DE102004010244A1 - High leakage current trench capacitor cells detecting method for use in dynamic RAM, involves comparing measure of leakage current of capacitor cells to recognize those cells having high leakage current - Google Patents

Abstract

The method involves directing an electron beam (3) toward an area (8) having trench capacitor cells (4) so that secondary electrons from the capacitor cells are emitted. A measure of leakage current of the capacitor cells are determined based on the quantity of the secondary electrons. The measure of leakage current of the capacitor cells are compared to recognize those cells having high leakage current. An independent claim is also included for a device for detecting trench capacitor cells having high leakage current on a substrate disk.

Description

The The invention relates to a method for detecting capacitance cells with elevated Leakage current in an exposed capacitance cell field on a substrate wafer, in particular, a method of detecting trench capacitance cells with elevated Leakage current. The invention further relates to a device for Detecting capacity cells on a substrate disk.

DRAM memory cells store information in the form of charges in capacity devices. These become common as capacity cells trained in the capacity is arranged in a trench on a semiconductor surface of a substrate. Due to their manufacturing process, it comes in the operation of the integrated Memory circuit to leakage currents in the capacity cells, can drain through the stored charges and thus possibly the stored information is lost.

Around To avoid the loss of information, are usually the charges in the capacity cells reinforced at regular intervals. It will thereby avoiding that the information stored therein is lost goes. This process is called refreshing and is done at regular intervals in all capacity cells carried out. The time intervals the refreshing processes are on the one hand as possible big too choose, to limit the power consumption of the integrated memory circuit. On the other hand, it is necessary that the time between refresh operations be sufficient chosen small is, so that's in the capacity cells stored information can not be lost. The so-called Retention time is the set time period in which a capacity cell holds the charge information stored therein reliably, and whose minimum value is specified according to specification. In the manufacture of the integrated memory circuit, it is thus necessary that the retention time is larger as the predetermined refresh period.

During the Making the integrated memory circuit can reduce the retention time the capacity cells not yet monitored so that the time between processing the capacity cells and testing the retention time in the finished device becomes very large. This is the process development in terms of retention time very difficult and time consuming.

It is therefore an object of the present invention, a method and a device available to put up with that already during the production of the integrated circuit as soon as possible after the Processing the capacity cells a measure of the retention time, which correlates with the leakage current behavior of the capacitance cell determined can be.

These The object is achieved by the method according to claim 1, as well as by the Device solved according to claim 7.

Further advantageous embodiments of the invention are specified in the dependent claims.

According to one The first aspect of the present invention is a method for detecting of capacity cells with elevated Leakage current to an exposed capacitance cell array on a substrate wafer intended. On an area with one or more capacity cells on the substrate disk, an electron beam is directed, so that secondary electrons from the surface of the substrate are emitted. A measure of the leakage current of a capacitance cell in the area becomes dependent from the amount of emitted secondary electrons from the capacitance cell certainly. The dimensions for the leakage current the multiple capacity cells are compared to capacity cells with elevated To detect leakage current.

The inventive method offers a way already during the processing of integrated memory circuits with capacity cells to see if and which of the capacity cells one in comparison to the rest Capacitance cells increased leakage current exhibit. By irradiating the surface of the substrate with a Electron beam become secondary electrons from the surface emitted, the number of emitted secondary electrons on the size of the the surface located Charge in the substrate depends. That is, ever lower the potential at a location on the surface of the Substrate is, the more electrons are there and the more become more secondary electrons emitted when irradiated with an electron beam.

aid The detected amount of emitted secondary electrons can draw conclusions about the at one point of the surface potential of the substrate are met. That at a capacity cell prevailing potential is dependent from their leakage current behavior with respect of the surrounding substrate and can be used as a measure of electrical resistance between the two electrodes of the capacity to be accepted by which determines the leakage current behavior of the relevant capacity cell is.

In a first embodiment, the emitted secondary electrons are optically detected in the area, wherein an intensity of the optically detected representation of each of the capacitance cells indicates a measure of the leakage current of the capacitance cells located in the area.

Preferably the substrate of the substrate wafer is biased with a bias voltage, the bias being chosen can be to the intensity to adjust the optical representation. The bias determined the height the stratoberfläche on the sub charge so that by adjusting the bias the Potential at the substrate surface to an optimum sensitivity range for the optical detection of emitted secondary electrons can be adjusted.

According to one another embodiment the substrate of the substrate wafer is biased with a bias voltage, wherein the amount of secondary electrons emitted in the region is detected by the current is detected in the substrate. One Measure for the average Leakage current of the capacitance cells in the area depends on the height of the detected current. By irradiating an area the substrate surface with an electron beam primary electrons are recorded in the surface, wherein the recorded primary electrons secondary electron from the surface knock out, which are discharged from the surface. The number in the surface recorded primary electrons and the number of emitted secondary electrons provide a surplus or a loss of electrons in the substrate disk with the Result that a current flows into the substrate or from the substrate. This Current is measured and provides a measure of the average leakage current the capacity cells located in the area.

By Comparison of the currents into the substrate when irradiating several areas of the capacitance cells with the electron beam can be detected, whether and which of Areas at least one capacity cell with an elevated Has leakage current.

According to one Another aspect of the present invention is a device for detecting capacity cells with increased Leakage current in an exposed capacitance cell array on a substrate wafer intended. The device has an electron beam source, around an electron beam on a region with one or more capacitance cells to direct, so that secondary electrons from the capacity cells be emitted. With a detection unit is an amount for the emitted secondary electron detected, with the help of an evaluation unit is a measure of the leakage current dependent is determined by the amount of emitted secondary electrons.

aid of such a device, it is possible to depend on the amount of emitted secondary electron when irradiated with an electron beam to the measure of the leakage current one or more capacity cells close.

According to one another embodiment the detection unit comprises an optical detection system, wherein an intensity an optically detected representation on each of the capacitance cells a measure of the leakage current which is present in the area of capacity cells.

According to one another embodiment the substrate of the substrate wafer is connected to a voltage source, wherein the detection unit comprises a current sensor for detecting the current to measure into the substrate, where the measured current is a measure of the amount the emitted secondary electrons represents.

preferred embodiments The invention will be described below with reference to the accompanying drawings explained in more detail. It demonstrate:

1 an apparatus for detecting capacitance cells with increased leakage current according to a first embodiment;

2 an apparatus for detecting capacitance cells with increased leakage current according to a second embodiment of the invention;

3 a cross-section of a section of a surface portion of the substrate wafer;

4 a representation of the optimal detection of multiple areas with multiple capacity cells with normal and increased leakage currents; and

5 a schematic representation of the operation of a method for detecting capacitance cells with increased leakage current.

In 1 Fig. 10 is an apparatus for detecting capacitance cells with increased leakage current according to a first embodiment of the present invention. It comprises an electron beam source 1 that has an electron beam 3 to one area 8th a substrate disk 2 directed, on the capacity cells 4 are arranged for an integrated memory circuit. The capacity cells 4 are exposed after their processing, so that their surfaces for the electron beam 3 without hindrance he are achievable. The exposure may be done, for example, by means of etch back or a chemical mechanical polishing (CMP) method. In the present case, these are trench capacitance cells, wherein the trench capacitances are arranged in trenches.

The capacity cells 4 wise, as in 2 shown one in a ditch 5 arranged conductive material 6 as an inner electrode, in particular a polysilicon material, which from the surrounding substrate as the outer electrode through an insulating layer 7 is isolated. Because the insulation layer 7 Leakage regions can flow through these areas, which drain a charge stored in the trench capacitance and thus destroy the information stored therein. The leakage current behavior of such a capacitance cell, ie, the time period in which the charge can be stored, is critical to the retention time of a memory cell formed with such a capacitance cell, and it is necessary that the retention time be predetermined by a specification Time exceeds. This is only possible if the flowing leakage currents do not exceed a certain level.

In order to recognize capacitance cells with increased leakage current already during the production of the integrated memory circuit, the in 1 shown device used.

The area 8th the capacity cells 4 on the substrate disk 2 by the electron beam 3 is irradiated by means of an optical detection device in the form of an electron-sensitive camera 9 captured, so by the electron beam 3 from the surface of the substrate disk 2 knocked out secondary electrons using the camera 9 can be recognized. The camera 9 is with a display unit 10 connected on the number of emitted secondary electrons at any point of the range 8th , eg in the form of gray levels, so that the darker a spot in the area on the display unit 10 is shown, the more secondary electrons are emitted at this point.

To the leakage current behavior of the capacitance cells of an entire substrate wafer 2 or a surface of a substrate wafer 2 that is larger than the range 8th to detect are the electron beam source 1 and the camera 9 and the substrate disk 2 so mutually displaceable that the electron beam 3 can be directed to different areas of the substrate wafer. This can be done, for example, by moving the substrate disk 2 or by shifting the electron beam source 1 and the camera 9 be achieved.

The camera 9 has a sensitivity range in which differences in the amount of emitted secondary electrons can best be determined and with the greatest contrast in the display unit Kon 10 can be represented. To adjust the amount of emitted secondary electrons, on the one hand, the energy of the electron beam 3 to be changed. The greater the energy of the surface of the substrate disk 2 incident primary electrons, the more secondary electrons can be knocked out of the surface by the incident primary electrons. On the other hand it is possible that substrate of the substrate disk 2 , which surrounds the capacitance cells, with a bias to occupy, so that depending on the leakage current behavior of the capacitance cells different potentials at the inner electrodes of the capacitance cell 4 available. This bias voltage can be applied to the substrate by the substrate wafer 2 on a conductive support 10 rests, with a voltage source 11 connected is. The voltage of the voltage source 11 is set to that on the display unit 10 shown measure of emitted secondary electrons, eg in the form of gray levels reliable detection of capacitance cells with respect to adjacent capacity cells increased leakage current can be detected.

In 3 For example, several areas of a substrate wafer with capacitance cells are shown. One recognizes the oval-shaped capacity cells, that of the isolation layer 7 are surrounded. The insulation layer 7 is shown on the display unit as a bright area, since this layer is insulating and thus only a few or no secondary electrons through the electron beam 3 can be knocked out.

Some of the capacitance cells have an inner electrode which is darker in color, ie, more secondary electrons are emitted there than in adjacent capacitance cells. This means that the potential of these internal electrodes is lower than the potential of the remaining capacitance cells. This potential results from the predetermined by the bias voltage potential of the substrate 2 , which influences the potential of the inner electrode via a leakage current path.

In the case of the capacitance cells, which do not have an increased leakage current, is ideally from a leakage current of the height 0 went out. The gray level of the internal electrodes of such capacitance cells then results from a compensation potential, which then results when the number of electrons absorbed by the electron beam 3 the number of emitted secondary electrons substantially corresponds. If a capacity cell 4 has a leakage current path, the potential of In changed and thus displayed in a different gray level. This can also be a lighter gray level, for example, when the bias voltage is positive than the compensation potential, than in the case of a capacitance cell with normal leakage current behavior.

Of course you can the amount of emitted secondary electrons be represented by other forms of presentation in the display unit, for example, by a color representation.

at an adjusted system, the gray level, with an inner electrode is shown with a certain leakage current and thus with a certain retention time are correlated, so that too quantitative Measurements using this system are possible.

In 4 a second embodiment of the device according to the invention is shown. It shows an electron beam source 20 that has an electron beam 21 to one area 22 a substrate disk 23 directed. At the surface of the substrate disk 23 there are capacity cells 24 whose leakage current behavior is to be investigated. The substrate disk 23 is on a carrier 25 that has a voltage source 26 is occupied by a bias voltage V _V. In the current path between the voltage source 26 and the carrier 25 is a current measuring unit 27 placed in the substrate of the substrate disk 23 to measure flowing electricity. The height of the in the current sensor 27 measured current while an area 22 with the electron beam 21 is irradiated, corresponds to a measure of the average leakage current in the area 22 located capacity cells 24 , Become now with the electron beam 21 in the manner described above, other areas of the substrate wafer 23 irradiated with substantially the same number of capacitance cells, it can be qualitatively concluded after comparing the measured currents for the different areas, whether one or more capacitance cells with increased leakage current in the area are.

Preferably, the comparison is made with respect to an average value resulting from the measured currents for all the measured ranges 22 on the substrate disk 23 results.

The Width of the electron beam is preferably chosen so that he possible Areas of equal size and in the Essentially covering the same number of capacity cells. Of course it is also possible, to direct the electron beam to only one capacitance cell, if this one on a correspondingly small area can be focused.

In 5 schematically a capacitance cell is shown, to which the electron beam 21 meets. It can be seen that the secondary electrons are emitted and the resulting current IS flowing into the substrate is the strength IP of the electron beam 21 and the amount of emitted secondary electrons.

1

electron beam source

2

substrate wafer

3

electron beam

4

Trench capacity cells

5

inner electrode the trench capacitance cell

6

polysilicon

7

insulation layer

8th

Area

9

camera

10

display unit

11

voltage source

12

carrier

20

electron beam source

21

electron beam

22

Area

23

substrate wafer

24

Trench capacitance cell

25

carrier

26

voltage source

27

power source

Claims (9)

Method for detecting capacitance cells ( 4 . 24 ) with increased leakage current in an exposed capacitance cell array on a substrate wafer ( 2 . 23 ), comprising the following steps: - directing an electron beam ( 21 ) to one area ( 8th ) with one or more capacity cells ( 4 . 24 ), so that secondary electrons from the capacitance cells ( 4 . 24 ) are emitted; Determining a measure of the leakage current as a function of the quantity of emitted secondary electrons for a plurality of capacitance cells ( 4 . 24 ); Comparing the leakage current dimensions of the plurality of capacitance cells ( 4 . 24 ) to capacity cells ( 4 . 24 ) with increased leakage current. The method of claim 1, wherein the emitted secondary electrons in the region ( 8th . 22 ) are optically detected, wherein an intensity of the optically detected representation at each of the capacitance cells ( 4 . 24 ) a measure of the leakage current in the area ( 8th . 22 ) capacity cells ( 4 . 24 ) indicates. Method according to claim 2, wherein a substrate of the substrate wafer ( 2 . 23 ) is biased with a bias voltage (V _V ). The method of claim 3, wherein the bias voltage (V _V ) is selected to adjust the intensity of the optical representation. Method according to claim 1, wherein the substrate of the substrate wafer ( 2 . 23 ) is biased with a bias voltage (V _V ), the amount of in the region ( 8th . 22 ) is detected by detecting the current in the substrate, whereby a measure of the average leakage current of the capacitance cells located in the region ( 4 . 24 ) is determined depending on the magnitude of the detected current. Method according to claim 5, wherein the electron beam ( 3 . 21 ) to several areas ( 8th . 22 ) of the capacitance cell array, whereby it is detected by comparing the currents through the substrate, whether and which of the areas ( 8th . 22 ) at least one capacity cell ( 4 . 24 ) having an increased leakage current. Device for detecting capacitance cells ( 4 . 24 ) with increased leakage current in an exposed capacitance cell array on a substrate wafer ( 2 . 23 ), with an electron beam source, to an electron beam ( 3 . 21 ) to one area ( 8th . 22 ) with one or more capacity cells ( 4 . 24 ), so that secondary electrons from the capacitance cells ( 4 . 24 ) are emitted, with a detection unit to detect a measure of the emitted secondary electrons, and with an evaluation unit to determine a measure of the leakage current depending on the degree of the emitted secondary electrons. Apparatus according to claim 7, wherein the detection unit is an optical detection system ( 9 . 10 ), wherein an intensity of an optically detected representation on each of the capacitance cells is a measure of the leakage current in the region ( 8th . 23 ) capacity cells ( 4 . 24 ) indicates. Apparatus according to claim 7, wherein the substrate of the substrate wafer with a voltage source ( 26 ), and wherein the detection unit comprises a current sensor ( 27 ) to measure the current into the substrate, wherein the measured current is a measure of the emitted secondary electrons.