procedure for performing baseline correction, off-axis alignment, and exposure using the apparatus of this embodiment shown in FIG. 1, and FIGS. 4, 5, and 6 are flowcharts showing detailed contents of steps S300, S400, and S1100 in FIG. 3, respectively.

The operation of the apparatus shown in FIG. 1 will be explained below with reference to FIGS. 2 to 6.

In FIG. 3, when the operation of this apparatus is started, first, in step S100, the reticle RT for measuring the baseline correction value is set on the reticle stage RS. Next, reticle RT and baked projection lens LN
Correctly align the reticle RT and the printed projection lens LN using the reticle alignment mark provided above. Furthermore, in step S200, off-axis alignment marks WML and WMR are
The baseline correction value measurement wafer WF on which the TTL alignment mark is printed is set on the wafer stage WS. Wafer used at this time
WF and reticle RT are dedicated to baseline correction value measurement, but if the exposure wafer and reticle used in the operations after step S800 have TTL alignment marks, they can also be used. good.

Next, in step S300, the wafer is aligned using off-axis alignment scopes SL and SR.
Align the WF mark with the marks provided on scopes SL and SR.

Referring to FIG. 4, the off-axis alignment procedure in step S300 will be described in detail.
First, in step S301, the wafer WF is moved so that the off-axis alignment marks WML and WMR are approximately directly below the off-axis alignment scopes SL and SR. Next, step
In S302, it is determined whether the off-axis alignment method is specified as automatic or manual, and if it is automatic alignment, the process proceeds to step S303. step
S303 has off-axis alignment scope SL,
The amount of deviation between the off-axis alignment mark provided on the SR and the off-axis alignment marks WML and WMR on the wafer WF is measured. Next, in step S304, it is determined whether the amount of deviation is within a predetermined tolerance, and if it is outside the tolerance, the process proceeds to step S305, and the XY stage XYS and wafer stage WS are driven to bring the amount of deviation to O. do. Thereafter, the process advances to step S306, and if the number of alignment drives is within a predetermined number of times, the process returns to step S303 again.

Above steps S303→S304→S305→S306→
The operation in S303 is repeated until the amount of deviation falls within the tolerance in step S304 or until it exceeds a predetermined number of times in step S306. Step when repeating
If the number of alignment drives exceeds the predetermined number in S306, or if manual alignment is determined in step S302, the process advances to step S307.
The operator manually performs alignment using monitor MON and joystick JS.

After the alignment is completed through step S304 or S307, proceed to step S308 and transfer the wafer WF.
Find the elongation rate and slope of .

Hereinafter, a method for calculating the elongation rate and slope will be explained with reference to FIG.

In Figure 7, _SL is the alignment scope
The position when SL is adjusted correctly, 〓 _SR is the position when alignment scope SR is adjusted correctly, 〓 _L is the amount of deviation of alignment scope SL (baseline correction value), 〓 _R is the position when alignment scope SR is adjusted. Amount of deviation (baseline correction value), 〓
_WML is the alignment mark on the wafer relative to the alignment mark on the alignment scope SL.
WML deviation amount, 〓 _WMR is alignment scope
Amount of deviation of the alignment mark WMR on the wafer with respect to the alignment mark on the SR, 〓 _LN indicates the position of the printed projection lens LN.

Note that all these positions and displacement amounts are shown as vectors. It is assumed that the coordinate system for determining the origin of the position vector is determined in advance. In addition, the values of the correction values 〓 _L and 〓 _R are undetermined immediately after the device starts operating, but during operation they are updated correctly during automatic baseline correction value measurement (step S400), which will be described later. Therefore, the previously measured value or (0, 0) may be used here.

As described above, the actual positions of alignment scopes SL and SR are considered to be 〓 _SL + 〓 _L and 〓 _SR + 〓 _R , respectively. Also, considering the amount of deviation that remains after performing the above-mentioned off-axis alignment, the positions of the off-axis alignment marks WML and WMR on the wafer 〓 _WML ,
〓 _WMR is respectively 〓 _WML =〓 _SL +〓 _L +〓 _WML 〓 _WMR =〓 _SR +〓 _R +〓 _WMR . Therefore, the elongation rate M _W and the slope θ _W of the entire wafer after off-axis alignment are M _W = ((B _Rx + D _WMRx ) − (B _Lx + D _WMLx ))/(P _SRx − P _SLx ) θ _W = ( (B _Ry +D _WMRy ) - (B _Ly +D _WMLy ))/(P _SRx - P _SLx ), which is calculated and stored in step S308. Note that the x and y components of each vector are expressed by adding subscripts x and y to each vector.
For example, let the x and y components of the vector 〓 _R be B _Rx and B _Ry , respectively. The same applies to the following description.

Next, the process proceeds to step S400 in FIG. 3, where the baseline correction values _〓L and _〓R are measured.

The contents of automatic baseline correction value measurement will be described in detail below with reference to FIGS. 5 and 8. First, in step S401, drive the XY stage
WML) Move a nearby shot, for example shot 25, directly below the printing projection lens LN. At this time, the amount of movement command given to the XY stage XYS is (〓 _LN -〓 _WMR ) - W〓 _TR .

However, W=1+M _W θ _W −θ _W 1+M _W Also, 〓 _TR is the vector shown in FIG. show.

Next, proceed to step S402 and select the detector DL.
By DR, the amount of deviation 〓 25L, 〓 _25R between the TTL alignment marks S25L, S25R _of the shot 25 and the alignment mark on the reticle RT is measured and stored. Furthermore, in step S403, mark the other off-axis alignment mark WML (or
WMR) Move a nearby shot, for example shot 20, directly below the printing projection lens LN. At this time, the amount of movement command given to the XY stage XYS is -W〓 _TRL . However, _TRL is a vector shown in FIG. 8, which is a vector from the center of shot 25 to the center of shot 20 on wafer WF in a state without expansion/contraction and inclination, that is, a vector from alignment mark WMR to alignment mark WML. shows. Next, proceed to step S404, and proceed to step S402.
Similarly, TTL alignment mark S20L,S
Measure and store the deviation amount of 20R 〓 _20L , 〓 _20R .

Based on the above measurement data, the shortfall in the baseline correction values _〓L and _〓R is calculated in step S405.
In this calculation, first, 〓 _L = (〓 _20L + 〓 _20R ) / 2 〓 _R = (〓 _25L + 〓 _25R ) / 2, and the alignment scopes SL and SR are calculated based on 〓 _L and 〓 _R measured by TTL. The growth rate M _T of the distance between them and the inclination θ _T between the alignment scopes SL and SR are calculated as M _T = (D _Rx − D _Lx )/S _TRLx θ _T = (D _Ry − D _Ly )/S _TRLx . Next, the center positions of the shots 20 and 25 on the wafer WF in a state where there is no expansion/contraction and no tilting are 〓 _L and 〓 _R , respectively, and the positions of the off-axis alignment marks WML and WMR are 〓 _ML and 〓 _M respectively.
As _R , 〓 _L , 〓 _R used in step S308
The correction value shortages _L and _R are calculated as _L = A _ML + _L − A _{L L R} = A _MR + _R − A _R. However, A=M _T θ _T −θ _T M _T.

Next, the process advances to step S500 in Fig. 3, and it is determined whether the baseline correction values 〓 _L + 〓 _L , 〓 _R + 〓 _R updated by the measured shortfalls 〓 _L , 〓 _R are within a predetermined range. If it is determined that it is outside the range, the process advances to step S600 and the process is continued or remeasured at the discretion of the operator. If it is determined in step S500 that it is within the range, the process advances to step S700, where the baseline correction values 〓 _L and 〓 _R are updated and stored as 〓 _L ←〓 _L +〓 _L 〓 _R ←〓 _R +〓 _R , respectively.

The baseline correction value is obtained in the above manner, and the process then proceeds to exposure.

First, in step S800, the reticle used for exposure is
Set the RT on the reticle stage RS, and using the reticle alignment mark provided on the baked projection lens LN, align the reticle RT and the baked projection lens.
Align the LN correctly. Next, step
In S900, the wafer WF on which the pattern PT is to be printed is set on the wafer stage WS, and in step S1000, off-axis alignment is performed in the same manner as in step S300. At this time, the updated baseline correction values _〓L , _〓R are used to calculate the wafer elongation rate _MT and the slope _θT in step S308. Therefore, accurate values are calculated.

Next, exposure is performed in step S1100. below,
The contents of step S1100 will be explained with reference to FIG.

First, in step S1101, the first exposure shot area 1 is moved directly below the printing projection lens LN. At this time, the movement command amount given to the XY stage XYS is (〓 _LN -〓 _WMR ) - W〓 _T1 . However, _T1 is a vector shown in FIG. 8, which indicates a vector from the alignment mark WMR on the wafer WF to the center of the shot 1 in a state where there is no expansion, contraction, or inclination. Next, in step S1102, exposure is performed, and in step S1103, it is determined whether the exposure of all shot areas on one wafer has been completed. If there are still shots left to be exposed, in step S1104, the shot area to be exposed next is determined. Move it directly below the burned projection lens LN. At this time, the movement command amount given to the XY stage XYS is -W〓. However, 〓 is a vector from the center of the current shot to the center of the next shot on the wafer WF in a state where there is no expansion/contraction inclination.

Next, the process returns to step S1102 again, and exposure and wafer movement are continued until it is determined in step S1103 that all shot exposure has been completed.

After the exposure in step S1100 is completed, the process advances to step S1200 in FIG. 3, where it is determined whether exposure has been completed for all of one lot of wafers. If not, the process returns to step S900 and the wafers are exposed until one lot is completed. Repeat the exposure. When one lot is completed, proceed to step S1300, and proceed to step S1300 according to the operator's judgment or a predetermined procedure.
From step S100, the process branches to either perform baseline correction again, expose the next lot with the same correction value from step S800, or terminate the process.

[Effect of the invention] As explained above, according to the present invention, TTL
It has two methods of measuring the amount of deviation: one using an off-axis alignment scope, and the other using an off-axis alignment scope.
From the TTL measurement results, the relative positional relationship (baseline) of each off-axis alignment scope with respect to the projection optical system, as well as the interval error and rotational error between each off-axis alignment scope, can be determined quickly and accurately. By performing off-axis alignment based on the results, highly accurate and highly productive alignment can be performed without mechanically adjusting the apparatus itself.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an alignment apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing the shot arrangement and marks on a wafer, and FIG. 3 is a diagram showing the operation of the apparatus of the above embodiment. FIG. 4 is a flowchart for explaining the operation of off-axis alignment, FIG. 5 is a flowchart for explaining the operation of automatic baseline measurement, and FIG. 6 is a flowchart for explaining the operation of automatic baseline measurement. FIG. 7 is a flowchart for explaining the operation, FIG. 7 is an explanatory diagram for determining the wafer elongation rate and inclination, and FIG. 8 is an explanatory diagram for calculating the XY stage movement amount. XYS...XY stage, WS...wafer stage, WF...wafer, RT...reticle, RS...
Reticle stage, LI...printed projection lens, SL,
SR……Off-axis alignment scope, CB
...Control box, WML, WMR...
Off-axis alignment mark.

Claims (1)

[Claims] 1 off-axis measurement means for measuring positional errors of a plurality of wafer marks on a wafer using a plurality of off-axis alignment scopes;
After aligning the wafer using the positional error of each wafer mark measured by the off-axis measuring means, projecting a pattern onto the wafer based on the positional error of each of the plurality of shot area marks on the wafer. A TTL measuring means sequentially measures through the projection optical system, and each relative position of the off-axis alignment scope with respect to the projection optical system is determined by using the positional error of each shot area mark measured by the TTL measuring means. An alignment device characterized by having a calculation means for calculating a relationship.