JP2875125B2 - System for recording data patterns on planar substrates - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the generation of photographic means, and more particularly to the generation of masks and reticles used in the semiconductor industry.

The prior art in the semiconductor industry uses different methods to expose a layer of photoresist deposited on top of a metal layer to generate photographic means. After exposure, the photoresist is developed and used as a mask to etch the metal layer (typically chromium deposited on quartz). Because it involves a development process,
The pattern cannot be inspected during exposure. A second disadvantage of the development process is the potential increase in the number of defects caused by using a multi-step process. Prior art attempts to generate photographic means without photolithography include ablation of metal or polymer layers. These attempts have not been entirely successful because very short wavelengths generated only by excimer lasers are needed for clean ablation. Excimer lasers have low repetition rates, which has hindered their use in high data rate applications. Conventional light valves, such as liquid crystals, do not adequately pass the short wavelengths of excimer lasers.

[0003]

SUMMARY OF THE INVENTION In accordance with the present invention, a deformable mirror spatial light modulator is used with a guided excimer laser.
A number of data bits are recorded with each laser pulse. Deformable mirror light modulators are available from Texas Instruments
Incorporated (Texas Instrument)
nts Inc. ) (Texas) and its operating principle is U.S. Pat. No. 4,441,441.
No. 791. A detailed description of the operation is given in L. J. “Deformable Mirror Spatial Light Modulator (Deformable-) by Hornbeck
Mirror Spatial Light Modu
lors) "(The minutes of the 1989 SPIE, 11th edition)
50). No further details regarding this device will be given here. The deformable mirror array is imaged on a polymer coated quartz substrate at a typical reduction ratio of about 100: 1. Due to the large reduction ratio, the energy density on the deformable mirror is thousands of times lower than in the polymer, so that the polymer is ablated without damage to the mirror (a
bate). To avoid solid waste (primarily carbon) as a by-product of ablation, ablation is performed in an atmosphere of an inert gas (to prevent combustion) or an oxygen atmosphere (to complete the combustion of solid waste).
Made in Two levels of polymer coating can be used to generate the phase shift mask. It is an object of the present invention to provide a fast and photolithographic free method for generating photographic means such as masks and reticles for the semiconductor industry. It is a further object of the invention to demonstrate the photographic means at the same time that it is being generated by comparing the written data with the transmission of the photographic means. Another object of the present invention is to generate and demonstrate a phase shift mask. It is yet another object of the present invention to have an apparatus suitable for both photographic means generation and direct imaging on photoresist (ie, direct writing on silicon wafers).

[0004] These and other objects of the present invention will become apparent in the following description taken in conjunction with the drawings.

[0005]

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a two-dimensional deformable mirror spatial light modulator 1 is pulsed by an excimer laser 3 and emitted by a mirror 4 onto a modulator 1. Irradiated by the beam. 1
When the deformable mirror at is not activated, the light beam 2 becomes the light beam 5 as an absorber
6 is reflected. The activated mirror forms a beam 7 directed to a lens 8. The lens 8 forms an image 10 of the activated mirror on the coated substrate 9. The substrate 9 is moved in one direction by the precision step 11 and in the other direction by the precision step 12. The position of stage 11 is measured by interferometer 13 and the information provided by interferometer 13 is used to synchronize both the light pulses from excimer laser 3 and the data loaded into modulator 1. The details of the precision stages 11, 12 and the interferometer 13 need not be shown here, since this type of XY stage is a common practice in the semiconductor industry. The only difference between industrial practice and the present invention in the area of precision stages is that the interferometer 13 is not used to control the position of stage 11, The fact that it is only used to generate timing information based on position. This means that step 11
Easier and more accurate than trying to control the position of

[0006] The photographic means can be generated from the substrate 9 in two different ways. The first is a conventional method using a quartz / chrome / photoresist structure, exposing the photoresist and etching chromium using it as a mask. The same method is used when utilizing the present invention to write on a photoresist coated silicon wafer. A second method consists of coating the quartz substrate with a thin polymer layer using, for example, about 1 micron thick polyimide. This layer can be ablated by an excimer laser and forms a photographic means without the need for any further processing. A process gas 15 is supplied by a nozzle 14 through the ablation zone to prevent the formation of solid waste as a by-product of the ablation. The process gas can be an inert gas or an oxidizing gas. By way of example, excimer laser 3 is a XeCl waveguide laser operating at 308 nm. The laser is powered by Potomac Photonics, Inc.
Inc. (Made by Lanham, MD) and generates up to 100 microjoules per pulse at a repetition rate of 1,000 Hz. It has 1,000 x 1,000 elements on a 17 micron pitch. The numbers in Texas Instruments
By using a deformable mirror modulator 1 (typical of a modulator made by Incorporated) and an 85 × reduction lens, an exposed image 1 is obtained.
Each pixel at 0 is 0.2 × 0.2 microns. The size of the image is 200 × 200 microns. The energy density of the image 10 is 0.1 mJ / 0.02 × 0.
Equivalent to 02 cm ² = 0.255 J / cm ² , which is sufficient for ablation. The energy density on the modulator is a factor less than (85) ² = 7225, which is low enough not to damage the modulator. When photographic means are used for other wavelengths, such as g-line and i-line steppers, the optical density of the polyimide at a particular wavelength can be increased by the addition of a UV absorbing dye.

[0007] When the completed photographic means is used in an excimer laser stepper, further ablation is eliminated. This is because the typical reduction ratio in a stepper is 5X, and therefore the energy density on the photographic means is a factor 25 times lower than the energy density on the wafer.

[0008] Because the beam cross section of a guided excimer laser is not uniform and tends to be Gaussian in at least one direction, some form of beam profile modification is required to achieve uniform exposure. Referring now to FIG. 2, the overlap method is shown, where each point is exposed four times. This makes it possible to perform a very uniform exposure using a beam having a Gaussian distribution and a trapezoidal distribution, as is apparent from the exposure state schematically shown in FIG. Another advantage of multiple exposures stems from the fact that excimer laser ablation is a non-linear process, and that the first pulse of light tends to remove less material than subsequent pulses. In order to realize the exposure method shown in FIG. 3, data has to be shifted in the modulator 1 in a direction opposite to the direction of travel of the substrate 9. The data shift is synchronized with the movement of the substrate 9 as follows. Referring now to both FIG. 1 and FIG. 2, a 1,000 × scaled image is drawn at an 85 × ratio to form a 200 × 200 micron area, which is the numerical example above.
By using 1,000 pixel modulators, a new exposure pulse must be generated every 100 microns of substrate 9 advance. The sequence of the exposure is shown in FIG. The interferometer 13 generates a pulse every 100 microns. This pulse causes the laser 3 to emit a very short (typically less than 100 ns) pulse of light,
In addition, a process of loading data into the modulator is started. Since the laser 3 operates at about 1,000 pulses per second, the data rate to the modulator is about 1 Gbit / sec. The effective writing speed is 250 Mbits / sec since each bit is exposed four times. Due to the larger modulator and faster repetition rate of the laser, effective writing speeds in excess of 1 Gbit / s are possible. The speed of advance with respect to the substrate 9 is 100 per ms.
Microns or 100 mm / sec. At the end of each scan (typically 200 mm or 2 seconds), the positioner 12 moves 100 microns in the orthogonal direction. After each exposure pulse, the data is shifted in the modulator as shown in FIG. Characters A, B, C in FIG.
Etc. symbolize the data pattern loaded into the modulator.

The structure of the photographic means is shown in FIG. Typically, a quartz substrate 9 having a thickness of 3 mm to 6 mm is about 1 mm.
Coated with micron polyimide 16. Polyimides include organic dyes and may increase their optical density at certain wavelengths, such as g-line or i-line. An overcoat 19 of a polymer having a higher ablation threshold can be provided to increase the damage threshold when used in an excimer laser stepper.
The thickness of the overcoat 19 is a fraction of 1 micron, typically between 0.1 and 0.2 microns. The ablation process is self-limiting when the quartz substrate is exposed.

In order to increase the resolution when used in a stepper, a "Levenson-type phase shift mask (Lev.
enson type phase shift-ma
A mask type known as “sk)” can also be manufactured using the present invention. In this mask, the alternating apparent features have a 180 ° optical phase shift imparted to them. By way of example, a phase shift mask suitable for an i-line stepper and consistent with the present invention is shown in FIG. The quartz substrate 9 is covered with a layer of positive photoresist 20. The thickness of layer 20 is exactly 180 ° at the i-line wavelength
Is calculated. On top of layer 20, about 1
A layer of micron polyimide 16 is deposited. By using different ablation ratios of the polyimide positive photoresist and using multiple exposures, the pattern is that the alternating features are cut down to the quartz while the other features are cut only in the top layer Can be cut in such a way as to be done. The completed mask is shown in cross section in FIG. After completion, the entire mask is exposed to intense i-line irradiation from a mercury arc lamp. This causes the positive resist to become transparent to the i-line. As an example, a 5-minute flood exposure to an arc lamp will result in the phase shift layer being i-
It will cause it to have 99% transparency at the line wavelength. Opaque layer 16 is not affected by the i-line.

An additional feature possible with the present invention is the demonstration of the photographic means being generated. This step is schematically illustrated in FIG. Lens 17 is a charge coupled device (C
CD) Draw a completed portion of the currently imaged area on the array 18. Using the example of FIG. 2, the completed portion is the portion that will receive the fourth exposure. This part forms one quarter of the exposed area. 250x2 of current exposure
250x to draw the completed part of 50 pixels in the image
By using a 250 element CCD array, high resolution is obtained for data validation and defect detection. This operation is widely used in optical data storage devices and is known as "read after write". No further details on data handling are given. The analog output of the CCD is compared by a comparator 21 to a preset reference 22 and converted to binary data. This data is compared to the data loaded into the modulator to generate a defect map for the write pattern.

The threshold 22 is set to a level representing the threshold of the photoresist to be used in the photographic means (eg, the photoresist used on a silicon wafer when exposed in a stepper by the photographic means). By doing so, the performance of the mask can be quickly evaluated. This is especially important for phase shift masks.
This is because their performance is hard to predict. If the lens 17 in FIG. 4 has similar performance to the lens used in a stepper, the data output from the comparator 21 will provide a reliable indication of the performance of this mask on the stepper. For demonstration of mask performance, the resolution of the CCD 18 must be higher than the modulator to minimize errors caused by quantization. For example, 1,000 × 1,000
A zero element CCD can be used in the previous example of 250 × 250 bit imaging.

[0013] These and other objects of the present invention will become apparent in the following description in conjunction with the accompanying drawings.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a preferred embodiment.

FIG. 2 illustrates a method of overlapping written images used to increase exposure uniformity.

FIG. 3 is a graph illustrating the increase in exposure uniformity achieved by the overlapped exposure method.

FIG. 4 is a cross-sectional view of the photographic means also showing the inspection principle.

FIG. 5 is a diagram showing a cross-sectional view of a photographic means when making a phase shift mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mirror spatial light modulator 4 Mirror 5 Light beam 8 Lens 9 Substrate 10 Image 13 Interferometer 14 Nozzle

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Amos Michelson Canada, Buoy 6, N2, J3, Vancouver BC, Double Thirty Force Avenue, 2697 (56) References JP Hei 6-95257 (JP, A) Special table Hei 5-502141 (JP, A) Special table Hei 6-510632 (JP, A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) G03F 1 / 00-1/16

Claims (18)

(57) [Claims] 1. A system for recording a data pattern on a planar substrate having a thin coating, comprising: a laser operating in a pulsed mode; and a deformable mirror array light modulator illuminated by the laser. And means for loading the data pattern onto the modulator; and a reduction lens for forming a reduced image of the modulator on the substrate, wherein the reduction lens is activated by the data pattern. Positioned relative to the modulator in a manner that allows only light reflected by the deformable mirror to reach the reduction lens, and light incident on the modulator without damaging the modulator And that the light incident on the planar substrate has sufficient power density to image the coating thereon. Means for reducing the image of the modulator on the substrate, and generating relative motion between the substrate and the reduction lens; and the data pattern and the pulsed laser light at the modulator. Means for synchronizing a pulse with the relative motion, which records the data pattern on a portion of the substrate that is larger than the reduced image by combining a plurality of the reduced images. A system wherein the laser light reaching the planar substrate is capable of ablating a thin coating on the planar substrate. 2. The system for recording a data pattern on a planar substrate according to claim 1, wherein said pulsed laser is an excimer waveguide laser. 3. The system for recording a data pattern on a planar substrate according to claim 1, wherein the planar substrate is a reticle used for manufacturing a semiconductor. 4. The system for recording a data pattern on a planar substrate according to claim 1, wherein the planar substrate is a silicon wafer used in semiconductor manufacturing. 5. The planar substrate of claim 1, wherein the recording is performed by ablation of a thin layer of an ultraviolet absorbing dye deposited on the substrate, and no further processing of the substrate is required after recording. A system for recording data patterns on top. 6. The recording is performed by ablation of a thin layer of an ultraviolet absorbing dye deposited on the substrate,
And for recording a data pattern on a planar substrate according to claim 1, wherein the recorded data is verified by measuring the amount of light passed through the substrate immediately after the recording of the data. System. 7. The recording is performed by ablation of a thin layer of an ultraviolet absorbing dye deposited on the substrate,
The system for recording a data pattern on a planar substrate according to claim 1, wherein the ablation is performed in an atmosphere of a gas other than air. 8. The substrate is coated with at least two thin layers of material, one of said layers being used to shift the phase of light transmitted through the substrate, while another is 2. The method for recording a data pattern on a planar substrate according to claim 1, wherein the mask forms an opaque mask that can be recorded by the laser and the combination of the substrate and the layer forms a phase shift mask. system. 9. The substrate is coated with at least two thin layers of material, one of the layers being used to shift the phase of light transmitted through the substrate, while another layer is the laser. A phase shift mask that forms an opaque mask that can be ablated by and that the combination of layers can be demonstrated by measuring the amount of light transmitted through the substrate after the recording of the data Form,
A system for recording a data pattern on a planar substrate according to claim 1. 10. A system for recording a data pattern on a planar substrate having a thin coating, comprising: a laser operating in a pulsed mode; and a deformable mirror array light modulator illuminated by said laser. And means for loading the data pattern onto the modulator; and a reduction lens for forming a reduced image of the modulator on the substrate, wherein the reduction lens is activated by the data pattern. Positioned relative to the modulator in a manner that allows only light reflected by the deformable mirror to reach the reduction lens, and light incident on the modulator without damaging the modulator And that the light incident on the planar substrate has sufficient power density to image the coating thereon. Minute, means for reducing the image of the modulator on the substrate, and generating relative movement between the substrate and the reduction lens; and for each spot on the substrate, data corresponding to the spot. Means for loading and shifting a data pattern to the modulator in synchronism with pulses and relative motion from the laser for multiple exposures. 11. The system for recording a data pattern on a planar substrate according to claim 10, wherein said pulsed laser is an excimer waveguide laser. 12. The system for recording a data pattern on a planar substrate according to claim 10, wherein the planar substrate is a reticle used for manufacturing a semiconductor. 13. The system for recording a data pattern on a planar substrate according to claim 10, wherein the planar substrate is a silicon wafer used in semiconductor manufacturing. 14. The planar substrate of claim 10, wherein the recording is performed by ablation of a thin layer of an ultraviolet absorbing dye deposited on the substrate, and no further processing of the substrate is required after recording. A system for recording data patterns on top. 15. The method according to claim 15, wherein the recording is performed by ablation of a thin layer of an ultraviolet absorbing dye deposited on the substrate, and wherein the recorded data is passed through the substrate immediately after the recording of the data. The system for recording a data pattern on a planar substrate according to claim 10, which is demonstrated by measuring the amount of 16. The method of claim 10, wherein the recording is performed by ablation of a thin layer of an ultraviolet absorbing dye deposited on the substrate, and wherein the ablation is performed in an atmosphere of a gas other than air. A system for recording data patterns on a computer. 17. The substrate is coated with at least two thin layers of material, one of said layers being used to shift the phase of light transmitted through the substrate, while another is The method for recording a data pattern on a planar substrate according to claim 10, wherein the opaque mask capable of being recorded by the laser is formed, and a combination of the substrate and the layer forms a phase shift mask. system. 18. The method according to claim 18, wherein the substrate is coated with at least two thin layers of material, one of the layers being used to shift the phase of light transmitted through the substrate, while another layer is provided with the laser. A phase shift mask that forms an opaque mask that can be ablated by and that the combination of layers can be demonstrated by measuring the amount of light transmitted through the substrate after the recording of the data A system for recording a data pattern on a planar substrate according to claim 10, wherein the system forms.