JPH04124808A - Method of exposure - Google Patents

Abstract

PURPOSE:To improve the accuracy of focusing by, continuously measuring the surface height of a wafer along the direction of a wafer face and by setting a focal point within a range where the measured value shows the least change. CONSTITUTION:In a method for exposure by an exposure device for forming the pattern of a mask 20 by exposure on the surface of a wafer 22 placed on a stage, the surface height of the wafer 22 is continuously measured along the direction of the face of the wafer 22 and a focal point is set within a range where the measured value shows the least change. For example, a signal Sh showing the height Ph of the reflection point of the wafer 22 is outputted from a light sensor 28 and a profile generation circuit 30 takes in a series of signals Sh outputted while the wafer 22 is moved in the xy-direction, to generate a curve(profile) of the change of height of the reflection point Ph. The generated profile is sent to a region extraction circuit 31, which circuit 31 extracts, as the focal point, a region which shows the least change in the profile.

Description

[Detailed Description of the Invention] [Summary] This is an exposure method using an exposure device that forms a mask pattern on the surface of a wafer placed on a stage by exposing it to the surface of a wafer placed on a stage, with the aim of improving the precision of focus adjustment. The method is characterized in that the surface height of the wafer is continuously measured along the surface direction toward the wafer, and a focus point is set in a range where the measured value fluctuates least.

[Industrial application field]

The present invention relates to an exposure method for manufacturing semiconductor circuits.

2. Description of the Related Art In recent years, semiconductor circuits have become increasingly finer, and the resolution of exposure apparatus used to manufacture them has become even higher. In general, resolution can be improved by shortening the wavelength λ of exposure light or by increasing the numerical aperture NA (numerical aperture) of the lens.
This can be improved by increasing the NA, but on the other hand, increasing the NA has the disadvantage that the depth of focus (so-called depth of focus) becomes shallower, making it easier to lose focus, and accurate focus adjustment is required.

[Conventional technology]

As a conventional exposure apparatus having such a focus adjustment function, for example, as shown in FIG. For example, the optical sensor 10 has a PSD (Position 5en
sitive Device) is used.

The height of the wafer surface (exposure surface) is measured by the optical sensor 10, and the wafer height is finely adjusted so that the measured value coincides with a predetermined value that allows proper focus to be obtained.

[Problem to be solved by the invention]

However, such conventional exposure equipment is configured to perform focus adjustment based on the measured height of an arbitrary position on the wafer surface, so for example, if the arbitrary position coincides with a chip boundary groove (scribe line), To,
There is a problem in that the measurement light is diffusely reflected at the bottom and walls of the groove, causing an error in the measurement height, resulting in incorrect focus adjustment.

The present invention was made in view of these problems, and
The purpose is to improve the accuracy of focus adjustment.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an exposure method using an exposure apparatus that forms a mask pattern on the surface of a wafer placed on a stage by exposing the surface of the wafer along the surface direction of the wafer. It is characterized in that it measures continuously and sets a focus point in the range where the measured value fluctuates the least.

[Effect]

In the present invention, the focus point is set in the range where the height profile of the wafer surface has the least variation.

Here, the height profile varies greatly depending on the position of unevenness such as a scribe line or the position where the material of the surface changes.

Therefore, by setting the focus point while avoiding positions where such fluctuations are large, the error with the actual wafer surface height can be reduced and focus accuracy can be improved.

[Example〕 Hereinafter, the present invention will be explained based on the drawings.

1 to 4 are diagrams showing an embodiment of an exposure apparatus to which an exposure method according to the present invention is applied.

First, the configuration will be described. In FIG. 1, 20 is a mask, and the pattern of the mask 20 is formed by exposure on a wafer 22 through an optical lens 21.

The wafer 22 is placed on a stage (not shown), and is moved by an xy-direction moving mechanism 23 and a two-direction moving mechanism 24.
The wafer 22 is driven in the plane direction 1ii1 (xy direction) and in the direction perpendicular to the plane (two directions), respectively.

On the other hand, 2S is a light source for focusing, and this light source 25
The measurement light Pa from the wafer 22 is guided by the first mirror 26 to the surface of the wafer 22, and the reflected light Pb from the surface of the wafer 22 is guided by the second mirror 27 to the optical sensor 28. The optical sensor 28 includes, for example, a PSD (Pos
The optical sensor 28 outputs a signal sh indicating the height Ph of the reflection point on the wafer 22.

The signal sh is input to the profile generation circuit 30, and the profile generation circuit 30 takes in a series of signals sh while moving the wafer 22 in the X and Y directions, and generates a height change curve (hereinafter referred to as profile) of the reflection point Ph. generate.

The generated profile is sent to the region extraction circuit 31, and the region extraction circuit 31 extracts the region with the least variation in the profile as the focus point.

The two drive mechanisms 23 and 24 drive the wafer 22 in the x and y directions and in two directions so that the irradiation position of the measurement light on the wafer 22 matches the focus point extracted by the extraction circuit 31.

Here, FIG. 2 is a diagram showing an example of the moving direction of the wafer 22 when the profile is formed.

In this example, two moving directions A and B are set diagonally across the scribe line.

FIG. 3 is a diagram showing measurement profiles in two moving directions A and B, where the solid line corresponds to the moving direction A and the broken line corresponds to the moving direction B. FIG. The vertical axis represents the measurement height, and the horizontal axis represents the moving distance.

The part where the measurement height drops significantly corresponds to the scribe line position. In this part, an excessive drop (4.93 micrometers in the figure) than the actual depth of the line groove was observed due to the influence of diffuse reflection of light by the line groove. On the other hand, there are relatively flat parts in the profile. This flat portion exists in the area between the scribe lines.

The region extraction circuit 31 extracts such a friable region. Specifically, the difference value of the measured height between two adjacent moving points (○ in the profile) is calculated, and the difference value is determined based on a predetermined standard (l! δ) is recognized as a flat region.

Next, the effect will be explained.

FIG. 4 is a flowchart showing the processing of the embodiment. In this figure, S is an arbitrary chip number, So is a specific chip number, h is the focus measurement height, ho is the height of the best focus point, and 1 is the position number of the measurement location within the chip.

In this flowchart, first, in step S, a specific chip S0 is designated from among a large number of chips. The measurement point index of is initially set (i=1) at the measurement start position (step SZ). Then, the coordinates (X
8. After the stage is moved so that the measurement light Pa hits point y, ), and the height of that point is measured (step S4), the measurement point is moved until the measurement index reaches the final number (leFld). While counting up the indicators (
Steps Ss, Ss') and steps S3 and S4 described above are repeated.

As a result, from i=1st to j=Ie of specific chip S0
,, the height of the measurement point up to the dth point is measured continuously,
Generated as a height profile.

Next, after extracting the focus stable 9M region (above flat region) in the profile (step S),
Initialize the 7-bit index (S=1) L (step St), move the stage to the predetermined coordinates (xo, ye) of the S=1st chip indicated by the chip index (step SS)
.

Here, the predetermined coordinates (Xo, yo) correspond to the focus stable region in the profile, and therefore correspond to the coordinates at which the best focus point height h0 of the specific chip S0 is measured.

Next, focus measurement is performed on the predetermined coordinates (Xc+, yo), and the height h of the coordinate point is determined (step S9
), it is determined whether the difference value (lh-h, l) between this measured height and the height ho of the best focus point in the focus stable area falls within a reference value (δ) (step S1
゜). If it does not fit, in other words, if proper focus cannot be obtained, the height of the stage is changed.Step 5II), Steps S, , S, above. repeat.

In other words, the stage movement here is such that the height h of the predetermined coordinates (xo, yo) of the chip S is adjusted to the height ho of the best focus point in the focus stable area extracted previously.
The height ho is an accurate value that is not affected by scribe lines, etc.
Highly accurate autofocus is possible.

When such autofocus processing is completed, the stage is moved to the exposure start coordinates Ps (0, 0) of the chip (step S+z), and normal exposure processing is executed (step 513).

Then, the chip index is counted up until the chip index reaches the final number (S-, , a) in step S1. )
, the above steps S@~SI3 are repeated for each count amplifier until the chip index reaches the final number (S,...)
When this is reached (step 515), the series of processing is completed.

As described above, in this embodiment, (1) one specific chip S is selected from among a large number of chips; Specify this specific chip S0 as x
Generate the height profile of the chip surface while moving in the y direction; ■ Extract the area with the smallest variation in this profile as the focus point; ■ Set the coordinate height ho of the focus point to the same coordinate height of other chips. Since a series of autofocus processes such as aligning the scribe lines are executed, it is possible to avoid the scribe line and set an accurate focus standard (ho), thereby improving focus accuracy.

As a result, exposure and patterning of particularly miniaturized semiconductor circuits can be performed stably and with good reliability.

〔Effect of the invention〕

According to the present invention, it is possible to set an accurate focus reference while avoiding scribe lines, and it is possible to improve focus accuracy.

[Brief explanation of drawings]

1 to 4 are diagrams showing an embodiment of an exposure apparatus that uses the exposure method according to the present invention. 3 is a diagram showing the generated profile, FIG. 4 is a flowchart of the processing, and FIG. 5 is a schematic configuration diagram showing a conventional example. 20...Mask, 21...Optical lens, 22...Wafer, 23...--xy direction movement mechanism, 24...2-direction movement Mechanism, 25... Light source, 26... First mirror 27... Second mirror 28... Optical sensor 30... Profile generation Circuit, 31...
...Region extraction circuit. ＼-１７ Configuration diagram of one embodiment Fig. 1

Claims (1)

[Scope of Claims] An exposure method using an exposure apparatus that exposes and forms a mask pattern on the surface of a wafer placed on a stage, the method comprising: continuously measuring the surface height of the wafer along the surface direction of the wafer; An exposure method characterized by setting a focus point in a range where the measured value has the least variation.