JP3175765B2 - Inspection method for semiconductor wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for inspecting a semiconductor wafer having a plurality of contact holes.

[0002]

2. Description of the Related Art Conventionally, a semiconductor substrate is provided with a large number of holes called contact holes. The contact hole refers to a hole provided in an insulating film such as a silicon oxide film and having a diameter smaller than 0.2 μm to electrically connect different conductive layers. Contact hole is usually RI
Although the silicon oxide film is formed by etching such as E, the aspect ratio, which is the ratio of the depth to the diameter of the hole, tends to change year by year, and the shape is longer and thinner.

[0003] The shape of the contact hole is determined after the etching process is completed. Usually, when a contact hole is formed under the correct conditions, a through hole is formed in the substrate. However, if the conditions are not set correctly, the hole does not penetrate the substrate and the oxide film remains at the bottom.

[0004] Therefore, an electron beam is injected into a semiconductor device having a contact hole formed therein, and a current flowing through the semiconductor substrate is measured to determine the presence or absence (thickness) of a silicon oxide film. There is a method of determining whether or not it is formed as described above. According to this method, an electron beam is sequentially injected into each and every fine hole formed in a wafer, and a predetermined reference value is compared with a current value of the penetrating electron beam. Is determined based on whether or not is larger than a reference value.

[0005]

However, in recent years, the fine processing technology of a semiconductor substrate has been advanced, and an innumerable millions of fine contact holes have been formed on a single substrate. The number of contact holes has increased by one digit in five years. Inspecting these holes one by one takes a great deal of time. Therefore, it is difficult to measure a practical number of wafers.

At present, there is no inspection apparatus capable of measuring many contact holes in a short time. For example, one wafer is extracted from several lots and the contact holes of the wafer are inspected. Therefore,
A statistically effective inspection quantity required for process management has not been secured.

Further, even if a contact hole exists in a semiconductor substrate, a large amount of time is required for inspection.
There is a problem that it takes a long time to find a defective contact hole, and it is not possible to perform feedback processing for maintaining a manufacturing process immediately after finding a defective contact hole.

[0008]

According to the present invention, there is provided a method of inspecting a semiconductor wafer having a plurality of contact holes, the method comprising dividing the semiconductor wafer into a plurality of desired first regions. By irradiating each first region with an electron beam, measuring the current value of the electron beam penetrating the contact hole in each first region, and comparing the current value with a desired threshold value A ratio of a contact hole that is not formed normally among the plurality of contact holes in the first region is inspected.

That is, according to the present invention, a semiconductor wafer is divided into a plurality of regions, and it is inspected for each region whether or not a contact hole included in the region is formed normally.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

First, a method for inspecting whether a contact hole of a semiconductor device is formed will be described.
In general, there are two methods for checking whether or not a contact hole is formed correctly. One is a method of irradiating a semiconductor substrate having an etched oxide film with an electron beam to measure and inspect a current value of an electron beam penetrating a contact hole. In this method, an electron beam is irradiated to measure and measure the amount of secondary electrons from the bottom of the contact hole that is not formed normally and does not penetrate and the surface of the semiconductor substrate.

FIG. 1 is a view showing a method of measuring whether or not a contact hole is formed by measuring a current value of a penetrating electron beam, and shows an oxide film in which a plurality of non-penetrating contact holes 4 are formed. When the electron beam 1 is irradiated on the semiconductor substrate having the above, a current penetrates the bottom of the contact hole 4. The amount of the through current 2 is measured to determine whether the contact hole 4 is formed normally.

That is, in this method, the electron beam penetrates through the etched contact hole 4 because the oxide film is thinner than other regions. The through current 2 is the sum of the through currents passing through the bottoms 3 of the individual contact holes,
The current is proportional to the number of contact holes 4.

On the other hand, FIG. 2 is a view showing a technique for measuring whether or not a contact hole has been formed by measuring the amount of secondary electrons, and includes an oxide film having a plurality of non-penetrating contact holes. Electron beam 21 on a semiconductor substrate
Irradiation, secondary electrons 25 and 23 are generated from the contact hole bottom 26 and the oxide film surface 22, respectively. The number of secondary electrons (the amount of secondary electrons) is measured to check whether a contact hole is formed.

Generally, the area of the oxide film surface 22 is larger than the area of the contact hole bottom 26, so that the ratio of the secondary electrons 25 to the detected secondary electrons 23 and 25 is small.

Further, since the area of the oxide film surface 22 has no relative relationship with the area of the contact hole bottom 26,
When the measurement position of the secondary electron quantity 25 is changed, a secondary electron signal independent of the thickness of the oxide film at the contact hole bottom 26 is obtained.

Therefore, in the embodiment described below, an electron beam 1 is applied to a substrate, and a through current 2 passing through a contact hole 4 is measured to check whether a contact hole is formed. The method shown in FIG.

In the process of manufacturing a semiconductor substrate, the frequency of occurrence of defective contact holes is extremely low except for the initial stage of mass production of the semiconductor substrate. Therefore, the contact holes of most of the substrates on which the devices are formed are non-defective, and it is wasteful to inspect all the contact holes one by one.

That is, the conventional inspection method employs a so-called brute force method in which all contact holes are inspected one by one, but in this embodiment, the contact holes are divided into several blocks (regions). ), A through current generated from the block is obtained, and an inspection is performed from a region where a defective contact hole is likely to be present, so as to efficiently detect the defective contact hole in a short time.

More specifically, the wafer is divided into several blocks, each block is irradiated with an electron beam, and the current value of the current passing through the contact hole in each block is calculated as follows.
Compared with a preset threshold value of a non-defective contact hole, the difference between the two is detected, and the inspection is performed first from a place where the difference is large. When a certain amount of electron beam accelerated by a specific acceleration voltage is injected into the contact hole when the contact hole is formed well, the maximum value of the through current generated from one contact hole is imax
Then, the maximum through-current amount Imax of the block including N contact holes is N times the maximum through-current amount imax.

Therefore, assuming that a part of the contact hole included in the block to be inspected is a defective contact hole, the amount of through current passing through the block is Imax
The value is smaller than. Therefore, the smaller the measured through-current value Imes is smaller than the maximum through-current amount Imax, the larger the number of defective contact holes, and the block has approximately N * (Imax−Imes) / Imax defective contact holes. Will exist.

In the above inspection method, the wafer is first divided into blocks having a chip size or a size equivalent to a functional block in one chip, and each block is numbered. A perpendicular electron beam is sequentially applied to a block to be inspected, and a through current passing through a contact hole in the block is measured. Arrange the blocks in the order of the measured through current. Since a contact hole included in a block having a smaller through-current value is not formed properly in a block having a smaller through-current value, a detailed inspection is performed first on a contact hole in a block having a smaller through-current value.

One block is further divided into smaller sub-blocks. The sub-block size is smaller than 100 micron square. Each sub-block is numbered so that it can be identified from each other. The entire sub-block in one block is sequentially irradiated with an electron beam, and a through current value is measured. Then, the sub-blocks are arranged in ascending order of the through current value.

Since the sub-block size is smaller than 100 micron square, if the measured through current value is displayed at a position corresponding to each sub-block on the wafer, a bit map showing a failure distribution in the wafer is obtained.

When the bit map is statistically calculated, a value such as an average value or a standard deviation of the through current values can be obtained. Further, in order to detect the location of a specific defective contact hole, a sub-block having a defective contact hole is selected, and an electron beam is applied to each of the contact holes constituting the sub-block. The quality of each contact hole is inspected to identify a defective contact hole.

As described above, the inspection is progressed hierarchically in the order of the block of the contact holes, the sub-blocks, and the individual contact holes, so that the inspection time can be reduced by eliminating the trouble of inspecting a place where there is no defective contact hole.

Also, from the result of statistical analysis of defective contact holes generated in a large number of semiconductor wafers, it has been confirmed that a place where a defective contact hole occurs after etching has a rule. The location where a defective contact hole occurs is often a fixed area of the wafer. So, using the analysis results,
The inspection is performed from a place where a defective contact hole occurs frequently. This shortens the time for inspecting the contact hole formed in the semiconductor substrate.

Further, it is known that the frequency of occurrence of etching defects greatly depends on the layout of the blocks since the number of contact holes provided for each block is different. Therefore, a block in which a defective contact hole is likely to be generated is selected, and the location is inspected preferentially.

Further, in the wafer inspection at the time of mass production, when a wafer having the number of defective contact holes equal to or more than a predetermined reference value is confirmed, the wafer is removed from the manufacturing line, or the location where the defective contact hole is generated is from a high frequency area. It is used for inspection. Therefore,
Blocks in which the number of defective contact holes is less than a predetermined reference value pass through the manufacturing line, and blocks in which the number of defective contact holes are equal to or more than the predetermined reference value reduce the inspection time by focusing on the region. .

(Embodiment 1) FIGS.
This will be described with reference to FIG. In this embodiment, the contact holes are divided into blocks, and it is checked whether or not the contact holes are formed normally for each block. FIG. 3 is a schematic diagram of a wafer divided into a plurality of blocks and each block is numbered.
An area which is finally scribed and divided is defined as a block 32, and a number is assigned to each block 32 so that they can be identified from each other.

FIG. 4 is a diagram showing, for each block 32, a through current value 41 penetrating through a contact hole of the block. FIG. 5 is a diagram in which the numbers assigned to the blocks 32 are arranged in ascending order of the through current value 41.

Each block 32 shown in FIG. 3 is sequentially irradiated with a fixed amount of electron beam accelerated at a fixed acceleration voltage, and the through current value 41 of each block 32 is measured. The through-current value 41 is, for example, the value of the block 03, 1
In Nos. 2 and 16, the minimum value is 53 pA as shown in FIG. The contact holes included in these blocks have few through holes, and a large amount of an oxide film remains at the bottom of the contact holes. As shown in FIG. 5, the proportion of defective contact holes is larger than that of other blocks.

To inspect the distribution of finer defective contact holes, the blocks 03, 12, and 16 having many defective contact holes are further divided into a plurality of sub-blocks and measured for each sub-block. On the other hand, no further detailed inspection is performed on the block determined to have no defective contact hole.

Therefore, for example, assuming that a block estimated to have no defective contact hole is 90% of the total area of the semiconductor wafer, it is necessary to perform a detailed inspection only on a portion corresponding to the remaining 10% of the area. Good. That is, in such a case, the inspection speed is improved about 10 times as compared with the case where the contact holes are inspected one by one.

As described above, when the measured through current value is defined as Imes, and the through current amount when only non-defective contact holes are present is defined as Imax, these through current values are compared. You can see the ratio of contact holes. Further, as shown in FIG. 4, a distribution diagram showing a through current value for each block indicates a region where a defective contact hole is likely to occur in the wafer surface.

For example, when it is assumed that the through current value Imax is 56 pA, the through current value of the block 24 is 5
Since it is 6 pA, it can be estimated that etching has been completed. The through current value of block 16 is 5
Since it is 3 pA, it can be estimated that there is a defect in at least 5.4% of the area.

If the number of defective contact holes in a certain block is equal to or larger than the reference value, the number assigned to the block and the fact that the block has a defective contact hole are recorded as data to be used in future statistics.

(Embodiment 2) Next, Embodiment 2 will be described with reference to FIGS. In the second embodiment, the block 32 described in the first embodiment is further divided into a plurality of small sub-blocks, and whether or not a contact hole is normally formed in each sub-block is inspected.

FIG. 6 is a diagram showing a plurality of sub-blocks 62 obtained by further dividing the block 32. FIG. 7 shows the measured through current value 41 in each sub-block 62.
FIG. 8 is a diagram in which the sub-blocks 62 are arranged in descending order of the through current value 41, and are arranged in correspondence with the numbers assigned to the respective sub-blocks 62.

As shown in FIG. 6, each sub-block 6
2 is numbered. The size of the sub-block 62 is arbitrary, but the size of one sub-block is 10 to 1
When the thickness is set to about 00 microns, it is considered that the distribution diagram of the through current amount is easy to see. In this embodiment, a case of a very large sub-block is taken as an example.

The sub-blocks 62 are irradiated with electron beams in numerical order, and the current value of the electron beam penetrating through the contact holes in each sub-block is measured. The amount of electron beam applied to each sub-block 62 is set to be a constant reference amount per unit contact hole. In other words, if the area of the sub-block is large, the amount of electron beam current to be irradiated is large, and if it is small, it is small.

The measured through current value 41 is, for example, as shown in each sub-block 62 as shown in FIG. Next, as shown in FIG. 8, the sub-blocks 62 are arranged in descending order of the through current value 41. Here, as shown in FIG. 8, when the through current value 41 is represented by a small number of digits such as two digits, there is no difference in the order of each block, and effective weighting may not be performed. In such a case, the number of digits representing the measured current value is increased so that an effective ranking can be performed.

As shown in FIG. 8, the sub-block number 1
1 and 21 indicate the smallest through current value of 10 pA, which indicates that this sub-block has the largest number of defective contact holes as compared with other sub-blocks. When the proportion of defective contact holes existing in a sub-block size (10 to 100 microns) is displayed as an image in wafer size, a bitmap generally used for defect management of a memory or the like can be obtained. The cause of the contact hole can be estimated.

That is, as will be described later, from the bit map, for example, a defective contact hole is generated by an etching device for forming a contact hole, or a defective contact hole is generated by a transfer device for transferring a semiconductor wafer. Can be estimated.

In view of the whole wafer, if the size of one side of the block is 10 μm square, the number of sub-blocks is 10 ⁸ , and the number of sub-blocks is 10 ⁶ at 100 μm square. From these measured values, Process variations can be measured with an accuracy of eight or six orders of magnitude. If the current bitmap is
Considering that only 1-bit information indicating the presence or absence of dust or particles is simply displayed, the remaining amount of the silicon oxide film itself can be measured as an analog value of several digits. A statistically significant test can be performed by checking the blocks.

(Embodiment 3) Embodiment 3 will be described with reference to FIG. In the third embodiment, the blocks are divided into the same size as the size of the semiconductor device present in each chip (hereinafter, such divided blocks are referred to as functional blocks), and the contact holes are normally formed for each functional block. This is to check whether or not it has been performed. Also,
Weighting is performed in the order of inspection as in the first embodiment.

The system ASIC (application specific)
integrated circuit; IC for specific applications)
A memory such as a U-core, a DRAM, an SRAM, or an interface core for performing communication with an external chip is provided. Generally, each semiconductor device rarely operates at the same frequency, and has different output current and power consumption.

Therefore, since the feature size differs for each semiconductor device, the size of the contact hole differs for each functional block, and the difficulty of forming the contact hole differs. Therefore, in this embodiment,
For example, a name (number) such as blocks A, B, and C is assigned to each functional block, and a contact hole inspection is performed for each functional block. For example, among the blocks A, B, and C, if it is known that the block A is the most difficult block to form the contact hole, the block A
Is checked before other blocks.

In particular, when the inspection time is limited, it is possible to more efficiently inspect the presence or absence of a contact hole by narrowing the inspection target to blocks having a high frequency of defective contact holes. it can.

These blocks A, B, and C are respectively divided into blocks A, B, and C located at other positions of the same size.
May be considered as an aggregate. That is, for example, all the blocks divided into the size of the memory area are set to 1
One inspection target may be set. Further, the designation may be made in a region where a specific contact hole is formed or a region where the contact hole formation density is equal to or higher than a certain value.
Therefore, for example, if the area occupied by the block A is 1/100 of the entire area, the inspection speed is 100 times faster.

(Embodiment 4) FIG. 10 is a view showing an irradiation device for irradiating each block or each sub-block with an electron beam. Here, in general, in order to irradiate the electron beam into the contact hole, it is necessary that the electron beam be incident horizontally on the contact hole and that the condition be maintained over a wide area of the wafer. There is.

Normal SEM (scanning electron micros
When the electron beam is scanned left and right or back and forth by one deflection electrode as in the electron beam scanning method used in scanning electron microscopes (cope), the electron beam becomes a non-perpendicular angle of incidence with respect to the wafer, resulting in a wide angle. The electron beam applied to the area cannot be applied to the inside of the contact hole.

Therefore, in this embodiment, the electron gun 101
Is converted into a parallel electron beam by the lens 102. After that, a parallel electron beam is incident on the variable aperture 104 whose opening area can be changed,
The electron beam 10 is applied to the desired block or sub-block.
Irradiate 3.

The electron beam 103 passes through a contact hole existing in each block or the like, reaches an electrode 106 provided on the back surface of the wafer, and its current is measured by an ammeter 107.

(Embodiment 5) FIG. 11 shows the amount of electron beam current applied to each block. Since each block has a different area, in order to perform inspection with a good S / N ratio, it is necessary to adjust the amount of electron beam irradiation current so that the amount of electron beam irradiated for each contact hole is constant. There is. The irradiation current amount is, for example, 10 pA for block A, 50 pA for block B, and 100 pA for block C, as shown in FIG.

When a parallel electron beam source using the variable aperture 104 (FIG. 10) is used, the electron beam 103
Is constant regardless of the area of the variable aperture 104. However, the density of actually manufactured contact holes is not always constant with an increase or decrease in the area of the block.

Therefore, even if they change, the electron beam 103 generated from the electron gun 101 can be measured so that the current amount of the electron beam passing through the contact hole in the wafer 105 can be measured with the required precision of the required number of digits. Adjust the beam amount of. In addition to increasing the irradiation electron beam amount, the range of blocks that can be collectively measured can be increased by reducing the input conversion noise of the measuring instrument.

(Embodiment 6) FIG. 12 is a flowchart showing the procedure for changing the amount of electron beam for each measurement area. The contact hole inspection is performed for each wafer. The wafer is placed on an XY stage that can be moved two-dimensionally, and is controlled so that the wafer can be moved and an electron beam can be applied to an area to be measured.

In the inspection apparatus, layout information of devices formed on the wafer surface is set in advance, and it is possible to determine which block corresponds to the block irradiated with the electron beam. It has become.

This figure shows a procedure for changing the electron beam irradiation amount depending on the blocks when three blocks A, B and C are provided. First, the XY stage is moved. When the position to be irradiated with the electron beam is the block A, as shown in FIG.

On the other hand, when the position to be irradiated with the electron beam is not the block A, it is determined whether or not the position is the block B from the layout information and the stage position information. When the area is B, for example, 50 PA is set.

Similarly, when the position to be irradiated with the electron beam is not the block B, it is determined whether or not the position is the block C. In the case of the block C, the irradiation amount is set to, for example, 100 PA. When it is not any block, the irradiation amount is set to, for example, 1 PA. As described above, the irradiation amount of the electron beam is changed to the electron beam amount suitable for the type of the block based on the position information and the layout information of the XY stage.

(Embodiment 7) FIG. 13 is a diagram showing weighting in consideration of a defect distribution characteristic of a contact hole depending on an etching apparatus. Generally, silicon oxide film
When a contact hole is formed by using an etching technique such as RIE, the size of an etching apparatus is limited, so that the influence of abnormal plasma appears as the wafer advances in the radial direction.

Normally, plasma etching is performed by arranging a processing wafer facing a plasma generating electrode. The area of the electrode is finite, and the size of a container such as a vacuum chamber is also finite. Therefore, stable plasma is generated at the central portion 131 of the wafer, but abnormal plasma may be generated at the end 132.

In such a case, the frequency of occurrence of contact hole defects often changes concentrically. In particular, it is considered that more defective contact holes occur at the wafer end 132 than at the wafer center 131. Therefore, the wafer edge 13 is more
2 is weighted high to determine the order of inspection.

For example, as shown in FIG. 5, when a large number of through current values of the same block within the significant figures occur in each block, the through current value is closer to the wafer end 132 than to the block at the center 131 of the wafer. Inspect the block first. Of course, depending on the process, a large amount of defects may occur only in the central portion 131 of the wafer.
In that case, on the contrary, the inspection order is determined by giving high weight to the central portion 131 of the wafer.

FIG. 13 shows the central part 1 for convenience of explanation.
31 and the end 132 are shown uniformly, but there is no boundary line that clearly separates them, and in fact, as the wafer moves in the radial direction from the center, the etching apparatus becomes easily influenced.

(Embodiment 8) FIG. 14 is a diagram showing weighting in consideration of the defect distribution characteristics of contact hole defects depending on the semiconductor wafer transfer device. Usually, semiconductor wafers that are mass-produced in a semiconductor factory are transferred by various transfer means. In general, semiconductor wafers are stored in a wafer cassette in units of tens of wafers in units of one lot and transferred by a transfer device to a next processing device or the like.

The wafers stored in the transported cassette are taken out of the cassette by a transport device and carried into the processing device for processing one by one. At this time, the wafer always contacts the transfer device. Therefore, the contact area 14 where the wafer and the transfer device come into contact with each other
In the vicinity of 1, it is more likely that dust adheres or scratches occur as compared with other areas. Therefore, the contact region 141 is likely to have many defective contact holes.

Therefore, the transfer device weights the periphery of the region 141 in contact with the wafer with a higher weight than the other regions, and performs the inspection with priority over the other regions.

(Embodiment 9) FIG.
1 is a diagram showing a normal contact hole 152 and a defective contact hole 153 in FIG. Sub-block 151
If the contact hole in the inside is non-defective, if the maximum value of the penetrating current that passes through when a certain amount of electron beam is injected into the contact hole is imax, a sub-hole having N identically shaped contact holes Block 15
The maximum through current Imax passing through 1 is N times the maximum current imax. This has been described at the beginning of the embodiment.

For example, as shown in FIG. 15, when one defective contact hole 153 exists in sub-block 151 to be inspected, the amount of current penetrating through the contact hole in sub-block 151 is at most Imax-imax. Become. The smaller the through-current value Imes is less than the maximum current amount Imax, the greater the number of defective contact holes. In addition, at least N * (Imax−
There are (Imes) / Imax defective contact holes.

When a defective contact hole exists in a certain sub-block, the fact that there is a defective contact hole in the sub-block is recorded as data for use in future statistics together with the number assigned to the sub-block.

When the proportion of defective contact holes in the contact holes in the sub-block irradiated with the electron beam is equal to or larger than a predetermined reference value, it is estimated that the sub-block is a defective area. Note that this estimation is determined by the ratio of the amount of the through current that penetrates the contact hole and the noise of the measuring instrument that measures the through current in accordance with the amount of the irradiated electron beam.

For example, if the measured through current value is 1 nA
When the current noise of the measuring instrument is 1 pA, the measuring instrument can measure the through current value with three digits of accuracy. In this case, if one of the 1000 contact holes is defective, it can be detected. (Embodiment 10) FIG. 16 is a view showing an electron beam scanning apparatus for two-dimensionally applying an electron beam to a semiconductor wafer. A planar electron beam 162 is emitted vertically from the electron gun 161 toward the wafer 163. Wafer 1
63 is mounted on an XY stage 164 using a driving principle such as stepping motors 165 and 166 or a piezo actuator.

The XY stage 164 is moved so as to change the electron beam irradiation position in block units or sub-block units. The movement distance is measured from the number of drive pulses supplied to the stepping motor, the voltage applied to the piezo actuator, or the movement distance measurement using a laser.

For example, the XY stage 164 is adjusted so that the center coordinates of the first block to be irradiated with the electron beam 162 coincide with the center of the electron beam irradiation area.
Next, after irradiating one block with the electron beam 162 and measuring the through current, the XY stage 164 is moved and adjusted so that the center coordinates of the adjacent block and the center of the electron beam irradiation area coincide.

The XY stage 164 is sequentially moved to irradiate the entire wafer 163 with the electron beam 162. The size of the block is much larger than that of the contact hole, and an area without a circuit such as a scribe line is spread around the block. Generally, when the accuracy of alignment is increased, the time required for alignment is greatly increased. However, as in the present embodiment, an inspection is performed to determine whether or not a contact hole is formed normally in block units. In such a case, the required alignment accuracy is
Since it is as low as several hundred microns, alignment can be performed very quickly, and the electron beam 16
2 can be done in less than one minute.

When the sub-block is inspected, the XY stage 164 is moved and adjusted so that the center coordinates of the sub-block designated to be inspected first in the block inspection coincide with the center of the electron beam irradiation area. . The required alignment accuracy of the sub-blocks is about 1 micron. Next, the sub-block is irradiated with the electron beam 162 to measure a through current. Next, the XY stage 164 is moved and adjusted so that the center coordinates of the adjacent sub-block coincide with the center of the electron beam irradiation area.

As described above, the electron beam irradiation area is sequentially moved, and all the sub-blocks in one block are irradiated with the electron beam to measure a through current passing through the block.

(Embodiment 11) FIG. 17 is a view showing a procedure for stepwise inspecting the presence or absence of a defective contact hole from one wafer. Prior to the inspection, a threshold value for determining whether the contact hole is normal or defective is determined (step S1). The threshold value may be, for example, a standard through-current value indicated by one non-defective contact hole, the number of contact hole defects that may be present in one chip, or a defect that may be present in a wafer. Determined from the number of chips.

The non-defective contact hole determination standard is uniquely determined from physical restrictions such as the circuit configuration, speed, and wiring impedance. On the other hand, the number of defective contact holes allowed in one chip is determined by the circuit redundancy of the semiconductor product, and the number of defective chips allowed is a parameter that should be adjusted to minimize the manufacturing cost. Select an appropriate value from the past production results.

That is, for example, it is known that, even if the contact hole is a good contact hole, the resistance value of the contact hole changes many times due to the influence of the natural oxide film or the like. Due to the diffusion effect in the process, etc., it does not become a defective contact hole in a wide area.

Therefore, with respect to a contact hole used in a specific circuit of a specific semiconductor product, for example, a threshold value that is regarded as a non-defective contact hole is set up to half the through current value indicated by a complete contact hole. . All of these set values are stored in the determination device and are compared with each other to determine pass / fail.

Consider a setting of a threshold value of a contact hole included in a DRAM as a specific product. DRA
There are several types of contact holes included in M. If the penetration current value of a non-defective contact hole to be inspected is 50 and the allowable rate is 50%, the penetration current obtained by the inspection is 25 PA If not, the wafer is considered to be a good wafer.

A DRAM has circuit redundancy, and can normally be repaired even if about 1% of the storage elements are defective. Therefore, even if one or more defects occur in a contact hole in a memory element in one chip, the chip is not defective. Therefore, for example, if a failure of 1% or more occurs in the storage element portion, a threshold value is provided that the chip is defective. More than 100 DRAM chips are simultaneously formed on one wafer, but when the number of chips per wafer becomes less than a certain value, the manufacturing cost for one DRAM increases.

Therefore, when the number of chips taken out of one wafer is equal to or less than a certain value, it is regarded as a wafer defect and excluded from the manufacturing process. For example, if the threshold is 10
Set to%. The inspection is started by setting the threshold value as described above (step S2).

First, the position of the wafer is measured, and the block position and the electron beam irradiation position are matched. Each block is sequentially irradiated with an electron beam. At this time, the inspection order includes the failure characteristics of the machine, and the inspection is performed first from the end of the wafer, or the place where the transfer machine comes into contact is inspected first.

The value of the through current passing through the contact hole of each block can be estimated from the amount of through current passing through one contact hole in the block and the number of contact holes included in the block. Thus, the ratio of defective contact holes in each block can be estimated.

If the number of defective contact holes exceeds 10%, it is regarded as a defective block (step S3), and the number of chips is counted. If the counted number exceeds 10% of the total number, the inspection is interrupted even if the inspection is in progress, and this wafer is regarded as a defective wafer and removed from the production line. If not, the wafer is returned to the production line (step S4). In addition, when removing a defective wafer from the production line, to notify the process abnormality,
A warning signal such as a warning sound may be issued.

On the other hand, when the purpose is to obtain a bitmap (step S5), the block deemed to be defective is further divided into sub-blocks and inspected. The inspection reveals a finer defect distribution on the wafer. These data are stored together with the sub-block position information and become inspection outputs.

Further, in the case of finely specifying a defective position, an electron beam is applied to each of the contact holes inside the sub-block in which the inspection result is output if a defective contact hole is present, and the through current is reduced. Measure the quantity,
The quality of each contact hole is determined (step S6). Further, the thickness of the silicon oxide film remaining at the bottom of the contact hole is measured from the through current value.

As described above, the area of a region which is collectively measured in a hierarchical manner is sequentially reduced, fine locations are measured, and a bit map reflecting the size of the divided block is created. If necessary, each contact hole is measured, and the thickness of the silicon oxide film remaining at the bottom of the contact hole is measured (step S7) to check the state of the contact hole more precisely.

In the above embodiment, the case where all the block shapes are rectangular has been described. However, the shape of the block is not limited to this case, and may be a polygon, a circle, or an ellipse. Although the block has a structure including a scribe line, the scribe line has a TEG for performing a test different from that of the main circuit.
(Test element group; characteristic evaluation element) may be placed, and if they exist, they are excluded or defined in another block for inspection.

Further, it goes without saying that the inspection method described in the above embodiment can be used not only for inspection of contact holes but also for inspection of devices formed on all kinds of wafers. In addition, the method of dividing and weighting is based on the inspection output T obtained when the inspection output S of each part is inspected collectively for an aggregate of n parts.
However, when represented by S * n, the method of the present invention can be used.

The method of inspecting a semiconductor wafer according to the present embodiment is not limited to the inspection of a semiconductor wafer but can be applied to an inspection method of an SOI substrate.

[0097]

According to the present invention, a semiconductor wafer is divided into a plurality of desired regions, and it is sequentially inspected for each region by a so-called current penetration method to check whether or not a contact hole is normally formed. The inspection of the contact holes can be performed in a shorter time than when all the contact holes are inspected. Therefore, defective contact holes can be efficiently found, and the inspection throughput can be improved. Further, since many wafers can be inspected per unit time, precise manufacturing process management can be performed.

By setting the size of the region to be the same as that of a semiconductor device such as a memory mounted on a semiconductor chip, an inspection can be performed for each semiconductor device having a different feature size. The inspection of the contact hole can be performed in a short time.

According to the present invention, the above-mentioned region (first region)
Is divided into a plurality of regions (second regions) smaller than the second region), and it is inspected for each small region by a so-called current penetration method whether or not a contact hole is formed normally. For this reason, since the contact holes are inspected in stages, such as the first region, the second region, and the individual contact holes, the inspection can be performed efficiently and the contact holes can be inspected in a short time.

Further, by giving an identification number to the first area or the second area and inspecting from the area where there are many defective contact holes, the inspection time can be further shortened. Note that the area where the number of defective contact holes is large is, for example, an area close to an end of a semiconductor wafer or a place where a semiconductor wafer transfer machine comes into contact.

Further, an area to be inspected is specified from the position information of the electron beam irradiating the semiconductor wafer, the position information of the semiconductor substrate, and the layout information of the semiconductor circuit, and the electron beam irradiating the area is specified. Is changed according to the number of contact holes in the region. Therefore, even if the number of contact holes in the region is different, the amount of electron beam applied to the unit number of contact holes can be unified. Therefore, even if inspection is performed for each area,
Inspection with less influence can be performed.

Further, by obtaining a bitmap corresponding to the current value of the electron beam penetrating the contact hole in the region, if the penetration current method is used for inspecting the contact hole, the obtained inspection amount is continuous. Because it is a quantity, detailed test results can be obtained.

If the proportion of defective contact holes in the region is equal to or greater than the threshold value, the number of contact holes in the region is counted, and the inspection of the contact holes in the region is terminated. Further, when the process variation exceeds the threshold, a process abnormality can be notified by a warning signal or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing an inspection method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a comparison of inspection methods according to the embodiment of the present invention.

FIG. 3 is a view showing a wafer divided into a plurality of blocks according to the first embodiment of the present invention;

FIG. 4 is a diagram illustrating a relationship between a plurality of blocks and a through current value according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a wafer divided into a plurality of blocks and a through current value according to the first embodiment of the present invention;

FIG. 6 is a view showing a wafer divided into a plurality of sub blocks according to the second embodiment of the present invention;

FIG. 7 is a diagram illustrating a relationship between a plurality of sub-blocks and a through current value according to the second embodiment of the present invention.

FIG. 8 is a diagram showing a relationship between a wafer divided into a plurality of blocks and a through current value according to the second embodiment of the present invention;

FIG. 9 is a view showing a wafer divided into a plurality of functional blocks according to the third embodiment of the present invention.

FIG. 10 is a view showing an electron beam irradiation apparatus according to a fourth embodiment of the present invention.

FIG. 11 is a diagram showing a relationship between a functional block and a through current value according to a fifth embodiment of the present invention.

FIG. 12 is a flowchart for changing an irradiation amount of an electron beam according to a sixth embodiment of the present invention.

FIG. 13 is a view showing a central portion and an end portion of a wafer according to a seventh embodiment of the present invention.

FIG. 14 is a diagram showing a contact area and a non-contact area of a wafer according to an eighth embodiment of the present invention.

FIG. 15 is a view showing a sub-block and a contact hole according to a ninth embodiment of the present invention.

FIG. 16 is a diagram showing an electron beam scanning device according to a tenth embodiment of the present invention.

FIG. 17 is a flowchart showing an inspection order according to the eleventh embodiment of the present invention.

[Explanation of symbols]

 1, 103, 162 Electron beam 3 Contact hole bottom 4, 152 Contact hole 22 Oxide film surface 23 Secondary electron 24 Contact hole bottom 25 Secondary electron from contact hole bottom 31, 105, 163 Wafer 32 Block 41 Through current value 62 , 72, 151 Sub-block 101 Electron gun 102 Lens 104 Variable aperture 106 Electrode 107 Ammeter 131 Wafer center 132 Wafer end 141 Contact area 153 Bad contact hole 161 Electron gun 164 XY stage 165 X-axis stepping motor 166 Y-axis stepping motor 167 vacuum chamber

Claims (21)

(57) [Claims] In a method of inspecting a semiconductor wafer having a plurality of contact holes, the semiconductor wafer is divided into a plurality of desired first regions, and each of the first regions is irradiated with an electron beam, and each of the first regions is irradiated with an electron beam. The current value of the electron beam penetrating through the contact hole in the first region is measured, and the current value is compared with a desired threshold value, whereby the normally formed one of the plurality of contact holes in the first region is formed. A method for inspecting a semiconductor wafer, comprising: inspecting a ratio of contact holes that are not present. 2. The method according to claim 1, wherein the plurality of first regions are further divided into a plurality of second regions smaller than the plurality of first regions.
Is irradiated with the electron beam to measure the current value of the electron beam penetrating the contact hole in each second region, and comparing the current value with a desired threshold value, 2. The method according to claim 1, wherein a ratio of a contact hole that is not formed normally among a plurality of contact holes in the region is inspected. 3. The semiconductor wafer inspection method according to claim 1, wherein the size of the first region is set to be the same as the size of a semiconductor chip. 4. The method for inspecting a semiconductor wafer according to claim 1, wherein the size of the first region is set to be the same as the size of a semiconductor device such as a memory mounted on the semiconductor chip. . 5. The semiconductor according to claim 1, wherein the plurality of first regions are numbered so as to be distinguishable from each other. Wafer inspection method. 6. The method according to claim 2, wherein the plurality of second regions are numbered so as to be distinguishable from each other. 7. The first areas are arranged in descending order of the current value or in descending order of the current value, and the first areas are arranged in accordance with the order.
5. The method according to claim 1, wherein the contact holes in the region are inspected one by one. 8. The second regions are arranged in descending order of the current value or in descending order of the current value, and the second regions are arranged in accordance with the order.
3. The method for inspecting a semiconductor wafer according to claim 2, wherein it is inspected whether or not the contact holes in the region are normally formed one by one. 9. The method according to claim 1, wherein the plurality of first regions at a plurality of distant locations are regarded as an aggregate, and the aggregate is irradiated with an electron beam, and a current value of the electron beam penetrating through a contact hole in the aggregate is determined. 2. The method according to claim 1, wherein a ratio of a contact hole that is not formed normally among the plurality of contact holes in the assembly is inspected by measuring and comparing a current value thereof with a predetermined threshold value. 3. The method for inspecting a semiconductor wafer according to 1. 10. The semiconductor wafer according to claim 1, wherein the irradiation amount of the electron beam applied to the first region is changed according to the number of contact holes in the first region. Inspection methods. 11. The method according to claim 11, wherein the changing of the irradiation amount of the electron beam is performed based on irradiation position information of the electron beam, position information of the semiconductor substrate, and layout information of a semiconductor circuit. The method for inspecting a semiconductor wafer according to claim 10, wherein a first area to be irradiated with the electron beam is identified and changed for each of the first areas. 12. The inspection of a semiconductor wafer according to claim 1, wherein the inspection is performed from a region having a high frequency of having a defective contact hole among the plurality of first regions. Method. 13. The semiconductor wafer inspection method according to claim 2, wherein the inspection is performed from a region having a high frequency of defective contact holes among the plurality of second regions. 14. The method for inspecting a semiconductor wafer according to claim 1, wherein weights are assigned in an order of performing the inspection in a radial direction of the semiconductor wafer from the center of the semiconductor wafer. 15. The semiconductor wafer inspection method according to claim 1, wherein the closer the position where the semiconductor wafer and the semiconductor wafer transporter that transports the semiconductor wafer are in contact with each other, the more the inspection is performed. 16. The method according to claim 1, wherein a bit map corresponding to a current value of the electron beam penetrating the first region is obtained. 17. The method according to claim 17, wherein the ratio of the defective contact hole in the first region is equal to or more than a threshold value.
5. The method according to claim 1, wherein the number of contact holes in the first area is counted, and the inspection of the contact holes in the first area is terminated. 6. 18. The method according to claim 18, wherein the ratio of the defective contact hole occupying the second region is equal to or more than a threshold value.
3. The semiconductor wafer inspection method according to claim 2, wherein the number of contact holes in the region is counted and the inspection of the contact holes in the second region is terminated. 19. A semiconductor manufacturing process according to claim 19, wherein an average value and a standard deviation of the current amount are calculated from a current amount distribution of the electron beam penetrating the first region to detect a variation in a semiconductor manufacturing process. Item 5. The method for inspecting a semiconductor wafer according to any one of Items 1 to 4. 20. The method according to claim 1, wherein an average value and a standard deviation of the current amount are calculated from a distribution of a current amount of the electron beam penetrating the second region to detect a variation in a semiconductor manufacturing process. Item 3. The method for inspecting a semiconductor wafer according to Item 2. 21. The semiconductor wafer inspection method according to claim 17, wherein when the process variation exceeds a threshold, a warning signal for notifying a process abnormality is generated.